Bombesin affects the central nervous system to produce sodium intake inhibition in rats

The Sensory Psychobiology of Thirst and Salt Appetite

Thirst and the hunger for sodium containing fluids and food (i.e., sodium appetite) are the consequences of the generation of unique central nervous system states. Altered body fluid homeostasis produces sensory and perceptional changes that arise from signals generated in the body that serve as indices of body fluid balance and distribution. These signaling mechanisms activate networks of brain neurons that use specific neurochemicals to communicate between cells and process information. The brain integrates information derived from various bodily sources so that thirst and sodium appetite are in a true sense the synthetic products of the nervous system. In recent years much has been learned about the stimuli and receptor systems involved in signaling the brain to reflect the status of bodily fluids and about the central neural substrates that process such inputs to generate thirst and sodium appetite. Knowledge about the sensory nature of thirst and sodium appetite provides a basis for understanding the biological constraints under which thirst and sodium appetite operate. This information is important for appreciating the extent to which thirst and sodium appetite motivational states and behaviors can be relied on to maintain and repair disruptions of body fluid homeostasis.

Prolyl, cystyl and pyroglutamyl peptidase activities in the hippocampus and hypothalamus of streptozotocin-induced diabetic rats

Prolyl, cystyl and pyroglutamyl peptidases are emerging targets for diabetes and cognitive deficit therapies. The present study is focused on the influence of diabetes mellitus induced by streptozotocin on levels of representative hydrolytic activities of these enzymes in the rat hypothalamus and hippocampus. Streptozotocin-diabetic rats presented about 348mg glucose/dL blood, and a slightly increased hematocrit and plasma osmolality. The activities of soluble and membrane-bound dipeptidyl-peptidase IV, and soluble cystyl aminopeptidase did not differ between diabetic and control rats in both brain areas. Hippocampal soluble prolyl oligopeptidase presented similar activities between diabetic and controls. Increased activities in diabetics were observed for soluble prolyl oligopeptidase (1.78-fold) and membrane-bound cystyl aminopeptidase (2.55-fold) in the hypothalamus, and for membrane-bound cystyl aminopeptidase (5.14-fold) in the hippocampus. In both brain areas, the activities of membrane-bound and soluble pyroglutamyl aminopeptidase were slightly lower (<0.7-fold) in diabetics. All modifications (except hematocrit) observed in streptozotocin-treated rats were mitigated by the administration of insulin. Glucose and/or insulin were shown to alter in vitro the hypothalamic activities of soluble pyroglutamyl aminopeptidase and prolyl oligopeptidase, as well as membrane-bound cystyl aminopeptidase. These data provide the first evidence that diabetes mellitus generates direct and indirect effects on the activity levels of brain peptidases. The implied regional control of regulatory peptide activity by these peptidases suggests novel potential approaches to understand certain disruptions on mediator and modulatory functions in diabetes mellitus.

Effect of the disruption of body fluid balance on pyroglutamyl aminopeptidase (Type-1) in rat brain structures

The activity of soluble and membrane-bound pyroglutamyl aminopeptidase Type-1 (PAP I) was evaluated in the hypothalamus, hippocampus, thalamus, brain cortex, and pituitary gland of rats after applying certain hydromineral challenges. Compared to euhydrated rats, decreased enzyme activity was found in the hypophysis of rats deprived of water for 48 h, or rats drinking ad libitum hypertonic sodium chloride solution (2%) for 6 days or distilled water for 6 days and then submitted to acute water overload. PAP I cleaves the pGlu-amino acid bond of neuropeptides such as thyroliberin, luliberin, neurotensin, and bombesin. The decay of particulate PAP I activity may cause an increase of these pyroglutamate peptides in the whole pituitary. Although the deleterious or pro-homeostatic influence of this decay remains to be elucidated, the present data provide evidence for the involvement of this enzyme activity at this anatomical location in the water-electrolyte imbalance.

The extended amygdala and salt appetite

Both chemo- and mechanosensitive receptors are involved in detecting changes in the signals that reflect the status of body fluids and of blood pressure. These receptors are located in the systemic circulatory system and in the sensory circumventricular organs of the brain. Under conditions of body fluid deficit or of marked changes in fluid distribution, multiple inputs derived from these humoral and neural receptors converge on key areas of the brain where the information is integrated. The result of this central processing is the mobilization of homeostatic behaviors (thirst and salt appetite), hormone release, autonomic changes, and cardiovascular adjustments. This review discusses the current understanding of the nature and role of the central and systemic receptors involved in the facilitation and inhibition of thirst and salt appetite and on particular components of the central neural network that receive and process input derived from fluid- and cardiovascular-related sensory systems. Special attention is paid to the structures of the lamina terminalis, the area postrema, the lateral parabrachial nucleus, and their association with the central nucleus of the amygdala and the bed nucleus of the stria terminalis in controlling the behaviors that participate in maintaining body fluid and cardiovascular homeostasis.

Area postrema, lateral parabrachial nucleus, and the antinatriorexic effect of bombesin

Bombesin (BN) injected to sodium depleted rats either centrally, particularly into the paraventricular nucleus (PVN) or peripherally by intraperitoneal (IP) route, exerts a potent inhibitory effect on the intake of 2% sodium chloride. To determine whether the area postrema (AP) and the lateral parabrachial nucleus (LPBN), which are known to be involved in the control of ingestive behavior, could be sites for the antinatiorexic activity of BN, we studied the effects of injections of this peptide into the LPBN or, by IP or fourth ventricular route, to surgically AP-lesioned rats. We observed that in sodium depleted rats: 1) injected into the LPBN at a dose of 50, but not of 25, ng per nucleus, BN significantly reduced the intake of 2% sodium chloride; 2) administered either intraperitoneally or into the fourth brain ventricle, BN induced a potent antinatriorexic effect in AP-sham lesioned animals; and 3) in the same experimental conditions, surgical ablation of the AP did not reduce the antinatriorexic effect of the peptide. These data indicate that the LPBN may be, with the PVN, a site for the BN-ergic inhibitory control of salt appetite and that the AP, which has been implicated in BN-induced anorexia, does not play a role in the antinatriorexic effect of this peptide.