Distribution and release of adenosine triphosphate in rat brain

The steady-state level of brain ATP was measured after the tissue had been treated with a focused microwave irradiation system. The brain ATP content (1.50 nmol/mg tissue) obtained by microwave fixation is similar to that observed by others using fast-freezing and microwave fixation techniques. The concentrations of ATP in different brain regions show a rather uniform distribution, ranging from 1.918 +/- 0.059 (brainstem) to 2.393 +/- 0.19 (caudate) nmol/mg tissue; however, insufficient microwave fixation time seems to produce a greater regional variation of ATP. Release of ATP was investigated by placing a cup on the sensory-motor cortex. The rate for basal release of ATP is 1.43 +/- 0.14 femtomole/min/mm(2). A 30-fold increase in ATP release was obtained by direct stimulation of the cortex with 5 mA pulses of 0.2 msec duration at a rate of 20/sec over a period of 10 min. These results, in conjunction with others describing the potent pharmacological action of the nucleotide, seem to suggest that ATP could be a mediator in a "purinergic" system in the CNS.

Evidence for net uptake of GABA into mouse astrocytes in primary cultures--its sodium dependence and potassium independence

Content of GABA was measured in cultured, normal astrocytes [from the brain cortex of newborn mice] together with the effect of nonradioactive GABA on the efflux of labeled GABA from cells previously loaded with (14C)GABA. An increase of external GABA concentration from 0 to 25 micron evoked a rise of the GABA content in the cells to a level which was approximately 50 times that of the incubation medium. Neither 200 nor 2000 micron nonradioactive GABA had any effect on the rate of release of radioactivity from cells loaded with (14C)GABA. Both the high tissue/medium ratio and the lack of a GABA-induced enhancement of the release of radioactivity indicate that the previously observed high-affinity uptake of GABA in cultured astrocytes represents a net uptake and not a homoexchange with endogenous GABA. This uptake is sodium dependent but was found to be unaffected in potassium-free media; the quantitative correlation between GABA transport and sodium transport differed from that reported for synaptosomes.

The effects of reserpine and 6-hydroxydopamine on the concentrations of some arylakylamines in rat brain

1 The concentrations of p- and m-tyramine were measured in the caudate nucleus of the rat brain following subcutaneous injection of reserpine or intraventricular injection of 6-hydroxydopamine, beta-Phenylethylamine was analysed in the hypothalamus after reserpine. 2 Endogenous levels of p-tyramine and m-tyramine in the caudate nucleus, and beta-phenylethylamine in the hypothalamus were 8.02, 2.25 and 2.52 ng/g respectively. 3 Tyramine concentrations were reduced to less than 20% of control values one day after a reserpine injection of 1 or 10 mg/kg. A single dose of reserpine (0.4 mg/kg) significantly decreased the content of both tyramines in the caudate nucleus. The effects became apparent as early as 45 min after drug case of m-tyramine. 4 The hypothalamic content of beta-phenylethylamine was unaffected by reserpine. 5 Ten days after an intraventricular injection of 6-hydroxydopamine (250 mug), p- and m-tyramine concentrations in the caudate nucleus were significantly below control levels. 6 The results suggest that p- and m-tyramine may be stored by an intraneuronal reserpine-sensitive storage mechanism. Alternatively, the tyramines may replace some of the catecholamines from their storage granules and then be released as false transmitters by the nervous impulse. The observed changes in tyramine levels might also the fact that these amines may be metabolically related to another amine which is stored in reserpine-sensitive granules.

Some observations on the interaction of dopamine-beta-hydroxylase and its natural inhibitors in the rat brain

The difficulty of assaying dopamine beta-hydroxylase (DbetaH) (EC 1.14.17.1) has been circumvented by including N-ethylmaleimide (5 X 10(-2) M) in the incubation mixture along with a small amount of Cu2+ (20-60 muM). Such a procedure ensures that the maximum DbetaH activity is assessed in all extracts. As a result, the absolute levels of DbetaH in various regions of the rat brain have been established. The DbetaH values obtained are higher by 40% in the hypothalamus and 20% in the cerebral cortex, spinal cord, and caudate nucleus than those previously reported. The mechanism of the synergic effect seen when N-ethylmaleimide and Cu2+ are combined is not presently understood.

Metabolism distribution, and disappearance of injected beta-phenylethylamine in the rat

In the absence of a monoamine oxidase inhibitor, the bulk of intravenously injected radioactively labelled beta-phenylethylamine was oxidized to phenylacetic acid. In the presence of pargyline, most of the label in tissues remained as unchanged phenylethylamine; small amounts of labelled phenylethanolamine, tyramine and octopamine were also identified. After intravenous injection of [14-C]phenylalanine, only very small amounts of [14-C] phenylethylamine could be located in urine and faeces. Beta-Phenylethylamine became concentrated in all tissues, including brain, following intravenous introduction both in the presence and absence of pargyline. Its clearance from these tissues and from brain regions was very fast.

Distribution, metabolism, and disappearance of intraventricularly injected p-tyramine in the rat

The major cerebral metabolic products of intraventricularly injected p-tyramine were octopamine and p-hydroxyphenylacetaldehyde. Only tiny amounts of p-hydroxyphenylacetic acid and p-hydroxyphenylethanol were found and these were located in the cerebral cortex (i.e. 'rest'). In brain regions isolated in the absence of pargyline the principal metabolite was p-hydroxyphenylacetaldehyde recovered in an acidic–neutral fraction; in the presence of pargyline, however, the majority of the label was associated with the amines tyramine and octopamine. In the caudate nucleus octopamine was essentially absent both in the presence and absence of pargyline.The loss of octopamine from all regions in the presence of pargyline was approximately exponential (i.e. first order) whereas in the absence of the monoamine oxidase inhibitor the loss was more complicated than first order. In most cases the loss of p-tyramine was greater than first order. Approximate half-lives based on these clearance values indicated a rapid turnover for p-tyramine and octopamine in all regions both in the presence and absence of pargyline.

Distribution and metabolism of tryptamine in rat brain

Following intraventricular injection in untreated rats, the only metabolites of tryptamine isolated were indoleacetic acid and indoleacetaldehyde; the indication is that the acid is formed from the aldehyde during the isolation procedure. Additional metabolites (N-methyltryptamine and N,N-dimethyltryptamine) were formed in small quantities if the animals had been pretreated with pargyline. N-acetyltryptamine was not found if acetate ions were excluded during the isolation of the amine fraction.More tryptamine remained in the hypothalamus than any other region at all times following injection, both in the presence and absence of pargyline. Incubation with slices indicated a temperature dependent active uptake process in all regions.The loss of injected tryptamine from all regions in the presence of pargyline, and from the hypothalamus, cerebellum, and 'rest' in the absence of pargyline followed a pattern of rapid initial loss and then slower decline. This pattern was neither linear nor exponential. All the data, however, indicate a rapid turnover of the injected amine.

Biosynthesis of cerebral phenolic amines. II. In vivo regional formation of p-tyramine and octopamine from tyrosine and dopamine

In rats pretreated with pargyline the highest cerebral concentration of 14C-labeled p-tyramine and octopamine following an intraventricular injection of tyrosine-14C was found in the hypothalamus. In the case of dopamine-14C the maximum formation was in the hypothalamus and brainstem. In the absence of pargyline only very small quantities of these amines were found in some regions. Following injection of p-tyramine-3H, β-hydroxylation to octopamine-3H occurred in all regions, the most active being the hypothalamus. Unchanged p-tyramine was most actively concentrated in the caudate nucleus. The formation and localization of p-tyramine and octopamine from their respective precursors tyrosine, dopamine, and p-tyramine itself are discussed with regard to the endogenous distribution of p-tyramine and certain of the enzymes involved in the synthesis and metabolism of these phenolic amines.

Binding of some primary aromatic amines to certain rat brain particulate fractions

The unsubstituted aromatic amines β-phenylethylamine and tryptamine, on addition to rat brain homogenates, were found to form relatively stable 'complexes' with certain particulate fractions. Similar particulate 'complexes' were found following intraventricular injections. As a result of this binding the recovery of small quantities of these amines added to brain homogenates was variable and low when compared to other tissue homogenates. Although p-tyramine formed similar 'complexes' both the strength and extent of the binding was much reduced. Subcellular fractionation revealed that β-phenylethylamine, tryptamine, and p-tyramine were associated with a myelin and synaptosomal fraction.

Biosynthesis of cerebral phenolic amines. I. In vivo formation of p-tyramine, octopamine, and synephrine

Following the intraventricular injection of 14C-labelled dopamine, p-tyrosine, and p-tyramine to rats pretreated with a monoamine oxidase inhibitor, the labelled phenolic amines p-tyramine, octopamine, and synephrine were isolated and identified as their DNS derivatives. Differences in the amounts of the phenolicamines formed suggest that mechanisms other than just decarboxylation are involved.