Neuronal cell death during sexual differentiation and lateralisation of vocal communication.

A rodent analogy has been established to investigate the neural mechanisms occurring during sexual differentiation and lateralization. A sexually dimorphic hypothalamic nucleus (SDApc) is closely associated with a stereotyped, courtship vocalisation in male gerbils. Stereological analysis of SDApc cytoarchitecture reveals that neuron number and nuclear volume are asymmetric in male adults. Strikingly, neuron number on the left side of the SDApc correlates significantly with the rate of the courtship call in males. Exogenous testosterone treatment in female neonates masculinises and lateralises SDApc structure and function. Neuronal programmed cell death (apoptosis), manifested in SDApcs of neonates, is more frequent in females. Significantly, apoptosis in males is lateralised, as revealed by lateral asymmetry of neuron number at postnatal day 16. It is concluded that neuroendocrine-dependent, sexual differentiation and lateralization are concurrent and influenced by apoptotic mechanisms. It is suggested that apoptosis is the result of a genetically-driven device, inherent in postmitotic, undifferentiated cells which may have recently migrated into the SDApc. The genomic mechanism inducing lateralised apoptosis is apparently activated only neonatally in males.