[Modulation of the hypothalamo-neurohypophyseal system following environmental changes in rats]

The innate light-dark avoidance (step-through apparatus) was observed daily on 5 successive days in dehydrated and normal rats, the dehydration starting 24 hr before the first observation. We noted that latency scores from dehydrated groups and from the hydrated group tested together with a dehydrated group increased progressively. These significantly increased latencies did not appear when normally hydrated rats were tested alone. These changes in the temporal development of latencies seemed to be due to the fact that dehydrated rats were able to produce "fear odors" which increased the emotional reactivity of normal rats as well as theirs. The hypothalamo-neurohypophyseal function, characterized by the peripheral total neurophysins levels, also seemed to be modulated by these psychosocial and physical stresses. The neurophysins values from the hydrated group tested together with a dehydrated group were not statistically different from those of the latter group whereas they were higher than those of the hydrated group tested alone (Mann-Whithney; U = 28; n1 = n2 = 10; approach the significance). Further investigations are needed before establishing a definite relationship between the changes in latency scores on the one hand and the changes in neurophysins levels on the other hand. Nevertheless, one may well suppose that peripheral neurophysins levels play their own role in the adaptation of the organism to the environmental variations rather than only reflect the activity of the hypothalamo-neurohypophyseal axis.