Florey Department of Neuroscience and Mental Health - Research Publications

Permanent URI for this collection

http://hdl.handle.net/11343/269

Filters

2020 4
Reset filters

Settings
Statistics
Citations
Author: Dutschmann, Mathias × Type: Abstract ×

Search Results

Now showing 1 - 4 of 4
  • Item
    No Preview Available
    Descending forebrain projections targeting respiratory control areas in the midbrain and brainstem of rats
    Bau, P ; Dhingra, R ; Furuya, W ; Mazzone, S ; Dutschmann, M (WILEY, 2020-04)
    Breathing can be voluntarily modulated via descending inputs from the forebrain to evoke respiratory‐related behaviours, such as vocalization, sniffing, swallowing or breath‐holding. Such behaviors require controlled laryngeal adduction and thus, are conducted during the post‐inspiratory phase of respiratory cycle. However, descending pathways that connect forebrain regions with primary post‐inspiratory control areas such as the pontine Kölliker‐Fuse nucleus (KF) and the medullary Bötzinger complex (BötC) remain to be identified. Here, we investigated the topography of forebrain descending projection neurons to a variety of bulbar respiratory nuclei. We locally microinjected the conventional retrograde tracer cholera toxin subunit B (CT‐B, 100–150nL) into the BötC, KF, the pre‐Bötzinger complex (pre‐BötC), the midline raphé nuclei and the midbrain periaqueductal gray (PAG). Twelve days after unilateral CT‐B injections, brains were sectioned (40μm) and immunohistochemically stained with an anti‐CT‐B antibody. The strength of descending projections was qualitatively assessed: as strong (+++), moderate (++) or weak (+) numbers of CT‐B labeled cell bodies. Retrogradely labelled neurons after unilateral injections into the lateral PAG confirmed the predominantly ipsilateral location of strong and moderate descending projection neurons in the cingulate (+++), pre‐limbic (+++), ectorhinal (++), motor (+++) and insular (++) cortices, the lateral septum (++), amygdala (+++) and hypothalamus (+++). In comparison, retrogradely labeled neurons after unilateral KF injection were also found ipsilaterally in the motor (++), prelimbic (++) and insular cortices (+++), the amygdala (++) and hypothalamus (+++). However, amongst all analysed descending target areas, only the KF receives substantial inputs from the ectorhinal (+++) and endopiriform (++) cortices. In addition, the medullary BötC receives weaker inputs from prelimbic (+) and insular (+) cortices and receives moderate inputs from the amygdala and hypothalamus. Descending projection neurons to the pre‐BötC were in accordance with the literature: motor (+) and insular (+) cortices, amygdala (+++) and hypothalamus (++). Finally, descending inputs to the medullary raphé obscurus and raphé magnus nuclei also arose from motor, prelimbic and insular cortices, amygdala and hypothalamus. However, these projections were significantly weaker compared to KF or PAG. The results suggest that descending forebrain projections into respiratory control areas are organized in general pathways that originate from motor, prelimbic and insular cortices as well as the amygdala and hypothalamus. However, only the KF, a key area for the gating of post‐inspiratory activity and respiratory plasticity, receives projections arising from the endopiriform and ectorhinal cortex. The functional implications of these descending control pathways need to be explored in future studies. Support or Funding Information Melbourne Research Scholarship (University of Melbourne) [181858] to PT‐B.
  • Item
    No Preview Available
    Relaxin-3 receptor (RXFP3) mediated modulation of central respiratory activity
    Furuya, W ; Dhingra, R ; Gundlach, A ; Hossain, M ; Dutschmann, M (WILEY, 2020-04)
    The neuropeptide, relaxin‐3, is expressed by pontine nucleus incertus (NI) neurons. Relaxin‐3 and synthetic agonist peptides modulate arousal and cognitive processes via activation of the rela xin‐ family peptide 3 receptor (RXFP3). We recently demonstrated that a double‐chain RXFP3 peptidomimetic (RXFP3‐A2) in the nucleus of the solitary tract (NTS) triggered a mild stimulation of respiration and augmented the chemoreceptor reflex in an in situ perfused brainstem preparation ( Furuya et al., 2020). In the present study, we assessed the central respiratory effects of systemic application and local microinjection into the NTS, Kölliker‐Fuse nucleus (KF) or NI of a single chain RXFP3 peptidomimetic (B18) in the perfused brainstem preparation. Systemic application of B18 (2 μM) triggered a dose‐dependent increase in respiratory rate by 22 ± 8%. At this concentration of B18, the NaCN‐evoked (0.1% w/v, 100 μl, bolus injection) tachycardia of the arterial chemoreceptor reflex was augmented by 95 ± 14% compared to control (p<0.001, n=4). Local microinjections into the NTS also increased respiratory frequency (28 ± 5%, p<0.05, n=6) and enhanced the NaCN‐evoked tachycardia by 59%. Microinjections into the KF only triggered a mild increase in respiratory frequency (18 ± 7%, p<0.05, n=6) but had no effect on the NaCN‐evoked chemoreceptor reflex. Finally, microinjections into the NI (n=6) had no effect on either stationary breathing activity, or on the chemoreceptor reflex. We conclude that relaxin‐3 neurons target RXFP3 in respiratory control areas and acts as a general respiratory stimulant, causing mild increases in respiratory frequency. Importantly, RXFP3 stimulation significantly enhanced the respiratory response of arterial chemoreceptor reflex, implicating a major neuromodulatory role in this specific reflex pathway.
  • Item
    No Preview Available
    Spinal Oxygen Sensors (SOS): A Novel Oxygen Sensing Mechanism Involved in Cardiovascular Responses to Hypoxia
    Barioni, N ; Derakhshan, F ; Lopes, L ; Heidari, N ; Bharadia, M ; Roy, A ; Baghdadwala, M ; McDonald, F ; Scheibli, E ; Harris, M ; Dutschmann, M ; Onimaru, H ; Okada, Y ; Wilson, R (WILEY, 2020-04)
    BACKGROUND In healthy individuals, when blood oxygenation decreases, cardiorespiratory reflexes are triggered in an attempt to restore oxygen supply to vital organs. The carotid bodies are the primary respiratory oxygen chemoreceptors but cardiovascular responses to hypoxia such as increase in heart rate and blood pressure persist in their absence, suggesting an additional high‐fidelity oxygen sensor. Previously we discovered that spinal sympathetic preganglionic neurons (SPN), are exquisitely sensitive to oxygen; here we investigate the oxygen sensing mechanisms and test the role of these spinal oxygen sensors (SOS) in cardiorespiratory responses to asphyxia‐like stimuli. OBJECTIVE To study the cellular oxygen sensing mechanism and contribution of the SOS in responses to cardiorespiratory crisis. METHODS We investigated the cellular mechanism of oxygen sensing in artificially‐perfused (in situ) and slice (in vitro) thoracic spinal cord preparations, recording sympathetic nerve root and single cell responses to hypoxia during pharmacological interrogation. To determine if the SOS are involved in cardiorespiratory responses to asphyxia, we also used an in situ rat spinal cord – carotid body ‐ brainstem preparation in which each oxygen sensitive compartment is separately perfused while recording phrenic (respiratory) and splanchnic (sympathetic) nerve activity. RESULTS Our data suggest the SOS use a novel oxygen sensing mechanism. This mechanism involves two interacting NADPH and oxygen‐dependent enzymes: Neuronal Nitric Oxide Synthase (NOS1) and NADPH oxidase (NOX2). NOS1 is expressed in surprising abundance in the SOS and is oxygen sensitive across the entire physiological range. Hence, in the presence of oxygen, NOS1 is likely to utilize most of the available NADPH in the cell. When oxygenation falls during hypoxia, NOS1 activity is reduced, increasing NADPH availability for NOX2. NOX2 produces Reactive Oxygen Species (ROS) which in turn, activate ROS‐dependent internal Ca2+ stores and/or Ca2+ channels leading to increased intracellular Ca2+, neuronal firing and, consequently, SOS responses to hypoxia. Functionally, during hypoxia, the SOS enhance sympathetic and breathing activity, while shortening apnea and gasping towards recovery, and are capable of triggering brief periods of sympathetic and respiratory‐like activity in the brainstem’s absence. CONCLUSIONS The results provide critical new knowledge required to unlock the cellular mechanisms involved in how the body mounts emergency responses to conditions that involve chronic and acute hypoxia. Support or Funding Information University of Calgary Eyes High; Hotchkiss Brain Institute; Alberta Children’s Hospital Research Institute; Alberta Innovates Health Solutions; MITACS Globalink; Canadian Institutes of Health Research.
  • Item
    No Preview Available
    Volumetric mapping of the functional neuroanatomy of the brainstem respiratory network in the perfused brainstem preparation of rats
    Dhingra, R ; Dick, T ; Furuya, W ; Galan, R ; Dutschmann, M (WILEY, 2020-04)
    One of the major goals of modern neuroscience is to understand the relationship between the functional neuroanatomy/connectivity of neural circuits and the behavior of an animal. The key challenge to addressing this goal with respect to control of breathing is the distributed nature of the respiratory network. While in cortical networks, short‐range connections (10–100 μm) out‐number long‐range connections (1+ mm), the opposite may be true of brainstem circuits. Specifically, anatomical tracing studies have identified many long‐range projections between brainstem respiratory nuclei that led to the concept that the brainstem respiratory network is compartmentally organized. Thus, measuring the functional neuroanatomy of the respiratory network—a task required to phenotype the functional role of neuronal populations identified in molecular mapping studies—requires monitoring the activity of respiratory neurons which may be spread over many millimeters. We hypothesized that the spatio‐temporal structure of the brainstem respiratory network is sufficient to generate macroscopic local field potentials (LFPs), and if so, respiratory (r) LFPs could be used to map the functional neuroanatomy of the respiratory network in single preparations. To address our hypothesis, we developed an approach using silicon multi‐electrode arrays to record spontaneous LFPs from hundreds of electrode sites across the ponto‐medullary volume of the respiratory network while monitoring the respiratory motor pattern on phrenic and vagal nerves. Our results revealed the expression of rLFPs across the brainstem respiratory network. rLFPs were expressed selectively at the three transitions between respiratory phases: (1) from late‐expiration (E2) to inspiration (I), (2) from I to post‐inspiration (PI), and (3) from PI to E2. Thus, respiratory network activity was maximal at respiratory phase transitions, rather than being equally distributed across the respiratory cycle. Spatially, the E2‐I (inspiratory on‐switch), and PI‐E2 transitions were localized to the ventral and dorsal respiratory groups, respectively, whereas the I‐PI (inspiratory off‐switch) transition was distributed across the ventral, dorsal and pontine respiratory groups. An independent component analysis (ICA) confirmed this spatio‐temporal organisation of rLFPs and identified a traveling wave of rLFPs that occurred at the I‐PI transition. Finally, a group‐wise ICA demonstrated that all preparations exhibited rLFPs with a similar temporal structure. Overall, under intact network conditions, our results confirm that inspiration is initiated by the pre‐Bötzinger complex, whereas post‐inspiration and late‐expiration depend on activity throughout the brainstem respiratory network. In conclusion, we have developed a general approach to volumetrically map spontaneous‐ or evoked‐respiratory network activity at the brainstem‐wide scale in single preparations to inform our understanding of the network mechanisms underlying the neural control of breathing. Support or Funding Information This work was supported by grants from the Australian Research Council (to MD), National Institutes of Health (to TED) and the Hartwell Foundation (to RFG).