Influence of alpha-receptor blocking agents upon metabolic activity in nuclei involved in central control of blood pressure

Specific alterations in cardiovascular function and in glucose utilisation within lower brainstem nuclei following intracisternal neuropeptide Y in the conscious rat

In the conscious normotensive rat, intracisternal neuropeptide Y (NPY) (1.25 nmol i.c.) gave rise to alterations in peripheral haemodynamic variables and glucose use within discrete areas of the CNS as measured by [14C]2-deoxyglucose autoradiography. The haemodynamic response to i.c. NPY comprised a transient hypertension followed by a prolonged hypotension and bradycardia. These cardiovascular responses to NPY were accompanied by a significant reduction in function related glucose use in the area postrema (-29% from vehicle-injected controls), nucleus tractus solitarius (caudal portion -24%, rostral portion -19%), Kolliker-Fuse nucleus (-14%), inferior colliculus (-18%) and subfornical organ (-19%). It is proposed that the area postrema, nucleus tractus solitarius and Kolliker-Fuse nucleus in the brainstem are involved functionally in the haemodynamic response to i.c. NPY.

Metabolic mapping of the effects of intravenous methamphetamine administration in freely moving rats

The 2-[14C]deoxyglucose method was used to examine the effects of acute intravenous administration of methamphetamine (0.5-2.5 mg/kg) on rates of local cerebral glucose utilization in freely-moving rats. These effects were correlated with the effects of methamphetamine on locomotor activity assessed simultaneously in the same animals. Methamphetamine administration resulted in widespread dose-dependent increases in glucose utilization within structures of the extrapyramidal motor system. Rates of glucose utilization were positively correlated with locomotor activity in the globus pallidus, substantia nigra reticulata, entopeduncular nucleus, subthalamic nucleus, and the lateral cerebellar cortex. In contrast, within the limbic system alterations in metabolic activity were smaller and more selective. Glucose utilization was increased in the nucleus accumbens at all doses tested, but alterations in glucose utilization in the ventral tegmental area, amygdala, and anterior cingulate were observed only at the highest doses of methamphetamine tested. Significant increases in rates of glucose metabolism were also found in the substantia nigra compacta and in the median and dorsal raphe nuclei. Dopamine and serotonin are depleted in these regions, as well as in the ventral tegmental area where glucose utilization was also increased, following chronic treatment with high doses of methamphetamine. These changes in glucose utilization may be indicative of disturbances in the biochemical processes involved in the neurotoxic effects of methamphetamine.

The effects of melatonin and pinealectomy upon local cerebral glucose utilization in awake unrestrained rats are restricted to a few specific regions

The effects of the infusion of melatonin (MT) and/or of pinealectomy upon glucose utilization in anatomically discrete regions of the brain of freely moving rats have been studied by the quantitative autoradiographic 2-deoxy-D-[1-14C]glucose technique. The experiments were made from 14.00 to 16.00 h, when MT is normally not secreted by the pineal gland, in order to compare the local cerebral glucose utilization (LCGU) response to MT from animals with long-term (pinealectomized) or short-term (pineal intact) absence of MT secretion. The majority of the 98 brain areas examined showed no change in LCGU after MT administration and/or pinealectomy. Pinealectomy increased the LCGU in the median mammillary nucleus only, whereas following MT administration, an increase in LCGU was observed in 3 cerebral regions of intact rats (paraventricular nucleus of the hypothalamus, nucleus of the solitary tract, choroid plexus of the third ventricle) and in 5 cerebral regions of pinealectomized rats (paraventricular nucleus of the hypothalamus, nucleus of the solitary tract, choroid plexuses of the lateral ventricles, third and fourth ventricles). Except for the choroid plexuses of the fourth ventricle, there was no difference in LCGU response to MT between pinealectomized and intact animals. This does not favor the hypothesis of receptor supersensitivity under the conditions of this experiment. Our results suggest that the hypothalamus, nucleus of the solitary tract and choroid plexuses represent a neural substrate through which MT could influence the activity of the central nervous system when administered at a low dose under near-physiological conditions.

Quantitative autoradiographic maps of local cerebral glucose metabolism in awake rats: I. Septal region and anterior hypothalamus

Quantitative 14C-2-deoxyglucose autoradiography was used to determine the local cerebral glucose metabolic rate (lCMRG) of nuclei in the septal region and anterior hypothalamus of awake, unanesthetized rats. The lCMRG of the medial and lateral septal areas, preoptic areas, medial preoptic nuclei, suprachiasmatic nuclei, supraoptic nuclei, anterior hypothalamic nuclei, and paraventricular nuclei were measured. The lCMRG of each nucleus was mapped at successive rostral-caudal levels to determine significant internuclear and intranuclear variations. These data provide a detailed neuroanatomic map of cerebral energy metabolism of the septal and anterior hypothalamic regions in animals under standardized conditions.

Co-dergocrine, cerebral glucose utilization and maze performance in middle-aged rats

The objective of this study was to determine the effect of co-dergocrine in rats on local cerebral glucose utilization and performance in a complex T-maze. Middle-aged (12-16 months) male Fischer-344 rats were given injections of co-dergocrine (3 or 10 mg/kg, IP) 35 min before behavioral testing or the administration of 2-deoxy-D-[1-14C]glucose ([14C]DG), a radiotracer for local cerebral glucose utilization (LCGU). Both doses stimulated LCGU in the locus ceruleus and median raphe nucleus and in subcortical structures associated with learning and memory (hippocampus and subiculum). The higher dose also stimulated LCGU in motor areas (caudate-putamen, globus pallidus, internal capsule). In contrast, co-dergocrine decreased LCGU in the frontal cortex. Poorer performance in a complex maze (increased shocks, errors and run time) was observed in middle-aged as compared with younger animals (3 months). Acute co-dergocrine treatment did not improve performance of middle-aged rats in this task. Thus, in the present experimental paradigm employing single dose administration, co-dergocrine's stimulation of LCGU was not associated with an alteration of maze performance in age-matched animals.

Effects of prolonged co-dergocrine mesylate (Hydergine) treatment on local cerebral glucose uptake in aged Fischer 344 rats

Hydergine (co-dergocrine mesylate) was administered orally for 4 weeks to adult (10-12 months old) and aged (28 months old) Fischer 344 rats at dosages ranging from 0.1 mg to 4.0 mg/kg daily, in order to investigate its effect on 14C-deoxyglucose (DOG) uptake by the brain and the dose-effect relation. In the aged rats the dose-effect curve was bell-shaped, with maximal increases in DOG uptake at 0.6 mg/kg co-dergocrine. These were particularly pronounced in the caudoputamen (+47%), nucleus ventralis thalami (+32%), nucleus ventromedialis hypothalami (+57%) and the nucleus suprachiasmaticus (+39%), while the nucleus ambiguus, nucleus dorsalis nervi vagi, nucleus cuneatus and nucleus loci coeruleus also showed increases in DOG utilisation of between 23% and 29%. The dose-effect curve for the adult rats was similar in shape to that for the aged rats, but the peak was much lower and occurred at the lowest dosage (0.1 mg/kg). Cerebral DOG uptake responded considerably more sensitively in the adult rats than in the aged rats, so that the higher dosages were associated with a fall in DOG uptake. Parallels may be detected between the pharmacological effects exerted by co-dergocrine and its effects on DOG uptake in the nuclei of the extrapyramidal system (dopaminergic stimulation), in the hypothalamus (autonomic and neuroendocrine effects, regulation of body temperature and sleep) and in the alpha-receptor nuclei (alpha-blockade, cardiovascular regulation).

Effects of clonidine, alpha-methyldopa and hydralazine on met-enkephalinergic neurons in cerebral nuclei of spontaneously hypertensive rats

Immunocytofluorescent and microautoradiographic methods were applied to measure met-enkephalin-like immunoreactivity (MELI) and ME receptor binding (MERB) levels in cerebral nuclei of serial brain slices from SHR which received clonidine, alpha-methyldopa and hydralazine at equivalent hypotensive doses. All three drugs increased both MELI and MERB levels in the caudal part of the n. tractus solitarii and its functionally related dorsomedullary nuclei and decreased them in the n. accumbens septi, in accordance with the correspondent change in glucose utilization rates in these nuclei as reported previously. Both CNS-active agents (not hydralazine) also increased MELI and MERB levels in the n. intercalatus and substantia grisea centralis, and they decreased them in the n. ventromedialis hypothalami. Differences in both CNS-active agents were minor. Vasodilative hydralazine alone decreased these levels both in the n. reticularis medialis and n. tegmenti ventralis, and it increased them slightly in the area lateralis hypothalami. The present studies indicate that ME neurons of these dorsomedullary and supramedullary nuclei may act as direct as well as homeostatic controls of blood pressure.

Alterations of local cerebral glucose utilization during chronic dehydration in rats

The quantitative autoradiographic deoxyglucose method was used to study changes in local cerebral glucose utilization in conscious dehydrated rats. Animals were either given saline to drink or were deprived of water for 5 days. Saline ingestion did not alter the rates of glucose metabolism in any brain region when compared to the rates of glucose metabolism in animals which had free access to water. Glucose utilization was increased by 140%, however, in the pituitary neural lobe. Water deprivation produced both increases and decreases in glucose metabolism, depending on the particular structure. In 20 of 44 brain structures analyzed, there were significant decreases from -18 to -34% in glucose utilization. Four forebrain structures, the subfornical organ, septal triangular nucleus, and hypothalamic paraventricular and supraoptic nuclei, had increases in glucose utilization of 30-73%. The rate of glucose utilization in the pituitary neural lobe was increased by 367% in water-deprived rats. The results demonstrate that metabolic activity is stimulated in some, but not all, of the structures participating in fluid regulation during an intense thirst challenge. Many brain regions have depressed metabolism in chronic severe dehydration.

Functional consequences of unilateral lesion of the locus coeruleus: a quantitative [14C]2-deoxyglucose investigation

The functional consequences, as reflected in local rates of glucose utilization, of ablation of the locus coeruleus (the nucleus from which a major portion of the ascending noradrenergic fibres arise) have been examined in conscious rats with the quantitative autoradiographic [14C]2-deoxyglucose technique. Measurements of glucose utilization were made 72 h after histologically verified unilateral electrolytic lesions of the locus coeruleus. In the overwhelming majority of the 35 grey matter regions examined, the rate of glucose utilization was unaltered by lesions of the locus coeruleus, and in the limited number of CNS regions in which significant alterations were observed, the magnitude of the changes was invariably modest (less than 20% different from sham-operated control animals). Reductions in glucose use were observed in ipsilateral ventral (by 14%) and lateral thalamic nuclei (by 17%), and rates of glucose utilization in most regions of cerebral cortex were significantly lower (about 10%) in the ipsilateral hemisphere relative to the hemisphere contralateral to the lesion. In one region, the median raphe nucleus, glucose utilization was significantly elevated (by 19%) following lesions of the locus coeruleus. Attempts to accentuate the effects of locus coeruleus lesions by pharmacological manipulation of CNS adrenoreceptors by means of the systemic administration of phenoxybenzamine (30 mg/kg, 40 min prior to measurement of glucose use) in animals bearing unilateral locus coeruleus lesions were unsuccessful; the modest alterations in glucose utilization observed following locus coeruleus lesion alone were even less pronounced in lesioned animals receiving phenoxybenzamine. The alterations in local glucose utilization provoked by phenoxybenzamine were similar in sham-lesioned and locus coeruleus-lesioned animals. It would appear that the functional consequences, in terms of glucose utilization, are much less pronounced when a single neurotransmitter system (in the present studies, noradrenergic neurones) is lesioned than when a multiple neurotransmitter, functionally integrated pathway (such as the visual system) is disrupted.

The postnatal metabolic development of the nucleus commissuralis and nucleus medialis of the nucleus tractus solitarius

The ontogeny of the metabolic requirements in the nucleus commissuralis (NC) and nucleus medialis (NM) of the nucleus tractus solitarius was studied in the postnatal rat using the [3H]2-deoxy-D-glucose autoradiography technique. It was found that the metabolic requirements in the NC and NM are not constant between 2 and 12 weeks of age. A high level of metabolic activity at 2 and 8 weeks is contrasted by a lower level at 4 and 12 weeks. The apparent changes in metabolic requirements are not related to the changes in blood pressure of the rats or neuronal densities of the subnuclei which occur as the rats mature, or to exchange vessel densities of the subnuclei. Thus the higher energy requirements of the NC and NM at 2 and 8 weeks of age suggest that developmental and/or functional processes are more active at these stages.

Differential effects of locus coeruleus lesions upon metabolic activity in CNS nuclei involved in cardiovascular regulation

The alterations of local cerebral glucose utilization in 5 medullary and 6 supramedullary regions involved in cardiovascular regulation, which result from unilateral electrolytic lesions of the locus coeruleus, have been examined in conscious rats, using the quantitative autoradiographic [14C]2-deoxyglucose technique. Unilateral lesions of the locus coeruleus (72 h prior to study) did not result in any significant alteration in glucose utilization in any of medullary (e.g. nucleus of the tractus solitarius, dorsal motor nucleus of the vagus) or diencephalic (e.g. periventricular and paraventricular hypothalamic nuclei, lateral habenular nucleus) regions which were examined. However, the increased glucose utilization which occurred in some medullary nuclei (e.g. nucleus of the solitary tract, dorsal motor nucleus of the vagus) following administration of the alpha-receptor antagonist, phenoxybenzamine (30 mg/kg, i.v.), was significantly attenuated by lesions of the locus coeruleus, whereas the increased glucose utilization elicited in hypothalamic nuclei by the drug was unaffected by locus coeruleus lesions. In contrast, glucose utilization in the lateral habenular nucleus was elevated significantly following phenoxybenzamine only in animals bearing unilateral locus coeruleus lesion; the drug being without effect in this region in sham-lesioned rats. These differential consequences of locus coeruleus lesions upon glucose utilization in nuclei involved in cardiovascular regulation emphasize the complex nature of the influence of the locus coeruleus upon blood pressure control.

Th central noradrenergic system in the rat: metabolic mapping with alpha-adrenergic blocking agents

Rates of cerebral glucose utilization were measured by means of the autoradiographic 2-deoxy-D-[14C]glucose technique in 73 normal, awake rats treated with different doses of the alpha-adrenergic blockers, phenoxybenzamine, phentolamine and yohimbine. Three types of responses were elicited by the administration of these drugs. The predominant effect observed after administration of all alpha-blockers was a widespread depression of glucose utilization, particularly within the neocortex. The effect was most pronounced with phenoxybenzamine. In a few structures (locus coeruleus, interstitial nucleus of the stria terminalis, medial forebrain bundle, periventricular nucleus and some medullary and hypothalamic nuclei associated with the regulation of blood pressure) marked increases in glucose utilization were observed. Administration of phentolamine resulted in increased glucose utilization in all the central components of the auditory system (cochlear n., superior olivary n., n. lateral lemniscus, inferior colliculus, medial geniculate body and auditory cortex). Phenoxybenzamine and yohimbine tended to decrease glucose utilization in the auditory system. Alternating columns with higher and lower rates of local glucose consumption were observed in most of the neocortical areas and in the cerebellar vermis. The significance of these columns is not clear.