Pyroglutamyl-N 3im-methyl-histidyl-prolineamide (methyl-thyrotrophin releasing hormone, methyl-TRH) is a potent synthetic analogue of TRH. N 3im-Methyl-histidine is present in mammalian brain and it has been suggested that methyl-TRH is a physiological releasing hormone normally present in the hypothalamus. A non-gradient cation-exchange chromatography system that uses SP-Sephadex C-25 and completely resolves methyl-TRH and TRH has been developed. Because methyl-TRH cross-reacts in the immunoassay for TRH, this assay was used to measure TRH and methyl-TRH in the chromatographic fractions. By this means it has been demonstrated that the amount of methyl-TRH present in the rat is less than 0·025 ng/hypothalamus.
A. E. PEKARY, J. E. MORLEY, and J. M. HERSHMAN
KANJI SEIKI and MASAKAZU HATTORI
Short-term experiments (Seiki, Higashida, Imanishi, Miyamoto, Kitagawa & Kotani, 1968; Seiki, Miyamoto, Yamashita & Kotani, 1969) have failed to show any specific progesterone-binding receptors in the hypothalamus and pituitary gland. These sites do not show selective uptake of progesterone compared with other parts of the brain after i.v. administration of [3H]progesterone to rats in various experimental conditions. To investigate more extensively the existence of specific receptor sites in the hypothalamus and pituitary gland, a long-term experiment was carried out.
Female Wistar rats, weighing about 230 g, were used. Ovariectomy was carried out only on animals in dioestrus, as determined by vaginal smears. Two to three weeks after the operation, the animals were given an i.v. injection of 50 μCi [7α-3H]progesterone/100 g body weight (sp. act. 18·1 Ci/μmol) in 0·2 ml 0·9% NaCl solution containing 5% (v/v) ethanol. The animals were killed by decapitation at varying intervals of
C. A. BARRACLOUGH and B. A. CROSS
Unit activity in the hypothalamus and other diencephalic regions was recorded with stereotaxically oriented steel microelectrodes in adult female rats under light urethane anaesthesia.
Spontaneous firing rates of neurones varied from < 1/10 sec. to > 50/sec., but the majority fired at 1–10/sec. Some variations in the pattern of firing are described.
Acceleration of firing rate was most readily induced by pain stimuli (64% of neurones) and then by cold (60%), probing the cervix (47%), smell (20%), light (5%) and noise (3%) in that order. A minority of neurones were inhibited by the stimuli.
Many neurones responded to several different stimuli, most commonly by accelerating to cervical probing, cold and pain. Inhibitory convergence was also observed, e.g. blockade of the response to cervical probing by an olfactory stimulus, and inhibition by cervical probing of the response to cold or pain.
The proportion of neurones excited by smell in prooestrous rats was more than double that in oestrous or dioestrous rats. Oestrous rats had relatively more neurones which were unresponsive or inhibited by the test stimuli.
Slow intravenous injection of 400 μg. progesterone induced a selective depression of the response of lateral hypothalamic neurones to cervical probing. The effect was maximal at about 30 min. and full recovery occurred in 1 hr.
The possible significance of these observations is discussed with particular reference to the neural control of luteotrophin secretion.
A. Chatelain, F. Boudouresque, T. Chautard, J. P. Dupouyt, and C. Oliver
Corticotrophin-releasing factor-41 (CRF-41) immunoreactivity has been measured in hypothalamic extracts of fetal (on days 17, 19 and 21 of gestation), neonatal (1, 2, 3 and 4 weeks of age) and adult rats with a specific radioimmunoassay developed for synthetic rat CRF-41. The hypothalamic content (fmol) and concentration (fmol/mg protein) of immunoreactive CRF-41 gradually increased with age. Chromatography of hypothalamic extracts on Sephadex G-50 Fine showed one single peak of immunoreactive CRF-41 which co-eluted with synthetic rat CRF-41. The retention time of hypothalamic CRF-41 during high-performance liquid chromatography was identical to that of synthetic rat CRF-41 at all stages investigated. These results are consistent with the development of neurones containing CRF-41-like molecules in both the hypothalamus and the median eminence of the fetus, as well as with the hypothalamic control of the cortico-stimulating function of the pituitary gland as early as day 19 of gestation.
J. Endocr. (1988) 119, 59–64
G. B. MAKARA, E. STARK, M. PALKOVITS, T. RÉVÉSZ, and K. MIHÁLY
Corticotrophin (ACTH) release induced by various stressful stimuli has been studied in rats with antero-lateral deafferentation of the medial basal hypothalamus (MBH). The plasma corticosterone level was determined as an index of ACTH release.
In rats with antero-lateral deafferentation of the MBH, ACTH release was prevented after exposure to noise and vibration, sham adrenalectomy and s.c. injection of 1% formalin. ACTH release induced by the injection of histamine (1 mg./100 g., i.p.) and capsaicin (0·25 mg./100 g., s.c.) was significantly less than in the controls. Escherichia coli lipopolysaccharide (25 μg./100 g., i.p.) induced an ACTH release that could not be distinguished from that in the controls.
We suggest that (a) noise and vibration, sham adrenalectomy and injection of 1% formalin trigger ACTH release through neural pathways arriving at the MBH from anterior, lateral and dorsal directions, (b) histamine or capsaicin releases ACTH partly through antero-lateral neural afferents to the MBH. In contrast, the ACTH-releasing stimulus of bacterial endotoxin injection reaches the hypothalamo—hypophysial unit by humoral pathways and/or posterior nerve fibres.
G Wiesner, BA Morash, E Ur, and M Wilkinson
White adipose tissue is now recognized as the source of a growing list of novel adipocyte-specific factors, or adipokines. These factors regulate energy homeostasis, including the response to food deprivation. We hypothesized that the brain and pituitary gland would also express adipokines and their regulatory factors and subsequently demonstrated that the rodent brain-pituitary system expresses mRNA and protein for leptin and resistin. We now report that the adipokines FIAF and adiponutrin, as well as the nuclear hormone receptor PPAR gamma, are expressed in pituitary, brain and adipose tissue. In pituitary gland, 24 h of food restriction reduced PPAR gamma expression by 54% whereas both adiponutrin and FIAF were increased 1.7 and 2.3 fold, respectively. These changes in expression were similar to those observed in fat, except for adiponutrin, which by contrast is dramatically reduced 95% by fasting. Furthermore, whereas PPAR gamma 2 is the main isoform affected by fasting in adipose tissue, our data suggest that only PPAR gamma 1 is present and downregulated by fasting in pituitary tissue. In contrast to the sensitivity of pituitary tissue to the effects of fasting, no significant change in expression was observed in basal hypothalamus for any of the genes studied. Overall, our data suggest that pituitary-derived adipokines may play an unexpected role in the neuroendocrine regulation of energy homeostasis.
F. Petraglia, M. Baraldi, G. Giarrè, F. Facchinetti, M. Santi, A. Volpe, and A. R. Genazzani
Immunoreactive (Ir) β-endorphin concentrations were determined in plasma, anterior pituitary (AP), neurointermediate pituitary lobe (NIL) and mediobasal hypothalamus (MBH) of pregnant (12–14 and 18–20 days) and fertile control rats, during labour and lactation. Immunoreactive Met-enkephalin concentrations were also evaluated in the MBH.
Concentrations of Ir β-endorphin in plasma, AP and NIL of rats during early and late pregnancy were significantly higher than in controls, the plasma and AP contents showing an increasing pattern in the second half of gestation. During labour, Ir β-endorphin concentrations in plasma and AP reached the highest values, whereas those in NIL remained unchanged. Lactating rats showed Ir β-endorphin concentrations in NIL and plasma in a range similar to that found in pregnant rats, resulting in concentrations in the AP not significantly different from those of non-pregnant controls.
Immunoreactive β-endorphin and Ir Metenkephalin concentrations in MBH of pregnant rats were almost twice as high as in controls, rising markedly during labour; during lactation levels were in the same range as in non-pregnant controls.
These results indicate that pregnancy and labour are characterized by high plasma, pituitary and hypothalamic concentrations of Ir β-endorphin as well as by high hypothalamic Ir Met-enkephalin levels, and that Ir β-endorphin concentrations vary differently during pregnancy, lactation and labour in the two pituitary lobes, supporting the existence of different control mechanisms in the AP and NIL.
J. Endocr. (1985) 105, 239–245
M. E. VELASCO and S. TALEISNIK
The effects of interruption of amygdaloid and hippocampal afferents to the hypothalamus on ovulation and on the release of luteinizing hormone (LH) were studied in rats. Animals acutely deprived on the morning of pro-oestrus of amygdaloid influences either by transection of the stria terminalis (ST) or lesions of the amygdala, failed to show the expected ovulation. Control lesions had no effect. In contrast, rats with long-term transection of either the ST, the cortico-hypothalamic tract (CHT), or both, had regular oestrus cycles and ovulated normally. Studies of ovulation which was induced after the administration of ovarian steroids revealed a differential response to oestrogen and progesterone. In animals with long-term transection of the ST the ovulatory response to oestrogen was similar to that induced in non-lesioned rats but fewer ovulations were induced by progesterone administration. The decreased ovulatory response after progesterone treatment was attributed to activation of inhibitory influences originating in the hippocampus, since administration of picrotoxin or section of the fornix re-established a normal response. Long-term interruption of the limbic efferents did not alter the increased levels of plasma LH found after ovariectomy. However, the release of LH induced by progesterone in ovariectomized rats primed with gonadal steroids was decreased after transection of the ST and increased after interruption of the CHT. These results are consistent with the concept that the amygdala and the hippocampus exert a modulating influence on gonadotrophin release; the influence of the amygdala being facilitatory and that of the hippocampus inhibitory.
RG Denis, C Bing, EK Naderali, RG Vernon, and G Williams
We investigated the effects of lactation on diurnal changes in serum leptin and hypothalamic expression of the leptin receptor isoforms, Ob-Ra, -Rb, -Rc, -Re and -Rf in rats. In non-lactating rats, serum leptin concentration was increased at night while hypothalamic mRNA levels of Ob-Rb, -Rc and -Re decreased; by contrast, expression of Ob-Ra and Ob-Rf was unchanged at night. There were significant negative correlations between serum leptin and mRNA expression of Ob-Rb (P<0.001) and Ob-Re (P<0.05), which were independent of time of day. In lactating rats, the nocturnal rise in serum leptin was attenuated. Daytime hypothalamic Ob-Rb mRNA levels were significantly lower than in non-lactating controls, and the normal nocturnal decreases in expression of Ob-Rb, -Rc and -Re were lost. The relationship between serum leptin and Ob-Re expression was not changed by lactation. Lactation had no effect on the expression of Ob-Ra mRNA in the hypothalamus. Decreased daytime Ob-Rb expression could lead to reduced hypothalamic sensitivity to leptin, and thus contribute to increased daytime appetite in lactating rats. Moreover, maintaining high levels of Ob-Re expression could, by increasing hypothalamic leptin-binding protein concentration and reducing local leptin bioavailability, further accentuate hyperphagia. Thus, selective changes in expression of specific isoforms of the leptin receptor may contribute to the hyperphagia of lactation in rats.
D Olchovsky, J F Bruno, and M Berelowitz
Growth hormone-releasing factor (GRF) mRNA expression in male rats occurs predominantly in the hypothalamus (mainly in the arcuate nucleus), and among extraneural sites primarily in the testis. Hypothalamic GRF is the physiological tropic stimulus to growth hormone secretion. However, the role of GRF in the testis is unknown. We have shown previously that hypothalamic GRF mRNA expression is significantly reduced in streptozotocin (STZ)-diabetic rats. This reduction is confined to the arcuate nucleus and probably accounts for the suppression of growth hormone pulsatility.
The present studies were performed to evaluate GRF expression in the testis of streptozotocin (STZ)-diabetic rats. Diabetes was induced by injection of STZ (100 mg/kg i.p.). Seventeen to twenty days later diabetic rats were hyperglycemic compared with vehicle-injected controls and demonstrated growth failure. Insulin treatment reduced the glycemia and increased body weight towards normal. Total RNA was extracted from the hypothalamus and testis, and GRF mRNA levels estimated by solution hybridization/nuclease protection assay. Levels of hypothalamic somatostatin mRNA were measured to serve as control values. GRF mRNA was significantly (P<0·001) decreased in the hypothalamus of STZ-diabetic rats (0·2 ± 0·07 mean relative densitometric units, n=8) compared with controls (1·0 ± 0·19, n=8) with no change in somatostatin mRNA expression. In contrast, testicular GRF mRNA was increased 70% (P<0·05) in STZ-diabetic rats. Insulin treatment resulted in normalization of hypothalamic GRF mRNA levels (1·1 ± 0·17, n=5) with no effect on testicular GRF mRNA expression.
In conclusion GRF gene expression is discordantly regulated in tissues of male STZ-diabetic rats. While reduced GRF expression may account for the low growth hormone state in this model, increased testicular GRF mRNA (with the previously reported reduction of insulin-like growth factor-I mRNA) resembles the response seen in growth hormone-sensitive tissue (especially the hypothalamus) to this growth hormone-deficient state.
Journal of Endocrinology (1996) 148, 189–192