THE EFFECT OF HYPOTHALAMIC LESIONS ON LITTER GROWTH IN RATS

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Abstract
In order to investigate the hypothalamic control of lactation, bilateral electrolytic lesions were given stereotaxically in the hypothalamus of lactating rats.Lactational performance of these rats bearing hypothalamic lesions were estimated mainly by litter growth curves.The animals recovered quickly from the operation and were in good condition and they were divided into the following 2 groups on the basis of the location of the lesions: 1. animals with anterior hypothalamic lesions (Group A), 2. animals with lesions of the medial part of the hypothalami (Group M). Each group was classified into 2 subgroups according to their ability to rear their young. The regression coefficient of the growth curve of the litters of the animals which reared their young in both Groups A and M was significantly lower than those of the normal and sham operated groups.The litters, of the animals which failed to rear their young, lost their weight gradually and died within 7 days after the operation and no milk was found in their stomachs in spite of their vigorous suckling;however, milk could be squeezed from the mother's teats even 10 days after the operation.A lactational vaginal smear was obtained whenever suckling lasted, and after cessation of the suckling stimulus an oestrous smear reappeared within a few days.These findings imply the possibility of selective impairment of the part of the hypothalamus, which is linked to the secretion of oxytocin.

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