Synaptic plasticity of feedback connections in rat visual cortex

The issue we want to address in the present paper is to establish whether electrical stimulation of latero medial (LM) area, a secondary visual area in the rat, is able to induce Long Term Potentiation (LTP) and Long Term Depression (LTD) in primary visual cortex (V1). To this aim rat slices containing area V1 and LM were prepared at P23 and P40 and field potentials in layers 2/3 of area V1 were recorded stimulating LM. We showed that it was never possible to induce LTP in area V1, unless bicuculline, a gamma-aminobutyric acid (GABA) receptors blocker, was applied to the slice. In contrast, LTD was normally inducible. Thus, cortical gabaergic circuitry in area V1 controls LTP but not LTD elicited by stimulation of feedback connections from LM.