Robert Gerstner

Effects of growth hormone upon erythropoiesis in the hypophysectomized rat.

Summary Administration of STH to hypophysectomized rats results in peripheral reticulocytosis and increases in the percentages of nucleated erythroid elements within the bone marrow. Considerable repair of the hypoplastic marrow is induced by this agent. A rise in peripheral erythrocytic values fails to occur probably because of a concomitant increase in plasma volume.

Tissue cultures of pulpal elements

Abstract Odontoblasts in living cultures can be examined at rest, in an active phase, and transitionally between these states. With phase microscopy, granular origins and movements and other cellular activities can be observed, photographed, and analyzed. Tissue-culture experiments indicate that the odontoblasts have many more potentialities and the capacity to perform more functions than we now realize.

Onset and Type of Salivary Secretion in Fetal Rats

During the course of examining the effects of hormones on rat fetal salivary glands growing in in vitro organ cultures, the present authors noticed and reported an apparent fetal secretary activity (Anat. Rec., 142:305, 1962 [abstract]). A similar observation was made by Szymanska (Folia morph., 13: 195-201, 1962), who used fetal rats either at or just before term. Neither report indicated when in fetal life secretary activity began, nor the specific sites of activity. Since these appear to be the only references to submandibular and sublingual secretary function in the fetal rat, it was thought useful to determine more precisely the onset and sites of this function in these animals. Our in vitro experiments had shown that submandibular and sublingual gland anlagen did not differentiate morphologically before the 13th fetal day. Cervical and oral regions of rats were dissected daily from fetal day 12 to fetal day 17 and fixed in solutions that would allow a variety of morphologic and histochemical staining procedures to be carried out. From the 14th fetal day to birth (21st fetal day) the submandibular and sublingual glands in their common capsule were dissected out daily, under low-power microscopy, and prepared in similar fixatives. Postnatal glands were also fixed. In this way a day-by-day histologic series of sections of the glands from the 12th fetal day to early postnatal life was available for a continuous study of morphologic and physiologic development and differentiation. Modified histochemical procedures that would (1) indicate any secretary activity and (2) differentiate between mucous and serous types of secretion were carried out on serial sections of the two glandular structures. Other staining techniques were used to observe the morphologic development and differentiation of these glands. Sex of the fetuses was also determined as far as possible: macroscopically in the older fetuses and microscopically or by serial sections in the younger ones. These procedures indicated, among other findings: Although the sublingual gland begins developing one day later than the submandibular gland, sublingual secretary activity begins earlier. Beginning secretary activity of both glands is first detectable by the methods described on the 17th fetal day as an accumulation of positive staining material in the largest ducts, trace amounts in submandibular ducts, and larger amounts in sublingual ducts. Secretory activity in terminal cells is first seen during the 18th fetal day in the sublingual gland, and faintly during the 19th fetal day in the submandibular gland. Although the earliest detectable secretary product in both fetal glands is a mucoid type, histochemical procedures indicate that significant differences exist at this time in the character of the mucous secretions of the two glands. Our investigations failed to demonstrate a serous type of secretion in these fetal glands. Additional procedures to confirm this negative finding are planned. The morphologic and physiologic development and the cytology of the secretary elements of these glands in the fetal rat will be reported in detail elsewhere.

Effect of Rate of Freezing on the Preservation of Viable Tooth Germs

THE effects of rates of freezing on the preservation of tooth germs, pretreated to withstand the harmful effects of low temperatures, were investigated by varying the immersing time of the tissues into a single freezing agent, liquid nitrogen. Previous work by the authors had shown the superiority of solid carbon dioxide (dry ice)-ethyl alcohol mixtures (-780 C.) over liquid nitrogen (-1980 C.) as a preserving agent in maintaining viability of the tooth germs when each agent was used to freeze the tissues as rapidly as possible. The results were assumed to be due to either the slower rate of freezing at -780 C. or to the higher freezing temperature of the dry ice alcohol mixture. Incisor and molar tooth germs from rats, approximately 18 days fetal age, were removed aseptically and placed into glycerol-physiological saline (Tyrode) solutions (glycerol concentrations 20 per cent and 30 per cent by volume) for 15 to 30 minutes. The tissues were then transferred to sterile wood splints and sealed into thick-walled test tubes in such a way that the tooth germs did not adhere to the glass. The tubes were slowly lowered into the freezing agent, liquid nitrogen, at the rate of 10 minutes per inch, until they were completely immersed in the freezing fluid. Ten minutes after complete immersion, the tissues were removed for thawing. The tissue-bearing splints were quickly withdrawn and immediately plunged into physiological saline at about 38° C. After thawing the glycerol was removed from the tooth germs by washing them for 10 minutes in each of 3 changes of Tyrode solution. All tissues were cultured in Carrel flasks for observation of viability and ability to resume growth. Since the object of culturing was to determine the state of vitality of the tooth germs at the time of explanting, chiefly by the extent of cellular outgrowth from the tissues, the cultures were maintained for only 7 days. The medium used was fresh frozen chick plasma, fresh frozen chick embryo extract, and horse serum in ratios of 1:1:2. The tissues were incubated at 360 C. and examined daily. The tooth germs frozen slowly by delayed immersion into thhe liquid nitrogen appeared as viable as, and grew to somewhat larger size than, the controls frozen by rapid immersion into solid carbon dioxide-alcohol mixtures. The extent of cellular outgrowth from the liquid nitrogen slowly frozen tissues was greater than from the dry ice cooled controls, probably indicating that more cells survived the slower freezing method, although cytologically the cells appeared equally healthy after both methods. These results are interpreted as indicating that the rate of freezing, and not the freezing temperature, is of greater significance in the freezing and preservation of oral tissues for storage purposes. Experiments are under way extending these methods to an examination of tooth germs frozen by delayed immersion into dry ice mixtures at -780 C.

Effects of Withdrawal of Growth Hormone and Cortisone Treatment on the Blood Picture of Hypophysectomized Rats

Peripheral red cell counts of hypophysectomized rats were largely unaffected by chronic treatment with either cortisone or growth (STH) hormone. However, upon withdrawal of treatment, red cell counts tended to rise in the STH-treated rats and to fall in those administered cortisone. The values at this time mirrored the alterations observed in the bone marrows of the treated rats. The postinjection shifts in peripheral red cell numbers were probably the result of oppositely occurring alterations in plasma volume. Leucocytic values induced by prolonged cortisone treatment tended to return to normal levels at approximately 2 weeks after stoppage of injections.