Bradley / Costa Neuropharmacology

Studies of Narcotic Drugs
1. Auflage 2014
ISBN: 978-1-4831-4000-1
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 60 Seiten

Neuropharmacology is a collection of papers presented at a symposium of the XXVI International Congress of Physiological Sciences, held in New Delhi, India in 1974. Contributors focus on the neurochemical action of central analgesics and their biochemistry, particularly Viminol R2 and azidomorphine, based on evidence derived using neurohistochemical techniques. This text is comprised of six chapters; the first of which deals with cholinergic mechanisms in narcotic analgesics. This topic is followed by a discussion on the research on the effects of drugs such as morphine on the central nervous system using amine fluorescence histochemistry; the effect of dextromoramide and methadone on dopamine metabolism in comparison with haloperidol and amphetamine; and the use of pharmacological models to predict opiate dependence. A chapter is devoted to a pharmacological study of the in vivo increase in the cyclic AMP content of rat striatum and nucleus accumbens due to the action of amphetamine, apomorphine, opiates, and antipsychotic drugs, along with the effect of this change on dopamine receptors. This book will appeal to scientists representing all the major areas of pharmacology, including clinical pharmacology and toxicology, as well as to internists, psychiatrists, neurologists, and anesthesiologists.

Autoren/Hrsg.

Bradley, P. B.

Costa, E.

Leseproben

THE USE OF AMINE FLUORESCENCE HISTOCHEMISTRY IN THE STUDY OF DRUGS, ESPECIALLY MORPHINE, ON THE CNS

K. FUXE, L. AGNATI, P. BOLME, B.J. EVERITT, T. HÖKFELT, G. JONSSON, Å. LJUNGDAHL and A. LÖFSTRÖM,     Department of Histology, Karolinska Institutet, S-104 01 Stockholm, Sweden

Publisher Summary

This chapter discusses the use of amine fluorescence histochemistry in the study of drugs, especially morphine, on the central nervous system. With the introduction of the Falck-Hillarp technique, it became possible to demonstrate dopamine (DA), noradrenaline (NA), and 5-hydroxytryptamine (5-HT) in nerve cell bodies, axons, and terminals of the central nervous system. The method is based on the conversion of DA, NA, and 5-HT into intensely fluorescent compounds . Thus, these amines can be localized by fluorescence microscopy. Very early, it became evident that with this method it might be possible to study the action of drugs on discrete monoamine cell body and terminal systems in the central and peripheral nervous system. Recently, quantitative microfluorimetric studies have been performed on DA fluorescence in the nucleus caudatus, tuberculum olfactorium, and nucleus accumbens. A significant increase of DA turnover is observed in all these three areas, whereas no clear effect is seen in the DA nerve terminals of the median eminence. Also it has been found that morphine can block adrenaline receptors in a high dose and stimulate adrenaline receptors in a low dose. Thus, morphine can be described as a partial adrenaline agonist. In agreement with this hypothesis, morphine has been found to block Clonidine-induced hypotension and bradycardia and in this dose, it will itself cause hypotension and bradycardia just as clondine does. An adrenaline receptor stimulation in these doses of morphine could also explain why morphine in doses of 2–4 mg/kg causes an inhibition of spontaneous activity in the NA nerve cells of the locus coeruleus.

With the introduction of the Falck–Hillarp technique (FALCK, HILLARP, THIEME and TORP, 1962) it became possible to demonstrate dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) in nerve cell bodies, axons and terminals of the central nervous system. The method is based on the conversion of DA, NA and 5-HT into intensely fluorescent compounds Thus, these amines can be localized by fluorescence microscopy. Very early it became evident that with this method it might be possible to study the action of drugs on discrete monoamine cell body and terminal systems in the central and peripheral nervous system (see FUXE and HÖKFELT, 1971).

Together with microfluorimetric quantitation, fluorescence histochemistry offers the unique possibility of studying quantitatively drug actions on monoamine levels and turnover at their normal site of storage in the relatively intact tissue. So far, drugs, provided they are not analogues of monoamines or of their precursors, have not been found to interfere with the formaldehyde induced fluorescence (see FUXE and HÖKFELT, 1971). However, it must be emphasized that studies on the 5-HT terminal systems are hampered by the low sensitivity of the technique for 5-HT, which makes it impossible to detect many of the 5-HT terminals in the forebrain. 5-Hydroxytryptamine fluorescence also shows a rapid photodecomposition, which makes it necessary to control the intensity of the excitation light so that photodecomposition does not exceed 10% of the original value during the measurement procedure. Therefore, most of the amine fluorescence studies on drugs have been performed on the catecholamine neurone systems of the brain.

Microfluorimetric quantitation of catecholamines

These studies have mainly been performed on the diffuse DA fluorescence in various parts of the external layer of the median eminence (LÖFSTRÖM, JONSSON and FUXE, 1975a; LÖFSTRÖM, JONSSON, WIESEL and FUXE, 1975b), in the nucleus caudatus (EINARSSON, HALLMAN and JONSSON, 1975) and in the limbic forebrain (FUXE, AGNATI, TSUCHIYA, HÖKFELT, JOHANSSON, JONSSON, LIDBRINK, LÖFSTRÖM and UNGERSTEDT, 1975b; FUXE, AGNATI, HÖKFELT, JONSSON, LIDBRINK, LJUNGDAHL, LÖFSTRÖM and UNGERSTEDT, 1975a). These regions are easy to identify, and the field in which to measure the fluorescence intensity can be relatively large when working in the forebrain because the DA fluorescence distributes over large areas of tissues. In this way, a very weak DA fluorescence can also be discovered in these areas. Details concerning fluorescence intensity measurements are given in the paper of EINARSSON (1975). Briefly, the equipment consists of a Leitz microspectrofluorograph with a MPV system using a circular measuring field, which is adjusted to have a similar size as the excited area. Epiillumination from a mercury lamp with a TAL 405 (50% transmission at 405 nm) interference filter is used and an interference filter (TAL 480) with 50% transmission at 480 nm is used as secondary filter. The signal from the photomultiplier is fed into a digital voltmeter.

The specific fluorescence is given in arbitrary units and is calculated by subtracting the unspecific tissue fluorescence, which is obtained by measuring the fluorescence in adjacent areas lacking specific fluorescence. So far all DA fluorescence intensities have been found to be within the linear part of the DA concentration–fluorescence relationship as studied in agar-albumin model systems or in freeze-dried gelatin solutions containing various concentrations of DA. It is even possible to detect increases in DA levels above normal (EINARSSON , 1975). Using the tyrosine-hydroxylase inhibitor -methyltyrosine methylester (H 44/68) it was found that the DA fluorescence disappeared in an exponential manner from the various areas of the brain (Fig. 1). The turnover rates (2–3 hr) obtained in this way were found to be similar to those obtained using chemical-analytical determinations of DA (massfragmentographical analysis, KOSLOW, CATTABENI and COSTA, 1972; radioenzymatic assay, CUELLO, HILEY and IVERSEN, 1973) showing the validity of the quantitative microfluorimetric technique.

Fig. 1 Disappearance of catecholamine fluorescence in the medial palisade zone after tyrosine hydroxylase inhibition in normal (untreated) male rats. Common slope (5 experiments) was derived after analysis of covariance. Fluorescence intensity is represented on the ordinate, whereas the abscissa indicates time intervals after treatment with H44/68 (250 mg/kg, i.p.). The dots represent unadjusted means of fluorescence intensities obtained in individual animals (LÖFSTRÖM , 1974a).

In order to compensate for possible differences in the fluorescence yield from one brain piece to the other, protein models containing DA can be put into each brain piece before the histochemical procedure. In this way variability may be reduced. On the other hand, this type of a standard is not ideal, since DA in these models may probably react differently from the DA stored in the DA nerve terminals. Other types of standards should therefore be developed.

Using this technique it has been possible to show that acute treatment with neuroleptic drugs such as pimozide and haloperidol increase DA turnover in the caudatus, tuberculum olfactorium and nucleus accumbens but not in the median eminence (FUXE , 1975a, b; EINARSSON , 1975). Repeated doses of neuroleptics, however, cause a profound increase of DA turnover in the median eminence (FUXE , 1975a, b), probably due to the sustained hypersecretion of prolactin caused by these drugs, since prolactin increases DA turnover in the median eminence (HÖKFELT and FUXE, 1972). Clozapine, a novel antischizophrenic drug with few extrapyramidal side-effects, has only little effects on DA turnover in rat forebrain and increases DA turnover only in nucleus accumbens but only with a dose as high as 25 mg/kg (FUXE , 1975b). The only central NA nerve terminals studied so far with the quantitative microfluorimetric approach are those in the subependymal layer of the median eminence (LÖFSTRÖM , 1975b).

Recently, DA nerve terminals have been discovered in the limbic cortex (HÖKFELT, FUXE, JOHANSSON and LJUNGDAHL, 1974) by increasing the sensitivity of the Falck-Hillarp technique. In this modification of the technique, sections of unembedded tissue are made after glyoxylic acid...