Göran Wahlström

Differences in anaesthetic properties between the optical antipodes of hexobarbital in the rat

Abstract The two optical antipodes of hexobarbital have been tested with an anaesthesia threshold method. As the threshold was taken the dose of hexobartial needed to obtain a burst suppression of 1 second or more in the EEG (the silent second) during a constant rate intravenous infusion. When the threshold was reached the infusion was stopped and the ensuing sleeping times recorded. There was a marked difference between the threshold doses needed to obtain the silent second with the two antipodes. On the average 43 mg/kg of (+)-hexobartial was needed as compared with more than 114 mg/kg of (-)-hexobarbital. The antipodes seemed to be directly additive. Approximately one quarter of the activity in the racemate is due to (-)-hexobarbital. While threshold doses of racemic hexobarbital and (+)-hexobarbital caused approximately equal sleeping times a dose of (-)-hexobarbital just about to give the silent second caused much larger sleeping time.

Increased number of muscarinic binding sites in brain following chronic barbiturate treatment to rat

Abstract Rats received as their only drinking fluid a solution of sodium barbital (3.33 mg/ml) for more than 40 weeks. In two groups (A3, A12) the barbital solution was withheld and replaced by water 3 and 12 days before sacrifice. Two other groups consisted of animals drinking barbital until sacrifice (B) and untreated controls (C). Synaptosomes from different parts of the brain were incubated with radioactive quinuclidinyl benzilate ( 3 H-QNB) (0.2 nM) for 60 min. A significantly increased number of 3 H-QNB binding sites was found in the striatum and midbrain + medulla oblongata + cerebellum of rats abstinent for 3 days (A3) in comparison with controls (C). Saturation studies indicated that group A3 had significantly more receptors in the midbrain + medulla oblongata + cerebellum than group C, while there was no differences in receptor affinity.

Effect of long-term forced oral barbital administration on endogenous acetylcholine in different regions of rat brain

Rats received a solution of sodium barbital as their only drinking fluid for 25 and 30 weeks. Four groups were studied: (1) control; (2) barbital until sacrifice; (3) barbital withheld (abstinent) for 3 days; (4) abstinent for 12 days. Abstinence convulsions in groups 3 and 4 were recorded with jiggle cages. The rats were killed by decapitation and the concentration of acetylcholine (ACh) was measured in 3 parts of the brain: striatum, hippocampus + cerebral cortex, cerebellum + medulla oblongata + midbrain. In animals receiving barbital until sacrifice, no significant change in ACh content was found in any of the brain regions compared with controls. In animals abstinent for 3 days and with a maximal frequency of spontaneous convulsions a decreased content of ACh (--35%) was found in the striatum. On the 12th day of abstinence, when the convulsive activity clearly had decreased, the ACh content was still decreased (--30%) in the striatum and a significant decrease compared with controls was also found in the cerebellum + medulla oblongata + midbrain.

Tolerance, physical dependence and changes in muscarinic receptor binding sites after chronic ethanol treatment in the rat.

Rats were treated with ethanol in the drinking water for 73-75 weeks. The daily drinking periods were restricted to only 2x1 h to get significant ethanol blood concentrations. After the end of the ethanol treatment (last day of treatment denoted day 0 of the abstinence) tolerance to sedatives were recorded with a hexobarbital threshold method, convulsions recorded with jiggle cages, and muscarinic receptor binding sites determined with 3H-quinuclidinyl benzilate. Tolerance to hexobarbital was found to have a maximum on day 8 in the abstinence while convulsions recorded from the rats participating in the hexobarbital threshold determinations had a maximum on day 14. Atropine administered as a single dose on day 8 decreased the tolerance to hexobarbital on that day and seemed to reduce the number of convulsions on the following days. Muscarinic receptor sites were significantly increased in the striatum on day 8 of the abstinence at the time of maximal tolerance, This increase in muscarinic receptors was less in rats which had had convulsions during the abstinence before sacrifice. Thus the results indicate that cholinergic mechanisms are involved in the changes seen during the abstinence after chronic ethanol exposure.

Changes in populations of cholinergic binding sites in brain after chronic exposure to barbital in rats.

Male rats were treated with barbital in their drinking fluid for about 40 weeks (daily dose 200 mg/kg). The treatment was stopped on day 0 and the number of muscarinic binding sites was measured in 3 brain parts (striatum; cortex and hippocampus; medulla oblongata and midbrain) during the abstinence with labeled quinuclidinyl benzilate (QNB) as ligand. Nicotine-like binding sites were quantified in the cortex with labeled tubocurarine. An increased number of QNB-binding sites was found in the striatum during the early part of the abstinence (days 0--3), found by another increase later in the abstinence (days 12--21). In the cortex preparation a variable increase in QNB binding was measured from days 2--9 of the abstinence, whereas in the midbrain preparation the QNB binding was found to be increased only on day 9 in comparison to controls. A change in the proportion between high and low affinity muscarinic binding sites (measured by agonist-antagonist competition) was found in the cortex preparation during the period when the QNB binding was increased. Prior to the maximum abstinence convulsions the QNB binding was higher in rats without recorded spontaneous convulsions in comparison to rats with convulsions. A negative correlation between the time after the last convulsion and the number of QNB binding sites was observed in data from rats where the maximum convulsions had occurred before sacrifice. In addition, a negative relationship between the number of muscarine- and nicotine-like binding sites was found in the cortex during days 5--9 of the abstinence.

REGIONAL BIOSYNTHESIS OF ACETYLCHOLINE IN BRAIN FOLLOWING FORCED ORAL CHRONIC BARBITONE TREATMENT TO RAT

Rats received a solution of sodium barbitone as their only drinking fluid for 33 and 42–44 weeks. In three groups (A3, A12 and A30) the barbitone solution was withheld and replaced by water 3, 12 and 30 days respectively before death. Two other groups consisted of animals drinking barbitone until death (B) and untreated controls (C). Abstinence convulsions were recorded by jiggle cages.

Changes in a hexobarbital anaesthesia threshold in rats induced by repeated long-term treatment with barbital or ethanol

The quantity of intravenously infused hexobarbital needed to produce a burst suppression of 1 sec or more in the EEG was determined in male rats after chronic barbital or ethanol treatments. The ensuing “sleeping times” were also recorded.At the end of the first treatment with barbital (200 mg/kg/day i.p. for 5 weeks) the hexobarbital thresholds had increased by approximately 45% compared with a pre-experimental average. The thresholds were back to normal after approximately a week. At the end of a second treatment with barbital there was a similar, slightly more prolonged, immediate increase in threshold. Three weeks after the second treatment there was also a new increase in threshold (Figs. 2 and 3). The ensuing “sleeping times” were unaffected.Ethanol treatment (10% W/V in the drinking water allowed twice 1 h each day for 16 weeks) caused a gradual increase in threshold which reached a maximum (20%) around day 9–10 after the end of the treatment (Fig.5). Two weeks after the ethanol treatment the thresholds were essentially normal. In an earlier barbital treated (200 mg/kg/day i.p. for 5 weeks) group a second slightly larger increase was also seen around 3 weeks after the end of the ethanol treatment. In this group an increase was also seen in the ensuing “sleeping times” but this increase seemed to be unrelated to the increases in threshold.These late changes in threshold after a second treatment seem to be due to a “summation” of changes induced by the two treatments. In this respect ethanol and barbital are probably related. They are, however, not identical with respect to their effects on the hexobarbital threshold after interruption of chronic treatment. This is shown by the longer latency of the immediate changes after ethanol treatments.

Decreased brain weights in rats after long-term barbital treatments

Abstract To study dependence on barbiturates, rats were in three experiments given a solution of barbital as their only drinking fluid for periods around 30 weeks. The animals were sacrificed after abstinence periods of up to 30 days and the brains were weighed. Compared with untreated controls the barbital treated animals in these experiments consistently had reduced wet brain weights. This reduction was not restituted after an abstinent period of 30 days. The decrease did not seem to be secondary to a reduced body weight. The decrease in brain weight found throughout the abstinence period was not influenced by changes in water intake. In a 4th experiment 12 weeks of barbital treatment caused a similar slightly smaller reduction in wet brain weight. Since there was no difference in water content the dry weight was also reduced. The possibility that this finding is related to the brain atrophy found in humans after long-term ethanol abuse is pointed out.

Enzyme regulation of melatonin synthesis in the pineal gland of Japanese quail

Abstract The enzymes N-acetyltransferase and hydroxyindole-O-methyltransferase (HIOMT) which are responsible for the conversion of serotonin to melatonin were assayed in pineal glands from both sexes of the Japanese quail in the middle of the dark and the light period of a 12:12 hour light-darkness cycle. The measured N-acetyltransferase activities were twice as high during the dark period as compared to the light period in both sexes. HIOMT activity was not significantly different between quails sacrificed at noon and at midnight. Thus, N-acetyltransferase activity might be responsible for the diurnal variation in melatonin content in the Japanese quail.

Acute and Chronic Effects of Barbiturates on Regional Turnover of Acetylcholine in Brain

Data concerning both the acute and chronic effects of barbiturates on acetylcholine [ACh] turnover in mouse and rat brain are presented. A single anaesthetic dose of pentobarbital [60 mg/kg, i.p.] to mice increased the endogenous content of ACh and decreased the turnover of ACh in the hippo-campus and cortex. No effect was found in the striatum. At sacrifice after chronic treatment with barbital to rats for about 30 weeks no effect was found on the endogenous ACh content. 3 days after the barbital solution was replaced by water [at the day with maximal number of abstinence convulsions] the amount of endogenous ACh was decreased by 35% in the striatum in comparison with control and the decrease was still significant after 30 days of abstinence. The biosynthesis of radioactive ACh from a tracer dose of radioactive choline [Ch] was increased in the cerebellum+midbrain+medulla oblongata of rats receiving barbital until sacrifice and rats abstinent for 3 days. It was also increased in the hippocampus+cortex on the 3rd abstinent day. No significant effect on the ACh formation was found in the striatum. Calculation of the specific radioactivity [SA] of ACh showed an increased SA in all brain regions in the abstinence indicating that the turnover of ACh might be increased during the abstinence after long-term barbital treatment. An increased number of muscarinic binding sites [measured by quinuclidinyl benzilate, QNB, as ligand] was also found in synapotosomes from the striatum of rats abstinent for 3 days.