Localization of dopamine D2 receptor in rat spinal cord identified with immunocytochemistry and in situ hybridization.

In the present study the distribution of dopamine D2 receptors in rat spinal cord was determined by means of immunocytochemistry using an anti-peptide antibody, directed against the putative third intracellular loop of the D2 receptor and in situ hybridization (ISH) using a [35S]UTP labelled anti-sense riboprobe. With the immunocytochemical technique, labelling was confined to neuronal cell bodies and their proximal dendrites. Strongest labelling was present in the parasympathetic area of the sacral cord and in two sexually dimorphic motor nuclei of the lumbosacral cord, the spinal nucleus of the bulbocavernosus and the dorsolateral nucleus. Moderately labelled cells were present in the intermediolateral cell column, the area around the central canal and lamina I of the dorsal horn. Weak labelling was present in the lateral spinal nucleus and laminae VII and VIII of the ventral horn. Except for the two sexually dimorphic motornuclei of the lumbosacral cord labelled motoneurons were not encountered. With the ISH technique radioactive labelling was present in many neurons, indicating that they contained D2 receptor mRNA. The distribution of these neurons was very similar to the distribution obtained with immunocytochemistry, but with ISH additional labelled cells were detected in laminae III and IV of the dorsal horn, which were never labelled with immunocytochemistry. The present study shows that the D2 receptor is expressed in specific areas of the rat spinal cord. This distribution provides anatomical support for the involvement of D2 receptors in modulating nociceptive transmission and autonomic control. Our data further indicate that D2 receptors are not directly involved in modulating motor functions with the exception, possibly, of some sexual motor functions.