Parabrachial nucleus projections to midline and intralaminar thalamic nuclei of the rat

The projections from the parabrachial nucleus to the midline and intralamin ar thalamic nuclei were examined in the rat. Stereotaxic injections of the retrograde tracer cholera toxin-p (CTb) were made in each of the intralamin ar nuclei of the dorsal thalamus (the lateral parafascicular, medial parafa scicular, oval paracentral, central lateral, paracentral, and central media l nuclei), as well as the midline thalamic nuclei (the paraventricular, int ermediodorsal, mediodorsal, paratenial, rhomboid, reuniens, parvicellular p art of the ventral posterior, and caudal ventral medial nuclei). The retrog rade cell body labeling pattern within the parabrachial subnuclei was then analyzed. The paracentral thalamic nucleus received an input only from the internal lateral parabrachial subnucleus. However, this subnucleus also pro jected to all the other intralaminar thalamic nuclei, except for the centra l lateral thalamic nucleus, which received no parabrachial afferent inputs. The external lateral parabrachial subnucleus projected to the lateral para fascicular, reuniens, central medial, parvicellular part; of the ventral po sterior, and caudal ventromedial thalamic nuclei. Following CTb injections in the paraventricular thalamic nucleus, retrogradely labeled cells were fo und in the central lateral, dorsal lateral, and external lateral parabrachi al subnuclei. The medial and ventral lateral parabrachial. subnuclei projec ted to the oval paracentral, parafascicular, and rhomboid thalamic nuclei. Finally, the waist area of the parabrachial nucleus was densely labeled aft er CTb injections in the parvicellular part of the ventral posterior thalam ic nucleus. Nociceptive, visceral, and gustatory signals may reach specific cortical and other forebrain sites via this parabrachial-thalamic pathway. (C) 2000 Wiley-Liss, Inc.