Ultrastructure and motility of the caudal epididymis spermatozoa from the volcano mouse (Neotomodon alstoni alstoni Merriam, 1898)

The volcano mouse Neotomodon alstoni alstoni is a genus endemic to the high er elevations of the Mexican transvolcanic belt. In the present study we ex amined for the first time the morphological features of the spermatozoa tak en from the caudal epididymis of this species by transmission and scanning electron microscopy. Spermatozoan motility was studied in sucrose and bicar bonate solutions; vitality and morphology were observed by light microscopy . Transmission electron microscopy shows that the head of spermatozoon is a symmetric and possesses a large and curved hook. The axoneme of the spermat ozoan tail is highly developed at fibers 1, 5, and 6. Absolute and relative measurements of the length of the head, the midpiece, and the rest of the tail were also obtained. N. alstoni alstoni spermatozoa were hyperactive in the presence of 290 mM sucrose and 10 and 20 nM bicarbonate solutions exhi bited high motility (180-190 mu m/sec), and high flagellum beating frequenc y (10-12 Hz). In contrast, the spermatozoa in 310 mM sucrose solution showe d scarce motility (13.5 +/- 3.8 mu m/sec) and low beating frequency (1.5 +/ - 0.4 Hz). It is proposed that the volcano mouse spermatozoa possess some f eatures very similar to other mammalian spermatozoa and that bicarbonate tr iggers caudal epididymal sperm motility of this species. (C) 2000 Wiley-Lis s, Inc.