Lesions to the medial preoptic nucleus differentially affect singing and nest box-directed behaviors within and outside of the breeding season in European starlings (Sturnus vulgaris)

Abstract

Little is known about how the brain regulates context-appropriate communication. European starlings produce song in various social contexts. During the breeding season, males with nest sites sing high levels of sexually motivated song in response to a female. Outside of this context, song rates are not affected by female presence. The medial preoptic nucleus (POM) regulates male sexual behavior, and studies in songbirds implicate the POM in sexually motivated song. Recent data suggest that the role of the POM might extend to song produced in other contexts as well. To examine this possibility, effects of bilateral electrolytic lesions of the POM on singing and other behaviors in adult male starlings within sexually relevant and nonsexual contexts were studied. Lesions to the POM exclusively reduced song and nest box-directed behaviors within highly sexually relevant contexts. Unexpectedly, POM lesions increased song in a nonsexual context, suggesting an inhibitory role for the POM in this context. These data suggest that the POM interacts with the song control system so that song occurs in an appropriate social context in response to appropriate stimuli.

Figure 1. Location and size of lesion damage

(A) Reconstruction of POM lesion damage, cumulative across all 21 POM lesioned subjects. The POM is highlighted with light shading. Dark gray ovals represent lesion damage located in one bird. Black ovals represent lesioned areas common to multiple males (see text for details). (B, C) Photomicrographs of approximate boundaries of POM and lesion damage for a rostral POM lesion and a caudal POM lesion in Nissl stained tissue. Abbreviations: POM, medial preoptic nucleus; TrSM, tractus septomesencephalicus; nCPa, nucleus commissurae pallii; DSV, ventral supraoptic decussation; Rt, nucleus rotundus; AC, anterior commissure; PVN, paraventricular nucleus; VMN, ventromedial nucleus of the hypothalamus; vIII, third ventricle. Scale bar at the lower left corner of (F) = 1 mm.

Figure 2. Graphs of Song Production

Effect of POM lesions and stimulus sex on song produced from a nest box (presumably sexually relevant song) and on song produced away from a nest box in three different contexts: (A, B) among Spring^box males, (C, D) among Spring^{no box} males, and (E, F) among Fall males. Dark bars indicate song produced in the presence of a female stimulus. Light bars indicate song produced in the presence of a male stimulus. N values reported in the dark bars also correspond to the associated light bar. Significant results of negative binomial tests are indicated. * indicates a significant post hoc effect.

Figure 3. Graphs of Nest Box-Directed Behavior

Effect of POM lesions and stimulus sex on the number of times Spring^box males (A) gathered nest material and (B) entered a nest box. Dark bars indicate behavioral response in the presence of a female stimulus. Light bars indicate behavioral response in the presence of a male stimulus. N values reported in the dark bars also correspond to the associated light bar. Significant results of negative binomial tests are indicated. * indicates a significant post hoc effect.