Distribution, parabrachial region projection, and coexistence of neuropeptide and catecholamine cells of the nucleus of the solitary tract in the pigeon

The chemical nature of the cells of the nucleus of the solitary tract (NTS) that project to the parabrachial nucleus (PB) was investigated in the pigeon by the use of fluorescent bead retrograde tracer and immunofluorescence for the detection of substance P (SP), leucine-enkephalin (LENK), cholecystokinin (CCK), neurotensin (NT), somatostatin (SS), and tyrosine hydroxylase (TH). Cells immunoreactive for CCK were located in subnuclei lateralis dorsalis pars anterior (LDa) and medialis superficialis pars posterior, and caudal NTS (cNTS); 22-26.5% of these cells were double-labeled bilaterally. Immunoreactive SP cells were found in ventral NTS subnuclei; 24-25% of these cells were double-labeled bilaterally. Cells immunoreactive for LENK and NT were concentrated in the anterior NTS; 5.5-7.5% of the LENK cells were double-labeled bilaterally, while 11% (ipsilateral) and 21% (contralateral) of the NT immunoreactive cells were double-labeled. Many SS immunoreactive cells were found in peripherally located subnuclei; 5.5-6.5% of these cells were double-labeled bilaterally. Catecholamine cells were distributed in LDa, peripheral subnuclei, and cNTS; 23% of these cells were double-labeled ipsilaterally and 8.5% contralaterally. A two-color double-labeling immunofluorescence technique revealed many cells immunoreactive for both NT and LENK, only a rare cell immunoreactive for both SS and SP, and no cells immunoreactive for both TH and SP. Cells immunoreactive for SP, CCK, NT, and TH are major contributors to NTS projections to PB. The confinement of these substances to specific NTS subnuclei, which receive visceral sensory information from specific organs, may contribute to the chemical encoding of ascending visceral information.

Distribution of [3H]quinuclidinyl benzilate, [3H]nicotine, and [125I]alpha-bungarotoxin binding sites in the nucleus tractus solitarii of the cat

The distribution of muscarinic and nicotinic cholinergic binding sites in the cat nucleus tractus solitarii was studied by the technique of in vitro autoradiography. Using the antagonist [3H]quinuclidinyl benzilate, muscarinic binding sites were differentially located in subdivisions of the nucleus tractus solitarii. The majority of muscarinic binding sites were located predominantly in the caudal half of the nucleus, reaching their greatest amounts at the mid levels of the nucleus tractus solitarii. The medial, dorsolateral, intermediate, and interstitial subdivisions contained the highest densities of quinuclidinyl benzilate binding sites. Nicotinic cholinergic binding sites, using [3H]nicotine and [125I]alpha-bungarotoxin, had unique patterns of distribution. With [3H]nicotine the majority of binding sites were located in rostral levels of the nucleus with very few binding sites present in the caudal half. In contrast, [125I]alpha-bungarotoxin binding sites were present mainly in subdivisions located in the caudal half of the nucleus, i.e., commissural, ventrolateral, dorsolateral, medial, and intermediate subdivisions, and dropped off precipitously at more rostral levels. The differential distribution of [3H]nicotine and [125I]alpha-bungarotoxin suggests the two ligands may be labeling different types of nicotinic binding sites in the nucleus tractus solitarii. The unique distribution of muscarinic and nicotinic cholinergic binding sites in the various subdivisions of the nucleus solitarii suggests that muscarinic and nicotine mechanisms may play an active role in the regulation of the diverse autonomic functions at the level of the nucleus tractus solitarii.

The induction and suppression of c-fos expression in the rat brain by cholecystokinin and its antagonist L364,718

Immunohistochemical techniques were used to map c-fos expression in the rat brain after the i.p. administration of CCK-8 (8 micrograms/kg). C-fos expression was observed in the rostral and the caudal parts of the nuclei of the solitary tract (NTS), and the paraventricular nuclei (PVN) in the hypothalamus. The c-fos expression in these areas was suppressed by the administration of L364,718 (120 micrograms/kg). Since L364,718 is known to be a powerful selective antagonist to the peripheral CCK-A receptors, these data suggest that the effects produced by exogenous CCK are due to peripheral receptors that project to the NTS.

Nicotinic acetylcholine receptor in dissociated rat nucleus tractus solitarii neurons

The ACh-activated response of the acutely dissociated neuron from the rat nucleus tractus solitarii (NTS) was investigated using conventional and perforated-patch techniques. In the present preparation, ACh and nicotine evoked inward transient currents in approximately 30% of NTS neurons tested. The ACh-activated inward current reversed the direction near 0 mV and was inhibited by D-tubocurarine in a dose-dependent manner. In contrast, muscarine resulted in no detectable changes in the NTS neurons. Some populations of the NTS had nicotinic but no muscarinic acetylcholine receptors.

Increased blood-brain barrier permeability of amino acids in chronic hypertension

A previous communication from this laboratory reported that brain uptake of libenzapril, a small polar molecule, was enhanced in chronic hypertension (1). The objective of this investigation was to determine if this was a more generalized phenomenon. Therefore, experiments were undertaken to examine the effect of chronic hypertension on the brain uptake of tryptophan (an amino acid with high brain permeability) and glutamic acid (one with low permeability). Brain concentrations of these two amino acids were 5- to 12-fold greater in chronic hypertensive rats, as compared to normotensive rats; the corresponding brain uptake index (BUI) values were 2- to 5-fold higher in the former group. Since blood-brain barrier transport of amino acids involve both saturable (carrier) and non-saturable (most likely, diffusion via pores) mechanisms, data from this study show that hypertension can enhance BBB transport of amino acids by affecting one or both of these pathways.

Glucose metabolism in the brain of patients with essential tremor

Using positron emission tomography with [18F]fluoro-2-deoxyglucose, we determined the regional cerebral metabolic rate of glucose utilization at rest in 8 medication-free patients with essential tremor and in 10 normal subjects. Taking the metabolic values of regions of interest as ratios to the mean hemispheric metabolism, the patients showed significant glucose hypermetabolism of the medulla and thalami, but not of the cerebellar cortex. This study lends support to earlier suggestions that circuits involving the inferior olivary nuclei in the medulla and the thalmus are involved in the generation of essential tremor.

Angiotensin II binding in area postrema and nucleus tractus solitarius of SHR and WKY rats

The distribution of angiotensin II (AII) binding sites in the area postrema (AP) and adjacent nucleus tractus solitarius (NTS) was compared in spontaneously hypertensive (SHR) rats and normotensive Wistar-Kyoto (WKY) rats. 125I[Saralasin-1-Isoleucine8]-Angiotensin II (125I[SI]-AII) binding density was quantitated from autoradiographic images by computer-assisted image analysis. Seventeen 30 microns serial coronal sections inclusive of the entire AP were analyzed as either individual sections or as groups of sections designated as caudal, middle, or rostral area postrema regions. 125I[SI]-AII binding density was greatest in caudal AP and declined progressively in the rostral direction in both strains; however, binding density in SHR was significantly higher than in WKY rats at each level of the AP analyzed. 125I[SI]-AII binding in the entire area postrema was approximately 46% higher in SHR rats. In the NTS, however, there were no differences in binding density between strains. At the middle level of the AP, 125I[SI]-AII binding was highest in the ventral midline and lowest in the dorsolateral region. In the NTS, the highest 125I[SI]-AII binding density was found in the pars commissuralis and pars medialis. In conclusion a) 125I[SI]-AII binding density was nonhomogeneous in the AP and NTS of both strains, b) qualitatively similar patterns of nonhomogeneity of binding in the AP and NTS were noted in both strains; however, c) the SHR strain consistently had higher density AII binding than WKY in AP, but not in NTS.

Endothelin as a neuropeptide. Cardiovascular effects in the brainstem of normotensive rats

The relevance of endothelin in central cardiovascular function was studied in urethane-anesthetized Sprague-Dawley rats. Blood pressure (BP) was monitored intra-arterially, and cerebrospinal fluid (CSF) was collected through an intracisternal catheter for radioimmunoassay of endothelin-1 (ET-1). Endothelin levels in the CSF were significantly higher (39 +/- 3 pg/ml) than in plasma (10 +/- 3 pg/ml, n = 11). ET-1 in CSF or plasma was not affected by systemic infusion of saline, but its levels significantly decreased when a sustained increase in BP was elicited with phenylephrine (14 +/- 7 pg/ml in the CSF and 6 +/- 4 pg/ml in plasma, n = 5). In sinoaortic-denervated animals, phenylephrine failed to reduce CSF endothelin levels. In different experiments, intracisternal administration of ET-1 (10 pmol) evoked an initial decrease in BP and heart rate (HR), followed by pronounced hypertension, bradycardia, and, in 70% of the animals, death from cardiorespiratory failure. Intracisternal administration of endothelin-3 (ET-3, 80 pmol, n = 11) evoked only a modest hypotensive and bradycardic response without cardiorespiratory impairment. Microinjection of ET-1 (0.5, 1, 2, 4, and 6 pmol/60 nl) into the nucleus of the solitary tract or area postrema produced a decrease in BP and HR. On the other hand, injection of low concentrations of ET-3 into the nucleus of the solitary tract increased BP and HR (at 2 pmol, 17 +/- 3 mm Hg, 14 +/- 6 beats per minute, n = 7), whereas ET-3 in the area postrema produced a prominent dose-related decrease in BP and HR. In the rostroventrolateral medulla, the lowest doses of ET-1 first modestly increased BP and renal sympathetic nerve activity. These effects were followed by hypotension, bradycardia, increase in respiratory frequency, and further enhancement of sympathetic nerve traffic. In 29% of the animals, these effects were followed by cardiorespiratory arrest. The specificity of the cardiovascular response to endothelin was demonstrated by the inhibitory effects of the receptor antagonist BQ-123. These results demonstrate that endothelin has specific cardiovascular effects in the brainstem of the rat and support a role for endothelin in cardiovascular regulation.

Excitatory amino acid receptors in commissural nucleus of the NTS mediate carotid chemoreceptor responses

Stimulation of carotid body chemoreceptors by saline saturated with 100% CO2 elicited an increase in mean arterial pressure, respiratory rate, tidal volume, and minute ventilation (VE). Microinjections of L-glutamate into a midline area 0.5-0.75 mm caudal and 0.3-0.5 mm deep with respect to the calamus scriptorius increased VE. Histological examination showed that the site was located in the commissural nucleus of the nucleus tractus solitarii (NTS). The presence of excitatory amino acid receptors [N-methyl-D-aspartic acid (NMDA); kainate, quisqualate/alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) and trans 1-amino-cyclopentane-trans-1,3-dicarboxylic acid (ACPD)] in this area was demonstrated by microinjections of appropriate agonists. Simultaneous blockade of NMDA and non-NMDA receptors by combined injections of DL-2-aminophosphonoheptanoate (AP-7; 1 nmol) and 6,7-dinitro-quinoxaline-2,3-dione (DNQX; 1 nmol) abolished the responses to stimulation of carotid body on either side. Combined injections of AP-7 and DNQX did not produce a nonspecific depression of neurons because the responses to another agonist, carbachol, remained unaltered. Inhibition of the neurons in the aforementioned area with microinjections of muscimol (which hyperpolarizes neuronal cell bodies but not fibers of passage) also abolished the responses to subsequent carotid body stimulation on either side.(ABSTRACT TRUNCATED AT 250 WORDS)

Moxonidine, a centrally acting antihypertensive agent, is a selective ligand for I1-imidazoline sites

Both the hypotension and the sedation elicited by centrally acting antihypertensive agents are traditionally attributed to activation of alpha 2 adrenergic receptors. Second-generation centrally acting agents such as moxonidine are less sedating but retain antihypertensive efficacy. A novel receptor which recognizes imidazolines may contribute to their vasodepressor action in the ventrolateral medulla (VLM). We sought to determine whether moxonidine was a selective ligand for these putative I1-imidazoline receptors in different species and tissues. Moxonidine inhibited [3H]clonidine binding to bovine VLM membranes in a heterogeneous manner, showing 40-fold selectivity for one component. Masking studies using selective inhibitors to block either I1-imidazoline or alpha 2 sites established that the population of sites showing high affinity for moxonidine were I1-imidazoline sites. Moxonidine also showed 70-fold selectivity for I1-imidazoline sites labeled by [125I]p-iodoclonidine in the VLM. Moxonidine competitively inhibited [3H]clonidine binding to I1-imidazoline sites at concentrations that failed to inhibit alpha 2 binding. In the rat renal medulla, moxonidine showed almost 700-fold selectivity for I1-imidazoline sites relative to the alpha 2B receptor subtype. The high affinity of moxonidine for I1 sites was confirmed by using membranes prepared from bovine adrenomedullary cells, which lack alpha 2 adrenergic receptors. Among centrally acting antihypertensives, clinical potency correlated with binding affinity at bovine VLM I1-imidazoline sites (r = 0.996, N = 4), but not with alpha 2 adrenergic affinity (r = -0.239, N = 6). The potent action of moxonidine on I1-imidazoline receptors may account for its antihypertensive efficacy.

Effects of Hypnorm (fentanyl) on ACTH/beta-endorphin levels in plasma, pituitary and brain of 10-day old rats

Administration of Hypnorm, an anaesthetic containing the known mu-opiate receptor agonist fentanyl, elicited dose- and time-related elevation of plasma ACTH, beta-endorphin and corticosterone levels in 10-day old rat pups. Pretreatment with specific antibodies (raised against CRH, AVP and ACTH resp.) revealed that Hypnorm administration activated the ACTH-corticosterone system in the 10-day old rat and its effect is mediated by CRH and/or AVP. Hypnorm anaesthesia was associated with significant decrease in the ACTH and beta-endorphin levels in the pituitary lobes as well as in beta-endorphin content of the hypothalamus and medulla oblongata. Latter results may indicate that the beta-endorphinergic system in the brain of the 10-day old rat is activated by Hypnorm, an effect most probably elicited by the opiate agonist fentanyl.

Effects of vagotomy on neurotransmitter receptors in the rat dorsal vagal complex

The dorsal vagal complex contains many different neurotransmitter receptors. The cyto-architectural localizations of some of these receptors remain largely unknown. In rats, vagotomy was performed to destroy vagal afferents terminating in the nucleus of the solitary tract and to produce chromatolysis of preganglionic motoneurons in the dorsal motor nucleus of the vagus. Quantitative receptor autoradiography was then employed to determine the effect of vagotomy upon the distribution of receptors for thyrotropin-releasing hormone, substance P, and serotonin within individual regions and subnuclei of the entire dorsal vagal complex. Vagotomy reduced the concentrations of thyrotropin-releasing hormone and substance P, but not serotonin1A, or serotonin1B, receptors in the dorsal motor nucleus of the vagus. Within the nucleus of the solitary tract, substance P receptors were reduced in only the medial and central subnuclei after vagotomy. In contrast, no effect was observed upon the concentrations of thyrotropin-releasing hormone, serotonin1A, or serotonin1B receptors in any subnuclei of the solitary tract following vagotomy. These results suggest that in the dorsal motor nucleus of the vagus, thyrotropin-releasing hormone and substance P receptors are localized upon vagal preganglionic motoneurons, while serotonin1A and serotonin1B receptors are present upon interneurons or other neuronal elements. These results also suggest that thyrotropin-releasing hormone, substance P, serotonin1A, and serotonin1B receptors in the nucleus of the solitary tract are localized upon internuncial neurons in the nucleus of the solitary tract.

Brain levels of neuropeptide Y in experimental pneumococcal meningitis

Neuropeptide Y (NPY), which is found in high concentrations in several regions of the brain including nuclei of the brain stem and in nerve fibers surrounding cerebral vessels, has been proposed to play a role in regulating cerebral blood flow (CBF) and systemic vegetative functions. Since CBF is altered during meningitis, we examined whether NPY concentrations changed in various regions of the rabbit brain in response to experimental pneumococcal meningitis. Changes were most pronounced in the medulla, where NPY concentration increased threefold after 48 h of infection. Concomitantly, there was an increase in NPY immunoreactive fibers surrounding small vessels in the dorsolateral medulla, especially in the nucleus tractus solitarius. These results suggest that NPY may play a role in inducing some of the hemodynamic changes seen during pneumococcal meningitis.

Release of immunoreactive neuropeptide Y from brainstem sites in the cat during isometric contractions

Fatiguing isometric contractions of the left hind-limb muscles in cats anesthetized with alpha-chloralose caused mean arterial pressure to increase by 82 +/- 18 mmHg above resting and post-contraction levels and heart rates to increase by 15 +/- 5 beats/min. Contractions were performed by stimulating the tibial nerve via a microprocessor-controlled stimulator. Glass microprobes, coated with antibody specific for neuropeptide Y (NPY) were inserted bilaterally into the periaqueductal grey (P 0.5-1.0, LR 2.0 mm) or into the right ventrolateral medulla (3.0 mm rostral to obex; LR 3.5 mm) prior to, during and following fatiguing contractions to determine whether immunoreactive NPY was released. No release of immunoreactive NPY was detected from the site in the ventrolateral medulla. Immunoreactive NPY was released from the contralateral but not the ipsilateral periaqueductal grey during the isometric contractions, suggesting that NPY-like substances maybe involved with the integration of muscle afferent input into this area of the brainstem.

Preproenkephalin RNA increases in the hypothalamus of rats stressed by social deprivation

1. Pharmacological evidence indicates that stress induced by brief (14 to 20-day) social deprivation in the rat is associated with an activation of the central preproenkephalin (ENK) opioid system. This study examines the neurochemical evidence that substantiates such an activation. 2. Using a specific ENK complementary DNA probe, ENK RNA levels were measured by dot blot and Northern blot analyses in different brain areas of socially deprived rats. Immunoreactivity to met-enkephalin-derived peptides was also evaluated by radioimmunoassay in the same brain regions. 3. Brief social deprivation increased the levels of ENK RNA and enkephalin immunoreactivity in whole hypothalamus. 4. Our data suggest that this type of stress appears to be associated to an induction of ENK gene transcription in hypothalamus.

Effects of hypoxia, hyperoxia and hypercapnia on graded cerebral ischemic responses in rabbits

This study was designed to determine how several factors interact to modify the cerebral ischemic pressor response (CIR) in anesthetized rabbits. After the carotid sinus and aortic nerves were bilaterally sectioned, blood flow through the left internal carotid artery (ICF), which was surgically restricted as the sole route of blood supply to the brain, was reduced by a servo-controller during ventilation with room air, and 8% and 90% O2 and 2 and 5% CO2 gas mixtures. Blood flow (MBF), tissue PO2, PCO2, and interstitial pH were measured in the rostral ventrolateral medulla. Internal carotid arterial pressure, tissue PO2, and MBF decreased proportionately as ICF decreased in the range from 4 to 0 ml/min. Hypoxia significantly increased the rise in renal nerve activity (RNA) and CIR caused by cerebral ischemia, while hyperoxia significantly decreased them. Hypercapnia had almost no influence on the increases in RNA and mean arterial pressure produced by cerebral ischemia. CIR showed a much higher correlation with changes in tissue PO2 than with the other factors. We examined how these factors interact to modify CIR and found that central hypoxia is the main factor in producing CIR.

Light microscopic localization of angiotensin II binding sites in canine medulla using high resolution autoradiography

Angiotensin II (Ang II) produces dose-related, site-specific cardiovascular effects in the canine and rat dorsal medulla. Our previous studies suggested that Ang II binding sites are associated with presynaptic vagal afferent fibers in the nucleus tractus solitarii (nTS) and vagal efferent neurons in the dorsal motor nucleus of the vagus (dmnX). High resolution autoradiography now establishes the relationship of putative Ang II receptors to the cytoarchitecture of these nuclei. Sections of the canine medulla oblongata were processed for film or emulsion autoradiography with 0.3-1 nM 125I-Ang II. Quantitative densitometry of films before and after processing sections for emulsion coating confirmed no selective alteration in labeling. In emulsion coated sections, dense labeling was seen over the majority of the large perikarya and surrounding neuropil in the ventral dmnX. Bands of label overlaid vagal efferent fibers coursing ventrolaterally to exit the medulla. In the nTS, Ang II binding was restricted to regions with heavy vagal afferent innervation. In the dorsal nTS, label was distributed over both cell bodies and neuropil, with highest density capping the solitary tract. In the medial nTS, label was concentrated over perikarya, with scattered grains over the intervening neuropil. The discrete subnuclear association of Ang II binding sites in the dorsal medulla with vagal cells and fibers documents that Ang II receptors are present on both afferent vagal fibers and intrinsic medullary neurons, and reveals an anatomical substrate for the autonomic effects of Ang II in this region.

Presence of a dynorphin-like peptide in a restricted subpopulation of catecholaminergic neurons in rat nucleus tractus solitarii

Immunofluorescence colocalization techniques were used to examine the extent of coexistence of the endogenous opioid peptide dynorphin with catecholamines and the related opioid peptide enkephalin within neurons of the rat medulla oblongata. Immunoreactivities for dynorphin and the catecholamine-synthesizing enzyme tyrosine hydroxylase were found to coexist within a limited subpopulation of A2 catecholamine cells, localized to the medial nucleus of the nucleus tractus solitarii. Colocalization of the two opioid peptides was found mainly within perikarya situated in the medial and ventrolateral nuclei of the nucleus tractus solitarii. Triple-labeling studies revealed only rare cases of catecholamine/dynorphin/enkephalin coexistence. These data demonstrate that dynorphin is present within a restricted subpopulation of catecholamine neurons in the dorsal medulla oblongata. In addition, the content of either of the opioids enkephalin or dynorphin appears to distinguish subsets of medullary catecholamine neurons.

Action of externally applied ATP on rat reticulospinal vasomotor neurons

In anesthetized rats, iontophoretic application of ATP excited the spinal cord-projection neurons in the rostral ventrolateral reticular nucleus of the medulla oblongata. The neuronal response to ATP was mimicked and then blocked by alpha,beta-methylene-ATP, a metabolically stable ATP analogue, and the response was abolished by suramin. Microinjections of ATP (3-100 pmol) into the rostral ventrolateral medulla produced a powerful pressor response. The results suggest that ATP may function as a neurotransmitter or neuromodulator involved in medullary regulation of cardiovascular functions.

Effects of aging on the content, composition and synthesis of sphingomyelin in the central nervous system

Sphingomyelin (SPH) content and composition in different regions of the brain were analyzed in 2.5, 21.5 and 26.5-month-old rats. SPH content increased in the cerebral hemispheres, cerebellum and medulla oblongata plus pons as age increased. The highest SPH content was observed in 26.5-month-old rats, with values increasing by 1.74, 2.75 and 0.88-fold, respectively, over 2.5-month-old rats. The SPH fatty acid composition of brains from aged rats was markedly different from that of adult rats. Between 2.5 and 26.5 months of age the monoenoic/saturated fatty acid ratio increased from 0.22, 0.30 and 0.54 to 0.54, 0.68 and 1.03 in cerebral hemispheres, cerebellum and medulla oblongata plus pons, respectively. The percentage and content of fatty acids longer than 22 carbon atoms esterified to SPH increased with age from 18, 26 and 44 to 48, 52 and 62 mole % in cerebral hemispheres, cerebellum and medulla oblongata plus pons in 26.5-month-old rats. In subcortical white matter from aged rats, monoenoic 22-26 carbon atom fatty acids increased more than the saturated ones in 21.5-month-old rats relative to 2.5-month-old rats. In vitro synthesis of SPH from [3H]choline and [3H]palmitic acid in cerebral cortex and cerebellum showed no significant differences between adult rats and those 21.5 months of age. In cerebellum and in cerebral cortex, [14C]serine incorporation increased in aged rats. The results suggest that aging induces increases in both SPH content and in the monoenoic/saturated fatty acid ratio. These increases are quantitatively different in all brain regions analyzed.

Contribution of catecholaminergic neurons of the dorsomedial and ventrolateral medulla oblongata to the hypotensive effect of clonidine in spontaneously hypertensive rats: in vivo voltammetric studies

OBJECTIVE

Our previous electrochemical studies in the normotensive Wistar-Kyoto (WKY) rat showed a positive correlation between the hypotensive effect of low doses of clonidine (2-10 micrograms/kg intravenously) and inhibition of the activity of catecholaminergic neurons within the brainstem, and that this action was mediated by imidazoline-preferring receptors. In the present study the possibility of a relationship between the centrally mediated hypotensive effect of clonidine and the metabolic activity of catecholaminergic neurons of the ventrolateral and dorsomedial medulla oblongata was investigated in pentobarbital-anaesthetized spontaneously hypertensive rats (SHR).

DESIGN AND METHODS

Neuronal metabolic activity was monitored by in vivo electrochemistry in the nucleus reticularis lateralis region of the ventrolateral medulla and in the nucleus tractus solitarii region of the dorsomedial medulla oblongata.

RESULTS

Hypotensive doses of intravenously administered clonidine (10 micrograms/kg) failed to inhibit the neuronal metabolic activity of the nucleus reticularis lateralis region; fivefold higher doses were required to inhibit these neurons. The low dose of clonidine (10 micrograms/kg) decreased the metabolic activity of the nucleus tractus solitarii region. Nevertheless, this effect did not appear to be correlated with a reduction in blood pressure and it was not attenuated by a prior central injection of idazoxan (5 nmol/kg intracisternally), which almost completely prevented the hypotensive and the neuronal inhibitory effects of clonidine in the nucleus reticularis lateralis region of the normotensive rat.

CONCLUSION

Both the site and the mechanism of the central hypotensive action of clonidine in the SHR appear to be different from those in normotensive control WKY rats.

Differential effects of long-term hypoxia on norepinephrine turnover in brain stem cell groups

The influence of long-term hypoxia on noradrenergic cell groups in the brain stem was assessed by estimating the changes in norepinephrine (NE) turnover in A1, A2 (subdivided into anterior and posterior parts), A5, and A6 groups in rats exposed to hypoxia (10% O2-90% N2) for 14 days. The NE turnover was decreased in A5 and A6 groups but failed to change significantly in A1. The NE turnover was increased in the posterior part of A2 and remained unaltered in the anterior part. In normoxic rats, the hypotensive drug dihydralazine induced a reverse effect, namely increased NE turnover in anterior A2 and no change in posterior A2. The neurochemical responses to hypoxia were abolished by transection of carotid sinus nerves. The results show that long-term hypoxia exerts differential effects on the noradrenergic cell groups located in the brain stem. Peripheral chemosensory inputs control the hypoxia-induced noradrenergic alterations. The A2 cell group displays a functional subdivision: the posterior part is influenced by peripheral chemosensory inputs, whereas the anterior part may be concerned with barosensitivity.

Effect of the duration of streptozotocin-induced diabetes on turnover of central biogenic amines in mice

The relationship between central catecholaminergic and serotonergic neurons and the development of streptozotocin-induced diabetic mice was examined over periods of 3, 14, 50 and 100 days. The accumulation of 3,4-dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) were measured after central decarboxylase activity was inhibited by m-hydroxybenzylhydrazine (NSD-1015). Results indicated that DOPA accumulation in the hypothalamus was not altered during the entire time course of the experiment. On the other hand, DOPA accumulation in the striatum was decreased in 50- and 100-day diabetic mice. The DOPA levels in the pons medulla were not increased until the mice had been diabetic for 100 days. The accumulation of 5-HTP was decreased in the hypothalamus of 14-day diabetic mice and was also present at 50 and 100 days, that in the striatum and pons medulla was not decreased until the mice had been diabetic for 50 days and persisted to 100 days in the striatum. These data showed that both DOPA and 5-HTP accumulation in the striatum and pons medulla were changed only in long-term diabetic mice and suggested that changes in catecholamine and serotonin turn-over rates are not generalized, but restricted only to some particular brain regions and time courses.

Treatment with triiodothyronine decreases the abundance of the alpha-subunits of Gi1 and Gi2 in the cerebral cortex

Treatment of rats for 3 days with T3 halved the abundance of the alpha-subunits of Gi1 and Gi2 in synaptosomal membranes isolated from the cerebral cortex. It is suggested that these changes could contribute to behavioural abnormalities in hyperthyroidism. Similar T3 treatment did not alter abundance of Gi1 alpha or Gi2 alpha in the medulla oblongata nor did it alter abundance of G(o) alpha-subunits in three tested brain regions.