Leticia Nicolás

Littermate presence enhances motor development, weight gain and competitive ability in newborn and juvenile domestic rabbits

Interest has been growing in the influence siblings may have on individual development. While mammalian research has tended to emphasize competition among siblings for essential but often limited resources such as the mothers milk, there is also evidence of mutual benefits to be had from sibling presence, most notably for altricial young in enhanced thermoregulatory efficiency. In the present study we asked whether littermates of an altricial mammal, the domestic rabbit, might gain other developmental benefits from sibling presence. From postnatal days 1 to 25 we raised rabbit pups either together with their littermates or alone except for the brief, once daily nursing characteristic of this species, while controlling for litter size and ambient nest box temperature. At weaning on Day 25 the young were then transferred to individual cages. Before weaning, we found that pups raised separately from their littermates obtained less milk, and showed lower weight gain and slower development of the ability to maintain body equilibrium than their litter-raised sibs. This was the case even though the two groups did not differ in birth weight or in the ratio of converting milk into body mass in their temperature-controlled nest boxes. Postweaning, the isolation-raised animals were also less successful in competing for food and water when tested after deprivation than their litter-raised sibs. The present study adds to the growing evidence of the influence, in this case positive, that sibs (or half sibs) may have in shaping one anothers development.

Spinal organization and steroid sensitivity of motoneurons innervating the pubococcygeus muscle in the male rat.

Male rat motoneurons innervating the pubococcygeus muscle were located in the ventral nucleus of lamina IX at the sixth lumbar (L6) and first sacral (S1) spinal cord segments. Retrograde labeling with horseradish peroxidase‐wheat germ agglutinin was transported up to second‐order dendrites and revealed that these motoneurons have a “U‐shaped arborization” of dendrites toward the intermediolateral and intermediomedial nuclei area of lamina VII. This dendritic organization makes a wide “final common path” that probably integrates afferent information from several sources, accounting for the participation of the pubococcygeus muscle in autonomic and somatic processes, such as those related to micturition and reproduction. Castration produced a decrement in the morphometry of these motoneurons. A main effect was a decrement in dendritic length. Steroid replacement indicated that testosterone and estradiol, but not dihydrotestosterone, are able to induce a recovery of morphometric alterations. However, estrogen induced recovery after 2 weeks of treatment, whereas testosterone took 4 weeks. Thus, it is proposed that supraspinal aromatization of testosterone in the male central nervous system might be an important process for the appropriate organization of the pubococcygeus muscle motoneurons and that estradiol seems to need a shorter time of action than testosterone because of differential up‐regulation and down‐regulation of steroid receptors. J. Comp. Neurol. 409:358–368, 1999.

Hypothyroidism affects differentially the cell size of epithelial cells among oviductal regions of rabbits.

Oviductal regions show particular histological characteristics and functions. Tubal pathologies and hypothyroidism are related to primary and secondary infertility. The impact of hypothyroidism on the histological characteristics of oviductal regions has been scarcely studied. Our aim was to analyse the histological characteristics of oviductal regions in control and hypothyroid rabbits. Hypothyroidism was induced by oral administration of methimazole (MMI) for 30 days. For both groups, serum concentrations of thyroid and gonadal hormones were determined. Sections of oviductal regions were stained with the Massons trichrome technique to analyse both epithelial and smooth muscle layers. The percentage of proliferative epithelial cells (anti-Ki67) in diverse oviductal regions was also quantified. Data were compared with Student t-test, Mann-Whitney U-test, or Fischers test. In comparison with the control group, the hypothyroid group showed: (i) a low concentration of T3 and T4, but a high level of TSH; (ii) similar values of serum estradiol, progesterone and testosterone; (iii) a large size of ciliated cells in the ampulla (AMP), isthmus (IST) and utero-tubal junction (UTJ); (iv) a large size of secretory cells in the IST region; (v) a low percentage of proliferative secretory cells in the fimbria-infundibulum (FIM-INF) region; and (vi) a similar thickness of the smooth muscle layer and the cross-sectional area in the AMP and IST regions. Modifications in the size of the oviductal epithelium in hypothyroid rabbits could be related to changes in the cell metabolism that may impact on the reproductive functions achieved by oviduct.

Components of the neural circuitry of the vaginocavernosus reflex in rabbits

In mammals the mechanisms underlying female sexual and reproductive biology are poorly understood. Little attention has been paid to striated muscles and their neural regulation. The aim of the present study was to describe the components of the vaginocavernosus reflex in adult rabbits. It was found that mechanical stimulation of the glans of the clitoris and the perineal vagina induced electromyographic (EMG) responses in bulbocavernosus (Bcm) and ischiocavernosus (Icm) muscles. Unilateral and bilateral nerve transection indicated that the clitoral nerve is the main afferent path of the reflex and that it recruits ipsilateral and contralateral perineal motoneurons. Injection of horseradish peroxides‐wheat germ agglutinin (HRP‐WGA) into the Bcm and Icm labeled spinal motoneurons scattered in L7 and S1 segments. According to the results of this study and previous work, the elements of the vaginocavernosus reflex may be described as follows. Mechanical receptors are located in the glans clitoris and in the wall of the perineal vagina. The main afferent pathway is the clitoral nerve. It activates ipsilateral and contralateral Bcm and Icm motoneurons in lumbosacral segments. Axons of efferent neurons travel through the clitoral and ischiocavernosus nerves, and the effectors are the Bcm and Icm perineal muscles. Identification of neural components of the vaginocavernosus reflex in rabbits will allow the use of this animal as a model to assess the physiological characteristics of the perineal motoneurons as well as the contribution of the Bcm and Icm in female urogenital functions. J. Comp. Neurol. 518:199–210, 2010.

Tissue alterations in urethral and vaginal walls related to multiparity in rabbits.

In rodents, vaginal distention after delivery or experimental manipulation affects innervations as well as the amount of striated/smooth musculature or collagen in both the urethra and vagina. These changes are associated with modifications in excretory and reproductive processes. Although successive and consecutive vaginal deliveries (multiparity) affect the contractile and functional properties of the female lower urogenital tract (LUT), its impact on LUT morphometry, including persistency, has been barely studied. The caudal urethra (CU) and cranial (V1) and caudal (V2) pelvic vaginal regions were excised from young and adult nulliparous (YN and AN, respectively) and multiparous (YM and AM, respectively) rabbits. Tissues were histologically processed and stained with Massons trichrome. The thickness of the tissue layers and areas covered by tissue components were measured and compared using two‐way ANOVA followed by Student‐Newmann‐Keuls tests to determine statistical differences (P ≤ 0.05). Compared to YN, YM, and AN tissues showed a reduction in the thickness of the epithelium, as well as in areas covered by striated musculature, collagen, and blood vessels of the LUT. In comparison with YM, only some morphometric changes were recovered in the AM group. Our study shows that multiparity and age can be associated with epithelial and muscular atrophy of urethral and vaginal walls. The morphometry of the LUT between young and adult female rabbits varies with multiparity. These findings may help to better understand the effects of multiparity on young and adult females and its correlation with the development of pelvic dysfunctions. Anat Rec, 297:1963–1970, 2014.

Morphological characteristics of the cervix in domestic sows

Artificial insemination is commonly practiced in several domestic animals, including sows. Postcervical insemination is used to increase the fertility index, given that the volume of semen is optimized. Knowledge of the anatomical and physiological characteristics of the genital tract can be used to improve our understanding of the fertilization process that occurs during artificial insemination, and possibly to improve the technique. The aim of our study was to examine the gross morphology and histological properties of the cervix of recently slaughtered multiparous sows, using different stains. The results indicate that the porcine cervix has two regions: a uterine region characterized by the presence of glandular acini, and a vaginal region with a large vascular network. Both regions showed a mixed secretory activity by epithelial cells, which produced sulfated mucins (mucous secretion), intermingled with abundant glycogen-rich cells (serous secretion). This study contributes to the understanding of the morphologic features of the porcine cervix.

The role of the pubococcygeus muscle in the urethrogenital reflex of male rats

To determine the response of the pubococcygeus muscle (Pcm) during the urethrogenital reflex (UGR).