Abstracts

AMPA receptors (AMPARs) mediate fast synaptic excitation in the CNS and are required for generalization of seizures. Hence their short and long term regulation will affect seizure susceptibility. AMPARs are phosphorylated by protein kinase C (PKC) leading to increased excitatory postsynaptic currents (EPSCs). Synapses in immature cortex contain AMPARs lacking the GluR2 subunit that exhibit facilitation due to a use-dependent polyamine (PA) unblocking. PA and PKC are bidirectionally regulated, but the functional effects of this interaction on AMPAR function has not been investigated. In this study, we determined whether PKC activity influences PA modulation of synaptic AMPARs in neocortex of young rats. Whole cell recordings were made to examine inward rectification and paired-pulse ratios (PPR) of EPSCs evoked at 50 ms intervals in layer V pyramidal neuron of P12-P14 rats [ndash] a developmental stage characterized by EPSCs with little GluR2 dependence. Spermine (50 [mu]M) was either included or excluded from the pipette solution. The PKC inhibitor (staurosporin, ST, 1 [mu]M) was applied via local perfusion. ST reversed the effects of exogenous PA such as significant inward rectification and PPF. Rectification Index was 0.36 [underline]+[/underline] 0.07 in control vs 0.66 [underline]+[/underline] 0.21 in ST (n = 6, p[lt] 0.05), while PPR was decreased by ST from 0.94 [underline]+[/underline] 0.07 to 0.62 [underline]+[/underline] 0.05 (n = 7, p[lt] 0.01). These results show that PKC modulates postsynaptic activation of AMPARs. In addition PA immunostaining demonstrated that ST treatment depleted PA from a subpopulation of layer V neocortical pyramidal neurons. Taken together, these data support involvement of post-synaptic PKC activation in both the inward rectification and facilitation in immature rat neocortical neurons, and suggests an important mechanism by which excitatory synaptic transmission can be dynamically modulated intracellular level of both PAs directly, and also secondarily through Ca²⁺-dependent PA regulation. (Supported by the NINDS and a fellowship to JS from the Epilepsy Foundation of America.)