Hemorrhage-induced regional brain thyrotropin-releasing hormone release in conscious rats measured by microdialysis

The septum, nucleus accumbens and preoptic area in the brains of conscious, freely moving rats were perfused using microdialysis probes. The TRH concentration significantly increased in the septum after withdrawal of 30% of the total blood volume but remained at constant levels in the other brain areas. Also, high potassium dose-dependently stimulated TRH release in vivo. These results suggest that blood loss stimulates septal TRH release, probably by membrane depolarization of TRH-containing nerve terminals.     

Regional distribution of in vitro release of thyrotropin releasing hormone in rat brain

To increase our knowledge of the TRH functions in brain and the processes of TRH compartmentalization and release, we studied the in vitro release of endogenous TRH in different brain areas. We also determined the correlation between TRH levels and release under both basal and stimulated conditions. TRH concentration was measured in tissues and media by specific radioimmunoassay. TRH-like material detected in olfactory bulb and hypothalamic incubates (basal or K+ stimulated) were shown to be chromatographically identical to synthetic TRH. Different brain regions showed high variability in the basal release of TRH (1-20% of tissue content). This suggests the existence of different pools. The response to depolarizing stimulus (56 mM K+) was significant only in the following regions: median eminence, total hypothalamus, preoptic area, nucleus accumbens-lateral septum, amygdala, mesencephalon, medulla oblongata and the cervical region of the spinal cord. These regions have been shown to contain a high number of receptors, a high concentration of TRH nerve endings and are susceptible to TRH effects. These results support the hypothesis that TRH functions as neuromodulator in these areas.     

Visualization and identification of TRH receptors in rodent brain by autoradiography and radioreceptor assays: focus on amygdala,N. accumbens,septum and cortex

Thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH₂) is a tripeptide found in numerous regions of the vertebrate central nervous system (CNS). This study has provided evidence for a heterogeneous distribution of specific, nanomolar-affinity recognition sites for MeTRH in mouse and rat CNS. Membrane binding experiments revealed the following profile of these sites in mouse CNS: amygdala (AM) > olfactory tubercle > olfactory bulb (OB) > hypothalamus > striatum > pons-medulla > hippocampus > spinal cord > midbrain > cerebral cortex (CC) ? retina (RT) ? pituitary (PIT). Concurrent assays of rat brain homogenates indicated a similar order of regional enrichment in MeTRH binding sites as the mouse but the former species appeared to have an exceptionally higher density in RT and PIT compared to the latter animal. In contrast, mouse OB and AM seemed to possess a greater density of MeTRH sites than the same rat tissues. The pharmacological specificity of mouse and rat AM and PIT MeTRH binding sites was, however, almost identical and helped identify these entities as TRH receptors. Qualitative light-microscopic autoradiographic localization of TRH receptors in rat and mouse brain sections confirmed the relative distribution data obtained from membrane assays. In particular, the regions most enriched in TRH receptors determined by this technique were the various amygdaloid and hypothalamic nuclei, medial septum, n. accumbens and the inner cortical layers, areas for which numerous functional correlates have been previously demonstrated for TRH. These membrane and radiohistochemical data support a transmitter role for TRH in rodent CNS and indicate its putative sites of action.     

Gonadotropin-releasing hormone (GnRH) neurons and pathways in the rat brain

Summary Gonadotropin-releasing hormone (GnRH) neurons and their pathways in the rat brain were localized by immunocytochemistry in 6-to 18-day-old female animals, by use of thick frozen or vibratome sections, and silver-gold intensification of the diaminobenzidine reaction product. GnRH-immunoreactive perikarya were observed in the following regions: olfactory bulb and tubercle, vertical and horizontal limbs of the diagonal band of Broca, medial septum, medial preoptic and suprachiasmatic areas, anterior and lateral hypothalamus, and different regions of the hippocampus (indusium griseum, Ammon's horn). In addition to the known GnRH-pathways (preoptico-terminal, preoptico-infundibular, periventricular), we also observed GnRH-immunopositive processes in several major tracts and areas of the brain, including the medial and cortical amygdaloid complex, stria terminalis, stria medullaris thalami, fasciculus retroflexus, medial forebrain bundle, indusium griseum, stria longitudinalis medialis and lateralis, hippocampus, periaqueductal gray of the mesencephalon, and extracerebral regions, such as the lamina cribrosa, nervus terminalis and its associated ganglia. By use of the silver-gold intensification method we present Golgi-like images of GnRH perikarya and their pathways. The possible distribution of efferents from each GnRH cell group is discussed.     

The osmotic component of ethanol and urea action is critical for their immediate stimulation of thyrotropin-releasing hormone (TRH) release from rat brain septum

There is considerable evidence linking alcohol consumption and sedation and TRH in the brain septum. Moreover, innate septal TRH concentration is inversely related to the degree of ethanol preference. Recently we demonstrated in rats that four-week ethanol drinking increased the septal TRH content by 50 %. We had shown previously that ethanol induces neuronal swelling, which is known to evoke the secretion of hormones, peptides and amino acids from various types of cells. We have therefore explored the effect of hyposmotic medium and of 80 and 160 mM ethanol and 80 mM urea (both permeant molecules) in isosmotic and hyperosmotic (preventing cell swelling) media on the in vitro release of TRH by the rat septum. Lowering medium osmolarity resulted in a hyposmolarity-related increase in TRH secretion. Both ethanol and urea stimulated TRH release only in isosmolar solution. Our data indicate that ethanol in clinically relevant concentrations can induce TRH release from the septum by a mechanism involving neuronal swelling.     

Neuroanatomical dissociation of thyrotropin-releasing hormone induced shaking behavior and thermogenic mechanisms

To more clearly characterize the neuroanatomical substrates mediating thyrotropin-releasing hormone (TRH) induced shaking and antagonism of pentobarbital hypothermia, TRH was microinjected into 140 individual sites of the rat forebrain and brainstem. Previously determined threshold dosages of 10 ng TRH for the temperature response and 50 ng TRH for the shaking response were used. A clear distinction in regional sensitivity between the two TRH-induced effects was observed. The shaking response was most consistently observed with microinjection of TRH into the floor of the 4th ventricle and the periventricular posterior diencephalon, including the posterior hypothalamus and rostral periventricular grey. In contrast, the temperature response was most effectively induced by TRH administered in the interpeduncular nucleus and the rostral preoptic region located medial to, and including the diagonal band of Broca. The sensitivity of some brain areas to nanogram doses of TRH supports the possibility that TRH may have a physiological function in the initiation of shaking behavior and/or thermogenesis. If such a function does exist, the brain regions identified in this study as most sensitive to exogenous TRH are likely neuroanatomical substrates for endogenous TRH.     

Distribution of immunoreactive thyrotropin-releasing hormone in the forebrain and hypophysis of the bullfrog,Rana catesbeiana

The distribution of immunoreactive thyrotropin-releasing hormone (TRH) in the forebrain and hypophysis of Rana catesbeiana was studied by means of specific radioimmunoassay and immunohistochemistry based on peroxidase-antiperoxidase (PAP) techniques. A relatively high concentration of immunoassayable TRH is present in the hypothalamus. Immunoreactive TRH cell bodies are found in the anterior part of the preoptic nucleus, the dorsal infundibular nucleus, the nucleus of diagonal band of Broca, and the medial part of the amygdala. Immunoreactive nerve terminals are observed in the neurohypophysis and the external layer of the median eminence, where the terminals are in close contact with the capillary loops of the hypophyseal portal vessels. The possible role of TRH in the frog brain is discussed.     

The effects of hemorrhagic shock on thyrotropin-releasing hormone and its receptors in discrete regions of rat brain

The effects of hemorrhagic shock on thyrotropin-releasing hormone (TRH) levels and its receptors were studied in different regions of the rat brain. Rats were bled for 30 min from the left femoral artery, and their mean arterial pressure was kept at 40 mmHg for the following hour. The rats were killed by decapitation. Rat brains were immediately removed and dissected into 7 regions. Hemorrhagic shock decreased TRH significantly in the frontal cortex, septum, hippocampus, and hindbrain but TRH was not changed in the striatum, hypothalamus, and midbrain. Hemorrhagic shock significantly decreased TRH receptor binding in the septum and hindbrain. Scatchard analysis of saturation isotherms of specific TRH binding showed that the decreased specific TRH binding in the hindbrain resulted not from an increase of the dissociation constant (Kd), but from a decrease in the maximum number of binding sites (Bmax). In the septum, the decrease in specific binding was due both to a decrease in Bmax and an increase in Kd. The findings indicate that TRH plays a role in the physiological response to hemorrhagic shock.     

Ontogenetic development of thyrotropin-releasing hormone (TRH)-immunoreactive structures in the brain of the mallard embryo

Summary Developmental changes of thyrotropin-releasing hormone (TRH)-immunoreactive structures in the brain of mallard embryos were studied by means of immunocytochemistry (PAP technique). The primary antibody was generated against synthetic TRH. Immunoreactive neurons were first detected in the hypothalamus of 14-day-old embryos. By day 20, increasing numbers of immunoreactive perikarya were observed in the paraventricular nucleus, anterior preoptic region and supraoptic region. Immunoreactive fiber projections were seen in the median eminence as early as embryonic day 20; they occurred also in some extrahypothalamic regions (lateral septum, accumbens nucleus). The number and staining intensity of the cell bodies increased up to hatching, and continued to increase during the first week after hatching.     

Central regulation of thyrotropin secretion in rats: methodological aspects, problems and some progress

The concept of the regulatory role of the hypothalamic and brain neurotransmitters in the secretion of the hypothalamic releasing hormones and corresponding anterior pituitary hormones has been generally accepted. The tuberoinfundibular portal vessels form an anatomical framework for regulating these hormones. Our present knowledge about the origin and course of the main aminergic and peptidergic bundles and their collaterals into the hypothalamus conforms with the accepted concept. The general methods in neuroendocrinology are well established. In our study, the unique TSH burst induced by a short cold-exposure has proved very useful, since it is mediated through the activation of TRH in the hypothalamus. When used together with the TSH-response caused by the exogenous TRH and with stereotaxic microinfusions of various chemicals into specific areas in the brain, the level of action of the pharmacological agents can be determined. Methodological pitfalls are, however, possible unless care is taken to avoid unspecific stress factors, general anaesthesia and intracerebral injections at unphysiological concentrations. The role of different neurotransmitters in the central TRH-TSH regulation has been clarified in recent years and the simple concepts of the early days elaborated accordingly. The cold-stimulated TSH secretion can be modified by several neurotransmitters. Noradrenaline is a stimulatory transmitter at high hypothalamic centers, but it may also retard TRH release into the portal vessels. It also seems possible that alpha 1- and alpha 2-receptors mediate opposite effects. Nigrostriatal (but not tuberoinfundibular) dopamine has only an inhibitory action on TRH release and/or synthesis. The importance of 5-HT is still controversial, partly because of the unspecificity of the experimental tools available. Evidently both stimulating and inhibiting components are involved. The role of different 5-HT receptors remains to be established. The function of GABA is complicated, too, the real GABAergic action being an inhibition of TRH release from the medial basal hypothalamus. Only histamine and some amino acids affect TRH-induced TSH secretion. Hence the anterior pituitary in the rat is not so important a locus as the hypothalamus in the action of neurotransmitters on the TRH-TSH regulation.     

Effect of immobilization stress on neuropeptides and their receptors in rat central nervous system

The effect of immobilization stress (IM-stress) on the concentration and the receptor binding of substance P (SP), methionine-enkephalin (ME) and thyrotropin-releasing hormone (TRH) was determined in eight brain regions and the spinal cord. The concentration of SP was decreased in the septum, striatum and hippocampus, and SP receptor binding was decreased in the septum, amygdala + pyriform cortex and hypothalamus. Scatchard analysis indicated that the decrease in the SP binding is mainly due to the decrease in the number of receptors. The concentration of ME was not changed, but ME receptor binding was decreased in the septum. The concentration of TRH was decreased in the frontal cortex, septum, amygdala + pyriform cortex and pons + medulla oblongata, but increased in the spinal cord. TRH receptor binding was decreased in the septum, amygdala + pyriform cortex and hypothalamus. Scatchard analysis indicated that the decrease in TRH binding is due to the decrease in the number of receptors. These results show that IM-stress affects the neuropeptide receptor as well as neuropeptide concentration, and that the septum is a very important region under IM-stress.     

Thyrotrophin-Releasing Hormone Analogues Increase Dopamine Release from Slices of Rat Brain

Abstract: Rat brain slices were incubated with a high concentration of K⁺, thyrotrophin-releasing hormone (TRH), or one of two biologically stable TRH analogues (CG 3509 or RX 77368). Basal release of endogenous dopamine, measured by electrochemical detection, was increased by K⁺ (30 m M ) from slices of hypothalamus, septum, nucleus accumbens, and striatum. CG 3509 (10⁵–10⁻³ M ) increased the release of dopamine from slices of nucleus accumbens, septum, and hypothalamus in a dose-dependent fashion, whereas RX 77368 (10⁻⁴ M ) increased the release of dopamine from the septum only. Neither analogue increased the release of striatal dopamine. The results provide further evidence for specific regional interactions between TRH and dopamine in rat brain.     

Immunocytochemical localization of the gonadotropin-releasing hormone-associated peptide portion of the LHRH precursor in the hypothalamus and extrahypothalamic regions of the rat central nervous system

Summary The gonadotropin-releasing hormone-associated peptide (GAP) of the LHRH precursor and the decapeptide LHRH were localized in the rat brain by immunocytochemistry in 12 to 18-day-old animals, by use of thick Vibratome sections and nickel intensification of the diaminobenzidinereaction product. Our results indicate that the GAP portion of the LHRH precursor is present in the same population of neurons that contain LHRH in the rat brain. An important difference observed was that the GAP antiserum, in contrast to LHRH antisera, stained several perikarya in the medial basal hypothalamus. GAP-immunoreactive perikarya were observed in the following regions: the olfactory bulb and tubercle, diagonal band of Broca, medial septum, medial preoptic and suprachiasmatic areas, anterior and lateral hypothalamus, and several regions of the hippocampus. In addition to the preoptico-terminal and the septopreoptico-infundibular pathways, we also observed GAPimmunopositive processes in several major tracts and areas of the brain, including the amygdala, stria terminalis, stria medullaris thalami, fasciculus retroflexus, stria longitudinalis medialis, periventricular plexus, periaqueductal gray of the mesencephalon and extra-cerebral regions, such as the nervus terminalis and its associated ganglion. These results confirm the specificity of previous immunocytochemical results obtained with antisera to LHRH. The presence of GAP immunoreactivity in nerve terminals of the rat brain indicates that GAP or a GAP-like peptide is located in the proper site to serve as a hypophysiotropic substance and/or as a neurotransmitter or neuromodulator.Supported by AKA No. 419427, OTKA No. 104, OKKFT 2.1.5.1 and NSF No. INT-8602688     

LHRH-immunoreactive structures in the sheep brain

Neural structures containing luteinizing hormone-releasing hormone (LHRH) are characterized in adult ewe and female lamb brains. Three anti-LHRH antisera are used in an immunofluorescent or immunoperoxidase method. On our preparations, all three gave the same results, expressed as number of labelled cells (about 2500 in a whole brain). It was found that 95% of the LHRH-immunoreactive cells are located in the preoptico-hypothalamic area, where cell bodies are localized mainly (50%) in the area surrounding the organum vasculosum of the lamina terminalis (OVLT); they are also found in a more anterior section of the medial part of the olfactory tubercle and the medial septum (14%), in a more posterior situation in the anterior and lateral hypothalamus (16%), and in the mediobasal hypothalamus (15%). Fibres originating in various part of the whole preoptico-hypothalamic group reach the OVLT and the median eminence. The remaining cells (5%) and fibres are found in various tel-, di-, and mesencephalic areas.     

Thyrotropin-Releasing Hormone Receptor Binding Sites: Autoradiographic Distribution in the Rat and Guinea Pig Brain

Thyrotropin-releasing hormone (TRH) binding sites were labeled in vitro in mounted brain tissue sections from rat and guinea pig brains with [3H]methyl TRH and localized autoradiographically using 3H-sensitive film. Regional densities of TRH binding sites were measured by computer-assisted microdensitometry. The distribution of sites in both species was highly heterogeneous. In both guinea pig and rat brains, the highest densities of binding sites were seen in the amygdaloid nuclei and the perirhinal cortex. In contrast, in other brain areas, a clear difference between the distribution of sites in rat and guinea pig was found. The temporal cortex, pontine nuclei, and interpeduncular nucleus, which contained high densities of binding in the guinea pig, were scarcely labeled in the rat. The accessory olfactory bulb and the septohippocampal area presented in the rat higher concentrations of binding sites than in the guinea pig. Other brain areas showing intermediate to low densities in both species were accumbens nucleus, bed nucleus of the stria terminalis, dentate gyrus, facial and hypoglossal nuclei, and gelatinosus subnucleus of the trigeminal nerve, among others. The anterior pituitary also presented low to intermediate concentrations of receptors. The distribution of TRH sites here described does not completely correlate with that of endogenous TRH, but is in good agreement with previous biochemical data. The results are discussed in correlation to the physiological effects that appear to be mediated by TRH.     

Neuro-evolutionary patterning of sociality

Evolutionary shifts in species-typical group size ('sociality') probably reflect natural selection on motivational processes such as social arousal, approach-avoidance, reward, stress/anxiety and dominance. Using four songbird species that differ selectively in sociality (one territorial, one modestly gregarious, and two highly gregarious species), we here examined immediate early gene (IEG) responses of relevant brain regions following exposure to a same-sex conspecific. The paradigm limited behavioural performance, thus species differences should reflect divergence in motivational and/or perceptual processes. Within the extended medial amygdala (which is involved in appetitive approach, social arousal and avoidance), we observed species differences in IEG response that are negatively graded in relation to sociality. In addition, brain areas that are involved in social stress and dominance-related behaviour (ventrolateral septum, anterior hypothalamus and lateral subdivision of the ventromedial hypothalamus) exhibited IEG responses that dichotomously distinguish the territorial species from the three gregarious species. The IEG responses of areas involved in reward (nucleus accumbens and ventral pallidum) and general stress processes (e.g. paraventricular hypothalamus, lateral bed nucleus of the stria terminalis and most areas of the lateral septum) do not correlate with sociality, indicating that social evolution has been accompanied by selection on a relatively discrete suite of motivational systems.     

Degradation and biological inactivation of thyrotropin releasing hormone (TRH): regulation of the membrane-bound TRH-degrading enzyme from rat anterior pituitary by estrogens and thyroid hormones

Thyrotropin releasing hormone (TRH, pyroGlu-His-Pro-NH2) is important in the regulation of adenohypophyseal hormone secretion and also serves important functions in extrahypothalamic brain areas, indicating that it is involved in neurotransmission and other forms of cellular communication. This hypothesis is strengthened by the observation that TRH is rapidly inactivated by a heterogeneously distributed ecto-enzyme which exhibits a high degree of substrate specificity. Moreover, in the rat, the activity of the membrane-bound TRH-degrading enzyme of the anterior pituitary is found to be stringently controlled by thyroid hormones and estrogens. In contrast, the activity of the TRH-degrading brain enzyme is neither influenced by thyroid hormones nor estrogens. These data indicate that the TRH-degrading brain enzyme serves specialized functions for the transmission of TRH signals and apparently represents the peptidergic equivalent to acetylcholine esterase, whereas the membrane-bound adenohypophyseal TRH-degrading enzyme itself fulfills a biologically important control function within feedback-regulatory mechanisms.     

Mass Fragmentographic Determination of Homovanillic Acid in Individual Dopaminergic Neuron Systems of Rat Brain: Application of Reaction Gas Chromatography

Abstract: Homovanillic acid (HVA) levels of 12 discrete rat brain areas were determined by a mass fragmentographic method using the reaction gas chromatographic technique. The use of reaction gas chromatography increased the sensitivity for determination of HVA. The sensitivity of this method allows measurement of HVA in small amounts of brain tissue. The HVA levels in polar, medial, and lateral fields of prefrontal cortex, anterior cingulate cortex, septum, amygdala, A₁₂, A₁₃, and A₁₄ dopaminergic neurons were 0.417 ± 0.018 ng/mg protein, 0.689 ± 0.004, 0.753 ± 0.024, 0.496 ± 0.029, 1.311 ± 0.046, 0.555 ± 0.008, 1.949 ± 0.077, 1.109 ± 0.112, and 0.489 ± 0.019, respectively. The HVA levels in these areas are first reported in the present paper.     

LHRH-immunoreactive structures in the sheep brain

Summary Neural structures containing luteinizing hormone-releasing hormone (LHRH) are characterized in adult ewe and female lamb brains. Three anti-LHRH antisera are used in an immunofluorescent or immunoperoxidase method. On our preparations, all three gave the same results, expressed as number of labelled cells (about 2500 in a whole brain). It was found that 95% of the LHRH-immunoreactive cells are located in the preoptico-hypothalamic area, where cell bodies are localized mainly (50%) in the area surrounding the organum vasculosum of the lamina terminalis (OVLT); they are also found in a more anterior section of the medial part of the olfactory tubercle and the medial septum (14%), in a more posterior situation in the anterior and lateral hypothalamus (16%), and in the mediobasal hypothalamus (15%). Fibres originating in various part of the whole preoptico-hypothalamic group reach the OVLT and the median eminence. The remaining cells (5%) and fibres are found in various tel-, di-, and mesencephalic areas.We would like to dedicate this work to the memory of Dr. M.P. Dubois     

Effect of low-iodine diet and propylthiouracil on glycolytic enzymes in brain areas of adult rats

Glycolytic activity of five brain areas in the rat was studied under two hypothyroid states: (1) induced by low-iodine diet from weaning, and (2) induced by propylthiouracil. The areas studied were the anterior cortex, amygdala, hypothalamus, septum and hippocampus. A low-iodine diet induced a decrease of pyruvate kinase activity in three region and of phosphofructokinase in the hippocampus, while hexokinase increased in both the amygdala and septum. Propylthiouracil treatment produced an increase in hexokinase activity in the hypothalamus and septum, and a decrease in the anterior cortex, while phosphofructokinase decreased significantly in the hippocampus. No significant changes of lactate dehydrogenase activity were observed. The correlation between the results and type of hypothyroidism is discussed.