Central nervous system effects of bombesin on the cardiovascular response to cold exposure

Central ventilatory and cardiovascular actions of trout gastrin-releasing peptide (GRP) in the unanesthetized trout

Gastrin-releasing peptide (GRP), a neuropeptide initially isolated from porcine stomach, shares sequence similarity with bombesin. GRP and its receptors are present in the brains and peripheral tissues of several species of teleost fish, but little is known about the ventilatory and cardiovascular effects of this peptide in these vertebrates. The goal of this study was to compare the central and peripheral actions of picomolar doses of trout GRP on ventilatory and cardiovascular variables in the unanesthetized rainbow trout. Compared to vehicle, intracerebroventricular (ICV) injection of GRP (1–50 pmol) significantly elevated the ventilation rate (ƒV) and the ventilation amplitude (VAMP), and consequently the total ventilation (VTOT). The maximum hyperventilatory effect of GRP (VTOT: +225%), observed at a dose of 50 pmol, was mostly due to its stimulatory action on VAMP (+170%) rather than ƒV (+20%). In addition, ICV GRP (50 pmol) produced a significant increase in mean dorsal aortic blood pressure (P_DA) (+35%) and in heart rate (ƒH) (+25%). Intra-arterial injections of GRP (5–100 pmol) were without sustained effect on the ventilatory variables but produced sporadic and transient increases in ventilatory movement at doses of 50 and 100 pmol. At these doses, GRP elevated P_DA by +20% but only the 50 pmol dose significantly increased HR (+15%). In conclusion, our study suggests that endogenous GRP within the brain of the trout may act as a potent neurotransmitter and/or neuromodulator in the regulation of cardio-ventilatory functions. In the periphery, endogenous GRP may act as locally-acting and/or circulating neurohormone with an involvement in vasoregulatory mechanisms.

Pattern of Fos expression in the brain induced by selective activation of somatostatin receptor 2 in rats

Central activation of somatostatin (sst) receptors by oligosomatostatin analogs inhibits growth hormone and stress-related rise in catecholamine plasma levels while stimulating grooming, feeding behaviors, gastric transit and acid secretion, which can be mimicked by selective sst(2) receptor agonist. To evaluate the pattern of neuronal activation induced by peptide sst receptor agonists, we assessed Fos-expression in rat brain after intracerebroventricular (i.c.v.) injection of a newly developed selective sst(2) agonist compared to the oligosomatostatin ODT8-SST, a pan-sst(1-5) agonist. Ninety min after injection of vehicle (10 microl) or previously established maximal orexigenic dose of peptides (1 microg=1 nmol/rat), brains were assessed for Fos-immunohistochemistry and doublelabeling. Food and water were removed after injection. The sst(2) agonist and ODT8-SST induced a similar Fos distribution pattern except in the arcuate nucleus where only the sst(2) agonist increased Fos. Compared to ODT8-SST, the sst(2) agonist induced higher Fos-expression by 3.7-times in the basolateral amygdaloid nucleus, 1.2-times in the supraoptic nucleus (SON), 1.6-times in the magnocellular paraventricular hypothalamic nucleus (mPVN), 4.1-times in the external lateral parabrachial nucleus, and 2.6-times in both the inferior olivary nucleus and superficial layer of the caudal spinal trigeminal nucleus. Doublelabeling in the hypothalamus showed that ODT8-SST activates 36% of oxytocin, 63% of vasopressin and 79% of sst(2) immunoreactive neurons in the mPVN and 28%, 55% and 25% in the SON, respectively. Selective activation of sst(2) receptor results in a more robust neuronal activation than the pan-sst(1-5) agonist in various brain regions that may have relevance in sst(2) mediated alterations of behavioral, autonomic and endocrine functions.

Spinal cord transection inhibits HR reduction in anesthetized rats immersed in an artificial CO2-hot spring bath

Like humans, the heart rate (HR) of anesthetized rats immersed in CO(2)-water is lower than that when immersed in tap water at the same temperature. To investigate the afferent signal pathway in the mechanism of HR reduction, Wistar rats were anesthetized with urethane and then the spinal cord was transected between T(4) and T(5). The animals were immersed up to the axilla in a bathtub of tap-water (CO(2) contents: 10-20 mg.l(-1)) or of CO(2)-water (965-1,400 mg.l(-1)) at 35 degrees C while recording HR, arterial blood pressure, and arterial blood gas parameters (PaCO(2), PaO(2), pH). Arterial blood gas parameters did not change during immersion, irrespective of CO(2) concentration of the bath water, whereas the HR was reduced in the CO(2)-water bath. The inhalation of CO(2)-mixed gas (5% CO(2), 20% O(2), 75% N(2)) resulted in increased levels of blood gases and an increased HR during immersion in all types of water tested. The HR reduction observed in sham transected control animals immersed in CO(2)-water disappeared after subsequent spinal cord transection. These results show that the dominant afferent signal pathway to the brain, which is involved in inducing the reduced HR during immersion in CO(2)-water, is located in the neuronal route and not in the bloodstream.

A comparison of the central gastrointestinal antitransit effects of morphine and bombesin in the mouse

The gastrointestinal motor effects of centrally-given morphine and bombesin were compared in mice. Both compounds produced a dose-related decrease in the propulsion of a marker along the gut when given by the intracerebroventricular (i.c.v.) or intrathecal (i.th.) routes. Co-administration of the same compound by both routes was found to produce a marked increase in potency for morphine, but only a slight increase in potency for bombesin. Isobolographic analysis of the gut effects of these compounds revealed a multiplicative brain-spinal cord interaction for morphine, but an additive interaction for bombesin. These results are consistent with the interpretation that morphine can act at either the level of the brain or the spinal cord, activating independent pathways which ultimately converge to alter gut propulsion. In contrast, spinal bombesin requires communication to supraspinal sites in order for its gut effects to occur, suggesting activation of a common outflow pathway from the central nervous system.

Bombesin alters the sympathetic nervous system response to cold exposure

The accumulation of dopamine in interscapular brown fat, heart, kidney and mesenteric white fat has been used as an index of sympathetic nervous activity in rats in which dopamine beta-hydroxylase has been blocked. Intracerebroventricular administration of bombesin impaired the cold-induced increase of dopamine accumulation in interscapular brown fat but not in other tissues. These studies provide evidence that bombesin acts within the central nervous system to modify efferent sympathetic nervous system responses to cold exposure in a viscerotopically specific manner. This action of bombesin is consistent with the other central nervous system actions of this peptide, i.e. inhibition of heat production and disruption of thermoregulation.