Hans Corrodi

Receptor activity and turnover of dopamine and noradrenaline after neuroleptics.

Abstract Fifteen neuroleptics of the phenothiazine, thioxanthene, dibenzazepine, butyrophenone or diphenylbutylamine type were studied in rats. The dopamine (DA) receptors in the corpus striatum were blocked by all the drugs. The effects on noradrenaline (NA) receptors in the spinal cord varied. Chlorpromazine blocked the two receptors about equally. Haloperidol, perphenazine, clothiapine and particularly spiroperidol had a greater effect on DA receptors. Pimozide and fluspirilene blocked only DA receptors. Turnover of DA and NA was studied using biochemical and histochemical techniques, after tyrosine hydroxylase inhibition. Perphenazine and clothiapine accelerated turnover of both amines whereas spiroperidol only accelerated that of DA. Pimozide and fluspirilene increased turnover of DA and, at higher doses, NA. The high doses usually reduced the endogenous DA and NA levels. Thus, the most potent and specific neuroleptics seemed to influence mainly the brain DA mechanisms, both functionally and chemically.

THE FORMALDEHYDE FLUORESCENCE METHOD FOR THE HISTOCHEMICAL DEMONSTRATION OF BIOGENIC MONOAMINES A REVIEW ON THE METHODOLOGY

The histochemical fluorescence method of Falck and Hillarp for the demonstration of biogenic monoamines is based on the finding that the amines can be condensed with formaldehyde to yield strongly fluorescent compounds, provided that they are enclosed in a dried protein layer, as in freeze-dried or air-dried tissues. This review deals mainly with certain principal features of the method: its chemistry, sensitivity, specificity and possibilities for histochemical differentiation between the various amines. Some comments are made on certain of the results obtained with this method.

Effect of antidepressant drugs on the depletion of intraneuronal brain 5-hydroxytryptamine stores caused by 4-methyl-α-ethyl-meta-tyramine

Abstract Mice were injected with 4-methyl-α-ethyl-meta-tyramine (two doses of 100 mg/kg i.p.). After 4 h the animals were killed and the brains analyzed for 5-hydroxytryptamine (5-HT) biochemically or examined under the fluorescence microscope after formaldehyde treatment. The amine caused more than 50 per cent depletion of 5-HT, probably by displacement. Pretreatment with antidepressant drugs of imipramine type largely prevented 5-HT depletion, probably by blocking the amine uptake mechanism of the cell membrane of 5-HT neurons. Tertiary amines, e.g. chlorimipramine, imipramine and amitriptyline, were more potent in this respect than the corresponding secondary amines, in contrast to previous observations on noradrenaline neurons. In rats similar observations were made (histochemical observations only). It is suggested that blockade of 5-HT re-uptake is involved in the mood-elevating action of tricyclic antidepressants, whereas blockade of noradrenaline re-uptake promotes drive in the depressed patient.

Effects of some antidepressant drugs on the depletion of intraneuronal brain catecholamine stores caused by 4,α-dimethyl-meta-tyramine☆

Abstract Rats and mice were injected intraperitoneally with 4,α-dimethyl-meta-tyramine. As shown by histochemical (rats) and biochemical (mice) techniques this agent caused a decrease in catecholamine levels in central and peripheral (heart) noradrenaline and central dopamine neurons, accompanied by sympathomimetic stimulation and central excitation. These effects could be largely prevented by protriptyline and desipramine, previously found to be potent blockers of amine uptake by central and peripheral noradrenaline neurons. Dopamine neurons were resistant to the depletion-preventing action of these agents. Imipramine and amitriptyline showed slight, though significant activity in preventing depletion of central noradrenaline. In general the drugs were more potent in protecting peripheral than central noradrenaline stores. The results cast some doubt on the view that the antidepressant properties of thymoleptics are essentially due to inhibition of noradrenaline re-uptake at central synapses. Important components of the clinical action might well be due to other factors, e.g. a corresponding effect at central 5-hydroxytryptamine synapses.

FLUORESCENCE METHODS FOR THE HISTOCHEMICAL DEMONSTRATION OF MONOAMINES. 3. SODIUM BOROHYDRIDE REDUCTION OF THE FLUORESCENT COMPOUNDS AS A SPECIFICITY TEST

It has been shown in previous papers that catecholamines and 5-hydroxytryptamine can under certain conditions be converted to highly fluorescent 6,7 - dihydroxy - 3,4 - dihydroisoquinolines and 6-hydroxy-3,4-dihydro-β-carboline respectively, and that this can be used as a highly sensitive and specific method for the histochemical demonstration of the monoamines at the cellular level. In the present paper it is shown that the fluorescent compounds are very readily reduced by sodium borohydride to the corresponding, non-fluorescent 1,2,3,4-tetrahydro-compounds—even if they are present in a non-extractable state in dried serum albumin spots or in tissue sections—and that the fluorescence can be regenerate by renewed formaldehyde treatment. The non-specific fluorescence (e. g. autofluorescence) in tissue sections was never observed to undergo any changes on borohydride treatment. On the basis of these findings a very simple histochemical test has been worked out to check directly in the tissue section whether or not an observed fluorescence is due to the presence of the reacting monoamines.

Minor tranquillizers, stress and central catecholamine neurons.

Abstract The effects of chlordiazepoxide, diazepam and nitrazepam on central DA and NA neurons of non-stressed and stressed rats were studied using histochemical and biochemical analysis of DA and NA. Estimations of DA and NA turnover in various regions of the brain were obtained by studying the decrease in stored DA and NA following treatment with a tyrosine hydroxylase inhibitor (H44/68) or a DA-β-hydroxylase inhibitor (FLA63). Stress was induced by immobilization. (1) Stress increased NA turnover in all parts of the brain and the spinal cord. By biochemical methods it was shown that DA turnover in the telencephalon was significantly reduced. (2) By histochemical methods it was shown that chlordiazepoxide and diazepam decreased NA turnover in the cortex cerebri and cortex cerebelli and the hippocampal formation but did not do so to any significant extent in the hypothalamus or the lower brain stem. These results show that the benzodiazepine derivatives decrease the impulse activity in the NA neurons of the locus coeruleus which innervate all cortices of the brain. (3) Chlordiazepoxide and diazepam caused a small but significant decrease in DA turnover in ascending DA neurons to the neostriatum and the limbic forebrain indicating reduced impulse flow in these neurons. (4) Chlordiazepoxide, diazepam and nitrazepam caused a blockade of the stress-induced activation of NA neurons by decreasing nervous activity in these neurons. (5) Chlordiazepoxide and diazepam potentiated the stress-induced decrease in nervous activity in ascending DA neurons. Stress combined with these drugs therefore decreased DA turnover in the telencephalon in comparison with normal controls. In view of the role which the central NA and DA neurons probably play in behavioral and EEG arousal it seems that the decrease in nervous activity in DA and NA neurons produced by chlordiazepoxide and diazepam may be responsible for part of the pharmacological effects of these tranquillizers such as sedation and EEG slowing.

Evidence for a central 5-hydroxytryptamine receptor stimulation by lysergic acid diethylamide

1 Lysergic acid diethylamide (LSD) and the 5‐hydroxytryptamine (5‐HT) precursor, 5‐hydroxytryptophan produced similar functional effects in rat spinal cord and brain to the 5‐hydroxytryptamine precursor 5‐hydroxytryptophan, which indicates that LSD stimulates central 5‐HT receptors. 2 By means of combined histochemical and biochemical techniques it was found that LSD reduced the turnover rate of brain and spinal cord 5‐HT, studied after inhibition of the tryptophan hydroxylase by α‐propyldopacet‐amide. The turnover of brain noradrenaline but not dopamine was somewhat accelerated. 3 The functional and chemical effects by LSD were related to dose and to time. They were not observed after the LSD analogues 2‐bromo‐LSD and methysergide. 4 The retardation of the 5‐HT turnover by LSD may be due to negative feed‐back mechanisms evoked by direct stimulation of the central 5‐HT receptors.

Effects of tyrosine hydroxylase inhibition on the amine levels of central monoamine neurons

Abstract As shown by both histochemical and biochemical methods, the methyl ester of α-methyl- p -tyrosine (H 44/68, 500 mg/kg i.p.), an inhibitor of the tyrosine hydroxylase, causes the catecholamines but not the 5-hydroxytryptamine in rat brain and spinal cord to disappear almost completely in 24 hours. There were no significant differences between the various regions in rate and degree of the depletion of the terminals and cell bodies. After transection the loss of noradrenaline from the spinal cord was prevented below but not above the lesion showing the importance of the impulse flow for the disappearance of the transmitter. A marked recovery was seen in all terminals and cell bodies after 48 hours. The reappearance was somewhat faster in the cell bodies suggesting that the tyrosine hydroxylase is formed in them.

Studies on central and peripheral noradrenaline neurons using a new dopamine-β-hydroxylase inhibitor

Abstract The effects of a new dopamine-β-hydroxylase inhibitor, FLA63, have been studied on central and peripheral noradrenaline (NA) neurons using histochemical and biochemical analysis of monoamines. FLA63 caused a rapid and selective depletion of central NA stores without affecting dopamine (DA) and 5-hydroxytryptamine (5-HT) stores. The histochemical findings indicated that practically all the NA cell bodies in the lower brain stem were localized to the medulla oblongata and pons whereas the DA cell bodies were localized to the mesencephalon. FLA63 induced NA depletion was nerve impulse dependent. NA formation from dopa was markedly blocked by FLA63 treatment. The results with dopa suggest that DA cannot accumulate in high amounts in the NA storage granules. The in vitro studies showed neither NA uptake blocking activity nor any inhibitory effects on monoamine oxidase activity by FLA63. Studies on cold stress and FLA63 indicated that central NA neurons were not of critical importance in thermoregulation.

The effect of immobilization stress on the activity of central monoamine neurons.

Abstract With the help of inhibitors of the amine synthesis and chemical determinations of DA, NA and 5-HT it has been possible to obtain good evidence that there is a specific activation of the various NA nerve terminal systems of the brain and the spinal cord under the influence of immobilization stress.