Functional plasticity and neurotransmitter receptor binding in the vibrissal barrel cortex

A form of activity dependent, functional plasticity can be induced in the barrel cortex by sensory deprivation without damage to the sensory receptors. Changes of cortical representation of a spared C3 vibrissa, when all other whiskers were plucked out, were mapped with 2-deoxyglucose autoradiography in mice and rats after a short-lasting deprivation. An increase in the volume of cortical column activated by the spared vibrissa was found already after one week of deprivation. We have found previously that if deprivation is commenced immediately after birth, the changes in cortical representation of the spared whisker appeared in the third week of life. In search of a possible reason for the delayed expression of functional plasticity in neonatal animals we examined the developmental curves of neurotransmitter receptor binding for several transmitters though to be involved in plastic processes of the cerebral cortex. We found that the beta noradrenergic and muscarinic cholinergic receptor binding increased rapidly at the end of the second postnatal week and subsequently remained high. By contrast, the metabotropic glutamate receptor binding decreased during the first month of postnatal development. The AMPA receptors binding values rose during the first two weeks of life, and then decreased. Together with our previous data on the development of NMDA and GABAa receptor and voltage dependent calcium channel binding, the results suggest that slow development of functional plasticity in neonatal animals may be due to low levels of receptors of several neurotransmitters implicated in brain plasticity.