The 5-HT3 receptor ligand, [3H]BRL 43694, binds to presynaptic sites in the nucleus tractus solitarius of the rat.

This study has employed receptor autoradiography to localise the distribution of binding sites for the 5-HT3 receptor ligand [3H]BRL 43694 in sections of the brain of the rat (using a concentration of 10 nM [3H]BRL 43694 with 100 microM GR38032F to define non-specific binding). The highest density of binding sites for [3H]BRL 43694 was observed in the nucleus tractus solitarius and amounted to 652 fmol/mg tissue. The binding of [3H]BRL 43694 was also examined in sections prepared 10 days after unilateral nodose ganglionectomy, in an attempt to determine the neuronal location of these binding sites. Denervation reduced the binding of [3H]BRL 43694 by around 50% in the ipsilateral side of the nucleus tractus solitarius, relative to the contralateral side. This would indicate that the 5-HT3 binding sites may have a presynaptic location on vagal afferent terminals.