UP-REGULATION OF GROWTH-ASSOCIATED PROTEIN-43 EXPRESSION AND NEURONALCOEXPRESSION WITH NEUROPEPTIDE-Y FOLLOWING INFERIOR ALVEOLAR NERVE AXOTOMY IN THE RAT

Growth associated protein 43 (GAP 43) is an acidic membrane-bound phos phoprotein produced at high levels in developing and regenerating neur ons. It is a substrate for protein kinase C and suggested to be involv ed in calcium-regulated release of axonal vesicular-contained neurotra nsmitters. Expression of GAP 43 has been demonstrated in the uninjured cat dental pulp which receives its sensory nerve supply from the trig eminal ganglion. The aim of this study was a detailed mapping of the s patial and time-dependent expression of GAP 43 and co-expression of ne uropeptide Y (NPY) in dental peripheral target tissues and trigeminal neurons subsequent to inferior alveolar nerve (IAN) axotomy in rats, a s background for later low-level laser studies. Unilateral sectioning of IAN, resulting in an almost complete loss of sensory nerve fibers i n the ipsilateral dental pulp of the first molar, was performed. The a vidin biotin complex (ABC) method was used to evaluate peripheral chan ges in GAP 43 expression at 4, 7 and 10 days. Ganglionic changes in GA P 43 and co-localization of neuronal NPY expression was examined at 4, 10 and 21 days using either the ABC method or double immunofluorescen ce labelling techniques and confocal microscopy. Axotomy resulted in a n early upregulation and change in the peripheral distribution of GAP 43 in nerve profiles already 4 days post IAN axotomy suggesting a Schw ann cell origin. Ten days post axotomy a pronounced upregulation of GA P 43 immunoreactivity could be demonstrated in neurons located in the mandibular region of the trigeminal ganglion, compared to the contrala teral uninjured side. The peripheral and ganglionic upregulation of GA P 43 continued to persist at 21 days. A concomitant time-delayed shift and co-expression of NPY was demonstrated throughout in the GAP 43-up regulated ganglion cells 10 days post axotomy. Furthermore: confocal m icroscopy indicated that the intraneuronal distribution of NPY and upr egulated GAP 43 expression showed a similar conformity and distributio n in both perinuclear regions and cell periphery.