Biomedical subjects

M C Bellingham

Publications and source records attributed to M C Bellingham.

22 records · Page 2Linked to original sources

PubMed1990

Respiratory interneurons in the C5 segment of the spinal cord of the cat.

Extracellular recordings were made in the C5 segment of the spinal cord of anaesthetised cats from 129 units which showed respiratory phased discharge. The majority of recordings (88%) were thought to arise from the somata of respiratory spinal interneurons. Inspiratory units and expiratory units comprised 42% and 52% of all recorded units. A small number of postinspiratory units were also found (n = 5). Most units did not respond to electrical stimulation of the ipsilateral superior laryngeal (SLN) and phrenic nerves (PN), but a few expiratory (n = 2) and postinspiratory units (n = 1) were excited by SLN stimulation, while 6 inspiratory units had their discharge suppressed by the same stimulus. PN stimulation evoked a long latency (2-7 ms) burst of firing in 2 inspiratory and 1 expiratory interneurons. It is concluded that these respiratory interneurons may provide a segmental input to phrenic motoneurons, in addition to synaptic drives mediated by bulbospinal pathways.

Animals↗

PubMed1989

Synaptic inhibition of phrenic motoneurones evoked by stimulation of the superior laryngeal nerve.

Synaptic responses evoked in phrenic motoneurones (PMNs) by stimulation of the superior laryngeal nerve (SLN) were analysed in anaesthetised cats. Stimulation of the SLN was followed by inhibition of ipsilateral phrenic nerve discharge with the latency of 9.5 +/- 2.3 ms (mean +/- S.D.) and hyperpolarizations of ipsilateral PMN membrane potentials (latency, 8.4 +/- 2.1 ms) which were observed after stimuli applied both during inspiration and expiration. During the injection of Cl ions, the hyperpolarizations were either reversed or flattened in all 28 tested PMNs, thus indicating a direct inhibition. The possibility that the inhibitory postsynaptic potentials are produced by segmental respiratory interneurones is discussed.

Action Potentials↗

PubMed1988

Limitations of the technique of pressure microinjection of excitatory amino acids for evoking responses from localized regions of the CNS.

The aim of this study, performed on anaesthetized cats and rabbits, was to test the assumption that pressure microinjections of excitatory amino acids cause long-lasting excitation of neurones located close to the injection site. Unitary action potentials or antidromic field potentials were recorded from respiratory or 'reticular' neurones in the medulla oblongata and from phrenic motoneurones at different distances from the injection site. Injection of 10-150 nl (5-150 nmol) of L-glutamate or DL-homocysteic acid into these areas resulted in complex and widespread neuronal events. Generally, more distant neurones (500-1300 microns) were excited for variable periods of time (3-15 min), while neurones in the vicinity of the injection site (0-500 microns) showed, after a brief period of excitation time, a long-lasting (up to 30 min) decrease in excitability or silencing of discharge, probably due to a depolarizing block and disturbances in the ionic composition of the extracellular space. These findings show that interpretation of physiological responses following such injections should not be based on an assumption of local neuronal excitation. Some recommendations regarding the use of this technique are made.

Action Potentials↗

PubMedDate not supplied

Cholinergic modulation of respiratory brain-stem neurons and its function in sleep-wake state determination.

1. Shifts in behavioural state are controlled by reciprocal changes in discharge of cholinergic and aminergic groups of brain-stem/pontine neurons. During rapid eye movement (REM) sleep, cholinergic neurons are most active and aminergic neurons are least active. 2. Significant changes occur in the central control of breathing during REM sleep; respiration rate increases in frequency and variability, brain-stem respiratory neuron discharge is generally enhanced and the outputs of some respiratory motor neuron pools are depressed. 3. Hypoglossal motor neurons (HM) control tongue movement and their depression during REM sleep has been implicated in obstructive sleep apnoea. The cellular basis of HM depression has been investigated in vitro and may be due to enhanced activation of cholinergic receptors or decreased activation of aminergic receptors. 4. In vitro preparations that show respiratory rhythmogenesis possess advantages for the investigation of the neurochemical basis of state-dependent changes in respiration. Cholinergic changes in respiratory modulation of HM recorded in rhythmic brain-stem slices from mice depend on the site of activation of cholinergic receptors.

Animals↗