Immunohistochemical localisation and molecular expression of the steroidogenic enzyme cytochrome P450 17α-hydroxylase /C(17,20)-lyase in the vestibular nuclei of adult male rats.

Many biologically active neurosteroids, including dehydroepiandrosterone (DHEA), are synthesised in the brain. DHEA is a potent endogenous modulator of several neuronal functions, and alterations of DHEA are correlated with various neurobiological deficits. The cytochrome P450 17α-hydroxylase/C(17,20)-lyase (P450C(17) ) plays a pivotal role in the synthesis of DHEA from pregnenolone and progesterone. We investigated the immunohistochemical localisation and molecular expression of P450C(17) in the superior, lateral, medial and inferior vestibular nuclei (VCN) of adult male rats by western blotting and indirect immunofluorescence analysis. Immunoreactive P450C(17) was widely distributed in all VCN and the expression of P450C(17) was confirmed by western blot analysis. The present study demonstrates, for the first time, the presence and anatomical distribution of P450C(17) in the VCN. Given that neurosteroids can modulate neuronal activities in the medial vestibular nucleus, DHEA synthesised in the VCN may play an important role in the control of specific activities at this level.

Hypoglossal nucleus projections to the rat masseter muscle.

We investigated in the rat whether hypoglossal innervation extended to facial muscles other than the extrinsic musculature of the mystacial pad. Results showed that hypoglossal neurons also innervate the masseter muscle. Dil injected into the XII nucleus showed hypoglossal axons in the ipsilateral main trunk of the trigeminal nerve. After Gasser's ganglion crossing, the axons entered into the infraorbital division of the trigeminal nerve and targeted the extrinsic muscles of the mystacial pad. They also spread into the masseter branch of the trigeminal nerve to target the polar portions of the masseter muscle spindles. Retrograde double labelling, performed by injecting Dil into the pad and True Blue into the ipsilateral masseter muscle, showed labelled hypoglossal neurons in the medio-dorsal portion of the XII nucleus. The majority of these neurons were small (15-20 microm diameter), showed fluorescence for Dil and projected to the mystacial pad. Other medium-size neurons (25 microm diameter) were instead labelled with True Blue and projected to the masseter muscle. Finally, in the same area, other small hypoglossal neurons showed double labelling and projected to both structures. Functional hypotheses on the role of these hypoglossal projections have been discussed.

Androgen receptor immunoreactivity in rat occipital cortex after callosotomy.

Gonadal steroidogenesis can be influenced by direct neural links between the central nervous system and the gonads. It is known that androgen receptor (AR) is expressed in many areas of the rat brain involved in neuroendocrine control of reproduction,such as the cerebral cortex.It has been recently shown that the occipital cortex exerts an inhibitory effect on testicular stereoidogenesis by a pituitary-independent neural mechanism. Moreover, the complete transection of the corpus callosum leads to an increase in testosterone (T) secretion of hemigonadectomized rats. The present study was undertaken to analyze the possible corticocortical influences regulating male reproductive activities. Adult male Wistar rats were divided into 4 groups: 1) intact animals as control; 2) rats undergoing sham callosotomy; 3) posterior callosotomy; 4) gonadectomy and posterior callosotomy. Western blot analysis showed no remarkable variations in cortical AR expression in any of the groups except in group I where a significant decrease in AR levels was found. Similarly, both immunocytochemical study and cell count estimation showed a lower AR immunoreactivity in occipital cortex of callosotomized rats than in other groups. In addition, there was no difference in serum T and LH concentration between sham-callosotomized and callosotomized rats. In conclusion, our results showthat posterior callosotomy led to a reduction in AR in the right occipital cortex suggesting a putative inhibiting effect of the contralateral cortical area.