The effects of nerve section and of colchicine treatment on the density of mechanosensory nerve endings in salamander skin.

Cooper, Ellis; Diamond, Jack; Turner, Christopher J.

doi:10.1113/jphysiol.1977.sp011691

Cited by 33 publications

(11 citation statements)

References 15 publications

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“…However, the low-threshold bin width we selected seems to be appropriate not only for comparative studies of receptor density, but for giving a good indication for absonlte density also, if our mapping of single receptive fields is accurate. In related investigations (Cooper et al 1977) we are obtaining morphological evidence supporting this conclusion. High-threshold receptors?…”

Section: The Density Of Receptorssupporting

confidence: 69%

“…In addition, the fields of the branches which were cut were also mapped to define the degree of their overlap with the CFP nerve field. The CFP nerve is made up of axons from the 16th and 17th segmental nerves only, their exact contribution varies from animal to animal, but there is good symmetry in this regard from side to side in any one animal (see results of this and accompanying paper, Cooper, Diamond & Turner, 1977). …”

Section: Field Mappingmentioning

confidence: 99%

“…A fuller description of the usefulness of this test in this kind of study is included in the Results section of the accompanying paper (Cooper et al 1977 (Fig. 2).…”

Section: Statisticsmentioning

confidence: 99%

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A quantitative study of the mechanosensory innervation of the salmander skin.

Cooper¹,

Diamond²

1977

The Journal of Physiology

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SUMMARY1. We have investigated by physiological means the characteristics and organization of the mechanoreceptors in the skin of the salamander hind limb. A controlled mechanical stimulator with a tip diameter of a few microns was used to activate single mechanoreceptors, and afferent impulses were recorded from whole spinal nerves.2. The mechanoreceptors of the skin are rapidly adapting. When random spots on the skin were tested, the stimulus strength needed to evoke an impulse varied from one location to another. The histogram of percentage occurrence of these critical stimuli in a given skin has the same form whether the sampled spots are 50,sm apart and are all included in a small area, or whether the spots are sampled as much as 1 mm apart across the entire limb. The histogram is skewed, with the highest percentage occurrence in the low-threshold range.3. One interpretation of the findings is that there is a single population of mechanoreceptors, of uniform threshold, spaced far enough apart for a stimulator of small diameter to be situated between them. By locating a low-threshold spot, and then determining the increase in stimulus required to excite it at a known distance away, it was possible to estimate the relationship between the strength of the stimulus and the receptive field size of such a population of receptors; we were then able to infer the average receptor spacing and receptive field size. The values are approximately 250 and 75 psm respectively. 4. From appropriate maps of detailed systematic surveys of the skin sensitivity to touch it was possible to define discrete low-threshold areas. These areas had approximate radii in the range 50-75,um, and their centres were about ,m apart; these values are consistent with those predicted above. We conclude that the experimentally determined sensitive areas represent the receptive fields (at threshold) of individual E. COOPER AND J. DIAMOND mechanosensory endings. There are approximately twenty to thirty of them per square millimetre.5. Receptive fields of single mechanosensory axons (i.e. of sensory 'units') were measured by an occlusion technique using two prodders. These fields vary from 005 to 2-5 mm2, and are generally organized as discrete areas with only a little overlap among them. Individual axons supply from five to seventy-five mechanoreceptors.6. The findings provide a basis for quantitative studies of plasticity involving the mechanosensory system of the salamander skin.

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Section: The Density Of Receptorssupporting

confidence: 69%

Section: Field Mappingmentioning

confidence: 99%

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A quantitative study of the mechanosensory innervation of the salmander skin.

Cooper¹,

Diamond²

1977

The Journal of Physiology

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“…To explain synapse elimination, Jansen and his collaborators postulate that the substance is produced in limited quantities and that nerve terminals can deplete the substance from surrounding regions of the fiber (see also Purves, 1976, for a history of the development of this idea). A similar scheme is implied by the results of Diamond and his collaborators for skin sensory connections in salamanders (Diamond et al, 1976;Cooper et al, 1977;Diamond, 1979). The Merkle cells in the skin produce a sprout-inducing or sensory nerve-attracting substance that is suppressed or removed by innervating sensory nerves (Purves, 1976;Diamond, 1979).…”

Section: Discussionsupporting

confidence: 57%

Regulation of synaptic position, size, and strength in anuran skeletal muscle

Nudell¹,

Grinnell²

1983

J. Neurosci.

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An analysis of the physiology, morphology, and position of endplates on identified fibers in the Xenopus laevis pectoralis muscle has revealed the following. 1. The percentage of fibers with one endplate is lower in large muscles, and within the same muscle, singly innervated fibers are smaller than dually innervated fibers.2. Single junctions tend to be stronger than junctions on dually innervated fibers. 3. Single junctions typically are located near the middle of their fibers, while the endplates on dually innervated fibers are located toward either end and usually are separated by at least 20% of the total fiber length. A significant proportion of dually innervated fibers appears to be innervated by the same axon at both junctions.4. Junctions on the same dually innervated fiber tend to be more similar in length than do junctions on different fibers of the same input resistance. This observation is the same whether both junctions on a given fiber are formed by the same or different axons. There is no corresponding tendency for greater similarity in physiological strength of paired junctions, which frequently show large differences in endplate potential amplitude.5. The total terminal length on dually innervated fibers of equivalent input resistance is inversely correlated with the mean release per unit length and total release of both junctions. There is no apparent correlation between the distance separating endplates and their strength or length.The data support a model of synaptic regulation in which nerve terminals are attracted, grow, and are maintained in proportion to the amount of a substance supplied by muscle fibers. Our findings suggest that such a substance is produced or distributed uniformly throughout each fiber in amounts proportional to the fiber size and inversely proportional to the total transmitter output of all junctions innervating the fiber. A form of competitive interaction between the terminals which helps to determine synaptic spacing may involve local depletion or inactivation of this substance.

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“…According to observations obtained in cutaneous receptive fields of salamanders (Aguilar, Bisby, Cooper & Diamond, 1973;Diamond, Cooper, Turner &Macintyre, 1976 andTurner, 1977) the target tissue promotes a sprouting of nerve endings that can be halted by inhibitory agents released by neighbouring terminals.…”

Section: Discussionmentioning

confidence: 99%

Dual innervation of end‐plate sites and its consequences for neuromuscular transmission in muscles of adult Xenopus laevis.

Angaut-Petit¹,

Mallart²

1979

The Journal of Physiology

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4. The sensitivity to acetylcholine and muscle fibre electrical properties were investigated; no differences were found between fibres with sub-or suprathreshold e.p.p.s.5. The nature of the factors responsible for this presumed small size of the nerve endings (competition between nerve endings for a limited synaptic space on the muscle membrane or reciprocal interaction between closely located terminals) as well as the possible origins of polyinnervation are discussed.

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The effects of nerve section and of colchicine treatment on the density of mechanosensory nerve endings in salamander skin.

Cited by 33 publications

References 15 publications

A quantitative study of the mechanosensory innervation of the salmander skin.

A quantitative study of the mechanosensory innervation of the salmander skin.

Regulation of synaptic position, size, and strength in anuran skeletal muscle

Dual innervation of end‐plate sites and its consequences for neuromuscular transmission in muscles of adult Xenopus laevis.

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