Arborization of corticothalamic axons in the auditory thalamus of the cat: a PHA-L tracing study.

As a result of Phaseolus vulgaris leucoagglutinin (PHA-L) injection in the primary auditory cortex of the cat, portions of corticofugal axons could be traced individually in the reticular complex of the thalamus (RE) and in the medial geniculate body (MGB). On their way to the MGB, axons were seen to give off collaterals which terminated in RE. In the MGB, an individual corticofugal axon was fully reconstructed. It ramified at 3 distinct frontal levels in the rostral half of the pars lateralis (LV). Its terminal branches gave rise to boutons en passant and terminaux in a stripe of LV (parallel to the isofrequency contours), overlapping a cluster of retrogradely labeled neurons, supporting at the microscopic level the principle of the reciprocity of thalamocortical and corticothalamic projections.