Jacques Bruinvels

Suppression of GABA-induced abstinence behaviour in naive rats by morphine and bicuculline

Abstract Intraperitoneal administration of n-dipropylacetate (DPA) to naive rats produced abstinence behaviour including shaking, digging, hunchback posture, piloerection and ptosis during 15 min and increased motor activity considerably. Treatment with a subconvulsive dose of the GABA antagonist bicuculline suppressed this DPA-induced abstinence behaviour, indicating that GABA was increased at receptor sites. Also morphine in a low dose of 1 mg/kg suppressed this behaviour, while administration of naloxone after morphine treatment could release the abstinence behaviour. Simultaneous treatment with morphine and naloxone or naloxone alone were without effect. The administration to DPA treated rats of doses higher than 1 mg/kg morphine resulted in a severe depression of motor activity. It is concluded that an increased availability of GABA at its receptor sites plays an important role in the behaviour observed after DPA administration. The experiments with morphine and naloxone suggest that morphine receptors are involved in DPA-induced abstinence behaviour.

A reproducible model of acute hepatic failure by transient ischemia in the pig.

A model of transient acute hepatic failure has been developed in the pig. Three days after a functional end-to-side portacaval shunt was introduced, 15 ambulant animals underwent total liver ischemia for 4 to 6 h by the closure of a mechanical clamp surrounding the hepatic artery. Four of the eight animals subjected to 4 hr of ischemia survived. All but one of the animals undergoing 6 hr of hepatic ischemia developed grade 4 encephalopathy after 24 to 30 hr and died within 50 hr. Quantitative estimation of liver cell necrosis revealed less than 40% necrosis in the survivors, and approximately 62% (range 49-75%) in animals who died of hepatic coma. As far as the putative toxins are concerned, significant differences were found between animals undergoing 4 and those undergoing 6 hr of ischemia, especially in the plasma ammonia levels and the plasma ratios for tyrosine and phenylalanine. Plasma arginine levels had fallen to zero in both groups at 24 hr and only rose to preischemic values in animals who survived. This large animal model fulfills the accepted criteria of potential reversibility, reproducibility, and death due to hepatic failure.

SCHIZOPHRENIA-LIKE PSYCHOSIS CAUSED BY A METABOLIC DISORDER

Four patients with an intermittent psychosis closely resembling hallucinogenic drug-induced states were suspected of having a porphyric disease and were investigated for a possible relation between the metabolic dysfunctions of porphyria and the psychotic syndrome. Theoretically the link could be in a disturbance of serine and glycine metabolism. This theory was supported by disturbances in serine and glycine excretion found in all patients during psychotic episodes. In addition, loading with one low oral dose of serine produced psychotic symptoms 5 h later which lasted 3-6 h. One patient reacted to glycine in the same way. These findings suggest that disturbed serine-glycine metabolism may have a key role in certain schizophreniform psychotic syndromes.

Endogenously formed norharman (β-carboline) in platelet rich plasma obtained from porphyric rats

Porphyria was induced in adult male Wistar rats starved for 24 hr by SC injection of 400 mg/kg allylisopropylacetamide (AIA). The presence of porphyria was shown by measuring excretion of delta-aminolevulinic acid (delta-ALA) and porphobilinogen (PBG) into the urine during 24 hr after AIA administration. Plasma levels of glycine, serine and of a number of other amino acids were decreased in porphyric rats as compared to controls. Intraperitoneal injection of 2 mmol/kg serine 24 hr after AIA administration was used as an animal model for an acute psychosis, by measuring catalepsy scores 30 min after serine injection. The concentration of 5 different beta-carbolines in platelet rich plasma (PRP) was measured using an HPLC-fluorometric method. An increase in the concentration of norharman (NH) in PRP, ranging from 0.57 nmoles/l in control rats to 1.88 nmoles/l in serine treated porphyric rats was found. The catalepsy duration was exponentially correlated with the NH concentrations in PRP. It is concluded that an elevated conversion of serine into glycine via serine hydroxymethyltransferase (SHMT) may be responsible for the enhanced NH biosynthesis.

Abnormal plasma levels of serine, methionine, and taurine in transient acute polymorphic psychosis

The present study explored the usefulness of plasma amino acid concentrations in discriminating a subgroup of patients with transient acute polymorphic psychoses characterized by psychosensory symptoms (APP+ patients). Levels of amino acids in the plasma of APP+ patients were compared with levels in psychiatric patients with other types of psychotic symptomatology and a healthy control group. Both the APP+ patients and patients with bipolar affective disorder had significantly lower plasma concentrations of serine compared with concentrations in the other groups studied. Since the plasma concentrations of taurine and methionine were also different in the APP+ patients, the ratio of taurine to the product of serine and methionine (the TSM ratio) was used in an attempt to increase the sensitivity in discriminating these patients. The TSM ratio in the APP+ patients was significantly higher than those in the other groups studied, except for the patients with bipolar affective disorder. It appears that the determination of serine and the TSM ratio in the plasma of psychotic patients may be a useful diagnostic validator in a group of patients with acute polymorphic psychoses.

High-performance liquid chromatography of tetrahydro-β-carbolines extracted from plasma and platelets

A fast method for extraction and concentration of tryptamine (TA), 5-hydroxy-TA, and 5-methoxy-TA was developed using reverse-phase C-18 sample preparation columns in combination with an ion-pairing reagent. Using this method, 1,2,3,4-tetrahydro-beta-carboline (THBC), 6-hydroxy-THBC, and 6-methoxy-THBC, the respective reaction products formed after reaction of formaldehyde with the primary amines mentioned above, and beta-carboline (BC, norharman) and 1-methyl-beta-carboline (1-Me-BC, harman) could also be extracted from human and rat platelets and platelet-poor plasma (PPP). A HPLC method combined with fluorometric detection was developed for the quantitative determination of these compounds in the picomole range. The formation of beta-carbolines during the extraction procedure was below the limit of detection of the assay procedure. 6-OH-THBC, THBC, 1-Me-BC, and 5-HT were identified as normal constituents of human platelets, whereas only 5-hydroxytryptamine (5-HT) and 6-OH-THBC could be identified in human PPP. In rat platelets and PPP 5-HT, but no THBCs, could be detected.

GABA-B receptor activation and conflict behaviour

Baclofen and oxazepam enhance extinction of conflict behaviour in the Geller-Seifter test while baclofen and diazepam release punished behaviour in Vogels conflict test. In order to investigate the possibility that the effect of the selective GABA-B receptor agonist baclofen is mediated indirectly via the GABA-A/benzodiazepine receptor complex, the effect of pretreatment of rats with baclofen on [3H]-diazepam binding to washed and unwashed cortical and cerebellar membranes of rats has been studied. Baclofen pretreatment increased Bmax in washed cerebellar membranes when bicuculline was present in the incubation mixture. No effect was seen in cortical membranes. The present results render it unlikely that the effect of baclofen on extinction of conflict behaviour and punished drinking is mediated via the GABA-A/benzodiazepine receptor complex.

Differential effect of morphine on dopaminergic neurons in frontal cortex and striatum of the rat.

Abstract Inhibition of dopamine synthesis by a single injection of α-methyl-para-tyrosine (200 mg/kg, i.p.) was complete from 30 to at least 300 min after administration. When morphine (20 mg/kg) was given intraperitonealy 30 min after α-MpT treatment an enhanced decline of dopamine was observed in frontal parts of the cortex but not in the striatum. These results indicate that morphine affects dopaminergic neurons in frontal parts of the cortex in a way differently from those in the striatum of the rat. This may be caused either by a difference in the properties of dopaminergic nerve endings in both structures or by an effect of morphine on the input to the cortical system which is lacking in the striatum.

Haloperidol inhibits the disappearance of acidic dopamine metabolites from rat striatum.

1 Administration of neuroleptic drugs to laboratory animals results in increased dopamine turnover. This has been shown by use of diverse techniques, like conversion of radioactive tyrosine to dopamine (Nyback & Sedvall, 1969; Zivkovic, Guidotti & others, 1975), dopamine loss after synthesis inhibition with a-methylp-tyrosine (r-MT) (Anden, Corrodi & others, 1971 ; Waldmeier & Maitre, 1976) and accumulation of the acidic dopamine metabolites homovanillic acid (HVA) and 3,4-dihydroxyphenyl acetic acid (DOPAC) (AndCn, ~ o o s & Werdinius, 1964; Westerink & Korf, 1976b). The latter method has also been used extensively to compare quantatively the effects of different neuroleptics in striatal and mesolimbic brain structures (Stawarz, Hill & others, 1975; Wiesel & Sedvall, 1975; Wilk, Watson & Stanley, 1975; Waldmeier & Maitre, 1976; Westerink & Korf, 1976b). A basic assumption in such studies is, that alterations in metabolite concentrations reflect alterations in functional activity of dopaminergic neurons. In the maintainance of normal metabolite concentrations, however, at least two processes are rate-limiting, i.e. the formation of the metabolites and their removal from the brain. The fact that considerable amounts of acidic metabolites are present in normal brain tissue may indicate that the removal from the brain is indeed a rate-limiting process. I t seems reasonable to assume that the rate of formation of acidic metabolites is related to the activity of dopaminergic neurons. The concentrations of these metabolites, however, are not only determined by the rate of formation, but also by the rate of transport from the brain. Drug-induced alterations of metabolite concentrations, therefore, cannot be taken as a reflection of the activity of dopaminergic neurons, when the transport of metabolites is also affected by the same drug. To test whether the increase in the acidic metabolites HVA and DOPAC by haloperidol (Andkn, Roos & Werdinius, 1964; Westerink & Korf, 1976b) was a t least in part the result of an inhibition of the transport of these metabolites, we inhibited the formation of acidic metabolites with pargyline after which the effect of haloperidol on the metabolite concentrations was studied. Since the formation of acidic metabolites will be inhibited by pargyline, an alteration in metabolite concentrations by haloperidol can only be ascribed to an alteration in the rate of transport (or conjugation). Similarly the effect of the dopamine agonist apomorphine was studied.

The anti-conflict effect of cyproheptadine is not mediated by its 5-hydroxytryptamine antagonistic property

Cyproheptadine, a 5HT2 receptor antagonist with prominent antimuscarinic and anti-histaminic properties, was shown to have an anti-conflict effect in rats using a modified Geller-Seifter test and also enhanced extinction of conflict behaviour. The selective 5HT2 receptor antagonist ritanserin, however, had neither an anti-conflict effect nor an effect on extinction of conflict behaviour. The muscarinic receptor antagonist scopolamine, on the other hand, was active in both paradigms. The effect of cyproheptadine on extinction of conflict behaviour was decreased by co-administration of physostigmine, an acetylcholinesterase inhibitor, but not affected by the concomitant administration of the muscarine receptor agonist oxotremorine. The results suggest that the anti-conflict effect of cyproheptadine has to be ascribed to its anti-muscarinic activity and is not due to its 5HT2 antagonism.