Brain Research 883 2000 22–30 www.elsevier.com locate bres
Research report
Identification of deflation-sensitive inspiratory neurons in the dorsal respiratory group of the rat
Kazuhisa Ezure , Ikuko Tanaka
Department of Neurobiology , Tokyo Metropolitan Institute for Neuroscience, 2-6 Musashidai, Fuchu, Tokyo 183-8526, Japan
Accepted 15 August 2000
Abstract
It has been well established that inspiratory neurons of the dorsal respiratory group DRG are classified into two types based on whether they receive inputs from slowly-adapting pulmonary stretch receptors SARs or not. Inspiratory neurons with SAR inputs are
called Ib and the others are called Ia neurons. In this study, we identified a novel group of inspiratory neurons in Nembutal-anesthetized, paralyzed, and artificially-ventilated rats. 1 These DRG inspiratory neurons were activated characteristically by lung deflation. 2 They
were orthodromically activated by electrical stimulation of the vagus nerve at a low intensity just above the threshold for afferents from SARs or rapidly-adapting pulmonary stretch receptors RARs. 3 The orthodromic latencies ranged from 1.9 to 2.5 ms indicated that
they receive direct inputs from low-threshold vagal afferents. 4 Unlike Ib neurons, they hardly responded to lung inflation and never exhibited tonic firing in response to maintained lung inflation. 5 The majority 92 of them were antidromically activated by electrical
stimulation of the cervical spinal cord. These deflation-sensitive inspiratory neurons clearly form a distinct group, and their firing pattern is consistent with the hypothesis that they receive inputs from RAR afferents as well as the central inspiratory drive. The results indicating
that DRG inspiratory neurons are classified into at least three groups provide new insights into the organization and role of the DRG.
2000 Elsevier Science B.V. All rights reserved.
Theme : Endocrine and autonomic regulation
Topic : Respiratory regulation
Keywords : Respiration; Nucleus tractus solitarii; Lung deflation; Inspiratory neuron; Rapidly-adapting pulmonary stretch receptor
1. Introduction the cat. However, detailed firing properties in some types
of DRG neurons are not necessarily the same as those of In our previous study in the rat [15], we could find too
cats. For instance, pump neurons P-cells [3] which few respiratory neurons in the dorsomedial medulla and
receive inputs from the slowly-adapting pulmonary stretch reported that the dorsal respiratory group DRG that was
receptors SARs [19] exhibit various properties which initially identified in the cat [2,3,6] might not exist in the
have not been described in the cat [26]. Furthermore, firing rat. The controversy about the presence or absence of rat
patterns of Ib neurons, which have combined central DRG [15,31,35] has been settled by de Castro et al. [13],
inspiratory and SAR inputs, seem different from those in who showed clearly the presence of inspiratory neurons
the cat [13]. Since the rat is now the most important which were located in the ventrolateral subnucleus of the
experimental animal for study of the neural control of tractus solitarii NTS. In addition, they showed that
breathing, we have re-examined the firing properties of various respiration-related neurons of rat DRG had firing
respiration-related neurons of the DRG. patterns generally similar to those previously described in
Lung inflation and withholding inflation are frequently- used maneuvers to examine inputs from lung stretch
receptors and classify respiratory neurons [8,10]. On the
Corresponding author. Tel.: 181-42-325-3881; fax: 181-42-321-
other hand, lung deflation generated by either lowering a
8678. E-mail address
: ezurektmin.ac.jp K. Ezure.
positive end-expiratory pressure PEEP or allowing the
0006-8993 00 – see front matter
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K . Ezure, I. Tanaka Brain Research 883 2000 22 –30
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lungs to collapse to atmospheric pressure is a specially lactated Ringer’s solution with 5 glucose was intraven-
useful maneuver to examine inputs from the rapidly-adapt- ously administered when necessary. Rectal temperature
ing pulmonary stretch receptors RARs [11,17,19] but has was maintained within 36–378C using a heating lamp. End
not been adopted for classifying respiratory neurons. In the tidal CO
was monitored and maintained at 4–5 by
2
present study, we found a group of inspiratory neurons adjusting tidal volume or frequency of a respirator.
which were characteristically activated by deflation of the lungs.
2.2. Recording and experimental protocol DRG neurons were recorded extracellularly with glass
2. Materials and methods micropipettes filled with 3 M KCl saturated with Fast
