Abstracts

RATIONALE: It has been shown that dentate gyrus granule cells develop basal dendrites after seizures (Spigelman et al. 1998; Buckmaster and Dudek 1999). To determine the potential functional implications of basal dendrites, granule cells with basal dendrites were recorded in slices made from pilocarpine-treated rats after status epilepticus and chronic seizures. Granule cells with and without basal dendrites were compared. METHODS: Adult male rats were injected with pilocarpine (380 mg/kg i.p.), and diazepam (5 mg/kg i.p.) was injected after 1 hr of status. Hippocampal slices were made 2-7 months after status from animals with spontaneous motor seizures and mossy fiber sprouting. Sprouting was verified immunocytochemically using an antibody to neuropeptide Y or using Timm stain in the hemisphere contralateral to the one used for slices. Recordings were also made from granule cells in age-matched, saline controls. Granule cells were recorded with sharp microelectrodes containing 4% Neurobiotin in 1 M potassium acetate. Perforant path fibers were stimulated by a monopolar electrode placed in the outer molecular layer just below the subiculum. RESULTS: Granule cells that had basal dendrites (n=9) were similar in membrane properties to granule cells from the same animals that had no basal dendrites (n=10). A subset of granule cells with basal dendrites (3/9), and some granule cells without basal dendrites (4/10) had high levels of spontaneous subthreshold synaptic potentials and also had abnormal evoked responses that resembled paroxsmal depolarization shifts. However, the other 6 granule cells with basal dendrites and the other 6 granule cells without basal dendrites had levels of spontaneous subthreshold activity and evoked responses that were similar to granule cells recorded in control slices. Suprathreshold stimulation in these cells produced 1 action potential per stimulus. CONCLUSIONS: The results suggest that granule cells in hippocampal slices from epileptic pilocarpine-treated rats that have basal dendrites can be heterogeneous morphologically and physiologically. Supported by NS 38285.