Neuropeptide Y perfused in the preoptic area of rats shifts extracellular efflux of dopamine,norepinephrine and serotonin during hypothermia and feeding

This study examined the localized action of neuropeptide Y (NPY) on monoamine transmitter activity in the hypothalamus of the unrestrained rat as this peptide induced hypothermia, spontaneous feeding or both responses simultaneously. A guide tube was implanted in the anterior hypothalamic pre-optic area (AH/POA) of Sprague-Dawley rats. Then either control CSF vehicle or NPY in a dose of either 100 ng/μl or 250 ng/μl was perfused by push-pull cannulae in this structure in the fully sated, normothermic rat. Successive perfusions were carried out at a rate of 20 μl/min for 6.0 min with an interval of 6.0 min elapsing between each. Samples of perfusate were assayed by HPLC for their levels of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their respective metabolites. Whereas control CSF was without effect on body temperature (T_b) or feeding, repeated perfusions of NPY over 3.0 hr caused dose—dependent eating from 4 to 39 g of food, hypothermia of 0.9 to 2.3°C or both responses concurrently. As the rats consumed 11–39 g of food, the efflux of NE, MHPG, DOPAC and 5-HT was enhanced significantly, whereas during the fall in T_b the efflux of NE, DOPAC and 5-HIAA from the AH/POA increased. When the T_b of the rat declined simultaneously with eating behavior, the levels in perfusate of DOPAC and HVA increased significantly while MHPG declined. During perfusion of the AH/POA with NPY the turnover of NE declined while DA and 5-HT turnover increased during hypothermia alone or when accompanied by feeding. These results demonstrate that the sustained elevation in NPY within the AH/POA causes a selective alteration in the activity of the neurotransmitters implicated in thermoregulation, satiety and hunger. These findings suggest that both DA and NE comprise intermediary factors facilitating the action of NPY on neurons involved in thermoregulatory and ingestive processes. The local activity of NPY on hypothalamic neurons apparently shifts the functional balance of serotonergic and catecholaminergic neurons now thought to play a primary role in the control of energy metabolism and caloric intake.     

Diencephalo-telencephalic changes of tyrosine hydroxylase in rats and grass frogs after sleep deprivation

Based on sleep deprivation-produced changes of electrographic parameters of the wakefulness-sleep cycle (WSC) in rats and frogs (Rana temporaria), dynamics of activity of tyrosine hydroxylase, the key enzyme of dopamine synthesis, was studied immunohistochemically in substantia nigra and nigrostriatal pathway in rats and in striatum, paraventricular organ, and extrahypothalamic pathways in frogs. Changes in dynamics of tyrosine hydroxylase in rats and in frogs are revealed after the 6-h sleep deprivation and after 2 h of postdeprivation sleep. This allows determining the degree of participation of corticostriatal neuroregulatory and hypothalamo-pituitary neurosecretory systems and their role in regulation of WSC. Possible evolutionary peculiarities of morphofunctional differences in homoiothermal and poikilothermal animals are discussed.     

Differential distribution and regulation of OX1 and OX2 orexin/hypocretin receptor messenger RNA in the brain upon fasting

To further understand the functions of the orexin/hypocretin system, we examined the expression and regulation of the orexin/hypocretin receptor (OX1R and OX2R) mRNA in the brain by using quantitative in situ hybridization. Expression of OX1R and OX2R mRNA exhibited distinct distribution patterns. Within the hypothalamus, expression for the OX1R mRNA was largely restricted in the ventromedial (VMH) and dorsomedial hypothalamic nuclei, while high levels of OX2R mRNA were contained in the paraventricular nucleus, VMH, and arcuate nucleus as well as in mammilary nuclei. In the amygdala, OX1R mRNA was expressed throughout the amygdaloid complex with robust labeling in the medial nucleus, while OX2R mRNA was only present in the posterior cortical nucleus of amygdala. High levels of OX2R mRNA were also observed in the ventral tegmental area. Moreover, both OX1R and OX2R mRNA were observed in the hippocampus, some thalamic nuclei, and subthalamic nuclei. Furthermore, we analyzed the effect of fasting on levels of OX1R and OX2R mRNA in the hypothalamic and amygdaloid subregions. After 20 h of fasting, levels of OX1R mRNA were significantly increased in the VMH and the medial division of amygdala. An initial decrease (14 h) and a subsequent increase (20 h) in OX1R mRNA levels after fasting were observed in the dorsomedial hypothalamic nucleus and lateral division of amygdala. Levels of OX2R mRNA were augmented in the arcuate nucleus, but remained unchanged in the dorsomedial hypothalamic nucleus, paraventricular hypothalamic nucleus, and amygdala following fasting. The time-dependent and region-specific regulatory patterns of OX1R and OX2R suggest that they may participate in distinct neural circuits under the condition of food deprivation.     

Aromatase inhibition abolishes courtship behaviours in the ring dove (Streptopelia risoria) and reduces androgen and progesterone receptors in the hypothalamus and anterior pituitary gland

The aim of this study was to determine in the ring dove, the effects of aromatase inhibition on the expression of aggressive courtship and nest-soliciting behaviours in relation to the distribution of cells containing immunoreactive androgen (AR) and progesterone (PR) receptor in the hypothalamus and pituitary gland. Isolated sexually experienced ring doves were transferred in opposite sex pairs to individual breeding cages, and then injected with the aromatase inhibitor, fadrozole (four males and four females), or saline vehicle (four males and four females) for 3 days at 12 hourly intervals. Saline-injected control males displayed aggressive courtship behaviours (bow-cooing and hop-charging) and nest-soliciting throughout the study, and control females displayed nest-soliciting. By day 3, fadrozole treatment resulted in the disappearance of all these behaviours and in a decrease or disappearance of AR and PR in the anterior pituitary gland, and in the nucleus preopticus paraventricularis magnocellularis (PPM), nucleus preopticus medialis (POM), nucleus hypothalami lateralis posterioris (PLH), and ventral, lateral and dorsal nucleus tuberalis in the hypothalamus (VTu, LTu, DTu). In the nucleus preopticus anterior (POA), fadrozole treatment decreased AR in both sexes and decreased PR in females but not in males. Cells containing co-localized nuclear AR and PR were found in all hypothalamic areas examined, and in the anterior pituitary gland. Fadrozole is suggested to reduce the local availability of estrogen required indirectly for the induction of AR, and except in cells containing PR in the male POA, for the direct induction of PR. It is suggested that aggressive courtship behaviour is terminated by “cross talk” between aromatase-independent PR and aromatase-dependent AR co-localized in neurons in the POA. Aromatase-independent PR may increase in the male POA in response to visual cues provided by a partner. Aromatase-dependent PR in the POM, and basal hypothalamus may play a role in the facilitatory effect of progesterone on estrogen-induced nest-orientated behaviours. (Mol Cell Biochem 276: 193–204, 2005)     

Involvement of Accessory Neurosecretory Nuclei of Hypothalamus in the Formation of Hypothalamohypohysial System during Prenatal and Postnatal Development in Rats

We studied the development of direct axonal connections of the accessory neurosecretory hypothalamic nuclei with the posterior pituitary lobe on the fixed rat brain from day 15 of embryogenesis until day 10 of postnatal development using the retrograde diffusion method of the lipophilic fluorescent carbocyanine dye 1,1"-dioctadecyl-3,3,3",3"-tetramethylindocarbocyanine perchlorate along the neuronal membranes. The marker was applied onto the posterior pituitary lobe and, after incubation in a fixative, fluorescing bodies of nerve cells were visualized in the hypothalamus. Neuronal axons of the retrochiasmatic nucleus were the first of the accessory nuclei to ingrow in the posterior pituitary lobe (on days 16–17 of embryogenesis). Neurons of the circular and dorsolateral nuclei and the nuclei of the median bundle of the forebrain sent their axons to the posterior pituitary lobe starting from the first days of postnatal development. No direct connections of the anterior commissure and perifornical accessory nuclei with the posterior pituitary lobe were found in perinatal development. These facts are discussed in the light of concepts about the different functional role of accessory peptidergic hypothalamic nuclei in rats.     

Daily profile in ghrelin and hypothalamic ghrelin receptors in obese and lean mice Neotomodon alstoni

Mice Neotomodon alstoni develops, in some individuals, overweight and obesity when kept in vivarium conditions and fed on standard rodent diet. In the present study, we explored the possible differences between lean and obese mice, on the daily expression of the hormone ghrelin, its total and active form, as well as the relative expression of ghrelin receptors (GSHR) in hypothalamic tissue. Plasma hormones were detected and quantified by immunological techniques by ELISA; the relative presence of GSHR was assessed by western blot. Mice were sacrificed at different times throughout the day. The results obtained indicate that there is a rhythm of presence of total and acylated ghrelin in lean mice, which dampers and changes its peak’s phase in obese mice. The GHSR expression tend to be more abundant in obese mice than in lean mice. The results indicate that, in the obese mice there is a possible resistance to ghrelin.     

Medial septum glutamatergic neurons control wakefulness through a septo-hypothalamic circuit

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Paternal aggression in a biparental mouse: parallels with maternal aggression

Environmental and social factors have important effects on aggressive behaviors. We examined the effect of reproductive experience on aggression in a biparental species of mouse, Peromyscus californicus. Estrogens are important in mediating aggressive behavior so we also examined estrogen receptor expression and c-fos for insights into possible mechanisms of regulation. Parental males were significantly more aggressive than virgin males, but no significant differences in estrogen receptor alpha or beta expression were detected. Patterns of c-fos following aggression tests suggested possible parallels with maternal aggression. Parental males had more c-fos positive cells in the medial amygdala, and medial preoptic area relative to virgin males. The medial preoptic area is generally considered to be relatively less important for male-male aggression in rodents, but is known to have increased activity in the context of maternal aggression. We also demonstrated through habituation-dishabituation tests that parental males show exaggerated investigation responses to chemical cues from a male intruder, suggesting that heightened sensory responses may contribute to increased parental aggression. These data suggest that, in biparental species, reproductive experience leads to the onset of paternal aggression that may be analogous to maternal aggression.     

In vitro TRH release from hypothalamus slices varies during the diurnal cycle

We have previously described a daily rhythm in thyrotropin releasing hormone (TRH) and TRH mRNA in the rat hypothalamus. To determine whether TRH release fluctuates in a diurnal manner, we have measured basal and potassium stimulated release from hypothalamic slices, and compared it to release from olfactory bulb slices, during the diurnal cycle. Basal TRH release was higher at 7:00 h than at any other time (1:00, 13:00 or 19:00 h) in either hypothalamus or olfactory bulb. The ratio of stimulated over basal release was higher in the hypothalamus at 19:00 h, when TRH content was highest. Potassium stimulated TRH release from olfactory bulb was not different from basal release at any time. TRH release fluctuations were not due to a rhythm of extracellular inactivation: the activity of pyroglutamyl aminopeptidase II, an ectoenzyme responsible for TRH inactivation, was constant throughout the cycle. Our data demonstrate that diurnal variations of TRH release occur in vitro and that the enhanced responsiveness to potassium stimulation in hypothalamus is correlated with increased levels of peptide.