HYPOGLOSSAL NERVE;

Objective: To study the neurons contributing sensory fibers to thehypoglossal nerve. Setting: Basic Medical Sciences Institute, Jinnah Postgraduate Medical Centre, Karachi. Period:From 1992 to 1995. Study Design: Experimental animal study. Material & Methods: Under general anaesthesia therequired hypoglossal nerves of twenty four albino rats were exposed and cut in the neck. Horse radish Peroxidase(HRP) crystals were applied to the central cut ends of the nerves and allowed to travel for about 48 hours. Aftertranscardial fixation with 1.25% gluteraldehyde and 1% paraformaldehyde solution, serial sections of upper cervicalDorsal Root Ganglia (DRG) were made on a freezing microtome, treated with Tetramethylbenzidine (TMB) andcounterstained by 1% neutral red. The number, size and segmental distribution of HRP labeled neurons were observedwith the help of light microscope. Results and Observations: In most of the animals, the HRP labeled sensory neuronsforming the right and the left hypoglossal nerves and their branches were localized ipsilaterally in (Cervical) C1 DRG(more than 90%) whereas in remaining cases labeled sensory neurons were observed in C2 DRG. Size spectrum forsensory neurons of the hypoglossal nerve and its branches ranged from 9 to 52:m, but more than 75% were less than40 microns.Conclusion: Neurons of DRG of C1&2 contribute sensory fibers to the hypoglossal nerve of the same side.