The poll glands of the dromedary (Camelus dromedarius): ultrastructural characteristics

Gas/Liquid Chromatography-Mass Spectrometry Analysis of Key Functional Substances Regulating Poll Gland Secretion in Male Camels during Seasonal Estrus

Increased poll gland secretion is a major characteristic and indicator of estrus in male Bactrian camels; however, research on these poll glands and their secretion is extremely rare. In this study, we determine the chemical composition of poll gland secretions and identify the key functional substances that regulate seasonal estrus in male camels. A GC/LC-MS dual platform was used to analyze ventral hair (control) and neck mane samples containing poll gland secretions from male Bactrian camels during estrus. Multidimensional and single-dimensional analyses were used to screen differentially expressed metabolites (DEMs) between groups. Functional prediction of enriched metabolites was performed using a Human Metabolome Database comparison and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis, which were then compared with a behavioral analysis of male Bactrian camels in estrus. A total of 1172 DEMs and 34 differential metabolic pathways were identified. One metabolite group was found to relate to steroid synthesis and metabolism, and another metabolite group was associated with neural metabolism. Therefore, we speculate that steroids and neurochemicals jointly regulate estrous behavior in male Bactrian camels, thus providing theoretical insights into the development and function of poll glands in Bactrian camels.

Morphological and histochemical changes in the dromedary camel epididymis in relation to reproductive activity

Environmental conditions such as temperature, light and food availability are known to influence the physiological status of animals. The male dromedary camel (Camelus dromedarius) is considered as a seasonal breeder with maximal sexual activity during certain period of the year followed by a decrease in activity during the remaining period. On the other hand, the male camel is also shown as an atypical seasonal breeder because this does not undergo sexual quiescence with complete cessation of spermatogenesis. This animal, however, shows remarkable physiological and behavioral changes during its maximal sexual activity. The annual breeding (rutting) period also influences the epididymis. In this review, an attempt has been made to present the available literature pertaining to gross anatomical, histological, histochemical, immunohistochemical and molecular changes in camel epididymis during breeding and nonbreeding periods, and the changes are believed to be correlated with male sexual behavior and libido. This review may also exhibit the dromedary camel breeding period, which is still unresolved, and thus may prove helpful in determining the exact time of mating, which is important for the success of assisted reproductive outcomes. Further, the review may contribute to a better understanding of the epididymal physiology in camel and may also prove useful in improving reproductive efficiency and population of this animal.

Seasonal morphology and immunoreactivity of cytokeratin and atrial natriuretic peptide in dromedary camel poll glands

Poll glands are characteristic feature of dromedary camels; although they yield a yellowish offensive secretion, especially during rutting (breeding) season, their function is not yet exactly specified. The present study shows the seasonal morphology and immunoreactivity of cytokeratin (CK) and atrial natriuretic peptide (ANP) in the camel poll gland; the result could clearly specify the role of the gland in camel reproduction. Poll glands are compound tubulo-alveolar in structure. During rutting season, the secretory units showed wide lumina and simple squamous epithelium surrounded by myoepithelial cells; the lumina became narrower and the epithelium changed to simple cuboidal during non-rutting season. Many glandular lobules showed abundant interlobular connective tissue with fewer and smaller secretory units during non-rutting season compared to rutting season. Positive CK and ANP immunoreactivity was detected in the cytoplasm of epithelial cells of secretory units and ducts together with the myoepithelial cells and blood vessels. Although CK immunoreactivity was more intense during rutting season in comparison to non-rutting season, there was no seasonal variation in ANP immunoreactivity. During both seasons, while the glandular capsule, connective tissue septa, interstitium showed negative CK immunoreactions, they reacted moderately to ANP. In conclusion, the poll gland undergoes annual structural and functional changes which are suggested to correlate with the male seasonal sexual behaviour. Further, the biological role of CK and ANP proteins together with their immunohistochemical expression in the camel poll gland suggests a stimulatory effect in the glandular secretory cells, and hence, they might modify camel sexual activity.

Ultrastructural Analysis of the Integument of a Desert-Adapted Mammal, the One-Humped Camel (Camelus dromedarius)

In this study, we conducted a light microscopic and ultrastructural analysis of the integument of the one-humped camel (Camelus dromedarius). In general, the epidermal strata of the camel integument appeared typical of those found in non-desert mammals. Two cell populations were noted in the stratum basale: one with a flat, non-serrated base and the other with a highly serrated base. Typical fine structure was observed in keratinocytes of the stratum spinosum and stratum granulosum. The stratum corneum was six to 10 cells thick. Within the different strata, overall cell morphologies and the general distribution and relative abundance of cellular organelles appeared typical. Dermal features included the presence of myoepithelial cells surrounding apocrine tubular glands. Inter- or intracellular canaliculi within the secretory cells of the apocrine glands, reported to be present in certain other non-desert mammals, were not evident in the camel. Together, these data indicate that while the camel is clearly adapted for a desert lifestyle, these adaptations do not include significant specializations at the cellular or subcellular level in the integument.

Secretion of mucous granules and other membrane-bound structures: a look beyond exocytosis

The substances that animals secrete at epithelial surfaces include not only small molecules and ions delivered by exocytosis, but also a wide variety of materials in membrane-bound form. The latter include mucous granules of pulmonate molluscs, milk fat globules, and products of apocrine and holocrine secretion. Contents include hydrophobic entities (e.g., lipids, hydrocarbons), protective substances (e.g., mucus), and potentially injurious substances (e.g., digestive enzymes, toxins). In some cases vesicles or granules perform significant functions through enzymatic or other properties of the membrane itself (e.g., mammalian prostasome). Much work is still needed to elucidate the ways in which cells release membrane-bound products and how these products are deployed. The current concentration of research effort on exocytosis as a secretory modus should not divert attention from the remarkable versatility of epithelial cells that are capable of utilizing a variety of ways besides exocytosis to transfer materials and information to the external environment.