Enhanced expression of CGRP in rat trigeminal ganglion neurons during cell and organ culture

The sensory innervation of intracranial vessels originates in the trigeminal ganglion with calcitonin gene-related peptide (CGRP), substance P (SP) and pituitary adenylate cyclase activating peptide (PACAP) as frequent neuronal messengers. The present study was designed to study the expression of these neuropeptides (a) in primary culture of adult rat trigeminal ganglion neuronal cells and (b) in organ culture of sections of the trigeminal ganglion. In cell culture, axons grow in the peripheral direction for up to 48 h. Immunocytochemistry revealed that the cell bodies showed increased expression of CGRP at 24 h and SP at 24–48 h (p < 0.05), whereas cell culture did not increase the expression of PACAP at 24 h (p > 0.05), but at 48 h (p < 0.05). A significant elevation of CGRP mRNA was seen at 12 h, i.e. before the increased CGRP immunoreaction was observed. In organ culture of sections of trigeminal ganglia, the number of CGRP immunoreactive (-ir) cells and the mRNA expression were significantly increased at 24 and 48 h of incubation as compared to control (p < 0.05), while the number of SP-ir cells was not altered (p > 0.05). In conclusion, neurons of rat trigeminal ganglia alter their expression of neuropeptides during cell and organ culture differently, but it is mainly the CGRP system that is up-regulated. We have compared two methods for future studies of underlying molecular mechanisms responsible for regulation of neuropeptide expression in the trigeminal system.