Separation of neuron types in the gustatory zone of the nucleus tractus solitarii on the basis of intrinsic firing properties

Abstract

1. Whole-cell current-clamp recordings were made from neurons in the rostral nucleus tractus solitarii (NTS) in an in vitro brain slice preparation in rats. On the basis of previous investigations, these neurons are believed to be involved with processing of gustatory as well as somatosensory information. 2. Rostral NTS neurons had a mean resting membrane potential of -47 mV. The mean input resistance was 336 M omega, and by fitting a double exponential function the membrane time constant had fast (2.3 ms) and slow (20.6 ms) components. 3. Neurons were separated into four different groups on the basis of their responses to a current injection pulse paradigm consisting of membrane hyperpolarization of different magnitudes and durations immediately followed by a long (1.200 ms) depolarizing pulse. The regular repetitive discharge pattern of the first group of neurons (Group I neurons) was changed into an irregular spike train by membrane hyperpolarization. Hyperpolarization of Group II neurons either delayed the occurrence of the first action potential or increased the length of the first interspike interval in the action-potential train produced by membrane depolarization. The length of the delay was related both to the magnitude and duration of the hyperpolarizing prepulse. Hyperpolarization had the least effect on the discharge pattern of Group III neurons. The discharge pattern of Group IV neurons consisted of a short burst of action potentials that was often shortened by prior hyperpolarization of the neuron. 4. Differences exist in other intrinsic properties of the four neuron groups. Group I and III neurons were capable of initiating the highest frequency of action potentials to a 100-pA 1,200-ms depolarizing pulse. In response to a short depolarizing pulse. Group II neurons had the longest latency to the first spike and responded with the fewest action potentials. Group IV neurons tended to have higher input resistance and membrane time constants than the other neuron groups. A subset of neurons in each neuron group showed membrane afterhyperpolarizations (AHP) after depolarization-induced action-potential trains (postburst AHP). Postburst AHP amplitudes ranged from 1.0 to 12.9 mV and were of greatest magnitude in Group II neurons. Postburst AHP durations ranged from 75 to 3,538 ms and were of longest duration in neurons belonging to Group III. Group II neurons, which had the largest postburst AHP magnitude, had the shortest postburst AHP duration. 5. These results demonstrate that neurons in the rostral NTS can be separated on the basis of their intrinsic membrane properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Angiotensin potentiates excitatory sensory synaptic transmission to medial solitary tract nucleus neurons

“…Resting membrane potential in these neurons averaged Ϫ54 Ϯ 0.59 mV (range Ϫ49 to Ϫ60 mV), and input resistance averaged 416 Ϯ 19 M⍀ (range 218-617 M⍀). These passive membrane property values were similar to those reported by others (18,39,54,84). The onset latency of EPSPs evoked in these 26 ANG-responsive neurons by stimulation of the TS was 2-6 ms and averaged 3.4 Ϯ 0.2 ms.…”

Relationship between structure and function of neurons in the rat rostral nucleus tractus solitarii

“…The pH was adjusted to 7.4 with KOH. Whole-cell recordings were made using the technique of Blanton et al (1989), as previously described in detail (Bradley and Sweazey, 1992). Once a giga-fl seal was formed and the patch ruptured, current stimulation protocols were performed and voltage data were acquired using the pCLAMP program (Axon Instruments).…”

Biophysical and Morphological Properties of Parasympathetic Neurons Controling the Parotid and von Ebner Salivary Glands in Rats

“…Examination of the repetitive discharge characteristics of both the rostral and caudal NST neurons has shown that neurons of the NST have similar response patterns to neurons of the parasympathetic cell column. NST neurons have been characterized as having delayed excitation, long first ISI, tonic, and burst patterns as well as expressing I A (Bradley and Sweazey 1992;Tell and Bradley 1994).…”

“…A number of other investigators have used this protocol to define different neuron groups based on biophysical characteristics (Bradley and Sweazey 1992;Champagnat et al 1986;Manis 1990;Yarom et al 1985).…”