IMMUNOCYTOCHEMICAL LOCALIZATION OF SEROTONIN(1A) RECEPTORS IN THE RATCENTRAL-NERVOUS-SYSTEM

Specific anti-rat 5-hydroxytryptamine(1A) (serotonin(1A)) receptor ant ibodies raised in a rabbit injected with a synthetic peptide correspon ding to a highly selective portion of the third intracellular loop of the receptor protein (El Mestikawy et al. [1990] Neurosci. Lett. 118:1 89-192) were used for immunohistochemical mapping of serotonin(1A) rec eptors in the brain and spinal cord of adult rats. The highest density of immunostaining was found in limbic areas (lateral septum, CA1 area of Ammon's horn and dentate gyrus in the hippocampus, and frontal and entorhinal cortices), in the anterior raphe nuclei, and in the interp eduncular nucleus, in agreement with previous autoradiographic studies with selective radioligands showing the enrichment of these regions i n serotonin(1A) receptor binding sites. Serotonin(1A) receptor-like im munoreactivity was also present, but at a moderate level, in the neoco rtex, in some thalamic and hypothalamic nuclei, in the nucleus of the solitary tract, in the dorsal tegmentum, in the nucleus of the spinal tract of the trigeminal nerve, and in the superficial layers of the do rsal horn in the spinal cord. In contrast, extrapyramidal areas, inclu ding the caudate putamen, the globus pallidus, and the substantia nigr a as well as the cerebellum, exhibited very low to no immunostaining b y antiserotonin(1A) receptor antibodies. At the cellular level, both t he plasma membrane of neuronal perikarya and fine neuronal processes p robably corresponding to dendritic fields were found to bind antiserot onin(1A) receptor antibodies. Regional differences were noted regardin g these two types of immunostaining, because only dendrites bound anti bodies within the hippocampus and the lateral septum, whereas both den drites and neuronal cell bodies were immunoreactive in the medial sept um, in the diagonal band of Broca, and in the dorsal and median raphe nuclei. Therefore, differential addressing of serotonin(1A) receptors could occur from one neuron to another. In general, the distribution a nd density of serotonin(1A) receptor-like immunoreactivity in the whol e brain and in spinal cord were consistent with the mapping of seroton in(1A) receptor binding sites and serotonin(1A) receptor mRNA previous ly established by immunoautoradiographic and in situ hybridization pro cedures. (C) 1996 Wiley-Liss, Inc.