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

CECILIA TUBERT; IRENE TARAVINI; GONZALO SANCHEZ; ALEJANDRA PROST; LORENA RELA; MARIO GUSTAVO MURER

Chicago

Congreso; Society for Neuroscience Annual Meeting 2015; 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 anhypercholinergic state. ACh is released in thestriaum bytonically active interneurons (ChIs). Recent work showsthatChIsare hyperexcitablein 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 ChIsaccommodationin 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 all tdTomato cells express ChAT in ChAT-Cre;rt mice, but not themarkers 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 studiesshowing more excitable ChIs in juvenile mice, we found that ChIsalmost 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 sectionsand 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 ofD1(SCH23390) and D2(sulpiride)type receptor antagonistsdoes not block accommodation. However, as it is the case in rats, fewer ChIsshow 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