Cortical repesentation of the common fur of mysticial pad is situated outside poster-medial barrel subfield (PMBSF) in rat primary somatosensory cortex.Following neonatal vibrissectomy, stimulation of the common fur activates the neurone in PMBSF.We examined if sparing of the mystacial vibrissa from the neonatal ablation, which results in a very extensive increase of its cortical repesentation, would prevent the invasion of the common fur inputs into the PMBSF.The cortical representation were mapped with 2-deoxyglucose (2DG).It was found that six weeks after neonatal vibrissectomy sparing C3 vibrissa and common fur inputs were representes into the PMBSF.Their representation shifed from its normal location into the barriel field.This effect was observed in cortical layers II/III, IV and V.
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 previously that if deprivation is commenced immediately after birth, yhe 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 thought to be involved in plstic processes of the cerebral cortex. We found that the beta noradrenergic and miscarinic 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 GABA 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.
The somatosensory barrel cortex of rodents and its afferent pathway from the facial vibrissae is a very useful model for studying neuronal plasticity. Dendritic spines are the most labile elements of synaptic circuitry and the most likely substrate of experience ? dependent alterations in neuronal circuits in cerebral cortex. We characterized morphologically and numerically a specific population of spines, i.e. double synapse spines, which have two different inputs ? one excitatory and the other inhibitory, in the B2 barrel of mouse somatosensory cortex. We also described changes in morphology of double synapse spines induced by classical conditioning in which stimulation of vibrissae was paired with a tail shock. The analysis was carried out by means of serial EM micrograph reconstruction. We showed that double spines account for about 10% of all analyzed spines. The morphology of a typical double synapse spine is similar to the morphology of single synapse spine and both consist of two parts ? a large head and a narrow, long neck. Excitatory synapses are preferentially located on the head of double synapse spines and inhibitory synapses are usually located on the neck of these spines. The length of the double synapse spine neck decreases and the cross-section area of the spine neck increases significantly as a result of sensory conditioning.
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