Comparison of electrical properties and action potentials in GnRH and non-GnRH neurons
| GFP-expressing GnRH neurons (n= 26) | Non-GFP-expressing hypothalamic neurons (n = 26) | Adult GnRH neuronsa (n = 8) | Embryonic GnRH neuronsb (n = 13) | Immortalized GnRH neuronsc,d (n = 26)c (n = 4)d | |
|---|---|---|---|---|---|
| Resting potential (mV) | −55.7 ± 3.65 | −57.0 ± 5.2 | −55.0 ± 8.5 | −50.8 ± 3.6 | −58 ± 6d |
| Input resistance (GΩ) | 1.2 ± 0.5 | 1.1 ± 0.7 | 0.5 ± 0.2 | 2.4 ± 2.0# | NR |
| Time constant (msec) | 30.4 ± 16.5 | 35.3 ± 13.8 | 23.0 ± 14.1 | 30.1 ± 25.5# | NR |
| Membrane capacitance (pF) | 25.9 ± 11.3 | 41.6 ± 20.8 | 46.0 | 10# | 6.5 ± 2.3c |
| Spontaneous action potentials (Hz) | 1.2 ± 1.2 | 2.2 ± 3.0 | 5.4 ± 4.0 | (Max = 4) | 1d |
| Evoked action potentials (Hz) | 25.4 ± 8.3 (Max = 44) | 25.7 ± 14.3 | NR | (Max = 16) | NR |
| Threshold (mV) | −32.2 ± 3.9 | −39.9 ± 5.7 | NR | −37.5 | NR |
| Amplitude (mV) | 79.5 ± 9.8 | 76.0 ± 12.0 | NR | 80 | NR |
| Duration at half-amplitude (msec) | 1.2 ± 0.3 | 1.2 ± 0.4 | 2.5 ± 0.7 at 1/3 amplitude | 2 | NR |
| dV/dt Rise (mV/msec) | 88.9 ± 33.1 | 105.0 ± 39.9 | NR | NR | NR |
| dV/dt Fall (mV/msec) | 53.1 ± 13.9 | 63.1 ± 23.6 | NR | NR | NR |
| Afterhyperpolarization potential (mV) | −67.4 ± 4.2 | −64.5 ± 5.8 | −62.6 ± 2.1 | NR | NR |
| Maximum interspike interval (msec) | 61.3 ± 27.2 | 82.1 ± 62.7 | NR | NR | NR |
| Minimum interspike interval (msec) | 33.5 ± 13.5 | 37.7 ± 39.3 | NR | 50 1st to 2nd | NR |
| Max/min interspike interval ratio | 1.9 ± 0.6 | 2.5 ± 1.5 | NR | NR | NR |
Values are shown for GFP-expressing GnRH neurons and non-GFP-expressing hypothalamic neurons (non-GnRH neurons) from the present study, as well as for adult GnRH neurons identified post hoc (aLagrange et al., 1995; Kelly, personal communication), embryonic GnRH neurons (bKusano et al., 1995), and immortalized GnRH neurons (cBosma, 1993;dHales et al., 1994). The input resistance was determined from the voltage response to a 1 sec application of hyperpolarizing current. The time constant was the time required to reach 63% of the maximum voltage response to hyperpolarizing current. The membrane capacitance was calculated by dividing the time constant by the input resistance. Action potentials were evoked by a 1 sec application of depolarizing current. Action potential characteristics were those in response to the amount of current that evoked the maximum firing frequency in each neuron. In the present study, this amount of depolarizing current ranged from 10 to 60 pA. Amplitude, Voltage difference between the threshold and the peak of the action potential; duration, duration of the action potential at half-amplitude; dV/dt rise, slope of the rising phase (threshold-to-peak) of the action potential; dV/dt fall, slope of the falling phase (peak-to-threshold) of the action potential; afterhyperpolarization potential, most hyperpolarized potential following each action potential. Interspike intervals are expressed as the maximum and minimum intervals between action potentials (present study) or as the interval between the first and second action potential (Kusano et al., 1995). Values are mean ± SD, mean only, or maximum, whichever was reported. NR, Not reported;
, n = 6.