Hypothalamic serotonin in the control of meal patterns and macronutrient selection

Serotonin (5-HT) is believed to have an inhibitory influence over feeding behavior. The present experiments were designed to investigate the effects of hypothalamic 5-HT on spontaneously motivated feeding and appetite regulation. Freely-feeding rats were injected with 5-HT or norfenfluramine (NORFENF) directly into the paraventricular hypothalamus (PVN), and precise changes in feeding behavior were monitored by a computer. Following PVN 5-HT or NORFENF injection, animals exhibited a marked suppression in food intake, associated with a decrease in meal size, duration and eating rate, and no change in the frequency of meals consumed. This suggests that brain 5-HT may influence primarily the induction of satiety rather than the suppression of hunger. The effect of drugs presumed to affect brain 5-HT transmission on diet selection was also investigated in groups of rats injected centrally with 5-HT or NORFENF or peripherally with either fenfluramine, quipazine or cyproheptadine. In a series of 2-diet tests, rats centrally injected with 5-HT or NORFENF exhibited a selective suppression of the carbohydrate-rich diets. In animals provided with three pure macronutrient diets, protein, carbohydrate, and fat, systemic administration of serotonergic agents had its greatest impact on fat and carbohydrate ingestion, as compared to protein consumption. These findings support a role for hypothalamic 5-HT in modulating meal patterns and appetite for particular macronutrients.     

Concurrent facilitory and inhibitory effects of amphetamine on stimulation-induced eating

At low doses (0.125 and 0.25 mg/kg, i.p.), amphetamine facilitated eating induced by lateral hypothalamic electrical stimulation. It decreased the frequency threshold for the behavior and it increased the probability of eating across a range of suprathreshold stimulation frequencies; it also accelerated eating, decreasing the average time to eat three 45-mg food pellets across the range of stimulation frequencies tested. At high doses (1.0 and 2.0 mg/kg), amphetamine increased the frequency threshold and decreased the probability of eating across the range of suprathreshold stimulation frequencies; on those trials where eating was observed, however, even these doses of amphetamine accelerated feeding. Several lines of evidence suggest that amphetamine influences feeding through multiple mechanisms, and that present data may be explained by independent facilitory and inhibitory mechanisms, with the inhibitory mechanism less sensitive to low doses but generally dominant when the two mechanisms are both activated by higher doses. Another possibility is that the well-known anorexic effects of amphetamine result at least in part from over-stimulation of the same mechanism as is involved in the more subtle facilitory effects of the drug.     

PVN steroid implants: effect on feeding patterns and macronutrient selection

The glucocorticoid corticosterone (CORT) plays a major role in feeding behavior, body weight regulation and metabolism. Recent work has demonstrated an interaction between circulating CORT and the alpha 2-noradrenergic feeding system of the hypothalamic paraventricular nucleus (PVN) and the existence of two different subtypes of glucocorticoid receptors in this nucleus. To examine the function of these specific PVN receptors, crystalline CORT and other steroid hormones were implanted directly into the PVN, and feeding patterns and macronutrient selection, of freely feeding adrenalectomized (ADX) and sham rats, were monitored at the beginning and end of the nocturnal feeding cycle. Results indicate that PVN CORT implants stimulate carbohydrate intake in ADX rats, at the onset of the dark cycle when the feeding-suppressive effects of ADX are strongest. Corticosterone was ineffective in sham rats and was also ineffective in potentiating food intake in ADX rats at the end of the dark phase. In contrast, implants of the mineralocorticoid aldosterone (ALDO) stimulated the ingestion of the fat diet, in both sham and ADX rats and during both the early and the late dark periods. Implants of ALDO also enhanced carbohydrate intake, but only in ADX rats and at dark onset. While the synthetic glucocorticoid, dexamethasone, had a small carbohydrate stimulatory effect similar to CORT, other steroids (deoxycorticosterone, progesterone and estrogen) were without effect. These results indicate a central site of action for the adrenal hormones in modulating nutrient intake. Based on a variety of evidence, it is suggested that the stimulatory effects of ALDO and CORT on macronutrient intake may be differentially mediated by Type 1 and Type 2 steroid receptor subtypes within the brain.     

Similar effects of estrogen and lateral hypothalamic lesions on feeding behavior of female rats

NANCE, D. M. AND R. A. GORSKI. Similar effects of estrogen and lateral hypothalamic lesions on feeding behavior offemale rats. BRAIN RES. BULL. 3(5) 549–553, 1978.—Many similarities exist between the inhibitory influence ofestrogen on food intake (FI) and body weight (BWt) in female rats and the effect of lateral hypothalamic (LH) lesions on energy balance. Thus, a possible interaction of small electrolytic LH lesions (0.8 mA/10 sec) with hormone-dependent changes in FI, BWt and feeding patterns of female rats was examined. Relative to sham operated controls, rats with LH lesions showed a transitory period of anorexia and initial loss of BWt. Subsequently, FI and BWt gains of lesioned rats returned to control levels although a small chronic reduction in mean BWt was observed relative to sham animals. Daily changes in FI and BWt during 4-day estrous cycles as well as post-ovariectomy increases in FI and BWt were comparable for lesion and sham animals. Also, both groups showed a similar decrease in FI and BWt following a SC injection of estradiol benzoate (EB). Possible effects of LH lesions were further examined by analyzing feeding patterns. Feeding behavior was continuously monitored with photodetectors and recorded on an Esterline Angus event marker before and after a single SC injection of 6 μg of EB. Relative to shams, LH animals showed an exaggerated diurnal distribution of meals, ate smaller meals of shorter duration and had larger intervals between meals during the light period. EB was found to shift the feeding patterns of sham animals towards the meal patterns shown by the lesioned rats (exaggerated diurnal distribution of meals, etc.). However the lesioned rats also showed a normal change in feeding patterns following EB, albeit these changes occurred from a markedly different baseline level. In general, these data indicate that LH lesions and estrogen have similar and perhaps additive effects on the feeding behavior of female rats and both may modify feeding by altering the long-term regulation of energy balance.     

Effects of paraventricular hypothalamic microinjections of phenylpropanolamine and d-amphetamine on mash intake in rats

The present experiment compared the effects of unilateral microinjections (40, 80 and 160 nmol/0.5 microliter) of phenylpropanolamine (PPA: d,l-norephedrine) and d-amphetamine sulfate within the paraventricular hypothalamus (PVN) on consumption of a palatable sweetened-mash diet in 15-hour food-deprived adult male rats. Intracranial microinjections were administered 5 minutes prior to each 30-minute feeding trial. PPA, at a dose of 160 nmol, suppressed feeding by 42%, whereas a similar dose of amphetamine suppressed feeding by 49%. Amphetamine or PPA doses of 40 and 80 nmol were without significant effect on feeding behavior. A relatively high dose of 160 nmol amphetamine was required to suppress feeding after injection into the PVN whereas much lower amphetamine concentrations are required to suppress feeding after injection into the perifornical hypothalamus. In contrast, PPA has some anorexic activity within the PVN but not within the perifornical hypothalamus.     

Effects of carbohydrate type on postprandial blood pressure,neuroendocrine and gastrointestinal hormone changes in the elderly

Previous studies have demonstrated that blood pressure falls postprandially in fit elderly subjects, the greatest changes occurring after meals with a high carbohydrate content. To evaluate the influence of the type of carbohydrate on postprandial blood pressure, the effects of equivalent energy content (2.4 MJ) high complex (starch) and high simple (monosaccharide) carbohydrate meals were studied in seven healthy elderly subjects. Blood pressure, heart rate, autonomic function, plasma catecholamines, insulin and neurotensin levels were measured pre- and postprandially. Greater falls in supine and erect systolic blood pressure occurred after the high simple than the high complex carbohydrate meal (p < 0.05). No differences were found in supine or erect diastolic blood pressure, heart rate or in any of the biochemical parameters measured between the meal types. It is concluded that a simple carbohydrate meal results in a greater postprandial fall in blood pressure than an equivalent energy complex carbohydrate meal in the elderly, although the mechanisms for these changes are unknown.     

Meal patterns and food selection during the development of obesity in rats fed a cafeteria diet

(1) Offering preferred foods in addition to laboratory chow led immediately to a marked increase in both mean meal size (MMS) and meal frequency (MF). (2) As body weight increased over a 5 months period, MF declined to a low level but MMS remained high. (3) Within a majority of meals there was substantial consumption of only one food item. Nonetheless, when “mixed” meals were eaten these were usually larger than “exclusive” meals. (4) With more than one preferred food available there was a significant tendency to alternate consumption of food types from one meal to the next. This disappeared at inter-meal intervals longer than 90 minutes. (5) With one preferred food available, only MMS (and not MF) was increased and the degree of hyperphagia and obesity were reduced. The findings suggest the following conclusions: Both palatability (preference value for a particular food) and variety (availability of different types of food) have incremental, but distinguishable, effects on food consumption and meal parameters. Palatability mainly influences meal size, whereas variety exerts an effect on meal size and inter-meal interval. However, the potential effect of variety on overall intake is probably somewhat reduced by the tendency to eat only one type of food in each meal. Obesity has an inhibitory influence on feeding, operating primarily through a reduction in meal frequency.     

Meal patterns and food selection during the development of obesity in rats fed a cafeteria diet

(1) Offering preferred foods in addition to laboratory chow led immediately to a marked increase in both mean meal size (MMS) and meal frequency (MF). (2) As body weight increased over a 5 months period, MF declined to a low level but MMS remained high. (3) Within a majority of meals there was substantial consumption of only one food item. Nonetheless, when “mixed” meals were eaten these were usually larger than “exclusive” meals. (4) With more than one preferred food available there was a significant tendency to alternate consumption of food types from one meal to the next. This disappeared at inter-meal intervals longer than 90 minutes. (5) With one preferred food available, only MMS (and not MF) was increased and the degree of hyperphagia and obesity were reduced. The findings suggest the following conclusions: Both palatability (preference value for a particular food) and variety (availability of different types of food) have incremental, but distinguishable, effects on food consumption and meal parameters. Palatability mainly influences meal size, whereas variety exerts an effect on meal size and inter-meal interval. However, the potential effect of variety on overall intake is probably somewhat reduced by the tendency to eat only one type of food in each meal. Obesity has an inhibitory influence on feeding, operating primarily through a reduction in meal frequency.     

Effects of dopamine and norepinephrine on neuronal activity of the olfactory tubercle

The effects of iontophoretic administration of norepinephrine (NE) and dopamine (DA) on olfactory tubercle (OT) neurons that respond to lateral hypothalamus (LH) or locus coeruleus (LC) electrical stimulation were studied. NE and DA decreased the frequency of OT neurons which were increased or decreased by the LH stimulation. An increased firing of OT neurons following NE or DA administration was less frequently observed. NE administration decreased the firing of OT neurons that responded to LC stimulation. These results suggest that the LC fibers which reach the OT use NE as a neurotransmitter. DA administration also suppressed the unitary discharge of OT neurons responding to LC stimulation. The increase in frequency of OT neurons observed following LH stimulation cannot be attributed to DA. The possibility that other suspected neural transmitters are involved in this effect is discussed.     

Effects of conditioned taste aversion on extracellular serotonin in the lateral hypothalamus and hippocampus of freely moving rats

This study used microdialysis to monitor extracellular levels of 5-HT and its metabolite, 5-hydroxyindole acetic acid (5-HIAA) in the lateral hypothalamus (LH) and hippocampus of freely moving rats that had developed a CTA to a 2.5 mM saccharin solution (CS) following its pairing with illness induced by lithium chloride (US). Results showed that oral infusion of the saccharin CS significantly enhanced extracellular LH 5-HT in animals that had developed a taste aversion compared with control groups, including unconditioned (CS-no US) and pseudoconditioned (no CS-US) subjects. As an anatomical control, the hippocampus was identified based on previous research suggesting that it is not integrally involved in CTA learning or retrieval and that 5-HT in this brain site does not directly mediate feeding behavior but is closely correlated with arousal. In contrast with the results obtained in the LH, hippocampal 5-HT was not preferentially elevated in subjects in the CTA group but rather was increased to the same extend in both CTA and control groups after saccharin infusion. Moreover, the increase in LH 5-HT for the CTA group was nearly twice that observed in the hippocampus for any group. Acute administration of LiCl elevated extracellular 5-HT to similar levels in both sites, well above the changes observed following conditioning. 5-HIAA was unaffected in either brain site by oral infusion of saccharin solution or injection of LiCl.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of intragastric water infusion and gastric distension on hypothalamic neuronal activity

The effects of gastric water infusion and distension were examined in neurons from various parts of the rat brain. Neurons in the lateral preoptic-lateral hypothalamic-medial forebrain bundle (LPA-LH-MFB) neuropil were sensitive to gastric water infusion and distension. Cells randomly selected and examined in other brain areas were less sensitive to the same stimulation which indicated that the effects were relatively specific. The results, in terms of changes in neuronal discharge frequency from an established baseline, indicate that many cells in the lateral preoptic-lateral hypothalamic-medial forebrain bundle area are affected by intragastric water infusion and gastric distension within a time period during which changes in drinking would normally occur. These neurons were also affected differentially by acute water deprivation. LPA-LH-MFB neurons in 24 hr water deprived animals were significantly more sensitive to water infusions and less sensitive to stomach distension when compared to cells recorded in animals maintained on ad lib eating and drinking. Some of these same neurons were also sensitive to changes in the extracellular concentrations of sodium and glucose. The results are discussed in terms of the involvement of the lateral preoptic-lateral hypothalamic-medial forebrain bundle neuropil in ingestive behavior.     

Nutritional influences on dietary selection patterns of obese and lean Zucker rats

Little is known about the behavioral, nutritional, and metabolic events that control dietary intake quality. Two experiments are described that manipulate nutritional conditions that have been hypothesized to affect dietary item choice so as to assess what effect, if any, the added factor of genetic obesity has in modifying the response to these manipulations. In the first experiment, 5 week old male obese and lean Zucker rats were fed a diet that varied in protein content (10%, 20%, or 60% casein by weight) for ten weeks. They were then allowed to select a diet from three separate macronutrient sources (casein, starch, or corn oil). Although body weights at the end of the 10 week maintenance period were markedly different, selection patterns were not influenced by pre-feeding different levels of protein. Obese rats selected a diet that was higher in fat and lower in protein than the diets composed by lean rats. In the second experiment, four groups of 7 month old obese and lean Zucker rats were given access to one of four diets that varied in protein content (5%, 10%, 15%, or 20% casein by weight). In addition, each rat was periodically given access to a 32% sucrose solution. Access to sucrose promoted increases in total caloric intake, independent of the protein content of the diet. Obese rats typically ate more calories per day than did their lean littermates. Results from these experiments suggest that food item selection is determined more by factors associated with obesity than by factors associated with dietary history.     

Effects of fibroblast growth factors and platelet-derived growth factor on food intake in rats

In the present study, the relations between acidic and basic fibroblast growth factors (aFGF and bFGF, respectively), platelet-derived growth factor (PDGF), and food intake were studied. When aFGF-, bFGF-, and PDGF-like activity in cerebrospinal fluid (CSF) was examined by bioassay, the activity of those factors significantly increased in postfeeding CSF, compared to prefeeding CSF. Injections of aFGF, bFGF, aFGF (synthetic amino-terminal peptide of aFGF), and PDGF into the third cerebral ventricle decreased food intake, and injections of anti-aFGF, anti-bFGF, and anti-aFGF antibodies into the lateral hypothalamus (LHA) increased food intake. The activity of LHA glucose-sensitive neurons was inhibited by electrophoretic application of aFGF. These results suggest that aFGF, bFGF and PDGF have in vivo physiological roles in the central nervous system, distinct from those as mitogens.     

Effects of prenatal nicotine exposure on neuronal development: Selective actions on central and peripheral catecholaminergic pathways

The effects of prenatal nicotine exposure on development of catecholaminergic pathways were examined through measurements of transmitter turnover and levels in both the central and peripheral nervous system. Administration of nicotine (3 mg/kg SC, twice daily) to pregnant rats on gestational days 3 through 20 resulted in growth retardation which did not spare the brain and which did not resolve until after weaning. Nicotine exposure produced an elevation in transmitter turnover in central noradrenergic pathways with a regional selectivity reflecting the timetable of cellular development: the most profound effects were seen in late-developing regions (cerebellum), intermediate effects were found in earlier-developing areas (cerebral cortex) and the least effect was obtained where maturation occurs earliest (midbrain + brainstem). Dopaminergic pathways were much less vulnerable than was the noradrenergic system. Effects on the peripheral sympathetic nervous system also were targeted toward specific neuronal populations: renal, cardiac and adrenal pathways were activated by prenatal nicotine exposure, whereas sympathetic innervation of the lung showed reduced activity. All the peripheral effects appeared only after the second postnatal week. These results indicate that prenatal nicotine exposure produces profound alterations in transmitter disposition which are targeted toward specific neuronal populations and which may depend upon generalized effects on cellular development of specific brain regions. Because altered peripheral nerve activity was seen only after the onset of central control of sympathetic tone, actions on central regulation may play a role in the relatively more profound effects in the autonomic nervous system.     

Somatostatin and the paraventricular hypothalamus: modulation of energy balance

The effects of somatostatin injections (0.1, 1 and 5 μg) into the paraventricular nucleus of the hypothalamus (PVN) were investigated in an open-circuit calorimeter. Wistar rats were tested, with no food available during the tests. The 0.1 and 1 μg doses produced large and long-lasting decreases in respiratory quotient, which indicates the preferential utilization of fats as an energy substrate. The 5 μg dose produced a brief decrease in energy expenditure. Locomotor activity was not affected by any treatment which indicates that the effects on respiratory quotient and energy expenditure are not secondary to changes in activity. These findings demonstrate that somatostatin in the PVN inhibits thermogenesis and induces the preferential utilization of fats while sparing carbohydrate reserves. However, it is significant that the effects on energy expenditure and energy substrate utilisation occured at different doses. These data constitute the first evidence that somatostatin in the PVN produces a primary modulation of the metabolic parameters central to energy balance. In separate experiments, all three doses of somatostatin increased blood glucose concentration over a one hour period, and the 5 μg dose decreased body weight over a 24 h period. Food and water intake were not affected by the somatostatin injections. Taken together, these findings are interpreted in a model in which somatostatin is a signal to the PVN of increased body fat. This mobilises sympathetic mechanisms which increase fat utilization and blood glucose levels.     

Comparison of Intracranial Self-Stimulation Evoked From Lateral Hypothalamus and Ventral Tegmentum: Analysis Based on Stimulation Parameters and Behavioural Response Characteristics

The comparison of intracranial self-stimulation (ICSS) derived across the anteroposterior axis of medial forebrain bundle (MFB) from the anterior border of lateral hypothalamus (LH) to the ventral mesencephalon including ventral tegmental area-substantia nigra (VTA-SN) in Wistar rats was assessed through stimulation parameters and behavioural response characteristics. The interpretation of response rate/charge consumption (μC/min) with respect to rectangular wave and sine wave electrical stimulation parameters suggests that the rectangular wave parameters are better in order to get the maximum responding rates. The most vigorous and robust responding was observed in the VTA or VTA-SN boundary placements, followed by placements in medial sector of LH. The acquisition of ICSS was fastest in the case of VTA-stimulation. The next site with respect to rapidity of ICSS was posterio-ventral LH. The extinction curves indicated that it is faster and exponential in case of VTA-SN, but it is slower with longer duration in case of LH-MFB. ICSS of SN were accompanied by exploratory locomotion and head bobbing. Thirty-one percent subjects with SN/VTA stimulation showed rotational behaviour. Seventy-eight percent of subjects with LH stimulations showed stimulus-bound ejaculations. Thirty-two percent of subjects with posterior LH stimulations showed biting of pedal edges. LH stimulations were accompanied by induced seizures and increased grooming in 18% and 13% of subjects, respectively. There was lateralisation of cerebral hemispheric function as right paw preference was noted in majority of rats, whether sites of stimulation were in the left or right cerebral hemisphere. The various other modes of pedal pressing operants like use of paw and mouth, alternate paw dribbling, use of head electrode assembly to manipulate the pedal were also recorded and analysed. Copyright © 1996 Elsevier Science Inc.     

Effects of Lipocortin 1 and Dexamethasone on the Secretion of Corticotrophin-Releasing Factors in the Rat: in vitro and in vivo Studies

Lipocortin 1 (LC1: also called annexin 1) was first described as a putative second messenger protein for the anti-inflammatory steroids in peripheral tissues. In the present study, in vitro and in vivo methods were used to examine its potential role within the hypothalamus as a mediator of the regulatory actions of the glucocorticoids on the hypothalamo-pituitary-adrenocortical axis of the rat. In the in vitro studies, the effects of human recombinant LC1 (hu-r-LC1) on the concomitant release of the two major corticotrophin-releasing factors (CRF-41 and arginine vasopressin, AVP) from isolated hypothalami removed from chronically adrenalectomized rats were compared with those of dexamethasone in the presence and absence of appropriate secretagogues, namely phospholipase A₂ (PLA₂), interleukin-6 (IL-6) and a non-specific depolarizing agent, K⁺ (56 mM). The spontaneous release of CRF-41 in vitro was unaffected by either hu-r-LC1 (5 to 100 ng/ml) or dexamethasone (1 μM). Both compounds however reduced the release of the neuropeptide evoked by IL-6 (5 ng/ml) but failed to modify the secretory responses to PLA₂ (25 U/ml) or K⁺ (56 mM). Dexamethasone (1 μM) had no effect on the basal release of AVP but effectively blocked the secretion of the peptide induced by either IL-6 (10 ng/ml) or PLA₂ (25 U/ml). In complete contrast, hu-r-LC1 (5 to 100 ng/ml) stimulated the release of AVP and potentiated the secretory responses to IL-6 (10 ng/ml) and PLA₂ (25 U/ml) but not to K⁺ (56 mM). The hypothalamic responses to PLA₂ stimulation (25 U/ml) were associated with significant (P<0.01) increases in prostaglandin E₂ release which, in some instances, were potentiated by hu-r-LC1 (5 to 20 ng/ml). In vivo, administration of histamine (0.6 mg/100 g body wt, ip) produced significant (P<0.01) increases in the serum corticosterone concentration and in the hypothalamic LC1 content. Neither hu-r-LC1 (0.6 to 1.2 μg) nor a polyclonal anti-LC1 antibody (3 μl, diluted 1:200), injected intracerebroventricularly (icv), influenced either the resting serum corticosterone concentration or the hypersecretion of the steroid evoked by histamine stress. A lower dose of the recombinant protein (0.3 μg icv) also failed to alter basal corticosterone release but, in contrast to the higher doses, potentiated the pituitary-adrenocortical responses to histamine. The results suggest that LC1 may contribute to some aspects of peptide release in the hypothalamus but that its actions are not necessarily related to those of the glucocorticoids.     

Sequential inhibition by progesterone: Effects on sexual receptivity and associated changes in brain cytosol progestin binding in the female rat

The purpose of this study was to examine the role of cytosol progestin receptors (CPRs) in the activation of mating behavior in the estrogen (E₂) stimulated, ovariectomized rat, following the administration of a dose of progesterone (P; 2.5 mg) which is sufficiently large to inhibit the re-induction of sexual receptivity by subsequent P (‘sequential inhibition’). In order to control for competition by unlabeled P in our binding studies, aliquots of cytosol supernatants were passed through LH-20 columns prior to in vitro incubation with the radioactive ligand, [^{staggered 3}H]R5020 (double column assay).Three days following E₂ priming, all animals used in biochemical studies received either P (2.5 mg) or vehicle injections (propylene glycol; PG) 24, 28 or 72 h prior to the administration of P (0.5 mg). When P (0.5 mg) was given 24 h after P or PG treatment, animals which had received P previously showed significantly decreased lordosis quotients (LQ), lordosis quality (LS) and proceptivity scores relative to PG controls (‘sequential inhibition’). The inhibitory effects of previous P (2.5 mg) were transient, and were not observed if P (0.5 mg) was delayed until 72 h after P or PG treatment.Three days following E₂ priming, all animals used in biochemical studies received either P (2.5 mg) or PG. When we did not control for competition by unlabeled P, [^{staggered 3}H]R5020 binding in the cortex, mediobasal hypothalamus-preoptic area (MBH-POA) and pituitary was decreased by 60%, 3 h after 2.5 mg P. When we used the double column assay to remove P in the tissue, [^{staggered 3}H]R5020 binding in all tissues was decreased by 20% at 3 h after 2.5 mg P. By 24 h, after 2.5 mg P, the competitive effect of tissue P on [^{staggered 3}H]R5020 binding was not measurable; and cytosol progestin receptor (CPR) levels were less than or equal to those seen at 3 h. By 72 h after 2.5 mg P, CPRs had returned to control levels in all tissues.Our data suggest: (1) the double column assay is necessary to estimate CPR levels when P is present in the tissue; (2) when one controls for competition by P, CPR depletion 3 h after P is measurable but not extensive; depletion occurs in tissues in which CPRs are induced by E₂ (pituitary, MBH-POA), as well in cerebral cortex, where CPR levels are not included by E₂; (3) at 24 h, CPR levels are less than or equal to those seen at 3 h in all tissues; this may be the result of the initial depletion associated with nuclear translocation, or it may indicate that P regulates its own receptor concentration in the central nervous system (down-regulation); and (4) after a large dose of P (2.5 mg), reduced CPR levels correlated with P's reduced ability to facilitate sexual receptivity.     

Rapid Effects of an Aggressive Interaction on Dehydroepiandrosterone,Testosterone and Oestradiol Levels in the Male Song Sparrow Brain: a Seasonal Comparison

Across vertebrates, aggression is robustly expressed during the breeding season when circulating testosterone is elevated, and testosterone activates aggression either directly or after aromatisation into 17β‐oestradiol (E₂) in the brain. In some species, such as the song sparrow, aggressive behaviour is also expressed at high levels during the nonbreeding season, when circulating testosterone is non‐detectable. At this time, the androgen precursor dehydroepiandrosterone (DHEA) is metabolised within the brain into testosterone and/or E₂ to promote aggression. In the present study, we used captive male song sparrows to test the hypothesis that an acute agonistic interaction during the nonbreeding season, but not during the breeding season, would alter steroid levels in the brain. Nonbreeding and breeding subjects were exposed to either a laboratory simulated territorial intrusion (L‐STI) or an empty cage for only 5 min. Immediately afterwards, the brain was rapidly collected and flash frozen. The Palkovits punch technique was used to microdissect specific brain regions implicated in aggressive behaviour. Solid phase extraction followed by radioimmunoassay was used to quantify DHEA, testosterone and E₂ in punches. Overall, levels of DHEA, testosterone and E₂ were higher in brain tissue than in plasma. Local testosterone and E₂ levels in the preoptic area, anterior hypothalamus and nucleus taeniae of the amygdala were significantly higher in the breeding season than the nonbreeding season and were not affected by the L‐STI. Unexpectedly, subjects that were dominant in the L‐STI had lower levels of DHEA in the anterior hypothalamus and medial striatum in both seasons and lower levels of DHEA in the nucleus taeniae of the amygdala in the breeding season only. Taken together, these data suggest that local levels of DHEA in the brain are very rapidly modulated by social interactions in a context and region‐specific pattern.     

Effects on plasma luteinizing hormone levels of microinjection of noradrenaline and adrenaline into the septo-preoptic area of the brain of the ovariectomized ewe: changes with season and chronic oestrogen treatment

We have investigated the effects on luteinizing hormone (LH) secretion of noradrenaline (NA) and adrenaline (A) microinjected (1 μl) into the septo-preoptic area of ovariectomized (OVX) ewes with or without oestrogen (E) treatment and across the breeding and non-breeding seasons. Guide tubes (19 gauge) were placed into the septo-preoptic area of OVX ewes using lateral ventriculograms for localization of the target area. The sheep were tamed so that injections could be made into conscious animals during blood sampling procedures. Jugular venous blood was collected at 10-min intervals for 3 h, an injection of NA or A (10 μg) or saline was given and samples collected for a further 3 h. The plasma samples were assayed for LH. On completion of the experiments the brains were sectioned to locate the site of injection. In the non-breeding season of the first year, 9 ewes were used of which 3 had correct guide tube placement; in these 3 ewes NA and A had no effect in OVX ewes. In OVX ewes treated with 0.5 cm Silastic ®implants of E for 1 week, plasma LH levels were reduced from 9.1 ± 1.96 nglrnl before E treatment to 2.8±0.95 ng/ml after E treatment. In these E-treated ewes NA and A caused a robust increase in plasma LH levels. In the breeding season, 9 ewes were used of which 7 had correct guide tube placement; in these 7 ewes NA and A had no effect in OVX ewes. When OVX ewes were treated with 0.5cm E implants, NA or A injection decreased LH interpulse interval. In OVX ewes which received 1.0 cm E, NA caused a pronounced but transient suppression of plasma LH secretion due to an increase in interpulse interval. When 3.0 cm E implants were given to OVX ewes there was a strong suppression of plasma LH secretion with pulsatility abolished; NA injection had no effect in these sheep. In the second year, in the non breeding-season, 17 ewes were used of which 14 had correct guide tube placement although a number of injections were above the target region. NA injection had no effect on plasma LH levels in OVX ewes but had a variable effect on OVX ewes treated with 0.5 cm E implants, depending upon the degree of suppression of plasma LH secretion by E. When plasma LH was fully suppressed by E, injection of 1Opg NA provoked a profound and sustained increase in plasma LH levels. When plasma LH secretion was pulsatile after E treatment, NA injection decreased LH interpulse interval. Similar responses were obtained with 0.5cm E-treated sheep when injected with 1.Opg NA. When OVX ewes were given 3.0cm E implants a small and non-significant (P = 0.09) rise in plasma LH levels occurred, following 10 pg NA injection. These results provide further evidence of involvement of NA/A systems in the regulation of gonadotrophin-releasing hormone (GnRH) secretion at the level of the GnRH cell bodies in the septo-preoptic area, with clear influences of season and E status on this regulation. In the OVX sheep the GnRH pulse generation system is probably subserved by endogenous permissive NA/A input rendering exogenous input ineffective. In the breeding season NAlA can inhibit GnRH/LH secretion in the presence of physiological doses of E whereas in the non-breeding season, E profoundly suppresses GnRH/LH secretion, possibly by the removal of permissive NA inputs, which can be overcome by the injection of NAlA into the septo-preoptic area.