Starvation-induced changes in rat brain corticotropin-releasing factor (CRF) and pituitary-adrenocortical response

Starvation-induced changes in CRF concentration in major brain regions and abnormalities in the pituitary-adrenal axis were examined in rats using rat CRF radioimmunoassay. The CRF concentrations in the hypothalamus and cerebellum were significantly reduced in the completely starved rats, while those in the midbrain, thalamus and neurointermediate lobe of the pituitary were significantly increased in the semi-starved or completely starved rats. No significant changes in the CRF concentrations were found in the pons, medulla oblongata and cerebral cortex. In the completely starved rats, the serum ACTH level was significantly reduced, whereas the serum corticosterone level was markedly elevated. These observations suggest that starvation may stimulate the CRF-ACTH-corticosterone system and that not only hypothalamic CRF but also extrahypothalamic CRF may be discretely related to feeding behavior or starvation. The reduced serum ACTH level in starved rats may be ascribed to the negative feedback effect of the elevated serum corticosterone.     

Opiate antagonist binding sites in discrete brain regions of spontaneously hypertensive and normotensive Wistar-Kyoto rats

The binding of 3H-naltrexone, an opiate receptor antagonist, to membranes of discrete brain regions and spinal cord of 10 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. The brain regions examined were hypothalamus, amygdala, hippocampus, corpus striatum, pons and medulla, midbrain and cortex. 3H-Naltrexone bound to membranes of brain regions and spinal cord at a single high affinity site with an apparent dissociation constant value of 3 nM. The highest density of 3H-naltrexone binding sites were in hippocampus and lowest in the cerebral cortex. The receptor density (Bmax value) and apparent dissociation constant (Kd value) values of 3H-naltrexone to bind to opiate receptors on the membranes of amygdala, hippocampus, corpus striatum, pons and medulla, midbrain, cortex and spinal cord of WKY and SHR rats did not differ. The Bmax value of 3H-naltrexone binding to membranes of hypothalamus of SHR rats was 518% higher than WKY rats but the Kd values in the two strains did not differ. It is concluded that SHR rats have higher density of opiate receptors labeled with 3H-naltrexone in the hypothalamus only, in comparison with WKY rats, and that such a difference in the density of opiate receptors may be related to the elevated blood pressure in SHR rats.     

Characteristics of central binding sites for [3H] DAMGO in spontaneously hypertensive rats

The binding of [3H] DAMGO, a highly selective ligand for mu-opiate receptors, to membranes of discrete brain regions and spinal cord of 10 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. The brain regions examined were hypothalamus, amygdala, hippocampus, corpus striatum, pons and medulla, midbrain and cortex. [3H] DAMGO bound to membranes of brain regions and spinal cord at a single high affinity site. The receptor density (Bmax value) and apparent dissociation constant (Kd value) of [3H] DAMGO to bind to membranes of hippocampus, corpus striatum, pons and medulla, cortex and spinal cord of WKY and SHR rats did not differ. The Bmax value of [3H] DAMGO in membranes of hypothalamus and midbrain of SHR rats was significantly higher than in WKY rats but the Kd values in the two strains did not differ. On the other hand, the Bmax value of [3H] DAMGO in membranes of amygdala of SHR rats was lower than that of WKY rats but the Kd values in the two strains were similar. It is concluded that SHR rats have higher density of mu-opiate receptors in hypothalamus and midbrain but lower density in amygdala in comparison with WKY rats, and that such differences in the distribution of mu-opiate receptors may be related to the elevated blood pressure in SHR rats.     

Proliferation of thyrotropin releasing hormone receptors in specific brain regions during the development of hypertension in spontaneously hypertensive rats

The binding of [3H] [3-MeHis2] thyrotropin releasing hormone [( 3H]MeTRH) to brain membranes prepared from 8 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. [3H]MeTRH bound specifically to rat brain membranes at a single high affinity site. The density (Bmax value) of [3H]MeTRH binding sites was significantly greater (28%) in SHR rats compared to WKY rats. The apparent dissociation constants (Kd values) for the binding of [3H]MeTRH in SHR and WKY rats did not differ. Binding in the various brain regions revealed that the density of [3H]MeTRH was highest in the hypothalamus followed in decreasing order by pons + medulla, midbrain, cortex and striatum. The binding of [3H]MeTRH was approximately 25% greater in cortex, hypothalamus and striatum of SHR rats in comparison to WKY rats. The binding in pons + medulla, midbrain and pituitary of SHR and WKY rats did not differ. To assess the significance of increased binding sites for [3H]MeTRH in some brain regions of SHR rats, the binding studies were carried out during normotensive and hypertensive stages of postnatal age in the two strains. In 3 and 4 week old SHR rats there was neither an increase in blood pressure nor any increase in [3H]MeTRH binding in the hypothalamus and striatum as compared to age matched WKY rats. With the development of elevated blood pressure at 6 weeks, an increase in [3H]MeTRH binding in the hypothalamus and striatum of SHR rats in comparison to the tissues from WKY rats was observed. The results provide, for the first time, evidence for a parallel increase in the density of brain TRH receptors with elevation of blood pressure, and suggest that brain TRH receptors may play an important role in the pathophysiology of hypertension.     

Repeated Idazoxan Increases Brain Imidazoline Receptors in Normotensive (WKY) but Not in Hypertensive (SHR) Rats

The specific binding of [3H]idazoxan in the presence of 10(-6) M (-)-adrenaline was used to evaluate the density of imidazoline receptors in the brain of spontaneously hypertensive (SHR) rats and sex- and age-matched normotensive Wistar-Kyoto (WKY) rats. In SHR rats the density of imidazoline receptors (cerebral cortex, hypothalamus, and medulla oblongata) was not different from that in normotensive (WKY) rats. However, repeated treatment with idazoxan consistently increased (23-80%) the density of imidazoline receptors in the various brain regions of WKY rats but not in SHR rats. In normotensive Sprague-Dawley rats, repeated treatment with the imidazoline drugs idazoxan and cirazoline also increased (33-37%) the density of imidazoline receptors in the cerebral cortex. The lack of regulation by idazoxan of the density of imidazoline receptors in the brain of SHR rats might reflect the existence of a relevant abnormality of these receptors in this genetic model of hypertension.     

自发性高血压大鼠中枢去甲肾上腺素与血管紧张...

The norepinephrine (NE) and angiotensin II (A II) contents in the brain regions of SHR and WKY (Wistar Kyoto) rats at different ages were determined by fluorospectrophotometry and radioimmunoassay. The systolic blood pressure (SBP) of the rats was measured indirectly with a tail cuff technique in conscious state. The results were as follows: There was no significant difference in the central A II and NE contents between SHR and WKY rats at 8-week age. Since 12th week age the SBP of SHR has increased gradually, up to 16th to 20th week and then maintained steady level. Whereas there was no significant change of SBP in WKY rats in the same span of age. In the early and late states of hypertension the A II contents in the medulla oblongata, pons, hypothalamus and nucleus caudatus of SHR were markedly higher than those of the age-matched WKY rats. But the change of NE content of SHR in the early stage showed a different picture as compared with that of WKY rats, i.e., NE decreased in medulla oblongata and anterior hypothalamus but increased in pons, posterior hypothalamus and nucleus caudatus. However, in the late stage there was no such significant difference between SHR and WKY rats. Consequently, it is suggested that the central A II and NE participated in the development of hypertension of SHR, and that the maintenance of hypertension is mainly dependent upon the increased A II content. Microinjection of captopril or 6-OHDA in the lateral cerebroventricle of SHR elicited a decrease of BP and reduction of both A II and NE contents in the medulla and hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Extrahypothalamic distribution of CRF-like immunoreactivity in the rat brain

CRF-like immunoreactivity was measured by radioimmunoassay in the brains of normal adult rats and found to be widely distributed in extrahypothalamic areas (e.g., thalamus, amygdala, hippocampus, frontal cerbral cortex, striatum, midbrain, pons-medulla and cerebellum) at levels approximately 10% of the hypothalamus. Sephadex G-50 gel filtration reveals that CRF-like immunoreactivity in the hypothalamus coelutes with synthetic ovine CRF and is also present in the void volume. However, in the extrahypothalamic areas of the rat brain, only CRF-like immunoreactivity that coelutes with synthetic ovine CRF was detected. High performance liquid chromatography revealed equal amounts of immunoreactivity coeluting with CRF and methionine sulfoxide CRF in hypothalamic extracts.     

Assay of 2-Hydroxyputrescine in Various Regions of Rat Brain by Gas Chromatography-Mass Spectrometry

2-Hydroxyputrescine in seven regions of single rat brains was measured with a sensitive, specific assay by gas chromatography-mass spectrometry. The regions were the cerebral cortex, cerebellum, medulla oblongata, hypothalamus, striatum, hippocampus, and midbrain. The level of 2-hydroxyputrescine was very high in the cerebral cortex and cerebellum, high in the medulla oblongata, hypothalamus, and hippocampus, and low in the striatum and midbrain. The level of 2-hydroxyputrescine in the cerebellum was significantly higher than in the striatum and midbrain.     

Metallothionein-I induction by stress in specific brain areas

The distribution of metallothionein-I (MT) in several areas of the brain and its induction by immobilization stress has been studied in the rat. MT content was highest in hippocampus and midbrain and lowest in frontal cortex and pons plus medulla oblongata. Immobilization stress for 18 hours (which was accompanied by food and water deprivation) significantly increased MT levels in the frontal cortex, pons plus medulla oblongata and hypothalamus, but not in midbrain and hippocampus. The effect of stress on MT levels was specific as food and water deprivation along had no significant effect on MT levels in any of the brain areas studied. The effect of stress on MT levels was independent of changes in cytosolic Zn content; this was generally unaffected by stress or food and water deprivation but decreased in pons plus medulla oblongata from stressed rats. The results suggest that MT is induced more significantly in the brain areas that are usually involved in the response of animals to stress.     

Circadian variation in the acetylcholinesterase activity of specific rat brain areas

Abstract

Acetylcholinesterase (AChE) activity of the adenohypophysis, cerebellum, cerebral cortex, hypothalamus, amygdala, hippocampus, midbrain, pons, medulla oblongata and caudate nucleus was determined by a spectro‐photometric method in adult, male rats adapted toan LD 12:12cycle. Results of the study show that AChE activity is highest during the light phase and lowest during the dark phase of the cycle in all the brain areas studied except the adenohypophysis, cerebellum, hippocampus and hypothalamus. These findings expand earlier observations on the circadian variation in rat brain AChE activity and suggests a relationship with reported circadian variation in the acetylcholine levels of rat brain.     

Down-regulation of alpha 2 adrenoceptors in ventrolateral medulla of spontaneously hypertensive rats.

The binding of [3H]idazoxan [correction of idaxazon] to imidazole sites and [3H]rauwolscine to alpha 2 adrenoceptors of neuronal membranes prepared from cerebral cortex and ventrolateral medulla of 10 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. [3H]idazoxan [correction of idaxazon] bound to the membranes of cerebral cortex and ventrolateral medulla at a single high affinity site. The binding of [3H]idazoxan [correction of idaxazon] in ventrolateral medulla and cerebral cortex was found to be similar in SHR and WKY rats. [3H]Rauwolscine bound to the membranes of cerebral cortex and ventrolateral medulla at a single high affinity site. The binding of [3H]rauwolscine in the cerebral cortex was found to be similar in SHR and WKY rats. However, in the ventrolateral medulla [3H]rauwolscine binding was found to be significantly lower in SHR as compared to WKY rats. The decreased binding was due a decrease (32%) in the Bmax value in SHR rats as compared to WKY rats. The Kd values were similar in SHR and WKY rats. It is concluded that imidazole binding sites are not affected while, alpha 2 adrenergic binding sites are decreased in the ventrolateral medulla of SHR rats and may be contributing to the regulation of blood pressure.     

Down-regulation of endothelin receptors in the ventrolateral medulla of spontaneously hypertensive rats.

The binding of [125I] sarafotoxin 6b (SRT 6b) and [125I] endothelin-1 (ET-1) to endothelin (ET) receptors of neuronal membranes prepared from cerebral cortex and ventrolateral medulla of 8 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. [125I] SRT 6b bound to the membranes of cerebral cortex and ventrolateral medulla at a single high affinity site. The binding of [125I] SRT 6b in the cerebral cortex was found to be similar in SHR and WKY rats. However, in the ventrolateral medulla [125I] SRT 6b binding was found to be significantly lower in SHR as compared to WKY rats. The decreased binding was due to decrease (48%) in the Bmax values in SHR rats as compared to WKY rats. The Kd values were similar in SHR and WKY rats. [125I] ET-1 also bound to the membranes of cerebral cortex and ventrolateral medulla at a single high affinity site. The binding of [125I] ET-1 in the cerebral cortex was found to be similar in SHR and WKY rats. However, in the ventrolateral medulla [125I] ET-1 binding was found to be significantly lower in SHR as compared to WKY rats. The decreased binding was due to 36% decrease in the Bmax values in SHR rats as compared to WKY rats. The Kd values were similar in SHR and WKY rats. It is concluded that the population of ET receptors is less in the ventrolateral medulla of SHR rats and may be contributing to the regulation of blood pressure.     

Neuropeptide Y administration acutely increases hypothalamic corticotropin-releasing factor immunoreactivity: lack of effect in other rat brain regions

The effect of acute central administration of Neuropeptide Y (NPY) to adult male rats on the brain content of corticotropin-releasing factor immunoreactivity (CRF-ir) was investigated. The brain regions studied included frontal cortex, hippocampus, medulla-pons, midbrain-thalamus, cerebellum, neurointermediate lobe of pituitary, median eminence and the remaining hypothalamus. CRF-ir was determined in each of these regions using a radioimmunoassay specific for rat CRF. CRF-ir was found to be significantly increased in the major site of CRF localization in the brain, the hypothalamus, in NPY-treated rats as compared to vehicle-treated controls either 15 minutes (p less than 0.025) or 45 minutes (p less than 0.005) post-injection. This increase was localized to the median eminence (p less than 0.05 after 15 minutes, p less than 0.01 after 45 minutes). No statistically significant differences were noted in any of the other brain regions assessed. Plasma adrenocorticotropin levels were also found to increase following NPY treatment, an effect which became significant after 45 minutes (p less than 0.05). These data show that NPY can alter the content of hypothalamic CRF and may play a role in its regulation.     

Increased expression of urotensin II-related peptide and its receptor in kidney with hypertension or renal failure

Urotensin II-related peptide (URP) is a novel vasoactive peptide that shares urotensin II receptor (UT) with urotensin II. In order to clarify possible changes of URP expression in hypertension and chronic renal failure (CRF), the expressions of URP and UT were studied by quantitative RT-PCR and immunohistochemistry in kidneys obtained from spontaneous hypertensive rats (SHR), Wistar-Kyoto rats (WKY), and WKY with CRF due to 5/6 nephrectomy. Expression levels of URP mRNA and UT mRNA were significantly higher in the kidneys obtained from SHR compared with age-matched WKY (at 5-16 and 16 weeks old, respectively). A dissection study of the kidney into three portions (inner medulla, outer medulla and cortex) showed that the expression levels of URP mRNA and UT mRNA were highest in the inner medulla and the outer medulla, respectively, in both SHR and WKY. The expression levels of URP and UT mRNAs were greatly elevated in the remnant kidneys of CRF rats at day 56 after nephrectomy, compared with sham-operated rats (about 6.5- and 11.9-fold, respectively). Immunohistochemistry showed that URP immunostaining was found mainly in the renal tubules, vascular smooth muscle cells and vascular endothelial cells. UT immunoreactivity was localized in the renal tubules and vascular endothelial cells. These findings suggest that the expressions of URP and UT mRNAs in the kidney are enhanced in hypertension and CRF, and that URP and its receptor have important pathophysiological roles in these diseases.     

Reduced adenosine deaminase activity in the CNS of spontaneously-hypertensive rats

The activity of adenosine deaminase (ADA) has been measured in the hypothalamus, pons medulla and cerebral cortex from 30-day-old and 100-day-old spontaneously-hypertensive rats (SHR) and age-matched WKY controls. At 100 days there was a significant reduction in ADA activity in the hypothalamus (18.0%), pons medulla (20.6%) and cerebral cortex (14.7%). In 30-day-old SHR animals (prior to the development of significant hypertension) no significant changes were seen in the cerebral cortex or pons medulla but there was a small but significant reduction in ADA activity in the hypothalamus (9.2%). There was no significant reduction in the ADA activity in heart or kidney. Extracts of 100-day-old pons medulla which had been briefly heated to destroy endogenous ADA activity did not differentially affect the activity of exogenous purified ADA.     

Detection of bikunin mRNA in limited portions of rat brain.

Tissue distribution of bikunin mRNA, which encodes a Kunitz-type serine protease inhibitor of the inter-alpha-inhibitor family (IalphaI), was studied in rats and mice by the reverse-transcripsion polymerase chain reaction (RT-PCR). We found that the liver as well as other tissues, such as the kidney, testis and adrenal gland, expressed bikunin mRNA. Although signals of bikunin mRNA were faint in the whole brain of rats and mice, distinct signals were found in limited portions of rat brain, such as the hippocampus, cerebral cortex and pituitary, but undetectable in cerebellum, medulla oblongata, hypothalamus, striatum, midbrain and choroid plexus. In three distinct types of cells, such as neurons, astrocytes and meningeal cells, in primary cultures isolated from the cerebral cortex and meninges of 1-day-old newborn rats, only neurons positively expressed bikunin mRNA. These results suggest that, in addition to peripheral tissues, neurons in the hippocampus and cerebral cortex produce bikunin, suggesting a potential role of bikunin/IalphaI family in these brain regions.     

Glutamate decarboxylase activity and GABA binding in the brain synaptic membranes in rats with compensatory activation of hypothalamo-pituitary-adrenal system in stress

The reaction of the rat adrenal cortex and medulla to stress was absent under conditions of compensatory activations of function of hypothalamic-pituitary-adrenal system. At the same time, glutamate decarboxylase activity was increased in the hypothalamus, decreased in the hyppocampus, and remained unchanged in medulla oblongata and cortex of cerebral hemispheres of hemiadrenalectomized rats after stress as compared to rats without stress. On the contrary, the intensity of specific GABA binding by synaptic membranes of medulla oblongata of hemiadrenalectomized rats was increased in response to stress effect it was decreased in the cortex of cerebral hemispheres, and remained unchanged in the hyppocampus.     

Developmental Changes in the NGF Content in the Brain of Young,Growing, Low-Birth-Weight Rats

The NGF content in each region of the brain of four-week-old rats was ranked in the decreasing order of cerebral cortex, hippocampus, cerebellum, midbrain/diencephalon, and pons/medulla ob-longata, and the NGF concentration, in the decreasing order of hippocampus, cerebral cortex, cerebellum, midbrain/diencephalon, and pons/medulla oblongata in both AFD and SFD groups. The NGF content and concentration in the cerebral cortex were about the same value at each age between those in the AFD and SFD groups. Those in the hippocampus were a little higher in the SFD group than in the AFD group at the ages of three and four weeks, unlike those in the other regions, where the values for the cerebellum, midbrain/diencephalon and pons/medulla oblongata tended to be somewhat higher in the AFD group than in the SFD group. The NGF concentrations in the hippocampus and cerebral cortex increased with growth: the concentration in the hippocampus at four weeks of age was about 4-fold of that at one week in the AFD group and about 5.7-fold of that at one week in the SFD group; and likewise the concentration in the cerebral cortex at four weeks of age was about 5.3-fold in the AFD group and about 7-fold in the SFD group. The NGF concentrations in the cerebellum decreased, and those in midbrain/diencephalon and pons/medulla oblongata hardly changed with growth in either AFD or SFD group. From these results NGF may have stronger implications for the neuronal growth in the hippocampus compared with those in the lower brain regions of the SFD rats.     

Regional Development of Glutamate Dehydrogenase in the at Brain

The development of glutamate dehydrogenase enzyme activity in rat brain regions has been followed from the late foetal stage to the adult and through to the aged (greater than 2 years) adult. In the adult brain the enzyme activity was greatest in the medulla oblongata and pons greater than midbrain = hypothalamus greater than cerebellum = striatum = cortex. In the aged adult brain, glutamate dehydrogenase activity was significantly lower in the medulla oblongata and pons when compared to the 90-day-old adult value, but not in other regions. The enzyme-specific activity of nonsynaptic (free) mitochondria purified from the medulla oblongata and pons of 90-day-old animals was about twice that of mitochondria purified from the striatum and the cortex. The specific activity of the enzyme in synaptic mitochondria purified from the above three brain regions, however, remained almost constant.     

Brain catecholamines at the early stage of emotional stress

The blood pressure (BP) dynamics and catecholamine (CA) levels in the brain regions of August and Wistar rats were studied two hours after immobilization in order to elucidate the central neurochemical mechanisms leading to the destruction of BR self-regulation under emotional stress during the experiment. The BP level did not differ from the normal. The CA concentration in the hypothalamus, midbrain, isthmus rhombencephali and medulla oblongata underwent considerable changes. It is suggested that the mechanism of the CA changes in both strains of the rats exposed to stress is similar in the hypothalamus and medulla oblongata while both strains of the rats studied showed specificity in the activity of NA-synthesizing neurons of the isthmus rhombencephali and DA-synthesizing neurons of the midbrain that might be a cause of different resistance of cardiovascular functions during the later stage of immobilization.