The Journal of Neuroscience, December 1, 2000, 20(23):8788-8801
Fetal Hippocampal Grafts Containing CA3 Cells Restore Host
Hippocampal Glutamate Decarboxylase-Positive Interneuron Numbers in a
Rat Model of Temporal Lobe Epilepsy
Ashok K.
Shetty and
Dennis A.
Turner
Departments of Surgery (Neurosurgery) and Neurobiology, Duke
University Medical Center. Durham, North Carolina 27710, and Medical
Research and Surgery (Neurosurgery) Services, Veterans Affairs Medical
Center, Durham, North Carolina 27705
Degeneration of CA3-pyramidal neurons in hippocampus after
intracerebroventricular kainic acid (KA) administration, a model of
temporal lobe epilepsy, results in hyperexcitability within both
dentate gyrus and the CA1 subfield. It also leads to persistent reductions in hippocampal glutamate decarboxylase (GAD) interneuron numbers without diminution in Nissl-stained interneuron numbers, indicating loss of GAD expression in a majority of interneurons. We
hypothesize that enduring loss of GAD expression in hippocampal interneurons after intracerebroventricular KA is attributable to
degeneration of their CA3 afferent input; therefore, fetal CA3 grafts
can restore GAD interneuron numbers through graft axon reinnervation of
the host. We analyzed GAD interneuron density in the adult rat
hippocampus at 6 months after KA administration after grafting of fetal
mixed hippocampal, CA3 or CA1 cells into the CA3 region at 45 d
after lesion, in comparison with "lesion-only" and intact
hippocampus. In dentate and CA1 regions of the lesioned hippocampus
receiving grafts of either mixed hippocampal or CA3 cells, GAD
interneuron density was both significantly greater than
lesion-only hippocampus and comparable with the intact
hippocampus. In the CA3 region, GAD interneuron density was
significantly greater than lesion-only hippocampus but less than the
intact hippocampus. Collectively, the overall GAD interneuron density
in the lesioned hippocampus receiving either mixed hippocampal or CA3
grafts was restored to that in the intact hippocampus. In contrast,
GADinterneuron density in the lesioned hippocampus receiving CA1 grafts
remained comparable with lesion-only hippocampus. Thus, grafts
containing CA3 cells restore CA3 lesion-induced depletions in
hippocampal GAD interneurons, likely by reinnervation of GAD-deficient
interneurons. This specific graft-mediated effect is beneficial because
reactivation of interneurons could ameliorate both loss of functional
inhibition and hyperexcitability in CA3-lesioned hippocampus.
Key words:
brain injury; GAD-67; hippocampus; neural grafting; nonpyramidal neurons; temporal lobe epilepsy
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