The vomeronasal system of the newborn capybara: a morphological and immunohistochemical study

Abstract

the vomeronasal system (VnS) is responsible for the perception mainly of pheromones and kairomones. primarily studied in laboratory rodents, it plays a crucial role in their socio-sexual behaviour. As a wild rodent, the capybara offers a more objective and representative perspective to understand the significance of the system in the Rodentia, avoiding the risk of extrapolating from laboratory rodent strains, exposed to high levels of artificial selection pressure. We have studied the main morphological and immunohistochemical features of the capybara vomeronasal organ (Vno) and accessory olfactory bulb (AoB). the study was done in newborn individuals to investigate the maturity of the system at this early stage. We used techniques such as histological stains, lectinslabelling and immunohistochemical characterization of a range of proteins, including G proteins (Gαi2, Gαo) and olfactory marking protein. As a result, we conclude that the VNS of the capybara at birth is capable of establishing the same function as that of the adult, and that it presents unique features as the high degree of differentiation of the AOB and the active cellular migration in the vomeronasal epithelium. All together makes the capybara a promising model for the study of chemical communication in the first days of life. The vomeronasal system (VNS) is the sensorial system responsible in most vertebrates for the detection of chemosensory signals linked to innate socio-sexual behaviours 1,2. In mammals, the VNS presents a high morphofunctional 3 and genomic 4 diversity among different species. The vomeronasal organ (VNO) specialises in detecting pheromones for the purpose of reproductive behaviours such as maternal aggression and sexual attraction 5. The VNS is also involved in the recognition of major histocompatibility complex (MHC) associated peptides 6 , kairomones 7 and aversive molecules 8. By performing an in-depth study of the macroscopic and microscopic morphological characteristics of the vomeronasal system in the newborn capybara, we aimed to achieve two objectives. On the one hand, we aimed to obtain general information regarding the vomeronasal system in a rodent model that is distinct from most studied laboratory rodents. On the other hand, because the capybara is a precocial animal species, we aimed to determine the degree to which the capybara vomeronasal system morphology at birth has adapted to the requirements of a demanding socio-cognitive environment. Most studies of the VNS have been done on laboratory rodent strains, exposed to artificial selection pressure that do not reflect the selection pressure present in the wild. Therefore, these laboratory strains present significant genetic and behavioural differences compared with wild rodent models 9. The laboratory mouse (Mus musculus) and rat (Rattus norvegicus) may not be representative of all animals that make up this family. A remarkable differential feature among rodents is the altricial character of mice and rats, compared with the precocial character presented by hys...

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“…It stains erythrocytes green, muscle fibers and collagen light blue, epithelium and glandular tissue red, bone dark blue and cartilage purple. The protocol used was described in detail in 54 as follows: sections were first stained with Ziehl acetic fuchsin for 2 min. After several washes they were introduced into formalin-acetic acid solution for 5 min.…”

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“…It stains erythrocytes green, muscle bers and collagen light blue, epithelium and glandular tissue red, bone dark blue and cartilage purple. The protocol used was described in detail in [51] as follows: sections were rst stained with Ziehl acetic fuchsin for 2 min. After several washes they were introduced into formalin-acetic acid solution for 5 min.…”

“…The histochemical and immunohistochemical protocols followed by the authors have been fully described in previous contributions [51,52]. Brie y:…”

“…The next day, the samples were (iv) 1.5 h incubation in Vectastain ABC reagent (Vector Laboratories, Burlingame, CA, USA). The samples were nally (v) developed in the same DAB solution as the UEA [51].…”

“…The next day, (iv) the samples were incubated for 20 min with the ImmPRESS VR Polymer HRP Anti-Rabbit IgG Reagent. (v) After rinsing in Tris-buffer (pH 7.61) for 10 minutes, (vi) the samples were nally developed using DAB in the same way as for the lectins [51,52].…”