In vivo studies on the effect of 6-hydroxydopamine on amino acid metabolism in brain

Local uptake of (14)C-labeled acetate and butyrate in rat brain in vivo during spreading cortical depression

Spreading depression severely disrupts ion homeostasis, causes sensory neglect and motor impairment, and is associated with stroke and migraine. Glucose utilization (CMR(glc)) and lactate production rise during spreading depression, but the metabolic changes in different brain cell types are unknown. Uptake of (14)C-labeled compounds known to be preferentially metabolized by the glial tricarboxylic acid cycle was, therefore, examined during unilateral KCl-induced spreading cortical depression in conscious, normoxic rats. [(14)C]Metabolites derived from [(14)C]butyrate in K+ -treated tissue rose 21% compared to that of untreated contralateral control cortex, whereas incorporation of H(14)CO(3) into metabolites in K+ -treated tissue was reduced to 86% of control. Autoradiographic analysis showed that laminar labeling of cerebral cortex by both (14)C-labeled acetate and butyrate was elevated heterogeneously throughout cortex by an average of 23%; the increase was greatest (approximately 40%) in tissue adjacent to the K+ application site. Local uptake of acetate, butyrate, and deoxyglucose showed similar patterns, and monocarboxylic acid uptake was highest in the structures in which apparent loss of labeled metabolites of [6-(14)C]glucose was greatest. Enhancement of net uptake of acetate and butyrate in cerebral cortex during spreading depression is tentatively ascribed to increased astrocyte metabolism.

The role of nerve-growth factor (NGF) in the central nervous system

NGF is a protein that stimulates growth and differentiation of sympathetic and sensory components of the peripheral nervous system. The purpose of this review is to examine the evidence that NGF has similar activity in the central nervous system. First, the primary mode of interaction of NGF with the nerve cell will be discussed, and the possibility that such an interaction takes place in the brain will be examined. Recent studies have demonstrated that NGF promotes regenerative sprouting of damaged catecholamine-containing neurons in the brain. The next part of the paper reviews this literature, and other findings that indicate or contraindicate a role of NGF in brain maturation of maintenance. The final part of this paper suggests specific avenues for future research in this area, and presents conclusions regarding the literatureon brain activity of NGF to date.

Drug-induced parkinsonism in the rat- a model for biochemical investigation of the parkinson-syndrome. III. The incorporation of D-glucose-14C(U) in amino acids of brain and liver from rats pretreated with reserpine or with phenothiazines

Following treatment with reserpine or alternatively with a combination of phenothiazines (Randolektil, Majeptil) a drug-induced parkinsonoid reaction was provoked in rats. Twenty min before decapitation, 18 muCi d-glucose-14C(U) was administered intravenously. Concentration and radioactivities of glutamic acid (glu), glutamine (gln), serine (ser), and glycine (gly) were assayed in some regions of brain and in liver. Separation was performed by a combination of paper electrophoresis and chromatography or by an automatic amino acid analyzer. 1 After reserpine, the concentrations of serine and glycine were increased ten-fold while their specific activities decreased by the same factor. The interconversion serine-glycine was not affected. The concentration of glutamic acid was reduced while its specific activity remained constant. 2. After phenothiazines, the concentrations of serine and glycine in brain were also increased but their specific activities were decreased to a different degree. This indicates an additional effect on the serine-synthesis from glucose. The interconversion serine-glycine was also altered. The concentration of glutamic acid was decreased but specific activity was constant except in the thalamus region tested. 3. The influence of both treatments on amino acid turnover in liver differed from the observed impairment of brain metabolism. 4. Possible correlations between the changes in amino acid metabolism, catecholamines, and the neurologic parkinsonian symptoms are discussed.

Neurochemical correlates of behavior: levels of amino acids in four areas of the brain of the rat during drug-induced behavioral excitation

The levels of GABA, aspartate, glutamate, glycine and alanine were determined in 4 specific brain areas (telencephalon, diencephalon-mesencephalon cerebellum and pons-medulla oblongata) of rats killed during a period of drug-induced behavioral excitation. Behavioral excitation was obtained in adult, male Wistar rats working on a Sidman shock-avoidance schedule following administration of 2 mg/kg tetrabenazine (TBZ) 18 hr after iproniazid (50 mg/kg) pretreatment. When compared to trained animals (working on the avoidance schedule but receiving no drugs), the excited rats had increased levels of GABA in the telencephalon and diencephalon-mesencephalon, decreased levels of aspartate in all 4 brain areas, and a lower content of glycine in the pons-medulla region. The changes in the levels of aspartate in all areas of the brain, GABA in the diencephalon-mesencephalon, and glycine in the pons-medulla were significantly correlated (p less than 0.01) with the degree of excitation. It was observed that avoidance training alone produced increases in the levels of four amino acids: aspartate in telencephalon and cerebellum, GABA in cerebellum, and glycine and glutamate in the pons-medulla. The injection of iproniazid alone or iproniazid followed by TBZ into naive animals had little effect on the levels of the five amino acids. The data are discussed in terms of aspartate and GABA interacting as neurotransmitters with cholinergic and catecholaminergic and/or serotonergic neurons to produced the behavioral excitation.

Compartmentation of amino acid metabolism in the rat dorsal root ganglion; a metabolic and autoradiographic study

The incorporation of radioactivity into glutamate, glutamine, GABA and other amino acids was followed after incubation of desheathed rat dorsal root ganglia in media containing [14C]glucose or [14C]acetate. The results indicated that [14C]glucose was incorporated into a large pool of glutamate, but that this glutamate pool did not synthesize glutamine or GABA to any great extent. [14C]Acetate, on the other hand, was incorporated into a small glutamate pool which was readily converted to glutamine, and which synthesized GABA to a greater extent than the large pool. Light microscopic autoradiography of ganglia incubated with [14C]glucose or [14C]acetate confirmed that the small pool labelled by acetate was probably associated with satellite glial cells, while the large pool was located within the ganglion neurons. The results are discussed within the context of previous work on compartmentation of glutamate metabolism in the central nervous system.