Effects of neonatal destruction of the medial forebrain bundle in the cat: Long-term disturbances in learning ability, response to amphetamine challenge, and reactivity to auditory stimuli

Abstract

These experiments ascertain some of the long-term behavioral effects of neonatal medial forebrain bundle (MFB) lesions in the cat. Bilateral electrolytic lesions ( N = 27) were made when the animals were 11 to 22 days of age. The long-term behavioral development of cats with these lesions were compared with that of a group of intact littermates ( N = 37) and a group of littermates that received lesions that did not encroach upon the MFB. When the animals were 18 to 40 days of age they were tested in a spatial discrimination. Animals with bilateral MFB lesions were capable of learning the discrimination but made more repeated errors than animals in the other groups. This effect was compensated for with additional training. When tested on a visual discrimination at 3 to 4 months of age, kittens with MFB lesions learned the discrimination in a normal manner. When the discrimination cues were reversed, however, they responded more frequently to the previously reinforced cue. The effects of d-amphetamine were assessed when animals were 7 to 12 months of age. Animals with bilateral MFB lesions displayed less frequent and intense head movement stereotypies and more locomotor responses to amphetamine than animals in other groups. The reactivity to a series of auditory stimuli was assessed when the animals were 1 to 2 years of age. Neonatal MFB lesions produced an impaired pattern of habituation of reactivity to auditory stimuli. Cats with these lesions responded normally to the initial presentations of the vocalizations. However, 24 h later they responded to the stimuli more vigorously than animals in the other groups. Taken together the results of this experiment and the previous report indicate that some effects of neonatal MFB damage were qualitatively different from those of lesions inflicted in mature animals and that a complex interaction among a number of factors was probably responsible for these differences.