Daily low intensity tetanic of stimulation of limbic and forebrain structures with stimulus intensities that initially elicit little or no behavioral response, gradually leads to development of generalized clonic convulsions. This phenomenon, referred to as kindling, represents a permanent change in neuronal function that persists for the life of the animal. Kindling serves as an excellent model system for studying the cellular mechanisms involved in expression of long-lasting changes in neuronal excitability that underlie epilepsy, as well as such processes as learning and memory. Recent studies suggest that the pyriform cortex (PC) plays a key role in kindling-induced epileptogenesis and that kindling results in prolonged enhancement of responses of pyramidal cells within this structure to stimulation of excitatory affects. Evidence suggests that activation of excitatory amino acid (EAA) receptors is important for development of kindling but the precise role that EAA receptors play bringing about kindling-induced changes in neuronal excitability is unknown. Kindling induces a long-lasting increase in EAA-stimulated inositol phosphate formation in amygdala/PC slices and may induce changes in the sensitivity of other EAA receptors. In the proposed studies the effect of kindling on EAA-induced formation of the physiologically relevant phosphoinositide hydrolysis-derived second massagers, diacylglycerol (DAG) and inositol-1,4,5-triphosphate (Ins[1,4,5]P3), will be measured directly to test the hypothesis that kindling enhances EAA-induced formation of these second messengers. Current clamp and single electrode voltage clamp techniques will then be used to determine whether increased formation of DAG and Ins[1,4,5]P3 increases modulation of specific ionic conductances that are important for limiting repetitive firing in vertebrate neurons. The conductances that will be investigated are known to be inhibited by phosphoinositide hydrolysis-derived second messengers and if kindling enhances inhibition of these currents, this could enhance repetitive firing and lead to seizure activity. In addition, current clamp techniques will be used to test hypothesis that kindling also increases the sensitivity of other EAA receptors and thereby enhances excitatory synaptic transmission in the PC. Finally biochemical and biophysical techniques will be used to test the hypothesis that activation of the N-methyl-D-aspartate (NMDA) subtype of EAA receptor and active form of protein kinase C. This could contribute to induction of seizure activity by inducing tonic modulation of specific ionic conductances by this enzyme. Thus, if a constitutively active for of PKC is generated, current clamp and single electrode voltage clamp techniques may reveal changes in electrical properties of PC pyramidal cells that contribute to induction of seizure activity. It is likely that these studies will further our understanding of the cellular mechanisms involved in expression of lasting changes in neuronal excitability in general, and the pathophysiology of epilepsy in particular.
