Distribution of tyrosine-hydroxylase (TH)-immunoreactive neurons in the diencephalon of the pigeon (Columba livia domestica)

The distribution of tyrosine-hydroxylase (TH)-immunoreactive cell bodies and fibers in the diencephalon has been investigated with immunohistological techniques in the pigeon. The results suggest that TH is present in a number of morphologically distinct neuronal systems. Preoptic and hypothalamic TH neurons were subdivided into a medial periventricular and a lateral group. The medial group starts with a rostral collection of small cells in the preoptic region. A significantly larger collection of TH neurons occupies the paraventricular nucleus (PVN) (stratum cellulare internum) and mainly consists of large multipolar cells. Further caudally, the main concentration of cells is in the hypothalamic posteromedial and the periventricular regions of the tuberoinfundibular (arcuate) nucleus. No TH neuron was found in the ventral and lateral parts of the tuberoinfundibular region, suggesting that the prominent tuberoinfundibular dopaminergic system described in mammals is absent in the pigeon. This further substantiated by the relative scarcity of TH immunoreactive fibers and varicosities in the neurohemal zone of the median eminence (ME). The caudalmost components of the medial group appear to be continuous with the large population of TH neurons distributed in the midline of the mesencephalon. Tyrosine-hydroxylase-immunopositive cells have not been found in the paraventricular organ. The lateral group consists of TH neurons loosely arranged in the lateral hypothalamus, including regions of the supraoptic nucleus and hypothalamic posterolateral nucleus. Tyrosine-hydroxylase containing neurons vary widely in size, shape, and dendritic arborization in each diencephalic region. However, it is possible to distinguish two main cell types. Small bipolar neurons with two simple arborizing dendrites were concentrated in the medial periventricular system. The second type of cell is large, multipolar with four to five branching dendrites. This latter cell type occurs mainly in the lateral system and in the PVN. Major fiber bundles containing TH immunoreactivity were identified in the lateral and periventricular hypothalamus. The paraventricular organ and the organum vasculosum laminae terminalis contained the densest arborization of fibers and varicosities. In the ME, dense innervation was found in the subependymal layer. Dense arborizations of TH positive fibers and varicosities were located in the septal nuclei and the paleostriatum augmentatum.     

The relationship between reproductive state and "sexually" dimorphic brain areas in sexually reproducing and parthenogenetic whiptail lizards

The anterior hypothalamus-preoptic area and ventromedial hypothalamus are sexually dimorphic in the reproductively active whiptail lizard Cnemidophorus inornatus. The anterior hypothalamus-preoptic area, which is involved in the control of male-typical copulatory behaviors, is larger in males, whereas the ventromedial hypothalamus, which is involved in the control of female-typical receptivity, is larger in females. In the parthenogenetic whiptail lizard C. uniparens, which is a direct descendant of C. inornatus and exhibits both male-like and female-like pseudosexual behaviors, both brain areas are comparable in size to those of female C. inornatus. This study was conducted to determine whether these brain areas change in size in either species or sex during a time of year when these animals are reproductively inactive, or after removal of the gonads. In male C. inornatus both brain areas changed during reproductive inactivity (either seasonally or surgically induced) and became equivalent to the size characteristic of reproductively active female C. inornatus. When corrected for brain size, the anterior hypothalamus-preoptic area was significantly smaller in intact hibernating and castrated males than in intact males from the summer breeding season. Conversely, the ventromedial hypothalamus was significantly larger in intact hibernating and castrated males than in intact males from the summer breeding season. The two brain areas were not significantly different among the groups of female C. inornatus or parthenogenetic C. uniparens. These results suggest that 1) the brain of whiptail lizards may differentiate seasonally and 2) the female state may be a neutral one to which the male brain reverts during reproductive inactivity.     

Differential expression of vasopressin receptor binding in the hypothalamus during lactation in golden hamsters

Vasopressin (AVP) receptor binding within hypothalamic sites was compared between cycling and lactating female golden hamsters. The density of AVP receptor binding was analyzed by quantitative autoradiography within the ventrolateral hypothalamus and dorsomedial hypothalamic nucleus. Lactation was correlated with a disappearance of AVP receptor binding within the ventrolateral hypothalamus. In contrast, lactation was associated with a two- to three-fold increase in the density of AVP receptor binding within the dorsomedial hypothalamic nucleus. These results suggest that AVP receptor binding within the ventrolateral hypothalamus is responsive to gonadal hormones in female golden hamsters. However, the increase in binding observed within the dorsomedial hypothalamus may be related to other neurobiological changes associated with lactation.     

Nerve growth factor and p75NGFR factor receptor mRNA change in rodent CNS following stress activation of the hypothalamo-pituitary-adrenocortical axis

The synthesis of nerve growth factor (NGF) by the hippocampus raises the possibility that NGF may play a role in the regulation of the hypothalamic-pituitary-adrenal axis (HPAA). Subchronic cold stress has been shown to activate the HPAA in a mild noninvasive manner, to stimulate serum glucocorticoid levels, and to perturb NGF binding in hippocampus and basal forebrain. One or repeated episodes of cold stress increased NGF mRNA levels in the hippocampus and p75^NGFR mRNA levels in the basal forebrain. These changes were not due to elevated serum glucocorticoid levels since treatment with exogenous corticosterone had no effect on NGF and p75^NGFR mRNA levels. Adrenalectomy did not prevent the stress induced increases in NGF and p75^NGFR mRNA. © 1993 Wiley-Liss, Inc.     

Glutamergic Action on Alpha-Melanocyte-Stimulating Hormone Release from the Rat Hypothalamus

Release of α-melanocyte-stimulating hormone (α-MSH) synthesized in the hypothalamus is regulated by monoaminergic neuronal systems. An endogenous dopaminergic system inhibits α-MSH release (1, 2) whilst serotoninergic systems exert a biphasic effect on peptide release (3). The toxic effects of neonatal peripheral administration of monosodium glutamate on hypothalamic neurons containing proopiomelanocortin- (POMC-) derived peptides (4, 5) suggest additionally the presence of glutamate receptors on or indirectly influencing the POMC neuron. By comparison of the effect of the excitatory amino-acid agonists N-methyl-D-aspartate (NMDA), quisqualate and kainate on the release of α-MSH from superfused slices of rat hypothalamus, we have demonstrated a stimulatory glutamergic action on α-MSH release mediated through NMDA-type receptors.     

Melatonin reduces nitric oxide synthase activity in rat hypothalamus

Abstract: In this report, rat hypothalamic nitric oxide synthase (NOS) activity is shown to be partially inhibited by physiological concentrations of the pineal hormone melatonin. In vitro studies demonstrate that 1 nM melatonin, which approximates the physiological concentration of the hormone at night, significantly inhibited NOS activity. In vivo studies show that administering melatonin or collecting the hypothalamus from animals at night, when endogenous melatonin levels are elevated, results in a significant decrease of NOS activity. Results also show that calmodulin may be involved in this process since its presence in the incubation medium prevents the inhibitory effect of melatonin on NOS activity.     

四季鹅下丘脑单位放电的研究

实验利用慢性微电极技术观察了清醒活动四季鹅(产蛋期鹅和休产期鹅)下丘脑细胞自发放电及第Ⅱ脑室注入去甲肾上腺素(NE)对单位放电的影响.结果表明无论是产蛋期鹅还是休产期鹅.其下丘脑放电均以中频为主,但产蛋期鹅高频放电高于休产期鹅.放电有单个连续、束状、组群式等3种形式,无论是产蛋期鹅还是休产期鹅,其下丘脑均以单个连续放电为主,但产蛋期鹅组群式放电高于休产期鹅.第Ⅱ脑室注入NE后,75%的单位放电数增加,25%的单位放电数减少.     

The effect of adrenalectomy on stress-induced c-fos mRNA expression in the rat brain

Previously, we determined the pattern of stress-induced c-fos mRNA expression throughout the brain in order to gain further insight into the identification of the neural circuits mediating stress-induced regulation of the hypothalamic-pituitary-adrenal axis. In the present study, we determined if rapid effects of increased glucocorticoid levels after stress contribute to changes in c-fos mRNA expression. To this end, stress-induced c-fos expression was characterized in adrenalectomized (ADX) or adrenalectomized and corticosterone replaced (ADX/B) male rats. Animals were sacrificed 30 min post-onset of a 10 min swim stress, and in situ hybridization histochemistry was used to detect c-fos mRNA throughout the brain. The pattern of c-fos induction in the ADX and ADX/B animals was similar to that observed in the sham operated animals. Additionally, densitometric measurements were made to quantify the c-fos response in the paraventricular nucleus of the hypothalamus and the CA1/2 region of the hippocampus. We found that ADX did not alter the magnitude of the c-fos response to stress in these areas, but there was a slight dampening of the response in ADX/B animals. In sum, these results suggest that the pattern of c-fos expression observed 30 min post-stress is independent of stress-induced increases in circulating glucocorticoid concentrations.     

Fever and feeding in the rat: Actions of intrahypothalamic interleukin-6 compared to macrophage inflammatory protein-1β (MIP-1β)

The chemokines, macrophage inflammatory protein-1 (MIP-1) and its subunit MIP-1β, induce an intense fever in the rat when they are injected directly into the anterior hypothalamic, pre-optic area (AH/POA), a region containing thermosensitive neurons. The purpose of this study was to compare the central action on body temperature (T_b) of MIP-1β with that of interleukin-6 (IL-6), which also has been implicated in the cerebral mechanism underlying the pathogenesis of fever. Following the stereotaxic implantation in the AH/POA of guide cannulae for repeated micro-injections, radio transmitters which monitor T_b continuously were inserted intraperitoneally in each of 15 male Sprague-Dawley rats. Each micro-injection was made in a site in the AH/POA in a volume of 1.0 μl of pyrogen-free artificial CSF, recombinant murine MIP-1β, or recombinant human IL-6. MIP-1β in a dose of 25 pg evoked an intense fever characterized by a short latency, a mean maximum rise in T_b of 2.4 ± 0.21°C reached by 3.7 ± 0.42 hr, and a duration exceeding 6.5 hr. Injected into homologous sites in the AH/POA, IL-6 induced a dose dependent fever of similar latency and a mean maximal increase in T_b of 1.2 ± 0.25°C, 1.8 ± 0.15°C, and 2.1 ± 0.22°C and duration of 6.2 ± 1.28 hr, 6.7 ± 0.49 hr, and 6.8 ± 0.65 hr when given in doses of 25, 50, and 100 ng, respectively. These results show that MIP-1β and the highest dose of IL-6 induce a fever of comparable intensity, but MIP-1β exerts its action in a much lower concentration. Thus, the de novo synthesis and subsequent action of the MIP-1 family of cytokines on neurons of the AH/POA in response to a pyrogen challenge apparently play a functional role in the pathogenesis of fever. Further, the endogenous activity of IL-6 in the hypothalamus which is enhanced in response to a lipopolysaccharide also may reflect its essential part in the acute phase response to a bacterial challenge. Copyright © 1994 Wiley-Liss, Inc.     

Down-Regulation of Estrogen Receptor Immunoreactivity by 17β-estradiol in the Guinea Pig Forebrain

Low amplitude pulses of estradiol-17β (E₂-17β) are more effective than large single bolus injections or constant exposure to E₂-17β in inducing progesterone-facilitated sex behavior in female rats and guinea pigs. The present study examined whether the increased responsiveness to E₂-17β is due to an increase in the number of estrogen receptors in the estrogen receptor rich areas of the hypothalamus and amygdala. Initial studies examined the rapid effects (20 min) of a high dose of E₂-17β (50 μg) on estrogen receptor immunostaining using either the H222 antibody or the ER 21 antiserum. ER 21 immunostaining was not affected by the E₂-17β treatment suggesting that it binds to both occupied and unoccupied estrogen receptors. Therefore the ER 21 antiserum was used to characterize the regulation of estrogen receptor immunoreactivity (ER-IR) by E₂-17β. ER-IR was examined for 48 h and serum E₂-17β for 24 h following a 2 μg s.c. injection of E₂-17β (a dose similar to that used in multiple pulse paradigms). Serum E₂-17β peaked 15 to 30 min following the injection and returned to baseline values by 1 h. In all but one area maximal suppression of ER-IR occurred at 12 h. In summary, 1) decreases in estrogen receptor immunoreactivity following E₂-17β are consistent with studies in which estrogen receptors were assayed by binding assays and estrogen receptor mRNA was determined by in situ hybridization; 2) the ER 21 antiserum is able to detect both occupied and unoccupied estrogen receptors and 3) H222 immunoreactivity is influenced by the presence of E₂-17β, so that the level of H222-IR is a reflection of ligand/receptor binding dynamics. The data suggest that up-regulation of estrogen receptors does not account for the increase in behavioral sensitivity which is observed following multiple pulses of E₂-17β.