Striatal afferent connections in the turtle (Chrysemys picta) as revealed by retrograde axonal transport of horseradish peroxidase.

Horseradish peroxidase (HRP, 30% solution, 0.1-0.3 mul, 72 h) was injected unilaterally into the basal striatum (STR) and the dorsal ventricular ridge (DVR) of adult turtles (Chrysemys picta) in order to demonstrate the cells of origin of some afferents to these telencephalic structures. After selective STR injection, HRP-labeled cells were visualized in the dorsal thalamus and midbrain tegmentum, ipsilaterally. At thalamic level, HRP-positive neurons were located around nucleus rotundus, i.e., mainly within nuclei dorsomedialis anterior, dorsolateralis anterior and less abundantly in nuclei ventralis and reuniens. At midbrain level, a large population of labeled neurons was disclosed within the ventrolateral portion of rostral tegmentum. Other HRP-positive neuronal somata were found scattered throughout the lateral portion of the caudal midbrain tegmentum. In addition, labeled axons were visualized in both peduncles of the lateral forebrain bundle (LFB) after STR injection. The HRP-positive fibers of the dorsal peduncle of the LFB were followed up to the ipsilateral labeled thalamic cells where they appear to arise, whereas the HRP-containing axons of the ventral peduncle were traced down to the lateral midbrain tegmentum where they appear to arborize. Most of the HRP injections into the DVR were confined to the mediodorsal quadrant of the rostral half of the DVR. In such a case, a very large number of HRP-positive cells were disclosed within all thalamic nuclei surrounding nucleus rotundus, ipsilaterally. In addition, numerous labeled neurons were also found in nucleus rotundus itself and within nucleus reuniens. No HRP-positive cells were disclosed caudally to the meso-diencephalic junction after DVR injection.