Biomedical subjects

R Fern

Publications and source records attributed to R Fern.

22 records · Page 2Linked to original sources

PubMed1993

Pharmacological protection of CNS white matter during anoxia: actions of phenytoin, carbamazepine and diazepam.

The effects of phenytoin (DPH), carbamazepine (CBZ) and diazepam (DZP) on anoxia-induced injury in CNS white matter were studied using the in vitro rat optic nerve preparation. Optic nerves were subjected to 60 min of anoxia and functional recovery was assessed using the area under the compound action potential. Under normoxic conditions, application of DPH, CBZ and DZP reduced compound action potential area over concentration ranges known to block sodium channels. All three compounds, however, protected against anoxic injury at concentrations below those that inhibited the normoxic compound action potential. Thus, the application of 1 microM DPH, CBZ or DZP during anoxia resulted in compound action potential recovery to 60.0, 53.8 and 69.2% of control, respectively, compared to compound action potential recovery of 34.8% in the absence of drugs (P < .05 in all three cases). In the cases of CBZ and DPH, 60% improvement in recovery from anoxia was produced by concentrations well below those employed clinically to treat epilepsy, suggesting a potential role for these drugs in the protection of CNS white matter from anoxic injury.

Action Potentials↗

PubMed1991

The effects of compression upon conduction in myelinated axons of the isolated frog sciatic nerve.

1. Action potential conduction along frog sciatic nerve fibres has been monitored during compression of a mid-portion of the nerve. 2. The effects of compressing a 24 mm length of nerve with a pressure of 250 mmHg applied pneumatically were investigated by recording unitary action potentials. A plot of time before conduction failure (survival time) against initial conduction velocity revealed that the faster myelinated axons tend to fail before the slower myelinated axons. A large degree of scatter was evident in the pooled data as well as in the data from individual experiments. 3. When the compression was made more severe by increasing the applied pressure to 750 mmHg, the order of block was reversed, i.e. the slower myelinated axons tended to block first. Similar scatter in the order of conduction block was observed. 4. The average survival time of units following application of compression was considerably different between these two series of experiments. When 750 mmHg pressure was applied, units survived for, on average, 10.9 min (n = 246). When 250 mmHg pressure was applied units survived for, on average, 50.4 min (n = 148). 5. The results are discussed in relation to the underlying causes of conduction failure as a result of compression and in relation to results from previous investigations.

Action Potentials↗

PubMed1988

The dorsal column projection of muscle afferent fibres from the cat hindlimb.

1. The extent of the projection of hindlimb muscle afferent fibres ascending the dorsal columns has been studied in barbiturate-anaesthetized cats. This has been investigated using electrical stimulation of the dorsal columns at different spinal levels while recording from (i) peripheral muscle nerves, and (ii) single muscle afferent fibres within the dorsal columns. These two approaches have produced complementary results. 2. The conduction velocity of both group I and group II afferent fibres decreased progressively after entering the dorsal columns. 3. The majority of group I and group II fibres project at least as far as L2 but leave the dorsal columns at or before the lower thoracic segments. 4. By taking advantage of the lower electrical threshold of Ia compared to Ib fibres in the hamstring nerves, it could be shown that both Ia and Ib fibres leave the dorsal columns at similar locations. 5. A small number of afferent fibres were found to project to C1. On the basis of previous work it is likely that such fibres originate from Pacinian or paciniform corpuscles.

Action Potentials↗

PubMed1988

The ascending projection of interneurones activated by group I muscle afferent fibres of the cat hindlimb.

1. The level of the ascending projection of lumbosacral interneurones with a monosynaptic input from group I muscle afferents of the cat hindlimb has been investigated. The study was concerned particularly with the interneurones mediating group I non-reciprocal inhibition of motoneurones. 2. In chloralose-anaesthetized cats, single-unit microelectrode recordings were made, in the lateral funiculus at L6, from the ascending axons of lumbosacral interneurones. The axons studied were discharged by group I afferents primarily from extensor muscles of the knee and ankle. Some units were discharged in addition by cutaneous and/or joint afferents. 3. The extent of the ascending projection of the interneurones was assessed by antidromic activation of their axons in the lateral funiculus at different spinal levels. The great majority of axons tested (thirty-four out of thirty-six) were found to have an ascending projection to at least the L4 level and of these most (90%) did not project beyond the L4 or L3 segments of the cord. 4. The projection to at least L4, together with monosynaptic input from group I afferents and a pattern of peripheral input characteristic of interneurones in laminae V-VI of lumbosacral segments, identified thirty-four of the thirty-six units as interneurones mediating group I non-reciprocal inhibition. 5. These results suggest that the ascending group I inhibitory pathway, formed by these interneurones, is associated specifically with the group I relay of the dorsal spinocerebellar tract in Clarke's column, rather than being conterminous with group I afferents, which project throughout the rostral lumbar and lowest thoracic segments.

Animals↗