Stimulation and inhibition of food intake in sheep by centrally-administered hypothalamic releasing factors

Differential regulation of thyrotropin-releasing hormone mRNA expression in the paraventricular nucleus and dorsomedial hypothalamus in OLETF rats

Thyrotropin-releasing hormone (TRH) plays an important role in the regulation of energy balance. While the regulation of TRH in the paraventricular nucleus (PVN) in response to changes of energy balance has been well studied, how TRH is regulated in the dorsomedial hypothalamus (DMH) in maintaining energy homeostasis remains unclear. Here, we assessed the effects of food restriction and exercise on hypothalamic Trh expression using Otsuka Long-Evens Tokushima Fatty (OLETF) rats. Sedentary ad lib fed OLETF rats (OLETF-SED) became hyperphagic and obese. These alterations were prevented in OLETF rats with running wheel access (OLETF-RW) or food restriction in which their food was pair-fed (OLETF-PF) to the intake of lean control rats (LETO-SED). Evaluation of hypothalamic gene expression revealed that Trh mRNA expression was increased in the PVN of OLETF-SED rats and normalized in OLETF-RW and OLETF-PF rats compared to LETO-SED rats. In contrast, the expression of Trh in the DMH was decreased in OLETF-SED rats relative to LETO-SED rats. This alteration was reversed in OLETF-RW rats as seen in LETO-SED rats, but food restriction resulted in a significant increase in DMH Trh expression in OLETF-PF rats compared to LETO-SED rats. Strikingly, while Trh mRNA expression was decreased in the PVN of intact rats in response to acute food deprivation, food deprivation resulted in increased expression of Trh in the DMH. Together, these results demonstrate the differential regulation of Trh expression in the PVN and DMH in OLETF rats and suggest that DMH TRH also contributes to hypothalamic regulation of energy balance.

Brain and Gut CRF Signaling: Biological Actions and Role in the Gastrointestinal Tract

BACKGROUND

Corticotropin-releasing factor (CRF) pathways coordinate behavioral, endocrine, autonomic and visceral responses to stress. Convergent anatomical, molecular, pharmacological and functional experimental evidence supports a key role of brain CRF receptor (CRF-R) signaling in stress-related alterations of gastrointestinal functions. These include the inhibition of gastric acid secretion and gastric-small intestinal transit, stimulation of colonic enteric nervous system and secretorymotor function, increase intestinal permeability, and visceral hypersensitivity. Brain sites of CRF actions to alter gut motility encompass the paraventricular nucleus of the hypothalamus, locus coeruleus complex and the dorsal motor nucleus while those modulating visceral pain are localized in the hippocampus and central amygdala. Brain CRF actions are mediated through the autonomic nervous system (decreased gastric vagal and increased sacral parasympathetic and sympathetic activities). The activation of brain CRF-R2 subtype inhibits gastric motor function while CRF-R1 stimulates colonic secretomotor function and induces visceral hypersensitivity. CRF signaling is also located within the gut where CRF-R1 activates colonic myenteric neurons, mucosal cells secreting serotonin, mucus, prostaglandin E2, induces mast cell degranulation, enhances mucosal permeability and propulsive motor functions and induces visceral hyperalgesia in animals and humans. CRF-R1 antagonists prevent CRF- and stressrelated gut alterations in rodents while not influencing basal state.

DISCUSSION

These preclinical studies contrast with the limited clinical positive outcome of CRF-R1 antagonists to alleviate stress-sensitive functional bowel diseases such as irritable bowel syndrome.

CONCLUSION

The translational potential of CRF-R1 antagonists in gut diseases will require additional studies directed to novel anti-CRF therapies and the neurobiology of brain-gut interactions under chronic stress.

Food intake regulation in late pregnancy and early lactation

The dip in food intake, which starts in late pregnancy and continues into early lactation, has traditionally been interpreted as a depression in intake due to physical constraints. However, the rôle of physical constraints on intake has been overemphasized, particularly in early lactation. There is mounting evidence that the presence and mobilization of body reserves in early lactation play an important rôle in regulating intake at this time.

Conceptually, the dip in intake in early lactation observed when cows have access to non-limiting foods can be accounted for by assuming that the cow has a desired level of body reserves. When the cow is not compromised, the changes with time in body reserves and the dip in intake represent the normal case and provide the basis against which to assess true depressions in intake which may occur when the cow is compromised by limiting nutrition or environment.

The regulation of body reserves and intake in the periparturient cow is orchestrated through nervous and hormonal signals. Likely factors that are involved in intake regulation are reproductive hormones, neuropeptides, adrenergic signals, insulin and insulin resistance and leptin. Furthermore, oxidation of NEFA in the liver may result in feedback signals that reduce intake. The relative importance of these is discussed. A better understanding of the physiological signals involved in intake regulation and their interrelations with body weight regulation may provide important indicators of the degree of compromise that periparturient cows may experience.

Indoor space allowance: effects on growth, behaviour, adrenal and immune responses of finishing beef heifers

The objective was to determine the daily live-weight gain, behaviour, adrenal and immune responses of finishing beef heifers housed at two different space allowances. Heifers (no. = 32) with a mean live weight of466 (s.e. 3·6) kg were assigned to either 1·5 or 3·0 m2 average individual space allowance in four slatted-floor pens (two per treatment) for a period of 104 days. On days 5, 40, 68 and 96, heifers (no. = eight per treatment, four per pen) were challenged with 1·98 i.u. ACTH per kg M0·75, and serial blood samples were analysed for plasma cortisol concentrations. The other 16 heifers were immunized against keyhole limpet haemocyanin (KLH) on day 28, and blood samples collected on days 28, 42, 56, 70, 84 and 98 were analysed for anti-KLH immunoglobulin (Ig) concentrations. All heifers were blood sampled on days 0, 14, 56 and 98, and red and white blood cell numbers, packed cell volume (PCV) and plasma concentrations of creatine kinase (CK), non-esterified fatty acids (NEFA) and urea were determined. Behavioural observations were conducted on days 8, 43, 71 and 99 by scan sampling for 24 h (10-min intervals), and continuous 4-h observations were conducted on days 100 and 101.

Heifers at 1·5 m2 space allowance had a lower daily live-weight gain compared with those at 3·0 m2 (0·60 v. 0·87 (s.e. 0·04) kg; P < 0·001). Heifers at 1·5 m2 had lower pre-ACTH baseline cortisol concentrations (P < 0·05) and lower post-ACTH peak cortisol concentrations (P < 0·05). There were no effects of treatment on serum anti-KLH IgG1 or IgG2 responses (P > 0·05). Heifers at 1·5 m2 had lower plasma NEFA concentrations (P < 0·05). Red and white blood cell numbers, PCV, CK and urea were not affected by treatment (P > 0·05). The time spent lying down was lower for heifers at 1·5 m2 (10·0 v. 21·1 h/day; P < 0·05). Social interactions were fewer (P < 0·05), and incidence of head-resting behaviour was higher (P < 0·05) among heifers at 1·5 m2 compared with 3·0 m2 space allowance. In conclusion, the restricted space allowance resulted in a substantial decrease in daily live-weight gain, and changes in adrenal response and behaviour.

Neuroendocrine and physiological regulation of intake with particular reference to domesticated ruminant animals

The central nervous system undertakes the homeostatic role of sensing nutrient intake and body reserves, integrating the information, and regulating energy intake and/or energy expenditure. Few tasks regulated by the brain hold greater survival value, particularly important in farmed ruminant species, where the demands of pregnancy, lactation and/or growth are not easily met by often bulky plant-based and sometimes nutrient-sparse diets. Information regarding metabolic state can be transmitted to the appetite control centres of the brain by a diverse array of signals, such as stimulation of the vagus nerve, or metabolic 'feedback' factors derived from the pituitary gland, adipose tissue, stomach/abomasum, intestine, pancreas and/or muscle. These signals act directly on the neurons located in the arcuate nucleus of the medio-basal hypothalamus, a key integration, and hunger (orexigenic) and satiety (anorexigenic) control centre of the brain. Interest in human obesity and associated disorders has fuelled considerable research effort in this area, resulting in increased understanding of chronic and acute factors influencing feed intake. In recent years, research has demonstrated that these results have relevance to animal production, with genetic selection for production found to affect orexigenic hormones, feeding found to reduce the concentration of acute controllers of orexigenic signals, and exogenous administration of orexigenic hormones (i.e. growth hormone or ghrelin) reportedly increasing DM intake in ruminant animals as well as single-stomached species. The current state of knowledge on factors influencing the hypothalamic orexigenic and anorexigenic control centres is reviewed, particularly as it relates to domesticated ruminant animals, and potential avenues for future research are identified.

A review of behavioural and physiological responses of sheep to stressors to identify potential behavioural signs of distress

This paper discusses the potential for using observations of behaviour to recognise distress in sheep. The term distress is used to describe situations in which an animal is likely to be suffering, and is indicating this by overt behavioural signs. Literature on the behavioural responses of sheep to procedures that induce a physiological stress response is reviewed. This approach is based on human analogy and the assumption that physiological changes can be used to differentiate between stimuli that induce an emotional response in sheep and those that do not. The degree to which the behaviour of sheep in certain situations represents, at least in part, an expression of emotional behaviour, or whether it can be fully explained as a functional response to a specific situation, is a fundamental and unresolved question in ethological and psychological studies. Therefore, the validity of compiling a list of objective common behavioural indicators of distress in sheep will be contentious. However, it is important to be able to recognise and deal with suffering, and the use of behavioural methods for the identification of distress in sheep is a practical welfare issue. There is a need for further research to identify indicators of distress in sheep, but in the meantime it would be reasonable to make the judgement that, in some circumstances, sheep that are found to be vocalising, panting, and/or showing markedly increased locomotory activity could be experiencing distress.

Intraventricular insulin potentiates the anorexic effect of corticotropin releasing hormone in rats

Intraventricular corticotropin releasing hormone (CRH) suppresses food intake and body weight as a stress response. Insulin, acting within the brain, also suppresses food intake and body weight, and this suppression is related to caloric homeostasis. We determined if increased insulin within the brain potentiates the anorexic effects of intraventricular CRH. Rats were food deprived for 17 h each day and then given 30-min access to Ensure. One-half received continuous third ventricular infusion of synthetic cerebrospinal fluid via osmotic minipumps, and one-half received insulin (0.6 mU/day). During the infusion, rats also received 0, 0.1, 1.0, or 5.0 microg of CRH into the lateral ventricle just before access to Ensure. Insulin alone had no effect on Ensure intake or body weight. CRH dose dependently reduced Ensure intake in both groups, and the reduction was greater in the insulin group. Hence, central insulin potentiated the ability of centrally administered CRH to suppress food intake. These findings suggest that stress-related influences over food intake, particularly those mediated via CRH, interact with relative adiposity as signaled to the brain by central insulin.

Leptin and the regulation of food intake, energy homeostasis and immunity with special focus on periparturient ruminants

The biology of leptin has been studied most extensively in rodents and in humans. Leptin is involved in the regulation of food intake, energy homeostasis and immunity. Leptin is primarily produced in white adipose tissue and acts via a family of membrane bound receptors, including an isoform with a long intracellular domain (OB-Rb), and many isoforms with short intracellular domains (Ob-Rs). OB-Rb is predominantly expressed in the hypothalamic regions involved in the regulation of food intake and energy homeostasis. The other isoforms are distributed ubiquitously and are found in most peripheral tissues in far greater abundance than OB-Rb. The effects of leptin on food intake and energy homeostasis are central and are mediated via a network of orexigenic neuropeptides (neuropeptide Y, galanin, galanin-like peptide, melanin-concentrating hormone, orexins, agouti-related peptide) and anorexigenic neuropeptides (corticotropin-releasing hormone, pro-opiomelanocortin, alpha-melanocyte stimulating hormone and cocaine- and amphetamine-regulated transcript). In addition, leptin acts directly on immune cells to stimulate hematopoesis, T-cell immunity, phagocytosis, cytokine production, and to attenuate susceptibility to infectious insults. Emerging data in ruminants suggest that leptin is dynamically regulated by many factors and physiological states. Thus, leptin is secreted in a pulsatile fashion, but without a marked diurnal rhythm. A positive relationship between adiposity and plasma leptin concentration exists in growing and lactating ruminants. The concentration of plasma leptin increases during pregnancy, starts to decline 1--2 wk before parturition, and reaches a nadir in early lactation. The reduction of plasma leptin at parturition is likely to promote centrally mediated adaptations required in periods of energy deficit, but could have negative effects on immune cell function. Future research is needed in ruminants to address the roles played by leptin and the central nervous system in orchestrating metabolism during the periparturient period and during infectious diseases.

Intracerebroventricular corticotropin-releasing factor decreases food intake in white-crowned sparrows

Neuropeptides such as corticotropin-releasing factor (CRF) may play a role in regulating the pronounced seasonal changes in food intake shown by white-crowned sparrows (Zonotrichia leucophrys gambelii). White-crowned sparrows held on short day length received injections into the third ventricle (icv) of saline or 5.0, 15.0, and 30 microg/kg. Meal size over the subsequent 180 min was significantly depressed in a dose-dependent fashion. Other non-specific behaviors such as preening, hopping, and immobile behaviors appeared to not be affected by a dose that suppressed food intake. This experiment suggests that white-crowned sparrows, when weight-stable, respond to CRF in a manner comparable with several mammalian species.

Integration of metabolism and intake regulation: a review focusing on periparturient animals

There has been great interest in dry matter intake regulation in lactating dairy cattle to enhance performance and improve animal health and welfare. Predicting voluntary dry matter intake (VDMI) is complex and influenced by numerous factors relating to the diet, management, housing, environment and the animal. The objective of this review is to identify and discuss important metabolic factors involved in the regulation of VDMI and their integration with metabolism. We have described the adaptations of intake and metabolism and discussed mechanisms of intake regulation. Furthermore we have reviewed selected metabolic signals involved in intake regulation. A substantial dip in VDMI is initiated in late pregnancy and continues into early lactation. This dip has traditionally been interpreted as caused by physical constraints, but this role is most likely overemphasized. The dip in intake coincides with changes in reproductive status, fat mass, and metabolic changes in support of lactation, and we have described metabolic signals that may play an equally important role in intake regulation. These signals include nutrients, metabolites, reproductive hormones, stress hormones, leptin, insulin, gut peptides, cytokines, and neuropeptides such as neuropeptide Y, galanin, and corticotrophin-releasing factor. The involvement of these signals in the periparturient dip in intake is discussed, and evidence supporting the integration of the regulation of intake and metabolism is presented. Still, much research is needed to clarify the complex regulation of VDMI in lactating dairy cows, particularly in the periparturient animal.

The inhibitory effect of hormones associated with stress on Na appetite of sheep

Stress is a large stimulus of Na appetite in rabbits, rats, and mice. This study investigated the influence of some peptides implicated in stress, i.e., adrenocorticotropin (ACTH), corticotropin-releasing factor (CRF), and the recently discovered member of the CRF family, urocortin, on the ingestive behavior of sheep. Intracerebroventricular infusion of these peptides over 4 days decreased the need-free Na intake of Na-repleted sheep. Intracerebroventricular infusion of urocortin, however, did not alter Na intake of Na-depleted sheep. Systemic infusion of ACTH increased, whereas systemic infusion of either urocortin or CRF decreased, Na intake of Na-repleted sheep. The increase in Na intake caused by the peripheral infusion of ACTH was blocked by concurrent i.v. infusion of urocortin, substantiating the inhibitory role of this peptide on Na appetite. Central administration of all peptides and i.v. administration of urocortin or urocortin and ACTH combined decreased food intake. Water intake was not directly influenced by the peptides. Rather, decreased water intake, when observed, was secondary to decreased food intake, as determined by pair-feeding experiments. Whereas systemic infusion of ACTH mimics the increase in Na intake observed in several different stressful situations, CRF and urocortin actually inhibit Na intake, indicating a direct central action overriding any effect of these peptides on ACTH release. Indeed, the inhibition of Na intake by urocortin occurred despite its stimulation of ACTH release and the subsequent increase in peripheral level of cortisol. Thus it would appear that hormones associated with stress have both excitatory and inhibitory influences on Na intake. Presumably, other physiological processes entrained by stress also will be important in determining the quantitative outcome on Na appetite.

Behavioural and physiological responses of sheep to 16 h transport and a novel environment post-transport

The effect of a novel lairage environment on the ability of sheep to recover from 16 h of transport was investigated. Sheep were transported from grass paddocks to either novel outside paddocks or inside pens, and housed groups were transported to either familiar or novel inside pens. During transport, sheep from outside paddocks lay down less than those from inside pens. In sheep transported to inside pens, those from outside paddocks spent more time lying and spent less time eating; hay and water intakes during the first 12 h post-transport were lower than those previously kept inside. There was no obvious effect of a novel environment post-transport on blood biochemistry, suggesting that the lower post-transport feed and water intakes in a novel environment did not have a significant effect on the ability of the sheep to recover from the feed and water deprivation associated with transport.

Acute intraventricular CRF lowers the hoarding threshold in male rats

The influence of intracerebroventricular rat-CRF on the food-hoarding behavior of rats has been studied in relation to the animals' body weights. A group of six male rats was trained to feed every day from 1000 to 1200 h. Then their threshold for the onset of food hoarding was measured from the intercept of regression line of food hoarded during meal time vs. body weight with the x-axis. Thirty minutes before the hoarding session, the rats received 4 micrograms CRF, or saline control, in the lateral ventricle. The mean threshold for food hoarding was significantly lowered to 299 +/- 61 g after CRF, from control 418 +/- 68 g. Mean food intake during the hoarding sessions was also diminished to 6.0 +/- 0.6 g after CRF, from control 14.5 +/- 0.5 g. These results suggest that the set-point for body weight regulation is acutely lowered by intracerebral CRF.

Role of CRF in stress-related alterations of gastric and colonic motor function

Major advances have been made in the understanding of the pathophysiology of stress-related alteration of gut function. A wealth of information indicates that CRF is involved in the central mechanisms by which stress inhibits gastric emptying while stimulating colonic motor function. CRF acts in the PVN to trigger both the inhibition of gastric emptying and the stimulation of colonic motor function in response to stress, in addition to previously established endocrine and behavioral responses. Preliminary evidence exists that CRF acts in the locus coeruleus to induce a selective stimulation of colonic transit without influencing gastric emptying. The central actions of CRF to alter gastric and colonic motor function are conveyed by autonomic pathways and are unrelated to the associated stimulation of pituitary hormone secretion. The demonstration that central CRF plays a role in mediating gastric stasis resulting from surgery, peritonitis or high levels of central interleukin-1 provides new insight into the mechanisms involved in gastric ileus induced postoperatively or by infectious disease. Likewise, the demonstration that CRF in the PVN and locus coeruleus induce the anxiogenic and colonic motor responses to stress and that colonic distention activates neurons in the locus coeruleus opens new avenues for the understanding of the pathogenesis of a subset of IBS patients with colonic hypersensitivity associated with psychopathological disturbance and diarrhea-predominant symptoms.

Proteolytic degradation of rat growth hormone-releasing factor(1-29) amide in rat pituitary and hypothalamus

The identification of peptide bonds vulnerable to tissue peptidases is a valuable approach to design peptide agonists which exhibit a longer duration of action than the native molecules. Therefore, the kinetic of disappearance of rat growth hormone-releasing factor (rGRF(1-29)NH2) and the identification of its metabolites were studied in rat pituitary and hypothalamus. Synthetic rGRF(1-29)NH2 (10 microM) was incubated (0-120 min, 37 degrees C) in the presence of a pituitary (237 +/- 51 micrograms protein/ml) or hypothalamus homogenate (576 +/- 27 micrograms protein/ml). Using analytical high pressure liquid chromatography (HPLC), apparent half-lives of 22 +/- 3 min and 25 +/- 4 min were found in pituitary and hypothalamus, respectively. In both tissues, three degradation products, all less hydrophobic than the native peptide, were detected and isolated by preparative HPLC. The identification of the purified metabolites was ascertained by amino acid analysis, sequencing and chromatography with synthetic homologs. These results indicate that the main sites of cleavage in the pituitary and hypothalamus are Lys21-Leu22 (trypsin-like cleavage site), Leu14-Gly15 and Tyr10-Arg11 (chymotrypsin-like cleavage sites). TLCK and leupeptin did not affect the formation of fragment (1-21)OH while TPCK blocked the cleavage of Leu14-Gly15. The low affinity of fragment (1-21)NH2 for pituitary GRF binding sites suggests that hydrolysis of the Lys21-Leu22 bond inactivates rGRF(1-29)NH2 in this target tissue.

Effects of intracerebroventricular corticotropin-releasing hormone and intravenous morphine on cortisol, prolactin and growth hormone secretion in sheep

It has previously been demonstrated that naloxone and morphine modify the adrenocortical and pituitary responses of sheep to stress. Since CRH acts within the brain to co-ordinate the stress response, the present experiment was conducted to determine whether morphine has similar effects in sheep given oCRH centrally. Plasma concentrations of cortisol, prolactin and growth hormone were measured in blood samples collected at 10 min intervals from sheep (N = 5) over a 3-hr period. Intravenous injections of saline vehicle or morphine sulphate (0.4 mg/kg) were given after 40 min and intracerebroventricular injections of oCRH (0, 5 or 20 micrograms) were administered after 60 min. Sustained, dose-related, increases in cortisol were induced by oCRH and, in agreement with findings in stressed sheep, these responses were reduced by pretreatment with morphine. Prolactin levels appeared to increase after morphine but oCRH, on its own, did not increase prolactin secretion in this study. There was no change in growth hormone concentrations after oCRH whereas morphine transiently stimulated release.

Effects of corticotropin-releasing factor on neurons in the hypothalamic paraventricular nucleus in vitro

Effects of corticotropin-releasing factor (CRF) on paraventricular (PVN) neurons of the hypothalamus were investigated in rat brain slice preparations. Of 110 PVN neurons recorded extracellularly, bath application of 10(-7) M CRF excited 31 (28%) and inhibited 27 (25%). In 8 (7%) neurons, excitation was followed by inhibition. Five neurons tested were dose-dependently excited. To know whether these responses still remained under synaptic blockade, 10(-7) M CRF was applied to 30 PVN neurons in a low Ca2+, high Mg2+ medium. Seventeen PVN neurons were excited, but neither inhibition nor excitation followed by inhibition was observed. Of 13 intracellularly recorded PVN neurons, the membrane potential of 9 was depolarized by 10(-6) M CRF. The others were not affected. In the low Ca2+, high Mg2+ medium, the firing rates of the neurons did not decrease but increased even in neurons that decreased their firing rates in the control medium. These results suggest that CRF may excite PVN neurons directly, and depolarize the membrane potential.

Central administration of corticotropin releasing factor in the pig: effects on operant feeding, drinking and plasma cortisol

Four experiments were carried out to investigate the effects of corticotropin releasing factor (CRF) on ingestive behaviour and cortisol secretion in the prepubertal pig. In Experiment 1, 19-hr food-deprived animals were given intracerebroventricular (ICV) injections of 2.5, 10 or 20 micrograms CRF, or saline vehicle, 5 min after the start of a 30-min operant-feeding session. The total number of food reinforcements obtained in the posttreatment period did not change after 2.5 or 10 micrograms CRF, although the latter dose reduced intake in the final 5 min of the test; overall food consumption, however, was reduced after 20 micrograms CRF. In Experiment 2, pigs were treated intravenously with 20 micrograms CRF, or saline, using the same test situation as in Experiment 1; neither treatment significantly affected operant feeding. In Experiment 3, 19-hr water-deprived pigs were given ICV injections of 20 micrograms CRF, or saline, 15 min before the start of a 30-min operant-drinking session. Water intake was increased in the 5-min period directly after CRF injection, but there was no overall reduction in drinking. In Experiment 4, blood samples were taken at 15-min intervals for 30 min before and 90 min after ICV injection of 20 micrograms CRF, or saline, in food and water replete animals. Both treatments appeared to increase plasma cortisol levels, as determined by radioimmunoassay, but the effect was more pronounced after CRF.

Central nervous system action of peptides to influence gastrointestinal motor function

The central action of peptides to influence GI motility in experimental animals is summarized in Table 1. TRH stimulates gastric, intestinal, and colonic contractility in rats and in several experimental species. A number of peptides including calcitonin, CGRP, neurotensin, NPY, and mu opioid peptides act centrally to induce a fasted MMC pattern of intestinal motility in fed animals while GRF and substance P shorten its duration. The dorsal vagal complex is site of action for TRH-, bombesin-, and somatostatin-induced stimulation of gastric contractility, and for CCK-, oxytocin- and substance P-induced decrease in gastric contractions or intraluminal pressure. The mechanisms through which TRH, bombesin, calcitonin, neurotensin, CCK, and oxytocin alter GI motility are vagally mediated. An involvement of central peptidergic neurons in the regulation of gut motility has recently been demonstrated in Aplysia, indicating that such regulatory mechanisms are important in the phylogenesis. Alterations of the pattern of GI motor activity are associated with functional changes in transit. TRH is so far the only centrally acting peptide stimulating simultaneously gastric, intestinal, and colonic transit in various animals species. Opioid peptides acting on mu receptor subtypes in the brain exert the opposite effect and inhibit concomitantly gastric, intestinal, and colonic transit. Bombesin and CRF were found to act centrally to inhibit gastric and intestinal transit and to stimulate colonic transit in the rat. The antitransit effect of calcitonin and CGRP is limited to the stomach and small intestine. The delay in GI transit is associated with reduced GI contractility for most of the peptides except central bombesin that increases GI motility. Nothing is known about brain sites through which these peptides act to alter gastric emptying and colonic transit. Regarding brain sites influencing intestinal transit, TRH-induced stimulation of intestinal transit in the rat is localized in the lateral and medial hypothalamus and medial septum. The periaqueductal gray matter is a responsive site for mu receptor agonist- and neurotensin-induced inhibition of intestinal transit. The neural pathways from the brain to the gut whereby these peptides express their stimulatory or inhibitory effects on GI transit is vagal dependent with the exception of calcitonin. It is not known whether the vagally mediated inhibition of GI transit by these peptides results from a decrease activity of vagal preganglionic fibers synapsing with excitatory myenteric neurons or an activation of vagal preganglionic neurons synapsing with inhibitory myenteric neurons. The lack of specific antagonists for these peptides has hampered the assessment of their physiological role.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of cyclical unipolar depression on upper gastrointestinal motility and sleep

Cyclic 48-h unipolar depression is a rare form of recurrent affective disorder. We studied a single patient to determine (a) if there is an association between psychiatric status and migrating motor complex activity; and (b) if phase III of the migrating motor complex is in phase with rapid eye movement sleep in depression. There was marked reduction in phase III of the migrating motor complex during the depressed (n = 7) compared with the euthymic phase (n = 13), and a lack of coherence between phase III migrating motor complex activity and sleep stages in both depressed and nondepressed phases. The depressed state may be associated with altered upper gastrointestinal motor function.

Psychiatric implications of altered limbic-hypothalamic-pituitary-adrenocortical activity

Hormones of the limbic-hypothalamic-pituitary-adrenocortical (LHPA) system are much involved in central nervous system regulation. The major LHPA neuropeptides, corticotropin-releasing hormone (CRH), vasopressin (AVP) and corticotropin (ACTH) do not only coordinate the neuroendocrine response to stress, but also induce behavioral adaptation. Transcription and post-translational processing of these neuropeptides is regulated by corticosteroids secreted from the adrenal cortex after stimulation by ACTH and other proopiomelanocortin derived peptides. These steroids play a key role as regulators of cell development, homeostatic maintenance and adaptation to environmental challenges. They execute vitally important actions through genomic effects resulting in altered gene expression and nongenomic effects leading to altered neuronal excitability. Since excessive secretory activity of this particular neuroendocrine system is part of an acute stress response or depressive symptom pattern, there is good reason to suspect that central actions of these steroids and peptides are involved in pathophysiology determining the clinical phenotype, drug response and relapse liability. This overview summarizes the clinical neuroendocrine investigations of the author and his collaborators, while they worked at the Department of Psychiatry in Mainz. The major conclusions from this work were: (1) aberrant hormonal responses to challenges with dexamethasone, ACTH or CRH are reflecting altered brain physiology in affective illness and related disorders; (2) hormones of the LHPA axis influence also nonendocrine behavioral systems such as sleep EEG; (3) physiologically significant interactions exist between LHPA hormones, the thyroid, growth hormone, gonadal and other neuroendocrine systems; (4) hormones of the LHPA axis constitute a bidirectional link between immunoregulation and brain activity; and (5) future psychiatric research topics such as molecular genetics of affective disorders, familial risk studies, drug response analysis and neurobiology of aging will benefit from extended knowledge of neural corticosteroid effects at a clinical, cellular, and molecular level.

Coupling between hypothalamic alpha 2-adrenoceptors and [3H]mazindol binding site in response to several hyperglycaemic stimuli in mice

The hypothalamic response to circulating glucose and insulin levels was studied in the mouse by differentially attenuating glucose-homeostasis. The administration of glucose, 2-deoxyglucose or the alpha 2-adrenoceptor agonist UK 14.304 was accompanied by a persistent hyperglycaemia; however, an increase in insulin levels was obtained with glucose and a decrease with the other two manipulations. Both alpha 2-adrenoceptors (labeled with [3H]idazoxan) and the anorectic recognition site (labeled with [3H]mazindol) were upregulated by the three treatments. A good correlation was obtained between circulating glucose levels and either hypothalamic [3H]mazindol binding (r = 0.70, P less than 0.001) or [3H]idazoxan binding (r = 0.63, P less than 0.001), as well as between the two binding sites (r = 0.88, P less than 0.001). No correlation was obtained between circulating insulin levels and these binding sites (r = 0.18, r = 0.26, P = n.s. for [3H]mazindol and [3H]idazoxan binding, respectively). It is suggested the alpha 2-adrenoceptors and the anorectic binding sites are associated in their response to glucose as part of a hypothalamic center involved in the regulation of feeding mechanisms.

Central nervous system action of TRH to influence gastrointestinal function and ulceration

There is clear evidence in rats that TRH acts in the brain to stimulate gastric acid, pepsin, and serotonin secretion, mucosal blood flow, contractility, emptying, and ulceration through activation of parasympathetic outflow to the stomach (TABLE 3). A number of TRH analogues, including some devoid of TSH-releasing activity, mimic the effects of TRH. The most sensitive TRH sites of action to elicit gastric acid secretion and motility are located in the dorsal vagal complex and include the dorsal vagal, nucleus tractus solitarius, and nucleus ambiguus. The gastrointestinal tract is one of the most responsive visceral systems to the central effects of TRH, because doses in the range of 1-10 pmol in the dorsal vagal complex stimulate gastric function, whereas stimulation of cardiovascular and respiratory function on microinjection of the brainstem nuclei requires higher doses. Although fewer investigations have been carried out in other species, evidence from the available data clearly indicates that TRH acts in the brain to increase gastric secretion and motility in the rabbit, sheep, and cat. Lack of stimulation of gastric acid secretion after third ventricle injection in the dog may be related to species difference or to rapid degradation of the peptide before it reaches its site of action. TRH acts centrally to stimulate gastric function and also intestinal secretion, motility, and transit as reported mostly in rabbits (TABLE 3). TRH produces enteropooling and release of serotonin in portal blood, increases duodenal and intestinal contractility and colonic transit, and elicits diarrhea. All these effects were shown to be vagally mediated. Stimulation of intestinal motility and transit by central injection of TRH has been observed in rats and sheep. The biological activity of centrally injected TRH is well correlated with the presence of TRH immunoreactivity and receptors in the dorsal vagal complex containing afferent and efferent connections to the stomach. Moreover, endogenous release of brain TRH in rats mimics the stimulatory effect of centrally injected TRH on gastric function. Although the lack of a specific TRH antagonist has hampered assessment of the physiological role of TRH, converging neuropharmacological, neuroanatomical, and physiological findings support the concept that TRH in the dorsal vagal complex may play a physiological role in the vagal regulation of gastrointestinal function.(ABSTRACT TRUNCATED AT 400 WORDS)