THE HYPOTHALAMIC PARAVENTRICULAR NUCLEUS IN 2 TYPES OF WISTAR RATS WITH DIFFERENT STRESS RESPONSES .2. DIFFERENTIAL FOS-EXPRESSION

The present study investigates the role of corticotropin-releasing hor mone (CRH) neurons in stress regulation by a comparison of stress indu ced Fos-immunoreactivity and CRH-immunoreactivity in the hypothalamic paraventricular nucleus (PVH) of APO-SUS (apomorphine-susceptible), AP O-UNSUS (apomorphine-unsusceptible), normal Wistar and adrenalectomize d Wistar (ADX) rats. The first two types represent a good model to stu dy the role of the PVH in stress regulation, since they show different stress responses and a differential synaptic organization of the PVH. After placement on an open field for 15 min all rats showed an increa se in the number of Fos-immunoreactive nuclei compared to central hand ling. Interestingly, open field stress, but not control handling, indu ces significantly fewer Fos-immunoreactive nuclei in the PVH of APO-SU S rats (1255 +/- 49) compared to APO-UNSUS rats (1832 +/- 201). Experi ments with ADX rats revealed that 93% of the CRH-immunoreactive neuron s contained a Fos-immunoreactive nucleus, which suggests that the diff erential Fos-expression in APO-SUS and APO-UNSUS rats represents a dif ferential activation of the CRH neurons. This hypothesis is discussed in relation to reported differences in stress responses, stress-induce d ACTH levels and synaptic organization of the