A simple screening method for antiparkinsonian drugs in mice

Effects of anti-Parkinsonian drugs on neurobehavioural changes induced by bilateral 6-hydroxydopamine lesions in rats

1. Effects of anti-Parkinsonian drugs on neurobehavioural changes induced by bilateral lesions of dopaminergic neurons were investigated in rats. 2. Dopaminergic neurons in rats were lesioned bilaterally by injection of 6-hydroxydopamine (6-OHDA; 8 micrograms) into the medial forebrain bundle at the level of the posterolateral hypothalamus. As a result, a decrease in locomotor activity and marked catalepsy and prolongation of grasping time were observed. 3. Levodopa, talipexole, bromocriptine and theophylline dose-dependently antagonized the decrease in locomotor activity induced by bilateral 6-OHDA lesions. These drugs also showed antagonistic effects on the appearance of catalepsy and prolongation of grasping time induced by bilateral 6-OHDA lesions. In contrast, trihexyphenidyl showed no antagonizing effect on the neurobehavioural changes induced by 6-OHDA lesions at any concentration tested. 4. Combined treatment with levodopa and talipexole antagonized the neurobehavioural changes induced by bilateral 6-OHDA lesions, whereas no marked changes were observed when either drug was administered separately. The same findings were noted with the simultaneous use of either levodopa (2 mg/kg) and theophylline (2 mg/kg) or talipexole (0.005 mg/kg) and theophylline (2 mg/kg). 5. These results indicate that this model may be useful for estimating the effects of drugs in the treatment of Parkinson's disease.

Prevention of physostigmine-induced lethality by the opioid analgesic meptazinol in the mouse

The prophylactic action of meptazinol against physostigmine- and neostigmine-induced lethality was evaluated in mice. Meptazinol proved to be effective against physostigmine (1 mg kg-1 i.p.), but not against neostigmine (0.5 mg kg-1 i.p.). The antagonism by meptazinol of physostigmine-induced poisoning was maximal when the drug was administered 15 min before physostigmine. Under these conditions the ED50 (95% confidence limits) of meptazinol was 24 (22.0-26.1) mg kg-1 s.c. A 30 mg kg-1 dose of the drug prevented lethality in 89% of the animals. The action of meptazinol was not antagonized by naloxone hydrochloride (2 mg kg-1 i.p.), injected 10 min before meptazinol. Pretreatment of mice with 30 mg kg-1 meptazinol 15 min before physostigmine (1 mg kg-1) poisoning increased brain acetylcholinesterase (AChE) activity on average, from 8 to 31% of control values. The protection of cholinesterases against physostigmine- and neostigmine-induced inactivation was demonstrated in vitro directly on purified preparations of the enzymes using a dilution method. The ED50 values (95% confidence limits) for the protective effect of meptazinol of electric eel AChE against 1 and 3 microM physostigmine and 1 microM neostigmine were 2.6 (1.4-4.9), 9.5 (5-18) and 3 (1.6-5.7) microM, respectively, while for protection of horse serum butyrylcholinesterase (BuChE) against the same inhibitors, the ED50 values were 12 (5.4-26.4), 42 (27-65.1) and 8 (3.6-17.6) microM, respectively. It is suggested that prevention of physostigmine-induced lethality by meptazinol is a consequence of its protective action on AChE in the central nervous system.

Anti-tremor action of C10Dichol, a peripheral acetylcholine synthesis inhibitor

1 Anti-tremor action of decamethylene bis-(hydroxyethyl)-dimethylammonium bromide (C10Dichol), a peripheral acetylcholine synthesis inhibitor, was investigated. 2 C10Dichol inhibited tremor induced by oxotremorine, nicotine and physostigmine and afforded partial protection from physostigmine-induced mortality in mice. 3 In non-paralysing doses, C10Dichol antagonized the neuromuscular effects of oxotremorine, nicotine and physostigmine. 4 Prior administration of C10Dichol failed to prevent tremor and neuromuscular paralysis induced by harmine and arecoline. 5 In the absence of any antimuscarinic property of C10Dichol, its neuromuscular effects appeared to be casually related to its anti-tremor action. 6 This study reveals a possibility for the development of peripherally acting anti-Parkinson drugs.

Peripheral and central muscarinic receptor affinity of psychotropic drugs

The muscarinic receptor affinity of 27 psychotropic and 5 anticholinergic substances was examined in 2 in-vivo and 2 in-vitro models. A highly significant correlation was obtained between the effect of all compounds examined on the atropine sensitive binding of 3H-PrBCM and the effect in the conventional guinea-pig ileum preparation. Antagonism of oxotremorine induced tremors in mice by anticholinergics and neuroleptics was also significantly correlated to the corresponding data obtained in the in-vitro tests. Due to very low potency in the physostigmine induced mortality test in mice too few ED50 values were obtained to perform statistical comparisons. It is concluded, that the conventional guinea-pig ileum model and the 3h-prBCM binding model are equally predictive as tests for antimuscarinic properties. When in-vivo anticholinergic data for neuroleptics are used it must be considered that a possible dopamine receptor blockade may diminish the antimuscarinic effect of the substance.

A new probe for heterogeneity in muscarinic receptors: 2-methyl-spiro-(1, 3-dioxolane-4, 3')-quinuclidine

The title compound (MSDQ) is a new muscarinic agonist related to 3-acetoxyquinuclidine (3-AcQ) but also of a highly rigid structure. In view of this, it may constitute a probe for the detection of heterogeneity among muscarinic receptors. Indeed, equipotent molar ratios (EPMR) for ACh, 3-AcQ and MSDQ were as follows: guinea pig ileum, 1 : 14 : 240; vasodepressor effect in the cat, 1 : 6 : 188. But EPMR for 3-AcQ and MSDQ as stimulants of the superior cervical ganglion in the cat were 1 : 1 and for the induction of tremors in mice, 9 : 5. No such subtle differences in receptor specificity were detected when the probe used was the 2, 2-diphenyl analogue (DiPSDQ) of MSDQ which was a powerful competitive antagonist in all systems, more potent than atropine, but with a CNS/PNS activity of 1.1 compared to 26 for atropine. In view of this, the use of potent antagonists as probes for muscarinic receptor heterogeneity is questionable.

Tremorine-oxotremorine-induced tremor, hypothermia and analgesia, and physostigmine toxicity, in mice after pretreatment with beta-adrenoceptor antagonists

The beta-adrenoceptor blockers propranolol, PhQA33 and LB-46 exhibited appreciable activity against tremorine-(TMN) and oxotremorine-(OTMN) induced tremor, whereas pronethalol, (+)-H56/28, (-)-H56/28, Kö-592 and L(+)-INPEA possessed weak action. The two beta-blockers, namely D,L(+/-)-INPEA and D(-)-INPEA acted as weak tremorgens. None of the above compounds suppressed the induced peripheral cholinergic phenomena; or possessed any central anticholinergic activity, as they were unable to afford protection against physostigmine-induced death. Propranolol, PhQA33 and LB-46 antagonized TMN-induced hypothermia and analgesia, but were inactive against OTMN-induced changes. A correlation of the beta-blocking and anti-tremor activity of these agents is unlikely.