Hypothalamic "coding" in the unanesthetized monkey of noradrenergic sites mediating feeding and thermoregulation

Heat stress induced histopathology and pathophysiology of the central nervous system

The number of reports on the effects of heat stress is still increasing on account of the temperature is one of the most encountered stressful factors on the different biological systems. Because the heat stress (HS) considered a model of thermal injury to the central nervous system (CNS), the purpose of this review was to assess the histopathological changes of HS on CNS. Also, this review emphasized that the heat stress may retard partially the degree of the postnatal neurogenesis and growth of CNS. Taken together, owing to one of the most important functions of heat shock protein is to protect the organisms from the deleterious effects of temperature, thus, it can be hypothesized that the formation of heat shock proteins may be related to the deleterious effect of HS. On the other hands, the alterations of neurotransmitters in the central nervous system might be involved in the physiological and biochemical responses that occur during heat stress. The hypothalamic monoaminergic systems play an important role in the thermoregulation through regulate the heat production and heat dissipation. In addition, the disturbance in the biochemical variables due to the high temperature may be the cause of the histopathological changes and the partial retardation in CNS and the reverse is true. Thus, further studies need to be done to emphasize this concept.

Anorexic action of a new potential neuropeptide Y antagonist [D-Tyr27,36, D-Thr32]-NPY (27-36) infused into the hypothalamus of the rat

Neuropeptide Y (NPY) produces a vigorous feeding response in several species when it is injected into hypothalamic structures involved in eating behavior. The purpose of this study was to determine whether a unique carboxy terminal fragment of NPY would alter the pattern of eating induced in the rat either by NPY injected into the hypothalamus or by a 24-h period of food deprivation. In this case, two L-tyrosine residues and one L-threonine residue of the NPY27-36 fragment were transformed to their D-conformation to produce [D-Tyr27,36,D-Thr32]-NPY (27-36), i.e., D-NPY27-36. Guide cannulae for microinjection were implanted stereotaxically just dorsal to the paraventricular nucleus (PVN) or ventromedial hypothalamus (VMH) of 24 adult male Sprague-Dawley rats. Following postoperative recovery, a microinjection of artificial CSF or 1.1 microgram or 3.3 micrograms of a peptide was made directly into the PVN or VMH as follows: native NPY; D-NPY27-36; or [L-Tyr27,36, L-Thr32]-NPY (27-36), i.e., L-NPY27-36. Food intakes were measured at intervals of 0.25, 0.5, 1.1, 2.0, 4.0, and 24 h. When D-NPY27-36 was microinjected at NPY reactive sites in the PVN or VMH of the rat 15 min before a similar microinjection of NPY, the intense eating response induced by the peptide was reduced significantly. Not only was the effect dose dependent, but D-NPY27-36 also augmented the latency to feed. A mixture of the two doses of NPY and D-NPY27-36 injected at the same hypothalamic loci did not attenuate the intake of food but tended to enhance the feeding response in the rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Mapping of hypothalamic sites involved in the effects of NPY on body temperature and food intake

The objective of the present study was to identify hypothalamic sites that might be implicated in the effects of neuropeptide Y (NPY) on both body temperature and food intake. For this purpose, the effects of direct microinjections of NPY in several doses (0.156-20 micrograms) into discrete hypothalamic nuclei on body temperature were examined in rats. To examine specificity of effects, food consumption of animals following injections was also measured. Results indicate that the influence of NPY on body temperature varies with the hypothalamic region where the peptide is administered. NPY had no effect on temperature after administration into the ventromedial (VMH) and the perifornical hypothalamus (PeF). However, a significant hypothermia was seen following administration into the preoptic (POA) and arcuate nucleus (Arc), and hyperthermia was seen after injection into the paraventricular nucleus (PVN). Finally, a biphasic effect was observed after injection into the lateral hypothalamus (LH): hyperthermia with relatively small doses and hypothermia with higher doses. Similar effects were obtained when administered into the third ventricle (3V) but in an inverted dose-related fashion: hypothermia at low and hyperthermia at higher doses. For feeding, NPY consistently increased food intake in all regions examined, with the strongest effect obtained after administration into the PeF. The present results clearly dissociate the effects of NPY on food intake and body temperature, and demonstrate that these effects are related to specific hypothalamic nuclei.

Hypothermia and feeding induced simultaneously in rats by perfusion of neuropeptide Y in preoptic area

Changes in the body temperature (Tbo) of the unrestrained rat as well as the hyperphagic-like ingestion of food were simultaneously determined during the sustained elevation of neuropeptide Y1-36 (NPY) within the anterior hypothalamic preoptic area (AH/POA). A single guide tube was implanted stereotaxically in each rat for repeated perfusions by means of push-pull cannulae of either the CSF solvent vehicle or NPY. Following postoperative recovery, each site in the AH/POA was perfused for 6.0 min at a rate of 20 microliters/min over four successive intervals at a concentration of 100 ng/1.0 microliters or 250 ng/1.0 microliters, with an interval of 6.0 min intervening between perfusions. During repeated perfusions of NPY in the fully sated and normothermic rat, concentration-dependent eating, or a hypothermia or both responses occurred simultaneously. Mean cumulative intakes of food over 3.0 h were 12.1 +/- 1.4 and 21.5 +/- 2.7 g following the 100 and 250 ng concentrations of NPY, respectively. The mean maximal declines in Tbo were -0.92 +/- 0.21 and -1.1 +/- 0.28 degrees C, respectively after the lower and higher concentrations of the peptide. Push-pull perfusions of artificial CSF control vehicle at homologous anatomical sites in the AH/POA were without effect on feeding or the Tbo of the rats. These results demonstrate that repeated and sustained elevation of NPY in the AH/POA can cause a perturbation of the neuronal mechanisms underlying the normal "set-point" for body temperature as well as satiety.(ABSTRACT TRUNCATED AT 250 WORDS)

Sites in the brain at which cholecystokinin octapeptide (CCK-8) acts to suppress feeding in rats: a mapping study

In this study, an examination was made of the sites in the brain of the rat at which the injection of cholecystokinin octapeptide (CCK-8) would alter food intake. Rats fasted for 24 hr received intracerebral injections of CCK-8 (1 nmol) or an equal volume of saline (0.5 microliters), into various sites in the brain through permanently implanted stainless steel cannulae. After prior acclimatisation to individual plexiglass compartments, latency to feed, as well as consumption of food and water during 0-20, 20-40 and 40-60 min after the injection, were recorded. The available food was the standard rat pellets, to which the animal otherwise had constant daily access. With this paradigm, active sites at which CCK-8 suppressed feeding were defined as sites at which consumption of food for 0-20 min was reduced by 25% or more, or the latency to feed was increased by 3 min or more after the injection of CCK-8, as compared to the effect of the injection of saline, made at the same site. Such active sites were most densely distributed in the rostral diencephalon, e.g. hypothalamus, the medial pontine area and lateral medulla, in the vicinity of the nucleus tractus solitarii (NTS). By grouping data for injections according to histologically identified sites, statistical analysis of groups of injections confirmed that these three major areas of the brain were active with regard to the suppression of feeding by CCK-8. These data suggest that CCK may not only initiate satiety messages, as a circulating hormone at peripheral sites, but also participate in the conduction of such information to the target in the brain by serving as a neurotransmitter in the lateral medulla (e.g. NTS), medial pontine area (e.g. relay station between the NTS and hypothalamus) and the lateral hypothalamus, where local release of CCK-8 after stomach loading has been observed.

Microdialysis measurement of monoamine and amino acid release from the medial preoptic region of the sheep in response to heat exposure

Concentrations of monoamines and metabolites and amino acids were measured in microdialysis samples taken from the medial preoptic area of 5 conscious sheep before, during and after exposure to an ambient temperature of 45 degrees C. Concentrations of dopamine, noradrenaline and aspartate significantly increased, and those of the serotonin metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA), significantly decreased during heat exposure and although panting was induced, body temperature did not change. Concentrations of noradrenaline and aspartate declined and 5-HIAA increased to preheat exposure levels during the 60 min after the ambient temperature was reduced but levels of dopamine and its metabolite, homovanillic acid, remained elevated. Dopamine, noradrenaline, 5-HIAA and aspartate concentrations were not significantly altered by isolation stress and did not show significant changes in the cortex following heat exposure. These experiments provide further support for the proposed roles of dopamine, noradrenaline, serotonin and aspartate in the neural control of autonomic thermoregulatory responses.

Uric acid is released in the zona incerta of the subthalamic region of the sheep during rumination and in response to feeding and drinking stimuli

The technique of intracranial dialysis was used to sample changes in monoamine metabolite and uric acid concentrations in the zona incerta (ZI) of the subthalamic region of conscious sheep during rumination and in response to the presentation of feeding and drinking stimuli. Sequential 10-min dialysis samples were taken over a 5-h period with stimuli presented at hourly intervals. For each animal, sampling was carried out weekly for 2-3 months. Results from HPLC analysis showed that concentrations of uric acid rose significantly in the ZI, but not in the cortex or peripheral plasma, during rumination, eating, drinking or exposure to the sight or smell of food. No response to control stimuli--loud noise, smell of amyl acetate or sight of a syringe--was found. Concentrations of 5-hydroxyindol-3-yl-acetic acid in the ZI were unaffected.

Avian cerebrospinal fluid: repeated collection and testing for a possible role in food intake regulation

The objective of this study was to determine if a factor(s) involved in the regulation of food intake exists in the cerebrospinal fluid (CSF) of the domestic fowl. A technique was developed that allows blood-free CSF samples to be collected repeatedly from the cisterna magna for up to 6 weeks. Using this technique, CSF was collected from free-feeding and 24-hour fasted broiler cockerels and injected into the lateral cerebral ventricle of 8-week old Leghorn cockerels and 4-week old broiler cockerels. The free-feeding birds received 10 microliter intracerebroventricular injections of CSF either at normal concentration (1 X -CSF) (Experiments 1 and 3) or at four times normal concentration (4 X-CSF) (Experiments 2 and 4). Artificial CSF served as the control. Food and water consumption were monitored following injection. The 1 X- and 4 X-CSF collected from both the free-feeding and 24-hour fasted donors did not affect the food intake of either the Leghorn or the broiler recipients. Water intake, however, was significantly increased in the Leghorns and broilers receiving the 4 X-CSF collected from 24-hour fasted birds. Thus, there does not appear to be a factor(s) present in the CSF collected from the cisterna magna that alters food intake when injected into the lateral ventricle, but a factor may exist in the CSF collected from fasted donors that stimulates water intake.

Selection for growth alters the feeding response to injections of biogenic amines

Two experiments were conducted to determine if selection for growth altered the response to intracerebroventricular (ICV) injections of methoxamine and 5-hydroxytryptamine (5-HT). Lines of chickens divergently selected over 25 generations for 8-week body weight were used. The ICV injection of methoxamine into fully fed birds significantly increased food intake in the high-weight line but had no effect on food intake in the low-weight line. Conversely, the ICV injection of 5-HT had no effect in fully fed birds but significantly decreased food intake in 24-hr fasted birds in both weight-lines. Food intake was affected by 5-HT for a much longer period in the high-weight line than in the low-weight line. These results suggest that selection for growth alters the brain response to biogenic amines.

Food intake control in birds

The regulation of food intake has been a topic of intense investigation for several decades. Most investigators have used the rat in such studies while considerably fewer studies have been conducted using birds. Research concerned with the control of food intake in birds is discussed herein. In most instances, birds and mammals have similar control mechanisms. The alimentary tract and the liver are peripheral structures which function in the control of feeding in birds but much remains to be studied as to their role. Many brain loci, including the lateral hypothalamus, ventromedial hypothalamus, striatum and olfactory bulbs are also involved in controlling food intake. Studies with birds have revealed marked breed and line differences in the response to factors modulating food intake. The bird appears to provide an excellent model for studies designed to investigate how selection for growth can alter the mechanisms involved in food intake control.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants

This survey, the third in a series, presents extensive tabulations of literature, primarily since 1965, on thermoregulatory effects of adrenergic and serotonergic agonists and their antagonists including ergot alkaloids, amphetamines, tryptamines, monoamine oxidase inhibitors, tricyclic and other antidepressants, a variety of other agents which alter presynaptic aminergic mechanisms including reserpine, 6-hydroxydopamine, p-chlorophenylalanine, alpha-methyltyrosines, cocaine, guanethidine and bretylium. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug.

Dopamine in the hypothalamus of the cat: pharmacological characterization and push-pull perfusion analysis of sites mediating hypothermia

Within the rostral diencephalon of the cat, 113 sites were examined for their reactivity to 2.33--14.0 microgram dopamine (DA) or 2.33--14.0 microgram norepinephrine (NE) microinjected in a volume of 0.75 microliter. During each experiment, colonic temperature was monitored and additional physiological measures were recorded continuously. In contrast to CSF controls, an intrahypothalamic injection of either catecholamine at circumscribed sites evoked a dose-dependent fall in the cat's body temperature, with NE ordinarily evoking a more profound hypothermic response. The morphological sites of maximum sensitivity were localized in the anterior hypothalamic, preoptic region. At some but not all sites, a prior microinjection of 3.5--7.0 microgram phentolamine attenuated the magnitude of the DA-induced hypothermia and delayed its onset. Conversely, at all loci, the pretreatment by the injection of this alpha-adrenergic antagonist markedly reduced the absolute magnitude of the NE-induced fall in the cat's temperature. Similar pretreatment of a reactive hypothalamic locus with a beta-adrenergic receptor blocking agent, practolol (3.5 microgram), failed to alter the hypothermia following a microinjection of DA. Either of two DA receptor antagonists, haloperidol (0.04--7.0 microgram) or d-butaclamol (0.48--1.47 microgram), when given in a sufficient dose, effectively delayed the onset of the DA-hypothermia and reduced its absolute magnitude; however, the NE-induced decline in the cat's temperature was unaffected by DA receptor blockade. Endogenous stores of DA and/or NE in the cat's hypothalamus were radio-labeled with either 3H- or 14C-catecholamines or both, microinjected through the implanted guide tube into an identified amine-sensitive site. By using push-pull cannulae, the site was subsequently perfused for 5 min with artificial CSF at a rate of 25 microliter/min with samples collected at 15 min intervals. During either the third or fourth perfusion, the ambient temperature of the cat's chamber of 22--24 degrees C was elevated to 35--45 degrees C and maintained at this level for 15 or 30 min. This environmental warming evoked a release of either DA o; NE or both amines from certain circumscribed sites within the cat's rostral hypothalamus. Overall, these results provide pharmacological, physiological and anatomical evidence for a differential role of DA in the hypothalamic mechanism which mediates the heat loss processes.

Thermoregulatory responses to intraventricular norepinephrine in normal and hypothalamic-damaged rats

We examined the effects of intraventricular injection of low doses of norepinephrine (NE) on internal temperature and on behavioral and reflexive thermoregulatory responses in unrestrained rats. NE lowered the body temperature of the rats in cold and neutral environments but had little effect in the heat. The hypothermia was blocked by alpha-adrenergic antagonists but unchanged by beta-adrenergic antagonists. In the cold, the hypothermia was caused primarily by a lowered metabolic rate. At ambient temperature 25 degrees C, it was caused primarily by vasodilatation while metabolic rate increased. Thus, reflexive responses were not integrated to lower body temperature. Behavioral responding compensated for the hypothermia. In the cold, rats increased responding to get heat after NE. In a warm environment, they did not increase responding to escape heat. Thus, both reflexive and behavioral results support the idea that the set-point is unchanged after intraventricular NE. Wherever in the brain the NE may be acting, it is not in the preoptic-anterior hypothalamic area, because when this area was ablated, the hypothermia in response to intraventricular NE was greatly exaggerated.

Pattern of drinking and feeding produced by hypothalamic norepinephrine injection in the satiated rat

Injection of norepinephrine into the perifornical region of the anterior hypothalamus elicited both drinking and feeding in satiated rats. Analysis of these behaviors revealed the following: (1) Both responses were dose-dependent, occurring at doses at least as low as 0.5 mug. (2) The drinking response (1-4 ml) had a latency of around 1.5 min and a duration of 2-3 min. It was followed within a minute or two by eating (2-4 g) that lasted approximately 20 min. It was also followed by a period of drinking suppression that lasted approximately 60 min. (3) Satiation from the ingestion process appeared to be a primary factor in terminating the elicited feeding response, whereas a time-related factor was important in terminating the elicited drinking. (4) These ingestive responses produced by noradrenergic stimulation of the anterior perifornical hypothalamus were found to bear striking similarities to the rat's natural feeding behavior and premeal component of his natural food-associated drinking behavior. (5) These noradrenergically elicited responses could not be observed with lateral hypothalamic stimulation, while only feeding was elicited by ventromedial hypothalamic stimulation. (6) The drinking induced by central noradrenergic stimulation, in contrast to that induced by peripheral beta-adrenergic stimulation, was unaffected by nephrectomy.

Ingestion in the satiated rat: role of alpha and beta receptors in mediating effects of hypothalamic adrenergic stimulation

Anterior perifornical hypothalamic injection of l-norepinephrine in satiated rats elicits a brief, vigorous drinking response followed within a minute or two by a vigorous feeding response. These adrenergically elicited responses, which bear striking similarities to a rat's naturally motivated ingestive behaviors, were examined in the present series of experiments. It was found that: (1) Both responses could be elicited by perifornical hypothalamic injection of l-epinephrine, which was actually found to be more potent than l-norepinephrine. In contrast, only feeding could be elicited by the alpha-stimulant metaraminol, and neither feeding nor drinking could be elicited by hypothalamic injection of d-norepinephrine. l-isoproterenol, or dopamine. (2) The threshold doses of l-epinephrine for eliciting reliable ingestive responses were quite low, namely, 0.8 nmole (0.15 mug) for drinking and 0.2 nmole (0.04 mug) for feeding. (3) Pharmacological analysis of the ingestive behaviors induced by l-norepinephrine or l-epinephrine indicated that the eating response was mediated by alpha-adrenergic receptors, whereas the drinking response involved the synergistic action of both alpha- and beta-adrenergic receptors. No evidence for the involvement of dopaminergic or cholinergic (muscarinic) receptors was obtained. (4) A third adrenergically elicited phenomenon, namely, a suppression of drinking, was observed during and after the period of induced feeding. Analysis of this effect revealed its dependence solely upon alpha-adrenergic receptor activity.