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Highly sensitive in situ hybridization procedures (RNAScope) were used to quantify the expression of three dopamine receptors (Drd1, Drd2, and Drd3) in two song control nuclei (HVC and the Area X of the basal ganglia) that are known to receive dopaminergic inputs and in the periaqueductal gray (PAG) of male and female canaries. Both sexes were treated with testosterone to ensure they would sing actively. We also determined the excitatory versus inhibitory phenotype of the cells expressing these receptors as well as their activation following a period of song production. The three receptor types were identified in each brain area, with the exception of Drd3 in Area X. The density of cells expressing each receptor varied as a function of receptor type and brain area. Surprisingly few sex differences were detected; they do not seem to explain the sex differences in testosterone‐induced song. Overall, the density of Drd‐positive cells was much lower in PAG than in the two song control nuclei. In HVC, the majority of cells expressing the three receptor subtypes were VGlut2‐positive, whereas colocalization with Vglut2 occurred in few cells in Area X and in an intermediate proportion of cells in PAG. The number of inhibitory cells expressing dopamine receptors was limited. Most dopaminoceptive cells in Area X did not express either excitatory or inhibitory markers. Finally, cellular activation during singing behavior, as measured by the expression of Egr1, was observed in cells expressing each of the three dopamine receptor subtypes, except Drd3 in the PAG. [ABSTRACT FROM AUTHOR]

Domestic strains of canaries (Serinus canaria) variably respond to photoperiod changes and apparently stay in breeding state for extended periods. Fife Fancy canaries are supposed to be similar to the native species living at 27–39° north where photoperiod significantly changes across the year. Our birds showed reproductive cycles when exposed to light regimes mimicking the annual cycle of photoperiod. However after 6 months in short days (SD: 8L:16D), males developed large testes, as observed by X‐ray tomography, and intense singing. Switching to long days (LD: 16L:8D) did not further increase song rate nor testes size but increased song duration, number of syllables per song, and trill occurrence frequency. No sign of regression was observed after 12 weeks in LD but return to SD produced a rapid decrease in testes size and singing activity below values in birds maintained throughout in SD. Fife Fancy thus does not seem to develop absolute but only relative refractoriness. The relatively high singing activity expressed by SD‐photosensitive males does not seem to depend on high testosterone (T) concentrations. Singing did not correlate with plasma testosterone (T). Treatment with ATD + Flutamide only marginally decreased song rate and did not affect song quality nor song control nuclei volume. These birds are either supersensitive to low T levels or their reproductive physiology is activated by other mechanisms. Neurogenesis is increased by T and by LD but the function of new neurons incorporated in HVC is poorly understood. We developed a procedure based on X‐ray focal irradiation to deplete neural progenitors adjacent to HVC and study the functional consequences. The decrease in neurogenesis increased the variability of T‐induced songs in females and decreased their bandwidth. Neurogenesis in HVC thus plays a role in song production and X‐ray focal irradiation represents an excellent tool to analyze adult neurogenesis. [ABSTRACT FROM AUTHOR]

Dr. Gregory F. Ball has been awarded the 2024 Donald S. Farner Medal for Excellence in Research in the Field of Avian Endocrinology. The announcement was made at the International Symposium on Avian Endocrinology in April 2024. Dr. Ball, a professor at the University of Maryland, has made significant contributions to the study of hormones, brain, and behavior in birds. He has published over 350 papers and mentored numerous students and postdocs who have gone on to successful careers in academia. Dr. Ball's research has been funded by NIH and NSF grants, and he has received several prestigious awards throughout his career. [Extracted from the article]

Parvalbumin (PV) neurons play an integral role in regulating neural dynamics and plasticity. Therefore, understanding the factors that regulate PV expression is important for revealing modulators of brain function. While the contribution of PV neurons to neural processes has been studied in mammals, relatively little is known about PV function in non-mammalian species, and discerning similarities in the regulation of PV across species can provide insight into evolutionary conservation in the role of PV neurons. Here we investigated factors that affect the abundance of PV in PV neurons in sensory and motor circuits of songbirds and rodents. In particular, we examined the degree to which perineuronal nets (PNNs), extracellular matrices that preferentially surround PV neurons, modulate PV abundance as well as how the relationship between PV and PNN expression differs across brain areas and species and changes over development. We generally found that cortical PV neurons that are surrounded by PNNs (PV+PNN neurons) are more enriched with PV than PV neurons without PNNs (PV-PNN neurons) across both rodents and songbirds. Interestingly, the relationship between PV and PNN expression in the vocal portion of the basal ganglia of songbirds (Area X) differed from that in other areas, with PV+PNN neurons having lower PV expression compared to PV-PNN neurons. These relationships remained consistent across development in vocal motor circuits of the songbird brain. Finally, we discovered a causal contribution of PNNs to PV expression in songbirds because degradation of PNNs led to a diminution of PV expression in PV neurons. These findings reveal a conserved relationship between PV and PNN expression in sensory and motor cortices and across songbirds and rodents and suggest that PV neurons could modulate plasticity and neural dynamics in similar ways across songbirds and rodents. [ABSTRACT FROM AUTHOR]