Expression of alpha(2)-adrenergic receptor subtypes in prenatal rat spinal cord.

The results of molecular cloning have revealed three subtypes of the alpha(2)-adrenergic receptors (alpha(2) AR) that have been defined alpha(2)C10 (alpha(2A)), alpha(2)C2 (alpha(2B)) and alpha(2)C4 (alpha(2C)). The differential expression of alpha(2) AR subtypes is affected by developmental factors in rat submandibular gland, lung and brain. In the spinal cord of postnatal and adult rats, alpha(2A) and alpha(2C) AR subtypes are expressed and appear to mediate pain perception. However, the relative expression of alpha(2) AR subtypes in the prenatal spinal cord is unknown. In the present study subtype-specific antibodies and reverse transcription-polymerase chain reaction (RT-PCR) were used to determine the expression and localization of the alpha(2) AR subtypes in sections of embryonic day 14 rat spinal cords and primary cultures of cells isolated from these cords. Spinal cords were removed from day 14 embryos, and were sectioned or used for the preparation of cell cultures. After 9 days in culture, neurons were examined by immunofluorescence microscopy or used for preparation of total RNA. In both intact spinal cords and isolated cells, positive immunoreactivity was detected with antibodies against alpha(2A) and alpha(2B) subtypes, but not with antibodies against the alpha(2C) subtype. Using a dual-labeling approach, anti-alpha(2A) and anti-alpha(2B) immunoreactivity was present on the same population of neurons. RT-PCR results were consistent with immunofluorescence studies, and showed that mRNA encoding the alpha(2A) and alpha(2B) subtypes was present in total RNA prepared from primary cultures of rat spinal cord neurons. In contrast to spinal cords of postnatal or adult rats that express alpha(2A) and alpha(2C) AR subtypes on different neurons, prenatal spinal cords contain alpha(2A) and alpha(2B) AR subtypes, and these two subtypes appear to be co-expressed in the same cells.