INCREASED EXPRESSION OF PERIPHERAL BENZODIAZEPINE RECEPTORS IN THE FACIAL NUCLEUS FOLLOWING MOTOR-NEURON AXOTOMY

Peripheral benzodiazepine receptors (PBRs) are expressed in a variety of tissues but are normally found at low levels in the brain. Followin g various types of nerve injury, a reactive gliosis results that exhib its a high expression of this receptor. To further characterize the ex pression of PBRs following neuronal injury, we evaluated PBR expressio n in the facial nucleus following facial nerve axotomy (FNA). Injury t o a peripheral nerve results in a complex series of metabolic and morp hological changes around the injured neuron. Transections of the facia l nerve results in a rapid activation of both astrocytes and microglia around axotomized motor neurons. FNA resulted in an increase in the s taining for both astrocytes (glial fibrillary acidic protein) and acti vated microglia (OX42). There was also a reduction in synaptic contact s with the motor nucleus as evidenced by reduced staining for the syna ptic marker, synaptophysin. In sections labeled with [H-3]-PK11195, th e subsequent autoradiograms displayed marked increases in the labeling for PBRs. This increase was observed at 5, 7 and 10 days after nerve transection. The increase was primarily in the level of expression (B- max), with no change in the affinity of the ligand (K-d). The increase in PBR expression after FNA supports the hypothesis that PBRs can be used as a sensitive marker for CNS injury. (C) 1997 Elsevier Science L td.