Secretory pathways of neuropeptides in rat lumbar dorsal root ganglion neurons and effects of peripheral axotomy

Growth hormone inhibits the hypophysectomy-induced expression of galanin in hypothalamic neurons of the toad (Bufo arenarum hensel)

The expression of the neuropeptide galanin was analyzed by immunohistochemistry in magnocellular and preoptic hypothalamic neurons of toads following hypophysectomy (HPX) and pars distalectomy (PDX). There was a marked increase in the galanin-like immunoreactive expression in magnocellular hypothalamic cells 3 days after HPX, followed by a decrease to normal levels after 7 days. No changes in the expression of galanin were detected after PDX in these neurons when compared to controls. Moreover, 7 days after HPX or PDX the number of cells expressing galanin was significantly increased in the preoptic area, where numerous intraependymal cells were intensely immunoreactive. The hypophysis grafts into the hind limb in HPX or PDX animals prevented increased galanin-like immunoreactivity in preoptic cells but not in magnocellular neurons. Similarly, PDX toads given growth hormone showed no GAL-LI in the intraependymal preoptic cells. These results suggest the presence of a region regulation of galanin expression in the preoptic area by hypophyseal hormones, in particular growth hormone.

Evidence for galanin receptors in primary sensory neurones and effect of axotomy and inflammation

Using in situ hybridization, mRNA coding for the galanin R1 receptor (GAL-R1) was demonstrated in > 20% of all lumbar 4 and 5 dorsal root ganglion neurone profiles, mainly constituting small and medium sized neurones. Almost all of these neurones expressed CGRP mRNA as revealed by analysis of adjacent sections and of the same section using a double-labelling technique. GAL-R1 mRNA levels were down-regulated transiently by inflammation, and more strongly by peripheral nerve injury. These results suggest that DRG neurones are sensitive to galanin and that GAL-R1 receptors are involved in sensory processing.