Kv1.3 mediates cholinergic hyperexcitability in a mouse model of Parkinson's disease.

TUBERT C; TARAVINI IR; SANCHEZ G; PROST A; RELA L; MURER MG

Chicago, Illinois.

Congreso; 2015 Annual meeting of the Society for Neuroscience; 2015

Society for Neuroscience

Balanced actions of dopamine (DA) and Acetylcholine (ACh) shape striatal function. In Parkinson´s disease (PD) this balance is lost, leading to an hypercholinergic state. ACh is released in the striaum by tonically active interneurons (ChIs). Recent work shows that ChIs are hyperexcitable in a rat model of PD as a result of a lack of ?accommodation?, an intrinsic property that markedly slows firing during sustained current injection. Here our aim is to identify currents that regulate ChIs accommodation in mouse brain slices. ChIs represent less than 5% of the striatal neurons, so we used mice expressing tdTomato fluorescent protein in ChIs (ChAT-Cre;rt) to find them easily. By means of immunohistochemistry we demonstrate that alltdTomato cells express ChAT in ChAT-Cre;rt mice, but not the markers of other striatal interneurons including PV, NPY and NOS. Moreover, tdTomato-ChIs have electrophysiological properties similar to those of ChIs recorded from wild type mice. Extending previous studies showing more excitable ChIs in juvenile mice, we found that ChIs almost always show accommodation in adult mice but many ChIs do not in juvenile animals. Thus, accommodation is developmentally regulated. Margatoxin (MgTx), a blocker of Kv1.3 channels, markedly attenuated accommodation in ChIs, shown by an increase in the number of spikes fired (from 7.2±1.3 to 13.3±1.1 spikes; p=0.003) and a prolongation of firing (from 332.2±127.2 to 828.8±55.6 s; p=0.008) during a 1s depolarizing current step. Dendrotoxin, a less selective Kv1 blocker, also reduced accommodation, while blockers of Kv7 channels like XE991 and UCL2077, were ineffective. MgTx also increased spontaneous firing (p=0.0455) measured in cell-attached recordings. We have isolated and characterized the MgTx-sensitive current in accommodating ChIs (Vact=-38+7mV, V50=-3+8mV, Imax=1500pA). Immunohistochemistry in brain sections and PCR of laser dissected ChIs revealed the expression of Kv1.3 channels. Thus, ChIs express a functionally relevant Kv1 conductance. We have then evaluated the influence of endogenous DA on accommodation. Bath application of D1 (SCH23390) and D2(sulpiride) type receptor antagonists does not block accommodation. However, as it is the case in rats, fewer ChIs show accommodation in a mouse model of PD induced with 6-OHDA. Moreover, MgTx-sensitive currents are smaller in ChIs of 6-OHDA-lesioned mice compared to sham-mice (p