Somatostatin-mRNA expression in brainstem projections into the medial preoptic nucleus

The medial preoptic nucleus plays an important role in the regulation of neuroendocrine processes, vegetative functions, sexual behaviour and the modulation of the somatomotoric system. The connections of the medial preoptic nucleus to other areas of the central nervous system are very complex, and the area receives afferents using numerous transmitters and neuropeptides. Previous investigations have shown that this nucleus receives afferents from various brainstem nuclei that also contain somatostatinergic neurons. This study was carried out to investigate if somatostatin-projecting neurons of the brainstem are afferents to the medial preoptic nucleus. This was approached by combining somatostatin-mRNA in situ hybridisation with True Blue retrograde tracing. Our results demonstrate somatostinergic brainstem projections into the medial preoptic nucleus mainly in the pedunculopontine nucleus and in the nucleus of the solitary tract (50% together). Other important somatostatinergic afferents into the medial preoptic nucleus originate in the cuneiform area, the dorsal parabrachial nucleus and in the lateral reticular nucleus (37% together). Less important are the somatostatinergic projections coming from the central grey, the laterodorsal tegmental nucleus, the locus coeruleus and the nucleus raphe magnus. Considering that these areas are involved in diverse functions such as cardiovascular regulation (nucleus of the solitary tract), transmission of visceral sensibility (dorsal parabrachial nucleus), modulation of the somatomotoric system (pedunculopontine nucleus) and in the regulation of neuroendocrine mechanisms (locus coeruleus), it seems tenable that the somatostatin projections demonstrated here also have a diverse functional quality within the medical preoptic nucleus where they terminate.