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The ribonucleic acid (RNA) base percentages were estimated in the hypothalamus, amygdala, hippocampus, frontal cortex, cerebellum and spinal cord of adult intact female rabbits, and after ovariectomy followed by replacement therapy with oestradiol-17\g=b\,progesterone and oestradiol plus progesterone. The results indicate a lack of effect on the spinal cord, but a variable effect on all other brain regions examined. In response to the various treatments, all regions examined produced RNA very rich in guanosine monophosphate indicating synthesis of specific RNA. The hypothalamus showed the most significant overall changes. Progesterone injections resulted in the most persistent effects of the hormonal treatments employed. Hypotheses are proposed to explain the variable hormonal effects on brain RNA base composition. It is suggested that ovarian hormones produce specific molecular changes in nervous tissue related either to 'receptors' for the hormones or to neural functions related to behavioural phenomena which are mediated by these hormones.

Bilateral lesions produced by electrocoagulation in the basolateral and medial amygdaloid nuclei, subtotal amygdalectomy as well as implants of actinomycin D and cholesterol were all found to have profound effects on brain ribonucleic acid (RNA) base percentages and ratios. The most consistent effect was that on the pituitary and was produced by all treatments. Generally, the hypothalamus and frontal cortex showed varying effects due to the treatments, but the cerebellum uniformly showed no responses to the various treatments. Lesions placed in the medial amygdaloid complex and subtotal amygdalectomy had the greatest effect in changing the RNA base ratio. The bases adenosine monophosphate (AMP), cytidine monophosphate (CMP), guanosine monophosphate (GMP), and uridine monophosphate (UMP) were found to be the most affected. The newly synthesized RNA was found to be rich in UMP and deficient in AMP and CMP when compared to normal animal brain tissue. The assumption is made that lesions in the amygdala bring about an activation or stimulation of a genomic nature to produce specific RNA for a particular neural function.

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that lesions placed in the basolateral amygdaloid nuclear complex result in continuous release of luteinizing hormone (LH) from the hypophysis of the male and female deermouse. These changes in LH are accompanied by low levels of hypothalamic LH-releasing factor (Eleftheriou, 1967).The mechanism by which lesions in the amygdaloid complex affect changes in the hypophysial and plasma LH as well as in that of hypothalamic LH-RF is not established. The present report deals with the effects of lesions placed in the basolateral amygdala on the content of hypothalamic follicular-stimulating hormonereleasing factor (FSH-RF) in the female deermouse (Peromyscus maniculatus bairdii).Adult female deermice, weighing 15\p=n-\19 g., were lesioned bilaterally by thermocoagulation in the basolateral nuclear group of the amygdala according to the stereotaxic atlas for the species described previously (Eleftheriou & Zolovick, 1965;).Groups of 14 females each were killed 1, 2 and 3 weeks after the lesions had been produced. Two similar groups of sham-operated females were killed 1 and 2 weeks after the operation. In addition three similar groups were each killed at the dioestrous, pro-oestrous and oestrous stages of the cycle. The position of the lesions was confirmed by histological examination. Light and diet were not altered during the experiment and the body weight of operated animals did not change significantly.After the animals had been killed, the stalk-median eminence region and the adjacent ventral hypothalamus were dissected out (3-5 mg.) and pooled for each group of two animals. The pooled tissue was extracted according to Igarashi & McCann (19646). The extract was injected into male donor rats of the Holtzman strain (David, Fraschini & Martini, 1965) and the pituitary of each donor rat removed, weighed and homogenized in 0-9% NaCl solution (0-5 mg./0-l ml.). Extracts of control tissue (cortex) were also injected. The pituitaries were assayed for FSH content by the method of Igarashi & McCann (1964a). The recipient mice were females of the Charles-River (CD) strain, weighing 8-5-10-0 g. Pituitary preparations were injected as 0-5mg./0-l i.u. human chorionic gonadotrophin (HCG)/animal/day for 3 days. On the fourth day, the assay mice were killed, their uteri removed, cleaned