1-Hydroxy-3-amino-pyrrolidone-2(HA-966): a new GABA-like compound, with potential use in extrapyramidal diseases.

1. The drug HA-966 (1-hydroxy-3-amino-pyrrolidone-2), which chemically resembles the cyclic form of GABA, has been studied for neuro-pharmacological properties and for effects on the catecholamine content of the corpus striatum.2. The acute effects on spontaneous behaviour of rodents included flaccid catalepsy and reversible tranquillization in doses which were 5% or less of the lethal dose. Long lasting depression of the CNS, followed by complete recovery, was produced in the cat and the dog. In the monkey HA-966 caused periodical sleeping episodes.3. The exploratory behaviour and the amphetamine-induced motor activity in mice were blocked by HA-966. The toxicity of amphetamine in aggregated mice was only moderately reduced, suggesting that HA-966 differs from neuroleptics.4. Tremors induced by chemical agents (nicotine, zinc and tremorine) were markedly inhibited by HA-966. The muscarinic effects of tremorine were not reduced by HA-966, indicating a selective central antitremor effect.5. HA-966 elevated the threshold to strychnine convulsions and abolished the ipsilateral flexor reflex, while not having motor endplate blocking properties. It is suggested that HA-966 depresses central internuncial neurones.6. In rats and rabbits HA-966 produced synchronous EEG and inhibited the sensory arousal in doses not causing sedation. In the monkey the drug caused a periodical dissociation between ;sleep-EEG' and behaviour.7. In rat brain, HA-966 selectively elevated the dopamine content in the corpus striatum, while no changes in noradrenaline and 5-hydroxytryptamine contents could be demonstrated. The effect was still present when dopa synthesis was inhibited with alpha-methyl-p-tyrosine.8. Several effects of intravenously administered HA-966 became manifest after an appreciable delay and in hepatectomized mice the effects were much reduced. It is postulated that HA-966 is converted to a pharmacologically active metabolite.9. The results are discussed in the light of current views on drug therapy in extrapyramidal conditions and a GABA-related hypothesis as to the mode of action of HA-966 is presented.

Monitoring the specific activities of dopamine and its metabolites in striatum and olfactory tubercle after intravenous administration of l-[(3)H]tyrosine: Complex relations, indicating more than two compartments.

It is still a matter of debate whether in dopaminergic nerve endings dopamine (DA) is present in different functional and/or metabolic compartments. To investigate this, DA metabolism was studied in vivo by measuring the specific activity of DA and its metabolites after intravenous administration of l-[3,5-(3)H]tyrosine (200 ?Ci/rat) to freely moving animals. The incorporation of (3)H into DA and metabolites was determined in striatum and olfactory tubercle at 5, 10, 20, 40, 60 and 80 min after [(3)H]tyrosine administration. In both structures the level of [(3)H]tyrosine initially declined monoexponentially, but deviated from that pattern later on. The curves representing the formation in time of [(3)H]DA and [(3)H]metabolites were very similar in both structures, although as a whole, the levels in the olfactory tubercle were higher. The relative patterns of the specific activities of DA and those of its metabolites, a possible clue to DA compartmentation, neither indicated a clearcut metabolic one-compartment, nor a two-compartment system. The flow of radioactivity through DA metabolism could in fact only be explained by assuming more complex metabolic relations.

The effect of blocking dopamine release on synthesis rate of dopamine in the striatum of the rat.

Two experiments were carried out in rats to investigate the mechanisms by which dopamine (DA) synthesis is regulated. First, a unilateral lesion was made in the substantia nigra, thus interrupting the nervous impulse flow of the nigro-striatal pathway. Secondly, the release of DA in the striatum was blocked by means of 1-hydroxy-3-amino-pyrrolidone-2 (HA-966). In both experiments the synthesis rate of DA was accelerated as was shown by analysing the time course of the specific activity of striatal DA after an i.v. injection of 3,5-3H-tyrosine. Furthermore the influence of apomorphine on the rate of DA synthesis, accelerated by HA-966 or by lesion, was investigated. Apomorphine appeared to block the increase of DA synthesis. The results are discussed in the light of a transsynaptic feedback mechanism.

Electrical stimulation of the nigrostriatal pathway after HA-966 block of triatal dopamine release.

Striatal dopamine (DA) of rats increased twofold 1 h after blockade of DA release by either an electrolytic lesion of the substantia nigra (SN) or systemic administration of 1-hydroxy-3-amino-pyrrolidone-2 (HA-966). If the treatments were combined, no further increase was observed. The decrease in DA induced by alpha-methyl-p-tyrosine (alphaMT) in otherwise untreated animals was not enhanced by a 20 min electrical stimulation of nigrostriatal fibres. If, however, in addition to synthesis blockade by alphaMT, DA release was interrupted by a lesion of the SN and/or by HA-966, electrical stimulation caused a significant decrease in striatal DA. It is assumed that HA-966 exerts its action in the dopaminergic nigrostriatal system by way of blockade of the nerve impulse flow at the level of the SN.

Differential effects of acute and subacute HA-966 treatment on storage and release of striatal dopamine.

Acute injections of HA-966 (100 mg/kg) into rats caused a rapid elevation of dopamine (DA) content in the striatum. 3,4-Dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels increased after a latency period of 0.5 h and 1 h respectively. Repeated ("subacute") HA-966 treatment produced a smaller DA increase than did single administration, while DOPAC and HVA rose at the same rate after both treatments. In HA-966-pretreated rats no tolerance for DA increase followed a lesion of the dopaminergic fibres. Acute as well as subacute HA-966 prevented the disappearance of DA after alpha-methyl-p-tyrosine for about 3 h. In both cases DOPAC and HVA levels dropped sharply after HA-966. HA-966 had no influence on the decline of DOPAC and HVA levels after monoamine oxidase inhibition. It is concluded that the rises of DOPAC and HVA after HA-966 did not occur because the capacity of the vesicular DA stores was exceeded. Instead, HA-966 affects the storage mechanism for newly formed DA. Possible explanations for the observed tolerance to DA accumulation after HA-966 are discussed.

Appetite regulation by serotoninergic mechanisms and effects of d-fenfluramine.

In this literature review, evidence is presented for the theory that the neurotransmitter, serotonin (5-hydroxytryptamine, 5HT), in medial hypothalamic centres is an important regulator for appetite and for the selection of major food constituents. High local levels of 5HT cause a reduction of appetite and a preference for protein, low levels the opposite. The main antagonistic system is noradrenergic. The drug d-fenfluramine mimics the effects of 5HT by releasing 5HT from serotoninergic nerve endings and inhibiting its neuronal re-uptake. Further experimental data prove that a high-carbohydrate, low-protein diet promotes uptake of serum tryptophan in the brain and its conversion into 5HT. Hence, this serotoninergic system may function as a self-regulatory mechanism. In patients with decreased peripheral insulin sensitivity, the system may be disturbed, causing overconsumption of carbohydrates. This is sometimes compulsive ("carbohydrate craving"). It may be presumed that in the treatment of obesity, in addition to the use of serotoninergic drugs, successes with reducing diets may be enhanced by including periods of high-carbohydrate, low-protein intake. It would be worthwhile to explore whether similar alimentary self-regulatory mechanisms of neurotransmitter function exist in other regulatory systems.

[Ethical assessment of biomedical experiments in The Netherlands]. / Ethische beoordeling van biomedische experimenten in Nederland.

The ethical evaluation of biomedical experiments is loyally accepted in the Netherlands. It was introduced everywhere during the last 15 years. Among the targets we find not only the protection of the experimental objects--animals and humans--but also the protection of researchers who may find moral support in the approval of their projects by a Committee of Ethical Evaluation. Concerning experiments in animals, the legal framework is provided by the Law on Animal Experiments. This law was drawn up in accordance with the directive of the E.U. To be allowed to practice experiments in animals, an institute must possess a licence; the researchers are moreover obliged to be appropriately trained with regard to experiments in animals. To that end an adequately functioning organization has been set up. The intensive supervision is widely decentralized and effected for the greater part by experts working within the institutes. The "intra muros" Committees supervising the experiments in animals play an important part in the ethical evaluation. More than 50 of those Committees are active at this time. Setting the ethical standards is done in close collaboration between the Authorities and the researchers. Researchers and animal protection associations have established a "Platform for the Replacement of Experiments in Animals", in which they support development of alternative methods for research. The legislation concerning medical experiments in humans is not yet completely enforced, but in practice the ethical evaluation has been effected for many years in every hospital of the Netherlands. At present about 150 "Committees for medico-ethical evaluation" are at work. Their task may be very heavy, especially in the academic hospitals, where, mostly, over 150 projects are advised on every year. Adequate training facilities are provided for the members of the committees. The passing of the bill on experiments in humans is stagnating owing to political reasons. Besides the approval of the present practice, the bill-draft contains some elements that are difficult to accept by researchers; among other things, the researchers refuse a possible political influence on the ethical advice. Moreover, there exists a menace to see the insurers changing their rules: the legislation on privacy might also hamper the development of a research seeming too closely patient-linked. Sufficient attention is not given to the financial aspects of the evaluation-process. The real cost of the evaluation should be incorporated into the budget of research projects.

Assay of HA-966 in rat plasma by capillary gas-liquid chromatography with nitrogen-selective detection.

A gas-liquid chromatographic method for the determination of the gamma-aminobutyric acid-like drug 1-hydroxy-3-aminopyrrolidone-2 (HA-966) in plasma is described. HA-966 was converted into its diacetyl derivative AC2HA-966 with acetic anhydride. This compound could be suitable eluted from a capillary OV-17 support-coated open tubular column. A sensitive detection method was achieved by making use of nitrogen-phosphorus-selective flame ionization.