Enhanced fos expression in the zebra finch (Taeniopygia guttata) brain following first courtship.

Abstract

Young zebra finch males that court a female for the first time develop a stable preference for the females of that species. On the neuronal level, consolidation of the imprinted information takes place. Here we demonstrate that first courtship or being chased around in the cage leads to enhanced fos expression in forebrain areas implicated in learning and imprinting in zebra finch males compared with birds reared in isolation or in the aviary. Two of the forebrain areas highly active during first courtship (as demonstrated by the 14C-2-deoxyglucose technique), the imprinting locus latral neo/hyperstriatum ventrale (LNH) and the secondary visual area hyperstriatum accessorium/dorsale (HAD), demonstrate enhanced fos expression. Two other imprinting-related areas, the medial neo/hyperstriatum ventrale (MNH) and archistriatum/neostriatum caudale (ANC), do show c-fos induction; however, the areas are not congruous with those demarcated by the 2-DG autoradiographic studies. Additional telencephalic areas include the olfactory lobe, the information storage site lobus parolfactorius (LPO), the memory site hippocampus, the auditory caudomedial neostriatum implicated in the strength of song learning, and the caudolateral neostriatum, which is comparable to the mammalian prefrontal cortex. In addition, c-fos is induced by first courtship and chasing in neurosecretory cell groups of the preoptic area and hypothalamus associated with the repertoire of sexual behavior and stress or enhanced arousal. Enhanced fos expression is also observed in brainstem sources of specific (noradrenergic, catecholaminergic) and nonspecific (reticular formation) activating pathways with inputs to higher brain areas implicated in the imprinting process. Birds reared in isolation or alternatively in the aviary with social and sexual contact to conspecifics showed attenuated or no fos expression in most of the above-mentioned areas. First courtship and chasing both lead to enhanced uptake of 2-DG in the four imprinting areas, as well as subsequent changes in spine density-an anatomical manifestation of the imprinting process. fos expression in the imprinting and other telencephalic, preoptic, hypothalamic, and mesencephalic brain regions indicates processing of stimuli originating from exposure (like chasing) and the analysis of stimuli in a behaviorally relevant, sexually explicit context (like first courtship). c-fos induction in these brain areas indicates its involvement in the triggering of neural changes that accompany the learning process of imprinting, leading eventually to alterations in dendritic spine density in the zebra finch.