Pituitary adenylate cyclase-activating polypeptide induces hyperthermia in the rat

RNA-sequencing Reveals Differentially Expressed Genes of Laying Hens Fed Baihu Decoction Under Heat Shock

Egg production, an important economic trait in the poultry industry, is sensitive to heat stress. The hypothalamus is a crucial center for thermoregulation by detecting temperature changes and regulating the autonomic nervous system in poultry. Baihu decoction (BH), which contains four ingredients (Rhizoma Anemarrhenae, Gypsum Fibrosum, Radix Glycyrrhizae, and Semen Oryzae Nonglutinosae), is a traditional Chinese medicinal formula for clearing heat. Our study aimed to investigate the changes in gene transcription levels in the hypothalamus of laying hens treated with heat stress with and without BH using RNA sequencing. A total of 223 differentially expressed genes (DEGs) were identified in the heat-treated group compared with the control group and 613 DEGs were identified in the BH group compared with the heat-treated group. Heat shock led to significant changes in the expression of multiple genes involved in the "neuroactive ligand-receptor interaction" pathway. Moreover, feeding BH led to significant upregulation in the expression of eight genes encoding heat shock proteins (HSPs), which were highlighted as candidates to control the "protein processing in the endoplasmic reticulum (ER)" pathway. These results provide the novel insight that BH responds to heat stress by participating in regulation of the ER signaling pathway and HSPs expression.

Immunoregulatory Effects of Neuropeptides on Endothelial Cells: Relevance to Dermatological Disorders

Many skin diseases, including psoriasis and atopic dermatitis, have a neurogenic component. In this regard, bidirectional interactions between components of the nervous system and multiple target cells in the skin and elsewhere have been receiving increasing attention. Neuropeptides released by sensory nerves that innervate the skin can directly modulate functions of keratinocytes, Langerhans cells, dermal dendritic cells, mast cells, dermal microvascular endothelial cells and infiltrating immune cells. As a result, neuropeptides and neuropeptide receptors participate in a complex, interdependent network of mediators that modulate the skin immune system, skin inflammation, and wound healing. In this review, we will focus on recent studies demonstrating the roles of α-melanocyte-stimulating hormone, calcitonin gene-related peptide, substance P, somatostatin, vasoactive intestinal peptide, pituitary adenylate cyclase-activating peptide, and nerve growth factor in modulating inflammation and immunity in the skin through their effects on dermal microvascular endothelial cells.

Adipose Tissue Expression of PACAP, VIP, and Their Receptors in Response to Cold Stress

Obesity arises from disrupted energy balance and is caused by chronically higher energy intake compared to expenditure via basal metabolic rate, exercise, and thermogenesis. The brown adipose tissue (BAT), the primary thermogenic organ, has received considerable attention as a potential therapeutic target due to its ability to burn lipids in the production of heat. Pituitary adenylate cyclase-activating polypeptide (PACAP) has been identified as a key regulator of the physiological stress response both centrally and peripherally. While PACAP has been shown to increase thermogenesis by acting at the hypothalamus to increase sympathetic output to BAT, a peripheral role for PACAP-activated thermogenesis has not been studied. We identified PACAP receptor (PAC1, VPAC1/2) expression for the first time in murine BAT and confirmed their expression in white adipose tissues. PAC1 receptor expression was significantly altered in all three adipose tissues studied in response to 3.5-week cold acclimation, with expression patterns differing by depot type. In primary cell culture, VPAC1 was increased in differentiated compared to non-differentiated brown adipocytes, and the same trend was observed for the PACAP-specific receptor PAC1 in gonadal white fat primary cultures. The primary PAC1R mRNA splice variant in interscapular BAT was determined as isoform 2 by RNA-Seq. These results show that PACAP receptors are present in adipose tissues and may have important functional roles in adipocyte differentiation, lipid metabolism, or adipose sensitization to sympathetic signaling in response to thermogenic stimuli.

PACAP in the Defense of Energy Homeostasis

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) mediates diverse physiology from neuroprotection to thermoregulation. PACAP is well established as a master regulator of the stress response, regulating psychological and physiological equilibrium via the autonomic nervous system. Neuroanatomical and functional evidence support a role for PACAP in energy metabolism, including thermogenesis, activity, mobilization of energy stores, and appetite. Through integration of this evidence we suggest PACAP be included in the growing list of neuropeptides that mediate energy homeostasis. Future work to uncover the intricacies of PACAP expression and the molecular pathways responsible for PACAP signaling may show potential for this neuropeptide as a therapeutic target as well as further elucidate the complex neuroanatomical networks involved in defending energy balance.

Differential responses of the somatotropic and thyroid axes to environmental temperature changes in the green iguana

Growth hormone (GH), together with thyroid hormones (TH), regulates growth and development, and has critical effects on vertebrate metabolism. In ectotherms, these physiological processes are strongly influenced by environmental temperature. In reptiles, however, little is known about the direct influences of this factor on the somatotropic and thyroid axes. Therefore, the aim of this study was to describe the effects of both acute (48h) and chronic (2weeks) exposure to sub-optimal temperatures (25 and 18°C) upon somatotropic and thyroid axis function of the green iguana, in comparison to the control temperature (30-35°C). We found a significant increase in GH release (2.0-fold at 25°C and 1.9-fold at 18°C) and GH mRNA expression (up to 3.7-fold), mainly under chronic exposure conditions. The serum concentration of insulin-like growth factor-I (IGF-I) was significantly greater after chronic exposure (18.5±2.3 at 25°C; 15.92±3.4 at 18°C; vs. 9.3±1.21ng/ml at 35°C), while hepatic IGF-I mRNA expression increased up to 6.8-fold. Somatotropic axis may be regulated, under acute conditions, by thyrotropin-releasing hormone (TRH) that significantly increased its hypothalamic concentration (1.45 times) and mRNA expression (0.9-fold above control), respectively; and somatostatin (mRNA expression increased 1.0-1.2 times above control); and under chronic treatment, by pituitary adenylate cyclase-activating peptide (PACAP mRNA expression was increased from 0.4 to 0.6 times). Also, it was shown that, under control conditions, injection of TRH stimulated a significant increase in circulating GH. On the other hand, while there was a significant rise in the hypothalamic content of TRH and its mRNA expression, this hormone did not appear to influence the thyroid axis activity, which showed a severe diminution in all conditions of cold exposure, as indicated by the decreases in thyrotropin (TSH) mRNA expression (up to one-eight of the control), serum T4 (from 11.6±1.09 to 5.3±0.58ng/ml, after 2weeks at 18°C) and T3 (from 0.87±0.09 to 0.05±0.01ng/ml, under chronic conditions at 25°C), and Type-2 deiodinase (D2) activity (from 992.5±224 to 213.6±26.4fmolI(125)T4/mgh). The reduction in thyroid activity correlates with the down-regulation of metabolism as suggested by the decrease in the serum glucose and free fatty acid levels. These changes apparently were independent of a possible stress response, at least under acute exposure to both temperatures and in chronic treatment to 25°C, since serum corticosterone had no significant changes in these conditions, while at chronic 18°C exposure, a slight increase (0.38 times above control) was found. Thus, these data suggest that the reptilian somatotropic and thyroid axes have differential responses to cold exposure, and that GH and TRH may play important roles associated to adaptation mechanisms that support temperature acclimation in the green iguana.

Neurotransmitter-mediated anxiogenic action of PACAP-38 in rats

The action of PACAP-38 was studied by measuring the anxiogenic-anxiolytic behavior of rats in an elevated plus maze. PACAP-38 was administered into the lateral brain ventricle and the behavior of the animals was measured 3h later. The possible involvement of transmitters was measured by pretreating the animals with receptor blockers which alone did not influence the task, but in the doses used were effective with other neuropeptides. The receptor antagonist PACAP 6-38 (a PAC 1/VPAC2 receptor antagonist of PACAP-38 receptor), haloperidol (a non-selective dopamine receptor antagonist), phenoxybenzamine (an α1/α2β-adrenergic receptor antagonist), propranolol(a β-adrenergic receptor antagonist), bicuculline (a gamma-aminobutyric acid subunit A receptor antagonist), methysergide (a nonselective 5-HT2 serotonergic receptor antagonist), atropine (a nonselective muscarinic acetylcholine receptor antagonist), naloxone (a nonselective opioid receptor antagonist) and nitro-l-arginine which acts by blocking the enzyme nitric oxide synthase, thereby blocking the nitric oxide synthesis, were tested. The following parameters were measured: the time spent in open arms/the time spent in total entries. PACAP-38 decreased the ratio of time spent in open arms to the time spent in total entries, indicating anxiogenic action. The total number of entries was not altered significantly either by PACAP-38 or by the receptor blockers. The following receptor blockers diminished the action of PACAP-38: PACAP 6-38,haloperidol, methysergide, naloxone and nitro-l-arginine. Pretreatment with atropine, phenoxybenzamine, propranolol and bicuculline did not influence the action of PACAP-38 on the time spent in open arms. The results demonstrate that PACAP-38 administered into the lateral brain ventricle exerted anxiogenic action at 3 h following treatment. Pretreatment of the animals with various receptor blockers indicated that a nonselective dopaminergic receptor antagonist, 5HT2 serotonergic and opioid receptors, nitric oxide and PAC1 receptors are involved in the anxiogenic action induced by PACAP-38.

Mediators involved in the hyperthermic action of neuromedin U in rats

Neuromedin U (NmU), first was isolated from the porcine spinal cord, has subsequently been demonstrated in a number of species, in which it is present in the periphery and also the brain. Two receptors have been identified: NmU1R is mainly present in peripheral tissues, and Nmu2R in the central nervous system. NmU, a potent endogenous anorectic, serves as a catabolic signaling molecule in the brain; it inhibits food uptake, increases locomotion, activates stress mechanism, having cardiovasscular effects and, causes hyperthermia. The mechanism of this hyperthermia is unknown. In the present experiments, the effects of NmU on the colon temperature following i.c.v administration were studied in rats. For an investigation of the possible role of receptors in mediating hyperthermia, the animals were treated simultaneously with CRF 9-41 and antalarmin, a CRH1 receptor inhibitors, astressin 2B, a CRH2 receptor antagonist, haloperidol a dopamine receptor antagonist, atropine a muscarinic cholinergic receptor antagonist, noraminophenazone a cyclooxygenase inhibitor or isatin, a prostaglandin receptor antagonist. NmU increased the colon temperature, maximal action being observed at 2-3h. CRF 9-41, antalarmin, astressin 2B haloperidol, atropine, noraminophenazone and isatin prevented the NmU-induced increase in colon temperature. The results demonstrated that, when injected into the lateral brain ventricle NmU increased the body temperature, mediated by CRHR1 and CRHR2, dopamine and muscarinic cholinergic receptors. The final pathway involves prostaglandin.

Characterization of the thermoregulatory response to pituitary adenylate cyclase-activating polypeptide in rodents

Administration of the long form (38 amino acids) of pituitary adenylate cyclase-activating polypeptide (PACAP38) into the central nervous system causes hyperthermia, suggesting that PACAP38 plays a role in the regulation of deep body temperature (T b). In this study, we investigated the thermoregulatory role of PACAP38 in details. First, we infused PACAP38 intracerebroventricularly to rats and measured their T b and autonomic thermoeffector responses. We found that central PACAP38 infusion caused dose-dependent hyperthermia, which was brought about by increased thermogenesis and tail skin vasoconstriction. Compared to intracerebroventricular administration, systemic (intravenous) infusion of the same dose of PACAP38 caused significantly smaller hyperthermia, indicating a central site of action. We then investigated the thermoregulatory phenotype of mice lacking the Pacap gene (Pacap (-/-)). Freely moving Pacap (-/-) mice had higher locomotor activity throughout the day and elevated deep T b during the light phase. When the Pacap (-/-) mice were loosely restrained, their metabolic rate and T b were lower compared to their wild-type littermates. We conclude that PACAP38 causes hyperthermia via activation of the autonomic cold-defense thermoeffectors through central targets. Pacap (-/-) mice express hyperkinesis, which is presumably a compensatory mechanism, because under restrained conditions, these mice are hypometabolic and hypothermic compared to controls.

The effect of pituitary adenylate cyclase-activating polypeptide on elevated plus maze behavior and hypothermia induced by morphine withdrawal

The aim of the present investigation was to study the effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on morphine withdrawal-induced behavioral changes and hypothermia in male CFLP mice. Elevated plus maze (EPM) and jump tests were used to assess naloxone-precipitated morphine withdrawal-induced behavior responses. Different doses of subcutaneous (s.c.) naloxone, (0.1 and 0.2 mg/kg, respectively) were used to precipitate the emotional and psychical aspects of withdrawal on EPM and 1 mg/kg (s.c.) was used to induce the somatic withdrawal signs such as jumping, and the changes in body temperature. In our EPM studies, naloxone proved to be anxiolytic in mice treated with morphine. Chronic intracerebroventricular (i.c.v.) administration of PACAP alone had no significant effect on withdrawal-induced anxiolysis and total activity at doses of 500 ng and 1 μg. At dose of 500 ng, however, PACAP significantly counteracted the reduced motor activity in the EPM test in mice treated with morphine and diminished the hypothermia and shortened jump latency induced by naloxone in mice treated with morphine. These findings indicate that anxiolytic-like behavior may be mediated via a PACAP-involved pathway and PACAP may play an important role in chronic morphine withdrawal-induced hypothermia as well.

Stimulation of the hypothalamic ventromedial nuclei by pituitary adenylate cyclase-activating polypeptide induces hypophagia and thermogenesis

Numerous studies have demonstrated that the hypothalamic ventromedial nuclei (VMN) regulate energy homeostasis by integrating and utilizing behavioral and metabolic mechanisms. The VMN heavily express pituitary adenylate cyclase-activating polypeptide (PACAP) type I receptors (PAC1R). Despite the receptor distribution, most PACAP experiments investigating affects on feeding have focused on intracerebroventricular administration or global knockout mice. To identify the specific contribution of PACAP signaling in the VMN, we injected PACAP directly into the VMN and measured feeding behavior and indices of energy expenditure. Following an acute injection of PACAP, nocturnal food intake was significantly reduced for 6 h after injections without evidence of malaise. In addition, PACAP-induced suppression of feeding also occurred following an overnight fast and could be blocked by a specific PAC1R antagonist. Metabolically, VMN-specific injections of PACAP significantly increased both core body temperature and spontaneous locomotor activity with a concurrent increase in brown adipose uncoupling protein 1 mRNA expression. To determine which signaling pathways were responsive to PACAP administration into the VMN, we measured mRNA expression of well-characterized hypothalamic neuropeptide regulators of feeding. One hour after PACAP administration, expression of pro-opiomelanocortin mRNA was significantly increased in the arcuate nuclei (ARC), with no changes in neuropeptide Y and agouti-related polypeptide mRNA levels. This suggests that PAC1R expressing VMN neurons projecting to pro-opiomelanocortin neurons contribute to hypophagia by involving melanocortin signaling. While the VMN also abundantly express PACAP protein, the present study demonstrates that PACAP input to the VMN can influence the control of energy homeostasis.

Pituitary adenylate cyclase activating polypeptide: an important vascular regulator in human skin in vivo

Pituitary adenylate cyclase-activating peptide (PACAP) is an important neuropeptide and immunomodulator in various tissues. Although this peptide and its receptors (ie, VPAC1R, VPAC2R, and PAC1R) are expressed in human skin, their biological roles are unknown. Therefore, we tested whether PACAP regulates vascular responses in human skin in vivo. When injected intravenously, PACAP induced a significant, concentration-dependent vascular response (ie, flush, erythema, edema) and mediated a significant and concentration-dependent increase in intrarectal body temperature that peaked at 2.7°C. Topical application of PACAP induced marked concentration-dependent edema. Immunohistochemistry revealed a close association of PACAP-immunoreactive nerve fibers with mast cells and dermal blood vessels. VPAC1R was expressed by dermal endothelial cells, CD4+ and CD8+ T cells, mast cells, and keratinocytes, whereas VPAC2R was expressed only in keratinocytes. VPAC1R protein and mRNA were also detected in human dermal microvascular endothelial cells. The PACAP-induced change in cAMP production in these cells demonstrated VPAC1R to be functional. PACAP treatment of organ-cultured human skin strongly increased the number of CD31+ vessel cross-sections. Taken together, these results suggest that PACAP directly induces vascular responses that may be associated with neurogenic inflammation, indicating for the first time that PACAP may be a crucial vascular regulator in human skin in vivo. Antagonists to PACAP function may be beneficial for the treatment of inflammatory skin diseases with a neurogenic component.

Involvement of CRH receptors in urocortin-induced hyperthermia

The actions of individual corticotropin-releasing hormone (CRH) receptor (CRHR1 and CRHR2) were studied on the hyperthermia caused by urocortin 1, urocortin 2 and urocortin 3 in rats. Urocortin 1, urocortin 2 or urocortin 3 was injected into the lateral brain ventricle in conscious rats and the colon temperature was measured at different times following injection, up to 6h. In order to study the possible role of CRH receptors, the animals were treated with a urocortins together with the urocortin receptor inhibitors CRF 9-41, antalarmin and astressin 2B to influence the action of urocortins in initiating hyperthermia. Urocortin 1 at a dose of 2microg caused an increase in colon temperature, maximal action being observed in body temperature at 3h. CRH 9-41 and antalarmin, CRHR1 receptor antagonists, prevented the urocortin-induced increase in colon temperature while astressin 2B (CRHR2 receptor antagonist) was ineffective. Urocortin 2 at a dose of 2microg showed a byphasic action in increase in colon temperature having the first peak between 30 min and 1h and the second peak at 4h following treatment. CRF (9-41) and antalarmin was ineffective while astressin 2B fully blocked the action of urocortin 2. Urocortin 3 in a dose of lmicrog increased colon temperature; the maximal effect was observed at 2h. CRF (9-41) and antalarmin was ineffective while astressin 2B fully blocked the action of urocortin 3. The results demonstrated that urocortin 1, 2 or 3 when injected into the lateral brain ventricle caused increases in body temperature is mediated by urocortin receptors. The action of urocortin 1 is mediated by CRHR1 receptor, while in the action of urocortin 2 and urocortin 3 CRHR2 receptor is involved.

Changes of PACAP levels in the brain show gender differences following short-term water and food deprivation

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic neuropeptide exerting diverse actions in the central and peripheral nervous systems. A few studies indicate that PACAP is involved in the regulation of feeding and water homeostasis. The aim of the present study was to investigate changes in PACAP38 concentrations in different brain areas following food or water deprivation in male and female rats. Rats were sacrificed 12, 36 and 84h after water or food removal. PACAP levels were determined by radioimmunoassay. Our results show that levels of PACAP decreased in the hypothalamus in both sexes after water deprivation, with a more marked, significant decrease in females at 12h. A decrease was observed also in the telencephalon, with a similar pattern in both genders: levels were lowest after 12h, and showed a gradual increase at the other two time-points. PACAP levels increased in the brainstem of male rats, while females had a decrease 12h after water deprivation. The pattern of changes in PACAP levels was very different after food deprivation. In male rats, PACAP levels showed a significant increase in the hypothalamus, telencephalon and brainstem 12h after the beginning of starvation. In females, a less marked increase was observed only in the hypothalamus while no changes were found in the other brain areas. Our results show a sensitive reaction in changes of endogenous PACAP levels to water and food deprivation in most brain areas, but they are differentially regulated in male and female rats.

Central administration of vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide differentially regulates energy metabolism in chicks

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are the members of the glucagon superfamily and bind to common receptors while PACAP also acts via the PACAP-specific receptor, PAC1. The aim of the present study was to investigate whether intracerebroventricular (i.c.v.) injection of VIP and PACAP acts in a similar or different manner to affect body temperature and energy expenditure in the domestic chick. I.c.v. injection of VIP did not significantly affect rectal temperature, but decreased energy expenditure. On the other hand, i.c.v. injection of PACAP significantly increased both body temperature and energy expenditure. These specific actions of PACAP could be explained by an interaction with the PAC1 receptor, since they were partly, but not entirely, attenuated by PACAP (6-38), a PAC1 receptor antagonist. In addition, it was observed that central administration of both VIP and PACAP induced a reduction in respiratory quotient and increased plasma non-esterified fatty acid concentrations. This suggests that both peptides act centrally to regulate a catabolic response. In summary, brain VIP and PACAP both appear to exert generally catabolic effects on energy metabolism in the chick, but their influence on body temperature and glucose metabolism differs and their central effects do not appear to be mediated by the same receptors.

Comparative aspects of GH and metabolic regulation in lower vertebrates

In all vertebrates, the regulations of growth and energy balance are complex phenomena which involve elaborate interactions between the brain and peripheral signals. Most vertebrates adopt and maintain a life style after birth, but lower vertebrates may have complex life histories involving metamorphoses, migrations and long periods of fasting. In order to achieve the complex developmental programs associated with these changes, coordinated regulation of all aspects of energy metabolism is required. Somatotropic axis (somatostatin (SRIH) growth hormone (GH) and insulin-like growth factor 1 (IGF1), is known to be involved in the regulation of growth and energy balance. Interestingly, recent studies showed that additional factors such as pituitary adenylate cyclase-activated polypeptide (PACAP), corticotropin-releasing hormone (CRH), ghrelin and leptin could also have major roles in the control of growth and metabolism in lower vertebrates (fish, amphibians and reptiles). This mini-review will survey the function of GH and metabolic regulation in lower vertebrates.

The action of urocortins on body temperature in rats

The actions of individual urocortins on colon temperature were studied in rats. Urocortin 1, urocortin 2 or urocortin 3 was injected into the lateral brain ventricle in conscious rats and the colon temperature was measured at different times following injection, for up to 6 h. In order to study the possible role of prostaglandins, the animals were treated with either a urocortin together with the pyrazolone derivative noraminophenazone to inhibit the action of cyclooxygenase in initiating hyperthermia, or with noraminophenazone 30 min following urocortin administration to act on existing hyperthermia. Noraminophenazone was administered intramuscularly in a dose of 50 mg/kg. Urocortin 1 caused a dose-related increase in colon temperature, maximal action being observed at a dose of 2 microg with the maximal increase in body temperature at 4 h. Noraminophenazone prevented the urocortin-induced increase in colon temperature and attenuated the already existing elevated body temperature. Somewhat similar action was observed with urocortin 2. However, following treatment with 0.5 or 1.0 microg urocortin 2, the action was already over at 2 h, whereas 2 microg increased the colon temperature steadily, with a maximum at 4 h. Noraminophenazone blocked or diminished the action of urocortin 2. Urocortin 3 in a dose of 1 microg was the most effective in increasing the colon temperature; the maximal effect was observed at 2 h. Noraminophenazone blocked the development of urocortin 3-induced hyperthermia, or attenuated it when the hyperthermia was already present. The results demonstrated that urocortin 1, 2 or 3 caused increases in body temperature when injected into the lateral brain ventricle, though the optimal dose and the duration of hyperthermia differed for the individual urocortins. The cyclooxygenase inhibitor blocked or diminished the action of these urocortins, indicating the involvement of prostaglandins in urocortin-induced hyperthermia.

Behavioral effects of local microinfusion of pituitary adenylate cyclase activating polypeptide (PACAP) into the paraventricular nucleus of the hypothalamus (PVN)

Pituitary adenylate cyclase activating polypeptide (PACAP) has been implicated in the regulation of several autonomic and neuroendocrine functions. In the hypothalamic paraventricular nucleus (PVN), for example, PACAP-immunoreactive fibers densely innervate corticotropin-releasing hormone (CRH)-containing neurons in the medial parvocellular region, suggesting that PACAP acts to mediate stress responses. Therefore, we examined the behavioral effects of an intra-PVN PACAP injection (25 pmol) in combination with a mild stressor. PACAP or artificial cerebrospinal fluid (aCSF) was microinjected into the PVN (0.25 l) and then animals were restrained or placed in their home cage for 5 min. Exploratory activity (total distance traveled) and scored behaviors (face washing, body grooming, wet dog shakes, and rearing) were observed in a familiar open field for 10 min. In animals receiving aCSF, there were no behavioral differences between restrained and unrestrained groups. For the entire 10-min observation period, animals receiving PACAP, whether restrained or not, displayed elevated face washing and body grooming with decreased locomotor activity and rearing. Among PACAP-injected animals, restrained animals displayed increased body grooming compared to unrestrained animals during the first 2 min in the open field suggesting a summation of the effects of peptide injection and stressor. The observed elevation in grooming is consistent with previous studies reporting similar increases following electrical-, NMDA-, CRH-, or stressor-induced activation of the PVN. Thus, at the level of the PVN, PACAP may act as an excitatory neuropeptide and augment behavioral responses to stressors.

Effects of pituitary adenylate cyclase polypeptide (PACAP) on extinction of active avoidance learning in rats: involvement of neurotransmitters

The effects of PACAP-38 on the extinction of active avoidance learning were studied in rats. The action of transmitter mediation was followed by pretreating the animals with appropriate receptor antagonists. PACAP-38 administered into the lateral brain ventricle caused a transitory facilitation of the extinction of a learned active avoidance response at 3 and 6 h following extinction, which had returned to or even above the control level at the 24-h testing. PACAP 6-38, which is an antagonist of PACAP-38, and an antibody against PACAP-38, prevented this action. When the animals were retested during a further 10 days, the control animals demonstrated response extinction on day 7, while the PACAP-38-treated animals still showed a high proportion (70%) of positive responses. The following receptor blockers diminished the action of PACAP-38 on the facilitation of extinction: propranolol, haloperidol, naloxone, bicuculline and nitro-L-arginine, the latter by blocking nitric oxide formation. Phenoxybenzamine and atropine were ineffective. The data reveal that the transitory action of PACAP-38 within 24 h on the facilitation of extinction is mediated by beta-adrenergic, dopaminergic, GABA-ergic and opiate receptors and nitric oxide. This transitory facilitated extinction is caused partly by depressed locomotion and presumably also an increased body temperature. Following a transitory facilitation of extinction from 24 h on, PACAP-38 demonstrated a greatly delayed extinction, which lasted for more than 7 days, while the control animals displayed complete extinction. The data suggest that PACAP-38 facilitates memory retrieval processes in the extinction of the active avoidance reflex.

Involvement of different receptors in pituitary adenylate cyclase activating polypeptide induced open field activity in rats

The action of pituitary adenylate cyclase activating polypeptide (PACAP) 38 was tested in an open field 30 min, 3 h, 6 h and 24 h after icv PACAP 38 administration in rats. The effects on locomotion, rearing and grooming were measured. The possible roles of different receptors were tested in animals that had been pretreated with different receptor blockers followed by PACAP 38 administration. The locomotion, rearing and grooming activities were increased at 30 min, after PACAP 38 administration, whereas at 3 and 6 h there was no change in grooming, while the locomotion and rearing activities were sharply decreased. At 24 h after PACAP administration, there was no change in any of the parameters studied. PACAP antiserum, a PACAP antagonist (PACAP 6-38), haloperidol, phenoxybenzamine, propranolol and naloxone each prevented the changes observed at 30 min and 3 h. Atropine, nitro-l-arginine, bicuculline and methysergide were ineffective. The data demonstrate that the action of PACAP 38 on the open-field activity is regulated by D2, alpha- and beta-adrenergic and opiate receptors.

The effects of isatin (indole-2, 3-dione) on pituitary adenylate cyclase-activating polypeptide-induced hyperthermia in rats

BACKGROUND

Previous studies have demonstrated that centrally administered natriuretic peptides and pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) have hyperthermic properties. Isatin (indole-2, 3-dione) is an endogenous indole that has previously been found to inhibit hyperthermic effects of natriuretic peptides. In this study the aim was to investigate the effects of isatin on thermoregulatory actions of PACAP-38, in rats.

RESULTS

One microg intracerebroventricular (icv.) injection of PACAP-38 had hyperthermic effect in male, Wistar rats, with an onset of the effect at 2 h and a decline by the 6th h after administration. Intraperitoneal (ip.) injection of different doses of isatin (25-50 mg/kg) significantly decreased the hyperthermic effect of 1 microg PACAP-38 (icv.), whereas 12.5 mg/kg isatin (ip.) had no inhibiting effect. Isatin alone did not modify the body temperature of the animals.

CONCLUSION

The mechanisms that participate in the mediation of the PACAP-38-induced hyperthermia may be modified by isatin. The capability of isatin to antagonize the hyperthermia induced by all members of the natriuretic peptide family and by PACAP-38 makes it unlikely to be acting directly on receptors for natriuretic peptides or on those for PACAP in these hyperthermic processes.