AUTORADIOGRAPHIC COMPARISON OF [I-125] LSD-LABELED 5-HT2A RECEPTOR DISTRIBUTION IN RAT AND GUINEA-PIG BRAIN

Although the density and distribution of 5-HT2A(5-hydroxytryptamine-2A ) receptors is well established for rat brain, the 5-HT2A receptor dis tribution and density in guinea pig brain has not been extensively stu died. In the present in vitro study, we have utilized I-125-lysergic a cid diethylamide ([I-125]LSD) to quantify and compare 5-HT2A receptor density in coronal sections of rat and guinea pig brain. Spiperone (1 mu M) and sulpiride (1 mu M) were used to displace [I-125]LSD binding from 5-HT2A and D-2 binding sites, respectively. Ligand binding was qu antified by computer-aided image analysis densitometry (MCID). Similar to the rat, areas of highest specific 5-HT2A receptor binding (fmol/m g protein) in guinea pig brain included the claustrum and Layer 4 of t he cerebral cortex. Significant binding was also found in remaining ne ocortical layers, islands of Calleja, caudate putamen, olfactory bulb, nucleus accumbens, and choroid plexus. While the rat brain exhibited a high level of specific binding in the tenia tecta and mammillary nuc lei, little binding was observed in these regions in the guinea pig. I n both rat and guinea pig, low specific binding was found in amygdaloi d, thalamic, or cerebellar areas. These studies indicate a general sim ilarity between 5-HT2A binding site distribution and relative density in guinea pig and rat brain but point to a few brain regions where sig nificant differences exist.