A further study on the effect of physostigmine on memory in rats

Antiepileptic and antiamnesic effect of carbamazepine in experimental limbic epilepsy

Carbamazepine (20 mg/kg, 40 mg/kg or 60 mg/kg) given three times a day, has been demonstrated to have a significant anti-epileptic effect in rats with chronic limbic epilepsy induced by injecting tetanus toxin bilaterally into their hippocampi. This effect involved a reduction in the maximum number of fits occurring on one day, and with the highest dose, a significant reduction in the total number of fits. In a pilot experiment in which continuous EEG records were obtained throughout the syndrome, it appeared that the effect of carbamazepine was to reduce the proportion of EEG seizure discharges which lead to overt motor fits. With the higher drug dose plasma levels of carbamazepine were maintained around 2 micrograms/ml. This experimental epilepsy produces enduring deficits in the rats' memories for a light-discrimination task in a Y-maze learned before induction of epilepsy (8 weeks after initial learning). If the rats are dosed with carbamazepine during their epilepsy this memory deficit is abolished.

Time-dependent changes in the effects of cholinesterase inhibitors on shuttle-box avoidance

Physostigmine and neostigmine were compared for their effects on shuttle-box avoidance acquisition and retention. Physostigmine impaired acquisition at doses lower than neostigmine. Avoidance performance 1, 7, or 14 days after acquisition was impaired by the administration of 0.4 mg/kg physostigmine or an equimolar dose of neostigmine. The effects of lower doses of physostigmine, but not of neostigmine, were dependent upon the time of original training relative to drug administration and retesting. The results suggest that the peripheral effects of higher doses of cholinesterase inhibitors impair avoidance performance. The effects of lower doses of physostigmine on acquisition and the time-dependent effects on subsequent performance are probably due to the central actions of this drug.