The question was asked whether the proximo-distal regional organization of regenerating urodele limbs is the result of a n epidermal-mesodermal interaction, as is the case i n the embryonic limb bud, Epidermal deletion experiments on regeneration blastemas of various stages have answered this question i n the affirmative. The mechanisms involved in the morphogenesis of the regeneration blastema are therefore very similar to those operating in the morphogenesis of embryonic limb buds.

The fidelity of the regenerative response in the adult newt, Notophthalmus viridescens, was examined following repeated amputations at the level of the distal one-third of humerus. Three to four months following amputation, all regenerates were scored for gross morphology, reamputated, and stained with methylene blue for skeletal elements. The occurrence of abnormal regeneration with respect both to gross morphology and to skeletal structure was found to increase directly with the number of times the limb stumps were required to initiate dedifferentiation and repair. The initial amputation-regeneration process produced structurally normal replacement limbs in 91% of the cases examined. Reamputations of 4-digit regenerates (3--4 months after the previous transection) resulted in structurally abnormal regenerates in 28% of the cases following two amputations; 50% of the cases following three amputations; 65% of the cases following four amputations; and 81% of the cases following five amputations. The relationships between repeated dedifferentiation, proliferation, and redifferentiation and normal limb development are discussed.

Denervation-induced alterations in the composition of the soluble protein population of various stages of forelimb regenerates in the adult newt were examined. Denervation alters the normal protein arrays in three ways: (1) proteins may be eliminated from an array, (2) proteins not normally present in an array may be induced to appear, and (3) proteins unique to d e nervated regenerates may appear in an array. The character of the denervationinduced alteration at five days post-amputation is basically different from that at later stages of regeneration. The stages during which the regenerate is b e coming independent of the nerve for its morphogenetic activity are the ones in which the protein profiles are the most drastically altered. Morphogenetic independence of the nerve therefore does not require the synthesis of nerve dependent proteins, and it is concluded that nerve independence is a property generated by the production of a critical number of blastema cells. Nerve dependent proteins are required for the mitotic activity which leads to attainment of the critical mass, and the failure of denervated early regenerates to continue regeneration may be due solely to mitotic inhibition.

The sea anemone, Metridium senile, is covered with a sticky mucus which facilitates the trapping of plankton from the sea water. Histochemical procedures indicate that this acid mucopolysaccharide-like (AMPSlike) mucus is secreted by the columnar epithelial cells of the body surface.

Reductions in testicular mass, sperm motility, and mating frequency have been attributed to the stresses caused by confinement of Sprague-Dawley male rats in nose-only inhalation exposure tubes. Testicular changes, including an increase in testicular atrophy, have been detected at an increased incidence in male rats used in inhalation studies as compared with rats of the same age and strain used in oral toxicity studies. This study was designed to determine whether nose-only exposure of male rats caused testicular toxicity under conditions of cooling of the exposure room and appropriate acclimation to the exposure tubes. In order to acclimate the rats to the nose-only inhalation exposure apparatus, all male rats were placed in the exposure tubes for at least four successively increasing time intervals (15, 30, 45, and 60 min) on 4 separate days, with a rest period of approximately 48 h between the first and second acclimation. Twenty male rats were exposed nose-only to filtered air for approximately 2 h per day for 28 days before cohabitation and continuing throughout a 14-day cohabitation period. To reduce thermal stress, the exposure room temperature was maintained at 64 to 70 degrees F. Twenty control rats were housed in the same room as the exposed rats but were not placed in exposure tubes. End points monitored were body weight, testicular weight, sperm count, sperm motility, and histopathology of the testes, epididymides, prostate, and seminal vesicles. The control rats gained weight more rapidly than the exposed rats. All the rats in both groups mated successfully, and testicular weights, normalized to body weight, were similar for both groups. More importantly, there were no microscopic changes that could be considered an adverse effect on the reproductive tissues in the male rats placed in exposure tubes. Thus, nose-only exposure for up to 2 h per day for a total of 42 days did not cause adverse effects on the reproductive organs, fertility, or reproductive performance of male rats under the conditions of this study.