A canine model used to simultaneously assess potential neurobehavioural and cardiovascular effects of candidate drugs

INTRODUCTION

Unwanted effects of drugs on neurobehavioural and cardiovascular functions are normally assessed in separate studies and using different animals. A new model using dogs which allows for the integration of these assessments into a single study was established and validated, adopting the most sophisticated technologies for both monitoring behaviour by video recordings and cardiovascular parameters by telemetry.

METHODS

Conscious male beagle dogs (n=4) were given single oral doses of vehicle, and D-amphetamine (0.25, 0.75, 1.5 mg/kg) or acepromazine (0.05, 0.3, 2 mg/kg) within two different studies. Blood pressure, heart rate, electrocardiogram (EKG), body temperature, motor activity and behaviour (by video) were monitored continuously for 24 h post-dose. Animals underwent a full neurobehavioural examination the day before dosing, at the time to the maximal plasma concentration (Tmax) and 24 h post-dose.

RESULTS

D-Amphetamine: a dose-dependent increase in arterial blood pressure was noted at all doses and was generally associated with an increase in the QA interval, an index of cardiac contractility. Heart rate also increased but only at the 1.5 mg/kg dose. A dose-dependent general excitatory state of the nervous system was observed, characterised mainly by hyper-reactivity, and stereotyped activities. Acepromazine: a decrease in systolic blood pressure was detected at 0.3 and 2 mg/kg generally associated with a decrease in pulse pressure reflecting a negative inotropic effect. A dose-related increase in heart rate accompanied this effect. Dose-dependent general depression of the nervous system was noted; mainly characterised by half-closed eyes, subdued behaviour and impaired posture. In both studies, all dogs completely recovered at approximately 16 h after treatment.

DISCUSSION

Cardiovascular and neurobehavioural changes expected from the pharmacology of test substances were accurately detected. No significant fluctuations of the telemetric parameters recorded were noted as a consequence of the handling associated with the direct neurobehavioural examination. These results confirm the validity of this combined model capable of providing a reliable neurobehavioural and cardiovascular assessment of drugs.

The brain matrix and multifocal brain damage following a single injection of ketamine in young adult rats: conspicuous changes in old age

Male rats were seized with lithium and pilocarpine and then injected within 30 min. with either acepromazine or ketamine. These rats as well as age-matched normal rats were observed daily for one year. The rats which had received the ketamine after the seizures were significantly heavier than either the normal rats or the other group of seized rats. The bulk of this increased weight was due to the marked increase in white, extremely dense adipose tissue. Compared to the acepromazine-treated rats, the ketamine-treated rats did not exhibit spontaneous seizures and exhibited cerebral widths comparable to normal rats. These results suggest that the multifocal, graded neuronal loss associated with this seizure model may allow other "configurations" to emerge that can support normal behaviors as well as new characteristics.

Optimization of intraperitoneal injection anesthesia in mice: drugs, dosages, adverse effects, and anesthesia depth

PURPOSE

The goals of the study were to find a safe intraperitoneal injection anesthesia protocol for medium-duration surgery in mice (e.g., embryo transfer/vasectomy) coupled with a simple method to assess anesthesia depth under routine laboratory conditions.

METHODS

Eight anesthetic protocols consisting of combinations of dissociative anesthetics (ketamine, tiletamine), alpha2-agonists (xylazine, medetomidine), and/or sedatives (acepromazine, azaperone, zolazepam) were compared for their safety and efficacy (death rate, surgical tolerance), using observations and reflex tests. The four best protocols were further evaluated during vasectomy: physiologic measurements (respiratory rate, electrocardiogram, arterial blood pressure, body temperature, blood gas tensions, and acid-base balance) were used to characterize the quality of anesthesia. The reactions of physiologic parameters to surgical stimuli were used to determine anesthesia depth, and were correlated with reflex test results.

RESULTS

The protocol with the highest safety margin and the longest time of surgical tolerance (54 min) was ketamine/ xylazine/acepromazine. Three further anesthetic combinations were associated with surgical tolerance: ketamine/ xylazine, ketamine/xylazinelazaperone, and tiletamine/xylazine/zolazepam (Telazol/xylazine). The protocols consisting of ketamine/medetomidine and ketamine/azaperone were not associated with clearly detectable surgical tolerance. The most reliable parameter of surgical tolerance under routine laboratory conditions was the pedal withdrawal reflex.

CONCLUSIONS

The best intraperitoneal injection anesthesia regimen consisted of ketamine/xylazine/acepromazine. The dose must be adapted to the particulars of each experimental design (mouse strain, sex, age, mutation). This is best done by measuring surgical tolerance, using the pedal withdrawal reflex.

Pharmacodynamic interactions of cypermethrin and centrally acting drugs in mice

Cypermethrin a widely used insecticide of Pyrethroids (type II) group, was administered in mice at two dose levels (1/10 of LD50 i.e. 2.5 mg/kg and 1/5 of LD50 i.e. 5.0 mg/kg) and pharmacodynamic interactions of insecticide were studied with centrally acting drugs viz. pentobarbital sodium, amphetamine, pentylenetetrazole, acepromazine and analgin. Cypermethrin pretreatment potentiated the actions of pentobarbital and pentylene-tetrazole as evidenced by an increase in pentobarbital induced hypnosis and duration of pentylene-tetrazole induced chemoshock seizures. Tranquilizing action of acepromazine was potentiated but there was decrease in amphetamine influenced locomotor activity at both the dose levels. Cypermethrin pretreatment, however, did not have any pharmacodynamic interaction with analgin.