Carl, The effect of hormones on bird brains may be of interest to some of the posters on this board:
J Neurobiol 1988 Oct;19(7):624-635
Joint hormonal and sensory stimulation modulate neuronal number in
adult canary brains.
Bottjer SW, Dignan TP
Department of Biology, University of Southern California, Los Angeles 90089-0371.
Treatment of adult female canaries with testosterone (T) causes them to produce male-typical vocalizations and results in
striking growth of brain nuclei that control song behavior (Nottebohm, 1980). The song-control nucleus HVc (caudal nucleus
of the ventral hyperstriatum) contains cells that concentrate testosterone or its metabolites, suggesting that steroid hormones
may induce the growth of HVc directly by regulating the expression of specific genes in those HVc neurons that have steroid
receptors. However, we have previously provided evidence that is inconsistent with the idea that steroids promote growth of
HVc solely via a direct action on hormone receptors: testosterone treatment of deafened adult females results in very little
growth of HVc, relative to T-treated hearing birds (Bottjer et al., 1986b). Thus, birds in the former group undergo very little
overall growth of HVc despite high circulating levels of hormone. We show here that the slightly increased size of HVc in
T-treated deaf birds is attributable to an increase in neuronal spacing; the greatly increased size of HVc in T-treated hearing
birds is due to an increase in neuronal number as well as spacing. There was virtually no increase in number of HVc neurons in
T-treated deafened birds relative to control groups, whereas T-treated hearing birds showed a marked increase in neuron
number. The song-control nucleus RA (robust nucleus of the archistriatum), which receives direct afferent input from HVc, also
increases in size in response to testosterone treatment. However, the volume of RA increases in both hearing and deafened
birds; this increase is primarily due to an increase in neuronal spacing as well as a small increase in neuron number. These
results demonstrate that the number of neurons in a specific vocal-control nucleus (HVc) can change dramatically in adult
canaries and suggest that some synergistic action of hormonal and sensory stimulation is necessary to induce such a change.
PMID: 3225559, UI: 89140739 |
