Trigeminal projections to the dorsal thalamus in a lacertid lizard, Podarcis hispanica

Trigeminothalamic projections in the lizard Podarcis hispanica were investigated by means of biotinylated dextranamine (BDA) injections into different nuclei of the dorsal thalamus. Previous studies of lizards found a projection from the sensory trigeminal nuclei in the brainstem to the nuclei ventromedialis and ventrolateralis of the ventral thalamus. The present results show that, in addition to these projections to ventral thalamic nuclei, neurons of the nucleus of the descending tract and the principal sensory nucleus project contralaterally to the pretectal nucleus lentiformis thalami and bilaterally to the nucleus dorsolateralis anterior thalami of the dorsal thalamus. The contralateral projection to the nucleus dorsolateralis anterior is more developed than its ipsilateral counterpart and appears to be topographically organized. Since the nucleus dorsolateralis thalami has ascending projections to the cortex telencephali, this nucleus may be the thalamic relay of trigeminal sensory information to the telencephalon.