Localization of tachykinin receptors and fos-like immunoreactivity inducedby substance P in guinea-pig brain

1. In the present study, a comparison was made between the distribution of tachykinin NK1 and NK3 receptor immunoreactivity and the distribution of Fo s-like immunoreactivity induced by the tachykinin agonist substance P (SP) in the guinea-pig brain. 2. In agreement with results from previous studies in rat brain, NK1 recept or-immunoreactive neurons were found to be widely distributed throughout th e brain in the striatum and in diencephalic and mesencephalic structures, w hile NK3 receptor-immunoreactive neurons were mainly in telencephalic struc tures. Considerable overlap was observed between NK1 and NK3 receptor distr ibutions. 3. Substance P induced Fos-like immunoreactivity (Fos-LI) in extensive area s of the guinea-pig brain. The induction of Fos-LI was markedly inhibited i n many areas by pretreatment with the NK1 receptor antagonist SR 140333. Th e NK3 receptor antagonist SR 142801 reduced Fos-LI staining in fewer areas, although a reduction was observed in the cortex, striatum and hypothalamus . 4. In general, tachykinin receptors were located at sites corresponding to areas of functional activation by SP, as shown by Fos-LI. These results ext end previous studies by adding a functional dimension to tachykinin recepto r localization studies.