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Galanin has been ascribed several physiological roles that are thought to be mediated via multiple galanin receptors. Recently, two galanin receptors--galanin receptor-1 (GalR1) and galanin receptor-2 (GalR2)--have been cloned and characterized and shown to have differences in amino acid sequence, pharmacology, and second messenger signaling systems. Previous studies have demonstrated an up-regulation of galanin expression in damaged neurons of several different types. Using in situ hybridization histochemistry this study investigated whether adult cranial motor neurons express mRNAs encoding GalR1 and/or GalR2 and explored possible time-dependent changes in these transcripts following facial nerve injury. GalR2 mRNA levels were increased in the ipsilateral facial nucleus 3 (approximately 1.8-fold) and 7 days (approximately 3.7-fold) after unilateral facial nerve crush and had returned to levels equivalent to those in contralateral controls by 14-21 days. GalR1 mRNA was not detected in facial nuclei of naive, sham-operated, or operated rats but was present in adjacent reticular nuclei. Galanin mRNA levels were also increased eight- to 10-fold in the ipsilateral facial nucleus following nerve injury. These experiments confirm the putative importance of galanin signaling systems after nerve injury by demonstrating a differential response of galanin receptor subtypes and suggest an important "autoreceptor" role for the GalR2 receptor in these processes. |
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