Release from brain tissue of compounds with possible transmitter function: interaction of drugs with these substances

Contributions to the field of neurotransmitters by Japanese scientists, and reflections on my own research

PART I DESCRIBES IMPORTANT CONTRIBUTIONS MADE BY SOME JAPANESE PIONEERS IN THE FIELD OF NEUROTRANSMITTERS: (their achievements in parentheses) J. Takamine (isolation and crystallization of adrenaline); K. Shimidzu (early hint for acetylcholine as a neurotransmitter); F. Kanematsu (donation of the Kanematsu Memorial Institute in Sydney); T. Hayashi (discovery of the excitatory action of glutamate and the inhibitory action of GABA); and I. Sano (discovery of a high concentration of dopamine in striatum, its reduction in a patient with Parkinson's disease and the treatment with DOPA). In Part II, I present some of my reflections on my research on neurotransmitters. The work of my colleagues and myself has made some significant contributions to the establishment of neurotransmitter roles played by GABA and substance P, the first amino acid and the first peptide neurotransmitters, respectively. By the early 1960s, 3 substances, i.e., acetylcholine, noradrenaline, and adrenaline, had been established as neurotransmitters. Now the number of neurotransmitters is believed to be as many as 50 or even more mainly due to the inclusion of several amino acids and a large number of peptide transmitters.

Acetylcholine

This article traces the development of knowledge about the physiology and pharmacology of acetylcholine and its receptors between 1930 and 2005, with emphasis on contributions by members of the British Pharmacological Society, and by other British pharmacologists and physiologists.

Drug effects on the release of endogenous acetylcholine in vivo: measurement by intracerebral dialysis and gas chromatography-mass spectrometry

Intracerebral microdialysis was combined with a sensitive and specific gas chromatographic-mass spectrometric assay to measure the release of endogenous acetylcholine in the rat striatum in vivo. In rats anesthetized with urethane (1.2 g/kg i.p.), the levels of striatal acetylcholine dialyzed into a Ringer's perfusate were: (a) reliably measurable only in the presence of physostigmine; (b) stable at between 3 and 8 h of perfusion (30-75 pmol/20 min in the presence of 75 microM physostigmine); (c) reduced by calcium-free Ringer's solution, tetrodotoxin (0.1 microM), and vesamicol (1.0 microM); and (d) increased by elevated potassium (100 mM), atropine (3-300 microM), and haloperidol (0.75 mg/kg i.p.). In conscious unrestrained rats, the spontaneous release of striatal acetylcholine was not altered significantly following the administration of urethane. The changes in acetylcholine release observed in this study are consistent with the known actions of some drugs or ionic conditions on striatal cholinergic neurotransmission and are evident under the condition of urethane anesthesia. The present results demonstrate the sensitivity and suitability of this method for monitoring endogenous striatal acetylcholine release in vivo.

Simultaneous determination of monoamine transmitters, precursors and metabolites in a single mouse brain

A simple and sensitive procedure for simultaneous determination of monoamine transmitters and related substances including precursors and metabolites has been developed for a single mouse brain. The proposed procedure involves (1) primary butanol extraction, (2) separation of the substances into either acid or alkaline aqueous layers according to their physicochemical properties, and (3) determination by means of high-performance liquid chromatography with electrochemical detection. Three transmitters (noradrenaline, dopamine and 5-hydroxytryptamine) and their precursors (tyrosine, 3,4-dihydroxyphenylalanine and tryptophan) and major metabolites (normethanephrine, 3-methoxy-4-hydroxyphenylethylene glycol, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylacetic acid and 5-hydroxyindoleacetic acid) were selectively separated and sensitively detected in mouse whole brain sample. Although 3-methoxy-4-hydroxymandelic acid was also separated from other substances by authentic chromatography, the substance was not detected in mouse brain. Changes in levels of these substances were examined for drugs whose effects had been previously confirmed. These changes reflected putative effects of the drugs and confirmed that the procedure is effective for neurochemical research into the transmitter system.

Evidence for dopaminergic vasodilator innervation of the canine paw pad

1 In chloralose-anaesthetized dogs pretreated with guanethidine and pancuronium, electrical stimulation (0.2 to 5 Hz) of the peripheral end of the cut tibial nerve caused a frequency-dependent increase in femoral blood flow which was restricted to the paw pads. 2 This neurogenic vasodilatation was not attenuated by atropine, mepyramine plus burimamide, indomethacin or propranolol. It was, however, attenuated in a dose-dependent manner by intra-arterial administration of the dopamine receptor antagonist, ergometrine (0.05 to 0.5 mg). 3 The effect of ergometrine could not be explained by non-specific effects on axonal conduction or transmission or by vasospasm of the blood vessels of the paw-pads. 4 In dogs with intact tibial nerves, a pharmacologically similar dilator response localized to the paw-pads could be elicited by electrical stimulation of loci in the ipsilateral diencephalon and midbrain. This response was not due to inhibition of adrenergic vasomotor tone and was abolished by systemic ganglion blockade or by tibial nerve section as well as by femoral arterial administration of ergometrine. 5 It is suggested that the vasculature of the canine paw pads is innervated by a population of autonomic axons which utilize dopamine or a related substance as a transmitter substance and activation of which causes vasodilation.

In vivo voltammetry: monitoring of dopamine metabolites in CSF following release by electrical stimulation

An in vivo electrochemical system which continuously records the concentration of metabolites of biogenic amines in small animal CSF is described. A small electrode, immersed in lateral ventricle CSF through a guide cannula, measures the amine metabolites by voltammetric oxidation. The detailed results of HVA release following electrical stimulation of the nigrostriatal pathway in rats are presented and compared with previous perfusion data. All the electrochemical results are verified by independent liquid chromatographic (chemical) analysis.

CYCLIC AMP/*SECRETl cyclic AMP into push-pull perfusates in freely moving rats

Cyclic AMP was found in perfusates of push-pull cannula's, chronically placed in the lateral ventricle of freely moving rats. After addition of norepinephrine, dopamine or adenosine to the perfusates the output of cyclic AMP was enhanced, whilst serotonin and histamine were found to be ineffective. The effects of noradrenaline and dopamine on cyclic AMP were found to be mediated by different receptors: haloperidol antagonized only the dopamine response. The effect of norepinephrine was mimicked by isoprenaline, a beta-adrenergic agonist, but was not blocked by propranolol. L-DOPA, given intraperitoneally, increased cyclic AMP levels in the perfusate. We conclude that the release of cyclic AMP into the extracellular medium is a normally occurring phenomenon in brain tissue.

The release of gamma-aminobutyric acid during inhibition in the cat visual cortex

1. The release of gamma-aminobutyric acid (GABA) from the surface of the posterior lateral gyrus of the cerebral cortex was measured by a sensitive enzymic fluorimetric assay procedure. Experiments were performed with anaesthetized cats during resting conditions and during cortical inhibition produced by electrical stimulation of the brain surface or of the lateral geniculate nucleus (l.g.n.).2. The average resting release of endogenous GABA was 0.20 n-mole/ 7 min.cm(2) cortex; this was increased during stimulation of both the cortical surface (2.9 times resting release during monopolar stimulation and 7.4 times resting release during bipolar stimulation) and the l.g.n. (5.7 times resting release).3. Removal of calcium ions from the collection fluid did not affect the resting release of endogenous GABA but prevented the increase in GABA release normally evoked by stimulation of the cortical surface.4. The stimulus parameters used to increase the release of GABA also inhibited the glutamate-induced firing of single cells in the visual cortex and this inhibition was abolished in the absence of calcium ions.5. In three experiments the total amino acid content of cortical samples was examined using an amino acid analyser. With the exception of GABA, there were no significant differences between the rates of release of any other detected amino acids during periods with and without electrical stimulation of the cortex.6. It is suggested that since the release of GABA observed during inhibitory stimulation of the cortex is calcium-dependent and specific, it may originate from inhibitory nerve terminals in the cortex. The present findings support the view that GABA is a central inhibitory neurotransmitter.