Inhibitory DREADD Research Articles

Schizophrenia pathology reverse-translated into mouse shows hippocampal hyperactivity, psychosis behaviors and hyper-synchronous events.

Decades of research into the function of the medial temporal lobe has driven curiosity around clinical outcomes associated with hippocampal dysfunction, including psychosis. Post-mortem analyses of brain tissue from human schizophrenia brain show decreased expression of the NMDAR subunit GluN1 confined to the dentate gyrus with evidence of downstream hippocampal hyperactivity in CA3 and CA1. Little is known about the mechanisms of the emergence of hippocampal hyperactivity as a putative psychosis biomarker. We have developed a reverse-translation mouse to study critical neural features. We had previously studied a dentate gyrus (DG)-specific GluN1 KO, which displays hippocampal hyperactivity and a psychosis-relevant behavioral phenotype. Here, we expressed an inhibitory DREADD (pAAV-CaMKIIa-hM4D(Gi)-mCherry) in granule cells of the mouse dentate gyrus, and continuously inhibited the region for 21 days in adolescent (6 weeks) and adult (10 weeks) C57BL/6 J mice with DREADD agonist Compound 21 (C21). Following this period, we quantified activity in the hippocampal subfields by assessing cFos expression, hippocampally mediated behaviors, and hippocampal local field potential with an intracerebral probe with continual monitoring over time. DG inhibition during adolescence generates an increase in hippocampal activity in CA3 and CA1, impairs social cognition and spatial working memory, as well as shows evidence of increased activity in local field potentials as spontaneous synchronous bursts of activity, which we term hyper-synchronous events (HSEs) in hippocampus. The same DG inhibition delivered during adulthood in the mouse lacks these outcomes. These results suggest a sensitive period in development in which the hippocampus is susceptible to DG inhibition resulting in hippocampal hyperactivity and psychosis-like behavioral outcomes.

Permethrin exposure primes neuroinflammatory stress response to drive depression-like behavior through microglial activation in a mouse model of Gulf War Illness

Gulf War Illness (GWI) is a chronic multisymptom disorder that affects approximately 25–32% of Gulf War veterans and is characterized by a number of symptoms such as cognitive impairment, psychiatric disturbances, chronic fatigue and gastrointestinal distress, among others. While the exact etiology of GWI is unknown, it is believed to have been caused by toxic exposures encountered during deployment in combination with other factors such as stress. In the present study we sought to evaluate the hypothesis that exposure to the toxin permethrin could prime neuroinflammatory stress response and elicit psychiatric symptoms associated with GWI. Specifically, we developed a mouse model of GWI, to evaluate the effects of chronic permethrin exposure followed by unpredictable stress. We found that subjecting mice to 14 days of chronic permethrin exposure followed by 7 days of unpredictable stress resulted in the development of depression-like behavior. This behavioral change coincided with distinct alterations in the microglia phenotype, indicating microglial activation in the hippocampus. We revealed that blocking microglial activation through Gi inhibitory DREADD receptors in microglia effectively prevented the behavioral change associated with permethrin and stress exposure. To elucidate the transcriptional networks impacted within distinct microglia populations linked to depression-like behavior in mice exposed to both permethrin and stress, we conducted a single-cell RNA sequencing analysis using 21,566 single nuclei collected from the hippocampus of mice. For bioinformatics, UniCell Deconvolve was a pre-trained, interpretable, deep learning model used to deconvolve cell type fractions and predict cell identity across spatial datasets. Our bioinformatics analysis identified significant alterations in permethrin exposure followed by stress-associated microglia population, notably pathways related to neuronal development, neuronal communication, and neuronal morphogenesis, all of which are associated with neural synaptic plasticity. Additionally, we observed permethrin exposure followed by stress-mediated changes in signal transduction, including modulation of chemical synaptic transmission, regulation of neurotransmitter receptors, and regulation of postsynaptic neurotransmitter receptor activity, a known contributor to the pathophysiology of depression in a subset of the hippocampal pyramidal neurons in CA3 subregions. Our findings tentatively suggest that permethrin may prime microglia towards a state of inflammatory activation that can be triggered by psychological stressors, resulting in depression-like behavior and alterations of neural plasticity. These findings underscore the significance of synergistic interactions between multi-causal factors associated with GWI.

Role of the caudal Nucleus Tractus Solitarius and the Postinspiratory Complex in swallow production

The production of swallowing and its coordination with breathing is essential for homeostasis in most organisms. The postinspiratory complex (PiCo) is thought to regulate the transition between swallowing and breathing. Activation of PiCo triggers swallow production and stimulates laryngeal activation in a respiratory phase specific manner. However, little is known about PiCo’s role in swallow generation, which is thought to be controlled by the caudal portion of the Nucleus Tractus Solitarius (cNTS), presumably the swallow pattern generator (SPG). We hypothesize the cNTS is necessary for PiCo to trigger a swallow. Using both male and female Vglut2cre mice, a cre-dependent ChR2 AAV was bilaterally injected into PiCo and a cre-dependent inhibitory DREADD was bilaterally injected into the cNTS, specifically targeting the interstitial (SolI) and intermediate (SolIM) solitary nucleus. Twenty-one days after injection, using our freely breathing urethane anesthetized mouse model, swallows were stimulated by 1) injection of water into the oral cavity and 2) optogenetic stimulation of PiCo neurons; before and after DREADD activator, clozapine-N-oxide (CNO). Swallow and laryngeal activity were measured via monopolar suction electrodes of the hypoglossal (XII) and vagus (X) nerves as well as bipolar electromyogram (EMG) of the submental, laryngeal complex and costal diaphragm muscles. Post-hoc histological analysis was done to confirm areas of interest were targeted. We found that after activation of the inhibitory DREADD, located in the cNTS, swallow was not evoked by water stimulation nor optogenetic stimulation. We propose that PiCo relies on direct feedback from the cNTS in order to trigger swallow production. NIH F32 HL160102. 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.

Concurrent, dual perturbations of the 5-HT and NA systems reveal dynamic interplay in regulating the neonate autoresuscitation reflex

Sudden Infant Death Syndrome (SIDS) is a leading cause of infant mortality worldwide. Failure of the neonate auto-resuscitation reflex is hypothesized to be a common endpoint in many SIDS cases. Although SIDS is idiopathic, postmortem studies indicate abnormalities in the serotonergic (5-HT) and noradrenergic (NA) systems of the respiratory network. To better understand the contributions and interactions of these two systems in autoresuscitation, we combined a novel series of Cre- and FLPo- recombinase driver mouse lines and conditional inhibitory and excitatory DREADD lines for singular excitation or inhibition of either the whole 5-HT or whole NA systems. These models were then uniquely combined to further enable 1) concurrent excitation or inhibition of both systems in the same neonate or 2) inhibition of one system while exciting the other system in the same neonate. In total, we developed 8 distinct sets of conditional genetic mouse models for singular and combined 5-HT and NA system perturbation paradigms. The 8 experimental groups and 2 control groups were repeatedly assayed for the autoresuscitation reflex using a robotic neonate cardiorespiratory assessment platform, Looper. Neonates are repeatedly tested until they succumb. Resulting data were analyzed with our recently published waveform analysis software, Breathe Easy, to calculate operant outcomes. In 320 mice total, we found 4 groups with decreased autoresuscitation success: NA activation, NA activation + 5-HT activation, NA activation + 5-HT inhibition, and 5-HT activation. There was no change in survival in any of the other groups including 5-HT inhibition. Preliminary results suggest a potential cardiovascular mechanism of autoresuscitation failure independent of respiratory outcomes. At baseline, all 4 groups with decreased survival showed increased heart rate (HR) whereas the other groups either had the same HR or a decreased HR. During early recovery, defined as beginning at the 10th breath following the primary gasp until recovery, the 4 groups with decreased survival show higher HR than the other groups following the 1st bout of autoresuscitation. As recovery progressed in these groups, HR continued to increase as well until the next autoresuscitation test. Ventilatory frequency, tidal volume, and ventilation all increased in the 3 groups where NA was activated either in isolation or in combination, but there were decreases in all other groups, including 5-HT activation. As the underlying genetic and environmental mechanisms driving SIDS are likely to have pleiotropic effects across multiple neural systems, our first-of-its-kind dual 5-HT and NA system modulations set the stage to more comprehensively model key aspects of SIDS neuropathology that reveal a previously uncharacterized dynamic functional interplay between the NA and 5-HT systems in protective respiratory reflexes. NIH: 1F32HL160073-01A1, R01HL130249 44617-S4. BCM McNair Scholar Program, March of Dimes Basil O'Connor Research Award, Parker B. Francis Fellowship, CJ Foundation for SIDS. 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.

Investigation of the Fasciola Cinereum, Absent in BTBR mice, and Comparison with the Hippocampal Area CA2.

The arginine vasopressin 1b receptor (Avpr1b) plays an important role in social behaviors including social learning, memory, and aggression, and is known to be a specific marker for the cornu ammonis area 2 (CA2) regions of the hippocampus. The fasciola cinereum (FC) is an anatomical region in which Avpr1b expressing neurons are prominent, but the functional roles of the FC have yet to be investigated. Surprisingly, the FC is absent in the inbred BTBR T+tf/J (BTBR) mouse strain used to study core behavioral deficits of autism. Here, we characterized and compared transcriptomic expression profiles using single nucleus RNA sequencing and identified 7 different subpopulations and heterogeneity within the dorsal CA2 (dCA2) and FC. Mef2c, involved in autism spectrum disorder, is more highly expressed in the FC. Using Hiplex in situ hybridization, we examined the neuroanatomical locations of these subpopulations in the proximal and distal regions of the hippocampus. Anterograde tracing of Avpr1b neurons specific for the FC showed projections to the IG, dCA2, lacunosum molecular layer of CA1, dorsal fornix, septofibrial nuclei, and intermediate lateral septum (iLS). In contrast to the dCA2, inhibition of Avpr1b neurons in the FC by the inhibitory DREADD system during behavioral testing did not impair social memory. We performed single nucleus RNA sequencing in the dCA2 region and compared between wildtype (WT) and BTBR mice. We found that transcriptomic profiles of dCA2 neurons between BTBR and WT mice are very similar as they did not form any unique clusters; yet, we found there were differentially expressed genes between the dCA2s of BTBR and WT mice. Overall, this is a comprehensive study of the comparison of Avpr1b neuronal subpopulations between the FC and dCA2. The fact that FC is absent in BTBR mice, a mouse model for autism spectrum disorder, suggests that the FC may play a role in understanding neuropsychiatric disease.

Dopamine activity in the nigrostriatal pathway alters cue-induced risky choice patterns in female rats.

Deficits in cost/benefit decision making is a critical risk factor for gambling disorder. Reward-paired cues may play an important role, as these stimuli can enhance risk preference in rats. Despite extensive research implicating the dorsal striatum in the compulsive aspects of addiction, the role of nigrostriatal dopaminergic activity in cue-induced risk preference remains unclear, particularly in females. Accordingly, we examined the effects of manipulating the dopaminergic nigrostriatal pathway on cue-induced risky choice in female rats. TH:Cre rats were trained on the cued version of the rat Gambling Task. This task was designed such that maximal reward is attained by avoiding the high-risk, high-reward options and instead favouring the options associated with lower per-trial gains, as they feature less frequent and shorter time-out penalties. Adding reward-paired audiovisual cues to the task leads to greater risky choice on average. To assess the role of the nigrostriatal pathway, a viral vector carrying either Cre-dependent inhibitory or excitatory DREADD was infused into the substantia nigra. Rats then received clozapine-N-oxide either during task acquisition or after a stable performance baseline was reached. Inhibition of this pathway accelerated the development of risk preference in early sessions and increased risky choice during performance, but long-term inhibition actually improved decision making. Activation of this pathway had minimal effects. These results provide evidence for the involvement of the dopaminergic nigrostriatal pathway in cue-induced risk preference in females, therefore shedding light on its role in cost/benefit decision-making deficits and expanding our knowledge of the female dopaminergic system.

Chemogenetic inhibition of the ventral hippocampus but not its direct projection to the prelimbic cortex attenuates context-specific operant responding.

Previous work has demonstrated the importance of the prelimbic cortex (PL) in contextual control of operant behavior. However, the associated neural circuitry responsible for providing contextual information to the PL is not well understood. In Pavlovian fear conditioning the ventral hippocampus (vH) and its projection to the PL have been shown to be important in supporting the effects of context on learning. The present experiments used chemogenetic inhibition of the direct vH-PL projection or the vH to determine involvement in expression of context-specific operant behavior. Rats were injected with an inhibitory DREADD (hM4Di) or mCherry-only into the vH, and subsequently trained to perform a lever press response for a food pellet in a distinct context. The DREADD ligand clozapine-n-oxide (CNO) was then delivered directly into the PL (experiment 1) and then systemically (experiment 2) prior to tests of the response in the training context as well as an equally familiar but untrained context. vH (systemic CNO) but not vH-PL (intra-PL CNO) inhibition was found to attenuate operant responding in its acquisition context. A third experiment, using the same rats, showed that chemogenetic inhibition of vH also reduced Pavlovian contextual fear. The present results suggest that multisynapatic connections between the vH and PL may be responsible for integration of contextual information with operant behavior.

Ghrelin-responsive mediobasal hypothalamic neurons mediate exercise-associated food intake and exercise endurance.

Previous studies have implicated the orexigenic hormone ghrelin as a mediator of exercise endurance and the feeding response postexercise. Specifically, plasma ghrelin levels nearly double in mice when they are subjected to an hour-long bout of high-intensity interval exercise (HIIE) using treadmills. Also, growth hormone secretagogue receptor-null (GHSR-null) mice exhibit decreased food intake following HIIE and diminished running distance (time until exhaustion) during a longer, stepwise exercise endurance protocol. To investigate whether ghrelin-responsive mediobasal hypothalamus (MBH) neurons mediate these effects, we stereotaxically delivered the inhibitory designer receptor exclusively activated by designer drugs virus AAV2-hSyn-DIO-hM4(Gi)-mCherry to the MBH of Ghsr-IRES-Cre mice, which express Cre recombinase directed by the Ghsr promoter. We found that chemogenetic inhibition of GHSR-expressing MBH neurons (upon delivery of clozapine-N-oxide) 1) suppressed food intake following HIIE, 2) reduced maximum running distance and raised blood glucose and blood lactate levels during an exercise endurance protocol, 3) reduced food intake following ghrelin administration, and 4) did not affect glucose tolerance. Further, HIIE increased MBH Ghsr expression. These results indicate that activation of ghrelin-responsive MBH neurons is required for the normal feeding response to HIIE and the usual amount of running exhibited during an exercise endurance protocol.

FRI277 Temporal Coordination Of Female Reproductive Axis Activity By Vasoactive Intestinal Polypeptide (VIP) Expressing Cells In The Suprachiasmatic Nucleus

Abstract Disclosure: C. Phumsatitpong: None. S.R. Bever: None. S.L. Hu: None. M.C. Ambrose: None. L.J. Kriegsfeld: None. Circadian rhythms orchestrated by a master clock in the suprachiasmatic nucleus (SCN) are essential for ovulation in spontaneously-ovulating rodents. SCN signaling integrates with estradiol positive feedback to generate the preovulatory luteinizing hormone (LH) surge. Additionally, subordinate clocks in reproductively-relevant SCN targets temporally gate responsiveness to upstream signaling to coordinate ovulation with the active time of day. We have previously shown that the SCN communicates directly to kisspeptin (Kp) and RFamide-related peptide-3 (RFRP-3) neurons to temporally balance key stimulatory and inhibitory input to GnRH neurons required for LH surge generation. Because VIP-expressing neurons in the SCN have been implicated in the LH surge, we employed a cell-specific chemogenetic approach to determine the functional role of this cell phenotype in female reproductive axis regulation required for surge generation. We hypothesized that temporal gating by subordinate cellular clocks will prevent morning stimulation of VIP-expressing cells from increasing Kp and GnRH, and decreasing RFRP-3, cellular activity. In the afternoon, we expected inhibition of VIP-expressing cells to decrease Kp and GnRH, and increase RFRP-3, cellular activity. Specifically, female VIP-Cre mice were stereotaxically injected with either AAV-hM3Dq or hM4Di to express activating (3Dq) or inhibitory (4Di) DREADDs in VIP-expressing SCN cells. Following recovery, mice were injected clozapine n-oxide (CNO) either in the morning, prior to the LH surge (3Dq experiment), or the afternoon, around the time of the LH surge (4Di experiment). Brains were collected to examine neuronal activation in Kp, GnRH, and RFRP-3 neurons using FOS immunofluorescence as a marker. Morning stimulation of SCN VIP neurons decreased RFRP-3 neuronal activation, whereas Kp and GnRH neurons were unaffected at this time, suggesting a temporal gating mechanism at GnRH and/or Kp cells prevents premature ovulation. In contrast, afternoon inhibition of SCN VIP-expressing neurons led to an increase in neuronal activation in RFRP-3 neurons concomitant with a decrease in GnRH and Kp neurons, suggesting that VIP stimulation is required to remove RFRP-3 inhibition on the GnRH and Kp systems. We confirmed this possibility by localizing afternoon injections of CNO to RFRP-3 cells, which led to comparable decreases in GnRH and Kp cellular activity. These data indicate the importance of SCN VIP neurons in the temporally coordinated disinhibition of RFRP-3 neuronal activity required for stimulation of GnRH and Kp neurons around the time of LH surge. Supported by NIH Grant HD-050470. Presentation: Friday, June 16, 2023

Concurrent, dual perturbations of the 5-HT and NA systems reveal dynamic interplay in regulating the neonate autoresuscitation reflex

Sudden Infant Death Syndrome (SIDS) is a leading cause of infant mortality worldwide. Postmortem studies indicate abnormalities in the serotonergic (5-HT) and noradrenergic (NA) systems of the respiratory network. To better understand the relative and potential combined contributions and interactions of these two neurotransmitter systems to SIDS pathology, we developed a novel series of conditionally expressed inhibitory (hM4De) and excitatory (hM3D) DREADD models that allows for singular excitation or inhibition of either the whole 5-HT or whole NA systems as defined by cre- and FLPo- drivers. These models were then uniquely combined to further enable 1) concurrent stimulation or inhibition of both the NA and 5-HT systems in the same animal or 2) inhibition of one system while exciting the other system in the same animal. In total, after two years of complex breeding combining 3 loci and 6 alleles, we developed 8 distinct sets of conditional genetic mouse models for various singular and combined 5-HT and NA system perturbation paradigms.Failure of the neonate auto-resuscitation reflex is hypothesized to be a common endpoint in many SIDS cases. The autoresuscitation reflex can be readily assayed in neonate mice by repeated bouts of exposure to an anoxic gas to induce bradycardia and apnea followed by restoration of room air to observe successful or failed autoresuscitation. The 8 experimental groups and 2 control groups were repeatedly assayed for the autoresuscitation reflex using a new closed loop robotic neonate cardiorespiratory assessment platform and outcomes were analyzed with our recently developed comprehensive respiratory analysis platform, Breathe Easy, to calculate operant outcomes. In >170 mouse pups (≈17 pups per group) assayed over three months, we found that singular DREADD-mediated activation or inhibition of the NA system results in decreased survival. Interestingly, we found that DREADD-mediated 5-HT activation decreases survival. In contrast to previous studies, we found that DREADD-mediated 5-HT inhibition does not impact survival, particularly when all neonates are challenged to autoresuscitation failure. Furthermore, we show survival is restored to control levels when NA inhibition is combined with 5-HT inhibition; however, failure via NA activation is not rescued by 5-HT inhibition. Controls used for comparison were CNO-injected controls as we also show an effect of CNO on survival that cannot be attributed to time of day, rig, experimenter, weight, background genotype, etc. As the underlying genetic and environmental mechanisms driving SIDS are likely to have pleiotropic effects across multiple neural systems, our first-of-its-kind dual 5-HT and NA system modulations sets the stage to more comprehensively model key aspects of SIDS neuropathology that reveal a previously uncharacterized dynamic functional interplay between the NA and 5-HT systems in protective respiratory reflexes. NIH: 1F32HL160073-01A1, R01HL130249 44617-S4. BCM McNair Scholar Program, March of Dimes Basil O'Connor Research Award, Parker B. Francis Fellowship, CJ Foundation for SIDS. This is the full abstract presented at the American Physiology Summit 2023 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.

Alcohol dependence and the ventral hippocampal influence on alcohol drinking in male mice.

Examining neural circuits underlying persistent, heavy drinking provides insight into the neurobiological mechanisms driving alcohol use disorder. Facilitated by its connectivity with other parts of the brain such as the nucleus accumbens (NAc), the ventral hippocampus (vHC) supports many behaviors, including those related to reward seeking and addiction. These studies used a well-established mouse model of alcohol (ethanol) dependence. After surgery to infuse DREADD-expressing viruses (hM4Di, hM3Dq, or mCherry-only) into the vHC and position guide cannula above the NAc, male C57BL/6J mice were treated in the CIE drinking model that involved repeated cycles of chronic intermittent alcohol (CIE) vapor or air (CTL) exposure alternating with weekly test drinking cycles in which mice were offered alcohol (15% v/v) 2h/day. Additionally, smaller groups of mice were evaluated for either cFos expression or glutamate release using microdialysis procedures. In CIE mice expressing inhibitory (hM4Di) DREADDs in the vHC, drinking increased as expected, but CNO (3mg/kg intraperitoneally [i.p.]) given 30min before testing did not alter alcohol intake. However, in CTL mice expressing hM4Di, CNO significantly increased alcohol drinking (∼30%; p<0.05) to levels similar to the CIE mice. The vHC-NAc pathway was targeted by infusing CNO into the NAc (3 or 10 μM/side) 30min before testing. CNO activation of the pathway in mice expressing excitatory (hM3Dq) DREADDs selectively reduced consumption in CIE mice back to CTL levels (∼35-45%; p<0.05) without affecting CTL alcohol intake. Lastly, activating the vHC-NAc pathway increased cFos expression and evoked significant glutamate release from the vHC terminals in the NAc. These data indicate that reduced activity of the vHC increases alcohol consumption and that targeted, increased activity of the vHC-NAc pathway attenuates excessive drinking associated with alcohol dependence. Thus, these findings indicate that the vHC and its glutamatergic projections to the NAc are involved in excessive alcohol drinking.

Theta oscillations in anterior cingulate cortex and orbitofrontal cortex differentially modulate accuracy and speed in flexible reward learning.

Flexible reward learning relies on frontal cortex, with substantial evidence indicating that anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) subregions play important roles. Recent studies in both rat and macaque suggest theta oscillations (5-10 Hz) may be a spectral signature that coordinates this learning. However, network-level interactions between ACC and OFC in flexible learning remain unclear. We investigated the learning of stimulus-reward associations using a combination of simultaneous in vivo electrophysiology in dorsal ACC and ventral OFC, partnered with bilateral inhibitory DREADDs in ACC. In freely behaving male and female rats and using a within-subject design, we examined accuracy and speed of response across distinct and precisely defined trial epochs during initial visual discrimination learning and subsequent reversal of stimulus-reward contingencies. Following ACC inhibition, there was a propensity for random responding in early reversal learning, with correct vs. incorrect trials distinguished only from OFC, not ACC, theta power differences in the reversal phase. ACC inhibition also hastened incorrect choices during reversal. This same pattern of change in accuracy and speed was not observed in viral control animals. Thus, characteristics of impaired reversal learning following ACC inhibition are poor deliberation and weak theta signaling of accuracy in this region. The present results also point to OFC theta oscillations as a prominent feature of reversal learning, unperturbed by ACC inhibition.

Modulating the activity of human nociceptors with a SCN10A promoter-specific viral vector tool

Despite the high prevalence of chronic pain as a disease in our society, there is a lack of effective treatment options for patients living with this condition. Gene therapies using recombinant AAVs are a direct method to selectively express genes of interest in target cells with the potential of, in the case of nociceptors, reducing neuronal firing in pain conditions. We designed a recombinant AAV vector expressing cargos whose expression was driven by a portion of the SCN10A (NaV1.8) promoter, which is predominantly active in nociceptors. We validated its specificity for nociceptors in mouse and human dorsal root ganglia and showed that it can drive the expression of functional proteins. Our viral vector and promoter package drove the expression of both excitatory or inhibitory DREADDs in primary human DRG cultures and in whole cell electrophysiology experiments, increased or decreased neuronal firing, respectively. Taken together, we present a novel viral tool that drives expression of cargo specifically in human nociceptors. This will allow for future specific studies of human nociceptor properties as well as pave the way for potential future gene therapies for chronic pain.

Adult-born neurons inhibit developmentally-born neurons during spatial learning

Ongoing neurogenesis in the dentate gyrus (DG) subregion of the hippocampus results in a heterogenous population of neurons. Immature adult-born neurons (ABNs) have physiological and anatomical properties that may give them a unique role in learning. For example, compared to older granule neurons, they have greater somatic excitability, which could facilitate their recruitment into memory traces. However, recruitment is also likely to depend on interactions with other DG neurons through processes such as lateral inhibition. Immature ABNs target inhibitory interneurons and, compared to older neurons, they receive less GABAergic inhibition. Thus, they may induce lateral inhibition of mature DG neurons while being less susceptible to inhibition themselves. To test this we used a chemogenetic approach to silence immature ABNs as rats learned a spatial water maze task, and measured activity (Fos expression) in ABNs and developmentally-born neurons (DBNs). A retrovirus expressing the inhibitory DREADD receptor, hM4Di, was injected into the dorsal DG of male rats at 6w to infect neurons born in adulthood. Animals were also injected with BrdU to label DBNs or ABNs. DBNs were significantly more active than immature 4-week-old ABNs. Silencing 4-week-old ABNs did not alter learning but it increased activity in DBNs. However, silencing ABNs did not affect activation in other ABNs within the DG. Silencing ABNs also did not alter Fos expression in parvalbumin- and somatostatin-expressing interneurons. Collectively, these results suggest that ABNs may directly inhibit DBN activity during hippocampal-dependent learning, which may be relevant for maintaining sparse hippocampal representations of experienced events.

Inactivation of the Basolateral Amygdala to Insular Cortex Pathway Makes Sign-Tracking Sensitive to Outcome Devaluation.

Goal-tracking (GT) rats are sensitive to Pavlovian outcome devaluation while sign-tracking (ST) rats are devaluation insensitive. During outcome devaluation, GT rats flexibly modify responding to cues based on the current value of the associated outcome. However, ST rats rigidly respond to cues regardless of the current outcome value. Prior work demonstrated disconnection of the basolateral amygdala (BLA) and anterior insular cortex (aIC) decreased both GT and ST behaviors. Given the role of these regions in appetitive motivation and behavioral flexibility, we predicted that disrupting BLA to aIC pathway during outcome devaluation would reduce flexibility in GT rats and reduce rigid appetitive motivation in ST rats. We inhibited the BLA to aIC pathway by infusing inhibitory DREADDs (hM4Di-mcherry) or control (mCherry) virus into the BLA and implanted cannulae into the aIC to inhibit BLA terminals using intracranial injections of clozapine N-oxide (CNO). After training, we used a within-subject satiety-induced outcome devaluation procedure in which we sated rats on training pellets (devalued condition) or homecage chow (valued condition). All rats received bilateral CNO infusions into the aIC before brief nonreinforced test sessions. Contrary to our hypothesis, BLA-IC inhibition did not interfere with devaluation sensitivity in GT rats but did make ST behaviors sensitive to devaluation. Intermediate rats showed the opposite effect, showing rigid responding to cues with BLA-aIC pathway inactivation. Together, these results demonstrate BLA-IC projections mediate tracking-specific Pavlovian devaluation sensitivity and highlights the importance of considering individual differences in Pavlovian approach when evaluating circuitry contributions to behavioral flexibility.

Agouti-related peptide neuronal silencing overcomes delayed puberty in neonatally underfed male mice.

Agouti-related peptide (AgRP) neurons are thought to indirectly regulate the activity of hypothalamic gonadotrophin-releasing hormone neurons which control fertility. AgRP neurons also drive caloric intake and are modulated by metabolically-relevant hormones, providing a link to the hypothalamic-pituitary-gonadal axis. In mice expressing Cre-dependant designer receptors (DREADDs) in AgRP neurons, we activated or silenced these neurons in vivo using the synthetic ligand clozapine-N-oxide (CNO) to observe the effect of AgRP neuron activity on timing of puberty. To validate these animals, we chronically treated both stimulatory (hM3Dq) and inhibitory (hM4Di) DREADD × AgRP-Cre mice with CNO, observing a pronounced increase and decrease of food intake, respectively, consistent with the known orexigenic effects of these neurons. RNAscope was performed to visually confirm the activation of AgRP neurons. Puberty onset was assessed in males and females. There was no effect on preputial separation in males or vaginal opening and first oestrus in females after CNO treatment from day 26 to 30 to chronically modulate AgRP neurons. Next, to determine whether the delay in puberty onset occurring in response to neonatal underfeeding could be overcome by inhibiting AgRP neuronal activity, mice were raised in large (neonatally underfed) or normal litter sizes. The delay in puberty from underfeeding was completely reversed in CNO-treated AgRP-hM4Di male mice. These data highlight the inhibitory role of AgRP neurons to delay puberty onset when undernutrition occurs during the neonatal period, at least in male mice. TRAIL REGISTRATION NUMBER: JNE-22-0081-OA.R2.

An extended amygdala-midbrain circuit controlling cocaine withdrawal-induced anxiety and reinstatement.

SUMMARYAlthough midbrain dopamine (DA) circuits are central to motivated behaviors, our knowledge of how experience modifies these circuits to facilitate subsequent behavioral adaptations is limited. Here we demonstrate the selective role of a ventral tegmental area DA projection to the amygdala (VTADA→amygdala) for cocaine-induced anxiety but not cocaine reward or sensitization. Our rabies virus-mediated circuit mapping approach reveals a persistent elevation in spontaneous and task-related activity of inhibitory GABAergic cells from the bed nucleus of the stria terminalis (BNST) and downstream VTADA→amygdala cells that can be detected even after a single cocaine exposure. Activity in BNSTGABA→midbrain cells is related to cocaine-induced anxiety but not reward or sensitization, and silencing this projection prevents development of anxiety during protracted withdrawal after cocaine administration. Finally, we observe that VTADA→amygdala cells are strongly activated after a challenge exposure to cocaine and that activity in these cells is necessary and sufficient for reinstatement of cocaine place preference.

Activation of the Central Medial Thalamic Afferent to the Orbitofrontal Cortex Contributes to Successful Reversal Learning

Stress‐related psychiatric disorders, such as major depressive disorder and anxiety disorders, have cognitive symptoms that are not well‐treated by classical antidepressants and cause major detriments to patients’ quality of life. Reversal learning, a form of cognitive flexibility necessary to adapt to a changing environment, is disrupted in stress‐related psychiatric disorders. The orbitofrontal cortex (OFC) mediates reversal learning, and hyperactivity in the OFC is associated with psychiatric disorders in humans. Using a reward‐based discrimination digging task to assess reversal learning in rodents, we have previously reported that chronic stress impairs reversal learning and that inducing long‐term depression in the mediodorsal thalamus to OFC pathway reverses these deficits. However, the circuit‐level mechanisms underlying reversal learning are not well established. Preliminary data using Fos immunohistochemistry, showed a significant decrease in Fos in the lateral OFC following reversal learning, and a significant increase in Fos induction in the central medial thalamus (CM). Converging evidence from other laboratories indicates the CM inhibits the prefrontal cortex. Therefore, we next tested the hypothesis that input to the OFC from the CM, inhibiting the OFC, contributes to successful reversal learning. We used an adeno‐associated virus to deliver an inhibitory (Gi) DREADD or GFP control construct into the CM under the control of the CaMKII promoter, and implanted guide cannulae into the lateral OFC for administration of the DREADD agonist directly at the DREADD‐expressing terminals from the CM. Animals received microinjections of DREADD agonist clozapine‐N‐oxide (300 µM, i.c.) directly preceding the reversal learning task. Activating the Gi DREADD significantly impaired reversal learning, increasing the number of trials it took animals to make six consecutive correct responses. These results suggest that excitatory input from the CM to the OFC is critical for successful reversal learning, indicating a novel role for the CM in cognitive flexibility. Future experiments will investigate the role of thalamic inputs to the OFC in the effects of stress on reversal learning.

Impact of putamen inhibition by DREADDs on schedule-induced drinking in rhesus monkeys.

The putamen is a nucleus within the sensory-motor striatal network that is involved in automatic, habitual actions. Schedule-induced polydipsia (SIP) is highly automated behavior, reliably occurring under intermediate interval schedules of reinforcement. The effect of putamen inhibition in mediating SIP of water and ethanol (4% w/v) under a Fixed Time 5-min (FT-5 min) schedule for food delivery was tested in 12 rhesus monkeys (6 male, 6 female). Water and ethanol SIP sessions ended after set volumes were consumed. Baseline patterns of SIP intake differed between water and ethanol SIP in volume but not in pattern of drinking. Activation of the designer receptor exclusively activated by designer drug (DREADD: hM4Di) with deschloroclozapine (DCZ; 300 μg/kg, i.m.) administered 30 min prior to the onset of the SIP session, for four consecutive sessions. DCZ administration increased the postpellet drink volume and reduced the time to drink both water and ethanol. Although the effect of DCZ treatment was similar for increasing SIP with either water or ethanol, post-DCZ return to baseline SIP rates of differed, perhaps highlighting the effect of a state dependency with ethanol SIP. Overall, the study shows that targeting the putamen with the inhibitory DREADD produces a reversible, reproducible and reliable increase in adjunctive drinking.

Sex differences and the lack of effects of chemogenetic manipulation of pro-opiomelanocortin (POMC) neurons on alcohol consumption in male and female mice

The endogenous opioid system has been implicated in the rewarding and reinforcing effects of alcohol. Pro-opiomelanocortin (POMC) neurons located within the arcuate nucleus of the hypothalamus (ArcN) secrete multiple peptides associated with alcohol consumption, including β-endorphin (β-END), α-melanocyte stimulating hormone (α-MSH), and adrenocorticotropic hormone (ACTH). In this study, we utilized chemogenetics to bidirectionally modulate ArcN POMC neurons to determine their role in alcohol and saccharin consumption and regional levels of POMC-derived peptides. Male and female POMC-cre mice were infused with viral vectors designed for cre-dependent expression of either excitatory and inhibitory DREADDs or a control vector into the ArcN. Following recovery, animals were allowed to consume alcohol or saccharin using the drinking-in-the-dark (DID) paradigm of binge-like intake for 4 consecutive days. Prior to the final test session, animals were injected with clozapine-N-oxide (2.5 mg/kg, i.p.) for DREADD activation. Following the last DID session, animals were euthanized and the ArcN, VTA, amygdala and NAc were dissected and assessed for POMC peptide expression utilizing western blotting. We found that female mice consumed more alcohol than males during DID sessions 2–4, and that chemogenetic activation had no effect on alcohol or saccharin consumption in either sex. We found that β-END expression within the ArcN positively correlated with alcohol consumption. Given the molecular and functional heterogeneity of ArcN POMC neurons, future studies are needed to assess the effects of modulation of specific subpopulations of these neurons within the ArcN on consumption of rewarding substances such as alcohol and saccharin.