Charybdotoxin and apamin sensitivity of the calcium-dependent repolarization and the afterhyperpolarization in neostriatal neurons

Abstract

1. Intracellular recordings from neostriatal neurons in an in vitro slice preparation of the rat brain were used to analyze the pharmacological sensitivity of the action potential (AP) repolarization and the afterhyperpolarization (AHP) that follows a single action potential. The interspike voltage trajectory and the AHP could be divided into two main parts: a fast component lasting a few milliseconds and better observed during a train of spikes, and a slow component lasting approximately 250 ms and that comprises the main portion of the AHP. In some cells, a slow (up to 1 s) component of low amplitude was also detected. 2. Single APs were elicited at two imposed membrane potentials (around -60 and around -80 mV). The AP amplitude was larger, the repolarization rate was faster, and the duration was shorter when spikes were evoked at -80 mV. When measured from the -60 mV holding potential, the afterpotential was an AHP with peak amplitude of -5 mV. The afterpotential became a delayed depolarization (DD) at -80 mV. 3. Firing frequency adaptation was voltage sensitive. The firing of APs induced by long intracellular current pulses from a holding potential of -80 mV exhibited only a slow-frequency adaptation (time constant of seconds). However, at -60 mV, an initial and faster frequency adaptation was evident (time constant of tens of milliseconds). 4. The Ca2+ channel blocker Cd2+ retarded AP repolarization rate. This effect correlated with a significant block of the fast and slow components of the AHP. In contrast, Ni2+ had no significant effects on the same parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Modeling functions of striatal dopamine modulation in learning and planning

“…2 and 3). Although this model feature does not hold exactly for medium spiny neurons (Pineda et al, 1992), the simulated subthreshold membrane potentials and firing rates reproduce approximately those for the medium spiny neuron shown on top of Fig. 3.…”

“…Medium spiny neurons fire with a maximal firing rate y max of about 6 Spikes per 100 msec (Apicella et al, 1992;Pineda et al, 1992;Nisenbaum et al 1994). A factor a = 0.3 Spikes/(100 msec * mV) is used to scale the firing rate to experimental data and is estimated from firing rates for constant current injections in the absence of dopamine agonists (estimated from figure 1 in Nisenbaum et al 1994; similar in figure 3 in Pineda et al, 1992). Eq.…”

“…3 does not take into account that firing rate adaptations occur during a few hundreds of milliseconds after current step injections ( Fig. 3; Pineda et al, 1992). The dopamine-dependent signal W mem (t) influences the firing rate (eq.…”

D1Receptor Activation Enhances Evoked Discharge in Neostriatal Medium Spiny Neurons by Modulating an L-Type Ca2+Conductance

“…The enhancement was blocked by the L-channel antagonist calciseptine (200 M, n ϭ 2). These experiments show not only that L-type Ca 2ϩ currents contribute to the regulation of repetitive discharge in medium spiny neurons (see also Galarraga et al, 1989;Bargas et al, 1991;Pineda et al, 1992;Hernández-López et al, 1996a) but that D 1 class receptors are capable of enhancing evoked activity by augmenting these currents.…”

Comparison of Normal and Parkinsonian Microcircuit Dynamics in the Rodent Striatum

“…MSNs are the major cell population commonly being in a resting state with a polarized membrane potential (ca., -80 mV) and relatively low input resistance (ca., 100 www.intechopen.com M in adult neurons) Reyes et al, 1998). Upon depolarization, these neurons fire tonically due to persistent voltage-activated K + -currents Nisenbaum and Wilson, 1995;Bargas et al, 1999), with a long latency to first spike due inactivating K + -currents (Surmeier et al, 1988;Bargas et al, 1989), inward rectification (Galarraga et al, 1994;Nisenbaum and Wilson, 1995), and interspike intervals partially dependent on Ca 2+ -activated K + -currents (Pineda et al, 1992;Bargas et al, 1999), among other outward currents (Nisenbaum and Wilson, 1995;Shen et al, 2005). MSNs can be classified as striatopallidal or indirect pathway neurons and striatonigral or direct pathway neurons, based on their axonal projections, receptors and peptide expression (Gerfen et al, 1990;Smith et al, 1998).…”