Influence of ongoing activity on striatal medium spiny neurons response to cortical stimulation

FERNANDO KASANETZ; MARIANO A. BELLUSCIO; LUCILA KARGIEMAN, JORGE H PAZO, M.GUSTAVO MURER, LUIS A RIQUELME; M GUSTAVO MURER

San Diego

Congreso; Neuroscience 2004 34th SFN Annual Meeting; 2004

SFN

Themembrane potential (Vm) of striatal Medium Spiny Neurons (MSN)fluctuates between a hyperpolarized down state and a depolarized upstate, when recorded in vivo. Because MSN can fire action potentialsonly during the up state, these events appear to be relevant forinput information processing. It has been shown that the MSN Vmalternation is driven by frontal cortex network activity. We analyzedthe influence of ongoing cortical network activity (estimated fromEEG recordings) and the cortically-driven MSN Vm fluctuation on theMSN response to focal cortical electrical stimulation in control ratsand in rats bearing a nigrostriatal lesion (6-OHDA), and in micelacking dopamine D2 receptors and their wild type siblings. Allexperimental groups had similar cortically-evoked response patterns,which usually consisted of an excitatory postsynaptic potential(EPSP) followed by an early hyperpolarization (EH) and a latedepolarization (LD). The shape of the EH-LD sequence closely followedthat of the evoked EEG waveform, supporting that the LD (like the upstate) is driven by the cortex. In fact, the time course of EH and LDwere strongly dependent on the ability of the electrical stimulus toreset cortical activity. When the cortical stimulus failed to turnoff cortical network activity the EPSP was not followed by thetypical EH-LD sequence. Furthermore, the latency of the LD and theevoked EEG wave depended on the timing of the resetting stimulusrelative to the ongoing cortical activity. Our results furthersuggest that variability in EPSP features (amplitude, rise and decayslopes) also depends on the pattern of cortical network activity atthe time of electrical stimulus arrival.