Pyroglutamyl peptidase II activity is not in the processes of bulbospinal TRHergic neurons

Pyroglutamyl peptidase II (PPII) is a neuronal ectoenzyme involved in released thyrotropin-releasing hormone (TRH) inactivation. In an attempt to define if it is present in the pre or postsynaptic membrane, we induced neuronal degeneration of serotonin-TRHergic cells that project from raphe nuclei to the spinal cord. 2-4 weeks after intracisternal injection of 5,7-dihydroxytryptamine, TRH levels decreased over 70% in the cervical, thoracic or lumbar regions of spinal cord. In contrast, no change of PPII activity was observed. Longer times after injection (6-8 weeks), a 59-66% increase in activity was detected in the lumbar region. These data suggest that PPII is not localized in these TRHergic neurons but probably in the target cells.