PHARMACOLOGICAL ASPECTS OF PARKINSONISM

Muscular rigidity and delineation of a dopamine-specific neostriatal subregion: tonic EMG activity in rats

In order to investigate the role of neostriatal dopamine receptors in muscular rigidity we have studied catalepsy and spontaneous muscle tone in rats receiving haloperidol injections into various parts of the neostriatum. It was found that low doses of haloperidol (250-750 ng/0.5 microliter) induced a tonic activity in the EMG of the gastrocnemius-soleus muscle when injected into the most rostral part of the neostriatum (A 8620-9650). This tonic EMG activity was found to be both dose-dependent and dopamine-specific: the haloperidol effect of 500 ng could be inhibited by 500 ng apomorphine. No muscular rigidity could be observed when haloperidol (500 ng/0.5 microliter) was injected further caudally into the neostriatum or into the medial part of the nucleus accumbens. With regard to the haloperidol-induced catalepsy as measured by means of the bar test, a similar distribution of effective and ineffective injection sites was observed; however, higher doses of haloperidol (1.5-2.5 micrograms/0.5 microliter) were required. Thus catalepsy and muscular rigidity were found to be closely related phenomena within the neostriatum. Finally, it is discussed how information relevant to tonic EMG activity is transmitted from the substantia nigra pars compacta to the superior colliculus and the ventromedial thalamus via the neostriatum and the substrate nigra pars reticulata.

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.

The production of an alternative laboratory model of the Parkinson syndrome using a new benzylimidoylurea derivative LON 954

N-carbamoyl-2-(2,6-dichlorophenyl) acetamidine hydrochloride (LON 954) causes a reproducible rest tremor in mice, of rapid onset and short duration with no associated rigidity or akinesia and in the absence of any marked changes in body temperature or accompanying peripheral parasympathomimetic effects. This tremor can be antagonised by the dopamine receptor agonists L-Dopa, bromocriptine, nomifensine and piribedil, as well as by anticholinergic anti-Parkinson drugs having an inhibitory effect on dopamine uptake such as benapryzine and benztropine. In contrast, benzhexol, orphenadrine and amantadine had no effect. LON 954 appears to be more specific than oxotremorine for the detection of drugs having therapeutic potential in the treatment of Parkinson's disease, particularly those exerting their effect through dopaminergic systems. An antagonist (BS 100-141), which is a structural isomer of LON 954, is also described.

Histochemical characterization of the monoamine-containing cells of the adenohypophysis in the Chinese quail

The demonstration of biogenic amine-containing cell is classically performed by means of the formaldehyde-induced fluorescence technique after administration of the monoamine precursors, L-dopa or 5-hydroxytryptophan (5-HTP. The injection of these two two compounds rapidly leads to the formation of large amounts. The biochemical pathway evoked above is studied in the avian adenohypophysis by two different methods involving enzyme...

Effect of oxotremorine on the response of antidromically activated Renshaw cells in decerebrate cats

In intercollicular decerebrate cats, some of which were made spinal in addition, the effect of oxotremorine (intravenous injection, 10-30 mug/kg) was tested on antidromically activated Renshaw cells. Methylatropine premedication prevented the otherwise often fatal drop in blood pressure; ipsilateral dorsal roots L6-S1 and contralateral hindlimb nerves were cut to exclude segmental receptor interference. During supramaximal stimulation of ventral root L7 or the gastrocnemius nerves, an increase of activity ranging from 10-110% was observed. The drug occasionally evoked spontaneous discharges in Renshaw cells, or enhanced activity already present. Alpha motoneuron activity decreased in most cases. The interaction of oxotremorine with atropine and eserine was also investigated on Renshaw cells. Our results suggest that one of the effects of oxotremorine may be a disbalance between motor output and recurrent inhibition.

Potentiation of oxotremorine lethality by antihistamines

Antihistamines, representing the major chemical classes, administered intraperitoneally to mice in non-toxic doses potentiated the lethal effects of an LD10 dose (3·5 mg/kg) of oxotremorine in a dose related manner. Atropine and methylatropine were highly effective in blocking oxotremorine lethality alone and when it was potentiated by antihistamines. The antagonism by methylatropine suggests a peripheral site of toxicity. Antihistamines might enhance lethality by interfering with the inactivation of oxotremorine by liver microsomal drugs enzymes in a manner similar to SKF 525A.

Effects of drugs on tremor and increase in brain acetylcholine produced by oxotremorine in the rat

1. In rats the effect of drugs on oxotremorine tremor and oxotremorine-induced increase in brain acetylcholine has been investigated.2. Reserpine, (+/-)-alpha-methylmetatyrosine and diethyldithio-carbamic acid, drugs which have in common the ability to decrease tissue noradrenaline concentration, inhibited oxotremorine tremor without preventing the oxotremorine-induced increase in brain acetylcholine.3. (+/-)-p-chlorophenylalanine, a depletor of tissue 5-hydroxytryptamine, did not inhibit oxotremorine tremor.4. Phenoxybenzamine and propranolol inhibited oxotremorine tremor, and propranolol was without effect on oxotremorine-induced increase in brain acetylcholine.5. The toxicity of oxotremorine was increased by reserpine and phenoxybenzamine.6. The significance of these findings is discussed with regard to the mode of action of oxotremorine.

Rat brain amines, blood histamine and glucose levels in relationship to circadian changes in sleep induced by pentobarbitone sodium

1. The circadian patterns for onset and duration of sleep after the administration of a constant dose of pentobarbitone sodium have been measured in rats adapted to and maintained under a fixed illumination cycle. The relationship of these patterns to others for rectal temperature and motor activity as well as for noradrenaline (NA), 5-hydroxytryptamine (5-HT) and histamine in mid-brain and caudate nucleus, and histamine and glucose in blood serum, has been examined.2. The onset of sleep is longest and duration shortest during the phase of the illumination cycle when motor activity and rectal temperature are maximal. An inverse relationship for these parameters is found during the light phase of the illumination cycle.3. In untreated rats, mid-brain NA and histamine and caudate nucleus histamine levels are maximal and 5-HT minimal during the dark phase of the illumination cycle. An inverse relationship for these parameters is found during the light phase of the illumination cycle.4. Pentobarbitone sodium treatment significantly elevates mid-brain NA and histamine and caudate nucleus histamine levels during the dark phase of the illumination cycle. Although 5-HT levels are reduced over the entire circadian cycle this change is significant only during the light phase of the illumination cycle.5. Pentobarbitone sodium treatment reverses the circadian pattern for body temperature, producing a mirror image of the control pattern.6. The circadian pattern for blood serum histamine levels differs from the C.N.S. pattern for histamine. Peak levels occur at the end of the light phase of the illumination cycle. After pentobarbitone sodium these levels are reduced, although the circadian pattern is similar to the control.7. Circadian blood glucose patterns have bimodal peaks; a primary peak at the end of the dark phase, a secondary peak at the end of the light phase of the illumination cycle. Pentobarbitone sodium did not significantly alter the pattern. The relationship between this pattern and C.N.S. and peripheral histamine and catechol amines is discussed.