Sensory stimulation reduces seizure severity but not afterdischarge duration of partial seizures kindled in the hippocampus at threshold intensities

Epilepsy is a family of neurological disorders that result in seizure activity that is characterized by transient hypersynchronous activation of a large population of neurons. In animal models, focal tetanic electrical stimulation of sufficient duration and intensity, can elicit epileptiform, activity, that if repeated results in progressive intensification of seizure activity known as kindling. Kindling serves as a model of partial as well as secondarily generalized temporal lobe epilepsy. We utilized hippocampal kindling to provide a means of evaluating the effect of sensory stimulation on the duration and severity of the induced seizure activity. Sensory stimuli targeted either the olfactory, auditory or somatosensory systems in an attempt to retard or suppress seizure activity. To that end, rats were chronically implanted with electrodes in the CA1 region of dorsal hippocampus and kindled once daily until the seizure behaviour was fully generalized. Kindling stimulation consisted of daily application of 1-s trains of biphasic square wave pulses applied at a frequency of 60 Hz, at the afterdischarge (AD) threshold. Sensory stimulation was applied 6-8 s after the kindling stimulation every third day. One group of rats received a different sensory stimulus (novel) every third day, while another group was presented with the same sensory stimulus (repeated) every third day. Kindling stimulation applied to the dorsal hippocampus resulted in progression of the AD characteristics and seizure behavior, which typically developed very slowly in the early stages. The application of both the novel and repeated sensory stimulation during partial seizures (stages I and 2) resulted in a reduction in the seizure severity but not in the afterdischarge duration. Sensory stimulation delivered during secondarily generalized seizures (stages 4 and 5) failed to affect either parameter. (C) 2005 Elsevier Ireland Ltd. All rights reserved.