Biomedical Engineering Reference
In-Depth Information
the ability to undergo capacitation and acrosome reactions,
the epididymal sperm maturation process includes remod-
eling of sperm chromatin to a highly condensed form.
Studies in hypogonadal cynomolgus monkeys concluded
that chromatin condensation is a gonadrotropin-independent
process (
Golan et al., 1997
).
The basic morphology of spermatozoa among
nonhuman primates is similar, although species differences
do exist. Generally speaking, sperm consists of four basic
components: (1) the head, which contains chromatin and is
capped by the acrosome; (2) the neck, which contains the
basal plate, connecting pieces, and a centriole; (3) the
midpiece, which contains the mitochondria; and (4) the tail.
Several comparative studies on the morphology of
nonhuman primate spermatozoa utilizing scanning electron
microscopy (
Bedford, 1967; Matano et al., 1975; Gould
and Martin, 1978
) include details of the ultrastructural (and
identifying) features of numerous prosimian species
(
Gould, 1980; Harrison and Lewis, 1986
). Sperm parame-
ters have been assessed in a number of New World species
(
Bush et al., 1975; Gould and Martin, 1978; Harrison and
Wolf, 1985
). In the platyrrhine, the midpiece often inserts
eccentrically into the posterior border of the head. The
posterior acrosomal margin of squirrel monkey sperm has
a serrated appearance and is smaller than the capuchin
sperm, which have typical paddle-shaped sperm heads
(
Barr, 1973
).
Sperm from various Cercopithecidae species appear
uniform in shape, particularly compared with sperm from
the great apes (
Harrison and Lewis, 1986
). The sperm heads
appear flat and paddle-shaped, with the midpiece long in
relation to the head and the mitochondria of the midpiece
small and well organized (
Harrison and Lewis, 1986
),
whereas the sperm heads from the baboon are short, oval,
paddle-shaped, and taper anteriorly (
Flechon et al., 1976
).
The anterior segment of the acrosome in this species is
surrounded by a marginal thickening and covers roughly
two thirds of the head. The midpiece is characterized by
a relatively long and regular helical sheath of mitochondria,
with the ends of the mitochondria randomly distributed.
Morphology and dimensions have been compared with
those of other nonhuman primates and are very similar to
those of Cercopithecidae (Flechon et al., 1976).
Gould
(1980)
has provided an excellent description of sperma-
tozoa for various great apes. Among these, the spermatozoa
of the chimpanzee (P. troglodytes and P. paniscus) are the
most uniform, with the sperm heads relatively small and
thickened posteriorly and the midpiece similar to that of the
gorilla.
Nonhuman primates display a wide variety of mating
systems, from monogamy to promiscuity (see Chapter 5).
This variety has elicited interest in the effects of sexual
selection on reproductive parameters among nonhuman
primates.
Anderson and Dixson (2002)
reported that the
nonhuman primate sperm midpiece volume is associated
with relatively large testis size and with multiple male
mating systems, arguing that the larger midpieces may
reflect increased mitochondrial loading and increased
sperm motility in those species experiencing more intense
sexual selection.
Epididymal and Seminal Fluids
The fluid of the epididymis contains a variety of
compounds derived from rete testicular fluid, which is
modified by the epididymal epithelium. Testicular fluid has
low concentrations of spermatozoa and is characterized by
a low glucose and high inositol content (
White, 1981
).
Collection of fluid from the cauda epididymis indicates that
the composition is similar among species, although slight
variations are noted. The chief characteristics of the cauda
epididymal plasma are low concentrations of inorganic ions
and high levels of organic constituents such as glycer-
ylphosphylcholine, carnitine, sialic acid, hypotaurine,
glycosidases, and phosphatases. The concentrations of
sodium ions are ~20 mEq/liter. The potassium ion levels are
generally greater than or equal to sodium levels, although in
the rhesus, the potassium concentration is twice that of
sodium. It is generally accepted that pH varies along the
length of the epididymis but is usually within the 6.5
e
7.0
range, although it may occasionally be slightly higher
(
White, 1981
). The composition of the epididymal fluids
has been reported for the rhesus monkey (
Bose and Kar,
1968; Riar et al., 1973a,b; Arora et al., 1975; Jones, 1978
)
and to a more limited extent, for the langur (
Gupta and
Dixit, 1981
).
Information on the biochemical parameters associated
with testicular and epididymal fluids is limited, with the
most data available for the rhesus. Although some
species differences have been noted, these differences
may be dependent on the methods used for analyses
(
Harrison and Lewis, 1986
). Inasmuch as fluids vary in
the different regions of the male reproductive tract owing
to absorptive and secretive mechanisms, there are
significant differences between blood and reproductive
tract fluids, which in many cases are due to the presence
of the blood
e
testis barrier (
White, 1981
). For example,
testicular fluid in the rhesus consists of greater volumes
of lactate dehydrogenase, glucose-6-phosphate dehydro-
genase, lactic acid, and ascorbic acid than those present
in serum, and the converse is true for glucose and total
lipids.
Ackerman and Roussel (1968)
reported one of the few
comparative studies of semen among nonhuman primates
and humans.
Table 8.3
lists three biochemical parameters
e
lactic acid, citric acid, and fructose
e
found in the semen of
10 nonhuman primate species. Although our current
understanding of the functional aspects of these fluids is
