The relationships between the release of LHRH, β-endorphin (β-END) and noradrenaline (NA) from the hypothalamic infundibular nuclei/median eminence (NI/ME) during the periovulatory period in the ewe was studied. Neurohormone release was assayed in perfusates collected from the NI/ME via push-pull cannulae. LHRH concentrations in perfusates ranged from below detectable values (5 pg) to 50 pg and from 15 to 240 pg/20 min perfusate on the days of proestrus and estrus, respectively. β-END concentrations in perfusates ranged from 320 to 6,000 pg on the day of proestrus and fell to a range between 100 and 380 pg/20 min perfusate on the day of estrus. The NA content of perfusates ranged from an undetectable level to 0.9 × 10⁴ pg/perfusate during proestrus, and rose from 1.0 × 10⁴ to 6.6 × 10⁴ pg/perfusate shortly before the preovulatory release of LHRH and LH. On the basis of the present observations, the following sequence of events leading to the massive LH ovulatory surge in the sheep is suggested: (1) increased secretion of β-END in the NI/ME on the day of proestrus generates an increase in the releasable pool of LHRH through inhibition of LHRH release; (2) on the day of estrus a decreased release of β-END allows the expression of NA activity in the NI/ME and the augmentation of NA tone facilitates the release of newly accumulated LHRH; (3) the resultant intensified LHRH output with its significantly changing pattern of release triggers the preovulatory surge of LH.

L. CHOMICKA') and S. GARWACKI2) With 2 Figure3Summary. Two different stressors footshocking and immobilization applied for 3 days induced in sheep differential behavioural and hormonal responses in cortisol and prolactin secretion Immobilization drastically disturbed rumen motoric activity (significantly attenuated its contractions), caused loss of appetite and severe general depression. Footshocking did not induce any of these symptoms Immobilization induced 2-3 fold higher rise of plasma cortisol mesors on the days of stressing as compared to footshocking. On the poststressing days after footshocking as well as after immobilization plasma cortisol mesors fell to 50% of the prestimulatory values. The rise of plasma prolactin mesors in footshocked and in immobilized animals on the days of stressing was nearly of the same magnitude. However, a significant difference in the response of prolactin secretion between footshocked and immobilized animals occurred in the circadian rhythmicity of the hormone secretion. Footshocking induced circadian rhythmicity with characteristic acrophases, while immobilization did not induce the circadian pattern of prolactin secretion.An attempt of interpretation of the described phenomena has been undertaken.

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5-Hydroxytryptamine (serotonin, 5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were investigated in various regions of the brain on the day of normal and spontaneously prolonged dioestrus in the rat. The 5-HT/5-HIAA concentration ratio and 5-HT content were found to be higher in the medial-basal hypothalamus (MBH) and the fronto-parietal cerebral cortex (Bc), and lower in the preoptic-anterior hypothalamic area (PAHA), when dioestrus was prolonged. No significant difference was observed with 5-HT and 5-HIAA concentrations in the hippocampus (Hipp). It was concluded that there are significant alterations in 5-HT activity in the MBH, PAHA and the Bc when dioestrus is spontaneously prolonged.