CHANGES IN OVINE PINEAL-GLAND NEURON-SPECIFIC ENOLASE IMMUNOREACTIVITY FOLLOWING BILATERAL, BUT NOT UNILATERAL, SUPERIOR CERVICAL GANGLIONECTOMY

Pineal gland tissue from control and from unilaterally or bilaterally superior cervical ganglionectomized (SCGX) sheep was found to contain neuron-specific enolase immunoreactive cells and nerve fibers. Morphol ogical characteristics of pineal cells exhibiting immunoreactivity ind icated that they were predominantly pinealocytes, while other cell typ es were nonimmunoreactive. Whereas bilateral SCGX resulted in a reduct ion in the size, and possibly number, of immunoreactive cells in the p ineal, unilateral denervation did not result in any significant effect s when compared with control pineals. Concomitant with the reduction i n immunoreactivity in bilaterally denervated pineals was a significant increase in the volume of interstitial space, but not the number of n onimmunoreactive cells. These results suggest that sympathetic nerve f ibers innervating the pineal of unilaterally sympathectomized sheep ex hibited a degree of neural plasticity that resulted in denervated pine alocytes being reinnervated by remaining intact nerve terminals, thus preventing the occurrence of degenerative changes normally associated with complete loss of neural input through bilateral denervation. The fact that in unilaterally denervated sheep neither left nor right SCGX produced any discernible effects in either half of the pineal indicat es that nerve fibers from each of the ganglia cross over to innervate the contralateral as well as the ipsilateral pineal half. In the stalk of the pineal an extensive network of immunoreactive nerve fibers was found in both the caudal and habenular commissures, and occasionally these fibers were observed to enter the body of both intact and sympat hetically denervated pineals. This latter result suggests that the sym pathetic innervation enters the pineal over its surface and not via th e stalk.