Anatomical findings are presented that identify cortical and
subcortical sources of afferents to the nucleus reticularis
tegmenti pontis (NRTP) and basal pontine nuclei. Projections
from the middle temporal visual area (MT), medial superior temporal
visual area (MST), lateral intraparietal area (LIP), and areas
7a and 7b to the basal pontine nuclei were studied using
3H-leucine autoradiography. The results complemented a
parallel study of retrograde neuronal labeling attributable to
injecting WGA-HRP into NRTP and neighboring pontine nuclei. Small
3H-leucine injections confined to MT, MST, LIP, area
7a, or area 7b, produced multiple patches of pontine terminal
label distributed as follows: (1) An injection within
MT produced terminal label limited to the dorsolateral and lateral
pontine nuclei. (2) Injections restricted to MST or
LIP showed patches of terminal label in the dorsal, dorsolateral,
lateral, and peduncular pontine nuclei. (3) Area 7a
targets the dorsal, dorsolateral, lateral, peduncular, and ventral
pontine nuclei, whereas area 7b projects, additionally, to the
dorsomedial and paramedian pontine nuclei. Notably, no projections
were seen to NRTP from any of these cortical areas. In contrast,
injections made by other investigators into cortical areas anterior
to the central sulcus revealed cerebrocortical afferents to
NRTP, in addition to nuclei of the basal pontine gray. With
our pontine WGA-HRP injections, retrograde neuronal labeling
was observed over a large extent of the frontal cortex continuing
onto the medial surface which included the lining of the cingulate
sulcus and cingulate gyrus. Significant subcortical sources
for afferents to the NRTP and basal pontine nuclei were the
zona incerta, ventral mesencephalic tegmentum, dorsomedial
hypothalamic area, rostral interstitial nucleus of the medial
longitudinal fasciculus, red nucleus, and subthalamic nucleus.
The combined anterograde and retrograde labeling data indicated
that visuo-motor cortico-pontine pathways arising from parietal
cortices target only the basal pontine gray, whereas the NRTP,
together with select pontine nuclei, is a recipient of afferents
from frontal cortical areas. The present findings implicate
the existence of parallel direct and indirect cortico-pontine
pathways from frontal motor-related cortices to NRTP and
neighboring pontine nuclei.