Differences in auditory and physiological properties of HVc neurons between reproductively active male and female canaries (Serinus canaria)

Based on neuronal recordings in the HVc, this study investigated difference s between reproductively active male and sexually receptive female canaries . It is the first study to describe auditory responses and cell characteris tics of HVc neurons in female songbirds and to compare them with the respon ses and characteristics obtained in males. Extracellular single unit record ings showed that in males HVc cells exhibited two types of auditory respons es to conspecific and heterospecific song playbacks: tonic and phasic respo nses. The major finding of the present study is the absence of tonic respon ses in females. Neurons in the HVc of females only responded phasically to song playbacks. In both sexes, neurons exhibiting auditory responses had th inner action potentials than the others. As all the tonic cells recorded in males were thin spike cells (action potential = 0.6 ms) and had high firin g rates (6 Hz in average), they are potentially interneurons. In both sexes , two categories of nonresponsive cells were found: neurons that did not fi re at song onset and had the lowest spontaneous firing rate; and neurons th at did not exhibit changes in activity in response to song playbacks. Analy ses of physiological characteristics of HVc neurons revealed that the rate of spontaneous activity was higher in males than in females. This study is a first step towards in dentifying the cellular bases of the sexual dimorph ism in HVc function and highlights the pivotal role of interneurons in HVc auditory processing.