Skip to main content
NCBI home page
The Journal of Physiology logoLink to The Journal of Physiology
. 2003 Apr 11;549(Pt 1):327–332. doi: 10.1113/jphysiol.2003.040204

Connections between respiratory neurones in the neonatal rat transverse medullary slice studied with cross-correlation

Yan Mei Li *, Linlin Shen *, John H Peever *, James Duffin *,†
PMCID: PMC2342932  PMID: 12692183

Abstract

In the transverse medullary slice prepared from neonatal rats the hypoglossal nerve rootlets exhibit a bursting ‘respiratory’ rhythm as do neurones in the pre-Bötzinger complex (PBC). We used cross-correlation analysis of the rhythmic multiunit discharges recorded from hypoglossal nerve rootlets, hypoglossal nucleus neurones and PBC neurones to investigate the connections between these groups. All cross-correlograms computed between left and right hypoglossal nerves, and between hypoglossal neurones and contralateral hypoglossal nerves, displayed central peaks with broad half-amplitude widths (mean ± s.d. of 29.6 ± 10.4 and 37.3 ± 6.0 ms, respectively), which we interpreted as evidence for activation from a common source. Five of the 18 cross-correlograms computed between left and right PBC neurones displayed peaks either side of time zero with narrower half-amplitude widths (mean ± s.d. of 9.3 ± 1.9 ms) superimposed on broader central peaks, which we interpreted as evidence for mutual excitation and common activation, respectively. Cross-correlograms computed between PBC neurones and contralateral hypoglossal neurones or nerves did not display consistent features, but some of those computed between PBC and ipsilateral hypoglossal neurones (two of eight) or nerves (two of five) displayed peaks with broad half-amplitude widths (mean ± s.d. of 36.8 ± 6.9 ms), offset from time zero by 6 ms (except for one at 18 ms), which we interpreted as evidence for excitation of hypoglossal neurones and motoneurones by PBC neurones. We concluded that rhythm is synchronised between left and right sides by mutual excitatory connections between left and right PBC neurones. The rhythm is transmitted to ipsilateral hypoglossal neurones by a paucisynaptic pathway. Both hypoglossal neurones and PBC neurones receive a common activation from as yet unidentified sources.

The transverse medullary slice preparation of neonatal rats has been used to study respiratory rhythm generation (Smith et al. 1991; Rekling & Feldman, 1998; Richter & Spyer, 2001). In this preparation, hypoglossal nerve rootlets generate spontaneous rhythmic discharges (Al-Zubaidy et al. 1996; Peever et al. 1999), which are synchronous with the firing of neurones in the pre-Bötzinger complex (PBC) of the slice (Koshiya & Smith, 1999; Johnson et al. 2001; Tokumasu et al. 2001). Both left and right sides are synchronised to the same rhythm (Peever & Duffin, 2001). The rhythmic hypoglossal discharge is likely to result from excitation originating from the PBC neurones, and although the transmitters involved have been identified in brainstem slice preparations from neonatal rats (Funk et al. 1993; Wang et al. 2002), the connection has not been functionally demonstrated.

Other connections, such as that transmitting a CO2 drive to hypoglossal motoneurones and PBC neurones, are also unknown. Their presence is deduced from the observation that the frequency of the rhythm recorded from the transverse medullary slice prepared from neonatal rats increases in response to the addition of CO2 to the superfusing bathing medium (Peever et al. 1999). Since both the raphe nuclei and the central chemoreceptor neurones (Okada et al. 2002) are sensitive to local pH changes (Peever et al. 2001b; Richerson et al. 2001), these are likely to be sources of excitation for PBC and hypoglossal neurones.

We set out to apply the technique of cross-correlation of multiunit rhythmic discharges recorded from PBC neurones, hypoglossal nucleus neurones and hypoglossal nerves to detect interconnections in the transverse medullary slice prepared from neonatal rats. A previous such attempt to detect the activation of left and right hypoglossal motoneurones from a common source failed (Peever & Duffin, 2001). That study used cross-correlation of the discharges from left and right hypoglossal nerve rootlets and found no evidence for common activation, but this time we recorded from hypoglossal neurones as well as the hypoglossal nerve. Cross-correlograms with peaks centred on time zero would be evidence for a common activation by excitatory or inhibitory inputs (Kirkwood, 1979; Turker & Powers, 2001). In addition, we wished to detect excitatory connections from PBC neurones to hypoglossal neurones; these would be indicated by peaks at short latencies in the cross-correlograms (Kirkwood, 1979). We also expected to detect excitatory connections between left and right PBC neurones, because anatomical projections between them have been demonstrated by retrograde dye transport from the midline (Koshiya & Smith, 1999), and cross-correlograms computed between the firing of left and right inspiratory neurones in the isolated brainstem–spinal cord preparation from neonatal rats have shown bilateral peaks, evidence for reciprocal excitation (Kashiwagi et al. 1993).

Methods

Transverse medullary slice preparation

All procedures used conformed with the guidelines of the University of Toronto Animal Care Committee. Under deep halothane anaesthesia (administered in an atmosphere of 5 % halothane until no limb withdrawal to a paw pinch) 1 to 7 (median 2)-day-old Sprague-Dawley rats were decapitated at the fifth and sixth cervical spinal level. The head was immediately immersed in ice-cold artificial cerebrospinal fluid (composition (mm): 125 NaCl, 3 KCl, 1 KH2PO4, 2 CaCl2, 1 MgSO4, 25 NaHCO3, and 30 d-glucose). The artificial cerebrospinal fluid was bubbled with 5 % CO2 in O2 to produce a pH of ∼7.4.

The parietal and occipital bones were carefully removed after the skin and muscle over the skull and cervical spinal column were cut away. Then a dorsal laminectomy from the first to fourth cervical vertebrae was performed, the olfactory, cranial and spinal nerves were cut and the whole brainstem-spinal cord excised. After removing both the cerebrum and cerebellum, the brainstem- spinal cord was then mounted on a block of agar by its dorsal surface (cyano-methacrylate) and placed rostral end down. Thin slices were then cut from caudal to rostral using a vibratome (752M Vibroslice, Campden Instruments Inc. or Vibratome 1000 Plus, The Vibratome Company) until the two most rostral hypoglossal nerve rootlets were seen. At this point, a 700–1500 μm (median 1000 μm) slice incorporating the nerve rootlets was made and constituted the transverse brainstem slice.

The transverse brainstem slice preparation was then transferred into a recording chamber mounted on the viewing stage of a microscope (BX50WI Fixed Stage Upright Microscope, Olympus Optical Co.), and perfused with the artificial cerebrospinal fluid at 15–20 ml min−1 at 25–28.6 °C (median 27 °C), and over the next 30 min the KCl concentration was increased from 3 to 9 mm to establish and maintain a stable respiratory rhythm (Smith et al. 1991; Ramirez et al. 1996). Slices prepared in this way generated a stable rhythm for up to 4.5 h.

Nerve recording

The activity of hypoglossal nerve rootlets was recorded with a glass suction electrode mounted on a micromanipulator (Model 10606, Narshige Instruments) clamped to the fluorescence microscope stage to allow precise movement of the suction electrode tip. The signal was pre-amplified (AxoProbe 1A, Axon Instruments) and then amplified further (Neurolog, NL104), filtered (bandpass 0.12–8 kHz) and integrated (time constant = 50 ms).

The activity of single or pairs of hypoglossal neurones and PBC neurones was recorded extracellularly using glass-coated tungsten microelectrodes (0.5–1 MΩ at 1 kHz), positioned with micromanipulators (Narishige) and advanced into brain tissue using micro steppers (Significat, Digitimer). The recorded signals (AxoProbe 1A) were amplified (Neurolog, NL106), filtered (500–5000 Hz; Neurolog, NL126) and displayed on an oscilloscope (Tektronix).

The resulting signals were displayed on oscilloscopes (Tektronix Nicolet) and monitored using loudspeakers. A thermal array chart recorder (Graphtec, WR3600) provided a permanent record, and a digitised videotape recording (Vetter) was made for archival purposes.

Protocol

Multiunit recordings were obtained in simultaneous pairs from hypoglossal nerve rootlets, hypoglossal neurones and PBC neurones. Action potentials were amplitude discriminated (Bak), and the pulses from the two gates were input to a computer via an A/D interface (AT-MIO-16XE-10, National Instruments), and specially written software (National Instruments, LabVIEW, source code available on request) calculated cross-correlograms covering a total time of either ± 50 or ± 100 ms, at bin widths of 0.2 ms.

Further analysis of the cross-correlation data was accomplished with a spreadsheet (Microsoft Excel) where the cross-correlograms could be displayed at bin widths of 0.2 ms or more. The broad peaks in the cross-correlograms were quantified using the k-ratio (Sears & Stagg, 1976), by dividing the peak bin count by the base bin count away from the peak, and tested for statistical significance (Graham & Duffin, 1981). All reported peaks were significant at P < 0.001, except for two of those for cross-correlograms of PBC neurone pairs, which were significant at the P < 0.05 level. The peaks are described as central (straddling zero time) or offset from time zero by a latency to the peak, together with their half-amplitude width.

Results

Figure 1 illustrates the discharge patterns of the multiple units recorded from hypoglossal nerve, hypoglossal neurones and PBC neurones. Altogether 57 slices were used; most (39) yielded a single cross-correlogram, with two per slice computed on 11 occasions and three per slice on seven occasions. Only in one slice were we able to compute cross-correlograms between the three discharges of major interest, left to right PBC neurones, and PBC neurones to contralateral and ipsilateral hypoglossal neurones; the cross-correlogram features observed in this case confirmed the observations detailed below. In general the cross-correlogram features were broad peaks, and so we adopted 4 ms bin widths for display as others have done for cross-correlograms computed in in vitro preparations (Kashiwagi et al. 1993).

Figure 1. Examples of simultaneous multiunit recordings, with an expanded time scale of the same recording on the right.

Figure 1

Open in a new tab

A, left and right PBC neurones. B, left PBC neurones and right hypoglossal (XII) neurones. C, left and right hypoglossal (XII) neurones.

The most common cross-correlogram feature was a central peak straddling time zero; all of the 14 cross-correlograms computed between contralateral discharges recorded from the hypoglossal neurones and nerves displayed such central peaks, as did 9 of the 18 computed between discharges recorded from left and right PBC neurones; the others were featureless.

Figure 2 shows examples of cross-correlograms computed between contralateral pairs of hypoglossal neurones and nerves. For the eight cross-correlograms computed between discharges recorded from left and right hypoglossal neurones, the base bin counts ranged from 35 to 1300 (mean ± s.d. = 223 ± 408), and the half-amplitude widths ranged from 20 to 40 ms (mean ± s.d. of 27.5 ± 8.1 ms). For the six cross-correlograms computed between discharges recorded from the hypoglossal nerve and contralateral hypoglossal neurones, the base bin counts ranged from 35 to 225 (mean ± s.d. = 108 ± 80), and the half-amplitude widths ranged from 28 to 44 ms (mean ± s.d. = 37.3 ± 6.0 ms).

Figure 2.

Figure 2

Open in a new tab

Examples of cross-correlograms computed between the multiunit discharges recorded from hypoglossal neurones and the contralateral hypoglossal nerve (top 3 recordings), and from left and right hypoglossal neurones (bottom 3 recordings) that displayed central peaks (14/14, 100 %). Bin widths are 4 ms.

Some of the cross-correlograms computed between discharges recorded from left and right PBC neurones that featured central peaks (9/18) also featured peaks on either or both sides of time zero (5/18). Examples are shown in Fig. 3; their base counts ranged from 75 to 1500 (mean ± s.d. = 352.8 ± 417.0), and the half-amplitude widths of the central peaks ranged from 36 to 64 ms (mean ±s.d. = 45.8 ± 7.3 ms), with those for the peaks offset from time zero ranging from 8 to 12 ms (mean ± s.d. of 9.3 ± 1.9 ms). The latter peaks were offset by times ranging from 9 to 17 ms (mean ± s.d. of 13.1 ± 2.8 ms).

Figure 3.

Figure 3

Open in a new tab

Examples of cross-correlograms computed between the multiunit discharges recorded from left and right PBC neurones that displayed central peaks (9/18, 50 %) and peaks (indicated by circles: filled, P < 0.01; open, P < 0.05) on one or both sides of time zero (5/18, 30 %). Bin widths are 4 ms.

Cross-correlograms computed between recordings from PBC neurones and contralateral hypoglossal neurones or nerves did not display consistent or significant features, but some of those for ipsilateral hypoglossal neurones (two of eight) or nerves (two of five) displayed broad peaks offset from time zero (Fig. 4); the others were featureless.

Figure 4.

Figure 4

Open in a new tab

Cross-correlograms that displayed central peaks offset from time zero computed between the multiunit discharges recorded from PBC neurones and ipsilateral hypoglossal neurones (2/8, 25 %, middle 2 histograms), and from PBC neurones and ipsilateral hypoglossal nerves (2/5, 40 %, top and bottom histograms). Bin widths are 4 ms.

Discussion

Although the neonatal rat slice preparation has been used to investigate respiratory rhythm generation and its transmission to hypoglossal motoneurones for the past several years, this study is the first to examine connections among the respiratory neurones in the slice preparation. The cross-correlation technique detects functional connections, and our interpretation of these findings is as follows: rhythm is synchronised between left and right sides by mutual excitatory connections between left and right PBC neurones. The rhythm is transmitted to ipsilateral hypoglossal neurones by a paucisynaptic pathway. Both hypoglossal neurones and PBC neurones receive a common activation from as yet unidentified sources.

Our success rate in detecting connections by observing features in cross-correlograms was 50 % for left and right PBC groups of neurones, much higher than that for inspiratory premotor neurones of in vivo preparations (Shen et al. 2002), but similar to that for pairs of inspiratory neurones of in vitro preparations (Kashiwagi et al. 1993). Although the rhythm of both sides was always synchronised we did not detect connections between left and right groups of PBC neurones in all of the slices tested, probably because the neurones recorded did not include sufficient numbers of those that projected across the midline. In addition, there was likely to be considerable heterogeneity in the sample of respiratory neurones in terms of their function. For left and right groups of hypoglossal neurones, central peaks were observed in all their cross-correlograms; although a previous attempt to detect them by cross-correlating hypoglossal nerve discharge failed (Peever & Duffin, 2001). One reason for the success in these experiments could have been the use of thicker slices that were at a higher temperature and KCl concentration, and another could have been that one of the recordings was always made from hypoglossal neurones that may have included hypoglossal interneurones rather than been confined to hypoglossal motoneurones.

The features observed in these in vitro cross-correlograms had considerably wider half-amplitude widths than those for in vivo cross-correlograms (e.g. Tian & Duffin, 1997) for both central peaks and peaks offset from time zero. We suggest that this difference is due partly to the cross-correlograms here being computed for discharges resulting from groups of neurones rather than single neurones, and partly because the low temperature of the in vitro preparation slows conduction times and synaptic processes and so results in a spread of the excitation arrival times. There are other factors that affect the widths of peaks such as excitatory pathways containing interneurones (Kirkwood et al. 1982) and synchronisation of presynaptic neurones (Davies et al. 1985), but these would apply to both in vitro and in vivo preparations. We note that another in vitro study using cross-correlation by Kashiwagi et al. (1993) also found peaks of similar widths to ours, and that our interpretations are similar to theirs.

We used cross-correlation as a means to detect connections between the neurones, interpreting the features (Moore et al. 1970; Kirkwood, 1979; Turker & Powers, 2001) as follows. The central peaks observed in cross-correlograms for contralateral pairs of hypoglossal neurones and nerves were taken as evidence for shared excitatory inputs, as were the central peaks observed in cross-correlograms of left and right pairs of PBC neurones. The broad peaks that included time zero but whose peaks were displaced from time zero were interpreted as evidence for a mixture of shared excitatory inputs and an excitatory connection from one group of neurones to another. These were observed in some cross-correlograms of PBC neurones with ipsilateral hypoglossal neurones or nerves and so we suggest that these groups of neurones share excitatory inputs and the hypoglossal neurones and motoneurones are excited by ipsilateral but not contralateral PBC neurones.

Finally, the narrower peaks to either or both sides of time zero in cross-correlograms of left and right PBC groups of neurones were interpreted as evidence for a mutual excitation between PBC neurones on opposite sides of the midline. This interpretation is one of several possible (Moore et al. 1970); for example, these peaks could also have resulted from several combinations of shared excitatory inputs with different conduction times to left and right sides. Thus, while we cannot rule out the possibility that the narrow peaks on either or both sides of time zero are indicative of shared inputs, we believe that an interconnection is more likely because it would serve to synchronise the two sides, and because there is anatomical evidence for such an interconnection; dye injected into the midline is retrogradely taken up by PBC neurones (Koshiya & Smith, 1999). The latencies to the peaks and their half-amplitude widths are consistent with a monosynaptic connection when the in vitro conditions of slower conduction times are taken into consideration.

The picture of the connections involving PBC and hypoglossal neurones in the slice emerging from these interpretations is as follows (Fig. 5). PBC neurones have excitatory connections across the midline so that mutual excitation occurs. These PBC neurones on both sides of the midline also share excitatory inputs, although the source is unidentified; both raphe neurones (Peever et al. 2001b) and central chemoreceptor neurones (Peever et al. 1999; Nattie, 2001; Richerson et al. 2001; Okada et al. 2002) are likely to be candidates. If these are the sources then their projections are bilateral.

Figure 5. An illustration of the pathways hypothesised to have produced the features observed in the cross-correlograms.

Figure 5

Open in a new tab

XIIn, hypoglossal nucleus; R, raphe; VLn, PBC neurones; CC, central chemoreceptors.

A similar argument may be made for the hypoglossal neurones, although our recordings did not distinguish between motoneurones and interneurones. These receive a shared excitation, possibly from the same sources as for the PBC neurones; acidification of raphe neurones excites hypoglossal motoneurones (Peever et al. 2001b), and increases in CO2 in the slice bathing medium increases hypoglossal amplitude (Peever et al. 1999). But the source of the shared excitation is unlikely to be the PBC neurones; otherwise we would have found evidence for excitation of both ipsilateral and contralateral hypoglossal neurones by PBC neurones.

The connections between PBC neurones and hypoglossal neurones were not well defined by the cross-correlograms; only some evidence for a connection from PBC neurones to ipsilateral hypoglossal neurones was obtained, and that consisted of off-centred peaks, which did not separate shared excitation from an offset peak due to a possible connection. While the latencies to the peaks were short enough to be due to a monosynaptic connection, the width of the peak was such as to suggest that interneurones might be part of the connection pathway. Overall our judgement was that the case for a direct monosynaptic connection was not supported by these results, as concluded for in vivo experiments (Peever et al. 2001a, 2002).

Acknowledgments

This research was supported by the Canadian Institutes of Health Research.

References

  1. Al-Zubaidy ZA, Erickson RL, Greer JJ. Serotonergic and noradrenergic effects on respiratory neural discharge in the medullary slice preparation of neonatal rats. Pflugers Arch. 1996;431:942–949. doi: 10.1007/s004240050089. [DOI] [PubMed] [Google Scholar]
  2. Davies JGM, Kirkwood PA, Sears TA. The detection of monosynaptic connexions from inspiratory bulbospinal neurones to inspiratory motoneuronees in the cat. J Physiol. 1985;368:33–62. doi: 10.1113/jphysiol.1985.sp015845. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Funk GD, Smith JC, Feldman JL. Generation and transmission of respiratory oscillations in medullary slices: role of excitatory amino acids. J Neurophysiol. 1993;70:1497–1515. doi: 10.1152/jn.1993.70.4.1497. [DOI] [PubMed] [Google Scholar]
  4. Graham K, Duffin J. Cross correlation of medullary expiratory neurones in the cat. Exp Neurol. 1981;73:451–464. doi: 10.1016/0014-4886(81)90279-x. [DOI] [PubMed] [Google Scholar]
  5. Johnson SM, Koshiya N, Smith JC. Isolation of the kernel for respiratory rhythm generation in a novel preparation: the pre-Botzinger complex ‘island’. J Neurophysiol. 2001;85:1772–1776. doi: 10.1152/jn.2001.85.4.1772. [DOI] [PubMed] [Google Scholar]
  6. Kashiwagi M, Onimaru H, Homma I. Correlation analysis of respiratory neurone activity in ventrolateral medulla of brainstem-spinal cord preparation isolated from newborn rat. Exp Brain Res. 1993;95:277–290. doi: 10.1007/BF00229786. [DOI] [PubMed] [Google Scholar]
  7. Kirkwood PA. On the use and interpretation of cross-correlation measurements in the mammalian central nervous system. J Neurosci Methods. 1979;1:107–132. doi: 10.1016/0165-0270(79)90009-8. [DOI] [PubMed] [Google Scholar]
  8. Kirkwood PA, Sears TA, Tuck DL, Westgaard RH. Variations in the time course of the synchronization of intercostal motoneuronees in the cat. J Physiol. 1982;327:105–135. doi: 10.1113/jphysiol.1982.sp014223. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Koshiya N, Smith JC. Neuroneal pacemaker for breathing visualized in vitro. Nature. 1999;400:360–363. doi: 10.1038/22540. [DOI] [PubMed] [Google Scholar]
  10. Moore GP, Segundo JP, Perkel DH, Levitan H. Statistical signs of synaptic interaction in neurones. Biophys J. 1970;10:876–900. doi: 10.1016/S0006-3495(70)86341-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Nattie EE. Central chemosensitivity, sleep, and wakefulness. Respir Physiol. 2001;129:257–268. doi: 10.1016/s0034-5687(01)00295-x. [DOI] [PubMed] [Google Scholar]
  12. Okada Y, Chen ZB, Jiang WH, Kuwana SI, Eldridge FL. Anatomical arrangement of hypercapnia-activated cells in the superficial ventral medulla of rats. J Appl Physiol. 2002;93:427–439. doi: 10.1152/japplphysiol.00620.2000. [DOI] [PubMed] [Google Scholar]
  13. Peever JH, Duffin J. Bilateral synchronisation of respiratory motor output in rats: adult versus neonatal in vitro preparations. Pflugers Arch. 2001;442:943–951. doi: 10.1007/s004240100621. [DOI] [PubMed] [Google Scholar]
  14. Peever JH, Mateika JH, Duffin J. Respiratory control of hypoglossal motoneuronees in the rat. Pflugers Arch. 2001a;442:78–86. doi: 10.1007/s004240000502. [DOI] [PubMed] [Google Scholar]
  15. Peever JH, Necakov A, Duffin J. Nucleus raphe obscurus modulates hypoglossal output of neonatal rat in vitro transverse brain stem slices. J Appl Physiol. 2001b;90:269–279. doi: 10.1152/jappl.2001.90.1.269. [DOI] [PubMed] [Google Scholar]
  16. Peever JH, Shen L, Duffin J. Respiratory pre-motor control of hypoglossal motoneurones in the rat. Neuroscience. 2002;110:711–722. doi: 10.1016/s0306-4522(01)00594-2. [DOI] [PubMed] [Google Scholar]
  17. Peever JH, Tian GF, Duffin J. Temperature and pH affect respiratory rhythm of in-vitro preparations from neonatal rats. Respir Physiol. 1999;117:97–107. doi: 10.1016/s0034-5687(99)00059-6. [DOI] [PubMed] [Google Scholar]
  18. Ramirez JM, Quellmalz UJ, Richter DW. Postnatal changes in the mammalian respiratory network as revealed by the transverse brainstem slice of mice. J Physiol. 1996;491:799–812. doi: 10.1113/jphysiol.1996.sp021258. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Rekling JC, Feldman JL. PreBotzinger complex and pacemaker neurones: hypothesized site and kernel for respiratory rhythm generation. Annu Rev Physiol. 1998;60:385–405. doi: 10.1146/annurev.physiol.60.1.385. [DOI] [PubMed] [Google Scholar]
  20. Richerson G, Wang W, Tiwari J, Bradley S. Chemo sensitivity of serotonergic neurones in the rostral ventral medulla. Respir Physiol. 2001;129:175–189. doi: 10.1016/s0034-5687(01)00289-4. [DOI] [PubMed] [Google Scholar]
  21. Richter DW, Spyer KM. Studying rhythmogenesis of breathing: comparison of in vivo and in vitro models. Trends Neurosci. 2001;24:464–472. doi: 10.1016/s0166-2236(00)01867-1. [DOI] [PubMed] [Google Scholar]
  22. Sears TA, Stagg D. Short-term synchronization of intercostal motoneurone activity. J Physiol. 1976;263:357–381. doi: 10.1113/jphysiol.1976.sp011635. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Shen L, Peever JH, Duffin J. Bilateral coordination of inspiratory neurones in the rat. Pflugers Arch. 2002;443:829–835. doi: 10.1007/s00424-001-0752-2. [DOI] [PubMed] [Google Scholar]
  24. Smith JC, Ellenberger HH, Ballanyi K, Richter DW, Feldman JL. Pre-Bötzinger complex: a brainstem region that may generate respiratory rhythm in mammals. Science. 1991;254:726–729. doi: 10.1126/science.1683005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Tian GF, Duffin J. Synchronization of ventral-group, bulbospinal inspiratory neurones in the decerebrate rat. Exp Brain Res. 1997;117:479–487. doi: 10.1007/s002210050244. [DOI] [PubMed] [Google Scholar]
  26. Tokumasu M, Nakazono Y, Ide H, Akagawa K, Onimaru H. Optical recording of spontaneous respiratory neurone activity in the rat brain stem. Jpn J Physiol. 2001;51:613–619. doi: 10.2170/jjphysiol.51.613. [DOI] [PubMed] [Google Scholar]
  27. Turker KS, Powers RK. Effects of common excitatory and inhibitory inputs on motoneurone synchronization. J Neurophysiol. 2001;86:2807–2822. doi: 10.1152/jn.2001.86.6.2807. [DOI] [PubMed] [Google Scholar]
  28. Wang JJ, Irnaten M, Venkatesan P, Evans C, Baxi S, Mendelowitz D. Synaptic activation of hypoglossal respiratory motorneurones during inspiration in rats. Neurosci Lett. 2002;332:195–199. doi: 10.1016/s0304-3940(02)00957-6. [DOI] [PubMed] [Google Scholar]

Articles from The Journal of Physiology are provided here courtesy of The Physiological Society

RESOURCES