Tonically rhythmic neurons within a cardiorespiratory region of the nucleus tractus solitarii of the rat
J. F. Paton, W. T. Rogers and J. S. Schwaber Neural Computation Group, E. I. Du Pont de Nemours, Wilmington, Delaware 19880-0352. 1. Accumulated evidence from the literature led us to investigate whether centrally generated activity was present within a central neuronal network for cardiovascular co...
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Veröffentlicht in: | Journal of neurophysiology 1991-09, Vol.66 (3), p.824-838 |
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Zusammenfassung: | J. F. Paton, W. T. Rogers and J. S. Schwaber
Neural Computation Group, E. I. Du Pont de Nemours, Wilmington, Delaware 19880-0352.
1. Accumulated evidence from the literature led us to investigate whether
centrally generated activity was present within a central neuronal network
for cardiovascular control. An in vitro approach using a brain stem slice
preparation was employed to study the cardiorespiratory region of the
nucleus of the solitary tract (NTS) in the rat. 2. We have discovered
rhythmically active neurons within a restricted part of the
cardiorespiratory NTS. These neurons were localized to regions directly
medial and dorsomedial to the solitary tract (ts) at levels 0.2 mm rostral
to obex extending caudally to the rostral part of the commissural
subnucleus, an area considered to be concerned with cardiovascular
regulation. Although other subnuclei were explored for neurons with ongoing
activity (i.e., dorsolateral, dorsal, and interstitial) at levels 1.5 mm
caudal to 0.75 mm rostral to obex, we failed to find similarly tonically
active cells. 3. Intra- or extracellular recordings were made from 85
neurons with a mean firing rate of 5.1 +/- 0.3 (SE) Hz (range 1-15). The
majority of these (n = 75) received an excitatory synaptic input from the
ipsilateral ts, with latencies ranging between 4 and 20 ms. 4. To determine
whether the tonically rhythmic cells were dependent on synaptic excitatory
drives or were inherent to the cell, we tested, in 45 neurons recorded
extracellularly, the effect of blocking synaptic inputs mediated by
excitatory amino acids by applying either DL-2-amino-5-phosphonovaleric
acid [APV; N-methyl-D-aspartate (NMDA) antagonist] or MK-801 (NMDA
antagonist) with kynurenic acid (Kyn; NMDA, quisqualate, and kainate
receptor blocker) to the bath. After bath application of APV and Kyn or
MK-801 and Kyn, two different responses were observed. In 19 cells ongoing
rhythmic activity was unperturbed, but firing was completely silenced in 26
neurons. In all cases neurons failed to respond to glutamate delivered
locally, and the synaptic input evoked from the ts was blocked. This
evidence indicates the existence of two cell types: autoactive (AA) or
pacemaker-like neurons, the discharge pattern of which depends on intrinsic
properties, and synaptically driven (SD) neurons, the activity of which is
driven by synaptic inputs. 5. Cobalt chloride (Co) was used to block
synaptic effects and was found to increase the discharge rate of AA neurons |
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ISSN: | 0022-3077 1522-1598 |
DOI: | 10.1152/jn.1991.66.3.824 |