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Biomedical subjects

H Wallace

Publications and source records attributed to H Wallace.

At least 55 records · Page 3Linked to original sources
PubMed1984

The California Statewide Family Health Education and Training Program 1981-1982.

Through support from the California State Department of Health Services, San Diego State University continued a statewide program in family life education, which consisted of: 1) establishment of a statewide advisory committee representative of many diverse points of view; 2) performance of a study of the teaching of family life education in the ninth and 10th grades of public schools in the state, as well as an examination of the present status of training of teachers; 3) provision of consultation and training programs for local school districts, including community support and implementation training, program development consultation teacher training and a limited number of small block grants to improve local family life education program efforts; and 4) preservice education classes to be conducted at teacher preparation campuses in the California State University system. The paper describes some of the findings of the study of the ninth and 10th grades, as well as the details of methodology of all four components of the statewide program.

California↗
PubMed1984

The response of denervated axolotl arms to delayed amputation.

Forearms of juvenile axolotls can be kept denervated for up to 4 weeks by deflecting brachial nerves to the flank. A more orthodox second denervation prolongs this state up to a total of six weeks. The denervated arms are unable to regenerate for the whole period, but eventually become reinnervated and then regenerate normally. These results and analogous experiments on adult newts prompt a partial retraction and reinterpretation of my previous report on regeneration after prolonged denervation.

Ambystoma mexicanum↗
PubMed1982

Partial denervation effects on limb cartilage regeneration.

Partially innervated axolotl arms gave regenerates of reduced size with deficient skeletal element replacement. This deficiency was most pronounced when nerve 4 (the largest of the brachial nerves) estimated to make up 50-60% of forelimb axons was removed by repeated resection. Nerve 3 or 5 removal gave less pronounced reduction deformities in the newly formed regenerate. The dependency of skeletal element formation upon nerves is emphasized but does not follow a strict segmental subtraction in axolotl forelimbs--perhaps because of overlapping innervation of nerves 3, 4, and 5 to all four digits. These effects of partial innervation add tentative support for an hypothesis of neurotome subtraction that was proposed to account for the syndrome of thalidomide abnormalities.

Ambystoma mexicanum↗
PubMed1981

Regeneration of subnormally innervated axolotl arms.

Forearms of juvenile axolotls contain about 5000 axons, of which only 25% are myelinated and visible by light microscopy. Virtually all the axons degenerate after transection of the brachial plexus, but repeated operations fail to keep the arm completely denervated. Regrown nerve fibres were detected by electron microscopy after 6 weeks of attempted denervation and related to the quantity usually considered necessary for limb regeneration. Such arms regenerated quite normally, provided their innervation had been depleted for several weeks before amputation. Among other ways of reconciling these observations to the neurotrophic theory of limb regeneration, it is suggested that tissues can adapt to deprivation of their nerve supply.

Ambystoma↗
PubMed1980

Regeneration of reversed aneurogenic arms of the axolotl.

Aneurogenic arms of young axolotls were implanted into the flank as heterotopic autografts with reversed proximo-distal orientation. The formerly proximal ends of such arms regressed to a variable extent, and then either regenerated or could do so following a second amputation. The regenerate always contained a complete sequence of skeletal elements between the adjacent stump skeleton and terminal digits, being a mirror image of the implanted arms with identical transverse axes but an opposed proximo-distal axis. Many reversed arms also regenerated fingers from the implanted hand. Identical results were obtained from reversed arms of control larvae, confirming previous studies on reversed well-innervated arms. Nerves are not required for the establishment of a new proximo-distal axis, therefore, and probably have no influence on the determination of any limb axis. Morphogenesis of the regenerate is clearly related to the position along the proximo-distal axis where the blastema originates. Although this axis is reasonably envisaged in terms of a gradient, its polarity is ignored during regeneration.

Ambystoma↗
PubMed1979

I. W. Whimster.

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Dermatology↗
PubMed1979

Duplicated axolotl regenerates.

Three series of palette stage regenerates were prepared by amputating both arms of juvenile axolotls in the mid-forearm, above the elbow, or close to the shoulder. Within each series, excised regenerates were replaced in their original orientation (as a control) or rotated at 90 degrees intervals about the proximodistal axis, or were transplanted to the contralateral arm with identical rotations. Control grafts occasionally caused the formation of a single extra digit. All experimental rotations provoked duplicate or triplicate structures, ranging from accessory digits to extra forearms. Shoulder level grafts were subject to a pronounced correctional derotation and yielded a variable proportion of duplications. Forearm and elbow-level rotations invariably yielded duplications, which therefore result from an axial discrepancy rather than complete axial opposition between graft and host. These results are incompatible with the clockface model of positional information and demand a modification of other current models. The recorded frequency and orientation of duplications suggest that a limb contains at least two polarized transverse axes which cannot be respecified during regeneration. A substantial discrepancy on either axis reduces the normal regulative interaction between graft and host, allowing either of them to regenerate independently.

Ambystoma↗
PubMed1978

Testing the clockface model of amphibian limb regeneration.

Contrary to the predictions of the clockface model, rotating a regenerate by 90 degrees produces duplications identical to those resulting from 180 degrees axial reversals. Exchanging regenerates between arms indicates the presence of 2 determined transverse axes.

Animals↗
PubMed1976

Irradiation inhibits the regeneration of aneurogenic limbs.

The developing arms of axolotl larvae from the 2-digit stage onward and the aneurogenic arms of surgically denervated larvae maintained in parabiosis are able to regenerate after amputation. Such regeneration is uniformly inhibited by local irradiation of the arm, whether innervated or not. This demonstration refutes a recent hypothesis that X-rays interfere with a special activity of nerves required for regeneration, and supports the earlier concept that X-rays act directly on those cells which must proliferate to form the regenerated tissues.

Ambystoma↗
PubMed1976

How x-rays inhibit amphibian limb regeneration.

The effects of an inhibiting dose of 2,000 rad of X-rays on the regenerating limbs of axolotl larvae have been examined in a histological and cytological study. Particular attention was paid to the mitotic indices of normal and irradiated epidermal and blastemal cells. Both the characteristic pattern of epidermal mitotic stimulation which normally follows amputation and the later increase in blastemal mitoses are suppressed by irradiation. In most cells the effects are permanent, but in a small proportion a mitotic delay is induced and upon subsequent division chromosome damage in the form of micronuclei is revealed. Thus irradiated cells which do divide almost certainly die. These results are discussed in relation to other theories of X-ray inhibition of regeneration with particular reference to the view that irradiated cells can be reactivated.

Ambystoma↗
PubMed1976

Dr. G.B. Dowling.

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Dermatology↗
PubMed1976

The cell cycle during amphibian limb regeneration.

The duration of the cell cycle in the blastema of regenerating limbs of axolotls has been measured by means of [3H]thymidine pulse labelling and autoradiography. A chase was required to define the pulse period. An average cell cycle at 20 degrees C takes 53 h, S-phase takes 38 h; including parts of mitosis, G1 is 10 h and G2 is 5 h long. The protracted cycle and S-phase are consonant with the large genome in axolotis and other urodeles. The rapidly growing blastema probably contains a steady population of about 5000 proliferating cells, as there is a regular withdrawal of differentiating cells from the population. The kinds of determination which exist in this population of cells, or are exerted on it, are briefly considered.

Ambystoma↗