Some neurochemical aspects of the depressant action of gamma-butyrolactone on the central nervous system

THE EXCITATION AND DEPRESSION OF MAMMALIAN CORTICAL NEURONES BY AMINO ACIDS

Amino acids related to L-glutamic and gamma-amino-n-butyric acid have been administered electrophoretically, and by pressure ejection, into the extraneuronal environment of single neurones in the pericruciate cortex of cats anaesthetized with allobarbitone or allobarbitone-urethane. Acidic amino acids related to glutamic acid, particularly N-methyl-D-aspartic acid, excited cortical neurones. Neutral amino acids related to gamma-amino-n-butyric acid, particularly 3-amino-1-propanesulphonic acid, depressed cortical neurones. Some of the depressants blocked the antidromic invasion of Betz cells by pyramidal volleys. There are no essential differences between the sensitivities of cortical and spinal neurones towards locally administered amino acids. A transmitter function of such amino acids within the mammalian central nervous system is considered unlikely.

Inhibition by gamma-hydroxybutyrate of chlorpromazine-induced increase in homovanillic acid

1. gamma-Hydroxybutyrate and its lactone precursor, gamma-butyrolactone, when administered in anaesthetic doses block the increase in the cerebral concentration of homovanillic acid normally observed after administration of chlorpromazine or haloperidol.2. Other hypnotics such as glutethimide, urethane, chloralose, chloral hydrate and thiopentone do not have this ability even when administered in anaesthetic doses.3. The ability of gamma-hydroxybutyrate to block the neuroleptic-induced increase in cerebral homovanillic acid is not due to a reduction in body temperature since a similar effect is observed in rats treated under conditions (32 degrees C) in which body temperature remains normal.4. Possible mechanisms for this action of gamma-hydroxybutyrate are discussed.

The effect of sodium -hydroxybutyrate on the metabolism of dopamine in the brain

1. Sodium gamma hydroxybutyrate (GHB-Na), when given to rats and mice, caused a sleep-like state and a fall in body temperature of about 10 degrees C.2. GHB-Na produced a dose-dependent increase in the concentration of dopamine (DA) in the brains of mice kept at an environmental temperature of 18-20 degrees C or 30-32 degrees C.3. The concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and 4-hydroxy-3-methoxyphenylacetic acid (HVA), the metabolites of DA, were increased in the striatal tissues of rats and mice, after the administration of GHB-Na. However there was a delay of 60 min before the concentration of HVA increased whereas there appeared to be little delay before the concentration of DOPAC increased.4. When GHB-Na was administered to reserpine-treated animals, no increase occurred in the concentration of dopamine in the brains of mice or rats, or of DOPAC in the rat brain.5. Reserpine did not prevent the induction of the sleep-like state by GHB-Na.6. The results presented suggest that the effect of GHB-Na in increasing the concentration of DA requires unimpaired storage mechanisms for the amine.

Release of monoamines from the striatum and hypothalamus: effect of -hydroxybutyrate

1. A simple in vitro system was developed to study the effect of gamma-hydroxybutyrate on nerve cell depolarization-induced release of labelled dopamine, noradrenaline and 5-hydroxytryptamine from brain slices.2. The release of (3)H-dopamine formed in rat striatal slices incubated with (3)H-tyrosine was followed either by transferring the slices through successive media or by using a superfusion system. A one to three minute exposure to K(+) (53 mM) caused up to a thirty fold increase in the release of newly synthesized (3)H-dopamine. This K(+)-induced release was antagonized when gamma-hydroxybutyrate (1 x 10(-3)M) was present in the medium.3. Potassium (53 mM) increased (eighteen to thirty fold) the release of (3)H-dopamine from striatal slices initially loaded by preincubation with (3)H-dopamine. However, the K(+)-induced release of this pool of dopamine was not antagonized by gamma-hydroxybutyrate.4. Potassium (53 mM) also increased the release from striatal slices of (3)H-5-hydroxytryptamine newly synthesized from (3)H-tryptophan. This K(+)-induced release of 5-hydroxytryptamine was also not inhibited by gamma-hydroxybutyrate.5. The release of newly synthesized (3)H-noradrenaline from hypothalamic slices was also increased by K(+). This K(+)-induced release, however, unlike that of 5-hydroxytryptamine, was antagonized when gamma-hydroxybutyrate was present in the superfusion medium.6. Removal of Ca(++) had no effect on K(+)-induced release of (3)H-dopamine when followed by transferring the slices through successive media. This K(+)-induced release was abolished, however, when Mg(++) (12 mM) was present in the medium.7. The removal of Ca(++) from the superfusion medium abolished almost completely the K(+)-induced release from striatal slices of either newly synthesized (3)H-dopamine or preloaded (3)H-dopamine. This is presumably due to a more effective washout of tissue Ca(++) by the superfusion technique.8. The ability of gamma-hydroxybutyrate to antagonize the K(+)-induced release of monoamines from brain slices does not appear to be unique to the release of newly synthesized dopamine from the striatum.

Effect of -hydroxybutyrate on the release of monoamines from the rat striatum

A simple in vitro system was developed to study the effect of gamma-hydroxybutyrate on nerve cell depolarization-induced release of labelled DA and 5-hydroxytryptamine. The release of (3)H-dopamine formed in rat striatal slices incubated with (3)3H-tyrosine was followed. A three minute exposure to K+ (53.0 mM) caused a thirty-fold increase in the release of newly synthesized (3)H-dopamine. This K + -induced release was antagonized when gamma-hydroxybutyrate (1 mM) was present in the medium. Potassium (53.0 mM) increased (eighteen-fold) the release of (3)H-dopamine from striatal slices initially loaded by preincubation with (3)H-dopamine. The K + -induced release of this pool of DA was, however, not antagonized by gamma-hydroxybutyrate.Potassium (53.0 mM) also increased the release from striatal slices of (3)H-5-hydroxytryptamine (5-HT) newly synthesized from (3)H-tryptophan. This K + -induced release of 5-HT was also not inhibited by gamma-hydroxybutyrate. The ability of gamma-hydroxybutyrate to antagonize only the K + -induced release of newly formed DA may explain why this agent causes a rapid and selective increase in brain dopamine.

Effects of gamma-hydroxybutyrate on chick behaviour, electrocortical activity and crossed extensor reflexes

1. Convulsant and anticonvulsant effects of gamma-hydroxybutyrate (GHB) have been studied in chicks.2. When administered alone, GHB produced weak myoclonic seizures accompanied by electrocortical synchrony and spikes.3. GHB was found to protect chicks against leptazol- and picrotoxin-induced seizures. A slight potentiation of strychnine-induced seizures was evident.

ynergy of ethanol and a natural soporific--gamma hydroxybutyrate

gamma-Hydroxybutyrate and ethanol, as well as gamma-butyrolactone and ethanol are potentiative with respect to duration of loss of the righting reflex (sleep time). The concentration of ethanol in the liver decreases from 30 to 90 minutes after rats are injected with ethanol, but there is no change when ethanol is injected with gamma-butyrolactone. In view of the fact that gamma-hydroxybutyrate is a natural intermediate in brain, the effects of ethanol on the central nervous system may be mediated through its interaction with gamma-butyrolactone.