Corticosterone, prolactin, and growth hormone responses to 5 s of handling or 3 min of novel environment were compared in rats at crest and trough of the diurnal adrenal rhythm 0, 5, 15, 30, and 60 min after stimulation. All hormones responded to stimulation, corticosterone and prolactin with a dramatic rise, and growth hormone with a precipitous fall. Resting corticosterone levels evidenced the expected diurnal variation, and prolactin but not growth hormone also showed a baseline diurnal variation of small magnitude at the times studied. Growth hormone response characteristics were unaffected by time of day or type of stimulation. Both corticosterone and prolactin response profiles differed at both times of day and following both types of stimulation. Corticosterone and prolactin levels were highly correlated and each was negatively correlated with growth hormone levels. This study confirms that hormone responses to stress are complex and depend not only on the stimulus but the context of stimulation.

Chronic daily administration of melatonin (MT) can have potent effects on reproduction in the hamster. Various theories have been elaborated to explain these effects but little information has been available on circulating levels of MT following MT administration. We have examined the serum MT response in the male hamster to a single dose of 25 µg MT administered in the morning or in the afternoon – the same timing and dose used by others to produce reproductive effects. With both morning and afternoon administration, serum MT increased above 1,000 pg/ml and remained above the highest basal levels during most of the 24-hour cycle. These levels are clearly supraphysiologic ones. The decline in serum MT showed two distinct components following morning administration. Half-life of the initial component which probably represents rapid distribution into tissues was 17.3 min. A half-life of 25.1 h was calculated for the second component. We conclude that use of a 25-µg dose of melatonin to study pineal effects may be misleading.

The effects of housing condition and type of stimulation on serum melatonin and N-acetylserotonin (NAS) were investigated. Male rats were housed under a 12/12-hour light-dark cycle, with ad libitum food and water, either individually or in groups of four. At the start of the light phase, separate groups were sacrificed at rest or subjected for 3 minutes to the stimulation of cold water, noise, novel environment, or ether vapour and then decapitated at 0, 5, 15, 30 or 60 minutes after the end of stimulation. Melatonin was measured by a modified radioimmunoassay and NAS by a specific radioimmunoassay. Melatonin levels responded to stimulation with an increase, while NAS levels responded with a decrease. Housing condition had no effect on hormone response. However, the pattern of response for each of the two hormones differed greatly among the stimuli. For melatonin, cold water was the most potent stimulus, followed by noise, novel environment, and ether. NAS responded most to ether, fleetingly to cold, and in a bimodal manner to noise. The data are interpreted as suggesting that separate mechanisms regulate serum melatonin and serum NAS is response to environmental stimulation and that under appropriate control conditions melatonin from the pineal is very responsive to environmental stimuli, in a manner similar to that of pituitary hormones.

Postoperative stimulation influenced transitory changes in affective behavior (septal syndrome) following septal 'ablation in rats. Septally-lesioned and nonlesioned rats, handled (H), shaken (S), or nonstimulated (N) for 20 days, were rated on 5 behavior items every 5 days beginning 24 hr. after surgery for a total of 5 sessions. Lesioned /Ss exhibited the septal syndrome and nonlesioned Ss did not (p < .001). Significant reductions in affective behavior followed H, S, and N treatments in all Ss over 5 sessions. Handling was more effective than shaking in reducing ratings for lesioned Ss. For nonlesioned Ss handling and shaking were equivalent. Lesioned Ss had heavier adrenal glands than nonlesioned Ss (p < .01) 22 days after surgery.Drastic behavioral changes, characterized by hyperreactivity and hyperemotionality (septal syndrome), have been reported in rats following septal ablation (Brady & Nauta, 1953, 1955 Nielson, Mclver, & Boswell, 1965). These behaviors included postural rigidity and explosive startle reaction to unexpected tactile or auditory stimuli. Any attempt to capture or handle a rat with a newly-formed septal lesion produced fierce struggling and biting, usually accompanied by considerable vocalization. The septal syndrome has been observed to persist for postoperative periods of 7-75 days (Krieckhaus, Simmons, Thomas, & Kenyon, 1964;Reynolds, 1965). Yutzey, Meyer, and Meyer (1967) found that recovery from the septal syndrome was related to the intactness of the cortex. Examination of the literature suggested that postoperative handling may also be a factor in the duration of the septal syndrome. The current experiment was designed to explore the possible influence of handling and somatosensory stimulation on the behavior of septally-lesioned rats. Since various areas of the limbic system, including the septum, have been implicated in the control of the 1 This research is based upon a thesis submitted in partial fulfillment of the requirements for the master's degree at York University, Ontario, Canada. The author would like to express her appreciation to her thesis supervisor, Leonard J.

Plasma corticosterone values were obtained using cortico-sterone-binding-globulin florisil assay for normal, sham-lesioned and septal-lesioned rats at 2 time periods, 12 h apart, corresponding to 2 h after the switch to light or dark under a 12:12 h light:dark regime. At a time 2 h after the switch to light, when normal and sham-lesioned animals evidenced low resting corticosterone responses, septal rats exhibited a fivefold increase in resting corticosterone levels compared to non-lesioned animals. At a time 2 h after the switch to dark, when basal corticosterone values are higher, normal, sham-lesioned and lesioned rats evidence no differences in their plasma corticosterone levels. Results suggest that the 24 h plasma-corticosterone rhythm is altered in rats following septal damage.

In order to characterize the effects of septal lesionsupon adrenal stress responses, plasma corticosterone levels were examined 2 days after surgery in normal and sham-operated rats and in rats with septal lesions 0, 5, 15, 30, and 60 min after either 5 sec of handling or 3 min of novel environment at both the crest and trough of the adrenal cycle. Baseline levels and diurnal variations were comparable in lesioned and non-lesioned groups. Non-lesioned rats reacted to stress with an elevation of corticosterone which peaked and leveled off 15 min after the end of stress. Their response was greater following 3 min of novel environment than after 5 sec of handling. 60 min after stress, corticosterone levels had begun to return to baseline levels at trough but not at crest of the adrenal cycle. Rats with a septal lesion had an overall stress-response pattern similar to that observed in non-lesioned animals, but the response latency of septally-lesioned rats was much shorter than that of non-lesioned animals, and their corticosterone levels at 0, 5, and 15 min after stress were greater than those of non-lesioned rats. The mean magnitude of overresponse in rats with septal lesions was greater at trough than at the crest of the cycle. It is concluded that baseline adrenal function is not altered by destruction of the septal nuclei but that septally-lesioned rats have a reduced threshold for adrenal activation which is demonstrated by elevated corticosterone levels during the first 15 min following stimulation and that this increased sensitivity to stimulation is greater at trough than at the crest of the adrenal cycle.

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