Roles of protein kinase A and protein kinase G in synaptic plasticity in the visual cortex

Monocular deprivation leads to clear physiological and anatomical changes in the visual cortex known as ocular dominance plasticity. Protein kinase A (PKA) is necessary for ocular dominance plasticity, while protein kinase G (PKG) is not. We have now tested the role of PKA and PKG in long-term potentiation (LTP) and long-term depression (LTD). We have shown that PKA inhibitors have a major effect on both LTP and LTD in the visual cortical slices, whereas a PKG inhibitor affects LTP but not LTD. The PKA activator, 8-chloroadenosine-3',5'-monophosphorothioate, Sp-isomer (Sp-8-Cl-cAMPS), by itself induces a slowly rising form of LTP, which is occluded by theta-burst stimulation (TBS)-induced LTP. These results support the point that the PKA signaling pathway is crucial for neuronal plasticity in visual cortex, and the dissociation of the role of PKA and PKG in long-term synaptic plasticity in the visual cortex suggests that LTP alone is not sufficient to support ocular dominance plasticity, or LTD plays a more fundamental role than LTP in ocular dominance plasticity.