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Biomedical subjects

R V Stirling

Publications and source records attributed to R V Stirling.

30 records · Page 2Linked to original sources
PubMed1977

The involvement of the noradrenergic system arising from the locus coeruleus in the postnatal development of the cortex in rat brain.

The effect on the developing cerebral cortex and hippocampus of removing the noradrenergic input was investigated in 3-month-old rats following unilateral electrolytic lesions performed semistereotaxically at 15 h postnatal. In 5 animals there was a significant reduction (mean = 74%) in noradrenaline in the cortex ipsilateral to the lesion, and the neuronal morphology on the two sides was studied with the Golgi technique. There was no apparent difference in the morphology of pyramidal cells in parietal cortex with respect to soma depth, apical dendritic length, number of basal dendrites or number of spines on selected dendritic regions. There was a small but significant increase in the number of dendritic branches of pyramidal cells in layers II and IV on the side ipsilateral to the lesion. No layer VI cells were identified which had retained their contact with layer I. An examination of the cell morphology of CA1 pyramidal and dentate granule cells in the hippocampus revealed no obvious differences between the two sides. These results suggest that the trophic influence of the noradrenergic innervation on the postnatal development of cells in the cerebral cortex and hippocampus, if it exists at all, is relatively minor.

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PubMed1977

The development of functional innervation in the chick wing-bud following truncations and deletions of the proximal-distal axis.

Selections of the proximal-distal axis were removed so as to produce wings lacking entire skeletal levels. The innervation of the resulting limb from the appropriate spinal nerves was tested by electrophysiological recording, gross dissection and serial sections. Ther nerves form repeatable and ordered patterns in the modified limbs which can be readily related to the normal pattern. In general the segmental nerves only innervate their appropriate territory irrespective of its location; the route followed by the nerves is characteristic for the skeletal level they traverse. If a target is missing then so is the normal nerve branch to that region.

Action Potentials↗
PubMed1975

The structural and functional development of the retina in larval Xenopus.

The structural transformations of the larval Xenopus retina at successive stages of development, and concomitant changes in response characteristics of retinal ganglion cells, were studied using histological and electrophysiological techniques. The first sign of visually evoked electrical responses appears at about the time when the ganglion cells spread out into a single layer and shortly after the inner and outer plexiform layers become discernible. Initially giving simple "on" responses, the cells progressively change their response characteristics and become "event" units. Subsequently, "dimming" units can be identified. Throughout larval life, response properties of these two types become more distinct from one another and approximate to those found in the adult. So do the arborization patterns of the dendritic trees of the ganglion cells. Two types of branching patterns are identifiable in Golgi preparations. Around metamorphic climax, a new type of ganglion cell appears, coinciding with the emergence of "sustained" units electrophysiologically. After metamorphosis, the retina still grows both in thickness (mainly in the inner plexiform layer) and diameter. The three unit types change such they they come to show pronounced inhibitory effects from the peripheral visual field on the receptive field and each unit type acquires a distinct pattern of endogenous discharge.

Action Potentials↗
PubMed1973

The effect of increasing the innervation field sizes of nerves on their reflex response time in salamanders.

1. A simple quantitative measure was sought which could describe the relationship between reflex coupling in the spinal cord of salamanders and the peripheral innervation fields of the nerves from which the reflexes were elicited.2. In decerebrate salamanders reflex responses were recorded between pairs of cut hind limb nerves. The latencies (S/R times) of these reflex responses were bilaterally symmetrical for a given pair of nerves and were shorter when the stimulated nerve of the pair had a large motor and sensory peripheral limb innervation field; this was especially obvious for reflexes between 15th and 17th segmental nerves.3. After cutting or crushing the 16th nerve in adult salamanders, the adjacent 15th and 17th nerves sprouted collaterally to innervate denervated skin and muscle. There was apparently complete recovery of normal tactile reflexes and walking movements within a month.4. The operation did not affect the reflex response (S/R) times for nerve combinations on the unoperated side, which were not significantly different from those of normal animals with similar sized peripheral nerve fields. The unoperated side therefore represented the preoperative condition.5. In animals where one or both the 15th and 17th nerves had increased its innervation field size, the S/R times between them were significantly shorter on the operated side when the nerve with the enlarged field was stimulated. The degree of shortening was greatest for nerves showing the largest increase in peripheral field area.6. The S/R times between the 15th and 17th nerves were similar to those measured in normal animals in which the peripheral fields were of similar size to the enlarged fields in the operated animals. In a few cases where the increase in field size was considerable, the S/R time between the 15th and 17th nerves became as short as that between the 15th and 16th nerves on the control side.7. After removal of the 15th nerve, the 14th nerve sprouted into the trunk skin and muscle previously innervated by the 15th nerve and the 16th nerve into denervated limb skin and muscle. In spite of the increased peripheral fields of both these nerves, there was no change in the S/R times between them, or between any other pair of limb nerves on the operated side.8. The decrease in the S/R times between the 15th and 17th nerves was only observed where the stimulated nerve had increased its peripheral limb innervation field. The possible causes and significance of this shortening reflex response times are discussed in the context of an apparently functionally appropriate adaptation in the spinal cord.

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PubMedDate not supplied

Electrophysiological evidence for transient topographic organization of retinotectal projections during optic nerve regeneration in the lizard, Ctenophorus ornatus.

In the lizard, Ctenophorus ornatus, anatomical studies have revealed that optic axons regenerate to visual centers within 2 months of nerve crush but that, from the outset, the regenerated projections lack topographic order (Beazley et al., 1997; Dunlop et al., 1997b). Here we assess the functional topography of the regenerated retinotectal projections by electrophysiological recording of extracellular multiunit responses to visual stimulation and by observing the lizards' ability to capture live prey. At the completion of the electrophysiology, DiI was applied locally to the retina and the topography of the tectal projection later assessed. Electrophysiology revealed that, at 2-4.2 months, responses were weak and habituated readily; no retinotopic order was detected. Between 4.5-6 months, responses were more reliable and the majority of lizards displayed a crude retinotopic order, especially in the ventro-temporal to dorso-nasal retinal axis. Although responses were variable between 6-9 months, they tended to be more reliable again thereafter. However, from 6-18 months, the projection consistently lacked topography with many retinal regions projecting to each tectal locus. Lizards, including those with electrophysiological evidence of crude retinotopy, were consistently unable to capture live prey using the experimental eye. Labelling with DiI confirmed the absence of anatomical retinotopy throughout. Taken together, the electrophysiological and anatomical data indicate that retinotopically appropriate axon terminals (or parts thereof) are transiently active whilst inappropriately located ones are silent. Presumably in lizard map-making cues fade with time and/or the mechanisms are lacking to stabilize and refine the ephemeral map. Moreover, the transient retinotopy is insufficient for useful visual function.

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