COLOCALIZATION OF ESTROGEN-RECEPTOR IMMUNOREACTIVITY AND PREPROENKEPHALIN MESSENGER-RNA EXPRESSION TO NEURONS IN THE SUPERFICIAL LAMINAE OFTHE SPINAL AND MEDULLARY DORSAL HORN OF RATS

A double-labelling procedure combining immunohistochemical staining wi th in situ hybridization using a radiolabelled cRNA probe was employed to demonstrate oestrogen receptor-like immunoreactivity and preproenk ephalin-A mRNA in the medullary and spinal dorsal horn of female rats. Both markers labelled large numbers of neurons in the substantia gela tinosa and its trigeminal homologue, Many of these neurons were double -labelled, displaying both oestrogen receptor-like-immunoreactivity an d preproenkephalin-A mRNA; cell counts showed that 40-60% of the of th e oestrogen receptor-like-immunoreactive cells in the superficial lami nae also were labelled for preproenkephalin-A mRNA, and that 60-70% of the preproenkephalin-A mRNA-labelled neurons in the same laminae disp layed oestrogen receptor-like immunoreactivity. Previous studies have shown that oestrogen receptors can bind to the promoter region of the preproenkephalin-A gene, and studies on the hypothalamus have demonstr ated that oestrogen regulates enkephalin expression in select neuronal populations. The present results demonstrate that enkephalinergic neu rons in the superficial dorsal horn contain oestrogen receptors and su ggest that oestrogen may play an important role in the modulation of s ensory and nociceptive processing in the lower medulla and spinal cord .