Reduced response to chronic mild stress in PACAP mutant mice is associated with blunted FosB expression in limbic forebrain and brainstem centers

PACAP regulates neuroendocrine and behavioral stress responses via CRF-containing neurons of the rat hypothalamic paraventricular nucleus

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide widely distributed in the brain including the hypothalamic paraventricular nucleus (PVN) implying a regulatory role in stress function. Recent evidence indicates that one of the main targets of PACAP within the PVN are corticotropin-releasing factor (CRF) neurons, which are key regulators of the hypothalamic-pituitary-adrenal (HPA) axis. However, the neural correlates that mediate PACAP effects on stress function are not fully understood. In the present study, we characterized the neuronal mechanism by which PACAP regulates neuroendocrine and behavioral stress responses in rats. We found that intracerebroventricular administration of PACAP increased the swim stress-induced c-Fos expression in distinct brain areas of the stress and anxiety circuitry including the parvocellular part of the PVN and changed behavioral stress coping during forced swimming to a more passive coping style (i.e., indicated by increased floating and reduced struggling behavior). Subsequently, PACAP administration directly into the PVN mimicked these behavioral effects and potentiated the plasma ACTH response to forced swim stress suggesting an excitatory role of PACAP on HPA stress axis reactivity. In addition, immunohistochemical analysis revealed a considerable portion of stress-activated CRF neurons in the medial parvocellular part of the PVN that co-localized PAC1 receptors suggesting that PACAP-induced effects on stress function are likely mediated directly by activation of CRF neurons in the PVN. Thus, these findings suggest that the PVN may represent one of the key areas where PACAP regulates the neuroendocrine and behavioral stress response.

Constitutive and conditional deletion reveals distinct phenotypes driven by developmental versus neurotransmitter actions of the neuropeptide PACAP

Neuropeptides may exert trophic effects during development, and then neurotransmitter roles in the developed nervous system. One way to associate peptide-deficiency phenotypes with either role is first to assess potential phenotypes in so-called constitutive knockout mice, and then proceed to specify, regionally and temporally, where and when neuropeptide expression is required to prevent these phenotypes. We have previously demonstrated that the well-known constellation of behavioral and metabolic phenotypes associated with constitutive pituitary adenylate cyclase-activating peptide (PACAP) knockout mice are accompanied by transcriptomic alterations of two types: those that distinguish the PACAP-null phenotype from wild-type (WT) in otherwise quiescent mice (cPRGs), and gene induction that occurs in response to acute environmental perturbation in WT mice that do not occur in knockout mice (aPRGs). Comparing constitutive PACAP knockout mice to a variety of temporally and regionally specific PACAP knockouts, we show that the prominent hyperlocomotor phenotype is a consequence of early loss of PACAP expression, is associated with Fos overexpression in hippocampus and basal ganglia, and that a thermoregulatory effect previously shown to be mediated by PACAP-expressing neurons of medial preoptic hypothalamus is independent of PACAP expression in those neurons in adult mice. In contrast, PACAP dependence of weight loss/hypophagia triggered by restraint stress, seen in constitutive PACAP knockout mice, is phenocopied in mice in which PACAP is deleted after neuronal differentiation. Our results imply that PACAP has a prominent role as a trophic factor early in development determining global central nervous system characteristics, and in addition a second, discrete set of functions as a neurotransmitter in the fully developed nervous system that support physiological and psychological responses to stress.

The functional heterogeneity of PACAP: Stress, learning, and pathology

Pituitary adenylate cyclase-activating peptide (PACAP) is a highly conserved and widely expressed neuropeptide that has emerged as a key regulator of multiple neural and behavioral processes. PACAP systems, including the various PACAP receptor subtypes, have been implicated in neural circuits of learning and memory, stress, emotion, feeding, and pain. Dysregulation within these PACAP systems may play key roles in the etiology of pathological states associated with these circuits, and PACAP function has been implicated in stress-related psychopathology, feeding and metabolic disorders, and migraine. Accordingly, central PACAP systems may represent important therapeutic targets; however, substantial heterogeneity in PACAP systems related to the distribution of multiple PACAP isoforms across multiple brain regions, as well as multiple receptor subtypes with several isoforms, signaling pathways, and brain distributions, provides both challenges and opportunities for the development of new clinically-relevant strategies to target the PACAP system in health and disease. Here we review the heterogeneity of central PACAP systems, as well as the data implicating PACAP systems in clinically-relevant behavioral processes, with a particular focus on the considerable evidence implicating a role of PACAP in stress responding and learning and memory. We also review data suggesting that there are sex differences in PACAP function and its interactions with sex hormones. Finally, we discuss both the challenges and promise of harnessing the PACAP system in the development of new therapeutic avenues and highlight PACAP systems for their critical role in health and disease.

Downregulation of PACAP and the PAC1 Receptor in the Basal Ganglia, Substantia Nigra and Centrally Projecting Edinger-Westphal Nucleus in the Rotenone model of Parkinson's Disease

Numerous in vitro and in vivo models of Parkinson's disease (PD) demonstrate that pituitary adenylate cyclase-activating polypeptide (PACAP) conveys its strong neuroprotective actions mainly via its specific PAC1 receptor (PAC1R) in models of PD. We recently described the decrease in PAC1R protein content in the basal ganglia of macaques in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD that was partially reversed by levodopa therapy. In this work, we tested whether these observations occur also in the rotenone model of PD in the rat. The rotarod test revealed motor skill deterioration upon rotenone administration, which was reversed by benserazide/levodopa (B/L) treatment. The sucrose preference test suggested increased depression level while the open field test showed increased anxiety in rats rendered parkinsonian, regardless of the received B/L therapy. Reduced dopaminergic cell count in the substantia nigra pars compacta (SNpc) diminished the dopaminergic fiber density in the caudate-putamen (CPu) and decreased the peptidergic cell count in the centrally projecting Edinger-Westphal nucleus (EWcp), supporting the efficacy of rotenone treatment. RNAscope in situ hybridization revealed decreased PACAP mRNA (Adcyap1) and PAC1R mRNA (Adcyap1r1) expression in the CPu, globus pallidus, dopaminergic SNpc and peptidergic EWcp of rotenone-treated rats, but no remarkable downregulation occurred in the insular cortex. In the entopeduncular nucleus, only the Adcyap1r1 mRNA was downregulated in parkinsonian animals. B/L therapy attenuated the downregulation of Adcyap1 in the CPu only. Our current results further support the evolutionarily conserved role of the PACAP/PAC1R system in neuroprotection and its recruitment in the development/progression of neurodegenerative states such as PD.

Functionally active TRPA1 ion channel is downregulated in peptidergic neurons of the Edinger-Westphal nucleus upon acute alcohol exposure

Introduction: The centrally projecting Edinger-Westphal nucleus (EWcp) contributes to the control of alcohol consumption by its urocortin 1 (UCN1) and cocaine- and amphetamine-regulated transcript (CART) co-expressing peptidergic neurons. Our group recently showed that the urocortinergic centrally projecting EWcp is the primary seat of central nervous system transient receptor potential ankyrin 1 (TRPA1) cation channel mRNA expression. Here, we hypothesized that alcohol and its metabolites, that pass through the blood-brain barrier, may influence the function of urocortinergic cells in centrally projecting EWcp by activating TRPA1 ion channels. We aimed to examine the functional activity of TRPA1 in centrally projecting EWcp and its possible role in a mouse model of acute alcohol exposure. Methods: Electrophysiological measurements were performed on acute brain slices of C57BL/6J male mice containing the centrally projecting EWcp to prove the functional activity of TRPA1 using a selective, potent, covalent agonist JT010. Male TRPA1 knockout (KO) and wildtype (WT) mice were compared with each other in the morphological studies upon acute alcohol treatment. In both genotypes, half of the animals was treated intraperitoneally with 1 g/kg 6% ethanol vs. physiological saline-injected controls. Transcardial perfusion was performed 2 h after the treatment. In the centrally projecting EWcp area, FOS immunohistochemistry was performed to assess neuronal activation. TRPA1, CART, and urocortin 1 mRNA expression as well as urocortin 1 and CART peptide content was semi-quantified by RNAscope in situ hybridization combined with immunofluorescence. Results: JT010 activated TRPA1 channels of the urocortinergic cells in acute brain slices. Alcohol treatment resulted in a significant FOS activation in both genotypes. Alcohol decreased the Trpa1 mRNA expression in WT mice. The assessment of urocortin 1 peptide immunoreactivity revealed lower basal urocortin 1 in KO mice compared to WTs. The urocortin 1 peptide content was affected genotype-dependently by alcohol: the peptide content decreased in WTs while it increased in KO mice. Alcohol exposure influenced neither CART and urocortin 1 mRNA expression nor the centrally projecting EWcp/CART peptide content. Conclusion: We proved the presence of functional TRPA1 receptors on urocortin 1 neurons of the centrally projecting EWcp. Decreased Trpa1 mRNA expression upon acute alcohol treatment, associated with reduced neuronal urocortin 1 peptide content suggesting that this cation channel may contribute to the regulation of the urocortin 1 release.

Anterior cingulate cortex, but not amygdala, modulates the anxiogenesis induced by living with conspecifics subjected to chronic restraint stress in male mice

Cohabitation with a partner undergoing chronic restraint stress (CRE) induces anxiogenic-like behaviors through emotional contagion. We hypothesized that the anterior cingulate cortex (ACC) and the amygdala would be involved in the modulation of this emotional process. This study investigated the role of the ACC and amygdala in empathy-like behavior (e.g., anxiety-like responses) induced by living with a mouse subjected to CRE. Male Swiss mice were housed in pairs for 14 days and then allocated into two groups: cagemate stress (one animal of the pair was subjected to 14 days of restraint stress) and cagemate control (no animal experienced stress). Twenty-four hours after the last stress session, cagemates had their brains removed for recording FosB labeling in the ACC and amygdala (Exp.1). In experiments 2 and 3, 24 h after the last stress session, the cagemates received 0.1 μL of saline or cobalt chloride (CoCl₂ 1 mM) into the ACC or amygdala, and then exposed to the elevated plus-maze (EPM) for recording anxiety. Results showed a decrease of FosB labeling in the ACC without changing immunofluorescence in the amygdala of stress cagemate mice. Cohabitation with mice subjected to CRE provoked anxiogenic-like behaviors. Local inactivation of ACC (but not the amygdala) reversed the anxiogenic-like effects induced by cohabitation with a partner undergoing CRE. These results suggest the involvement of ACC, but not the amygdala, in anxiety induced by emotional contagion.

Distribution of PACAP and PAC1 Receptor in the Human Eye

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with widespread distribution and diverse biological functions. Several studies show that PACAP has strong cytoprotective effects mediated mostly through its specific PAC1 receptor (PAC1-R) and it plays important roles in several pathological conditions. Its distribution and altered expression are known in various human tissues, but there is no descriptive data about PACAP and its receptors in the human eyebulb. Since PACAP38 is the dominant form of the naturally occurring PACAP, our aim was to investigate the distribution of PACAP38-like immunoreactivity in the human eye and to describe the presence of PAC1-R. Semiquantitative evaluation was performed after routine histology and immunohistochemical labeling on human eye sections. Our results showed high level of immunopositivity in the corneal epithelium and endothelium. Within the vascular layer, the iris and the ciliary body had strong immunopositivity for both PACAP and PAC1-R. Several layers of the retina showed immunoreactivity for PACAP and PAC1-R, but the ganglion cell layer had a special pattern in the immunolabeling. Labeling was observed in the neuropil within the optic nerve in both cases and glial cells displayed immunoreactivity for PAC1-R. In summary, our study indicates the widespread occurrence of PACAP and its specific receptor in the human eye, implying that the results from in vitro and animal studies have translational value and most probably are also present in the human eye.

Epigenetic and Neuronal Activity Markers Suggest the Recruitment of the Prefrontal Cortex and Hippocampus in the Three-Hit Model of Depression in Male PACAP Heterozygous Mice

Depression and its increasing prevalence challenge patients, the healthcare system, and the economy. We recently created a mouse model based on the three-hit concept of depression. As genetic predisposition (first hit), we applied pituitary adenylate cyclase-activating polypeptide heterozygous mice on CD1 background. Maternal deprivation modeled the epigenetic factor (second hit), and the chronic variable mild stress was the environmental factor (third hit). Fluoxetine treatment was applied to test the predictive validity of our model. We aimed to examine the dynamics of the epigenetic marker acetyl-lysine 9 H3 histone (H3K9ac) and the neuronal activity marker FOSB in the prefrontal cortex (PFC) and hippocampus. Fluoxetine decreased H3K9ac in PFC in non-deprived animals, but a history of maternal deprivation abolished the effect of stress and SSRI treatment on H3K9ac immunoreactivity. In the hippocampus, stress decreased, while SSRI increased H3K9ac immunosignal, unlike in the deprived mice, where the opposite effect was detected. FOSB in stress was stimulated by fluoxetine in the PFC, while it was inhibited in the hippocampus. The FOSB immunoreactivity was almost completely abolished in the hippocampus of the deprived mice. This study showed that FOSB and H3K9ac were modulated in a territory-specific manner by early life adversities and later life stress interacting with the effect of fluoxetine therapy supporting the reliability of our model.

Fluoxetine treatment supports predictive validity of the three hit model of depression in male PACAP heterozygous mice and underpins the impact of early life adversity on therapeutic efficacy

According to the three hit concept of depression, interaction of genetic predisposition altered epigenetic programming and environmental stress factors contribute to the disease. Earlier we demonstrated the construct and face validity of our three hit concept-based mouse model. In the present work, we aimed to examine the predictive validity of our model, the third willnerian criterion. Fluoxetine treatment was applied in chronic variable mild stress (CVMS)-exposed (environmental hit) CD1 mice carrying one mutated allele of pituitary adenylate cyclase-activating polypeptide gene (genetic hit) that were previously exposed to maternal deprivation (epigenetic hit) vs. controls. Fluoxetine reduced the anxiety level in CVMS-exposed mice in marble burying test, and decreased the depression level in tail suspension test if mice were not deprived maternally. History of maternal deprivation caused fundamental functional-morphological changes in response to CVMS and fluoxetine treatment in the corticotropin-releasing hormone-producing cells of the bed nucleus of the stria terminalis and central amygdala, in tyrosine-hydroxylase content of ventral tegmental area, in urocortin 1-expressing cells of the centrally projecting Edinger-Westphal nucleus, and serotonergic cells of the dorsal raphe nucleus. The epigenetic background of alterations was approved by altered acetylation of histone H3. Our findings further support the validity of both the three hit concept and that of our animal model. Reversal of behavioral and functional-morphological anomalies by fluoxetine treatment supports the predictive validity of the model. This study highlights that early life stress does not only interact with the genetic and environmental factors, but has strong influence also on therapeutic efficacy.

Age-Dependent FOSB/ΔFOSB Response to Acute and Chronic Stress in the Extended Amygdala, Hypothalamic Paraventricular, Habenular, Centrally-Projecting Edinger-Westphal, and Dorsal Raphe Nuclei in Male Rats

FOS proteins are early-responding gene products that contribute to the formation of activator protein-1. Several acute and chronic stimuli lead to Fos gene expression, accompanied by an increase of nuclear FOS, which appears to decline with aging. FOSB is another marker to detect acute cellular response, while ΔFOSB mirrors long-lasting changes in neuronal activity upon chronic stress. The notion that the occurrence of stress-related mood disorders shows some age dependence suggests that the brain's stress sensitivity is also a function of age. To study age-dependent stress vulnerability at the immediate-early gene level, we aimed to describe how the course of aging affects the neural responses of FOSB/ΔFOSB in the acute restraint stress (ARS), and chronic variable mild stress (CVMS) in male rats. Fourteen brain areas [central, medial, basolateral (BLA) amygdala; dorsolateral- (BNSTdl), oval- (BNSTov), dorsomedial-, ventral- (BNSTv), and fusiform- (BNSTfu) divisions of the bed nucleus of the stria terminalis; medial and lateral habenula, hypothalamic paraventricular nucleus (PVN), centrally-projecting Edinger-Westphal nucleus, dorsal raphe nucleus, barrel field of somatosensory cortex (S1)] were examined in the course of aging. Eight age groups [1-month-old (M), 1.5 M, 2 M, 3 M, 6 M, 12 M, 18 M, and 24 M] of rats were exposed to a single ARS vs. controls. In addition, rats in six age groups (2, 3, 6, 12, 18, and 24 M) were subjected to CVMS. The FOSB/ΔFOSB immunoreactivity (IR) was a function of age in both controls, ARS- and CVMS-exposed rats. ARS increased the FOSB/ΔFOSB in all nuclei (except in BLA), but only BNSTfu, BNSTv, and PVN reacted throughout the examined lifespan. The CVMS did not increase the FOSB/ΔFOSB in BLA, BNSTov, BNSTdl, and S1. PVN showed a constantly maintained FOSB/ΔFOSB IR during the examined life period. The maximum stress-evoked FOSB/ΔFOSB signal was detected at 2-3 M periods in the ARS- and at 6 M, 18 M in CVMS- model. Corresponding to our previous observations on FOS, the FOSB/ΔFOSB response to stress decreased with age in most of the examined nuclei. Only the PVN exerted a sustained age-independent FOSB/ΔFOSB, which may reflect the long-lasting adaptation response and plasticity of neurons that maintain the hypothalamus-pituitary-adrenal axis response throughout the lifespan.

Neurodegeneration in the centrally-projecting Edinger-Westphal nucleus contributes to the non-motor symptoms of Parkinson's disease in the rat

BACKGROUND

The neuropathological background of major depression and anxiety as non-motor symptoms of Parkinson's disease is much less understood than classical motor symptoms. Although, neurodegeneration of the Edinger-Westphal nucleus in human Parkinson's disease is a known phenomenon, its possible significance in mood status has never been elucidated. In this work we aimed at investigating whether neuron loss and alpha-synuclein accumulation in the urocortin 1 containing (UCN1) cells of the centrally-projecting Edinger-Westphal (EWcp) nucleus is associated with anxiety and depression-like state in the rat.

METHODS

Systemic chronic rotenone administration as well as targeted leptin-saporin-induced lesions of EWcp/UCN1 neurons were conducted. Rotarod, open field and sucrose preference tests were performed to assess motor performance and mood status. Multiple immunofluorescence combined with RNAscope were used to reveal the functional-morphological changes. Two-sample Student's t test, Spearman's rank correlation analysis and Mann-Whitney U tests were used for statistics.

RESULTS

In the rotenone model, besides motor deficit, an anxious and depression-like phenotype was detected. Well-comparable neuron loss, cytoplasmic alpha-synuclein accumulation as well as astro- and microglial activation were observed both in the substantia nigra pars compacta and EWcp. Occasionally, UCN1-immunoreactive neuronal debris was observed in phagocytotic microglia. UCN1 peptide content of viable EWcp cells correlated with dopaminergic substantia nigra cell count. Importantly, other mood status-related dopaminergic (ventral tegmental area), serotonergic (dorsal and median raphe) and noradrenergic (locus ceruleus and A5 area) brainstem centers did not show remarkable morphological changes. Targeted partial selective EWcp/UCN1 neuron ablation induced similar mood status without motor symptoms.

CONCLUSIONS

Our findings collectively suggest that neurodegeneration of urocortinergic EWcp contributes to the mood-related non-motor symptoms in toxic models of Parkinson's disease in the rat.

Global Cerebral Ischemia in Male Long Evans Rats Impairs Dopaminergic/ΔFosB Signalling in the Mesocorticolimbic Pathway Without Altering Delay Discounting Rates

Global cerebral ischemia (GCI) in rats has been shown to promote exploration of anxiogenic zones of the Elevated-Plus Maze (EPM) and Open Field Test (OFT). This study investigated changes in impulsive choice and/or defensive responses as possible contributors of heightened anxiogenic exploration observed after ischemia. Impulsivity was assessed using delay discounting (DD) paradigms, while the Predator Odour Test (PO) served to assess changes in defensive responses towards a naturally aversive stimulus. Male Long Evans rats underwent 9 days of autoshaping training and 24 days of DD training prior to GCI or sham surgery (n = 9/group). Post-surgery, rats completed the OFT, EPM, and PO, followed by 6 days of DD sessions. Blood droplets served to evaluate corticosterone secretion associated with PO exposure. With impulsivity being regulated through mesocorticolimbic monoaminergic pathways, we also characterised post-ischemic changes in the expression of dopamine D₂ receptors (DRD₂), dopamine transporters (DAT), and 1FosB in the basolateral amygdala (BLA), nucleus accumbens core (NAcC) and shell (NAcS), and ventromedial prefrontal cortex (vmPFC) using immunohistofluorescence. Our findings revealed no impact of GCI on delay discounting rates, while PO approach behaviours were minimally affected. Nonetheless, GCI significantly reduced DRD₂ and ΔFosB-ir in the NAcS and NAcC, respectively, while DAT-ir was diminished in both NAc subregions. Collectively, our findings refine the understanding of cognitive-behavioural and biochemical responses following stroke or cardiac arrest. They support significant alterations to the dopaminergic mesocorticolimbic pathway after ischemia, which are not associated with altered impulsive choice in a DD task but may influence locomotor exploration of the OFT and EPM.

Protective Effects of PACAP in a Rat Model of Diabetic Neuropathy

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide with a widespread occurrence and diverse effects. PACAP has well-documented neuro- and cytoprotective effects, proven in numerous studies. Among others, PACAP is protective in models of diabetes-associated diseases, such as diabetic nephropathy and retinopathy. As the neuropeptide has strong neurotrophic and neuroprotective actions, we aimed at investigating the effects of PACAP in a rat model of streptozotocin-induced diabetic neuropathy, another common complication of diabetes. Rats were treated with PACAP1-38 every second day for 8 weeks starting simultaneously with the streptozotocin injection. Nerve fiber morphology was examined with electron microscopy, chronic neuronal activation in pain processing centers was studied with FosB immunohistochemistry, and functionality was assessed by determining the mechanical nociceptive threshold. PACAP treatment did not alter body weight or blood glucose levels during the 8-week observation period. However, PACAP attenuated the mechanical hyperalgesia, compared to vehicle-treated diabetic animals, and it markedly reduced the morphological signs characteristic for neuropathy: axon–myelin separation, mitochondrial fission, unmyelinated fiber atrophy, and basement membrane thickening of endoneurial vessels. Furthermore, PACAP attenuated the increase in FosB immunoreactivity in the dorsal spinal horn and periaqueductal grey matter. Our results show that PACAP is a promising therapeutic agent in diabetes-associated complications, including diabetic neuropathy.

Social disruption-induced stress pre-exposure aggravates, while the presence of conspecifics diminishes, acetic acid-induced writhing

RATIONALE AND OBJECTIVE

This study was undertaken to assess the modulating effects of (1) pre-exposure to repeated social disruption and (2) group testing on writhing associated with visceral pain induced by intraperitoneal administration of acetic acid.

MATERIALS AND METHODS

Six consecutive days of social disruption were used to prime for stress, while group testing referred to 3 mouse cage-mates receiving the acetic acid-induced writhing test as a group.

RESULTS

Social disruption-induced stress-pre-exposed mice displayed a greater number acid-induced writhes compared to mice not receiving the pre-exposure. However, mice displayed fewer acid-induced writhes in a triad group vs. individually, suggesting group-mediated writhing-reducing effects. Likewise, group testing prevented the stress pre-exposure escalation in acid-induced writhes. Additional studies revealed that the stress-pre-exposed mice had increased expression in accumbal TRPV1 receptors. Systemic (0.25 mg/kg) and bilateral intra-accumbal (0.2 ng/0.2 µl/side) administration of SB366791, a TRPV1 receptor antagonist, reliably prevented the stress pre-exposure escalation in acid-induced writhing; SB366791 treatment alone did not affect acid-induced writhing, stress pre-exposure anxiety-like behavior, or the group testing effects. Furthermore, lower neuronal activation was found in the medial septal nucleus in group vs. individual tested mice. Intra-medial septum (0.2 µg/0.5 µl) infusion with bicuculline, a GABAA receptor antagonist, effectively prevented group-mediated writhing-reducing effects, but not individual acid-induced writhing effects.

CONCLUSIONS

These findings suggest that social disruption-induced stress pre-exposure may upregulate accumbal TRPV1 receptor expression and consequently aggravate acid-induced writhing. Group testing prevents such stress pre-exposure escalation of acid-induced writhing most likely by strengthening the GABAergic inhibition on local neural activity in the medial septum.

PACAP orchestration of stress-related responses in neural circuits

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic polypeptide that can activate G protein-coupled PAC1, VPAC1, and VPAC2 receptors, and has been implicated in stress signaling. PACAP and its receptors are widely distributed throughout the nervous system and other tissues and can have a multitude of effects. Human and animal studies suggest that PACAP plays a role responding to a variety of threats and stressors. Here we review the roles of PACAP in several regions of the central nervous system (CNS) as they relate to several behavioral functions. For example, in the bed nucleus of the stria terminalis (BNST), PACAP is upregulated following chronic stress and may drive anxiety-like behavior. PACAP can also influence both the consolidation and expression of fear memories, as demonstrated by studies in several fear-related areas, such as the amygdala, hippocampus, and prefrontal cortex. PACAP can also mediate the emotional component of pain, as PACAP in the central nucleus of the amygdala (CeA) is able to decrease pain sensitivity thresholds. Outside of the central nervous system, PACAP may drive glucocorticoid release via enhanced hypothalamic-pituitary-adrenal axis activity and may participate in infection-induced stress responses. Together, this suggests that PACAP exerts effects on many stress-related systems and may be an important driver of emotional behavior.

Both CRF1 and CRF2 receptors in the bed nucleus of stria terminalis are involved in baroreflex impairment evoked by chronic stress in rats

Chronic exposure to adverse events has been proposed as a prominent factor involved in etiology and progression of cardiovascular dysfunctions in humans and animals. However, the neurobiological mechanisms involved are still poorly understood. In this sense, chronic stress has been reported to evoke neuroplasticity in corticotropin-releasing factor (CRF) neurotransmission in several limbic structures, including the bed nucleus of the stria terminalis. However, a possible involvement of BNST CRF neurotransmission in cardiovascular dysfunctions evoked by chronic stress has never been reported. Thus, this study investigated the involvement of CRF₁ and CRF₂ receptors within the BNST in cardiovascular changes evoked by chronic stress in rats. We identified that exposure to a 10-day chronic variable stress (CVS) protocol decreased expression of both CRF₁ and CRF₂ receptors within the BNST. These effects were followed by increased arterial pressure and impairment of baroreflex function, but without changes on heart rate. Bilateral microinjection of either the selective CRF₁ receptor antagonist CP376395 or the selective CRF₂ receptor antagonist antisauvagine-30 into the BNST did not affect CVS-evoked arterial pressure increase. Nevertheless, BNST treatment with CP376395 decreased both tachycardic and bradycardic responses of the baroreflex in non-stressed rats; but these effects were not identified in chronically stressed animals. BNST pharmacological treatment with antisauvagine-30 decreased the reflex tachycardia in control animals, whereas reflex bradycardic response was increased in CVS animals. Altogether, the results reported in the present study indicate that down regulation of both CRF₁ and CRF₂ receptors within the BNST is involved in baroreflex impairment evoked by chronic stress.

PACAP-PAC1 Signaling Regulates Serotonin 2A Receptor Internalization

Mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP) display psychomotor abnormalities, most of which are ameliorated by atypical antipsychotics with serotonin (5-HT) 2A receptor (5-HT_2A) antagonism. Heterozygous Pacap mutant mice show a significantly higher hallucinogenic response than wild-type mice to a 5-HT_2A agonist. Endogenous PACAP may, therefore, affect 5-HT_2A signaling; however, the underlying neurobiological mechanism for this remains unclear. Here, we examined whether PACAP modulates 5-HT_2A signaling by addressing cellular protein localization. PACAP induced an increase in internalization of 5-HT_2A but not 5-HT_1A, 5-HT_2C, dopamine D₂ receptors or metabotropic glutamate receptor 2 in HEK293T cells. This PACAP action was inhibited by protein kinase C inhibitors, β-arrestin2 silencing, the PACAP receptor PAC1 antagonist PACAP_6-38, and PAC1 silencing. In addition, the levels of endogenous 5-HT_2A were decreased on the cell surface of primary cultured cortical neurons after PACAP stimulation and were increased in frontal cortex cell membranes of Pacap^-/- mice. Finally, intracerebroventricular PACAP administration suppressed 5-HT_2A agonist-induced head twitch responses in mice. These results suggest that PACAP-PAC1 signaling increases 5-HT_2A internalization resulting in attenuation of 5-HT_2A-mediated signaling, although further study is necessary to determine the relationship between behavioral abnormalities in Pacap^-/- mice and PACAP-induced 5-HT_2A internalization.

Characterization of Neurons Expressing the Novel Analgesic Drug Target Somatostatin Receptor 4 in Mouse and Human Brains

Somatostatin is an important mood and pain-regulating neuropeptide, which exerts analgesic, anti-inflammatory, and antidepressant effects via its Gi protein-coupled receptor subtype 4 (SST4) without endocrine actions. SST4 is suggested to be a unique novel drug target for chronic neuropathic pain, and depression, as a common comorbidity. However, its neuronal expression and cellular mechanism are poorly understood. Therefore, our goals were (i) to elucidate the expression pattern of Sstr4/SSTR4 mRNA, (ii) to characterize neurochemically, and (iii) electrophysiologically the Sstr4/SSTR4-expressing neuronal populations in the mouse and human brains. Here, we describe SST4 expression pattern in the nuclei of the mouse nociceptive and anti-nociceptive pathways as well as in human brain regions, and provide neurochemical and electrophysiological characterization of the SST4-expressing neurons. Intense or moderate SST4 expression was demonstrated predominantly in glutamatergic neurons in the major components of the pain matrix mostly also involved in mood regulation. The SST4 agonist J-2156 significantly decreased the firing rate of layer V pyramidal neurons by augmenting the depolarization-activated, non-inactivating K+ current (M-current) leading to remarkable inhibition. These are the first translational results explaining the mechanisms of action of SST4 agonists as novel analgesic and antidepressant candidates.

Beneficial Effects of Crocin against Depression via Pituitary Adenylate Cyclase-Activating Polypeptide

Depression is one of the foremost psychological illness, and the exact mechanism is unclear. Recent studies have reported that the pituitary adenylate cyclase-activating polypeptide (PACAP) signaling pathway is involved in the progression of depression. In the present study, we extracted crocin from the traditional Chinese medicine (TCM), Gardenia jasminoides Ellis, to evaluate its antidepressant effect and clarify the underlying mechanism. Here, we established a chronic unpredictable mild stress (CUMS) mouse model to assess whether crocin can improve depression-like behavior in an open field test (OFT), tail suspension test (TST), forced swimming test (FST), and sucrose preference test (SPT). A corticosterone (CORT) model of PC12 was set up to explore the antidepressant mechanism of crocin. We pretreated PC12 cells with crocin for 1 hour and then stimulated the cells with CORT for 24 hours. Cell survival was detected by Hoechst staining and MTT assay. The expression of PACAP, cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), and extracellular regulated protein kinases (ERK) were analyzed by western blotting. PACAP RNAi was used to interfere with PC12 cells to downregulate the content of PACAP. The results showed that crocin (30 mg/kg) significantly reversed the decrease of body weight and elevation of serum CORT, mitigated CUMS induced depression-like behaviors of mice, and crocin (12.5 μmol/L) protected PC12 cells against CORT (200 μmol/L)-induced injury. Furthermore, crocin greatly increased the protein expression of PACAP and phosphorylation of ERK and CREB in the CORT model. PACAP RNAi cancelled the neuroprotective effect of crocin. In conclusion, these results indicated that crocin exerted an antidepressant effect via upregulating PACAP and its downstream ERK and CREB signaling pathways.

The role of pituitary adenylyl cyclase activating polypeptide in affective signs of nicotine withdrawal

Recent evidence implicates endogenous pituitary adenylyl cyclase activating polypeptide (PACAP) in the aversive effect of nicotine. In the present study, we assessed if nicotine-induced conditioned place preference (CPP) or affective signs of nicotine withdrawal would be altered in the absence of PACAP and if there were any sex-related differences in these responses. Male and female mice lacking PACAP and their wild-type controls were tested for baseline place preference on day 1, received conditioning with saline or nicotine (1 mg/kg) on alternate days for 6 days and were then tested for CPP the next day. Mice were then exposed to four additional conditioning and were tested again for nicotine-induced CPP 24 hr later. Controls were conditioned with saline in both chambers and tested similarly. All mice were then, 96 hr later, challenged with mecamylamine (3 mg/kg), and tested for anxiety-like behaviors 30 min later. Mice were then, 2 hr later, forced to swim for 15 min and then tested for depression-like behaviors 24 hr later. Our results showed that male but not female mice lacking PACAP expressed a significant CPP that was comparable to their wild-type controls. In contrast, male but not female mice lacking PACAP exhibited reduced anxiety- and depression-like behaviors compared to their wild-type controls following the mecamylamine challenge. These results suggest that endogenous PACAP is involved in affective signs of nicotine withdrawal, but there is a sex-related difference in this response.

Corticotropin-Releasing Factor-Producing Cells in the Paraventricular Nucleus of the Hypothalamus and Extended Amygdala Show Age-Dependent FOS and FOSB/DeltaFOSB Immunoreactivity in Acute and Chronic Stress Models in the Rat

Corticotropin-releasing factor (CRF) immunoreactive (ir) neurons of the paraventricular nucleus of the hypothalamus (PVN) play pivotal role in the coordination of stress response. CRF-producing cells in the central nucleus of amygdala (CeA) and oval division of the bed nucleus of stria terminalis (BNSTov) are also involved in stress adaptation and mood control. Immediate early gene products, subunits of the transcription factor activator protein 1 (AP1) are commonly used as acute (FOS) and/or chronic (FOSB/deltaFOSB) markers for the neuronal activity in stress research. It is well known that the course of aging affects stress adaptation, but little is known about the aging-related stress sensitivity of CRF neurons. To the best of our knowledge, the stress-induced neuronal activity of CRF neurons in the course of aging in acute and chronic stress models was not studied systematically yet. Therefore, the aim of the present study was to quantify the acute restraint stress (ARS) and chronic variable mild stress (CVMS) evoked neuronal activity in CRF cells of the PVN, CeA, and BNSTov using triple-label immunofluorescence throughout the whole lifespan in the rat. We hypothesized that the FOS and FOSB content of CRF cells upon ARS or CVMS decreases with age. Our results showed that the FOS and FOSB response to ARS declined with age in the PVN-CRF cells. BNSTov and CeA CRF cells did not show remarkable stress-induced elevation of these markers neither in ARS, nor in CVMS. Exposure to CVMS resulted in an age-independent significant increase of FOSB/delta FOSB immunosignal in PVN-CRF neurons. Unexpectedly, we detected a remarkable stress-independent FOSB/deltaFOSB signal in CeA- and BNSTov-CRF cells that declined with the course of aging. In summary, PVN-CRF cells show decreasing acute stress sensitivity (i.e., FOS and FOSB immunoreactivity) with the course of aging, while their (FOSB/deltaFOSB) responsivity to chronic challenge is maintained till senescence. Stress exposure does not affect the occurrence of the examined Fos gene products in CeA- and BNSTov-CRF cells remarkably suggesting that their contribution to stress adaptation response does not require AP1-controlled transcriptional changes.

Chronic variable stress alters hypothalamic-pituitary-adrenal axis function in the female mouse

Chronic stress is often associated with a dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, which can greatly increase risk for a number of stress-related diseases, including neuropsychiatric disorders. Despite a striking sex-bias in the prevalence of many of these disorders, few preclinical studies have examined female subjects. Hence, the present study aimed to explore the effects of chronic stress on the basal and acute stress-induced activity of the HPA axis in the female C57BL/6 mouse. We used a chronic variable stress (CVS) paradigm in these studies, which successfully induces physiological and behavioral changes that are similar to those reported for some patients with mood disorders. Using this model, we found pronounced, time-dependent effects of chronic stress on the HPA axis. CVS-treated females exhibited adrenal hypertrophy, yet their pattern of glucocorticoid secretion in the morning resembled that of controls. CVS-treated and control females had similar morning basal corticosterone (CORT) levels, which were both significantly elevated following a restraint stressor. Although morning basal gene expression of the key HPA-controlling neuropeptides corticotropin releasing hormone (CRH), arginine vasopressin (AVP) and oxytocin (OT) was unaltered within the paraventricular nucleus (PVN) by CVS, CVS altered the PVN OT and AVP mRNA responses to acute restraint. In control females, acute stress decreased AVP, but not OT mRNA; whereas, in CVS females, it decreased OT, but not, AVP mRNA. Unlike the morning pattern of HPA activity, in the evening, CVS-treated females showed increased basal CORT with hypoactive responses of CORT and PVN c-Fos immunoreactivity to restraint stress. Furthermore, CVS elevated evening PVN CRH and OT mRNAs in the PVN, but it did not influence anxiety- or depressive-like behavior after a light/dark box or tail suspension test. Taken together, these findings indicate that CVS is an effective model for HPA axis dysregulation in the female mouse and may be relevant for stress-related diseases.

Therapeutic potential of PACAP in alcohol toxicity

Alcohol addiction is a worldwide concern as its detrimental effects go far beyond the addicted individual and can affect the entire family as well as the community. Considerable effort is being expended in understanding the neurobiological basis of such addiction in hope of developing effective prevention and/or intervention strategies. In addition, organ damage and neurotoxicological effects of alcohol are intensely investigated. Pharmacological approaches, so far, have only provided partial success in prevention or treatment of alcohol use disorder (AUD) including the neurotoxicological consequences of heavy drinking. Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous 38 amino-acid neuropeptide with demonstrated protection against neuronal injury, trauma as well as various endogenous and exogenous toxic agents including alcohol. In this mini-review, following a brief presentation of alcohol addiction and its neurotoxicity, the potential of PACAP as a therapeutic intervention in toxicological consequences of this devastating disorder is discussed.

PACAP deficiency as a model of aging

Dysregulation of neuropeptides may play an important role in aging-induced impairments. In the long list of neuropeptides, pituitary adenylate cyclase-activating polypeptide (PACAP) represents a highly effective cytoprotective peptide that provides an endogenous control against a variety of tissue-damaging stimuli. PACAP has neuro- and general cytoprotective effects due to anti-apoptotic, anti-inflammatory, and antioxidant actions. As PACAP is also a part of the endogenous protective machinery, it can be hypothesized that the decreased protective effects in lack of endogenous PACAP would accelerate age-related degeneration and PACAP knockout mice would display age-related degenerative signs earlier. Recent results support this hypothesis showing that PACAP deficiency mimics aspects of age-related pathophysiological changes including increased neuronal vulnerability and systemic degeneration accompanied by increased apoptosis, oxidative stress, and inflammation. Decrease in PACAP expression has been shown in different species from invertebrates to humans. PACAP-deficient mice display numerous pathological alterations mimicking early aging, such as retinal changes, corneal keratinization and blurring, and systemic amyloidosis. In the present review, we summarize these findings and propose that PACAP deficiency could be a good model of premature aging.

Both Basal and Acute Restraint Stress-Induced c-Fos Expression Is Influenced by Age in the Extended Amygdala and Brainstem Stress Centers in Male Rats

The hypothalamus-pituitary-adrenal axis (HPA) is the main regulator of the stress response. The key of the HPA is the parvocellular paraventricular nucleus of the hypothalamus (pPVN) controlled by higher-order limbic stress centers. The reactivity of the HPA axis is considered to be a function of age, but to date, little is known about the background of this age-dependency. Sporadic literature data suggest that the stress sensitivity as assessed by semi-quantitation of the neuronal activity marker c-Fos may also be influenced by age. Here, we aimed at investigating the HPA activity and c-Fos immunoreactivity 2 h after the beginning of a single 60 min acute restraint stress in eight age groups of male Wistar rats. We hypothesized that the function of the HPA axis (i.e., pPVN c-Fos and blood corticosterone (CORT) level), the neuronal activity of nine stress-related limbic areas (i.e., magnocellular PVN (mPVN), medial (MeA), central (CeA), basolateral nuclei of the amygdala, the oval (ovBNST), dorsolateral (dlBNST), dorsomedial (dmBNST), ventral and fusiform (fuBNST) divisions of the bed nucleus of the stria terminalis (BNST)), and two brainstem stress centers such as the centrally projecting Edinger-Westphal nucleus (cpEW) and dorsal raphe nucleus (DR) show age dependency in their c-Fos response. The somatosensory barrel cortex area (S1) was evaluated to test whether the age dependency is specific for stress-centers. Our results indicate that the stress-induced rise in blood CORT titer was lower in young age reflecting relatively low HPA activity. All 12 stress-related brain areas showed c-Fos response that peaked at 2 months of age. The magnitude of c-Fos immunoreactivity correlated negatively with age in seven regions (MeA, CeA, ovBNST, dlBNST, dmBNST, fuBNST and pPVN). Unexpectedly, the CeA, ovBNST and cpEW showed a considerable basal c-Fos expression in 1-month-old rats which decreased with age. The S1 showed a U-shaped age-related dynamics in contrast to the decline observed in stress centers. We conclude that the age- and brain area dependent dynamics in stress-induced neuronal activity pattern may contribute to the age dependance of the stress reactivity. Further studies are in progress to determine the neurochemical identity of neurons showing age-dependent basal and/or stress-induced c-Fos expression.

Review on PACAP-Induced Transcriptomic and Proteomic Changes in Neuronal Development and Repair

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with widespread occurrence and diverse biological effects. Among its several different effects, of special importance is the action of PACAP on neuronal proliferation, differentiation and migration, and neuroprotection. The neuroprotective mechanism of PACAP is both direct and indirect, via neuronal and non-neuronal cells. Several research groups have performed transcriptomic and proteomic analysis on PACAP-mediated genes and proteins. Hundreds of proteins have been described as being involved in the PACAP-mediated neuroprotection. In the present review we summarize the few currently available transcriptomic data potentially leading to the proteomic changes in neuronal development and protection. Proteomic studies focusing on the neuroprotective role of PACAP are also reviewed and discussed in light of the most intriguing and promising effect of this neuropeptide, which may possibly have future therapeutic potential.

What is stressful for females? Differential effects of unpredictable environmental or social stress in CD1 female mice

Stressful life events are a major factor in the etiology of several diseases, such as cardiovascular, inflammatory and psychiatric disorders (i.e., depression and anxiety), with the two sexes greatly differing in vulnerability. In humans and other animals, physiological and behavioral responses to stress are strongly dependent on gender, and conditions that are stressful for males are not necessarily stressful for females. Hence the need of an animal model of social chronic stress specifically designed for females. In the present study we aimed to compare the effects of two different chronic stress procedures in female mice, by investigating the impact of 4weeks of nonsocial unpredictable, physical stress by the Chronic Mild Stress paradigm (CMS; Exp.1) or of Social Instability Stress (SIS; Exp.2) on physiological, endocrine and behavioral parameters in adult female mice. CMS had a pronounced effect on females' response to novelty (i.e., either novel environment or novel social stimulus), body weight growth and hormonal profile. Conversely, 4weeks of social instability did not alter females' response to novelty nor hormonal levels but induced anhedonia. Our findings thus showed that female mice were more sensitive to nonsocial stress due to unpredictable physical environment than to social instability stressors. Neither of these stress paradigms, however, induced a consistent behavioral and physiological stress response in female mice comparable to that induced by chronic stress procedures in male mice, thus confirming the difficulties of developing a robust and validated model of chronic psychosocial stress in female mice.

Two Weeks of Variable Stress Increases Gamma-H2AX Levels in the Mouse Bed Nucleus of the Stria Terminalis

Recent reports demonstrate that DNA damage is induced, and rapidly repaired, in circuits activated by experience. Moreover, stress hormones are known to slow DNA repair, suggesting that prolonged stress may result in persistent DNA damage. Prolonged stress is known to negatively impact physical and mental health; however, DNA damage as a factor in stress pathology has only begun to be explored. Histone H2A-X phosphorylated at serine 139 (γH2AX) is a marker of DNA double-strand breaks (DSB), a type of damage that may lead to cell death if unrepaired. We hypothesized that a 14-day period of variable stress exposure sufficient to alter anxiety-like behavior in male C57BL/6J mice would produce an increase in γH2AX levels in the bed nucleus of the stria terminalis (BNST), a region implicated in anxiety and stress regulation. We observed that 14 days of variable stress, but not a single stress exposure, was associated with increased levels of γH2AX 24 h after termination of the stress paradigm. Further investigation found that phosphorylation levels of a pair of kinases associated with the DNA damage response, glycogen synthase kinase 3 β (GSK3β) and p38 mitogen-activated protein kinase (MAPK) were also elevated following variable stress. Our results suggest that unrepaired DNA DSBs and/or repetitive attempted repair may represent an important component of the allostatic load that stress places on the brain.

Alteration of the PAC1 Receptor Expression in the Basal Ganglia of MPTP-Induced Parkinsonian Macaque Monkeys

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a well-known neuropeptide with strong neurotrophic and neuroprotective effects. PACAP exerts its protective actions via three G protein-coupled receptors: the specific Pac1 receptor (Pac1R) and the Vpac1/Vpac2 receptors, the neuroprotective effects being mainly mediated by the Pac1R. The protective role of PACAP in models of Parkinson's disease and other neurodegenerative diseases is now well-established in both in vitro and in vivo studies. PACAP and its receptors occur in the mammalian brain, including regions associated with Parkinson's disease. PACAP receptor upregulation or downregulation has been reported in several injury models or human diseases, but no data are available on alterations of receptor expression in Parkinson's disease. The model closest to the human disease is the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced macaque model. Therefore, our present aim was to evaluate changes in Pac1R expression in basal ganglia related to Parkinson's disease in a macaque model. Monkeys were rendered parkinsonian with MPTP, and striatum, pallidum, and cortex were evaluated for Pac1R immunostaining. We found that Pac1R immunosignal was markedly reduced in the caudate nucleus, putamen, and internal and external parts of the globus pallidus, while the immunoreactivity remained unchanged in the cortex of MPTP-treated parkinsonian monkey brains. This decrease was attenuated in some brain areas in monkeys treated with L-DOPA. The strong, specific decrease of the PACAP receptor immunosignal in the basal ganglia of parkinsonian macaque monkey brains suggests that the PACAP/Pac1R system may play an important role in the development/progression of the disease.

Construct and face validity of a new model for the three-hit theory of depression using PACAP mutant mice on CD1 background

Major depression is a common cause of chronic disability. Despite decades of efforts, no equivocally accepted animal model is available for studying depression. We tested the validity of a new model based on the three-hit concept of vulnerability and resilience. Genetic predisposition (hit 1, mutation of pituitary adenylate cyclase-activating polypeptide, PACAP gene), early-life adversity (hit 2, 180-min maternal deprivation, MD180) and chronic variable mild stress (hit 3, CVMS) were combined. Physical, endocrinological, behavioral and functional morphological tools were used to validate the model. Body- and adrenal weight changes as well as corticosterone titers proved that CVMS was effective. Forced swim test indicated increased depression in CVMS PACAP heterozygous (Hz) mice with MD180 history, accompanied by elevated anxiety level in marble burying test. Corticotropin-releasing factor neurons in the oval division of the bed nucleus of the stria terminalis showed increased FosB expression, which was refractive to CVMS exposure in wild-type and Hz mice. Urocortin1 neurons became over-active in CMVS-exposed PACAP knock out (KO) mice with MD180 history, suggesting the contribution of centrally projecting Edinger-Westphal nucleus to the reduced depression and anxiety level of stressed KO mice. Serotoninergic neurons of the dorsal raphe nucleus lost their adaptation ability to CVMS in MD180 mice. In conclusion, the construct and face validity criteria suggest that MD180 PACAP HZ mice on CD1 background upon CVMS may be used as a reliable model for the three-hit theory.

Pituitary adenylate cyclase activating polypeptide (PACAP) and its receptor 1 (PAC1) in the human infant brain and changes in the Sudden Infant Death Syndrome (SIDS)

Pituitary adenylate cyclase activating polypeptide (PACAP) and its complementary receptor, PAC1, are crucial in central respiratory control. PACAP Knockout (KO) mice exhibit a SIDS-like phenotype, with an inability to overcome noxious insults, compression of baseline ventilation, and death in the early post-neonatal period. PAC1 KO demonstrate similar attributes to PACAP-null mice, but with the addition of increased pulmonary artery pressure, consequently leading to heart failure and death. This study establishes a detailed interpretation of the neuroanatomical distribution and localization of both PACAP and PAC1 in the human infant brainstem and hippocampus, to determine whether any changes in expression are evident in infants who died of Sudden Infant Death Syndrome (SIDS) and any relationships to risk factors of SIDS including smoke exposure and sleep related parameters. Immunohistochemistry for PACAP and PAC1 was performed on formalin fixed and paraffin embedded human infant brain tissue of SIDS (n=32) and non-SIDS (n=12). The highest expression of PACAP was found in the hypoglossal (XII) of the brainstem medulla and lowest expression in the subiculum of the hippocampus. Highest expression of PAC1 was also found in XII of the medulla and lowest in the midbrain dorsal raphe (MBDR) and inferior colliculus. SIDS compared to non-SIDS had higher PACAP in the MBDR (p<0.05) and lower PAC1 in the medulla arcuate nucleus (p<0.001). Correlations were found between PACAP and PAC1 with the risk factors of smoke exposure, bed sharing, upper respiratory tract infection (URTI) and seasonal temperatures. The findings of this study show for the first time that some abnormalities of the PACAP system are evident in the SIDS brain and could contribute to the mechanisms of infants succumbing to SIDS.

Early Neurobehavioral Development of Mice Lacking Endogenous PACAP

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide. In addition to its diverse physiological roles, PACAP has important functions in the embryonic development of various tissues, and it is also considered as a trophic factor during development and in the case of neuronal injuries. Data suggest that the development of the nervous system is severely affected by the lack of endogenous PACAP. Short-term neurofunctional outcome correlates with long-term functional deficits; however, the early neurobehavioral development of PACAP-deficient mice has not yet been evaluated. Therefore, the aim of the present study was to describe the postnatal development of physical signs and neurological reflexes in mice partially or completely lacking PACAP. We examined developmental hallmarks during the first 3 weeks of the postnatal period, during which period most neurological reflexes and motor coordination show most intensive development, and we describe the neurobehavioral development using a complex battery of tests. In the present study, we found that PACAP-deficient mice had slower weight gain throughout the observation period. Interestingly, mice partially lacking PACAP weighed significantly less than homozygous mice. There was no difference between male and female mice during the first 3 weeks. Some other signs were also more severely affected in the heterozygous mice than in the homozygous mice, such as air righting, grasp, and gait initiation reflexes. Interestingly, incisor teeth erupted earlier in mice lacking PACAP. Motor coordination, shown by the number of foot-faults on an elevated grid, was also less developed in PACAP-deficient mice. In summary, our results show that mice lacking endogenous PACAP have slower weight gain during the first weeks of development and slower neurobehavioral development regarding a few developmental hallmarks.