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Acknowledgements: We gratefully acknowledge Dr. Tamara Franz-Odendaal at Mount Saint Vincent University, Halifax, Nova Scotia, Canada, for generously providing surface fish embryos, which were crucial for the latter part of this study. We acknowledge the University of Manitoba for supporting the Atukorale lab.
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The somal distributions of orexigenic orexin-A, anorexigenic corticotropin-releasing factor (CRF) and melanin-concentrating hormone (MCH) were immunohistochemically investigated in the whitespotted conger eel (Conger myriaster) brain, with particular focus on the preoptic nuclei and hypothalamus. Immunoreactive somata of these three neuroactive peptides were categorised into large (around 30 μm in diameter) and small (around 10 μm in diameter) types. Large-type orexin-A-, CRF- and MCH-immunoreactive (ir) somata were present in the magnocellular preoptic nucleus. Large-type MCH-ir somata were also seen in the lateral tuberal nucleus (TL). Fibres of these large-type somata may penetrate the neurointermediate lobe of the pituitary. In contrast, the small-type immunoreactive somata of these three neuroactive peptides showed differential distributions in the hypothalamus. Small-type orexin-A-ir somata were mainly seen in the paraventricular organ. CRF-ir somata were seen in the posterior parvocellular preoptic nucleus, around the dorsal and ventral areas of the anterior lateral recesses, and around the dorsal area of the posterior lateral recesses. MCH-ir somata were seen in the TL and around the medial region of the posterior lateral recesses. Based on the hypothalamic differential localisations of these peptides, of which association with feeding behaviour is suggested, the presence of intra-hypothalamic functional localisation related to feeding is likely.
The order Chiroptera is one of the most diverse orders in terms of the number of species; however, very few studies have been conducted in this group regarding its embryonic development. In this area, studies have focused on staging through morphological characters, but those describing organogenesis are scarce. Therefore, this work describes the gonadogenesis of Eumops patagonicus, a Sudamerican insectivorous bat, with an emphasis on ovarian development and determination of the migration stage of the primordial germ cells (PGCs) through immunostaining. Pregnant females of this species were captured to carry out the study, and the embryos were processed to obtain histological sections using the conventional histology technique and immunohistochemistry (OCT4, PCNA, Bax and Bcl-XL). Critical stages of gonadal differentiation were described, starting from the formation of the urogenital ridge and the identification of PGCs with the positive reaction for OCT4 in embryological development stage 13. At stage 17 of development, an undifferentiated gonad with active proliferation is observed and then a defined testis (S. 21) and ovaries (S.23 and S.25). The embryo ovaries S. 23 show a cortex formed for ovogonia cysts/nets that have a craniocaudal development with differences in the immunolabelling of PCNA, Bax and Bcl-XL. The embryo ovaries S. 25 show the primordial follicles in the ovary cortex. The results determined that there is a conserved pattern in embryonic development in this order when comparing E. patagonicus with frugivorous bats. This information is important for the establishment of relations in development in mammals and within the order Chiroptera.
Osteopontin (OPN), osteocalcin (OC) and osteonectin (SPARC/ON) are multifunctional proteins present in both hard and soft tissues, where they contribute to various physiological processes, including reproductive function. However, their concurrent expression and distribution in the bull testis and epididymis have not been previously characterised. This study aimed to immunohistochemically evaluate the expression patterns and localisation of OPN, OC and SPARC/ON across different segments of the testicular and epididymal structures in bulls. The findings revealed that OPN exhibited variable expression across seminiferous tubules, with localisation in germ cells—particularly spermatogonia and spermatocytes—as well as in Sertoli and Leydig cells within the interstitial compartment. In the epididymis and associated ducts, OPN expression was predominantly observed in epithelial cells. OC demonstrated strong expression in the epithelial cells of the ductus epididymis and ductus deferens, as well as in select connective tissue and smooth muscle cells of the ductus deferens. SPARC/ON expression ranged from moderate to strong across spermatogenic cell lineages, Sertoli and Leydig cells and blood vessels within seminiferous tubules. These findings indicate that OPN, OC and SPARC/ON are differentially expressed throughout the bull testis, rete testis, ductuli efferentes, epididymis and ductus deferens, highlighting their potential roles in maintaining reproductive function under physiological conditions.
The testes of mammals are responsible for gamete production and the secretion of the sex hormone testosterone. Within the seminiferous tubules, spermatogenesis occurs, where germline cells undergo division and differentiation until the formation of spermatozoa. Meanwhile, in the intertubular compartment, Leydig cells produce and secrete testosterone, a hormone essential for spermatogenesis. Monodelphis americana is a marsupial species endemic to Brazil, commonly known as the three-striped short-tailed opossum. The reproductive biology of marsupials remains relatively unexplored despite being a crucial tool for understanding species-specific reproductive strategies, which can aid in management and conservation efforts. In this study, M. americana exhibited a body weight of 36.7 g, with a gonadosomatic index (GSI) of 0.47%, a tubular somatic index (TSI) of 0.36% and an interstitial somatic index (ISI) of 0.27%. The proportion of seminiferous tubules was 83.16%, indicating a significant investment in sperm production. The mitotic and meiotic indices were 1.87 and 2.64 cells per division, respectively, with an overall spermatogenic yield of 12.68. The intertubular compartment accounted for 16.84% of the testicular parenchyma, of which 13.13% consisted of Leydig cells, with a total count of 22.75 × 106 Leydig cells per testis. The findings suggest that M. americana prioritises spermatogenic parameters over the intertubular compartment, implying that males exhibit a promiscuous reproductive behaviour.
This study on the origin and distribution of the phrenic nerve to the diaphragm was conducted using 16 collared peccaries (Tayassu tajacu). The phrenic nerves originated from the fourth to the seventh cervical spinal nerves, and in a few specimens, from the fourth to the sixth cervical nerves. A contribution from the cranial pectoral nerve to the phrenic nerve was observed. The phrenic nerve terminated in the costosternal and lumbar branches, and less frequently as the lumbocostal trunk and sternal branch. The lumbar branch innervates the crura of the diaphragm, while the costal branch serves the entire costal region. The sternal branch is distributed to the ventrolateral costal area and the sternal portion of the diaphragm on both the left and right sides. These branches send ramifications to the central tendon and the dorsal and ventral surfaces of the caudal vena cava, and also form homo- and heterolateral connections between the branches.
Kinosternon scorpioides scorpioides is an omnivorous chelonian with a wide geographical distribution, occurring from Mexico to South America, especially in Brazil. While morphological observations of the species have described its oesophagus, little is known about the other organs constituting the tubular digestive tract. Therefore, the objective of this study was to describe the morphological aspects of the tubular portion of the digestive tract of this species. Ten adult specimens were analysed. After fixation in 10% formalin, organ fragments were embedded in paraffin using the routine histological technique. Sections of 5 μm thick were stained with haematoxylin–eosin (HE), Gomori trichrome (GT) and Alcian blue (AB) pH 0.4 and 2.5. The tubular portion of the digestive tract of K. s. scorpioides consisted of the oesophagus, stomach, small intestine (duodenum, jejunum and ileum), large intestine (caecum and colon) and cloaca. The wall of the tubular portion of the digestive tract of K. s. scorpioides was made up of four concentric layers: Mucosa, submucosa, muscularis externa and adventitia or serosa. The morphology of the tubular digestive tract of adult K. s. scorpioides described in this study shows structural patterns appropriate to their omnivorous feeding habits, such as a simple glandular stomach, long intestines, a well-developed caecum and the production of mucosecretions throughout the digestive tract. This study provides insights into the digestive physiology of the species and provides data for comparative analyses.
The tympanic bulla of South American camelids is a unique multi-compartmental structure with an internal architecture resembling that of honeycomb. This unique configuration creates surgical challenges for the treatment of refractory otitis media cases in llamas (Lama glama). Surgical interventions for otitis media in the llama can result in life-threatening arterial haemorrhage. Surgery in lesser described species, such as camelids, can result in unanticipated complications when surgeons rely solely on anatomic extrapolation of similar species. Descriptive anatomy of llama vascular structures surrounding the tympanic bulla is lacking in the published record. To elucidate the arterial pattern of the tympanic bulla region of the llama with the intent of identifying unexpected arterial structures, 10 llama heads were dissected and all major arterial structures were identified, described and compared to computed tomography scans of contrast-enhanced arterial latex. Bilateral variations of the caudal auricular, superficial temporal and transverse facial arteries were found to result in an arterial trunk lying immediately adjacent to the lateral margin of the tympanic bulla in the llama. The arterial structure situated at the lateral margin of the tympanic bulla interferes with direct surgical access to the tympanic bulla by standard surgical techniques. These unique anatomic variations in the llama may be responsible for the risk of life-threatening haemorrhage during surgery that results in abandonment or failure of the procedure.
Vision is a critical sensory modality in vertebrates, enabling diverse adaptations to environmental challenges. This review explores the remarkable adaptations of vertebrate eyes to low-light environments, such as nocturnal habitats, deep-sea ecosystems and subterranean niches. Key structural and functional modifications include enhanced eye size, rod-dominated retinas, reflective tapetal layers and photopigment spectral tuning. The role of photoreceptor specialisation and retinomotor movements in optimising photon capture and minimising light scatter is examined, alongside evolutionary trade-offs that prioritise sensitivity over resolution. Furthermore, adaptations such as bioluminescence detection in deep-sea fish and the regressive evolution of vision in subterranean species highlight the intricate relationship between ecological demands and visual evolution. By synthesising current research, this review provides insights into the evolution in vertebrate visual systems and offers future perspectives on the molecular and ecological drivers of these adaptations.
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