Repeated cocaine administration in vivo altered the membrane properties of NAc neurons recorded in vitro
| Saline | Cocaine | Lidocaine | |
|---|---|---|---|
| Number of neurons | 36 | 29 | 14 |
| Number of rats | 25 | 19 | 4 |
| Passive membrane properties | |||
| RMP (mV) | −79.1 ± 0.8 | −83.8 ± 0.6** | −76.9 ± 1.5 |
| Rin(mΩ) | 38.3 ± 3.1 | 42.4 ± 3.1 | 32.1 ± 2.9 |
| Time constant (τ, msec) | 5.6 ± 0.5 | 4.7 ± 0.8 | 5.9 ± 1.3 |
| Active membrane properties | |||
| Current to generate AP (nA) | 0.65 ± 0.03 | 0.96 ± 0.06** | 0.69 ± 0.09 |
| AP threshold (mV) | −46.7 ± 1.5 | −40.9 ± 1.7* | −46.1 ± 2.1 |
| AP amplitude (mV) | 61.1 ± 1.1 | 52.5 ± 1.7** | 59.2 ± 1.2 |
| AP duration (msec) | 2.1 ± 0.1 | 2.2 ± 0.1 | 1.5 ± 0.1* |
| AHP amplitude (mV) | 10.3 ± 0.6 | 12.8 ± 1.0 | 11.7 ± 1.0 |
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Intracellular recording was used to measure the membrane properties of nucleus accumbens neurons from brain slices obtained from the three groups of rats. Values represent the mean ± SEM for the number of neurons indicated (*p < 0.05; **p < 0.01; with Student’s t test used to compare with control). Resting membrane potential (RMP) was measured in the absence of injected current before the initiation of other manipulations. Apparent input resistance (Rin) and time constants were determined by the membrane potential changes induced by hyperpolarizing current pulses, with the aid of algorithms within the pCLAMP software. Action potentials (APs) were generated by injecting step depolarizing current pulses of 0.1 nA increments. AP characteristics were obtained from the initial spike evoked by the minimal depolarizing current pulse in every NAc neuron recorded; amplitudes were measured from the spike threshold. After hyperpolarization (AHP) amplitudes were measured from the equipotential point of the spike threshold to the maximum deflection of the hyperpolarization after the end of the AP. AP duration was measured at the broadest point of the AP.
