Regeneration of an identified central neuron in the cricket. II. Electrical and morphological responses of the soma

Abstract

The cell body of the medial giant interneuron (MGI) in the cricket normally does not spike in response to injected depolarizing currents. When axotomized 1 mm or more from the cell body (distant axotomy), the membrane properties of the soma remain unchanged. However, after axotomy close to the cell body (200 to 500 pm), the soma membrane becomes capable of generating action potentials by 6 hr after lesion. These regenerative spikes are 1 to 1.5 msec in duration and may reach 100 mV in peak amplitude. Ion substitutions indicate that these action potentials are primarily sodium dependent. A calcium-dependent component of soma membrane excitability that is normally present appears to be unaffected by axotomy. By 48 hr, the close axotomized MGI somata have lost the ability to generate action potentials and the membrane electrical properties return to normal.By 2 days after axotomy close to the soma, large, membrane-bound, electron-lucent vacuoles appear in the cytoplasm of the MGI cell body. Such vacuoles then disappear from axotomized MGI somata by 10 days. In addition, numerous arrays of densely packed, darkly staining microtubules are observed in the cell body, especially concentrated near the initial neurite. Neither of these specialized structures is observed in control, intact MGI somata. We propose that close axotomy disrupts the mechanisms which regulate the stability of the fully mature, differentiated neuron. The characteristic morphological and physiological stability of the MGI is lost: the dendritic arborization has been shown previously to be altered by extensive new outgrowth (Roederer, E., and M. J. Cohen (1983) J. Neurosci. 3: 1835-1847); there is a transient increase in soma membrane excitability, and new cytoplasmic organelles are induced.

Ionic Dependence of the Axotomy-Induced Long-Lasting Firing in an Identified Crayfish Motoneuron

“…Effects of axotomy on neural excitability have been investigated in motoneurons and interneurons of crayfish (Kuwada and Wine, 1981), locust (Goodman and Heitler, 1979), cockroach (Pitman et al, 1972), and cricket (Roederer and Cohen, 1983), yet none of them have shown a prolonged firing following axotomy (Titmus and Faber, 1990), except AML (Muramoto, 1993). The present study showed that not only axotomy, but also application of a prolonged depolarizing pulse can elicit an LLF in AML.…”

Synaptic integration at a sensory‐motor reflex in the leech.

“…The somata of unipolar motoneurones in some invertebrates are excitable (Kandel, 1976;Krauthamer & Ross, 1984), but in the leech and many other species they are not. For example in arthropods there is evidence for a differential distribution of voltage-gated sodium channels, which changes to include the soma after axotomy (Pitman et al 1972;Goodman & Heitler, 1979; Kuwada, 1981;Roederer & Cohen, 1983). A similarly enhanced somatic excitability occurs over days or weeks in leech motoneurones plated in tissue culture medium (Fuchs, Nicholls & Ready, 1981) and in goldfish Mauthner cells axotomized in vivo (Titmus & Faber, 1986), where a shift in the distribution of voltage-gated sodium channels has been demonstrated.…”

Extensive Dendritic Sprouting Induced by Close Axotomy of Central Neurons in the Lamprey

“…The effect of cations, in particular calcium, on the cytoskeletal elements involved with intracellular transport is well known (15)(16)(17). A change in microtubule organization has been reported in other central neurons after close axotomy and subsequent dendritic sprouting (18). It may be that the influx of cations from the injury current of the closely transected central nervous system of the lamprey is also involved with altering the cytoskeletal elements in the Muller cell somata after close axotomy.…”

“…(D) Gould's (7) "clock model" of heterochrony, where the curved trajectory represents differential travel along common growth allometries. If the dashed vertical line is taken as the condition in adult Pan troglodytes, the position of the clock's "hands" for the skull, trunk and forelimbs, and hind limbs indicates the relative position of adult Pan paniscus (17)(18)(19)(20)(21)(22); compare to (B). 4 NOVEMBER 1983 ochrony [shifts in the timing of developmental patterns (6)(7)(8)(9)] in an analysis of chimpanzee (and gorilla) morphology (9)(10)(11)(12)(13)(14)(15)(16).…”