Trigeminal nociceptive neurons in the subnucleus reticularis ventralis. II. Ascending projection.

Ascending projection of trigeminal nociceptive neurons in the subnucleus reticularis ventralis (SRV) was studied in urethane/chloralose-anesthetized cats. Thalamic neurons having complex trigeminal receptive fields similar to those of SRV neurons were found in the intralaminar nuclei, i.e. nuclei centralis lateralis, centralis medialis and parafascicularis. About half of the SRV units tested were antidromically activated by electrical stimulation of the nucleus centralis lateralis. It was also found that a significant proportion of SRV units was antidromically activated by electrical stimulation of the mesencephalic reticular formation (MRF), and retrogradely labelled neurons were found in the SRV after HRP injection into the MRF. These findings suggest that SRV neurons relay trigeminal nociceptive inputs directly or indirectly via the MRF to the intralaminar nuclei.