A different type of vertebrate thalamic organization.

The presence of a reptilian thalamic reticular nucleus was investigated in Caiman crocodilus. Injections of horseradish peroxidase made into the dorsal thalamus produced retrogradely labeled neurons in the nucleus of the dorsal peduncle of the lateral forebrain bundle. A separate population of thalamic neurons located in the nucleus of the dorsal peduncle of the lateral forebrain bundle with morphology different from those neurons projecting to the dorsal thalamus were found to be immunoreactive for glutamic acid decarboxylase. Taken together, these findings suggest that Caiman, like mammals, contain a thalamic reticular nucleus but that thalamic organization in Caiman differs significantly from that of mammals.