Effects of aging on the intrinsic membrane properties of medial NTS neurons of Fischer-344 XXXX .

@entity35 @entity5433 @entity4780
1. Recent studies have demonstrated that the arterial baroreflex is imparied with aging and have implicated central components of the baroreflex arc in this @entity5433 . Neurons in the medial portion of the nucleus tractus solitarius (mNTS) receive a major input from the arterial baroreceptors. The present study was undertaken to characterize the intrinsic membrane properties of mNTS neurons in young @entity35 and to test the hypothesis that these properties are altered with aging. An in vitro brain stem slice preparation was used to record intracellularly from mNTS neurons; passive membrane properties, action potential characteristics, and repetitive firing properties were examined and compared. 2. Neurons in the mNTS of young (3-5 mo old) Fischer-344 @entity35 (F-344; n = 35) had a resting membrane potential of -57 +/- 6.9 mV (mean +/- SD), a membrane time constant of 18 +/- 9.0 ms, and an input resistance of 110 +/- 60 @entity4780 . Action potential amplitude was 81 +/- 7.5 mV with a duration at half-height of 0.83 +/- 0.15 ms. The spontaneous firing rate in 24 cells was 4.3 +/- 2.9 Hz. The amplitude and duration of the action potential afterhyperpolarization (AHP) were 6.6 +/- 3.0 mV and 64 +/- 34 ms, respectively. All neurons expressed spike frequency adaptation, action potential AHP, and posttetanic hyperpolarization. Delayed excitation and postinhibitory rebound were present in 34 and 14% of neurons tested, respectively. Neurons from adult (10-12 mo old) F-344 @entity35 (n = 34) were similar to the young F-344 @entity35 with respect to all of these variables. 3. Neurons from aged (21-24 mo old) F-344 (n = 32) were similar to those from young and adult @entity35 , but there were two potentially important differences: the mean input resistance of the aged neurons was higher (170 +/- 150 @entity4780 ), with a larger proportion (46% of aged neurons vs. 20% of young neurons and 21% of adult neurons) having input resistances > 150 @entity4780 ; and there was a tendency for a smaller percentage of aged neurons (16% of aged neurons vs. 34% of young neurons and 29% of adult neurons) to express delayed excitation. 4. The potential significance of a high input resistance was tested by comparing the steady-state current-voltage (I-V) relationships and the frequency-current (f-I) relationships among low-resistance (1-100 @entity4780 ), medium-resistance (101-200 @entity4780 ).(ABSTRACT TRUNCATED AT 400 WORDS)
