Effect of L-DOPA on brain acetylcholine and choline in rats

D2 and D1 dopaminergic activity of 7-OH-DPAT

The D1 and D2 dopamine receptor agonist properties of 7-hydroxy-2-(N,N-di-n-propylamino) tetraline (7-OH-DPAT) was determined by investigating the effect of this compound on rat striatal acetylcholine (ACh) concentration and increase in cAMP formation in primary cerebellar granule cell cultures. 7-OH-DPAT at low doses (0.01 to 0.1 mumol/ kg) had no significant effect, and at high doses (0.3 to 30 mumol/kg) significantly (P < 0.01) increased striatal ACh levels. Likewise, quinpirole was found to significantly elevate ACh content. Pretreatment with haloperidol, a non-selective antagonist of the D2 family of receptors, significantly (P < 0.01) blocked 7-OH-DPAT- and quinpirole-induced increases in ACh. U-99194A, a D3 selective dopamine antagonist, had no significant effect on 7-OH-DPAT-induced increases in striatal ACh. However, raclopride, a D2 selective dopamine antagonist, completely blocked 7-OH-DPAT-induced elevations in ACh. 7-OH-DPAT in the mumolar range increased cAMP formation in granule cell cultures, and this effect was antagonized by SCH 23390, a D1 selective dopamine antagonist. The neurochemical study indicates that, at high doses, 7-OH-DPAT has both D1 and D2 agonist activities.

Drugs for Parkinson's disease reduce tremor induced by physostigmine

The effects of anticholinergic and dopaminergic drugs used for Parkinson's disease were studied on the tremor induced by physostigmine (0.3-3.0 mg/kg) in rats. For the measurement of tremor a new electronic device was employed. Atropine (0.3-1.2 mg/kg) and biperiden (0.01-1.0 mg/kg) reduced the physostigmine-induced tremor in a dose-related manner and could abolish it. Biperiden was less potent than atropine. Methylatropine in a dose of 1.2 mg/kg slightly inhibited the tremor. Amantadine (0.3-3.0 mg/kg) reduced the tremor but only to a certain degree. Bromocriptine (0.1-10.0 mg/kg) reduced it in a manner that was not dose-related. Pimozide potentiated the tremor in the dose of 0.2 mg/kg but not in larger doses. At the onset of the tremor, a small decrease in rectal temperature occurred. The hypothermia lasted significantly longer than the tremor. Neither the anticholinergic nor the dopaminergic anti-Parkinson drugs altered the hypothermic effect of physostigmine. The results show that those anti-Parkinson drugs, which act by increasing the dopaminergic activity can counteract the tremor induced by physostigmine. However, these drugs are clearly less active than th anticholinergic anti-Parkinson drugs.

Action of oxotremorine on the sub-cellular distribution of glycine in the rat spinal cord

Intraperitoneal (i.p.) injection of 250 micrograms/kg of oxotremorine (OT) caused a 50% decrease in the glycine content of the synaptosomal-mitochondrial fraction of spinal cord homogenates prepared from rats killed 15 min after treatment. The glycine content of the supernatant fraction was correspondingly raised. In synaptosomes isolated from the spinal cord of OT-treated rats, the decrease in glycine content was 30%. Prior administration of atropine, but not of methylatropine, abolished this effect of OT on synaptosomal glycine content. Eserine exerted a potentiating effect on the action of OT in lowering the glycine content of spinal synaptosomes. Prior administration of L-DOPA, apomorphine, haloperidol, muscarine or mecamylamine had no significant effect on the action of OT on synaptosomal glycine content. OT alone or in combination with eserine, and acetylcholine (ACh) in combination with eserine, did not alter the rate of release of glycine from spinal synaptosomes of untreated rats incubated under appropriate conditions. OT was also without effect on the rate of release of glycine from normal spinal synaptosomes subjected to electrical stimulation, as well as on the eventual glycine content of the synaptosomes. On the basis of the present findings it has been suggested that (i) glycine may be released from Renshaw cells at their synapses with motoneurones in response to the muscarinic action of OT; (ii) dopaminergic modulation may not be involved in the OT-induced glycine release from Renshaw cells; and (iii) excessive release of glycine onto motoneurones may be the causative factor of the akinesia observed in OT-induced experimental Parkinsonism.

Effect of hypnotic and anxiolytic agents on regional concentration of acetylcholine in rat brain

Pentobarbital (30 and 60 mg/kg) and chloral hydrate (300 and 600 mg/kg) administered in anesthetic/hypnotic doses produced significant increases in acetylcholine concentration in the cerebral cortex, striatum, hippocampus and brainstem. Hypnotic/anxiolytic agents like diazepam, flurazepam (100 mg/kg each) and triazolam (30 mg/kg) significantly increased the acetylcholine concentration only in the cerebral cortex and striatum. Alprazolam and ketazolam had no significant effect on regional distribution of acetylcholine in the brain. The results have been discussed with respect to the role of central cholinergic system in anesthetic and hypnotic actions of these drugs.

Cyclic GMP in the CSF of patients with schizophrenia before and after neuroleptic treatment

Cerebrospinal fluid (CSF) cyclic GMP may derive from central cholinergic neurotransmission. Measurement of CSF cyclic GMP may allow evaluation of possible implications of the dopaminergic hyperactivity in schizophrenia proposed by the dopamine hypothesis. The CSF cyclic GMP levels in 27 drug-free schizophrenic patients was measured and compared to that in 9 psychiatrically-healthy individuals. The mean CSF cyclic GMP level of the schizophrenic patients was 23 per cent lower than that of the control group, but this difference did not attain statistical significance. In addition the CSF cyclic GMP levels in a group of 10 schizophrenic patients were compared before and after 2 months of neuroleptic treatment. The mean level of cyclic GMP rose 50 per cent after treatment with phenothiazines (P less than 0.05). These results could indicate some tendency for decreased activity of central cholinergic neurons in schizophrenia as well as a restored dopaminergic-cholinergic balance after neuroleptic treatment.

Effect of anesthetic doses of gamma-hydroxybutyrate on the acetylcholine content of rat brain

Gamma-hydroxybutyrate administered in anesthetic doses produces a time dependent increase in the levels of rat barin acetylcholine. A maximal increase in whole brain and subcortical levels of acetylcholine is observed about 15 min after administration of the lactone form of the drug. A similar GHB-induced increase in acetylcholine is observed in the striatum and a 75% increase in the hippocampus 15 min after administration of the drug. A good temporal correlation was not obtained between the increase in acetylcholine and the depth of anesthesia produced by the drug. Gamma-hydroxybutyrate did not cause a significant change in the striatal or hippocampal levels of choline. Possible mechanisms involved in the production of this increase in acetylcholine are discussed.

Cholinergic-dopaminergic interaction in the striatum: the effect of 6-hydroxydopamine or pimozide treatment on the increased striatal acetylcholine levels induced by apomorphine, piribedil and d-amphetamine

Apomorphine (1 and 2 mg/kg), piribedil (15 and 60 mg/kg) and d-amphetamine (5 and 10 mg/kg) increased rat striatal acetylcholine levels without affecting choline. Pretreatment with pimozide (0.5 mg/kg) completely antagonized the effect of apomorphine and piribedil and by itself markedly decreased striatal acetylcholine levels. d-Amphetamine signigicantly antagonized the effect of pimozide. Nine days after pretreatment with 6-hydroxydopamine plus pargyline, striatal dopamine was decreased by 78% while acetylcholine and choline levels remained unaltered. Under these conditions, the effect of d-amphetamine was completely abolished while apomorphine and piribedil were just as active as in the vehicle-treated group. The results suggest that d-amphetamine acted indirectly to increase striatal acetylcholine levels probably through the release of dopamine and/or noradrenaline, while apomorphine and piribedil acted directly at dopamine receptor sites.

Effects of dopaminergic receptor agonists and antagonists on the activity of the neo-striatal cholinergic system

The effects of various neuroleptics and of apomorphine on the metabolism of ACh were examined in the neostriatum of the rat. For this purpose, a specific radio-enzymatic assay for brain ACh was used. This method is based on the preliminary purification of the choline esters by liquid cation exchange, separation of choline and ACh on thin layer chromatography plates, hydrolysis of ACh then reactylation of the choline moiety with a purified and stabilized rat brain choline acetyltransferase. The rat neostriatal ACh levels were decreased by neuroleptics of the phenothiazine and butyrophenone type and increased by apomorphine. An "in vivo" estimation of the rate of utilization of ACh was obtained by measuring the decline in neostriatal ACh content following the local microinjection of hemicholinium-3. This compound blocked almost totally the synthesis of ACh in these conditions. Chlorpromazine (15 mg/kg) enhanced neo-striatal ACh utilization and apomorphine (10 mg/kg) antagonized this effect. Neuroleptics did not effect ACh levels in the parietal cerebral cortex and the hippocampal formation. The modifications of the activity of neostriatal cholinergic neurons by chlorpromazine and apomorphine were still observed following the degeneration of the nigro-neostriatal dopaminergic fibers induced by the injection of 6-hydroxydopamine into the substantia nigra. The results strongly suggest that dopaminergic receptors as defined by their pharmacological interaction with neuroleptics and apomorphine are localized on neostriatal ACh neurons.