Substance P in the acoustic area of the cortex during neuronal development and maturation

Substance P has been proved an important neurotransmitter and neuromodulator, serving not only as an excitatory transmitter of the first afferent synapse of pain pathways but as a valuable neuromodulator in the primary cortical areas of sensosensorial integration. In the human acoustic cortex, substance P has been found in the presynaptic terminals as well as in the cell bodies of numerous polyhedral, triangular and bipolar neurons. Using histochemical techniques, we found recently that substance P is first accumulated in the neuronal elements of the human acoustic cortex in 18-gestational-week (GW) fetuses. Most of substance P is distributed in the neurons of the 3rd and 4th cortical layers, mainly in the cell bodies, the initial part of the axons and the axonic terminals. In 24-GW fetuses, substance P is found in the 2nd cortical area inside the cell body of the granular and bipolar neurons. In 28-GW fetuses, substance P is found in the pre- and postsynaptic terminals. We would suggest that substance P is accumulated increasingly as a function of the neuronal maturity of the primary acoustic cortical area, serving mainly as a neuromodulator.