EXPRESSION OF PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE (PACAP) IN THE MESENCEPHALIC TRIGEMINAL NUCLEUS OF THE RAT AFTER TRANSSECTION OF THE MASSETERIC NERVE

Pituitary adenylate cyclase-activating polypeptide (PACAP), a member o f the VIP (vasoactive intestinal polypeptide) family of peptides, has been demonstrated in neurons of the sensory system. PACAP expression o f these neurons is sensitive to nerve damages such as nerve crush or a xotomy. In the present study, PACAP expression in the mesencephalic tr igeminal nucleus of the rat was examined after transsection of the mai n trunk of the masseteric nerve. The primary sensory neurons of the nu cleus are considered to have purely proprioceptive functions. By quant itative in situ hybridization using a PACAP [S-35]cRNA probe, an incre ase in PACAP mRNA was observed on the side ipsilateral to transsection already after 3 h and the expression reached a peak 24 h after surger y after which the levels gradually decreased during the next 14 days. A low and constant expression of PACAP mRNA could be seen on the side contralateral to transsection. PACAP immunoreactivity was demonstrated on the ipsilateral side after 18 h, using a specific monoclonal PACAP antibody. Go-existence of PACAP with NPY and galanin was demonstrated 7 days after transsection. Analysis of the masseteric nerve by radioi mmunoassay on transsected and normal nerve stumps revealed an increase of PACAP-38 immunoreactivity in the nerve proximal to the transsectio n compared to the normal side (15.3 vs. 6.1 pmol/g wt). The results su ggest that PACAP has a role in the early phase of adaptation to nerve injury in the proprioceptive neurons.