Distribution of serotonin 4(a) receptors in the juvenile rat brain and spinal cord.

In the last 20 years there have been many studies investigating the distribution of 5-HT4-receptors in the brain of different species. Most studies are methodically based on RT-PCR or in situ hybridization and have analysed the receptors at the mRNA level. Furthermore there have been some autoradiographic studies using specific 5-HT4-receptor antagonists like [(3)H]GR113808, [(3)H]BIMU-1 or [(125)I]SB207710. This study investigates the topographical distribution of the 5-HT4(a)-receptor in the juvenile rat brain and spinal cord, which is important for neuromodulation of cellular excitability and could be involved in various developmental processes of the central nervous system. We analysed the 5-HT4(a)-receptor at protein level with a monospecific polyclonal antibody by using an immunohistochemical staining. We saw an intensive staining in some areas of the cortex, in the olfactory bulb, in most areas of the cerebellum, in hippocampal areas like the dentate gyrus and in several different areas of the brainstem, especially in the motor nuclei. Overall we have shown comparable results in accordance with the results of other studies investigating the distribution of 5-HT4(a)-receptors. Some areas like the islands of Calleja, the preoptic nucleus or the medial habenular nucleus showed a lower intensity of 5-HT4(a)-receptors in comparison with the results of other studies. As a novel result we found a higher intensity of 5-HT4(a)-receptor in several brain areas associated with motor function than was shown by other studies, especially in the motor cortex, in different areas of the cerebellum, in the red nucleus, in the motor nuclei of the brainstem or in the ventral horn cells of the spinal cord. We conclude that the 5-HT4(a)-receptor may play a more prominent role in the modulation of motor cortico-ponto-cerebellar, cortico-spinal, rubro-spinal, vestibulo-spinal and cortico-nuclear tracts during juvenile development.