Biomedical subjects

G W Knott

Publications and source records attributed to G W Knott.

3 recordsLinked to original sources

PubMed1995

Repair and recovery following spinal cord injury in a neonatal marsupial (Monodelphis domestica).

1. Repair and recovery following spinal cord injury (complete spinal cord crush) has been studied in vitro in neonatal opossum (Monodelphis domestica), fetal rat and in vivo in neonatal opossum. 2. Crush injury of the cultured spinal cord of isolated entire central nervous system (CNS) of neonatal opossum (P4-10) or fetal rats (E15-E16) was followed by profuse growth of fibres and recovery of conduction of impulses through the crush. Previous studies of injured immature mammalian spinal cord have described fibre growth occurring only around the lesion, unless implanted with fetal CNS. 3. The period during which successful growth occurred in response to a crush is developmentally regulated. No such growth was obtained after P12 in spinal cords crushed in vitro at the level of C7-8. 4. In vivo, in the neonatal (P4-8) marsupial opossum, growth of fibres through, and restoration of, impulse conduction across the crush was apparent 1-2 weeks after injury. With longer periods of time after crushing a considerable degree of normal locomotor function developed. 5. By the time the operated animals reached adulthood, the morphological structure of the spinal cord, both in the region of the crush and on either side of the site of the lesion, appeared grossly normal. 6. The results are discussed in relation to the eventual longterm possibility of devising effective treatments for patients with spinal cord injuries.

Animals↗

PubMed1993

The nature of the decrease in blood-cerebrospinal fluid barrier exchange during postnatal brain development in the rat.

1. The blood-cerebrospinal fluid (CSF) exchange of a wide range of passively transported lipid insoluble compounds (0.43-5.4 nm molecular radius) has been investigated in rats at different stages of postnatal development (2 days old to adult). A novel 'litter-based' model for investigating blood-CSF barrier exchange in immature animals is described. 2. At each age investigated there was a clear inverse correlation between molecular radius and blood-CSF barrier exchange, in addition to an overall decrease in blood-CSF barrier exchange with increasing age. 3. The decrease in blood-CSF barrier exchange with age was not consistent with a reduction in pore diameters, nor does it appear to be due to an increase in the CSF sink effect with age. It seems likely to be due to a relative decrease in the number of a population of large diameter pores.

Animals↗

PubMed1993

Development of connections by axons growing through injured spinal cord of neonatal opossum in culture.

The ability of neurites to grow through a lesion and form synaptic connections has been analyzed in a developing mammalian spinal cord in vitro. After isolation of the entire central nervous system (CNS) of the newly born South American opossum (Monodelphis domestica) the spinal cord was crushed. Outgrowth through and beyond the lesion was observed in living preparations for 2-5 days by staining axons with carbocyanine dyes. The structure of the acute crush and the growing neurites was examined by light and electron microscopy in tissue fixed immediately after the crush had been made. All axons had been severed and the site was filled with debris and amorphous vesicular structures. By 3 days after injury, numerous labelled neurites had grown into the lesion; by 4 days, many had extended several millimetres beyond it. At this time normal axonal profiles were apparent in electron micrographs of the crush site. Although fewer axons grew across the lesion than had been severed by the crush, the amplitudes of compound action potential volleys conducted across the crush in injured preparations were comparable with those recorded from uninjured spinal cords. Physiological experiments made with raised concentrations of extracellular magnesium in the culture fluid indicated that growing axons had formed synaptic connections. Thus, delayed major peaks of the response were abolished while the small component corresponding to through conduction remained unaffected by magnesium. These experiments demonstrate the development of synaptic interactions by the growing neurites and confirm the far greater powers of repair in neonatal mammals compared to adults. They set the stage for comparing molecular mechanisms involved in development and regeneration of the mammalian CNS.

Action Potentials↗