Localization of 5-HT2A receptor in rat cerebral cortex and olfactory system revealed by immunohistochemistry using two antibodies raised in rabbit and chicken

Serotonin 2A receptor (5-HT2A receptor) is widely distributed in the central nervous system, and has been suggested to be involved in a variety of behavioral conditions and neuropsychiatric disorders. Two polyclonal antibodies were raised against the N-terminus peptide of rat 5-HT2A receptor in chickens (5-HT2A-N) and a glutathione S-transferase fusion protein that contained the C-terminus of the mouse 5-HT2A receptor in rabbits (5-HT2A-C). Affinity-purified 5-HT2A-N and -C antibodies reacted strongly with a single band of 77-78 kDa in postsynaptic density proteins prepared from the rat cortex. The distribution pattern of immunoreactive structures in the rat brain was virtually the same for the two antibodies. The highest levels of immunoreactivity were observed in the olfactory bulb, neocortex, claustrum, piriform cortex, mamillary bodies, pontine nuclei, red nucleus and cranial motor nuclei. In the olfactory bulb, mitral cells were intensely labeled. In the neocortex, many immunoreactive neurons were found in layers II-VI. In layer IV of the neocortex, strong neuropil labeling was observed. In a double-labeling study using chicken 5-HT2A-N and rabbit anti-glial fibrillary acidic protein (GFAP) antibody, a considerable number of GFAP positive cells also showed 5-HT2A immunoreactivity. By using an immunoelectron microscopic technique, 5-HT2A receptor immunoreaction was shown to be localized just beneath the postsynaptic membrane thickening of asymmetric synapses.