Sympathomimetic anesthetics

Metaphit-induced audiogenic seizure and its inhibition by MK-801: electroencephalographic and behavioral characterization

Adult male Wistar rats were subjected to intense sound stimulation from an electric bell (100 dB and 12 KHz for 60 s) after a single intraperitoneal (i.p. 50 mg/kg) injection of metaphit [1-(1-/3 isothiocyanatophenyl-cyclohexyl) piperidine]. EEG recordings demonstrated appearance of paroxysmal activity and spike-wave complexes from cortical electrodes, with frequency and amplitude increasing with time. Metaphit-induced audiogenic seizures in the rats were tested 24 h after metaphit administration. The seizures consisted of wild running followed by clonic and tonic convulsions, and the seizure pattern could be elicited at hourly intervals for the next 24 h in all tested animals. Forty-eight hours after metaphit administration, susceptibility to sound stimulation began to decrease gradually. The first component of seizure response to disappear was tonic extension, followed by disappearance of clonic convulsion; the last component to disappear was running behavior. Each behavioral seizure response had a characteristic EEG correlate. After approximately 50 h, no animal responded to sound stimulation. The noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptors, MK-801 [5-methyl-10,11-dihydro-5H-dibenzo (a,d) cyclohepten-5,10-imine maleate] was evaluated as an anticonvulsant against metaphit-induced audiogenic seizures in two experiments. In the first experiment, MK-801 was administered in a single dose of 0.5 mg/kg i.p. 23.5 h after metaphit injection and 30 min before sound stimulation, which completely blocked both the EEG and the behavioral response to sound stimulation for 37 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Electroencephalographic characteristics of audiogenic seizures induced in metaphit-treated small rodents

Adult male mice, rats, and guinea pigs were subjected to intense sound stimulation of an electric bell (100 dB, 12 kHz for 60 s) after a single intraperitoneal (i.p.) injection of metaphit (1-(1-(3 isothiocyanatophenyl)-cyclohexyl)piperidine) (50 mg/kg). When the animals were tested 24 h after administration of metaphit, audiogenic seizures were observed. None of the control saline-injected animals had convulsions. EEG recordings demonstrated the appearance of paroxysmal activity and spike-wave complexes in the trace from cortical and hippocampal electrodes, with frequency and amplitude increasing with time. Behaviorally, myoclonic jerks of facial muscles, ears, and neck appeared, but no correlation was noted between EEG and the motor phenomena. Auditory stimulation was necessary to elicit the full-blown sequence of seizure responses consisting of wild running followed by clonic and then tonic extension. At the time of seizures, repetitive high-amplitude spikes and waves appeared in the EEG, followed by profound EEG and behavioral depression. None of the animals died during or immediately after seizures. The seizure response to sound stimulation of mice, rats, and guinea pigs was phenomenologically similar, with minor differences in quantitative pattern of convulsive components, which suggests that all three animal species share the common property of extreme susceptibility to audiogenic stimulation caused by metaphit administration.

Potentiation of phencyclidine-induced stereotyped behaviors in rats by thiorphan and bestatin

We investigated the effects of thiorphan, a specific inhibitor of enkephalinase A and bestatin, a specific inhibitor of aminopeptidase, on the stereotyped behaviors induced by phencyclidine (PCP) in cannulated rats. The PCP-induced turning was significantly potentiated when thiorphan (50 micrograms) and bestatin (50 micrograms) were injected simultaneously into the rat lateral ventricle. The increase of PCP-induced turning was completely antagonized by the pretreatment with naloxone. Thiorphan (50 micrograms) or bestatin (50 micrograms) alone failed to potentiate PCP-induced turning. Thiorphan and/or bestatin did not affect significantly the PCP-induced head weaving and back-pedalling except that thiorphan (50 micrograms) potentiated the PCP-induced head weaving 15-18 min after the PCP injection. The combination of thiorphan and bestatin alone did not induce any behavioral change. These results suggest that thiorphan and bestatin produce an increase of endogenous enkephalins and that as a result, PCP-induced turning may be enhanced.

Quantitative electrocortical changes in the rat induced by phencyclidine and other stimulants

An automated technique for the continuous analysis of different frequency bands of the electrocorticogram (ECoG) of the rat has been used to quantify the actions of phencyclidine (PCP) and various other stimulant drugs. It has been demonstrated that phencyclidine, etoxadrol and LY154045 produced similar changes in the individual frequency bands whereas amphetamine and apomorphine had different profiles of activity. The phencyclidine-like compounds exhibited extremely strong stimulation of the ECoG with very large increases recorded in high frequency (15-50 Hz) activity and reductions in all other frequency bands. Various compounds have been used in an attempt to antagonise the changes in the ECoG. Chlorpromazine caused a slight shift in the dose-response curves as did chlordiazepoxide when used with phencyclidine. The GABA agonists, THIP and muscimol, had no effect on the stimulation of the ECoG. In contrast another presumed GABA agonist, baclofen, proved to be the most effective agent for blocking the stimulation induced by phencyclidine. The role of the GABAB receptor in the action of phencyclidine is discussed.

Ketamine Induced Anesthesia in Hemorrhagic Shock and Increased Intracranial Pressure

In a considerable number of cases, many polytraumatized patients in a state of hemorrhagic shock, who require immediate surgical treatment, there is craniocerebral trauma. Ketamine is viewed, on one hand, as an appropriate induction anesthetic, due to its circulatory stimulating effect in treating shock victims, and, on the other hand, it is rejected for treating patients with craniocerebral injuries, because of the danger of possible increase in intracranial pressure (ICP). Therefore, we examined the effects of ketamine on ICP and calculated the cerebral perfusion pressure, using test animals in a state of hemorrhagic shock and a space occupying intracranial process.

Anesthetic and analgesic considerations in the experimental animal

Many new compounds and combinations of many of the more traditional drugs have been used in a wide range of species. This, plus the rapid development in equipment for inhalational anesthesia, has simplified the restraint, anesthetic, post-surgical, and analgesic management of experimental animals.

Acute and chronic phencyclidine effects on locomotor activity, stereotypy and ataxia in rats

Behavioral rating scales, developed to measure phencyclidine (PCP)-induced stereotypy and ataxia in rats, were tested using acute dose-response and chronic paradigms with concomitant assessment of locomotor activity by automated counters. Also, effects of chronic PCP on apomorphine-induced stereotypy were assessed as a test of dopamine supersensitivity. A linear dose-response effect was found for measures of all three behaviors through moderate dose levels (2-6 mg/kg), but only ataxia ratings continued to increase, showing a linear relationship through the higher (8 and 10 mg/kg) doses. Chronic daily PCP administration showed progressive augmentation of stereotypy, tolerance to ataxia at 10 min post-injection, and a biphasic increase followed by decrease to day 1 levels in locomotor activity over 14 days. No significant change was found in apomorphine stereotypy following chronic PCP treatment. The chronic behavioral changes demonstrated in this study may provide a model of PCP-induced psychological and cognitive changes seen following chronic usage in man.

Emergency management of acute phencyclidine intoxication

Phencyclidine (PCP) is a potent sympathomimetic and hallucinogenic dissociative anesthetic agent. As an abused street drug, it is most often smoked, thus allowing the user to titrate the dose. The clinical signs of PCP intoxication can be viewed in three dose-related stages, but waxing and waning of signs through the three stages is not uncommon. Treatment protocols for each stage address drug therapy and both clinical and psychological supportive measures.

Phencyclidine deaths

The potential for a pharmacologic "overdose" and the cause of death associated with phencyclidine abuse is discussed. Nineteen deaths associated exclusively with phencyclidine intoxication have been documented. In 13 cases the immediate cause of death was asphyxia by drowning or trauma with lower levels of phencyclidine present suggesting behavioral toxicity. In two cases, the presence of phencyclidine in high concentrations constituted the only finding, and the probable cause of death was primary respiratory depression accompanied by seizure activity. A secondary drug effect or concurrent disease process may have contributed to the death of the remaining four individuals.