Melvin H. Van Woert

DDT myoclonus: Sites and mechanism of action

Intragastric injection of the insecticide DDT produces a stimulus-sensitive myoclonus in mice and rats. Unilateral stereotaxic infusions of DDT into rat medullary reticular formation also induced generalized myoclonus, identical to that produced by systemic administration. Similar myoclonus, but of lesser intensity, occurred when DDT was injected into cerebellar nuclei, red nucleus, and the inferior olive. Multiple other regions of the brain were resistant to the myoclonic action of locally infused DDT. Direct infusions into the medullary reticular formation of allethrin, which has a similar action on neuronal membranes as DDT, or the glycine receptor antagonist, strychnine, also elicited myoclonus.

Serotonin-norepinephrine interactions in the tremorolytic actions of phenoxybenzamine and trazodone.

Phenoxybenzamine (5 mg/kg IP) and trazodone (5 mg/kg IP) reduced tremors produced in mice by administration of oxotremorine (10 mg/kg), harmaline (80 mg/kg), catechol (60 mg/kg), kepone (200 mg/kg) and clonidine (100 mg/kg). Azapetine (10 mg/kg IP) in combination with L-5-hydroxytryptophan (50 mg/kg IP) reduced the tremor induced by oxotremorine, catechol, kepone and clonidine. In mice with lower thoracic spinal cord transection, phenoxybenzamine and trazodone reduced catechol-induced tremor above and below the site of transection. These findings suggest that an alpha noradrenergic-serotonergic neuronal balance in the spinal cord may modulate tremors of different etiologies.

Behavioral and biochemical actions of p-chlorophenylethylamine (p-CPEA) in mice.

Abstract p-chlorophenylethylamine (p-CPEA), a metabolite of p-chlorophenylalanine (p-CPA) induces the “serotonin syndrome” which consists of lateral head weaving, Straub tail, hindlimb abduction, tremor, hyperactivity, reciprocal fore-paw treading, salivation and piloerection. These p-CPEA-induced behavioral signs were partially prevented by pretreatment with serotonin (5-HT) uptake blockers (fluoxetine, chlorimipramine, Org 6582) and 5-HT receptor blockers (methiothepin, methysergide, cinnanserin) but not by two depletors of brain 5-HT (p-CPA, reserpine). p-CPEA (50 mg/kg) produces an initial decrease in 5-HT associated with a concurrent increase in 5-hydroxyindoleacetic acid with a maximum change at 30 minutes after injection; these early biochemical changes are prevented by pretreatment with fluoxetine (10 mg/kg). p-CPEA also competes with ( 3 H)-5-HT for 5-HT receptors. The reported paradoxical effects of p-CPA on several behavioral paradigms could be due to its decarboxylation to p-CPEA which may both stimulate 5-HT receptors and enhance 5-HT release.

Urea-induced myoclonus: Medullary glycine antagonism as mechanism of action

Stimulus sensitive myoclonus is a prominent symptom of uremia in both man and animals. Intravenous injection of urea into cats had been previously reported to produce spike and sharp wave electrical discharges in the medullary reticular formation which correlated with the myoclonic movements. In the present investigations, intraperitoneal injections of 2 g/kg urea every 15 minutes for 4 injections produced myoclonus in rats accompanied by brain urea concentrations of 6.8 X 10(-2)M, which is sevenfold higher than normal. 10(-2) and 10(-1) M urea significantly reduced 3H-strychnine binding to rat medulla membranes by 30% and 43% respectively. Urea inhibition of 3H-strychnine binding was reversible and binding kinetics revealed that 10(-1)M urea decreased Bmax by 65% with no effect on the affinity. Brain glycine levels did not change after urea injections and urea had no effect on synaptosomal uptake of 3H-glycine. Urea did not alter 3H-GABA, 3H-glutamate and 3H-QNB receptor binding but decreased 3H-diazepam receptor binding in the medulla. Mannitol also reduced 3H-diazepam binding but had no effect on 3H-strychnine binding. Stereotaxic injection of the glycine receptor antagonist, strychnine, into the rat medullary reticular formation produced myoclonus, whereas Ro 15-1788, a benzodiazepine antagonist, had no effect. Urea may produce myoclonus by blockade of glycine receptors in the medullary reticular formation.

Comparative effects of various serotonin releasing agents in mice.

Abstract Five serotonin (5-HT) releasers, p -chlorophenylethylamine ( p -Cl-PEA), p -methoxyphenyl-ethylamine ( p -CH 3 O-PEA), 4-methyl-alpha-ethyl-meta-tyramine (H75/12), fenfluramine and p -chloro-amphetamine ( p -CA) were compared as to their effects on mouse brain 5-HT metabolism. All 5-HT releasers had similar ed 50 values (0.34–0.70 μM) for tritiated 5-HT ([ 3 H]5-HT) release from brain synaptosomes. With the exception of H75/12, they had similar potencies for the production of the ‘serotonin syndrome,’ which probably reflect their in vivo 5-HT releasing actions. H75/12 was also the only 5-HT releaser that did not elevate brain tryptophan concentration. p -CH 3 -PEA and H75/12 did not have any long-term effects on brain 5-HT, 5-hydroxyindoleacetic acid (5-H1AA), or tryptophan hydroxylase activity, in contrast to the reported neurotoxic effects of p -CA and fenfluramine. p -Cl-PEA and p -CH 3 O-PEA were the only 5-HT releasers that increased brain 5-HT and 5-HIAA levels. Despite the structural similarities of these five 5-HT releasers, we have found considerable differences in their actions on brain 5-HT metabolism.

Effect of inferior olive lesion on seizure threshold in the rat

Cerebellar stimulation has been associated with anticonvulsant activity in several experimental seizure models. We examined the effect of destruction of cerebellar climbing fibers, by systemic administration of 3-acetylpyridine (3AP) or electrothermic lesion of the inferior olive, on seizures produced by various chemical convulsants in rats. We found that inferior olive lesioned rats had lower threshold to seizures induced by strychnine and brucine, both glycine antagonists. The dose response curve for strychnine seizure was shifted 2.5 times to the left in 3AP lesioned rats. No difference in seizure threshold was seen when picrotoxin, bicuculline or pentylenetetrazole PTZ) were used to produce seizures. Abnormal motor behavior (AMB) including myoclonus, backward movement and hyperextension, produced by all of the convulsants tested, was significantly aggravated in 3AP pretreated rats. The inferior olive-climbing fiber projection to the cerebellum appears to modulate seizures induced by inhibition of glycinergic neurotransmission.

Role of prostaglandins in the antimyoclonic action of clonazepam

Abstract Possible involvement of prostaglandins (PG) in the antimyoclonic action of clonazepam was examined in the p,p′-DDT-animal model of myoclonus. PG synthesis inhibitors and the PG antagonist polyphloretin phosphate (PPP) counteracted the antimyoclonic action of clonazepam in mice. PGE2 reduced DDT-induced myoclonus; this effect was blocked by PPP. Another antimyoclonic drug combination, L-5-hydroxytryptophan plus chlorimipramine, was not blocked by PPP or indomethacin. The antimyoclonic action of clonazepam may be mediated by enhancement of PG synthesis.

The effects of inferior olive lesion on strychnine seizure

Bilateral inferior olive lesions, produced by systemic administration of the neurotoxin 3-acetylpyridine (3AP) produce a proconvulsant state specific for strychnine-induced seizures and myoclonus. We have proposed that these phenomena are mediated through increased excitation of cerebellar Purkinje cells, through activation of glutamate receptors, in response to climbing fiber deafferentation. An increase in quisqualic acid (QA)-displaceable [3H]AMPA [(RS)-alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid] binding in cerebella from inferior olive-lesioned rats was observed, but no difference in [3H]AMPA binding displaced by glutamate, kainic acid (KA) or glutamate diethylester (GDEE) was seen. The excitatory amino acid antagonists GDEE and MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10 imine] were tested as anticonvulsants for strychnine-induced seizures in 3AP inferior olive-lesioned and control rats. Neither drug effected seizures in control rats, however, both GDEE and MK-801 produced a leftward shift in the strychnine-seizure dose-response curve in 3AP inferior olive-lesioned rats. GDEE also inhibited strychnine-induced myoclonus in the lesioned group, while MK-801 had no effect on myoclonus. The decreased threshold for strychnine-induced seizures and myoclonus in the 3AP-inferior olive-lesioned rats may be due to an increase in glutamate receptors as suggested by the [3H]AMPA binding data.

Strychnine seizure potentiation by azaspirodecanedione anxiolytics in rats

Buspirone, gepirone and ipsaperone administered intraperitoneally (40 mg/kg) to naive rats were found to be proconvulsive for strychnine-induced seizures. The dose of strychnine required to induce seizures in 50% of test animals (CD50) was 2.18 mg/kg in naive rats, while CD50s for rats treated with the azaspirodecanediones ipsaperone, gepirone and buspirone were 1.65, 0.97 and 0.70 mg/kg respectively. Azaspirodecanediones have high affinity for the 5-HT1A serotonin receptor, however, the specific 5-HT1A agonist, 8-hydroxy-2-(di-n-propyl-amino)-tetralin (8-OH-DPAT) had no effect on strychnine seizure in naive rats (CD50 = 2.0 mg/kg). The strychnine specific proconvulsive effects of inferior olive lesions and buspirone were additive, resulting in a CD50 of 0.1 mg/kg. This observation indicates that the buspirone-induced decrease in strychnine seizure threshold does not require intact inferior olive-climbing fiber pathways. Cerebellar sites for possible azaspirodecanedione action are discussed.