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Biomedical subjects

M E Morris

Publications and source records attributed to M E Morris.

At least 163 records · Page 9Linked to original sources
PubMed1975

Substance P and spinal neurones.

When applied by microiontophoresis, substance P (sP) had a strong, but slow and prolonged excitatory action on nearly half the neurones tested in the lumbar spinal cord of cats. Motoneuronal antidromic field potentials only occasionally showed a significant effect of sP. Cerebral cortical neurones in cats and rats were much less readily excited than spinal interneurones. Some unresponsive units showed evidence of a depressant effect of sP. Although sP may have a significant function in central afferent pathways, it is not likely to be a quickly-acting synaptic transmitter.

Acetates↗
PubMed1975

Correlation between extracellular focal potentials and K+ potentials evoked by primary afferent activity.

There is a clear, positive correlation in amplitude between changes in potassium potentials (deltaEK) and focal potentials (deltaV) evoked by tetanic stimulation of afferent nerves in the cuneate nucleus and dorsal horn of cats under Dial anaesthesia or after decerebration. Data obtained with stimulations at various frequencies and intensities, or recording at different positions give a relatively constant slope of deltaV/deltaEK (varying between 0.2 and 0.6 in different experiments). These observations are fully consistent with the possibility that deltaV mainly reflects changes in extracellular potassium concentration caused by the release of K+ from active terminals. Differences in time course of deltaEK ANd deltaV evoked by single stimuli are a steep function of distance and therefore can be ascribed to the slowness of diffusion, without excluding the possibility of an early additional depolarizing effect by another mechanism.

Animals↗
PubMed1975

Factors determining the decay of K+ potentials and focal potentials in the central nervous system.

Post-tetanic undershoots in extracellular focal potential (deltaV) and K+ potential (EK) can be recorded in the cuneate nucleus and dorsal horn of Dial-anaesthetized or decerebrate cat. They are seen best at depths where the largest deltaEK and deltaV are recorded and they increase with the frequency and duration of stimulation. The very different time courses of undershoots of deltaV and deltaEK indicate two hyperpolarizing influences: first, electrogenic pumping, and later, a reduced external K+ concentration. The importance of active K+ removal in determining the amplitude and duration of deltaEK and deltaV is illustrated by their marked potentiation (as well as the disappearance of post-tetanic undershoots) induced by a lowering of blood pressure or local application of strophanthidin.

Animals↗
PubMed1971

The action of carbon dioxide on afferent transmission in the dorsal column-lemniscal system.

1. Transmission in the lemniscal afferent pathway was studied in thirteen decerebrate, unanaesthetized cats while changing the concentration of inspired P(CO2).2. 2-20% CO(2), when inhaled for </= 10 min, raised the mean tissue P(CO2), recorded from the surface of the medulla or cerebellum, from 22 torr to between 26 and 93 torr.3. Medial lemniscal potentials were evoked by stimulation of a forelimb nerve and recorded from the transected surface of the contralateral mid-brain. The transmission of supramaximal responses was progressively and reversibly depressed as tissue levels of P(CO2) were raised and lowered. The time course of the changes in transmission corresponded closely to changes in the tissue P(CO2).4. The amplitude of the main early lemniscal peak was decreased to 80% by the inhalation of 20% CO(2). A late component of the lemniscal response, presumably due to repetitive firing and conduction in smaller fibres and polysynaptic pathways, was more affected than the early main response.5. The failure of transmission was unrelated to threshold changes in the peripheral nerve, since potentials recorded close to the site of stimulation showed no changes.6. Increases in the transmission time of the main lemniscal potentials were uniform and < 10% during the administration of CO(2) and did not appear to contribute to amplitude changes.7. The inhibition of afferent transmission from one nerve by a preceding conditioning volley in a second nerve was not altered by hypercarbia.8. It is concluded that CO(2) has a blocking action on afferent transmission in the pre-thalamic lemniscal system. The site of this block may be at the synapses and/or other regions of low safety factor in the afferent fibres.

Animals↗
PubMed1971

The action of carbon dioxide on synaptic transmission in the cuneate nucleus.

1. The excitability of synaptic structures in the cuneate nucleus was studied in eighteen decerebrate, unanaesthetized cats during acute changes in inspired P(CO2).2. Micro-electrode stimulation in the caudal half of the cuneate nucleus evoked antidromic and orthodromic responses which were recorded simultaneously from a forelimb nerve and from the medial lemniscus at the transected mid-brain surface.3. Increases in the concentration of inspired CO(2) (2-20%) progressively decreased the direct excitability of both the afferent fibre terminals (reflected in the antidromic potentials) and the cuneate relay neurones (reflected in the alpha wave of the orthodromic lemniscal response). Synaptically mediated responses, recorded as the beta component of the lemniscal potentials, were also depressed.4. The relation between input and output at the cuneate was determined by plotting antidromic against trans-synaptic (beta lemniscal) responses for different intensities of stimulation. The mean slope for logarithmic values of control potential amplitudes was 1.17 (+/- S.E. 0.13). It therefore appears that the transfer function for the cuneate is linear over a wide range.5. In the majority of experiments the input-output relation was unchanged or increased by raising P(CO2). It was concluded that the efficiency of synaptic transmission and release of transmitter appeared to be well maintained or possibly increased at individual active synapses during hypercarbia.6. The depressant action of CO(2) on afferent transmission can therefore be attributed largely to a block of impulse conduction in the primary afferent fibres.

Animals↗
PubMed1969

Vacuum probe: new approach to the microbiological sampling of surfaces.

The need for a device to sample large areas that are lightly contaminated with microorganisms motivated the development of the vacuum probe. The intended use of the instrument is to sample clean surfaces in laminar flow clean rooms, but the device could be used for sampling surfaces in other clean environments. Such a device was designed, fabricated, and tested at Sandia Laboratories, Albuquerque, N.M. In these tests, the vacuum probe removed a mean of 89% and assayed a mean of 67% of bacterial spores, approximately 1 mum in length, settled on smooth surfaces which were free from viscous films.

Bacillus subtilis↗