Yoshiro Kohjimoto

Enhancement of [3H]dopamine release and its [3H]metabolites in rat striatum by nicotinic drugs

Recent evidence has identified directly muscarinic acetylcholine receptor (m-ACh R) and nicotinic acetylcholine receptor (n-ACh R) in the brain utilizing receptor binding assay. Several studies suggest that release of dopamine (DA) in the striatum is regulated by presynaptic receptors present on dopaminergic terminals. In the present study, the effects of cholinergic drugs on [3H]DA release were examined using micropunched tissue and synaptosomes obtained from rat striatum. ACh (5 x 10(-4) M) significantly increased spontaneous [3H]DA release, and the overflow was partially inhibited by D-tubocurarine (1 mM) but not atropine. Nicotine, lobeline, coniine and spartein, nicotinic agonists, significantly increased spontaneous and 25 mM K + evoked [3H]DA release almost in a dose-dependent manner. In contrast, oxotremorine (2 x 10(-4) M), muscarinic agonist, did not any change in [3H]DA efflux. Furthermore, the metabolites of [3H]DA were separated by column chromatography. The main metabolite of [3H]DA in the spontaneous release from rat striatal synaptosomes was [3H]DOPAC (3,4-dihydroxyphenylacetic acid). Lobeline (5 x 10(-5) M) accelerated the outflow of [3H]DOPAC and [3H]OMDA metabolites (O-methylated and deaminated metabolites). These results could give rise to the suggestion that there was n-ACh R on the dopaminergic nerve terminals in the striatum and n-ACh R might have related to a directly excitatory effect on the DA release.

Presynaptic modulation of the release of dopamine from striatal synaptosomes: Differences in the effects of high K+ stimulation, methamphetamine and nicotinic drugs

We examined the effects of nicotinic drugs on the metabolites of [3H]dopamine (DA) released from rat striatal synaptosomes in comparison with the effects of high K+ and methamphetamine stimulation. The pattern of outflow of [3H]DA and its metabolites induced by nicotine stimulants, acetylcholine (ACh), nicotine and lobeline, was different from that induced by high K+ and methamphetamine.

Properties and distribution of muscarinic cholinergic receptors in rat striatal micropunched tissue homogenates.

The properties of muscarinic receptors in rat striatal micropunched tissue homogenates were studied with a binding technique using [3H]quinuclidinyl benzilate (QNB) as ligand. Among the agonists, oxotremorine was the most potent inhibitor (ID50 value, 2.20 X 10(-5) M), followed by pilocarpine, acetylcholine, carbachol and bethanechol. No marked differences were found between the binding properties of QNB in the micropunched tissue homogenates and membrane fractions. Therefore, the detailed distribution of muscarinic receptors in the striatum was examined using the micropunched tissue homogenates. High levels of QNB binding in the striatum were found at dorso-lateral sites and low levels in the center regions of the striatum. The technique presented here for studying small regions of the striatum should be useful in further studies of the function of cholinergic neurons.

Apafant (a PAF receptor antagonist) suppresses the early and late airway responses in guinea pigs: A comparison with antiasthmatic drugs

We studied the effects of apafant (WEB 2086 BS), a specific and potent platelet activating factor (PAF) receptor antagonist, on the early and late airway responses in conscious and actively sensitized guinea pigs. An increase in airway resistance (Rs) was seen 1 min after the inhaled antigen challenge (early airway response), followed by another increase in Rs which peaked between 4 and 8 h after the provocation (late airway response). Oral administration of apafant as well as theophylline inhibited both early and late airway responses. Ozagrel, an inhibitor of thromboxane A2 synthetase, salbutamol, a beta2-adrenoceptor agonist, and dexamethasone significantly inhibited either the early or the late airway response only. Disodium cromoglycate inhibited neither the early nor the late airway response. The results showed that apafant inhibited both the early and late airway responses in sensitized guinea pigs and its effect was comparable or superior to that of anti-asthmatic drugs used clinically.

Studies on 125I-αbungarotoxin binding sites in rat brain

Abstract The distribution and properties of 125 I-αbungarotoxin ( 125 I-αBTX) binding in rat brain using micropunched tissue homogenates were examined with a binding technique. Highest level of 125 I-αBTX binding was observed in the hypothalamus, followed by hippocampus, cortex, globus pallidus, nucleus caudatus and nucleus accumbens. Although high levels of 3 H-quinuclidinyl benzilate ( 3 H-QNB) binding in the striatum were found at dorso-lateral sites and low levels in the central regions, the level of 125 I-αBTX binding within the striatum was almost equal. There was no significant correlation between 125 I-αBTX binding and choline uptake which could be useful as a marker for functional cholinergic nerve terminals. The inhibition of specific 125 I-αBTX binding to the hippocampal homogenates by nicotine, d-tubocurarine and other nicotinic drugs was studied. The results of these studies suggest that αBTX binding sites in the brain are not likely the binding sites of nicotine or the physiological ACh R sites.