Stress produces aversion and potentiates cocaine reward by releasing endogenous dynorphins in the ventral striatum to locally stimulate serotonin reuptake

Activation of the dynorphin/κ-opioid receptor (KOR) system by repeated stress exposure or agonist treatment produces place aversion, social avoidance, and reinstatement of extinguished cocaine place preference behaviors by stimulation of p38α MAPK, which subsequently causes the translocation of the serotonin transporter (SERT, SLC6A4) to the synaptic terminals of serotonergic neurons. In the present study we extend those findings by showing that stress-induced potentiation of cocaine conditioned place preference occurred by a similar mechanism. In addition, SERT knock-out mice did not show KOR-mediated aversion, and selective reexpression of SERT by lentiviral injection into the dorsal raphe restored the prodepressive effects of KOR activation. Kinetic analysis of several neurotransporters demonstrated that repeated swim stress exposure selectively increased the V(max) but not K(m) of SERT without affecting dopamine transport or the high-capacity, low-affinity transporters. Although the serotonergic neurons in the dorsal raphe project throughout the forebrain, a significant stress-induced increase in cell-surface SERT expression was only evident in the ventral striatum, and not in the dorsal striatum, hippocampus, prefrontal cortex, amygdala, or dorsal raphe. Stereotaxic microinjections of the long-lasting KOR antagonist norbinaltorphimine demonstrated that local KOR activation in the nucleus accumbens, but not dorsal raphe, mediated this stress-induced increase in ventral striatal surface SERT expression. Together, these results support the hypothesis that stress-induced activation of the dynorphin/KOR system produces a transient increase in serotonin transport locally in the ventral striatum that may underlie some of the adverse consequences of stress exposure, including the potentiation of the rewarding effects of cocaine.

Selective p38α MAPK deletion in serotonergic neurons produces stress resilience in models of depression and addiction

Maladaptive responses to stress adversely affect human behavior, yet the signaling mechanisms underlying stress-responsive behaviors remain poorly understood. Using a conditional gene knockout approach, the α isoform of p38 mitogen-activated protein kinase (MAPK) was selectively inactivated by AAV1-Cre-recombinase infection in specific brain regions or by promoter-driven excision of p38α MAPK in serotonergic neurons (by Slc6a4-Cre or ePet1-Cre) or astrocytes (by Gfap-CreERT2). Social defeat stress produced social avoidance (a model of depression-like behaviors) and reinstatement of cocaine preference (a measure of addiction risk) in wild-type mice, but not in mice having p38α MAPK selectively deleted in serotonin-producing neurons of the dorsal raphe nucleus. Stress-induced activation of p38α MAPK translocated the serotonin transporter to the plasma membrane and increased the rate of transmitter uptake at serotonergic nerve terminals. These findings suggest that stress initiates a cascade of molecular and cellular events in which p38α MAPK induces a hyposerotonergic state underlying depression-like and drug-seeking behaviors.

Cloning and differential expression of two beta-pigment-dispersing hormone (beta-PDH) isoforms in the crab Cancer productus: evidence for authentic beta-PDH as a local neurotransmitter and beta-PDH II as a humoral factor

Two beta-pigment-dispersing hormone (beta-PDH) isoforms have been identified in several decapod crustaceans, including the crab Cancer productus, but whether these peptides serve common or distinct physiological roles remains to be elucidated. Here we show that the distribution of beta-PDH-like immunoreactivity in the nervous system of C. productus is similar to that found in other brachyurans, suggesting roles as both a circulating hormone and a locally released transmitter for members of this peptide family. cDNAs encoding NSELINSILGLPKVMNDAamide (authentic beta-PDH; here termed Canpr-beta-PDH I) or NSELINSLLGLSRLMNEAamide [corrected](Canpr-beta-PDH II) were cloned. Double in situ hybridization revealed that these two beta-PDH isoforms are differentially distributed within the eyestalk. For example, in most neurons between the medulla interna (MI) and the medulla terminalis (MT), both isoforms appear present; however, in some neurons in this region, mRNA for only one or the other isoform was detected. Likewise, only prepro-beta-pdh I mRNA was detected in the somata of the lamina ganglionaris (LG) and in the brain. By direct tissue mass spectrometry, only Canpr-beta-PDH II was detected in the neurosecretory sinus gland (SG), whereas Canpr-beta-PDH I was found in all other parts of the eyestalk. Collectively, these data suggest distinct functions for each of the C. productus beta-PDHs; Canpr-beta-PDH II appears to be a neurohormone in the SG, whereas Canpr-beta-PDH I may function as a local transmitter/modulator. Our data support the hypothesis that duplication and subsequent mutation of a common neuropeptide gene may underlie the evolution of two differentially distributed transcripts that serve distinct physiological roles.

High-mass-resolution direct-tissue MALDI-FTMS reveals broad conservation of three neuropeptides (APSGFLGMRamide, GYRKPPFNGSIFamide and pQDLDHVFLRFamide) across members of seven decapod crustaean infraorders

Matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) has become an important method for identifying peptides in neural tissues. The ultra-high-mass resolution and mass accuracy of MALDI-FTMS, in combination with in-cell accumulation techniques, can be used to advantage for the analysis of complex mixtures of peptides directly from tissue fragments or extracts. Given the diversity within the decapods, as well as the large number of extant species readily available for analysis, this group of animals represents an optimal model in which to examine phylogenetic conservation and evolution of neuropeptides and neuropeptide families. Surprisingly, no large comparative studies have previously been undertaken. Here, we have initiated such an investigation, which encompasses 32 species spanning seven decapod infraorders. Two peptides, APSGFLGMRamide and pQDLDHVFLRFamide, were detected in all species. A third peptide, GYRKPPFNGSIFamide, was detected in all species except members of the Astacidean genus Homarus, where a Val(1) variant was present. Our finding that these peptides are ubiquitously (or nearly ubiquitously) conserved in decapod neural tissues not only suggests important conserved functions for them, but also provides an intrinsic calibrant set for future MALDI-FTMS assessments of other peptides in this crustacean order.

Direct tissue MALDI-FTMS profiling of individual Cancer productus sinus glands reveals that one of three distinct combinations of crustacean hyperglycemic hormone precursor-related peptide (CPRP) isoforms are present in individual crabs

Over the past decade, mass spectrometry has become a prominent technique for identifying peptide hormones. In crustaceans, studies directed at characterizing the peptide complements present in neuroendocrine structures have generally involved the isolation of tissue from a large number of individuals, which are pooled, extracted, purified, and then analyzed via chromatographic techniques coupled with mass spectrometry. While this approach provides information on the peptides present in the population of animals used as the tissue source, data on the peptide complement present in any individual animal are lost. Direct tissue matrix assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) of single tissues has the potential to identify differences in peptide expression between individuals. Here, we have used direct tissue MALDI-FTMS of individual sinus glands (SGs) to show that the four isoforms of crustacean hyperglycemic hormone precursor-related peptide (CPRP) identified previously from pooled Cancer productus SGs (i.e. Fu, Q., Christie, A.E., Li, L. 2005. Mass spectrometric characterization of crustacean hyperglycemic hormone precursor-related peptides (CPRPs) from the sinus gland of the crab, Cancer productus. Peptides 26, 2137-2150.) are differentially distributed in conserved patterns among individual crabs. Of the crabs examined, approximately 61% of the individuals possessed Capr-CPRP I and II, but not III or IV, approximately 26% Capr-CPRP I, II and III, but not IV, and approximately 13% Capr-CPRP I, II and IV, but not III. Our findings set the stage for future molecular investigations on the origin(s) of this individual-specific variation in CPRP complement, as well as investigations of the function and regulation of the individual isoforms. These data also lend a cautionary note to the assumption that the peptides identified via pooled tissues reveal an accurate picture of the peptides present in any given individual.

Midgut epithelial endocrine cells are a rich source of the neuropeptides APSGFLGMRamide (Cancer borealis tachykinin-related peptide Ia) and GYRKPPFNGSIFamide (Gly1-SIFamide) in the crabs Cancer borealis, Cancer magister and Cancer productus

Over a quarter of a century ago, Mykles described the presence of putative endocrine cells in the midgut epithelium of the crab Cancer magister(Mykles, 1979). In the years that have followed, these cells have been largely ignored and nothing is known about their hormone content or the functions they play in this species. Here,we used a combination of immunohistochemistry and mass spectrometric techniques to investigate these questions. Using immunohistochemistry, we identified both SIFamide- and tachykinin-related peptide (TRP)-like immunopositive cells in the midgut epithelium of C. magister, as well as in that of Cancer borealis and Cancer productus. In each species, the SIFamide-like labeling was restricted to the anterior portion of the midgut, including the paired anterior midgut caeca, whereas the TRP-like immunoreactivity predominated in the posterior midgut and the posterior midgut caecum. Regardless of location, label or species, the morphology of the immunopositive cells matched that of the putative endocrine cells characterized ultrastructurally by Mykles(Mykles, 1979). Matrix-assisted laser desorption/ionization-Fourier transform mass spectrometry identified the peptides responsible for the immunoreactivities as GYRKPPFNGSIFamide (Gly1-SIFamide) and APSGFLGMRamide [Cancer borealis tachykinin-related peptide Ia (CabTRP Ia)], respectively, both of which are known neuropeptides of Cancer species. Although the function of these midgut-derived peptides remains unknown, we found that both Gly1-SIFamide and CabTRP Ia were released when the midgut was exposed to high-potassium saline. In addition, CabTRP Ia was detectable in the hemolymph of crabs that had been held without food for several days, but not in that of fed animals, paralleling results that were attributed to TRP release from midgut endocrine cells in insects. Thus, one function that midgut-derived CabTRP Ia may play in Cancer species is paracrine/hormonal control of feeding-related behavior, as has been postulated for TRPs released from homologous cells in insects.

Members of the crustacean hyperglycemic hormone (CHH) peptide family are differentially distributed both between and within the neuroendocrine organs of Cancer crabs: implications for differential release and pleiotropic function

The crustacean hyperglycemic hormone (CHH) family of peptides includes CHH, moult-inhibiting hormone (MIH) and mandibular organ-inhibiting hormone (MOIH). In the crab Cancer pagurus, isoforms of these peptides, as well as CHH precursor-related peptide (CPRP), have been identified in the X-organ-sinus gland (XO-SG) system. Using peptides isolated from the C. pagurus SG, antibodies to each family member and CPRP were generated. These sera were then used to map the distributions and co-localization patterns of these peptides in the neuroendocrine organs of seven Cancer species: Cancer antennarius, Cancer anthonyi, Cancer borealis, Cancer gracilis, Cancer irroratus, Cancer magister and Cancer productus. In addition to the XO-SG, the pericardial organ (PO) and two other neuroendocrine sites contained within the stomatogastric nervous system, the anterior cardiac plexus (ACP) and the anterior commissural organ (ACO), were studied. In all species, the peptides were found to be differentially distributed between the neuroendocrine sites in conserved patterns: i.e. CHH, CPRP, MIH and MOIH in the XO-SG, CHH, CPRP and MOIH in the PO, and MOIH in the ACP (no immunolabeling was found in the ACO). Moreover, in C. productus (and probably in all species), the peptides present in the XO-SG and PO were differentially distributed between the neurons within each of these neuroendocrine organs (e.g. CHH and CPRP in one set of XO somata with MIH and MOIH co-localized in a different set of cell bodies). Taken collectively, the differential distributions of CHH family members and CPRP both between and within the neuroendocrine organs of crabs of the genus Cancer suggests that each of these peptides may be released into the circulatory system in response to varied, tissue-specific cues and that the PO- and/or ACP-derived isoforms may possess functions distinct from those classically ascribed to their release from the SG.

Bistable Behavior Originating in the Axon of a Crustacean Motor Neuron

Both vertebrate and invertebrate motor neurons can display bistable behavior in which self-sustained tonic firing results from a brief excitatory stimulus. Induction of the bistability is usually dependent on activation of intrinsic conductances located in the somatodendritic area and is commonly sensitive to action of neuromodulators. We have observed bistable behavior in a neuromuscular preparation from the foregut of the crab Cancer borealis that consists of the gastric mill 4 (gm4) muscle and the nerve that innervates it, the dorsal gastric nerve ( dgn). Nerve-evoked contractions of enhanced amplitude and long duration (>30 s) were induced by extracellular stimulation when the stimulus voltage was above a certain threshold. Intracellular and extracellular recordings showed that the large contractions were accompanied by persistent firing of the dorsal gastric (DG) motor neuron that innervates gm4. The persistent firing could be induced only by stimulating a specific region of the axon and could not be triggered by depolarizing the soma, even at current amplitudes that induced high-frequency firing of the neuron. The bistable behavior was abolished in low-Ca2+saline or when nicardipine or flufenamic acid, blockers of L-type Ca2+and Ca2+-activated nonselective cation currents, respectively, was applied to the axonal stimulation region of the dgn. Negative immunostaining for synapsin and synaptotagmin argued against the presence of synaptic/modulatory neuropil in the dgn. Collectively, our results suggest that bistable behavior in a motor neuron can originate in the axon and may not require the action of a locally released neuromodulator.

Identification and characterization of a tachykinin-containing neuroendocrine organ in the commissural ganglion of the crab Cancer productus

A club-shaped, tachykinin-immunopositive structure first described nearly two decades ago in the commissural ganglion (CoG) of three species of decapod crustaceans has remained enigmatic, as its function is unknown. Here, we use a combination of anatomical, mass spectrometric and electrophysiological techniques to address this issue in the crab Cancer productus. Immunohistochemistry using an antibody to the vertebrate tachykinin substance P shows that a homologous site exists in each CoG of this crab. Confocal microscopy reveals that its structure and organization are similar to those of known neuroendocrine organs. Based on its location in the anterior medial quadrant of the CoG, we have named this structure the anterior commissural organ (ACO). Matrix-assisted laser desorption/ionization Fourier transform mass spectrometry shows that the ACO contains the peptide APSGFLGMRamide, commonly known as Cancer borealis tachykinin-related peptide Ia (CabTRP Ia). Using the same technique, we show that CabTRP Ia is also released into the hemolymph. As no tachykinin-like labeling is seen in any of the other known neuroendocrine sites of this species (i.e. the sinus gland, the pericardial organ and the anterior cardiac plexus), the ACO is a prime candidate to be the source of CabTRP Ia present in the circulatory system. Our electrophysiological studies indicate that one target of hemolymph-borne CabTRP Ia is the foregut musculature. Here, no direct CabTRP Ia innervation is present, yet several gastric mill and pyloric muscles are nonetheless modulated by hormonally relevant concentrations of the peptide. Collectively, our findings show that the C. productus ACO is a neuroendocrine organ providing hormonal CabTRP Ia modulation to the foregut musculature. Homologous structures in other decapods are hypothesized to function similarly.

Identification, physiological actions, and distribution of VYRKPPFNGSIFamide (Val1-SIFamide) in the stomatogastric nervous system of the American lobsterHomarus americanus

In this study, the peptide VYRKPPFNGSIFamide (Val(1)-SIFamide) was identified in the stomatogastric nervous system (STNS) of the American lobster, Homarus americanus, using matrix-assisted laser desorption/ionization-Fourier transform mass spectrometry (MALDI-FTMS). When bath-applied to the stomatogastric ganglion (STG), synthetic Val(1)-SIFamide activated the pyloric motor pattern, increasing both burst amplitude and duration in the pyloric dilator (PD) neurons. To determine the distribution of this novel SIFamide isoform within the lobster STNS and neuroendocrine organs, a rabbit polyclonal antibody was generated against synthetic Val(1)-SIFamide. Whole-mount immunolabeling with this antibody showed that this peptide is widely distributed within the STNS, including extensive neuropil staining in the STG and commissural ganglia (CoGs) as well as immunopositive somata in the CoGs and the oesophageal ganglion. Labeling was also occasionally seen in the pericardial organ (PO), but not in the sinus gland. When present in the PO, labeling was restricted to fibers-of-passage and was never seen in release terminals. Adsorption of the antibody by either Val(1)-SIFamide or Gly(1)-SIFamide abolished all Val(1)-SIFamide staining within the STNS, including the STG neuropil, whereas adsorption by other lobster neuropeptides had no effect on immunolabeling. These data strongly suggest that the staining we report is a true reflection of the distribution of this peptide in the STNS. Collectively, our mass spectrometric, physiological, and anatomical data are consistent with Val(1)-SIFamide serving as a locally released neuromodulator in the lobster STG. Thus, our study provides the first direct demonstration of function for an SIFamide isoform in any species.

Hormone complement of theCancer productus sinus gland and pericardial organ: An anatomical and mass spectrometric investigation

In crustaceans, circulating hormones influence many physiological processes. Two neuroendocrine organs, the sinus gland (SG) and the pericardial organ (PO), are the sources of many of these compounds. As a first step in determining the roles played by hemolymph-borne agents in the crab Cancer productus, we characterized the hormone complement of its SG and PO. We show via transmission electron microscopy that the nerve terminals making up each site possess dense-core and/or electron-lucent vesicles, suggesting diverse complements of bioactive molecules for both structures. By using immunohistochemistry, we show that small molecule transmitters, amines and peptides, are among the hormones present in these tissues, with many differentially distributed between the two sites (e.g., serotonin in the PO but not the SG). With several mass spectrometric (MS) methods, we identified many of the peptides responsible for the immunolabeling and surveyed the SG and PO for peptides for which no antibodies exist. By using MS, we characterized 39 known peptides [e.g., beta-pigment-dispersing hormone (beta-PDH), crustacean cardioactive peptide, and red pigment-concentrating hormone] and de novo sequenced 23 novel ones (e.g., a new beta-PDH isoform and the first B-type allatostatins identified from a non-insect species). Collectively, our results show that diverse and unique complements of hormones, including many previously unknown peptides, are present in the SG and PO of C. productus. Moreover, our study sets the stage for future biochemical and physiological studies of these molecules and ultimately the elucidation of the role(s) they play in hormonal control in C. productus.