Fiber Photometry Research Articles

Chemogenetic Control of Striatal Astrocytes Improves Parkinsonian Motor Deficits in Mice.

Parkinson's disease (PD) is characterized by the degeneration of dopaminergic nigrostriatal inputs, which causes striatal network dysfunction and leads to pronounced motor deficits. Recent evidence highlights astrocytes as a potential local source for striatal neuromodulation. There is substantial evidence for norepinephrine-mediated recruitment of cortical astrocyte activity during movement and locomotion. However, it is unclear how astrocytes in the striatum, a region devoid of norepinephrine neuromodulatory inputs, respond during locomotion. Moreover, it remains unknown how dopamine loss affects striatal astrocyte activity and whether astrocyte activity regulates behavioral deficits in PD. We addressed these questions by performing astrocyte-specific calcium recordings and manipulations using invivo fiber photometry and chemogenetics. We find that locomotion elicits astrocyte calcium activity over a slower timescale than neurons. Acute pharmacological blockade of dopamine receptors only moderately reduced locomotion-related astrocyte activity. Yet, unilateral dopamine depletion significantly attenuated astrocyte calcium responses. Chemogenetic stimulation of Gi-coupled receptors partially improved this functional astrocyte deficit in dopamine-lesioned mice. In parallel, chemogenetic manipulation restored asymmetrical motor deficits and moderately improved open-field exploratory behavior. Together, our results establish a novel role for functional striatal astrocyte signaling in modulating motor function in PD and highlight non-neuronal targets for potential PD therapeutics.

Dopamine dynamics in chronic pain: music-induced, sex-dependent, behavioral effects in mice.

Chronic pain is a debilitating disease that is usually comorbid to anxiety and depression. Current treatment approaches mainly rely on analgesics but often neglect emotional aspects. Nonpharmacological interventions, such as listening to music, have been incorporated into clinics to provide a more comprehensive management of chronic pain. However, the underlying mechanisms of music-mediated pain relief are not fully understood. Our aim was to evaluate the effects and mechanisms of music exposure in an animal model of chronic pain. We injected mice with the complete Freund adjuvant (CFA) inflammatory agent into the hind paw and housed them for 14 days with background music, or ambient noise, during their active period (Mozart K.205, overnight). The effect of music exposure on nociception, anxiety-like behaviors, and depression-like behaviors was evaluated through different paradigms, including the hot plate, Von Frey, elevated plus maze, splash, and tail suspension tests. In addition, we conducted fiber photometry experiments to investigate whether music influences dopamine dynamics in the nucleus accumbens (NAcc), a crucial region involved in pain processing, anhedonia, and reward. Our findings indicate that music exposure prevents the decrease in NAcc activity observed in CFA-injected mice, linking with a sex-dependent reduction in allodynia, anxiety-like behaviors, and depression-like behaviors. Accordingly, female mice were more sensitive to music exposure than male mice. Collectively, our findings provide compelling evidence for the integration of music as a nonpharmacological intervention in chronic pain conditions. Moreover, the observed effect on NAcc suggests its potential as a therapeutic target for addressing chronic pain and its associated symptoms.

Nociceptor-localized KCC2 suppresses brachial plexus avulsion-induced neuropathic pain and related central sensitization

Lack in understanding of the mechanism on brachial plexus avulsion (BPA)-induced neuropathic pain (NP) is the key factor restricting its treatment. In the current investigation, we focused on the nociceptor-localized K+-Cl− cotransporter 2 (KCC2) to investigate its role in BPA-induced NP and related pain sensitization. A novel mice model of BPA on the middle trunk (C7) was established, and BPA mice showed a significant reduction in mechanical withdrawal threshold of the affected fore- and hind- paws without affecting the motor function through CatWalk Gait analysis. Decreased expression of KCC2 in dorsal root ganglion (DRG) was detected through Western blot and FISH technology after BPA. Overexpression of KCC2 in DRG could reverse the hyperexcitability of DRG neurons and alleviate the pain of BPA mice synchronously. Meanwhile, the calcium response signal of the affected SDH could be significantly reduced through above method using spinal cord fiber photometry. The synthesis and release of brain-derived neurotrophic factor (BDNF) was also proved reduction through overexpression of KCC2 in DRG, which indicates BDNF can also act as the downstream role in this pain state. As in human-derived tissues, we found decreased expression of KCC2 and increased expression of BDNF and TrκB in avulsed roots of BPA patients compared with normal human DRGs. Our results indicate that nociceptor-localized KCC2 can suppress BPA-induced NP, and peripheral sensitization can be regulated to reverse central sensitization by targeting KCC2 in DRG at the peripheral level through BDNF signaling. The consistent results in both humanity and rodents endow great potential to future transformation of clinical practice.

In vivo recording from calcitonin receptor-expressing neurons in the medial preoptic area during affiliative social behaviors.

Social animals, including mice, are motivated to seek social contact and avoid being alone due to the benefit of the group living in survival and reproductive values. We have previously reported that pup exposure and co-housing with adult female mice can induce the expression of c-Fos in calcitonin receptor (Calcr) neurons located in the medial preoptic area (MPOA) of female mice. These neurons mediate maternal and social contact behaviors among adult virgin females. However, the correlation of the activity of MPOACalcr+ neurons with specific social behaviors remains unclear. In this study, we used in vivo fiber photometry to study MPOACalcr+ neuron activity during affiliative social behaviors. We found that MPOACalcr+ neurons are activated during proactive contact with adult female mice but not during passive contact, suggesting that motivation to seek social contacts is associated with the activation of these neurons. MPOACalcr+ neurons are not activated during contact with non-social objects, such as novel foods and nesting materials, supporting their specific involvement in social behavior. Furthermore, these neurons are more robustly activated during alloparental behaviors such as pup retrieval. Overall, this study demonstrates the involvement of MPOACalcr+ neurons in motivated social interactions with pups and peer females.

Tachykinin-1-expressing parasubthalamic nucleus neurons are necessary for odorant-induced appetite suppression.

Odorants play a critical role in regulating feeding behavior by signaling potential threats or food sources in the environment. However, the neural mechanisms by which odorants affect feeding are not well understood. Tachykinin-1-expressing neurons in the parasubthalamic nucleus (PSTNTac1 neurons) are critical for reducing food intake in response to internal appetite-suppressing hormones, gastric distension, and external cues that signal danger. Therefore, we tested the hypothesis that activity in these neurons is modulated by exposure to aversive, attractive, and neutral odorants. Using fiber photometry in mice, we found that PSTNTac1 neurons increase activity in response to the aversive predator odorants 2-methyl-2-thiazoline (2MT) and 2,5-dihydro-2,4,5-trimethylthiazoline (TMT), but not to neutral or attractive odorants. This activation correlates with a reduction in food intake and an increase in the latency to initiate feeding. Furthermore, chemogenetic inhibition of PSTNTac1 neurons blocks the suppression of feeding caused by 2MT and TMT. These findings highlight the specificity of PSTNTac1 neurons in processing aversive olfactory signals and their critical role in integrating external threat cues with internal signals that regulate appetite.

Somatostatin-expressing neurons in the medial prefrontal cortex promote sevoflurane anesthesia in mice.

The medial prefrontal cortex plays a crucial role in regulating consciousness. However, the specific functions of its excitatory and inhibitory networks during anesthesia remain uncertain. Here we explored the hypothesis that somatostatin interneurons in the medial prefrontal cortex enhance the effects of sevoflurane anesthesia by increasing GABA transmission to pyramidal neurons. EEG was utilized to reflect the depth of anesthesia. Immunostaining and fiber photometry were employed to assess neuronal activities and GABA delivery. The regulation of neuronal activity was achieved by chemogenetics and optogenetics. The expression of c-Fos was increased in somatostatin neurons of the medial prefrontal cortex during sevoflurane anesthesia (air versus sevoflurane: 26.4 ± 6.5 % versus 48 ± 6.2 %, P=0.0007, n=5 mice). Chemogenetic inhibition or activation of somatostatin neurons in the medial prefrontal cortex reduced (from 84 ± 24 s to 51 ± 18 s, P=0.008, n=7 mice) or prolonged (from 97 ± 31 s to 140 ± 30 s, P=0.006, n=7 mice) the sevoflurane anesthesia recovery time. Increased GABA input to pyramidal neurons in the medial prefrontal cortex precedes sevoflurane-induced loss of consciousness (ΔF/F: from 0.46 ± 0.57 % to 2.25 ± 1.42 %, P=0.031, n=10 mice). Activation of somatostatin neurons in the medial prefrontal cortex, leading to a significant reduction in calcium signals within local pyramidal neurons (ΔF/F: from -0.14 ± 0.52 % to -10.08 ± 4.44 %, P=0.002, n=10 mice), and GABA input on pyramidal neurons increased (ΔF/F: from -0.001 ± 0.001 % to 0.28 ± 0.03 %, P=0.002, n=7 mice) in a time-locked manner. Chemogenetic inhibition of pyramidal neurons prolonged the recovery from sevoflurane anesthesia in mice (from 101 ± 46 s to 136 ± 54 s, P=0.017, n=19 mice). Cortical somatostatin neurons may inhibit local pyramidal neurons by enhancing GABA transmission, which increases the effectiveness of sevoflurane anesthesia.

Distinct spatially organized striatum-wide acetylcholine dynamics for the learning and extinction of Pavlovian associations.

Striatal acetylcholine (ACh) signaling has been proposed to counteract reinforcement signals to promote extinction and behavioral flexibility. ACh dips to cues and rewards may open a temporal window for associative plasticity to occur, while elevations may promote extinction. Changes in multi-phasic striatal ACh signals have been widely reported during learning, but how and where signals are distributed to enable region-specific plasticity for the learning and degradation of cue-reward associations is poorly understood. We used array fiber photometry in mice to investigate how ACh release across the striatum evolves during learning and extinction of Pavlovian associations. We report a topographic organization of opposing changes in ACh release to cues, rewards, and consummatory actions across distinct striatum regions. We localized reward prediction error encoding in particular phases of the ACh dynamics to a specific region of the anterior dorsal striatum (aDS). Positive prediction errors in the aDS were expressed in ACh dips, and negative prediction errors in long latency ACh elevations. Silencing aDS ACh release impaired behavioral extinction, suggesting a role for ACh elevations in down-regulating cue-reward associations. Dopamine release in aDS dipped for cues during extinction, but glutamate input onto cholinergic interneurons did not change, suggesting an intrastriatal mechanism for the emergence of ACh elevations. Our large scale measurements indicate how and where ACh dynamics can shape region-specific plasticity to gate learning and promote extinction of Pavlovian associations.

Cholinergic dynamics in the septo-hippocampal system provide phasic multiplexed signals for spatial novelty and correlate with behavioral states.

In the hippocampal formation, cholinergic modulation from the medial septum/diagonal band of Broca (MSDB) is known to correlate with the speed of an animal's movements at sub-second timescales and also supports spatial memory formation. Yet, the extent to which sub-second cholinergic dynamics, if at all, align with transient behavioral and cognitive states supporting the encoding of novel spatial information remains unknown. In this study, we used fiber photometry to record the temporal dynamics in the population activity of septo-hippocampal cholinergic neurons at sub-second resolution during a hippocampus-dependent object location memory task using ChAT-Cre mice. Using a general linear model, we quantified the extent to which cholinergic dynamics were explained by changes in movement speed, behavioral states such as locomotion, grooming, and rearing, and hippocampus-dependent cognitive states such as recognizing a novel location of a familiar object. The data show that cholinergic dynamics contain a multiplexed code of fast and slow signals i) coding for the logarithm of movement speed at sub-second timescales, ii) providing a phasic spatial novelty signal during the brief periods of exploring a novel object location, and iii) coding for environmental novelty at a seconds-long timescale. Furthermore, behavioral event-related phasic cholinergic activity around the onset and offset of the behavior demonstrates that fast cholinergic transients help facilitate a switch in cognitive and behavioral state before and during the onset of behavior. These findings enhance understanding of the mechanisms by which cholinergic modulation contributes to the coding of movement speed and encoding of novel spatial information.

Prolactin-mediates a lactation-induced suppression of arcuate kisspeptin neuronal activity necessary for lactational infertility in mice.

The specific role that prolactin plays in lactational infertility, as distinct from other suckling or metabolic cues, remains unresolved. Here, deletion of the prolactin receptor (Prlr) from forebrain neurons or arcuate kisspeptin neurons resulted in failure to maintain normal lactation-induced suppression of estrous cycles. Kisspeptin immunoreactivity and pulsatile LH secretion were increased in these mice, even in the presence of ongoing suckling stimulation and lactation. GCaMP fibre photometry of arcuate kisspeptin neurons revealed that the normal episodic activity of these neurons is rapidly suppressed in pregnancy and this was maintained throughout early lactation. Deletion of Prlr from arcuate kisspeptin neurons resulted in early reactivation of episodic activity of kisspeptin neurons prior to a premature return of reproductive cycles in early lactation. These observations show dynamic variation in arcuate kisspeptin neuronal activity associated with the hormonal changes of pregnancy and lactation, and provide direct evidence that prolactin action on arcuate kisspeptin neurons is necessary for suppressing fertility during lactation in mice.

Activation of locus coeruleus noradrenergic neurons rapidly drives homeostatic sleep pressure.

Homeostatic sleep regulation is essential for optimizing the amount and timing of sleep for its revitalizing function, but the mechanism underlying sleep homeostasis remains poorly understood. Here, we show that optogenetic activation of locus coeruleus (LC) noradrenergic neurons immediately increased sleep propensity following a transient wakefulness, contrasting with many other arousal-promoting neurons whose activation induces sustained wakefulness. Fiber photometry showed that repeated optogenetic or sensory stimulation caused a rapid reduction of calcium activity in LC neurons and steep declines in noradrenaline/norepinephrine (NE) release in both the LC and medial prefrontal cortex (mPFC). Knockdown of α2A adrenergic receptors in LC neurons mitigated the decline of NE release induced by repetitive stimulation and extended wakefulness, demonstrating an important role of α2A receptor-mediated auto-suppression of NE release. Together, these results suggest that functional fatigue of LC noradrenergic neurons, which reduces their wake-promoting capacity, contributes to sleep pressure.

Sequence termination cues drive habits via dopamine-mediated credit assignment.

Mesolimbic dopamine (DA) neurons are central to sequence learning and habit formation. Yet, the mechanisms by which cue-induced DA neural activity drives goal-directed or habitual sequence execution remain unknown. We designed two novel tasks to investigate how sequence initiation and termination cues influence DA-driven behavioral strategies and learning. We found that sequence initiation and termination cues differentially affect reward expectation during action sequences, with only the termination cue contributing to greater outcome devaluation insensitivity, automaticity and behavioral chunking. Mesolimbic fiber photometry recording revealed that this habit-like behavior was associated with a rapid backpropagation in DA signals from the reward to the immediately preceding cue and with attenuated DA reward prediction error signals, which reflected greater behavioral inflexibility. Finally, in absence of external cues, brief optogenetic stimulation of VTA DA neurons at sequence termination was sufficient to drive automaticity and behavioral chunking. Our results highlight the critical role of cue-evoked DA signals at sequence termination in mediating credit assignment and driving the development of habitual action sequence execution.

Phasic dopamine release in the nucleus accumbens influences REM sleep timing.

Based on the activity of dopamine (DA) neurons during behavioral states, the DA system has long been thought to be foundational in regulating sleep-wake behavior; over the past decade advances in circuit manipulation and recording techniques have strengthened this perspective. Recently, several studies have demonstrated that DA release in regions of the limbic system is important in the promotion of REM sleep. Yet how DA dynamics change within bouts of sleep, how these changes are regulated, and whether they influence future state changes remains unclear. To address these questions, in mice of both sexes we used in vivo fiber photometry and inhibitory optogenetics to identify a specific role of DA transients in the nucleus accumbens (NAcc) in state transitions from NREM sleep. We found that DA transients increase their frequency and amplitude over the duration of NREM sleep and that this increase is more pronounced during NREM bouts that transition into REM sleep. Next, we found that DA transients in NREM sleep are influenced by changes in REM sleep pressure. Finally, we show that transient DA release in the NAcc plays a functional role in regulating the timing of REM sleep entrances, as inhibition of midbrain DA neuron terminals in the NAcc prolonged bouts of NREM sleep and decreased the frequency of bouts of REM sleep. These findings demonstrate that DA release in the NAcc is dynamically regulated by sleep pressure and has a functional role in transitions from NREM sleep, particularly those into REM sleep.Significance Statement Sleep is a central component of daily life and is heavily influenced by midbrain dopamine neurons. Dopamine release in limbic regions, such as the nucleus accumbens, has been implicated in the promotion of REM sleep. However, dopamine release dynamics during sleep and how these influence future changes in state remain unclear. We used a fluorescence-based dopamine biosensor to elucidate the pattern of dopamine release during sleep and inhibitory optogenetics to disrupt dopamine release. Dopamine release increases across the duration of NREM sleep bouts and is sensitive to REM sleep need. Inhibition of dopamine terminals in the nucleus accumbens decreases the frequency of REM sleep. This suggests that phasic dopamine release during NREM sleep functionally influences REM sleep timing.

Dissociable roles of central striatum and anterior lateral motor area in initiating and sustaining naturalistic behavior.

Understanding how corticostriatal circuits mediate behavioral selection and initiation in a naturalistic setting is critical to understanding behavior choice and execution in unconstrained situations. The central striatum (CS) is well poised to play an important role in these spontaneous processes. Using fiber photometry and optogenetics, we identify a role for CS in grooming initiation. However, CS-evoked movements resemble short grooming fragments, suggesting additional input is required to appropriately sustain behavior once initiated. Consistent with this idea, the anterior lateral motor area (ALM) demonstrates a slow ramp in activity that peaks at grooming termination, supporting a potential role for ALM in encoding grooming bout length. Furthermore, optogenetic stimulation of ALM-CS terminals generates sustained grooming responses. Finally, dual-region photometry indicates that CS activation precedes ALM during grooming. Taken together, these data support a model in which CS is involved in grooming initiation, while ALM may encode grooming bout length.

Multi-dimensional oscillatory activity of mouse GnRH neurons in vivo.

The gonadotropin-releasing hormone (GnRH) neurons represent the key output cells of the neural network controlling mammalian fertility. We used GCaMP fiber photometry to record the population activity of the GnRH neuron distal projections in the ventral arcuate nucleus where they merge before entering the median eminence to release GnRH into the portal vasculature. Recordings in freely behaving intact male and female mice revealed abrupt ~8 min duration increases in activity that correlated perfectly with the appearance of a subsequent pulse of luteinizing hormone (LH). The GnRH neuron dendrons also exhibited a low level of unchanging clustered, rapidly fluctuating baseline activity in males and throughout the estrous cycle in females. In female mice, a gradual increase in basal activity that exhibited ~80 min oscillations began in the afternoon of proestrus and lasted for 12 hr. This was associated with the onset of the LH surge that ended several hours before the fall in the GCaMP signal. Abrupt 8 min duration episodes of GCaMP activity continued to occur on top of the rising surge baseline before ceasing in estrus. These observations provide the first description of GnRH neuron activity in freely behaving animals. They demonstrate that three distinct patterns of oscillatory activity occur in GnRH neurons. These are comprised of low-level rapid baseline activity, abrupt 8 min duration oscillations that drive pulsatile gonadotropin secretion, and, in females, a gradual and very prolonged oscillating increase in activity responsible for the preovulatory LH surge.

Multi-dimensional oscillatory activity of mouse GnRH neurons in vivo

The gonadotropin-releasing hormone (GnRH) neurons represent the key output cells of the neural network controlling mammalian fertility. We used GCaMP fiber photometry to record the population activity of the GnRH neuron distal projections in the ventral arcuate nucleus where they merge before entering the median eminence to release GnRH into the portal vasculature. Recordings in freely behaving intact male and female mice revealed abrupt ~8 min duration increases in activity that correlated perfectly with the appearance of a subsequent pulse of luteinizing hormone (LH). The GnRH neuron dendrons also exhibited a low level of unchanging clustered, rapidly fluctuating baseline activity in males and throughout the estrous cycle in females. In female mice, a gradual increase in basal activity that exhibited ~80 min oscillations began in the afternoon of proestrus and lasted for 12 hr. This was associated with the onset of the LH surge that ended several hours before the fall in the GCaMP signal. Abrupt 8 min duration episodes of GCaMP activity continued to occur on top of the rising surge baseline before ceasing in estrus. These observations provide the first description of GnRH neuron activity in freely behaving animals. They demonstrate that three distinct patterns of oscillatory activity occur in GnRH neurons. These are comprised of low-level rapid baseline activity, abrupt 8 min duration oscillations that drive pulsatile gonadotropin secretion, and, in females, a gradual and very prolonged oscillating increase in activity responsible for the preovulatory LH surge.

A stress-activated mid-insula to BNST pathway regulates susceptibility to abstinence-induced negative affect in female mice.

Stress is central to many neuropsychiatric conditions, including alcohol use disorder (AUD). Stress influences the initiation and continued use of alcohol, the progression to AUD, and relapse. Identifying the neurocircuits activated during stress, and individual variability in these responses is critical for developing new treatment targets for AUD, particularly to mitigate stress-induced relapse. Using a longitudinal approach, this study examined the relationship between sub-chronic stress exposure and negative affect during protracted abstinence following chronic ethanol exposure. Sub-chronic restraint stress heightened negative affect-like behavior in protracted abstinence. Interestingly, this was driven by a subset of "stress-susceptible" female mice. We examined the mid-insula, a hub in the brain's salience network, as a driver of this effect, given its role in emotional regulation and links to alcohol craving, consumption, and abstinence-induced negative affect. Mid-insula GCaMP fiber photometry revealed that GCaMP activity during stress exposure was positively correlated with activity during the novelty-suppressed feeding test (NSFT) two weeks into abstinence. A distinct subset of mice exhibited increasing activity during the consummatory phase, implicating the mid-insula as a neural basis for heightened negative affect in abstinence. Chemogenetic inhibition of mid-insula neurons projecting to the dorsal BNST during stress disrupted the emergence of stress susceptibility, highlighting this circuit as a key determinant of susceptibility to abstinence-induced negative affect. These outcomes were female-specific, addressing a critical gap in understanding AUD risk in women. Furthermore, female mice exhibited higher struggling behavior during stress than males. However, this effect was blocked by chemogenetic inhibition of the insula-BNST pathway during stress. By linking pre-alcohol stress response with abstinence outcomes, this work positions the insula-BNST pathway as a potential AUD circuit activity biomarker and therapeutic target.

Gene Deficiency of δ Subunit-Containing GABAA Receptor in mPFC Lead Learning and Memory Impairment in Mice.

Maintaining GABAergic inhibition within physiological limits in the medial prefrontal cortex (mPFC) is critical for working memory. While synaptic GABAAR typically mediate the primary component of mPFC inhibition, the role of extrasynaptic δ-GABAAR in working memory remains unclear. To investigate this, we used fiber photometry to examine the effects of δ-GABAAR in freely moving mice. Our results indicate that the loss of δ-GABAAR expression leads to learning and memory impairment. Specifically, activation of δ-GABAAR impaired learning and memory in WT mice but enhanced learning and memory in δ+/- knockout mice. Furthermore, δ-GABAAR activation increased calcium activity in the mPFC pyramidal neurons, an effect not observed in δ-Cas9-sgRNA virus-infected mice. Collectively, these findings suggest that δ-GABAAR deficiency impairs learning and memory by modulating the excitability of pyramidal neurons in the mPFC. These results delineate the functional contribution of δ-GABAAR to learning and memory, suggesting their role extends beyond the mere maintenance of information.

Cross-modal cortical circuit for sound sensitivity in neuropathic pain.

Hyperacusis, exaggerated sensitivity to sound, frequently accompanies chronic pain in humans, suggesting interactions between different sensory systems in the brain. However, the neural mechanisms underlying this comorbidity remain largely unexplored. In this study, behavioral tests measuring sound-evoked pupil dilation and reaction times to lick water following auditory stimuli showed hyperacusis-like behaviors in neuropathic pain model mice. Through viral tracing, fiber photometry, and multi-electrode recordings, we identified glutamatergic projections from primary somatosensory cortex (S1HLGlu) to the auditory cortex (ACx) that participate in amplifying sound-evoked neuronal activity following spared nerve injury in the hindlimb. Chemo- or optogenetic manipulation and electrophysiology recordings confirmed that the S1HLGlu → ACx pathway is essential for this heightened response to sound. Specifically, activating this pathway intensified glutamatergic neuronal activity in the ACx and induced hyperacusis-like behaviors, while chemogenetic suppression reversed these effects in neuropathic pain model mice. These findings illustrate the mechanism by which central gain increases in the ACx of neuropathic pain mice, improving our understanding of cross-modal sensory system interactions and suggesting circuit pathway targets for developing interventions to treat pain-associated hyperacusis in clinic.

CHOP-Mediated Disruption of Hippocampal Synaptic Plasticity and Neuronal Activity Contributes to Chronic Pain-Related Cognitive Deficits.

Endoplasmic reticulum (ER) stress-induced protein homeostasis perturbation is a core pathological element in the pathogenesis of neurodegenerative diseases. This study aims to clarify the unique role played by C/EBP homologous protein (CHOP) as a biomarker of the unfolded protein response (UPR) in the etiology of chronic pain and related cognitive impairments following chronic constrictive nerve injury (CCI). The memory capability following CCI was assessed utilizing the Morris water maze (MWM) and fear conditioning test (FCT). Activation of the UPR was quantified by assessing levels of CHOP and key ER stress sensors. The terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) assay and the levels of cleaved caspase-3 were utilized to assess apoptosis level. Synaptic plasticity was assessed via a modified Golgi-Cox staining method, and long-term potentiation (LTP) measurements were taken. Neuronal activity was determined by immunofluorescence and fiber photometry. Knockdown of CHOP and alleviation of ER stress were selectively induced by LV-Ddit3-shRNAs and the chemical chaperone 4-phenylbutyric acid (4-PBA), respectively. Mice subjected to CCI displayed enduring pain and cognitive impairments evident on Days 21-28 post-surgery. Following CCI, changes in the dorsal CA1 (dCA1) manifested as ER dilation, upregulation of CHOP and upstream signaling molecules, reduced dendritic spine density, and PSD95 levels, and impaired LTP. Additionally, the co-localization of CaMKIIα/c-Fos and CaMKIIαdCA1-mediated calcium signaling was significantly reduced, while the activation of CaMKIIα was found to mitigate cognitive impairments in CCI mice. Selective knockdown of CHOP enhanced synaptic plasticity and CaMKIIα neuron activity, while 4-PBA treatment alleviated ER stress, synergistically improving cognitive deficits associated with chronic pain. CCI-induced CHOP upregulation impairs dCA1 synaptic plasticity and neuronal activity, leading to chronic pain-related cognitive deficits.

Projection-targeted photopharmacology reveals distinct anxiolytic roles for presynaptic mGluR2 in prefrontal- and insula-amygdala synapses.

Dissecting how membrane receptors regulate neural circuits is critical for deciphering principles of neuromodulation and mechanisms of drug action. Here, we use a battery of optical approaches to determine how presynaptic metabotropic glutamate receptor 2 (mGluR2) in the basolateral amygdala (BLA) controls anxiety-related behavior in mice. Using projection-specific photopharmacological activation, we find that mGluR2-mediated presynaptic inhibition of ventromedial prefrontal cortex (vmPFC)-BLA, but not posterior insular cortex (pIC)-BLA, connections produces a long-lasting decrease in spatial avoidance. In contrast, presynaptic inhibition of pIC-BLA connections decreases social avoidance and novelty-induced hypophagia without impairing working memory, establishing this projection as a novel target for the treatment of anxiety disorders. Fiber photometry and viral mapping reveal distinct activity patterns and anatomical organization of vmPFC-BLA and pIC-BLA circuits. Together, this work reveals new aspects of BLA neuromodulation with therapeutic implications while establishing a powerful approach for optical mapping of drug action.