Biomedical subjects

Yutaka Fukuda

Publications and source records attributed to Yutaka Fukuda.

23 records · Page 2Linked to original sources

PubMed2002

Changes in visual response properties of cat retinal ganglion cells within two weeks after axotomy.

After optic nerve transection beta cells of cat retinal ganglion cells (RGCs) suffer from rapid cell death from 3 to 7 days, whereas alpha cells gradual cell death until 14 days. Here we report electrophysiological properties of Y- (morphological alpha) and X- (morphological beta) cells at 5 and 14 days after axotomy in comparison with those of intact Y- and X-cells. Most of the axotomized RGCs revealed characteristic visual response properties that enable us to classify them into Y- or X-cells. Physiological sampling ratio of X-cells sharply decreased from day 5 to 14 after axotomy, corresponding to the previous morphological results. As compared with intact RGCs, axotomized RGCs of both Y- and X-type revealed the following abnormalities: smaller receptive field centers, weaker visual responses and lower spontaneous activities. Intracellular injections of Lucifer yellow into axotomized and intact RGCs at eccentricities 0-6 mm from the area centralis revealed no sign of shrinkage in dendritic field size of either alpha or beta cells on day 5 and day 14 after axotomy, revealing that observed smaller receptive field centers of axotomized RGCs on day 5 were not due to the change of dendritic field sizes. These results suggest that the major events occurring shortly after axotomy are significant loss of synaptic inputs from afferent neurons in the retina and/or changes of membrane properties of axotomized RGCs. These events can also explain lower spontaneous activities and weaker visual responses of axotomized RGCs.

Action Potentials↗

PubMed2002

Attachment-inducing capacities of fish skin epithelial extracts on oncomiracidia of Benedenia seriolae (Monogenea: Capsalidae).

Attachment-inducing capacities of skin epithelial extracts of yellowtail, Japanese flounder and red sea bream on oncomiracidia of the monogenean Benedenia seriolae were examined. Clear differences were not detected in the capacity among the fish species, although B. seriolae infects only yellowtail and its congeners in Seriola. This suggests that either the capacity is not host specific or host-specific attachment-inducing capacity cannot be detected by the assay method. Further, the attachment-inducing capacities were suppressed by wheat-germ lectin and concanavalin A in skin epithelial extracts of Japanese flounder and yellowtail, respectively. This suggests that some sugar-related chemical substances existing in fish epithelia induce the attachment of B. seriolae oncomiracidia.

Animals↗

PubMed2002

Survival and axonal regeneration of retinal ganglion cells in adult cats.

Axotomized retinal ganglion cells (RGCs) in adult cats offer a good experimental model to understand mechanisms of RGC deteriorations in ophthalmic diseases such as glaucoma and optic neuritis. Alpha ganglion cells in the cat retina have higher ability to survive axotomy and regenerate their axons than beta and non-alpha or beta (NAB) ganglion cells. By contrast, beta cells suffer from rapid cell death by apoptosis between 3 and 7 days after axotomy. We introduced several methods to rescue the axotomized cat RGCs from apoptosis and regenerate their axons; transplantation of the peripheral nerve (PN), intraocular injections of neurotrophic factors, or an antiapoptotic drug. Apoptosis of beta cells can be prevented with intravitreal injections of BDNF+CNTF+forskolin or a caspase inhibitor. The injection of BDNF+CNTF+forskolin also increases the numbers of regenerated beta and NAB cells, but only slightly enhances axonal regeneration of alpha cells. Electrical stimulation to the cut end of optic nerve is effective for the survival of axotomized RGCs in cats as well as in rats. To recover function of impaired vision in cats, further studies should be directed to achieve the following goals: (1). substantial number of regenerating RGCs, (2). reconstruction of the retino-geniculo-cortical pathway, and (3). reconstruction of retinotopy in the target visual centers.

Animals↗

PubMed2000

Axonal regeneration of mouse retinal ganglion cells by peripheral nerve transplantation; a quantitative study.

Purpose: Retinal ganglion cells (RGCs) of adult mammals can regenerate their axons along a segment of the peripheral nerve (PN) that is transplanted to the cut optic nerve. There have been many trials of PN transplantation to induce axonal regeneration of RGCs in adult rodents, cats and ferrets. However, because of the technical difficulty in transplant operation, PN transplantation in adult mice has not been carried out in spite of the availability of many kinds of gene-manipulated animals. Here we report the procedures for successful PN transplantation in this species. Methods: We made intraretinal (IR) and retrobulbar (RB) approaches for PN transplantation. Four weeks after PN transplantation, RGCs with regenerated axons were identified by retrograde labeling with rhodamine or horseradish peroxidase applied into the PN segment. Results: A quantitative survey showed that the mean regeneration ratio was 1.0 % (n = 8) in IR transplantation, whereas it was only 0.1 % in RB transplantation (n = 11). As previously shown in other species, the regenerated RGCs were predominantly larger-bodied cells in com-parison to intact cells. Conclusion: Possible reasons for the difference in regeneration ratio between the two transplant approaches and the feature of soma size of regenerated RGCs are discussed.

Journal Article↗

PubMed1996

The role of spinal cord activation before neurectomy in the development of autotomy.

A model of deafferentation pain is provided by sectioning the sciatic and saphenous nerves in the rat and mouse. This procedure leads to self-mutilation of the denervated hindpaw (autotomy). A noxious stimulus to the denervated area before neurectomy is known to enhance the autotomy. To understand the mechanism underlying this enhancement by prior noxious stimuli, we examined the effects of intrathecal (i.t.) injection of substance P (SP) and somatostatin (SOM) on autotomy behavior. These peptides are known to be released from primary afferent terminals in the dorsal horn by noxious stimuli. A single i.t. injection of SP or SOM just before neurectomy dramatically enhanced autotomy behavior in mice. Autotomy was enhanced in a dose-dependent manner with i.t. injection of SP (0.1-20 nmol) 5 min before neurectomy or SOM (0.1-1.0 nmol) 20 min before neurectomy. Autotomy significantly decreased by extending the interval between i.t. injection of SP or SOM and neurectomy. Intact mice injected with the same doses of SP or SOM showed dose-dependent acute nociceptive responses directed to the hindpaw. The severity of autotomy in neurectomized mice and the duration of acute nociceptive responses induced by the same doses of SP or SOM in intact mice were related. These results suggest that neuropeptides applied to the spinal dorsal horn just before deafferentation induce a state of central neural activation with long-lasting effects on the function of CNS cells. Augmentation of autotomy is a result of this activation which is kept as a 'memory'.

Animals↗