Delineation of a brain nucleus: Comparisons of cytochemical, hodological, and cytoarchitectural views of the song control nucleus HVC of the adult canary

Abstract

The present investigation used stable area-specific, neuronal properties instead of Nissl stain to delineate the boundaries of the nucleus hyperstriatalis caudal c (HVc) in the telencephalon of the adult male canary. Immunocytochemical procedures combined with retrograde tracing labeled a large population of perennial long-projecting neurons that contain estrogen receptors in the canary HVc. The HVc area defined by the distribution of these neurons was congruent with the HVc area defined in Nissl-stained sections during the breeding period. The HVc area defined in Nissl-stained preparations showed an extensive seasonal change in size, confirming previous results (Nottebohm: Science, 214:1368-1370, '81). In contrast, the HVc area defined by the distribution of the estrogen receptor containing long-projection neurons showed little or no seasonal change in size. Because these neurons are permanent, the HVc seems to be of rather constant size year round. The internal morphology of the HVc, however, undergoes seasonal alterations, which are reflected in changes in size of the HVc area distinguishable in Nissl-stained sections. The combination of cytoarchitectural criteria of Nissl-stained preparations with area-specific cytochemical and hodological markers to delineate the boundaries of a brain nucleus might give new insights in the partitioning and neuronal plasticity of brain areas.

Mismatch in sexual dimorphism of developing song and song control system in blue-capped cordon-bleus, a songbird species with singing females and males

“…Alternatively, early born neurons might differentiate into RA neurons at a late time point. Thus, we need to consider that delineation problems of the brain areas (Gahr, 1990(Gahr, , 1997, i.e., the recognition of the outlines of RA (as well as of HVC for this argument) might have considerable effects on the estimated neuron numbers particularly in very young males and females.…”

Pattern of Interhemispheric Synchronization in HVc During Singing Correlates With Key Transitions in the Song Pattern

“…HVc contains 3 distinct classes of neurons that are thought to be distributed heterogeneously throughout the nucleus (Fortune and Margoliash 1995;Gahr 1990;Margoliash et al 1994). It has recently been shown that interneurons tend to be active during production of all song syllables, whereas RA-and X-projecting neurons are much more sparse in their firing patterns, producing in many cases only a single burst of action potentials during a given song motif (Hahnloser et al 2002).…”

Song- and Order-Selective Neurons in the Songbird Anterior Forebrain and their Emergence during Vocal Development

“…Lewicki and Arthur (1996) found that only 50% of song-responsive HVc neurons had a significantly greater response to forward than reversed song, versus 83% using the same criterion in the present study of LMAN. Anatomical and neurophysiological studies have shown that HVc contains two separate populations of auditory projection neurons, one to RA and the other to the AF (Katz and Gurney, 1981;Gahr, 1990;Doupe and Konishi, 1991;Kirn et al, 1991;Sohrabji et al, 1993;Vicario and Yohay, 1993). Thus, the properties of LMAN actually reflect a subset of HVc neurons, but whether the song-selective properties of this HVc subpopulation differ from the properties of RA-projecting neurons or from HVc as a whole has never been systematically studied.…”