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PubMed1999

Analysis of synaptotagmin I-IV messenger RNA expression and developmental regulation in the rat hypothalamus and pituitary.

Synaptotagmins are a large family of synaptic vesicle membrane proteins, that appear to be involved in neurotransmitter secretion from small secretory vesicles. We have quantitatively analysed the messenger RNA levels of synaptotagmin I-IV isoforms in adult hypothalamic and pituitary tissues in order to determine which of these isoforms dominate in these tissues which mainly secrete peptides from large dense core vesicles. We also studied the expression of these isoforms during prenatal (E15, and E17) and postnatal (P1, P7, P14 and P21) rat hypothalamic development. In order to assay small individual samples (e.g., pituitary and embryonic tissues), we employed quantitative reverse transcription-polymerase chain reaction methods. Our results show that synaptotagmin I messenger RNA is the most abundant isoform in all tissues, and is about 5.4- or 38-fold higher in hypothalamus than in neurointermediate and anterior pituitary lobe, respectively. Synaptotagmin II, which is very abundant in cerebellum, is relatively low in hypothalamus (5% of cerebellum) and virtually absent from the pituitary. Synaptotagmin III is about 10 times greater in the neural tissues versus the pituitary, and synaptotagmin IV was the least abundant isoform in all the tissues. Developmental analyses of the synaptotagmin isoforms in rat hypothalamus shows that all isoforms are at low levels during embryonic stages and increase postnatally. Synaptotagmin I and II have similar patterns and rise to maximum (adult) levels around P14, whereas synaptotagmin III and IV reach their maximum levels considerably earlier, at P1. These data show that synaptotagmin I is the dominant isoform in both predominantly peptide secreting systems (e.g., in pituitary tissues) and in neurotransmitter secreting systems (e.g., in cerebellum). While the developmental expression patterns of synaptotagmin I and II parallels the temporal development of synaptogenesis in the nervous system, the early maximal expression of synaptotagmin III and IV suggests that these isoforms may have other functions during early postnatal development.

Age Factors↗
PubMed2001

Differential distribution of Fos expression within the male rat preoptic area and hypothalamus in response to physical vs. psychological stress.

Recent studies on stress-induced adrenal glucocorticoid secretion have demonstrated quantitatively different effects of individual stress stimuli on hormone release, suggesting that the hypothalamic-pituitary-adrenal axis exhibits discriminative, rather than ubiquitous responses to such challenges, particularly psychological vs. physical stressors. The immediate-early gene, cfos, is expressed by central nervous system neurons in response to numerous physiological stimuli, including stress. The following study investigated whether the distribution and/or intensity of immunolabeling for Fos in the preoptic area and hypothalamus differ after imposition of stressors of variable intensity. Groups of male rats were sacrificed by transcardial perfusion 2 h after (1) transfer to a novel environment (NE stress), (2) confinement within a restraint tube (REST stress), or (3) immobilization (IM) stress. Nonstressed controls remained undisturbed in their home cages. Whereas the NE-stress group exhibited Fos immunoreactivity (ir) only within anterior and lateroanterior hypothalamus, both physical stressors induced immunostaining for Fos in the lateral preoptic area, median preoptic, paraventricular, arcuate, dorsomedial hypothalamic nuclei, and lateral hypothalamus, while numbers of Fos-ir-positive neurons were generally greater in the IM vs. REST stress group. In the IM-stressed rats, additional Fos-ir was observed in the supraoptic and suprachiasmatic nuclei. These studies show that neurons expressing Fos-ir in response to the relatively mild stress of novel environment are distributed differently than those that are transcriptionally activated by more aversive stressors. Findings that Fos-ir occurs in several common sites following exposure to REST or IM stress suggest that local neuron populations may comprise a common neural pathway(s) that is activated by intense forms of stress.

Animals↗
PubMed2003

Influence of the hypothalamus on the midbrain tonic inhibitory mechanism on metabolic heat production in rats.

Influence of the hypothalamus on increased body temperature was examined in male rats. Body temperature was increased by removing the midbrain tonic inhibitory mechanism (TIM) on heat production from brown adipose tissue (BAT) by microinjections of a local anesthetic, procaine, into the midbrain. Procaine microinjections in unanesthetized rats increased rectal temperature that was followed by a strong tail skin temperature rise. Procaine microinjections in unanesthetized and decerebrated rats also increased rectal temperature but without skin temperature rise. These decerebrated animals fatally developed hyperthermia. In anesthetized rats, procaine microinjections increased temperature of the interscapular BAT (IBAT) higher with shorter onset for temperature rise than rectal temperature. Increased IBAT temperature by procaine microinjections in anesthetized rats was attenuated during hypothalamic warming, and enhanced during hypothalamic cooling when compared with that observed during thermoneutral hypothalamic temperature. These results suggest that the midbrain TIM is able to function in unanesthetized conscious rats, and that the integrity of the midbrain mechanism to tonically inhibit metabolic heat production does not require the presence of intact hypothalamus. These results also suggest that the hypothalamus modulates directly or indirectly IBAT heat production that was induced by removal of the midbrain TIM.

Adipose Tissue, Brown↗
PubMed1981

Presence of immunoreactive calcitonin in the hypothalamus and pituitary lobes of rats.

We have found calcitonin-like immunoreactive material in extracts of hypothalami from six-month old, male rats. The level of this immunoreactivity, 0.21 ng/hypothalamus, is substantial considering out lower limit of detection of 0.006 ng of rat calcitonin. However, the hypothalamus contains less calcitonin-like immunoreactive material than either the anterior lobe (1.16 ng) or neurointermediate lobe (0.81 ng) of the pituitary. Taken together these three sources of calcitonin-like immunoreactive material contain less than one thousandth the immunoreactivity found in the thyroid. The exact nature of the calcitonin-like immunoreactive material found in these extrathyroidal sites and its physiological role, if any, remain to be discovered. The recent report of the occurrence of calcitonin receptors in the hypothalamus and other brain regions in conjunction with our finding of calcitonin-like immunoreactivity in the hypothalamus suggests that calcitonin-like molecules may be active within the brain.

Animals↗
PubMed1981

The descending afferent connections of the paraventricular nucleus of the hypothalamus (PVN).

The distribution of afferents to the paraventricular nucleus of the hypothalamus (PVN) was studied following iontophoresis of horseradish peroxidase (HRP) into the nucleus. This report describes the descending connections to this structure. The PVN receives a substantial input from limbic system structures, especially from the lateral septal nucleus and the ventral portion of the subicular cortex. A small number of labeled cells were found in the amygdala, primarily the medial nucleus. Of the circumventricular organs, the subfornical organ and OVLT both project to the PVN, the former very strongly. In both the preoptic area and hypothalamus, medial cell groups have more input than do the lateral areas. Labeled cells were found in the medial and hypothalamus, medial cell groups have more input than do the lateral areas. Labeled cells were found in the medial and lateral preoptic areas, suprachiasmatic nucleus, ventromedial nucleus, arcuate nucleus, retrochiasmatic and lateral hypothalamic areas. Of particular interest is the finding that the PVN receives input from the contralateral PVN and ipsilateral SON. Of the other diencephalic structures only the zone incerta showed a consistent number of labeled cells. The results are discussed in relationship to the possible neural structures that might mediate the response of the PVN neurons to adrenalectomy.

Afferent Pathways↗
PubMed1999

Gonadotrophin-releasing hormone and oxytocin secretion from the hypothalamus in vitro during pro-oestrus: the effects of time of day and melatonin.

An accurately timed surge of luteinizing hormone (LH), during the second half of the day of pro-oestrus in rats, is a crucial part of the endocrine signal that leads to expulsion of an ovum from an ovarian follicle. LH release is partly controlled by a number of peptides, including gonadotrophin-releasing hormone (GnRH) and oxytocin, which travel from the hypothalamus to the pituitary. The profile of secretion of these peptides is poorly understood. Therefore, the amounts of GnRH and oxytocin that were secreted from hypothalamic explants were determined at several time points during the day of pro-oestrus. Basal secretion of oxytocin from hypothalami taken later in pro-oestrus was greater than from hypothalami taken earlier in the day (p < 0.02). On the other hand, basal secretion of GnRH decreased during the day of pro-oestrus (p < 0.03). The different trends of GnRH and oxytocin secretion reveal that their secretion is regulated by distinct mechanisms. GnRH secretion was higher at midpro-oestrus than late in the day (o < 0.05) consistent with a peak of GnRH having been observed by others in portal blood in the second half of the day of pro-oestrus. Responsiveness of oxytocin to stimulation by K+ of the hypothalami declined from the early light hours to the evening dark hours (p < 0.02). Thus, oxytocin modulation might be achieved partly by modification of intracellular processes. Melatonin, secreted during hours of darkness, is frequently involved in modulating time-dependent events in mammals, but its contribution to peptide regulation during the ovulatory cycle is unclear. Melatonin was observed to inhibit basal oxytocin secretion from hypothalami collected during light hours (p < 0.05). The investigation has, therefore, revealed the potential for melatonin to modulate peptide secretion from the hypothalamus during the day of pro-oestrus. We also observed that secretion from the hypothalamus of the two LH-regulating peptides, GnRH and oxytocin, are differently regulated during the day of pro-oestrus.

Animals↗
PubMed1999

Increase of vasopressin mRNA in the hypothalamus of inbred polydipsic mice.

The genetically inbred polydipsic mice, STR/N strain, are characterized by extreme polydipsia and polyuria without arginine vasopressin (AVP) deficiency. The expression of AVP gene in the hypothalamus of polydipsic and non-polydipsic mice was examined by Northern blot analysis and in situ hybridization histochemistry. Northern blot analysis revealed that the total amount of AVP mRNA in the hypothalamus of the STR/N mice was approximately three-fold of that in the control, ICR mice. In situ hybridization histochemistry showed that the signals of AVP mRNA in the paraventricular (PVN) and supraoptic nuclei (SON) of the STR/N were stronger than those in the ICR. Although AVP gene transcripts were detected in the anteroventral parts of the PVN (avPVN) in the STR/N, there was a few AVP transcripts in the same area (avPVN) in the ICR. There were no differences in plasma osmolality and hematocrit between STR/N and ICR mice. These results suggest that upregulation of AVP mRNA in the hypothalamus of STR/N may be involved in the central mechanism responsible for the polydipsia in genetically polydipsic mice.

Animals↗
PubMed2000

Binding characteristics of [3H]17beta-estradiol in the hypothalamus of juvenile rainbow trout, Oncorhynchus mykiss.

Gonadal steroids in the salmonid brain, acting through cellular receptors, may be responsible for the modulation of neuronal activity and organization of reproductive behaviors. We report our findings on the use of [3H]17beta-estradiol (E2) to identify intracellular estrogen receptors (ERs) in the hypothalamus of juvenile rainbow trout, Oncorhynchus mykiss. Specific binding (B(SP)) of [3H]E2 was tissue dependent between 0.5 and 2.25 hypothalamus equivalents for cytosol and nuclear extract preparations, respectively. B(SP) in cytosol fractions increased with time and reached maximum levels (4.18 nM) at 2.5 h incubation; by contrast, B(SP) in nuclear extract increased with time to achieve maximum levels (3.9 nM) by 2 h incubation. The association rate constants (k(+1)) for cytosol and nuclear extract preparations were 1.10 +/- 0.02 x 10(8) M(-1) min(-1) and 1.27 +/- 0.04 x 10(8) M(-1) min(-1), respectively. Equilibrium bound B(SP) dissociated from cytosol preparations with a half life (t1-2) of 42 min and a dissociation rate constant (k(-1)) of 1.01 +/- 0.03 min(-1). B(SP) dissociated from nuclear extract preparations with a t1-2 = 45 min and k(-1)= 0.92 +/- 0.01 min(-1) x B(SP) was saturable in both extract preparations with a calculated equilibrium dissociation constant (Kd) of 1.46 +/- 0.1 nM (cytosol) and 2.37 +/- 0.2 nM (nuclear), and a maximum number of binding sites (B(MAX)) of 50.85 +/- 3.2 fmol mg(-1) protein and 61.74 +/- 2.65 fmol mg(-1) protein, respectively. In both preparations, B(SP) was differentially displaced by structurally similar compounds with a rank order of potency of E2 > estrone > estriol > 17alpha-ethynyl estradiol > testosterone >> progesterone = tamoxifen >> cortisol > dexamethasone >> > beta-sitosterol. These properties of specifically bound [3H]E2 suggest the presence of an ER in the hypothalamus of juvenile rainbow trout comparable with ERs identified in salmonid liver.

Animals↗
PubMed1996

In situ hybridization analysis of vasopressin mRNA expression in the mouse hypothalamus: diurnal variation in the suprachiasmatic nucleus.

The distribution, and diurnal variation of AVP mRNA-expressing neurons in the hypothalamus of the mouse has been investigated using in situ hybridization histochemistry. In general, cells hybridizing with an AVP mRNA-specific oligonucleotide probe in the mouse hypothalamus exhibit a similar distribution to the well-characterized distribution of AVP nuclei in the rat, but species-specific patterns of expression have been observed, a finding that confirms the results of earlier immunocytochemical studies. For example, prominent groups of AVP mRNA expressing cells are found in the region between the paraventricular (PVN) and suprachiasmatic (SCN) nuclei, forming the distinct mouse accessory nucleus, and a periventricular group that merges with the PVN neurons. Sampling of brains during both phases of the daily cycle (either 10.00 h (light) or 22.00 h (dark)) revealed a marked and significant variation in AVP mRNA abundance in the SCN whereas a similar variation was not consistently observed in the magnocellular neurons of the supraoptic nucleus (SON). This study has confirmed the distribution of AVP-synthesizing neurons in the mouse hypothalamus, and provided an anatomical substrate for molecular genetic studies in this species that are designed to investigate the basis of neuronal rhythmicity.

Animals↗
PubMed2000

The antiovulatory potential of progesterone antagonists correlates with a down-regulation of progesterone receptors in the hypothalamus, pituitary and ovaries.

These studies analyze the regulation of progesterone receptors (PRs) in central and peripheral tissues with the aim of further understanding mechanistically the inhibition of ovulation by progesterone antagonists (PA). Therefore, it was of interest to investigate the influence of the progesterone receptor antagonist, Onapristone (ON), on PRs in the ovary, pituitary (PT), and hypothalamus (HYP), since ON effectively inhibits ovulation in rats. For this study PMSG/hCG-primed immature and adult female rats were treated with ON. Immunohistochemistry was used for the detection of PRs. Progesterone (P4) and estradiol (E2) levels were determined by RIA. PR expression in the ovaries of immature rats was not detectable until after hCG administration. In these animals, ON caused a reduction in the staining intensity of PR in the tertiary follicles at the time when the preovulatory P4-surge was inhibited (6 h post hCG). Adult rats treated for 15 days with ON showed a decreased PR expression in PT and HYP. At this time (proestrus, 7 p.m.) the P4 and E2 levels are significantly lowered. These results suggest that after treatment with ON the expression of PR is reduced in the ovary, PT and HYP. The regulation of PR in the ovary seems to be less dependent on estrogens than on LH. Thus, it is conceivable that the reduced PR expression after ON treatment may be a result of decreased LH sensitivity in the ovary. In the pituitary and hypothalamus, PR expression is stimulated by estrogens and progesterone, and therefore the fall in the P4 and E2 levels in ON-treated animals may be responsible for the reduced PR expression in PT and HYP, and may contribute to the antiovulatory effect of ON. We therefore conclude that the mechanism of the antiovulatory potency of progesterone antagonists is based on a reduced preovulatory P4-production and PR expression in the ovary and also on the down-regulation of PR in the anterior pituitary and hypothalamus.

Animals↗
PubMed1999

Altered dopamine turnover in murine hypothalamus after low-dose continuous oral administration of aluminum.

Aluminum, a known neurotoxic substance, has been suggested as a possible contributing factor in the pathogenesis of Alzheimer's disease. Ground-water pollution by aluminum has been recently reported. In the current study groups of 5 male BALB/c mice were administered aluminum ammonium sulfate in drinking water ad libitum at 0, 5, 25, and 125 mg/L aluminum for 4 weeks. At the termination of aluminum exposure, their brains were removed and dissected into cerebrum, cerebellum, medulla oblongata, midbrain, corpus striatum, and hypothalamus. The concentration of norepinephrine (NE), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA), were determined in each brain area. DA, DOPAC, and HVA levels were lower in the hypothalamus of aluminum-treated mice, most notably in the low-dose group, as compared with control. No marked alterations in NE, 5-HT, and 5-HIAA levels were detected in any brain region. Changes in the concentration of DA and its metabolites measured in the hypothalamus suggest an inhibition of DA synthesis by aluminum.

Administration, Oral↗
PubMed2000

Extracellular norepinephrine in the medial hypothalamus increases during feeding in chicks: a microdialysis study.

Norepinephrinergic function in the medial hypothalamus is important for the regulation of feeding behavior in chicks as well as in rats. This study was conducted to clarify the variation of extracellular norepinephrine (NE) in the medial hypothalamus, including the paraventricular nucleus (PVN) and the ventromedial hypothalamic nucleus (VMN), during feeding behavior of layer-type chicks. To measure extracellular NE and 4-hydroxy-3-methoxyphenylglycol (MHPG), a major metabolite of NE, we used microdialysis and high-pressure liquid chromatography (HPLC) with electrochemical detection. After the collection of baseline samples, food-deprived animals were allowed access to the food for 3 h. Extracellular NE significantly increased during the first hour of access to food, and then returned to baseline levels. MHPG also increased during the feeding, but its increase continued throughout the remainder of the experiment. This study suggests that the variation of NE in the medial hypothalamus may be involved in the control of feeding in layer-type chicks.

Animals↗
PubMed2001

Feeding increases 5-hydroxytryptamine and norepinephrine within the hypothalamus of chicks.

It is thought that hypothalamic 5-hydroxytryptamine (5HT) and norepinephrine (NE) are involved in the regulation of feeding in chicks. The present study was conducted to elucidate changes in the levels of extracellular 5HT and NE in the hypothalamus during feeding of chicks. In order to measure 5HT, NE and 4-hydroxy-3-methoxyphenylglycol (MHPG), which is a major metabolite of NE, we used brain microdialysis and high-pressure liquid chromatography with an electrochemical detector. After collecting samples to determine the basal levels of 5HT, NE and MHPG, food-deprived birds were given access to food. 5HT levels in the medial hypothalamus (MH) and lateral hypothalamus (LH) increased during the first 30 min of feeding, and then returned to basal levels. NE and MHPG in the LH increased during feeding, and remained elevated throughout the experiment. This study supports an idea that hypothalamic monoamines in the chick brain are involved in the regulation of feeding.

Animals↗
PubMed2003

Nitric oxide induced heat shock protein 70 mRNA in rat hypothalamus during acute restraint stress under sucrose diet.

1. Sucrose feeding increases the level of stress-induced heat shock protein 70 mRNA in the rat hypothalamus. However, the mechanism by which a sucrose diet induces mRNA remains unclear. The issues investigated in this study were (1) whether a sucrose diet affects nitric oxide production in the hypothalamus, and (2) whether nitric oxide mediates the sucrose and stress-induced elevation of heat shock protein 70 mRNA. 2. To address the first question, we measured the level of nitrate, a final nitric-oxide-oxidation product measurable in vivo, using a microdialysis method. To address the second question, we administered a nitric oxide synthase inhibitor. NG-nitro-L-arginine methyl ester, prior to stress, then measured the mRNA level of heat shock protein 70 by the reverse transcription-competitive polymerase chain reaction method. 3. After the initiation of restraint stress, rats fed a sucrose-containing diet, unlike those fed standard chow, displayed a transient nitrate elevation. This nitrate elevation was attenuated by pretreatment with NG-nitro-L-arginine methyl ester. The mRNA level increases in rats fed a sucrose diet were dose-dependently attenuated by NG-nitro-L-arginine methyl ester. 4. These data suggest that a sucrose diet induces heat shock protein 70 under stress by enhancing nitric oxide production in the hypothalamus.

Animals↗
PubMed2003

Long-term imipramine treatment increases nitrate levels in the rat hypothalamus.

1. Animal experiments have shown nitric oxide synthase inhibitors to have antidepressant-like properties. However, the effects of clinically available antidepressants on nitric oxide production in the brain remain unclear. In the present study, we examined whether imipramine, a conventional antidepressant, changes the levels of type-II nitric oxide synthase mRNA and nitrate, a final nitric-oxide-oxidation product measurable in vivo, in the rat brain. 2. Type-II nitric oxide synthase mRNA was detected using a reverse transcription-polymerase chain reaction method and nitrate was measured with a combination of high-performance liquid chromatography and the Griess reaction. 3. In untreated rats, type-II nitric oxide synthase mRNA was not detected in the hypothalamus, hippocampus, cerebral cortex, brain stem, or cerebellum. However, after 28-day oral administration of imipramine, it was detected in every brain region tested. Nitrate levels in the hypothalamus and cerebral cortex increased after 28-day treatment. In the hypothalamus, nitrate levels increased dose-dependently. These dose-dependent nitrate level changes were prevented by pretreatment with a nitric oxide synthase inhibitor. Moreover, the preventive effect of NG-nitro-L-arginine methyl ester was reversed by coadministration of L-arginine, a nitric oxide substrate. 4. These results suggest that chronic imipramine treatment induces nitric oxide synthase gene expression in the brain, followed by augmented NO production.

Animals↗
PubMed2001

The developmental program of the hypothalamus and its disorders.

The hypothalamus integrates physiological processes essential for survival and reproduction. Recent studies have shown that developmental events can affect these processes. Pathways required for the induction of the ventral midline of the hypothalamus or for the differentiation of specific hypothalamic lineages have the potential of causing endocrine and metabolic disorders, including obesity. Also, some genes with paternal monoallelic expression are involved in the development of hypothalamic centers that are critical physiological regulators. Developmental defects affecting the hypothalamus might represent a more frequent cause of clinical disorders than previously suspected.

Animals↗
PubMed1975

Differential effects of amphetamine and food deprivation of self-stimulation of the lateral hypothalamus and medial frontal cortex.

Intracranial self-stimulation of the lateral hypothalamus of the rat was markedly increased by d-amphetamine administration and by food deprivation. In contrast, similar self-stimulation response rates obtained in the same animals from the medial frontal cortex were unaffected by food deprivation and only slightly increased by d-amphetamine administration. Furthermore, a large difference between d- vs. l-amphetamine on response rate was obtained for lateral hypothalamic but not for medial frontal cortex self-stimulation. The results of this study were consistent with a noradrenergic self-stimulation system for the lateral hypothalamus. Medial frontal cortex self-stimulation, however, appears to be mediated by a neuroanatomical and neurochemical system different from that of the lateral hypothalamus.

Amphetamine↗
PubMed1980

beta-Endorphin alters luteinizing hormone secretion via the amygdala but not the hypothalamus.

Morphine and enkephalins are able to alter pituitary hormone secretion. It has been postulated that they do not act directly at the pituitary, but rather that the hypothalamus is the site at which inhibition or stimulation of pituitary hormone secretion is initiated. On the other hand, endogenous opiates have been located in distinctly different neuronal regions, including areas outside the hypothalamus. The effects of beta-endorphin on plasma luteinizing hormone (LH) levels have not been explored, and the present experiments attempt to elucidate the contribution and the possible site of action of beta-endorphin in the control of LH secretion. The results show that beta-endorphin inhibits pituitary LH secretion if applied into the amygdala but not when given into the hypothalamus.

Amygdala↗