Specific Groups Of Neurons Research Articles

12502 Bdnf Production by Kiss1 Neurons Acts in a Sexually Dependent Way to Control Sexual Development and Energy Balance in Female and Male Mice

Abstract Disclosure: A.M. Zanesco: None. D. Cabral: None. J. Ferreira: None. F. Valdivieso-Rivera: None. A.L. Carvalho: None. N. Mendes: None. C. Sponton: None. R. Frazao: None. L.A. Velloso: None. The hypothalamus is a key region in the central nervous system that controls different functions such as energy balance, thermogenesis, and reproduction. Kiss1 neurons integrate two distinct neuronal pathways, reproduction, and energy balance, both essential to species survival and maintenance. Recent studies, identify that the Brain-derived neurotrophic factor, BDNF produced by neurons and astrocytes in the hypothalamus is essential to control homeostatic and hedonic feeding by acting in specific groups of hypothalamic neurons. No studies showed the action of BDNF produced in the arcuate nucleus (ARC) of the hypothalamus. Using single-cell RNA sequencing analysis of data obtained from mice hypothalamus reveals that Kiss1 neurons express BDNF and we confirmed this result by immunofluorescence assay. Curiously, there is more expression of BDNF in the female hypothalamus compared with the male hypothalamus. But, when we selected specifically the BDNF produced by KISS1 neurons, this difference disappears. Based on that, we used a Cre-loxP approach to selectively knockout BDNF in Kiss1 neurons and identify the changes in sexual development and energy balance in female and male mice. All experiments were approved by the Animal Use Ethics Committee of UNICAMP (CEUA: 5591-1/2020 and CIBio 04/2021). All female and male mice were evaluated daily to identify their sexual development. We identified no changes in metabolic parameters, such as body weight and adiposity in male and female mice fed on a chow diet. Additionally, BDNF ablation in Kiss1 neurons (BDNF-KO) leaded to a premature vaginal opening, a decreased in uterus and ovary weight, and compromises the regular cyclicity of the estrus cycle in females. No difference was found in the sexual development of male mice, indicating that this effect is sexually dependent. Based on the fact that BDNF produced in VMH and DMH acts as anorexigenic effects, and Kiss1 neurons integrate the neuronal pathway responsible for energy balance, we decided to investigate the effects of BDNF ablation in Kiss1 neurons in female and male mice fed on high-fat diet. Interestingly, male mice without BDNF production in Kiss neurons were protected from obesity development compared with wild-type mice, both fed on a high-fat diet. When they were fed on a chow diet, male BDNF-KO mice, exhibited hyperphagia compared to control mice, showing a disruption in control of food intake and body weight maintenance. No differences were identified in body weight gain, food intake, and adiposity in BDNF-KO female mice. Based on that, we conclude that BDNF produced by Kiss1 exerts different functions in male and female mice. In females, it is more related to sexual development, and males in control of energy balance. This is the first research showing the BDNF production by Kiss1 neurons and its dimorphism effects on male and female mice. Presentation: 6/2/2024

Inhibitory circuits generate rhythms for leg movements during Drosophila grooming.

Limbs execute diverse actions coordinated by the nervous system through multiple motor programs. The basic architecture of motor neurons that activate muscles that articulate joints for antagonistic flexion and extension movements is conserved from flies to vertebrates. While excitatory premotor circuits are expected to establish sets of leg motor neurons that work together, our study uncovered a new instructive role for inhibitory circuits: their ability to generate rhythmic leg movements. Using electron microscopy data for the Drosophila nerve cord, we categorized ~120 GABAergic inhibitory neurons from the 13A and 13B hemi-lineages into classes based on similarities in morphology and connectivity. By mapping their synaptic partners, we uncovered pathways for inhibiting specific groups of motor neurons, disinhibiting antagonistic counterparts, and inducing alternation between flexion and extension. We tested the function of specific inhibitory neurons through optogenetic activation and silencing, using an in-depth ethological analysis of leg movements during grooming. We combined anatomy and behavior analysis findings to construct a computational model that can reproduce major aspects of the observed behavior, confirming the sufficiency of these premotor inhibitory circuits to generate rhythms.

Descriptive study of perineuronal net in enteric nervous system of humans and mice.

Perineuronal nets (PNN) are highly specialized structures of the extracellular matrix around specific groups of neurons in the central nervous system (CNS). They play functions related to optimizing physiological processes and protection neurons against harmful stimuli. Traditionally, their existence was only described in the CNS. However, there was no description of the presence and composition of PNN in the enteric nervous system (ENS) until now. Thus, our aim was to demonstrate the presence and characterize the components of the PNN in the enteric nervous system. Samples of intestinal tissue from mice and humans were analyzed by RT-PCR and immunofluorescence assays. We used a marker (Wisteria floribunda agglutinin) considered as standard for detecting the presence of PNN in the CNS and antibodies for labeling members of the four main PNN-related protein families in the CNS. Our results demonstrated the presence of components of PNN in the ENS of both species; however its molecular composition is species-specific.

Identification of a Locus Coeruleus-amygdala Angiotensinergic Circuit: Implications for Stress-related Cardiovascular Diseases

Background: The locus coeruleus (LC) is a significant noradrenergic nucleus in the brain sensitive to afferent interoceptive signals. It responds to behavioral challenges by increasing noradrenaline release through ascending projections to the hypothalamus, thalamus, cortex, and amygdala. The brain renin-angiotensin system (RAS) plays a role in stress-related cardiovascular diseases, and previous research has identified angiotensin II (Ang II) and its receptors in the LC. The current study aimed to gain a deeper understanding of the function of the Ang II type 1 receptor (AT1R) in the LC, particularly its involvement in transmitting interoceptive cardiovascular signals by regulating LC activity. Methods: Using AT1R-eGFP and AT1R-Cre mice combined with neuroanatomical tract-tracing, chemogenetic and behavioral approaches, we examined AT1R expressing neurons in the LC. Dual immunohistochemistry was used in AT1R-eGFP reporter mice to characterize LC-AT1R-eGFP+ cells by looking at the colocalization of noradrenergic neuron maker tyrosine hydroxylase (TH) and GFP. Cre-inducible tracing with AT1R-cre mice was applied for circuit anterograde analysis and in vivo chemogenetics were used for behavior testing and analysis. Results: The majority of AT1R-eGFP+ neurons (94%) in the LC were found to be co-localized with TH. By using anterograde labeling with cre-inducible GFP virus (AAV-DIO-GFP) in AT1R-Cre mice, it was revealed that the AT1R+ neurons in the LC predominantly project to the amygdala and extended amygdala regions. Only a few or no projections to other brain areas known to receive LC inputs were observed. Within the amygdala, the AT1R+ nerve terminals were specifically limited to the medial division of the central amygdala (CeM) and the basomedial amygdala (BMA). Subsequently, AT1R was deleted from LC by injecting Cre virus into AT1R-Flox mice. Although the general anxiety level remained unchanged, restraint stress-induced anxiety was attenuated following LC AT1R deletion as shown by increased open arm distance in the elevated plus maze (EPM) test (21.7±6.6mm AAV-GFP vs. 98.1±27.5mm AAV-Cre, p<0.05, n=10). Moreover, the study employed Cre-dependent inhibitory and excitatory designer receptors exclusively activated by designer drug (hM4Di and hM3Dq DREADD) with Clozapine-n-oxide (CNO) to selectively silence and activate the AT1R+ neurons in the LC. The inhibition of AT1R+ neurons decreased the baseline anxiety level in mice (36.6±8.6mm Saline vs. 153.4±38.9mm CNO, p<0.01, n=8, EPM open arm distance), while activation of AT1R+ neurons increased baseline anxiety level (963.1±223.1mm Saline vs. 408.5±92mm CNO, p<0.01, n=10, EPM open arm distance). Additionally, the acoustic startle response, which is associated with anxiety levels, was reduced after silencing the LC AT1R+ neurons (324±39.2mV Saline vs. 168.8±54.1mV CNO, p<0.05, n=8). Conclusion: These findings suggest that a specific group of angiotensinergic LC neurons sends projections to the amygdala, highlighting the potential significance of AT1R in mediating noradrenergic activation between the LC and amygdala. Future investigations will explore the response of LC AT1R+ neurons to stress-induced cardiovascular stimuli and afferent interoceptive LC inputs, which may offer novel insights, and new therapeutic direction for the link between stress disorders and cardiovascular disease risk. NIH 1R01HL137103-01A1. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Paradoxical boosting of weak and strong spatial memories by hippocampal dopamine uncaging.

The ability to remember changes in the surroundings is fundamental for daily life. It has been proposed that novel events producing dopamine release in the hippocampal CA1 region could modulate spatial memory formation. However, the role of hippocampal dopamine increase on weak or strong spatial memories remains unclear. We show that male mice exploring two objects located in a familiar environment for 5 minutes created a short-term memory (weak) that cannot be retrieved one day later, whereas 10 minutes exploration created a long-term memory (strong) that can be retrieved one day later. Remarkably, hippocampal dopamine elevation during the encoding of weak object location memories (OLMs) allowed their retrieval one day later but dopamine elevation during the encoding of strong OLMs promoted the preference for a familiar object location over a novel object location after 24 hours. Moreover, dopamine uncaging after the encoding of OLMs did not have effect on weak memories whereas on strong memories diminished the exploration of the novel object location. Additionally, hippocampal dopamine elevation during the retrieval of OLMs did not allow the recovery of weak memories and did not affect the retrieval of strong memory traces. Finally, dopamine elevation increased hippocampal theta oscillations, indicating that dopamine promotes the recurrent activation of specific groups of neurons. Our experiments demonstrate that hippocampal dopaminergic modulation during the encoding of OLMs depends on memory strength indicating that hyperdopaminergic levels that enhance weak experiences could compromise the normal storage of strong memories.Significance statement Increased levels of dopamine have been related to cognitive enhancement. Hippocampal dopamine elevation caused by novelty exposure has been proposed as a strategy to enhance memory based on the observation that surprising events create flashbulb memories that are remembered for long time. However, hyperdopaminergic levels could also underlie maladaptive memories, such as non-desired preservation of traumatic experiences. Our experiments show that dopamine elevation in the dorsal hippocampus during the encoding of spatial memories has paradoxical effects, while the enhancement of weak memories allows their retrieval, the dopaminergic modulation of strong memories limits the ability to modify preexisting spatial memories by changes in the environment. We conclude that cognitive enhancement through dopamine boosting must consider diverse aspects of memory formation.

Reactive antibodies against brain antigens as serological biomarkers of neurodegenerative diseases

The aging of the population, attributed to increased life expectancy, coincides with a rise in the prevalence of neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. The symptoms of these disorders, such as motor disturbances and cognitive impairment, occur only after significant neurological damage, greatly diminishing the effectiveness of treatments. Consequently, achieving early diagnosis of neurodegenerative diseases stands as a paramount global health challenge. These conditions are characterized by the progressive loss of specific neuronal groups in the nervous system, resulting in dysfunction and eventual cell death in the brain. Although the exact cause of neuronal degeneration remains largely unknown, recent studies have revealed the significant involvement of the immune system in the pathogenesis of these diseases. Notably, the identification of reactive antibodies targeting specific antigens has highlighted a close association between immune mechanisms and the neurodegenerative process. Thus, the aim of this review is to explore the mechanisms of the adaptive immune system and their impact on the pathogenesis of neurodegenerative diseases, with a particular focus on reactive antibodies and their potential as diagnostic biomarkers.

Associative memory neurons of encoding multi-modal signals are recruited by neuroligin-3-mediated new synapse formation

The joint storage and reciprocal retrieval of learnt associated signals are presumably encoded by associative memory cells. In the accumulation and enrichment of memory contents in lifespan, a signal often becomes a core signal associatively shared for other signals. One specific group of associative memory neurons that encode this core signal likely interconnects multiple groups of associative memory neurons that encode these other signals for their joint storage and reciprocal retrieval. We have examined this hypothesis in a mouse model of associative learning by pairing the whisker tactile signal sequentially with the olfactory signal, the gustatory signal, and the tail-heating signal. Mice experienced this associative learning show the whisker fluctuation induced by olfactory, gustatory, and tail-heating signals, or the other way around, that is, memories to multi-modal associated signals featured by their reciprocal retrievals. Barrel cortical neurons in these mice become able to encode olfactory, gustatory, and tail-heating signals alongside the whisker signal. Barrel cortical neurons interconnect piriform, S1-Tr, and gustatory cortical neurons. With the barrel cortex as the hub, the indirect activation occurs among piriform, gustatory, and S1-Tr cortices for the second-order associative memory. These associative memory neurons recruited to encode multi-modal signals in the barrel cortex for associative memory are downregulated by neuroligin-3 knockdown. Thus, associative memory neurons can be recruited as the core cellular substrate to memorize multiple associated signals for the first-order and the second-order of associative memories by neuroligin-3-mediated synapse formation, which constitutes neuronal substrates of cognitive activities in the field of memoriology.

Associative memory neurons of encoding multi-modal signals are recruited by neuroligin-3-mediated new synapse formation.

The joint storage and reciprocal retrieval of learnt associated signals are presumably encoded by associative memory cells. In the accumulation and enrichment of memory contents in lifespan, a signal often becomes a core signal associatively shared for other signals. One specific group of associative memory neurons that encode this core signal likely interconnects multiple groups of associative memory neurons that encode these other signals for their joint storage and reciprocal retrieval. We have examined this hypothesis in a mouse model of associative learning by pairing the whisker tactile signal sequentially with the olfactory signal, the gustatory signal, and the tail-heating signal. Mice experienced this associative learning show the whisker fluctuation induced by olfactory, gustatory, and tail-heating signals, or the other way around, that is, memories to multi-modal associated signals featured by their reciprocal retrievals. Barrel cortical neurons in these mice become able to encode olfactory, gustatory, and tail-heating signals alongside the whisker signal. Barrel cortical neurons interconnect piriform, S1-Tr, and gustatory cortical neurons. With the barrel cortex as the hub, the indirect activation occurs among piriform, gustatory, and S1-Tr cortices for the second-order associative memory. These associative memory neurons recruited to encode multi-modal signals in the barrel cortex for associative memory are downregulated by neuroligin-3 knockdown. Thus, associative memory neurons can be recruited as the core cellular substrate to memorize multiple associated signals for the first-order and the second-order of associative memories by neuroligin-3-mediated synapse formation, which constitutes neuronal substrates of cognitive activities in the field of memoriology.

Caenorhabditis elegans: A transgenic model for studying age-associated neurodegenerative diseases.

Neurodegenerative diseases (NDs) are a heterogeneous group of aging-associated ailments characterized by interrupting cellular proteostasic machinery and the misfolding of distinct proteins to form toxic aggregates in neurons. Neurodegenerative diseases, which include Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and others, are becoming an increasing threat to human health worldwide. The degeneration and death of certain specific groups of neurons are the hallmarks of these diseases. Over the past decades, Caenorhabditis eleganshas beenwidely used as a transgenic model to investigate biological processes related to health and disease. The nematode Caenorhabditis elegans (C. elegans) has developed as a powerful tool for studying disease mechanisms due to its ease of genetic handling and instant cultivation while providing a whole-animal system amendable to several molecular and biochemical techniques. In this review, we elucidate the potential of C. elegans as a versatile platform for systematic dissection of the molecular basis of human disease, focusing on neurodegenerative disorders, and may help better our understanding of the disease mechanisms and search for new therapeutics for these devastating diseases.

Light and dark cycles modify the expression of clock genes in the ovaries of Aedes aegypti in a noncircadian manner.

Circadian oscillators (i.e., circadian clocks) are essential to producing the circadian rhythms observed in virtually all multicellular organisms. In arthropods, many rhythmic behaviors are generated by oscillations of the central pacemaker, specific groups of neurons of the protocerebrum in which the circadian oscillator molecular machinery is expressed and works; however, oscillators located in other tissues (i.e., peripheral clocks) could also contribute to certain rhythms, but are not well known in non-model organisms. Here, we investigated whether eight clock genes that likely constitute the Aedes aegypti clock are expressed in a circadian manner in the previtellogenic ovaries of this mosquito. Also, we asked if insemination by conspecific males would alter the expression profiles of these clock genes. We observed that the clock genes do not have a rhythmic expression profile in the ovaries of virgin (VF) or inseminated (IF) females, except for period, which showed a rhythmic expression profile in ovaries of IF kept in light and dark (LD) cycles, but not in constant darkness (DD). The mean expression of seven clock genes was affected by the insemination status (VF or IF) or the light condition (LD 12:12 or DD), among which five were affected solely by the light condition, one solely by the insemination status, and one by both factors. Our results suggest that a functional circadian clock is absent in the ovaries of A. aegypti. Still, their differential mean expression promoted by light conditions or insemination suggests roles other than circadian rhythms in this mosquito's ovaries.

Growth Hormone Action in Somatostatin Neurons Regulates Anxiety and Fear Memory.

Dysfunctions in growth hormone (GH) secretion increase the prevalence of anxiety and other neuropsychiatric diseases. GH receptor (GHR) signaling in the amygdala has been associated with fear memory, a key feature of posttraumatic stress disorder. However, it is currently unknown which neuronal population is targeted by GH action to influence the development of neuropsychiatric diseases. Here, we showed that approximately 60% of somatostatin (SST)-expressing neurons in the extended amygdala are directly responsive to GH. GHR ablation in SST-expressing cells (SSTΔGHR mice) caused no alterations in energy or glucose metabolism. Notably, SSTΔGHR male mice exhibited increased anxiety-like behavior in the light-dark box and elevated plus maze tests, whereas SSTΔGHR females showed no changes in anxiety. Using auditory Pavlovian fear conditioning, both male and female SSTΔGHR mice exhibited a significant reduction in fear memory. Conversely, GHR ablation in SST neurons did not affect memory in the novel object recognition test. Gene expression was analyzed in a micro punch comprising the central nucleus of the amygdala (CEA) and basolateral (BLA) complex. GHR ablation in SST neurons caused sex-dependent changes in the expression of factors involved in synaptic plasticity and function. In conclusion, GHR expression in SST neurons is necessary to regulate anxiety in males, but not female mice. GHR ablation in SST neurons also decreases fear memory and affects gene expression in the amygdala, although marked sex differences were observed. Our findings identified for the first time a neurochemically-defined neuronal population responsible for mediating the effects of GH on behavioral aspects associated with neuropsychiatric diseases.SIGNIFICANCE STATEMENT Hormone action in the brain regulates different neurological aspects, affecting the predisposition to neuropsychiatric disorders, like depression, anxiety, and posttraumatic stress disorder. Growth hormone (GH) receptor is widely expressed in the brain, but the exact function of neuronal GH action is not fully understood. Here, we showed that mice lacking the GH receptor in a group of neurons that express the neuropeptide somatostatin exhibit increased anxiety. However, this effect is only observed in male mice. In contrast, the absence of the GH receptor in somatostatin-expressing neurons decreases fear memory, a key feature of posttraumatic stress disorder, in males and females. Thus, our study identified a specific group of neurons in which GH acts to affect the predisposition to neuropsychiatric diseases.

Genetic exploration of roles of acid-sensing ion channel subtypes in neurosensory mechanotransduction including proprioception.

Although acid-sensing ion channels (ASICs) are proton-gated ion channels responsible for sensing tissue acidosis, accumulating evidence has shown that ASICs are also involved in neurosensory mechanotransduction. However, in contrast to Piezo ion channels, evidence of ASICs as mechanically gated ion channels has not been found using conventional mechanoclamp approaches. Instead, ASICs are involved in the tether model of mechanotransduction, with the channels gated via tethering elements of extracellular matrix and intracellular cytoskeletons. Methods using substrate deformation-driven neurite stretch and micropipette-guided ultrasound were developed to reveal the roles of ASIC3 and ASIC1a, respectively. Here we summarize the evidence supporting the roles of ASICs in neurosensory mechanotransduction in knockout mouse models of ASIC subtypes and provide insight to further probe their roles in proprioception.

Optogenetics for controlling seizure circuits for translational approaches

The advent of optogenetic tools has had a profound impact on modern neuroscience research, revolutionizing our understanding of the brain. These tools offer a remarkable ability to precisely manipulate specific groups of neurons with an unprecedented level of temporal precision, on the order of milliseconds. This breakthrough has significantly advanced our knowledge of various physiological and pathophysiological processes in the brain.Within the realm of epilepsy research, optogenetic tools have played a crucial role in investigating the contributions of different neuronal populations to the generation of seizures and hyperexcitability. By selectively activating or inhibiting specific neurons using optogenetics, researchers have been able to elucidate the underlying mechanisms and identify key players involved in epileptic activity. Moreover, optogenetic techniques have also been explored as innovative therapeutic strategies for treating epilepsy. These strategies aim to halt seizure progression and alleviate symptoms by utilizing the precise control offered by optogenetics.The application of optogenetic tools has provided valuable insights into the intricate workings of the brain during epileptic episodes. For instance, researchers have discovered how distinct interneuron populations contribute to the initiation of seizures (ictogenesis). They have also revealed how remote circuits in regions such as the cerebellum, septum, or raphe nuclei can interact with hyperexcitable networks in the hippocampus. Additionally, studies have demonstrated the potential of closed-loop systems, where optogenetics is combined with real-time monitoring, to enable precise, on-demand control of seizure activity.Despite the immense promise demonstrated by optogenetic approaches, it is important to acknowledge that many of these techniques are still in the early stages of development and have yet to reach potential clinical applications. The transition from experimental research to practical clinical use poses numerous challenges. In this review, we aim to introduce optogenetic tools, provide a comprehensive survey of their application in epilepsy research, and critically discuss their current potential and limitations in achieving successful clinical implementation for the treatment of human epilepsy. By addressing these crucial aspects, we hope to foster a deeper understanding of the current state and future prospects of optogenetics in epilepsy treatment.

Preclinical investigation in FAAH inhibition as a neuroprotective therapy for frontotemporal dementia using TDP-43 transgenic male mice

BackgroundFrontotemporal dementia (FTD) is a heterogeneous group of early onset and progressive neurodegenerative disorders, characterized by degeneration in the frontal and temporal lobes, which causes deterioration in cognition, personality, social behavior and language. Around 45% of the cases are characterized by the presence of aggregates of the RNA-binding protein TDP-43.MethodsIn this study, we have used a murine model of FTD that overexpresses this protein exclusively in the forebrain (under the control of the CaMKIIα promoter) for several biochemical, histological and pharmacological studies focused on the endocannabinoid system.ResultsThese mice exhibited at postnatal day 90 (PND90) important cognitive deficits, signs of emotional impairment and disinhibited social behaviour, which were, in most of cases, maintained during the first year of life of these animals. Motor activity was apparently normal, but FTD mice exhibited higher mortality. Their MRI imaging analysis and their ex-vivo histopathological evaluation proved changes compatible with atrophy (loss of specific groups of pyramidal neurons: Ctip2- and NeuN-positive cells) and inflammatory events (astroglial and microglial reactivities) in both cortical (medial prefrontal cortex) and subcortical (hippocampus) structures at PND90 and also at PND365. The analysis of the endocannabinoid system in these mice proved a decrease in the hydrolysing enzyme FAAH in the prefrontal cortex and the hippocampus, with an increase in the synthesizing enzyme NAPE-PLD only in the hippocampus, responses that were accompanied by modest elevations in anandamide and related N-acylethanolamines. The potentiation of these elevated levels of anandamide after the pharmacological inactivation of FAAH with URB597 resulted in a general improvement in behaviour, in particular in cognitive deterioration, associated with the preservation of pyramidal neurons of the medial prefrontal cortex and the CA1 layer of the hippocampus, and with the reduction of gliosis in both structures.ConclusionsOur data confirmed the potential of elevating the endocannabinoid tone as a therapy against TDP-43-induced neuropathology in FTD, limiting glial reactivity, preserving neuronal integrity and improving cognitive, emotional and social deficits.

In vivo reduction of age-dependent neuromelanin accumulation mitigates features of Parkinson's disease.

Humans accumulate with age the dark-brown pigment neuromelanin inside specific neuronal groups. Neurons with the highest neuromelanin levels are particularly susceptible to degeneration in Parkinson's disease, especially dopaminergic neurons of the substantia nigra, the loss of which leads to characteristic motor Parkinson's disease symptoms. In contrast to humans, neuromelanin does not appear spontaneously in most animals, including rodents, and Parkinson's disease is an exclusively human condition. Using humanized neuromelanin-producing rodents, we recently found that neuromelanin can trigger Parkinson's disease pathology when accumulated above a specific pathogenic threshold. Here, by taking advantage of this newly developed animal model, we assessed whether the intracellular build-up of neuromelanin that occurs with age can be slowed down in vivo to prevent or attenuate Parkinson's disease. Because neuromelanin derives from the oxidation of free cytosolic dopamine, we enhanced dopamine vesicular encapsulation in the substantia nigra of neuromelanin-producing rats by viral vector-mediated overexpression of vesicular monoamine transporter 2 (VMAT2). This strategy reduced the formation of potentially toxic oxidized dopamine species that can convert into neuromelanin and maintained intracellular neuromelanin levels below their pathogenic threshold. Decreased neuromelanin production was associated with an attenuation of Lewy body-like inclusion formation and a long-term preservation of dopamine homeostasis, nigrostriatal neuronal integrity and motor function in these animals. Our results demonstrate the feasibility and therapeutic potential of modulating age-dependent intracellular neuromelanin production in vivo, thereby opening an unexplored path for the treatment of Parkinson's disease and, in a broader sense, brain ageing.

Olfactory responses of Drosophila are encoded in the organization of projection neurons.

The projection neurons (PNs), reconstructed from electron microscope (EM) images of the Drosophila olfactory system, offer a detailed view of neuronal anatomy, providing glimpses into information flow in the brain. About 150 uPNs constituting 58 glomeruli in the antennal lobe (AL) are bundled together in the axonal extension, routing the olfactory signal received at AL to mushroom body (MB) calyx and lateral horn (LH). Here we quantify the neuronal organization in terms of the inter-PN distances and examine its relationship with the odor types sensed by Drosophila. The homotypic uPNs that constitute glomeruli are tightly bundled and stereotyped in position throughout the neuropils, even though the glomerular PN organization in AL is no longer sustained in the higher brain center. Instead, odor-type dependent clusters consisting of multiple homotypes innervate the MB calyx and LH. Pheromone-encoding and hygro/thermo-sensing homotypes are spatially segregated in MB calyx, whereas two distinct clusters of food-related homotypes are found in LH in addition to the segregation of pheromone-encoding and hygro/thermo-sensing homotypes. We find that there are statistically significant associations between the spatial organization among a group of homotypic uPNs and certain stereotyped olfactory responses. Additionally, the signals from some of the tightly bundled homotypes converge to a specific group of lateral horn neurons (LHNs), which indicates that homotype (or odor type) specific integration of signals occurs at the synaptic interface between PNs and LHNs. Our findings suggest that before neural computation in the inner brain, some of the olfactory information are already encoded in the spatial organization of uPNs, illuminating that a certain degree of labeled-line strategy is at work in the Drosophila olfactory system.

The Role of DNA Damage in Neural Plasticity in Physiology and Neurodegeneration.

Damage to DNA is generally considered to be a harmful process associated with aging and aging-related disorders such as neurodegenerative diseases that involve the selective death of specific groups of neurons. However, recent studies have provided evidence that DNA damage and its subsequent repair are important processes in the physiology and normal function of neurons. Neurons are unique cells that form new neural connections throughout life by growth and re-organisation in response to various stimuli. This “plasticity” is essential for cognitive processes such as learning and memory as well as brain development, sensorial training, and recovery from brain lesions. Interestingly, recent evidence has suggested that the formation of double strand breaks (DSBs) in DNA, the most toxic form of damage, is a physiological process that modifies gene expression during normal brain activity. Together with subsequent DNA repair, this is thought to underlie neural plasticity and thus control neuronal function. Interestingly, neurodegenerative diseases such as Alzheimer’s disease, amyotrophic lateral sclerosis, frontotemporal dementia, and Huntington’s disease, manifest by a decline in cognitive functions, which are governed by plasticity. This suggests that DNA damage and DNA repair processes that normally function in neural plasticity may contribute to neurodegeneration. In this review, we summarize current understanding about the relationship between DNA damage and neural plasticity in physiological conditions, as well as in the pathophysiology of neurodegenerative diseases.

Oxytocin Receptor-Expressing Neurons in the Paraventricular Thalamus Regulate Feeding Motivation through Excitatory Projections to the Nucleus Accumbens Core.

Oxytocin receptors (OTR) have been found in the paraventricular thalamus (PVT) for the regulation of feeding and maternal behaviors. However, the functional projections of OTR-expressing PVT neurons remain largely unknown. Here, we used chemogenetic and optogenetic tools to test the role of OTR-expressing PVT neurons and their projections in the regulation of food intake in both male and female OTR-Cre mice. We found chemogenetic activation of OTR-expressing PVT neurons promoted food seeking under trials with a progressive ratio schedule of reinforcement. Using Feeding Experimentation Devices for real-time meal measurements, we found chemogenetic activation of OTR-expressing PVT neurons increased meal frequency but not cumulative food intake because of a compensatory decrease in meal sizes. In combination with anterograde neural tracing and slice patch-clamp recordings, we found optogenetic stimulation of PVT OTR terminals excited neurons in the posterior basolateral amygdala (pBLA) and nucleus accumbens core (NAcC) as well as local PVT neurons through monosynaptic glutamatergic transmissions. Photostimulation of OTR-expressing PVT-NAcC projections promoted food-seeking, whereas selective activation of PVT-pBLA projections produced little effect on feeding. In contrast to selective activation of OTR terminals, photostimulation of a broader population of glutamatergic PVT terminals exerted direct excitation followed by indirect lateral inhibition on neurons in both NAcC and anterior basolateral amygdala. Together, these results suggest that OTR-expressing PVT neurons are a distinct population of PVT glutamate neurons that regulate feeding motivation through projections to NAcC.SIGNIFICANCE STATEMENT The paraventricular thalamus plays an important role in the regulation of feeding motivation. However, because of the diversity of paraventricular thalamic neurons, the specific neuron types promoting food motivation remain elusive. In this study, we provide evidence that oxytocin receptor-expressing neurons are a specific group of glutamate neurons that primarily project to the nucleus accumbens core and posterior amygdala. We found that activation of these neurons promotes the motivation for food reward and increases meal frequency through projections to the nucleus accumbens core but not the posterior amygdala. As a result, we postulate that oxytocin receptor-expressing neurons in the paraventricular thalamus and their projections to the nucleus accumbens core mainly regulate feeding motivation but not food consumption.

Striatal Indirect Pathway Dysfunction Underlies Motor Deficits in a Mouse Model of Paroxysmal Dyskinesia.

Abnormal involuntary movements, or dyskinesias, are seen in many neurologic diseases, including disorders where the brain appears grossly normal. This observation suggests that alterations in neural activity or connectivity may underlie dyskinesias. One influential model proposes that involuntary movements are driven by an imbalance in the activity of striatal direct and indirect pathway neurons (dMSNs and iMSNs, respectively). Indeed, in some animal models, there is evidence that dMSN hyperactivity contributes to dyskinesia. Given the many diseases associated with dyskinesia, it is unclear whether these findings generalize to all forms. Here, we used male and female mice in a mouse model of paroxysmal nonkinesigenic dyskinesia (PNKD) to assess whether involuntary movements are related to aberrant activity in the striatal direct and indirect pathways. In this model, as in the human disorder PNKD, animals experience dyskinetic attacks in response to caffeine or alcohol. Using optically identified striatal single-unit recordings in freely moving PNKD mice, we found a loss of iMSN firing during dyskinesia bouts. Further, chemogenetic inhibition of iMSNs triggered dyskinetic episodes in PNKD mice. Finally, we found that these decreases in iMSN firing are likely because of aberrant endocannabinoid-mediated suppression of glutamatergic inputs. These data show that striatal iMSN dysfunction contributes to the etiology of dyskinesia in PNKD, and suggest that indirect pathway hypoactivity may be a key mechanism for the generation of involuntary movements in other disorders.SIGNIFICANCE STATEMENT Involuntary movements, or dyskinesias, are part of many inherited and acquired neurologic syndromes. There are few effective treatments, most of which have significant side effects. Better understanding of which cells and patterns of activity cause dyskinetic movements might inform the development of new neuromodulatory treatments. In this study, we used a mouse model of an inherited human form of paroxysmal dyskinesia in combination with cell type-specific tools to monitor and manipulate striatal activity. We were able to narrow in on a specific group of neurons that causes dyskinesia in this model, and found alterations in a well-known form of plasticity in this cell type, endocannabinoid-dependent synaptic LTD. These findings point to new areas for therapeutic development.

Reelin Affects Signaling Pathways of a Group of Inhibitory Neurons and the Development of Inhibitory Synapses in Primary Neurons.

Reelin is a secretory protein involved in a variety of processes in forebrain development and function, including neuronal migration, dendrite growth, spine formation, and synaptic plasticity. Most of the function of Reelin is focused on excitatory neurons; however, little is known about its effects on inhibitory neurons and inhibitory synapses. In this study, we investigated the phosphatidylinositol 3-kinase/Akt pathway of Reelin in primary cortical and hippocampal neurons. Individual neurons were visualized using immunofluorescence to distinguish inhibitory neurons from excitatory neurons. Reelin-rich protein supplementation significantly induced the phosphorylation of Akt and ribosomal S6 protein in excitatory neurons, but not in most inhibitory neurons. In somatostatin-expressing inhibitory neurons, one of major subtypes of inhibitory neurons, Reelin-rich protein supplementation induced the phosphorylation of S6. Subsequently, we investigated whether or not Reelin-rich protein supplementation affected dendrite development in cultured inhibitory neurons. Reelin-rich protein supplementation did not change the total length of dendrites in inhibitory neurons in vitro. Finally, we examined the development of inhibitory synapses in primary hippocampal neurons and found that Reelin-rich protein supplementation significantly reduced the density of gephyrin–VGAT-positive clusters in the dendritic regions without changing the expression levels of several inhibitory synapse-related proteins. These findings indicate a new role for Reelin in specific groups of inhibitory neurons and the development of inhibitory synapses, which may contribute to the underlying cellular mechanisms of RELN-associated neurological disorders.