Effect of -hexachlorocyclohexane on metabolism and excretion of pentetrazol (cardiazol) in the rat

Immature rat convulsions and long-term effects on hippocampal cholinergic neurotransmission

Generalized tonic-clonic convulsions were induced on 2 consecutive days by pentylenetetrazol (PTZ) in immature rats (postnatal days 10 and 20), and hippocampal slices were prepared at different intervals post-injection. The anticholinesterase eserine provoked interictal-like discharges in the CA3 area of PTZ-injected rats (19/33), but not in controls (0/15), an effect mimicked by carbachol and reversed by atropine. This enhanced response to eserine was recorded in slices from 25-100% of the PTZ-injected rats, the percentage varying with the age at injection and post-injection interval. These results suggest that seizures in immature brain may have long-term consequences in cholinergic neurotransmission, converting a rise in endogenous ACh into an epileptogenic stimulus, which in turn would presumably facilitate the recurrence of seizures.

Chronic and single administration of pentylenetetrazol modifies benzodiazepine receptor-binding: an autoradiographic study

Benzodiazepine (BDZ) receptor-binding changes in the rat brain induced by pentylenetetrazol (PTZ) were investigated by in vitro autoradiography. Our experiments revealed that a single PTZ administration produced BDZ-binding decrease in cingulate, frontal, temporal, parietal and piriform cortices; caudate putamen; medial, basolateral and cortical amygdaloid nuclei; medial, ventromedial and ventroposterior thalamic nuclei; substantia nigra pars compacta and periaqueductal gray. Fully kindled rats with chronic PTZ treatment showed reduced BDZ receptor-binding in cingulate, frontal, parietal and piriform cortices; caudate putamen; medial, ventromedial and ventroposterior thalamic nuclei; and periaqueductal gray. These effects resulted from decrease in the binding capacity. Our results support that PTZ-induced chemical kindling may be associated with significant changes of the GABAergic systems and BDZ-binding from the first administration.

Cysteamine normalizes cerebral somatostatin level and binding in pentylenetetrazol-kindled rats

Rats were kindled by intraperitoneal injection of pentylenetetrazol (PTZ) (30 mg/Kg) every 48 h. Once kindled, some of the animals received a single injection of cysteamine (200 mg/Kg). Somatostatin-like immunoreactivity (SLI) and 125 I-Tyr11-somatostatin binding were measured in the frontoparietal cortex and hippocampus of the two experimental groups and the control rats. After PTZ kindling the following was observed: 1) SLI content was increased in the two areas; 2) Somatostatin receptor affinity decreased in the frontoparietal cortex and was unaltered in the hippocampus; 3) The number of somatostatin receptors decreased in the hippocampus and was unaltered in the frontoparietal cortex. Cysteamine, an agent which depletes brain somatostatin and suppresses kindled seizures in PTZ-treated rats, reversed the altered SLI levels and binding in these rats.

Somatostatin-like immunoreactivity and somatostatin receptor binding in rat brain in pentylenetetrazol-induced kindling

Kindling was induced in Sprague-Dawley rats by repeated injection of pentylenetetrazol (PTZ, 30 mg/kg, IP). Somatostatin-like immunoreactivity (SLI) and 125I-Tyr-somatostatin binding were measured in different areas of the brain in saline-injected controls, rats receiving PTZ but not kindled (prekindled rats), and kindled rats. Compared to SLI levels in controls, SLI increased (p < 0.01) in the frontal cortex, striatum (p < 0.05 in kindled rats), and hippocampus of both prekindled and kindled animals. Hypothalamic levels of SLI remained unchanged. Compared with the controls, no change was found in somatostatin receptor binding in the frontal cortex, striatum or hippocampus in prekindled or kindled animals. These results suggest that an increased level of somatostatin may be connected to the development and maintenance of kindling.

Differential effects of gamma-hexachlorocyclohexane (lindane) on pharmacologically-induced seizures

Gamma-hexachlorocyclohexane (gamma-HCH), the active ingredient of the insecticide lindane, has been shown to decrease seizure threshold to pentylenetrazol (PTZ) 3 h after exposure to gamma-HCH and conversely increase threshold to PTZ-induced seizures 24 h after exposure to gamma-HCH (Vohland et al. 1981). In this study, the severity of response to other seizure-inducing agents was tested in mice 1 and 24 h after intraperitoneal administration of 80 mg/kg gamma-HCH. One hour after the administration of gamma-HCH, the activity of seizure-inducing agents was increased, regardless of their mechanism, while 24 h after gamma-HCH a differential response was observed. Seizure activity due to PTZ and picrotoxin (PTX) was significantly decreased; however, seizure activity due to 3-mercaptopropionic acid (MPA), bicuculline (BCC), methyl 6,7-dimethoxy-4-ethyl-B-carboline-3-carboxylate (DMCM), or strychnine (STR) was not different from control. In vitro, gamma-HCH, pentylenetetrazol and picrotoxin were shown to inhibit 3H-TBOB binding in mouse whole brain, with IC50 values of 4.6, 404 and 9.4 microM, respectively. MPA, BCC, DMCM, and STR showed no inhibition of 3H-TBOB (t-butyl bicyclo-orthobenzoate) binding at concentrations of 100 micron. The pharmacological challenge data suggest that tolerance may occur to seizure activity induced by PTZ and PTX 24 h after gamma-HCH, since the response to only these two seizure-inducing agents is decreased. The in vitro data suggest that the site responsible for the decrease in seizure activity 24 h after gamma-HCH may be the GABA-A receptor-linked chloride channel.

Decreased GABA, benzodiazepine, and picrotoxinin receptor binding in brains of rats after cobalt-induced epilepsy

In previous studies of experimental and human epilepsy, defects have been shown in the gamma-aminobutyric acid (GABA) receptors. We further investigated the role of the GABA/benzodiazepine/picrotoxinin receptor complex in the epileptic focus and also in other regions of the rat brain. The focus was induced by cobalt implantation to the right motor cortex, and the brains were dissected 16-19 days after the operation. Benzodiazepine (using [3H]flunitrazepam as a ligand; FLU), GABA [3H]muscimol; MUS), and picrotoxinin [( 35S]t-butylbicyclophosphorothionate; TBPS) receptor bindings were measured in different brain areas and the values were compared with glass-implanted controls. In the focal area, the specific receptor binding decreased in the order TBPS greater than FLU greater than MUS. In the perifocal area only TBPS binding decreased, and Scatchard analysis showed a decrease in the number of binding sites (p less than 0.05) without any effect on binding affinity. No change was seen in the binding characteristics of the other areas studied. According to our results, in cobalt-induced epilepsy the GABA/benzodiazepine/picrotoxinin receptor complex is modulated in the focal area; this may lead to a defect in chloride conductance, which in turn induces disturbed control of neuronal activity in the epileptic focus.

Effect of disulfiram in combination with L-tryptophan and lithium on pentylenetetrazol-induced seizure

Disulfiram prolonged the latency to clonic seizure caused by pentylenetetrazol (PTZ, 100 mg/kg SC). The effect of disulfiram was augmented by combination with tryptophan plus lithium, although neither tryptophan or lithium prolonged the latency to clonic seizure. The latency to tonic seizure was also prolonged in disulfiram-treated animals in parallel with the prolongation of the latency to clonic seizure. Lithium treatment completely prevented the incidence of tonic seizure, while this effect was cancelled in disulfiram-treated animals. Disulfiram acts on the clonic and tonic seizures in different ways.

[On the toxicology of carbromal. III. Role of active metabolites in humans acutely poisoned with carbromal-containing sedatives (author's transl)]

Carbromal is metabolized extensively in humans. The major metabolites known to date are bromoethylbutyramide, ethylbutyrylurea and inorganic bromide. After ingestion of a therapeutic dose of 1.0 g carbromal (4.2 mmoles) by four healthy volunteers highest concentrations in serum were found to be for carbromal 30 mumoles/l, for bromoethylbutyramide up to 20 mumoles/l and for ethylbutyrylurea 2--3 mumoles/l. In patients acutely poisoned by carbromal-containing sedatives serum concentrations measured were in the range of 200 mumoles/l carbromal, 350 mumoles/l bromoethylbutyramide and 50 mumoles/l ethylbutyrylurea. These patients were comatose, apneic, had isoelectric encephalographic records and decreased body temperature. The degree of central nervous depression as judged by clinical signs was found to correlate with the serum concentrations of carbromal and of bromoethylbutyramide. Pharmacological activity and acute toxicity of carbromal and its two metabolites were examined in rats and compared with the activity of phenobarbitone. For intraperitoneal injection LD-50 values were found to be for carbromal 1.8 mmoles/kg, for bromoethylbutyramide 1.5 mmoles/kg, for ethylbutyrylurea 5.0 mmoles/kg and for phenobarbitone 0.9 mmoles/kg. Carbromal and bromoethylbutyramide severely decreased body temperature. The relative narcotic activity was estimated to be for carbromal = 100; bromoethylbutyramide = 66; ethylbutyrylurea = 33; phenobarbitone = 100. The anticonvulsive activity against pentetrazol-induced generalized seizures was nearly identical for carbromal, bromoethylbutyramide and phenobarbitone. Anticonvulsant activity of ethylbutyrylurea was two to three times less than that of carbromal. Inorganic bromide was found to increase the narcotic activity of carbromal and of bromoethylbutyramide. The findings show that the clinical signs of central nervous system depression seen in patients acutely poisoned with carbromal are caused mainly by unchanged carbromal and by its metabolite bromoethylbutyramide.

Factors responsible for reduced pharmacological activity in rats of pentetrazol administered orally

It was the aim of this investigation to find out why pentetrazol (PTZ) administered orally to rats has considerably lower convulsive effectiveness than PTZ injected parenterally. It could be demonstrated that PTZ is distributed to and eliminated from all organs analyzed, without any sign of storage or of redistribution. Biological halftime was found to be about 3.5 h after subcutaneous injection. PTZ is absorbed slowly from the gastrointestinal tract because PTZ given orally is retained in the stomach for many hours. PTZ absorption is slow from the stomach while it is rapid from the small intestine. Food taken in before and after PTZ administration decreases the rate of PTZ absorption. Retention in the stomach of PTZ given orally is probably due to delayed gastric emptying since PTZ is able to reduce the basal tone and the acetylcholine-induced contractions of isolated preparations of the fundus of the stomach.