Intrahippocampal transplantation of ES cell-derived neural precursor cells into a chronic epilepsy model – functional analysies

Despite the potential of embryonic stem (ES) cell-based reconstructive approaches, very little is known about the functional properties of these cells after in vivo transplantation into the adult central nervous system, especially into a pathologically altered environment. Here, we have analyzed the functional integration of ES cell-derived neurons (ESNs) into an adult rat model of chronic epilepsy.

The pilocarpine model, in which rats develop recurrent seizures with concomitant hippocampal atrophy, gliosis and neuron loss some weeks after a pilocarpine-induced status epilepticus, was used as a chronic epilepsy model. Tau enhanced green fluorescent protein (EGFP) ES cell-derived precursors exhibiting neuron-specific EGFP expression were transplanted bilaterally into the hippocampi of two month old pilocarpine and sham-control rats. Whole-cell current- and voltage-clamp recordings of green fluorescent ESNs in hippocampal slices at room temperature were performed 13 to 34 days after transplantation. After electrophysiology, the slices were processed for biocytin, GFP and M6 stainings.

The ESNs generally remained at the transplant site but showed clear outgrowth of processes into the host tissue. Current-clamp recordings revealed spontaneous rhythmic discharges in a majority of the ESNs at a frequency of around 3Hz. Action potentials seemed to become larger and narrower with time after transplantation. Burst discharges were observed in roughly 20% of the cells. In all ESNs, voltage-gated sodium and potassium currents were found, and most of them also showed inward-rectification. 80–90% of ESNs received spontaneous synaptic input. AMPA- and GABA-receptor mediated postsynaptic potentials (PSPs) could by identified pharmacologically, as well as by their typical reversal potentials. Intact short term plasticity in double pulse experiments was found for both PSP types at interpulse intervals between 20 and 160 ms. There were no obvious differences between the functional properties of ESNs in sham-control and in pilocarpine-treated rats.

In summary, ESNs transplanted intrahippocampally into an adult rat model of chronic epilepsy extend processes into the host tissue, and display typical intrinsic neuronal properties and synaptic communication. Incorporation of functionally active ESNs into the epileptic circuitry might be exploited for the development of ES cell-based approaches for seizure control.

Supported by the SFB TR3.