Sperm cell surface characteristics of Plumbago zeylanica L. in relation to transport in the embryo sac

Myosin associated with the male germ cells of angiosperms interacts with actin, promoting transport of the non-motile generative and later sperm cells in the pollen tube. Myosin localizing on the sperm cell plasma membrane seems negligible in Plumbago, as reflected by the absence of: (i) anti-myosin labeling using immunoelectron microscopy, (ii) sperm motility on actin matrices, and (iii) electrophoretic movement changes after addition of antibody. Sperm cells injected directly into actively streaming Nitella internodal cells, however, follow actin bundles and their movement is sensitive to ATP and Mg²⁺. This may be based on simple charge binding since negatively charged latex beads also migrate on actin, whereas neutral or positively-charged latex beads do not. Sperm cells are negatively charged according to capillary microelectrophoresis, whereas killed sperm cells, which are positively charged do not migrate. The sperm cell that normally fertilizes the egg has a higher calculated charge (8.277 × 10³ esu/cm²) compared with the sperm cell that fuses with the central cell (6.120 × 10³ esu/cm²). Received: 15 December 1998 / Accepted: 21 January 1999     

Mouse specific-locus test for the induction of heritable gene mutations by dibromochloropropane (DBCP)

The nematocide DBCP (1,2-dibromo-3-chloropropane) produced negative results in a specific-locus test for gene-mutation induction in the germline of male (101 X C3H)F1 mice, most of which were treated with 5 daily intraperitoneal injections of 80 mg/kg (total exposure, 400 mg/kg); a few received lower exposures. For treated spermatogonial stem cells, the finding of 2 mutations among 39519 offspring--a rate almost identical to the control rate--rules out (at the 5% significance level) an induced mutation frequency greater than 2.0 times the historical control rate. From treated poststem-cell stages, no mutants were found among 6240 offspring, ruling out (at the 5% significance level) a multiple of 8.0 times the control for these cell types. A multiple rearrangement (7 chromosomes involved in 3 translocations) found in one of the mutants probably arose as a postmeiotic event not associated with the DBCP treatment. The fertility of DBCP-treated males was not disturbed, in keeping with the absence of germ-cell toxicity and dominant lethals found by other investigators in these mice, and in contrast to results in certain other species. While the treated (101 X C3H)F1 mice are Ah-responsive, other findings make it questionable whether biotransformation of DBCP to reactive intermediates is accomplished via the Ah-receptor system.     

The role of GABA in dyskinesias induced by chemical stimulation of the striatum

The gamma aminobutyric acid (GABA) antagonists picrotoxin and bicuculline were injected into the striatum of rats via chronic cannulae. Dyskinesias were produced by these drugs which could be blocked by their injection combined with GABA. The intrastriatal (i.s.) injection of a cholinergic drug, carbachol, also produced dyskinesias which were blocked by GABA. The use of i.s. injection of GABA antagonists to produce an animal model of Huntington's chorea is discussed.     

Control of a teleost social signal

Territorial male Haplochromis burtoni (Teleostei; Cichlidae) have a dark facial stripe, the 'eyebar', which can appear and disappear within seconds, independently of other coloration patterns. It is used to signal territory ownership and aggressive intent. Some males, called 'barless', have functional melanophores in the eyebar region but never display this pattern, because melanin in eyebar pigment cells is never dispersed. The eyebar melanophores are controlled by a specialized branch of the maxillary nerve. Lesioning the 'eyebar nerve' resulted in immediate melanin dispersion and consequent darkening of the eyebar pattern, and it abolished the normal paling response in all behavioral situations. Nerve lesion produced similar results in both barred and barless males, except that the coloration of the denervated eyebar in barless males was more similar to camouflage markings than to the conspicuous black eyebar used as a social signal. Electrical stimulation of the maxillary nerve produced melanin aggregation. Photoelectric recordings of this paling response revealed no differences between barred and barless males, or between the eyebar and other facial chromatophores that do not function as visual displays. Thus, the difference in the physiological state of eyebar melanophores in intact barred and barless males cannot be explained by differences in peripheral nerve anatomy or physiology.     

Further observations of stage-specific effects seen after short-term hypophysectomy in the rat.

Although hypophysectomy has been a popular tool to study the effects of hormone deprivation as well as concomitant or subsequent hormone supplementation, there is relatively little morphological information available on the structural manifestation of pituitary removal on the testis. In the report, changes, in addition to those previously reported after short-term (6 days) hypophysectomy in the rat (Russell and Clermont, 1977), are described. Membrane-bound vacuoles (primarily) appeared within the basal region of the Sertoli cell at approximately the level of Sertoli-Sertoli junctions. In stages VIII through XI elongating spermatids were abnormal and manifested manchette indentation of the nucleus, a variety of other abnormal head shapes, acrosomal breaks and enlargement of the subacrosomal space. These defects were interpreted as the effect of declining hormonal levels in stage VII on spermatids that had survived the stage VII hormone sensitivity known to occur with severe hormone depletion. Abnormalities in the flagellum involving the mitochondrial sheath and fibrous sheath were detected. Preleptotene spermatocytes degenerated and could be identified in the process of doing so near the base of the seminiferous epithelium. The contact of preleptotene spermatocytes with the basal lamina was also significantly reduced. The results show that both Sertoli cell and germ cell abnormalities were present although germ cell abnormalities could be a secondary consequence of lack of appropriate stimulation of the Sertoli cell. Degeneration of basal compartment germ cells shows that germ cells other than those located in the adluminal compartment are vulnerable to hormonal withdrawal. The question of how hormone effects are mediated in the testis at midcycle to produce these effects is discussed.