In vitro action of cobra venom on goat spermatozoa ultrastructure by transmission and scanning electron microscopy

T. R. Rahmy(1), M. A. Ayoub(2)

(1)Department of Biology, Faculty of Science, (2)Department of Animal Production, Faculty of Agricultural Sciences, United Arab Emirates University, Al-Ain, 17551, UAE.

Goat spermatozoa were incubated in vitro in Tris-citrate buffer, pH 7.2, containing 0, 40, 80, or 160 mg of Naja haje venom/mL buffer for 4 hours. During incubation, the percentages of sperm motility were decreased, while percentages of dead spermatozoa were increased in a time and concentration-dependent manner. The effect of venom concentrations on the ultrastructure of incubated spermatozoa was examined hourly by scanning (SEM) and transmission (TEM) electron microscopy. SEM results showed plasma membrane wrinkling at heads of some spermatozoa after 2 h incubation with 40mg venom. Most spermatozoa suffered membrane wrinkling after 4 h incubation. However, incubation with 80 mg venom caused membrane fractures in most sperm heads after 1 h incubation. The extent and depth of these fractures were increased after 2-3 h incubation. After 4 h incubation, plasma membrane focal erosion of many spermatozoa heads was common. Incubation with 160 mg venom induced sperm head swollen plasma membranes after 1 h incubation. Ruptured and disintegrated membranes were seen after 2 h; lysis and removal of external surface of spermatozoa head plasma membranes were recorded after 3-4 h incubation. TEM indicated slightly swollen areas on the sperm head plasma membrane, but showed normal nuclei, acrosomes, and tail regions after 2 h incubation in 40 µg cobra venom. The swollen areas were accompanied by sperm head membrane disintegration as well as membrane irregularities and distortion of tail mitochondrial cristae after 3-4 h incubation. However, incubation with 80 µg venom showed focal areas of membrane lysis and discontinuity in the sperm heads and tails increasing with incubation time. Severe axoneme and tail longitudinal fiber degeneration and increased numbers of distorted mitochondrial cristae were also observed after 3-4 h incubation. Spermatozoa incubation with 160 µg venom increased severity of plasma membrane dissolution, disintegration, and rupture. Axoneme disorganization and tail longitudinal fiber fusion were seen after 1-2 h; complete deformation of the motility system was recorded after 3-4 h incubation. Nuclei were normal, but acrosomes were partially damaged, and distorted mitochondrial cristae were increased after 4 h incubation. The results indicated that cobra venom induced a concentration and time-dependent alterations on spermatozoa plasma membrane as well as obvious deformation on the motility system and tail mitochondria, which are responsible for sperm viability and fertilizing ability.

KEY WORDS: cobra venom, ultrastructure, goat spermatozoa, motility, Naja haje.

CORRESPONDENCE TO:

T. R. Rahmy - Department of Biology, Faculty of Science - United Arab Emirates University, Al-Ain, 17551, UAE. Email tarekr@uaeu.ac.ae