Biology subjects

Eiden, L. E.

Publications and source records attributed to Eiden, L. E..

15 recordsLinked to original sources

bioRxiv2026

Differential utilization of PACAP and glutamate in parabrachial neurons shapes pain and stress

The external parabrachial nucleus (elPBN) contributes to diverse behaviors, including pain and stress. Neurons in this region use glutamatergic and neuropeptidergic signaling, with pituitary adenylate cyclase-activating polypeptide (PACAP) expressed in a subset of glutamatergic neurons. Deletion of PACAP in elPBN neurons attenuates behavioral responses to stress, but the contribution of PACAP to pain sensitization and of glutamatergic neurotransmission to pain- and stress-related responses remain poorly understood. Here, we show that constitutive loss of PACAP markedly attenuated nerve injury-induced hypersensitivity across heat, pressure, cold and tactile modalities without altering baseline nociception, while also reducing inflammation-induced spontaneous pain-related behavior. Notably, selective deletion of PACAP within elPBN neurons phenocopied the suppression of injury-induced hypersensitivity, but left inflammation- induced pain-related behavior unaffected. Ex vivo optogenetic-assisted circuit mapping showed that activation of PACAP-expressing elPBN terminals elicited glutamatergic transmission onto central amygdala (CeA) PKC{delta}-expressing neurons. Selective deletion of VGluT2 in elPBN neurons reduced nerve injury-induced hypersensitivity but, unlike PACAP deletion, also reduced inflammation-induced pain-related behavior, while leaving stress-induced hypophagia intact. Together, these findings reveal differential requirements for PACAP and glutamatergic neurotransmission within the elPBN across pain- and stress-related behaviors.

neuroscience↗

bioRxiv2026

PACAPergic BAC engages basolateral amygdalar and anterodorsal thalamic networks during looming-threat learning and memory in a labyrinth

The bed nucleus of the anterior commissure (BAC) is a small pituitary adenylate cyclase-activating polypeptide (PACAP)-rich glutamatergic cell population located at the intersection of the anterior commissure, stria terminalis, stria medullaris, and fornix. Here, we provide functional neuroanatomical characterization of the BAC using PACAP-Cre mice and Cre-dependent viral tracing. BAC axons traverse these major forebrain conduits to engage distributed limbic and diencephalic networks, with dense innervation of the posterior basolateral amygdala (pBLA) and anterior dorsal thalamic nucleus (AD), both implicated in emotional processing and spatial orientation. To determine the functional significance of the BAC, we developed a novel looming-threat memory test (LTMT) paradigm in which mice learned the location of a shelter within a dual-maze labyrinth before exposure to an overhead looming stimulus. Chemogenetic inhibition of BAC PACAP neurons impaired shelter-directed escape, increased freezing behavior, prolonged escape trajectories, and disrupted efficient safety-seeking responses. Selective deletion of PACAP from BAC neurons also blocked key aspects of the looming-induced behavioral phenotype. Fos mapping revealed robust neuronal activation by the looming stimulus, within the AD, pBLA, and dorsal periaqueductal gray (dPAG). BAC silencing blocked Fos induction. PACAPBAC depletion blocked fos induction in AD, but not in pBLA or dPAG. Preliminary ex-vivo recordings further indicated that PACAP modulates the intrinsic excitability of AD (and pBLA) neurons. Together, these findings identify the BAC as a previously unrecognized PACAPergic forebrain hub that links emotional and spatial-orientation networks to coordinate looming-threat learning, memory, and adaptive defensive behavior.

neuroscience↗

bioRxiv2025

Design of peptide-based PAC1 antagonists combining molecular dynamics simulations and a biologically relevant cell-based assay

The PACAP receptor PAC1 is a Gs-coupled family B1 GPCR for which the highest-affinity endogenous peptide ligands are the pituitary adenylate cyclase-activating peptides PACAP38 and PACAP27, and whose most abundant endogenous ligand is PACAP38. PACAP action at PAC1 is implicated in neuropsychiatric disorders, atherosclerosis, pain chronification, and protection from neurodegeneration and ischemia. As PACAP also interacts with two related receptors, VPAC1 and VPAC2, highly selective ligands, both agonists and antagonists, for PAC1 have been sought. To date, the peptide PACAP(6-38) and polypeptide M65, which is related to maxadilan, a sandfly vasodilator peptide, have been identified as selective for PAC1. Several non-peptide small molecule compounds (SMOLs) have been reported to be specific antagonists at PAC1, albeit their specificities have not been rigorously documented. Here, we present a platform of cellular assays for the screening of biologically relevant antagonists at PAC1 and show that some currently proposed SMOL antagonists do not have activity in this cell reporter assay, while we confirm that PACAP(6-38) and M65 are competitive antagonists. We have used this assay system to explore other peptide antagonists at PAC1, guided by molecular dynamics analysis of the PACAP-PAC1 interaction based on cryo-EM structural models of PAC1 complexed with a number of biologically active ligands. The affinity-trap model for the PAC1-ligand interaction successfully predicts the engagement behavior of PACAP27 and PACAP38 peptide-based PAC1 inhibitors. In particular, C-terminal deletants of PACAP(6-38) that maintain equipotency to PACAP(6-38) allow the shorter sequence to function as a scaffold for further peptide-based antagonist exploration.

pharmacology and toxicology↗

bioRxiv2025

Cocaine-induced immediate-early gene expression in the nucleus accumbens: roles of separate cAMP sensors

Immediate-early gene (IEG) induction after administration of amphetamine or cocaine has been used to trace the signaling pathways that mediate neuronal plasticity required for the short- and long-term behavioral effects of these psychostimulants. We recently reported that a novel cyclic AMP (cAMP)-dependent Rap guanine nucleotide exchange factor-2 (RapGEF2)-ERK signaling pathway is required for Egr-1 induction in D1 medium-spiny neurons (MSNs) of the nucleus accumbens (NAc) after cocaine treatment, and that its deletion from the NAc neurons attenuates cocaine-induced locomotor sensitization and conditioned place preference (CPP). However, the cell type-specific neuronal mechanisms underlying this effect remain unclear. In this study, we used Cre-LoxP technology and a novel Cre-amplifier transgene to generate conditional RapGEF2 knockout mice targeting D1-MSNs and investigated the functional role of RapGEF2 in cocaine reward. Deletion of RapGEF2 in D1-MSNs blocked cocaine-induced ERK phosphorylation (p-ERK) and Egr-1 induction. D1-MSN-specific RapGEF2 deletion did not affect intravenous cocaine self-administration, nor did it affect Fos induction by cocaine, prompting us to examine more closely the role of metabotropic (cAMP-dependent) signaling to IEGs after cocaine administration. We used a battery of D1-MSN-specific genetic interventions targeting cAMP signaling, including Drd1-Cre::Rap1A/Bfl/fl mice, and AAV injection of a Cre-dependent catalytically active phosphodiesterase (PDE4D3-cat) or a Cre-dependent protein kinase A-inhibitor (PKI) in the NAc of Drd1-Cre mice, to explore further the underlying cAMP dependence of IEG induction by acute and chronic cocaine administration, and the cAMP sensors required. Rap1 is reported as a necessary component for both RapGEF2- and PKA-dependent ERK activation, but a requirement for Rap in Fos induction by cocaine has not been examined. Deletion of Rap1A/B in D1-MSNs blocked cocaine-induced p-ERK and Egr-1 expression, but not c-Fos, supporting the idea that the RapGEF2-Rap1-ERK pathway specifically regulates Egr-1, not c-Fos, expression. D1-specific expression of the PDE4D3-cat ablated up-regulation of both Egr-1 and Fos in NAc after cocaine administration, demonstrating that induction of both IEGs requires cAMP elevation in D1-MSNs. Notably, inhibition of PKA activity via AAV-mediated expression of PKI-alpha in D1-MSNs blocked both c-Fos and Egr-1 induction. Thus, acute or chronic cocaine administration activates at least two cAMP-dependent signaling pathways in D1-MSNs: a PKA-Fos pathway and a RapGEF2-ERK-Egr-1 pathway. The finding that PKA also activates the ERK-Egr-1 signaling pathway by convergence on Rap1, and concomitantly activates c-Fos independently of Rap1, may underlie selective effects of metabotropic activation of RapGEF2 and PKA activation by cAMP on cocaine-dependent behaviors in mice.

neuroscience↗

bioRxiv2025

Novel multi-transmitter calyx-like giant synapse revealed in the extended amygdala

We have discovered a highly specialized innervation of the forebrain by pituitary adenylate cyclase activating polypeptide (PACAP) immunohistochemistry originating from the brain stem that uses glutamate, acetylcholine and PACAP and other peptides as neurotransmitters. The parent neurons of the axons are in the Kolliker-Fuse nucleus and their terminals form calyx-like multi-release site synapses in the rodent forebrain extended amygdala similar to the calyx of Held in the auditory brain stem. The latter is a giant, excitatory, cup-like axo-somatic high-fidelity synapse. The PACAP-positive terminals also form enveloping axo-somatic specialization with mixed glutamatergic and cholinergic molecular identities, co-expressing VGluT1, VGluT2, VAChT, and the neuropeptides PACAP, CGRP, and neurotensin, together with calretinin in the presynaptic compartment. We identified a distinct neuronal subpopulation in the pontine Kolliker-Fuse region of the parabrachial complex that gives rise to these calyceal terminals, which engulf PKC/GluD1 somata in the capsular central amygdala and oval bed nucleus of the stria terminalis. Strikingly, GluD1 immunolabeling is concentrated at axo-somatic contact zones apposed to VAChT presynaptic vesicle clusters zones but is absent from postsynaptic densities of conventional type I synapses within the same terminals. The results demonstrate a previously unrecognized multimodal calyx-like synapse in the forebrain, with parallel fast ionotropic and modulatory peptidergic neurotransmission mechanisms, which is a substrate for high-fidelity signal transmission within viscerosensory -emotional circuits. Significance StatementA high-fidelity axo-somatic glutamatergic synapse is exemplified by the calyx of Held in the auditory brainstem, but is unknown in the forebrain. Here we reveal a multimodal calyceal synapse in the extended amygdala formed by glutamatergic afferents of the pontine Kolliker-Fuse nucleus that contain also several neuropeptides. These giant terminals co-package glutamate, acetylcholine, PACAP, CGRP and neurotensin. They envelop select PKC/GluD1 neurons in the capsular central amygdala and oval BNST. These unique forebrain synapses link viscerosensory input from the hindbrain to limbic autonomic centers. Such high-fidelity multimodal transmission is likely to underlie the precise synchronization of emotional and homeostatic control circuits.

neuroscience↗

bioRxiv2024

A comprehensive chemotyping and gonadal regulation of seven kisspeptinergic neuronal populations in the mouse brain

BackgroundKisspeptinergic signaling is well-established as crucial for regulation of reproduction, but its potential broader role in brain function is less understood. This study investigates the distribution and chemotyping of kisspeptin-expressing neurons within the mouse brain. MethodsRNAscope singleplex, duplex and multiplex in situ hybridization methods were used to assess kisspeptin mRNA (Kiss1) expression and its co-expression with other neuropeptides, excitatory and inhibitory neurotransmitter markers, and sex steroid receptors in intact and gonadectomized young adult mice. ResultsSeven distinct kisspeptin neuronal chemotypes were characterized, including within two novel Kiss1-expressing groups described here for the first time: the ventral premammillary nucleus, and the nucleus of the solitary tract. Kiss1 mRNA was also localized in the soma, and within the dendritic compartment, of hypothalamic neurons. Altered Kiss1 expression following gonadectomy suggests a previously unappreciated role for androgen receptors in regulating kisspeptin signaling. ConclusionThis study provides a detailed chemoanatomical map of kisspeptin-expressing neurons in the brain, highlighting their potential functional diversity. The discovery of new kisspeptin-expressing neuronal populations, and gonadectomy-induced changes in Kiss1 expression patterns, provide a basis for further exploration of non-endocrine roles for kisspeptin in brain function.

neuroscience↗

bioRxiv2023

Kisspeptin cell-type and fiber projection analysis suggests its potential role in central sensorial processing and behavioral state control

BackgroundKisspeptin (KP) signaling in the brain is defined by the anatomical distribution of KP-producing neurons, their fibers, receptors, and connectivity. Technological advances have prompted a re-evaluation of these chemoanatomical aspects, originally studied in the early years after the discovery of KP and its receptor Kiss1r. We have previously characterized(1) seven KP neuronal populations in the mouse brain at the mRNA level, including two novel populations, and examined their short-term response to gonadectomy. MethodsIn this study, we mapped KP fiber distribution in rats and mice using immunohistochemistry under intact and short- and long-term post-gonadectomy conditions. Kiss1r mRNA expression was examined via RNAscope, in relation to vesicular GABA transporter (Slc32a1) in whole mouse brain and to KP and vesicular glutamate transporter 2 (Kiss1 and Slc17a6) in hypothalamic RP3V and arcuate regions. ResultsWe identified KP fibers in 118 brain regions, primarily in extra-hypothalamic areas associated with sensorial processing and behavioral state control. KP-immunoreactive fiber density and distribution were largely unchanged by gonadectomy. Kiss1r was expressed prominently in sensorial and state control regions such as septal nuclei, the suprachiasmatic nucleus, locus coeruleus, hippocampal layers, thalamic nuclei, and cerebellar structures. Co-expression of Kiss1r and Kiss1 was observed in hypothalamic neurons, suggesting both autocrine and paracrine KP signaling mechanisms. ConclusionThese findings enhance our understanding of KP signaling beyond reproductive functions, particularly in sensorial and behavioral state regulation. This study opens new avenues for investigating KPs role in controlling complex physiological processes, including those not related to reproduction.

neuroscience↗

bioRxiv2022

Nucleus of the lateral olfactory tract (NLOT): a hub linking water homeostasis-associated SON-AVP circuit and neocortical regions to promote social behavior under osmotic challenge

Homeostatic challenges increase the drive for social interaction. The neural activity that prompts this motivation remains poorly understood. Here, we identify direct projections from the hypothalamic supraoptic nucleus (SON) to the cortico-amygdalar nucleus of the lateral olfactory tract (NLOT). Dual in situ hybridization (DISH) with probes for PACAP, and VGLUT1, VGLUT2, V1a and V1b revealed a population of vasopressin-receptive PACAPergic neurons in NLOT layer 2 (NLOT2). Water deprivation (48 hours, WD48) increased sociability compared to euhydrated subjects, assessed with the three-chamber social interaction test (3CST). Fos expression immunohistochemistry showed NLOT and its main efferent regions had further increases in rats subjected to WD48+3CST. These regions strongly expressed PAC1 mRNA. Microinjections of AVP into NLOT produced similar changes in sociability to water deprivation, and these were reduced by co-injection of V1a or V1b antagonists along with AVP. We conclude that during challenge to water homeostasis, there is a recruitment of a glutamatergic-multi-peptidergic cooperative circuit that promotes social behavior.

neuroscience↗

bioRxiv2022

Hippocampal cAMP-dependent synaptic potentiation, ERK-dependent immediate-early gene activation, and context-dependent fear conditioning in mice are linked through dependence on the guanine nucleotide exchange factor RapGEF2

The MAP kinase ERK is important for neuronal plasticity underlying associative learning, yet specific molecular pathways for ERK activation in hippocampus are still largely undetermined. RapGEF2 has emerged as a neuron-specific cAMP sensor that mediates ERK activation. We investigated whether RapGEF2 might also be required for cAMP-dependent ERK activation leading to synaptic potentiation, and how this involvement might be penetrant to hippocampus-dependent learned behavior. We demonstrate that conditional knockout of Rapgef2 in forebrain neurons, specifically in dentate gyrus and CA1 of the hippocampus, leads to an attenuation of context-dependent fear conditioning, but not of cue-dependent fear conditioning, in mice. RapGEF2 knockout is associated with a reduction in cAMP-dependent synaptic potentiation at two central hippocampal synapses-the entorhinal cortex-granule cell synapse and the CA3-CA1 synapse. Furthermore, cAMP-induced postsynaptic potentiation requires both RapGEF2 and activation of ERK. Induction of Egr-1/Zif268 (and pERK), but not of c-Fos, immediately following fear conditioning, was abolished in CA1 and detate gyrus, in the absence of RapGEF2 expression in these hippocampal regions, thus revealing a link between learning (conditioning) and molecular pathways activated during conditioned fear memory formation. Hence, we suggest that contextual fear conditioning is mediated via RapGEF2-dependent ERK activation and downstream induction of Egr-1, via an underlying mechanism of cAMP-dependent long-term potentiation at hippocampal synapses. Cyclic AMP-dependent GEFs have been genetically associated as risk factors for schizophrenia, a disorder associated with cognitive deficits. This study provides a functional link between one of these cAMP-dependent GEFs, RapGEF2, and cognitive processes involved in associative learning.

neuroscience↗

bioRxiv2021

ACE2 expression in rat brain: implications for COVID-19 associated neurological manifestations

We examined cell type-specific expression and distribution of rat brain angiotensin converting enzyme 2 (ACE2), the receptor for SARS-CoV-2, in rodent brain. ACE2 is ubiquitously present in brain vasculature, with the highest density of ACE2 expressing capillaries found in the olfactory bulb, the hypothalamic paraventricular, supraoptic and mammillary nuclei, the midbrain substantia nigra and ventral tegmental area, and the hindbrain pontine nucleus, pre-Botzinger complex, and nucleus of tractus solitarius. ACE2 was expressed in astrocytes and astrocytic foot processes, pericytes and endothelial cells, key components of the blood-brain-barrier. We found discrete neuronal groups immunopositive for ACE2 in brainstem respiratory rhythm generating centers including the pontine nucleus, the parafascicular/retrotrapezoid nucleus, the parabrachial nucleus, the Botzinger and pre-Botzinger complex and the nucleus of tractus solitarius; in arousal-related pontine reticular nucleus and in gigantocellular reticular nuclei; in brainstem aminergic nuclei, including substantia nigra, ventral tegmental area, dorsal raphe, and locus coeruleus; in the epithalamic habenula, hypothalamic paraventricular and suprammamillary nuclei; and in the hippocampus. Identification of ACE2-expressing neurons in rat brain within well-established functional circuits facilitates prediction of possible neurological manifestations of brain ACE2 dysregulation during and after COVID-19 infection. HighlightsO_LIACE2 is present in astrocytes, pericytes, and endothelia of the blood brain barrier. C_LIO_LINeuronal ACE2 expression is shown in discrete nuclei through the brain. C_LIO_LIBrainstem breathing, arousal-related, hypothalamic and limbic nuclei express ACE2. C_LIO_LIACE2 is expressed in circuits potentially involved in COVID-19 pathophysiology. C_LI

neuroscience↗

bioRxiv2021

Relationship between constitutive and acute gene regulation, and physiological and behavioral responses, mediated by the neuropeptide PACAP

Since the advent of gene knockout technology in 1987, insight into the role(s) of neuropeptides in centrally- and peripherally-mediated physiological regulation has been gleaned by examining altered physiological functioning in mammals, predominantly mice, after genetic editing to produce animals deficient in neuropeptides or their cognate G-protein coupled receptors (GPCRs). These results have complemented experiments involving infusion of neuropeptide agonists or antagonists systemically or into specific brain regions. Effects of gene loss are often interpreted as indicating that the peptide and its receptor(s) are required for the physiological or behavioral responses elicited in wild-type mice at the time of experimental examination. These interpretations presume that peptide/peptide receptor gene deletion affects only the expression of the peptide/receptor itself, and therefore impacts physiological events only at the time at which the experiment is conducted. A way to support real-time interpretations of neuropeptide gene knock-out is to demonstrate that the wild-type transcriptome, except for the deliberately deleted gene(s), in tissues of interest, is preserved in the knock-out mouse. Here, we show that there is a cohort of genes (constitutively PACAP-Regulated Genes, or cPRGs) whose basal expression is affected by constitutive knock-out of the Adcyap1 gene in C57Bl6/N mice, and additional genes whose expression in response to physiological challenge, in adults, is altered or impaired in the absence of PACAP expression (acutely PACAP-Regulated Genes, or aPRGs). Distinguishing constitutive and acute transcriptomic effects of neuropeptide deficiency on physiological function and behavior in mice reveals alternative mechanisms of action, and changing functions of neuropeptides, throughout the lifespan.

neuroscience↗

bioRxiv2020

Vasopressin acts as a synapse organizer in limbic regions by boosting PSD95 and GluA1 expression

Hypothalamic arginine vasopressin (AVP)-containing magnocellular neurosecretory neurons (AVPMNN) emit collaterals to synaptically innervate limbic regions influencing learning, motivational behaviour, and fear responses. Here, we characterize the dynamics of expression changes of two key determinants for synaptic strength, the postsynaptic density (PSD) proteins AMPAR subunit GluA1 and PSD scaffolding protein 95 (PSD95), in response to in vivo manipulations of AVPMNN neuronal activation state, or exposure to exogenous AVP ex vivo. Both long term water deprivation in vivo, which powerfully upregulates AVPMNN metabolic activity, and exogenous AVP application ex vivo, in brain slices, significantly increased GluA1 and PSD95 expression measured by western blot, in brain regions reportedly receiving direct ascending innervations from AVPMNN (i.e., ventral hippocampus, amygdala and lateral habenula). In contrast, the visual cortex, a region not observed to receive AVPMNN projections, showed no such changes. Ex vivo application of V1a and V1b antagonists to ventral hippocampal slices ablated the AVP stimulated increase in postsynaptic protein expression measured by western blot. Using a modified expansion microscopy technique, we were able to quantitatively assess the significant augmentation of PSD95 and GLUA1 densities in subcellular compartments in locus coeruleus tyrosine hydroxylase immunopositive fibres, adjacent to AVP axon terminals. Our data strongly suggest that the AVPMNN ascending system plays a role in the regulation of the excitability of targeted neuronal circuits through upregulation of key post-synaptic density proteins corresponding to excitatory synapse. Supported by grantsUNAM-DGAPA-PAPIIT-IN200121 & CONACYT-CB-238744 (LZ); CONACYT A1-S-8731 (LIE); MH002386, NIMH, NIH, USA (LEE)

neuroscience↗

bioRxiv2020

Microglial synaptic pruning on axon initial segment of dentate granule cells: sexually dimorphic effects on fear response of adult rats subjected to early life stress

Axon initial segments (AIS) of dentate granule cells (GC) in hippocampus exhibit prominent spines during early development that are associated with microglial contacts. Here, we asked if developmental changes in axon initial segment spines (AISS) could be modified by neonatal maternal separation through stress hormones and microglial activation and examined the potential behavioral consequences. We examined AISS densities at postnatal day (PND) 15 and 50, using Golgi-Cox staining and anatomical analysis. Neuron-microglial interaction was assessed using antibodies against ankyrinG, PSD95 and Iba1, for AIS, AISS and microglia, respectively, in normally reared and neonatal maternally separated (MS) male and female rats. We observed a higher density of AISS in MS groups at both PND15 and PND50 compared to control. Effects were more pronounced in female than in male rats. AIS-associated microglia showed a hyper-ramified morphology and less co-localization with PSD95 in MS compared to normally reared animals at PND 15. An MS-like alteration in microglial morphology and synaptic pruning could be produced ex vivo by vasopressin application in acute hippocampal slices from normally reared animals. MS rats exhibited increased freezing behavior during auditory fear memory testing which, like effects on AISS density, was more pronounced in females than males. Freezing behavior was associated with Fos expression in dorsal and ventral dentate GC. In summary, AIS associated microglial activity is altered by MS. Sex differences in the long-term effects of MS on AISS density are penetrant to a behavioral phenotype of increased stimulus reactivity in adult female subjects.

neuroscience↗

bioRxiv2020

Behavioral role of PACAP signaling reflects its selective distribution in glutamatergic and GABAergic neuronal subpopulations

The neuropeptide PACAP, acting as a co-transmitter, increases neuronal excitability, which may enhance anxiety and arousal associated with threat conveyed by multiple sensory modalities. The distribution of neurons expressing PACAP and its receptor, PAC1, throughout the mouse nervous system was determined, in register with expression of glutamatergic and GABAergic neuronal markers, to develop a coherent chemoanatomical picture of PACAPs role in brain motor responses to sensory input. A circuit role for PACAP was tested by observing fos activation of brain neurons after olfactory threat cue in wild type and PACAP knockout mice. Neuronal activation, and behavioral response, were blunted in PACAP knock-out mice, accompanied by sharply down-regulated vesicular transporter expression in both GABAergic and glutamatergic neurons expressing PACAP and its receptor. This report signals a new perspective on the role of neuropeptide signaling in supporting excitatory and inhibitory neurotransmission in the nervous system within functionally coherent polysynaptic circuits.

neuroscience↗

bioRxiv2020

Cocaine-dependent acquisition of locomotor sensitization and conditioned place preference requires D1 dopaminergic signaling through a cyclic AMP, NCS-Rapgef2, ERK and Egr-1/Zif268 pathway

Elucidation of the underlying mechanism of dopamine signaling to ERK that underlies plasticity in dopamine D1 receptor expressingneurons leadingto acquired cocaine preference is incomplete. NCS-Rapgef2 is a novel cAMP effector, expressed in neuronal and endocrine cells in adult mammals, that is required for D1 dopamine receptor-dependent ERK phosphorylation in mouse brain. In this report, we studied the effects of abrogating NCS-Rapgef2 expression on cAMP-dependent ERK[->]Egr-1/zif268 signaling in cultured neuroendocrine cells; in D1 medium spiny neurons (MSNs) of nucleus accumbens slices; and in mouse brain in a region-specific manner. NCS-Rapgef2 gene deletion in the nucleus accumbens (NAc) in adult mice, using AAV-mediated expression of cre recombinase, eliminated cocaine-induced ERK phosphorylation and Egr-1/Zif268 upregulation in D1-MSNs and cocaine-induced behaviors including locomotor sensitization and conditioned place preference (CPP). Abrogation of NCS-Rapgef2 gene expression in medium prefrontal cortex and basolateral amygdala, by crossing mice bearing a floxed Rapgef2 allele with a cre mouse line driven by calcium/calmodulin-dependent kinase II promoter also eliminated cocaine-induced phospho-ERK activation and Egr-1/Zif268 induction, but without effect on the cocaine-induced behaviors. Our results indicate that NCS-Rapgef2 signaling to ERK in dopamine D1-receptor expressing neurons in the NAc, butnotin corticolimbic areas, contributes to cocaine-induced locomotor sensitization and CPP. Ablation of cocaine-dependent ERK activation by elimination of NCS-Rapgef2 occurred with no effect on phosphorylation of CREB in D1 dopaminoceptive neurons of NAc. This study reveals a new cAMP-dependent signaling pathway for cocaine-induced behavioral adaptations, mediated through NCS-Rapgef2/phospho-ERK activation, independently of PKA/CREB signaling. SIGNIFICANCE STATEMENTERK phosphorylation in dopamine D1 receptor expressing neurons exerts a pivotal role in psychostimulant-induced neuronal gene regulation and behavioraladaptation, including locomotor sensitization and drug preference in rodents. In this study, we examined the role of dopamine signaling through the D1 receptor via a novel pathway initiated through the cAMP-activated guanine nucleotide exchange factor NCS-Rapgef2 in mice. NCS-Rapgef2 in the nucleus accumbens is required for activation of ERK and Egr-1/Zif268 in D1 dopaminoceptive neurons after acute cocaine administration, and subsequentenhanced locomotor response anddrugseeking behavior after repeated cocaine administration. This novel component in dopamine signaling provides a potential new target for intervention in psychostimulant-shaped behaviors, and new understanding of how D1-MSNs encode the experience of psychomotor stimulant exposure.

neuroscience↗