1. Sexual dimorphism in synaptic organization in the amygdala and its dependence on neonatal hormone environment.
Answers
Electron microscopic observation was made on coronal sections from the middle part of the medial amygdaloid nucleus (AMN) of the rats. According to postsynaptic elements, shaft synapses (SHS) terminating on dendritic shafts, spine synapses (SPS) made on dendritic spines and somatic synapses (SOS) made on neuronal cell bodies were differentially counted on a field of 10,000 sq. μm in a single section of the identical level of the nucleus in each brain.
The total number of SHS, SPS, and SOS per 10,000 sq. μm in normal adult male rats was significantly larger than in normal female rats. This sex difference in synaptic number was due to a significant increase in number of SHS in normal male rats, while the incidences of SPS and SOS in normal males were not significantly different from those in normal females. A single injection of 1.25 mg testosterone propionate (TP) to day 5 females caused a marked increase in the number of SHS, compared to normal females. The incidence of SHS in androgenized females was almost the same as that in normal males. However, the other two components of synaptic population (SPS and SOS) were not influenced by neonatal treatment with TP. On the other hand, neonatal orchidectomy resulted in a significant decrease in the number of SHS to the level comparable to that of normal females.
These results clearly indicate the existence of sexual dimorphism in the synaptic pattern in the AMN. Furthermore, this sex difference was highly dependent on the neonatal presence of androgen, which effectively stimulated shaft synaptogenesis during early postnatal period. The modification of synaptic patterns caused by neonatal exposure to androgen in the amygdala may participate in the possible process of sexual differentiation of neuroendocrine and behavioral parameters of the amygdaloid function.