GALANIN GENE-EXPRESSION DECLINES WITH ADULTHOOD IN THE CHOLINERGIC FIELDS OF THE HORIZONTAL DIAGONAL BAND OF MALE-RATS

The neuropeptide galanin (GAL) influences learning and memory processe s, perhaps by inhibiting cholinergic function. We recently reported th at, in the rat, the nucleus of the horizontal limb of the diagonal ban d (HDB) exhibits the highest level of GAL mRNA coexpression by basal f orebrain (BF) cholinergic neurons and, in the HDB, virtually all GAL m RNA-expressing neurons correspond to the cholinergic cell type. Since GAL gene expression is induced across puberty in many brain regions, w e used in situ hybridization histochemistry and quantitative autoradio graphy to assess GAL gene expression across the rostro-caudal extent o f the HDB in prepubertal and adult male rats and to determine whether GAL gene expression is also regulated during maturation in this BF reg ion. Our results show that the number of GAL mRNA-expressing cells per section is significantly reduced in the HDB with adulthood. Post-hoc analysis indicated that these age-associated differences in the number of GAL mRNA-expressing cells per section could be ascribed to the ros tral and central subregions of the HDB. Age-related differences in the labeling intensity of GAL mRNA-expressing neurons were also detected in the rostral and central subregions of the HDB. No age-associated di fferences in GAL gene expression were found in the caudal HDB subregio n. These results suggest that: (1) in contrast to other brain regions, GAL gene expression in the cholinergic BF may be negatively regulated by factors concomitant with puberty; and (2) the inhibition of cholin ergic function by cosecreted GAL may be enhanced prior to puberty with in cholinergic neurons of the rostral and central aspects of the HDB.