Differential rearing affects responsiveness of rats to depressant and convulsant drugs

The effects of postweaning housing in environmental complexity (EC) or isolation cage (IC) conditions upon the development of anesthesia following sodium pentobarbital administration and upon seizure susceptibility following metrazol administration were studied in separate groups of rats. Male and female EC rats lost the righting reflex and developed unconsciousness more rapidly following sodium pentobarbital injection (105 mg/kg, IP) than did littermate IC rats. Male EC and IC rats did not differ in the CD50 (50% convulsion dosage by log probit analysis) following injection of a range of metrazol doses (20 to 35 mg/kg, IP) when they were kept in a quiet dimly lighted room. However, the addition of stroboscopic light stimulation (1-100 Hz) to the above procedure (doses 17.5 to 30 mg/kg) reduced the CD50 for the IC rats but did not affect the CD50 for the EC rats. The results support the view that brain excitability is lower in animals reared in environments providing higher levels of sensory stimulation.