EPSPs in rat neocortical neurons in vitro. I. Electrophysiological evidence for two distinct EPSPs

Abstract

1. To investigate excitatory postsynaptic potentials (EPSPs), intracellular recordings were performed in layer II/III neurons of the rat medial frontal cortex. The average resting membrane potential of the neurons was more than -75 mV and their average input resistance was greater than 20 M omega. The amplitudes of the action potentials evoked by injection of depolarizing current pulses were greater than 100 mV. The electrophysiological properties of the neurons recorded were similar to those of regular-spiking pyramidal cells. 2. Current-voltage relationships, determined by injecting inward and outward current pulses, displayed considerable inward rectification in both the depolarizing and hyperpolarizing directions. The steady-state input resistance increased with depolarization and decreased with hyperpolarization, concomitant with increases and decreases, respectively, in the membrane time constant. 3. Postsynaptic potentials were evoked by electrical stimulation via a bipolar electrode positioned in layer IV of the neocortex. Stimulus-response relationships, determined by gradually increasing the stimulus intensity, were consistent among the population of neurons examined. A short-latency EPSP [early EPSP (eEPSP)] was the response with the lowest threshold. Amplitudes of the eEPSP ranged from 4 to 8 mV. Following a hyperpolarization of the membrane potential, the amplitude of the eEPSP decreased. Upon depolarization, a slight increase in amplitude and duration was observed, accompanied by a significant increase in time to peak. 4. The membrane current underlying the eEPSP (eEPSC) was measured using the single-electrode voltage-clamp method. The amplitude of the eEPSC was apparently independent of the membrane potential in 8 of 12 neurons tested. In the other 4 neurons, the amplitude of the eEPSC increased with hyperpolarization and decreased with depolarization. 5. Higher stimulus intensities evoked, in addition to the eEPSP, a delayed EPSP [late EPSP (lEPSP)] in greater than 90% of the neurons tested. The amplitude of the lEPSP ranged from 12 to 20 mV, and the latency varied between 20 and 60 ms. The amplitude of the lEPSP varied with membrane potential, decreasing with depolarization and increasing following hyperpolarization. The membrane current underlying the lEPSP (lEPSC) displayed a similar voltage dependence. 6. At stimulus intensities that led to the activation of inhibitory postsynaptic potentials (IPSPs), the lEPSP was no longer observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Dopamine D1 and D4 Receptor Subtypes Differentially Modulate Recurrent Excitatory Synapses in Prefrontal Cortical Pyramidal Neurons

“…The late EPSPs reported here by afferent stimulation in slices taken from developmentally mature rats (ie 6-8 weeks; Zhu, 2000) resemble the late EPSPs evoked in layer II/III frontal cortical pyramidal neurons by intracortical stimulation in slices from young prepubertal rats (o6 weeks; 120-150 g; Sutor and Hablitz, 1989) or in guinea-pig neocortical neurons that were characterized as stimulus intensity sensitive (Connors et al, 1982), as similarly reported here (see Figure 8). These neurons, which were mostly recovered in cortical deep layer V following intracellular recording/ labeling, had axons which ramified extensively and ascended to superficial layers, in addition to giving off several secondary axons that target subcortical structures (see Figure 1c).…”

Facilitation of an NMDA receptor‐mediated EPSP by paired‐pulse stimulation in rat neocortex via depression of GABAergic IPSPs.

“…For example, the latency to peak of the late EPSP in vivo (22 ms) was shorter than that obtained under control conditions in vitro (-50 ms), but similar to that of the pharmacologically isolated late EPSP (28 ms). Further, the optimal interpulse interval for eliciting the augmenting response (100-150 ms) was shorter than that optimal for paired-pulse facilitation of the late EPSP in vitro (200-300 ms Sutor & Hablitz, 1989a;) undoubtedly reflect partial suppression by IPSPs. Overlap with the early EPSP underlies the consistent observation that it contains a small but significant NMDA receptor-mediated component (Jones & Baughman, 1988;Hwa & Avoli, 1992).…”

“…9Ba; al. 1964;Douglas & Martin, 1991;Ferster & Jagadeesh, 1992;Metherate & Ashe, 1993a, b;Nunez et al 1993) and in vitro (Connors et al 1982;Jones & Baughman, 1988;Sutor & Hablitz, 1989a;Higashi et al 1991;Cox et al 1992). Synaptic interactions studied using the in vitro slice preparation probably occur in vivo, as well.…”

Coding of FM sweep trains and twitter calls in area CM of marmoset auditory cortex

“…In general, it has been observed that periodicity or temporal envelope coding degrades along the ascending auditory pathway (Joris et al, 2004), presumably due to the intervening synaptic relay (Berry et al, 1976;Miles, 1986;Sutor et al, 1989). If those principles also apply to auditory cortex, temporal resolution should be greater in the core than the belt areas.…”