Retrograde Cell Body Labeling Research Articles

Pallidal projections to the mesencephalic locomotor region (MLR) in the cat.

The entopeduncular nucleus (EN) in the cat, homologue of the primate internal globus pallidus and main output of the basal ganglia, is known to project to the mesencephalic tegmentum. We have been able to elicit antidromic responses in single EN neurons from a site in the posterior mesencephalon, then transect the brainstem (precollicular-postmamillary) and elicit locomotion and rhythmic movements of the limbs by stimulation of the same site in the same animal. These studies demonstrate the existence of a direct projection from the EN to the mesencephalic locomotor region (MLR). However, this is not a particularly large pathway since fewer than 5% of the EN cells appear to project to the MLR. In a parallel series of anatomical experiments, injections of fluorescent dyes into the area of the MLR induced retrograde labeling of cell bodies in the EN and motor cortex. Injections of tritiated amino acids into the motor cortex resulted in labeling in the area anterior to the MLR. We assume that these connections may be involved, in part, in the sequencing and ordering of series of voluntary movements in which locomotion is involved.

The origins of the afferent fibers to the lingual muscles of the dog, a retrograde labelling study with horseradish peroxidase.

The origin of the afferent fibers to the lingual muscles of the dog was investigated by means of retrograde transport of horseradish peroxidase (HRP) from injection sites in the tongue and the extrinsic lingual muscles. Intralingual injections were not satisfactory because the enzyme diffused beyond the intrinsic lingual muscles to include virtually all tissues within the tongue. Thus, the resultant retrograde labeling of cell bodies of the trigeminal, geniculate, glossopharyngeal, vagal, and first cervical (C1) spinal ganglia represented a composite of lingual sensory innervation. In order to confine HRP uptake to intramuscular nerve endings, injections were limited to surgically isolated extrinsic lingual muscles, i.e., the genioglossus, hyoglossus, and styloglossus. After these intramuscular injections, labeled neurons appeared ipsilaterally in the C1 spinal ganglion, the proximal vagal (jugular) ganglion, and trigeminal ganglion. Earlier suggestions that the lingual proprioceptive neurons of the dog reside in the distal vagal (nodose) ganglion and hypoglossal ganglia were not confirmed. The mesencephalic nucleus of the trigeminal nerve failed to label after enzyme injections into the tongue or the extrinsic lingual muscles. The retrograde labeling of cell bodies in the C1 spinal ganglion was abolished when HRP injections into the extrinsic lingual muscles were preceded by surgical interruption of the ansa cervicalis or distal section of the hypoglossal nerve. Retrograde labeling of neurons in the proximal vagal ganglion persisted after hypoglossal nerve transections.