Proceedings of The Physiological Society

Trinity College Dublin (2003) J Physiol 551P, PC39


Localisation of steroid receptor coactivator-1 in lumbosacral spinal cord neurons of male and female Wistar rats

Richard N. Ranson, Robert M. Santer and Alan H.D. Watson

Cardiff School of Biosciences, Cardiff University, Biomedical Sciences Building, Cardiff CF10 3US, UK

Steroid receptors belong to a superfamily of transcription factors that modulate hormone-responsive genes and are critically involved in regulating homeostasis and development. Circulating steroids operate in the brain by binding to intracellular neuronal steroid receptors to form a steroid-receptor complex. This complex binds to a hormone response element located on DNA where it co-ordinates gene transcription and subsequently neuronal function. Transcription is enhanced by the interaction between steroid receptors and other proteins termed nuclear receptor coactivators, including steroid receptor coactivator-1 (SRC-1), which increase their binding and effect at the hormone response element. SRC-1 has been shown to interact with a variety of nuclear receptors including thyroid receptors but particularly those for sex steroids (Onate et al. 1995). Consequently the localisation and levels of SRC-1 in the brain serve as a marker of general steroid levels and can be used to compare both age- and sex-related changes in distribution of steroid receptors. However few studies, to date, have investigated the immunolocalisation of SRC-1 and scant information is available on its distribution within sexually dimorphic nuclei in lumbosacral spinal cord. Our current study attempts to address this omission.

Three- and 24-month-old Wistar rats of both sexes were humanely killed by terminal anaesthesia (Euthatal, 200 mg kg-1 I.P.) then perfused with 4 % paraformaldehyde. Spinal cord segments L5-S1 were removed and sectioned at 45 µm before immunocytochemical processing. To localise SRC-1, sections were incubated for 72 h in anti-SRC-1 antibodies (Santa Cruz Biotechnology) at a dilution of 1:333. In addition two male rats underwent bilateral orchidectomy, under halothane anaesthesia (4 % in O2) 5 days prior to immunoprocessing.

In all rats SRC-1 immunostaining was seen in the nuclei of many neurones distributed throughout all laminae. However labelling was predominant in laminae I/II of the dorsal horn and within the motornuclei of lamina IX including the sexually dimorphic nuclei. Labelling was also notable in the region of the sacral parasympathetic nucleus. The distribution was similar in both sexes with the exception of the spinal nucleus of the bulbocavernosus which is absent in females. Labelled nuclei had a similar distribution in the aged rats though they contained fewer positive cells. In orchidectomised rats, in which circulating testosterone was abolished, SRC-1 reactivity was unchanged in motorneurons of sexually dimorphic nuclei which are known to express receptors to other steroids including glucocorticoids.

These results suggest that the distribution of SRC-1-containing cells closely follows that described previously for steroid receptors and that differences in the distribution patterns between sexes reflects their sexual dimorphism.

Where applicable, experiments conform with Society ethical requirements