Immunohistochemical localization of DARPP-32 in the brain and spinal cord of anuran amphibians and its relation with the catecholaminergic system

Abstract

The relationship between dopaminergic neuronal structures and dopaminoceptive structures in the amphibian brain and spinal cord are assessed by means of single and double immunohistochemical techniques with antibodies directed against DARPP-32 (a phosphoprotein related to the dopamine D 1-receptor) and tyrosine hydroxylase (TH) applied to the brain of the anurans Rana perezi and Xenopus laevis. The DARPP-32 antibody yielded a well-differentiated pattern of staining in the brain of these anurans. In general, areas that are densely innervated by TH-immunoreactive fibers such as the nucleus accumbens, striatum, amygdaloid complex, thalamus, optic tectum, torus semicircularis and spinal cord display a remarkable immunoreactivity for DARPP-32 in cell bodies and neuropil. Distinct cellular DARPP-32 immunoreactivity was also found in the septum, preoptic area, suprachiasmatic nucleus, tuberal hypothalamic region, habenula, retina, midbrain tegmentum, rhombencephalic reticular formation and solitary tract nucleus. Hodological data supported that striatal projection neurons were DARPP-32 immunoreactive. Double immunohistofluorescence staining revealed that catecholaminergic cells generally do not stain for DARPP-32, except for some cells in the ventral mesencephalic tegmentum of Xenopus and cells in the nucleus of the solitary tract of Rana. Several interspecies differences were noted for the DARPP-32 distribution in the brain of the two anurans, namely in the habenula, the thalamus and prethalamus, the cerebellum and octavolateral area and the structures with DARPP-32/TH colocalization. However, in general, the distribution of DARPP-32 in the brain of the anuran amphibians resembles in many aspects the pattern observed in amniotes, especially in reptiles.