Brain Research, 426 (1987) 257-269 257 Elsevier BRE 13060 Cholecystokinin innervation of rat thalamus, including fibers to ventroposterolateral nucleus from dorsal column nuclei C.A. Hunt, K.B. Seroogy*, C.M. Gall and E.G. Jones Department of Anatomy and Neurobiology, University of California-lrvine, Irvine, CA 92717 (U.S.A.) (Accepted 5 May 1987) Key words: Cholecystokinin; Thalamus; Ventroposterolateral nucleus; Immunocytochemistry; Dorsal column nucleus The distribution of cholecystokinin octapeptide immunoreactive fibers and puncta in the adult rat thalamus was studied using immu- nocytochemical methods. Small to moderate numbers of immunoreactive fibers were present in the lateral habenular nucleus, ventral lateral geniculate nucleus, zona incerta, parataenial, mediodorsal, medioventral, and submedial nuclei, the rhomboid, paracentral, central lateral and parafascicular nuclei, and in the medial geniculate and dorsal lateral geniculate nuclei. Moderate to large numbers of cholecystokinin (CCK)-positive fibers were present in the paraventricular nuclei, the reticular nucleus, the anteroventral, antero- medial, and central medial nuclei, and in the rostral extension of the internal medullary lamina between the parataenial and antero- ventral nuclei. Dense concentrations of immunoreactive fibers were also found in a principal sensory relay nucleus, the ventropostero- lateral nucleus (VPL), of the ventrobasal complex. The number of CCK-positive fibers in VPL showed a marked unilateral decrease in rats which had received lesions of the contralateral gracile and cuneate nuclei. The results of this study demonstrate that CCK-immu- noreactive fibers and puncta are widely distributed in the rat thalamus, and that the source of these fibers in VPL is probably the dorsal column nuclei. INTRODUCTION Despite the obvious role of the thalamus as a relay for all sensory information to the cerebral cortex and its involvement in controlling levels of cortical excit- ability, very little is known about its neurotransmit- ters other than y-aminobutyric acid (GABA) 2A6' 17.24,29,38,48.52-54.67.76. In many parts of the central ner- vous system, neuropeptides have received consider- able attention because of their potential roles as neurotransmitters or neuromodulators. With a few notable exceptions, however, the densities of neuro- peptide-immunoreactive cells and fibers in the thala- mus have been reported as being relatively low. Among the exceptions, moderate densities of opiate receptors and of enkephalin-immunoreactive fibers and terminals have been found in a number of dorsal thalamic nuclei, including the intralaminar, anterior, a n d m e d i o d o r s a l n u c l e i7'10'15'21'27'36'43'49'75. The para- ventricular nuclei of the epithalamus are the only nu- clei to contain fl-endorphin65. Neurons of a part of the ventral thalamus, the reticular nucleus, which are GABAergic, have also been shown to stain immuno- cytochemically for somatostatin 2°'47'51. Reports on the distribution of immunoreactivity for other neuro- active peptides until recently have shown relatively few or no such fibers in the thalamus. When present, peptide-immunoreactive fibers were localized within nuclei whose functions are not well understood. Sub- stance P-positive fibers were reported in the epitha- lamus, the zona incerta of the ventral thalamus, and the anterodorsal, rhomboid, and lateral geniculate nuclei9,39. Cholecystokinin (CCK)-positive fibers were found in the epithalamus, the intralaminar nu- clei, the lateral geniculate nucleus, the basal ventro- medial nucleus, and along the midline of the thala- * Present address: Department of Histology, Karolinska Institute, S-10401 Stockholm, Sweden. Correspondence: E.G. Jones, Department of Anatomy and Neurobiology, University of California, Irvine, CA 92717, U.S.A. 0006-8993/87/$03.50© 1987 Elsevier Science Publishers B.V. (Biomedical Division)