Aging effects in adrenal cortex of male Mongolian gerbil: A model for endocrine studies.

The adrenal gland produces steroid hormones that act in the homeostasis of organisms. During aging, alterations in the hormonal balance affect the adrenal glands, but these have not yet been fully described due to the lack of adequate animal models. The adrenal gland of the Mongolian gerbil has a morphology similar to the primate's adrenal gland, which makes it a possible animal model for endocrine studies. Therefore, the current study aimed to study the morphophysiology of the adrenal gland under the effect of aging. For this purpose, males Meriones unguiculatus, aged three, six, nine, twelve, and fifteen months were used. Morphometric, immunohistochemical, and hormonal analyses were performed. It was observed that during aging the adrenal gland presents hypertrophy of the fasciculata and reticularis zones. Lipofuscin accumulation was observed during aging, in addition to changes in proliferation, cell death, and cell receptors. The analyses also showed that the gerbil presents steroidogenic enzymes and the production of steroid hormones, such as DHEA, like that found in humans. The data provide the first comprehensive assessment of the morphophysiology of the Mongolian gerbil adrenal cortex during aging, indicating that this species is a possible experimental model for studies of the adrenal gland and aging.

Advances in research on the biology of the desert rodent Gerbillus tarabuli: a review.

Selection of the appropriate species and strain of laboratory animals are among the scientist's major concerns. Tarabul's gerbil (Gerbillus tarabuli) is a small, seasonally breeding, desert rodent native to Africa. Despite its unique biological features, which make it an ideal model candidate for biomedical research, only a few reports have used it in research. Hence, the present review aims to provide more data about this species, covering all aspects of its biology, such as taxonomy, morphology, anatomy, ecology, wildlife biology, molecular biology, physiology, neurobiology, genetics, reproduction, development, evolutionary biology, and conservation biology, and covers current progress in exploration of G. tarabuli, discussing its valuable characteristics, which are widely useful for research in various fields. This review paper is destined for biologists, scientists, mammologists, zoologists, academics, and students.

Anatomical, histological and biochemical studies of desert rodent Gerbillus tarabuli (Thomas, 1902) kidney.

The present work aimed to study the anatomy, histology, cytology and some biochemical parameters (urea, osmolality, haematocrit, serum natrium, serum kalium) of the kidney of Gerbillus tarabuli. The investigated animals (n = 16) were collected from the desert, weighed and transferred alive to the laboratory in separate cages. A blood sample was taken by puncture at the retro-orbital sinus of each animal using a Pasteur-type capillary pipette capillary. They were anaesthetized with urethane injection (25%), after which they were carefully dissected; their organs were taken out and prepared for the histological and cytological studies. Pasteur pipette capillary type the kidney of the Gerbillus tarabuli is subdivided into three regions: Cortex (1193.625±60µm), Outer Medulla (1316.72±73µm), Inner Medulla (2525.08±85 µm). Pasteur pipette capillary type the kidney of the Gerbillus tarabuli is subdivided into three regions: Cortex (1193.625±60µm), Outer Medulla (1316.72±73µm), Inner Medulla (2525.08±85 µm). The concentration of the biochemical parameters of urea (0.41 ± 0.02 g/L), osmolality (300.75 ± 3.33 mOs/kg), haematocrit (34.18 ± 1.3%), serum natrium (141.37 ± 2.31 mmol/L) and serum kalium (7.69 ± 0.39 mmol/L) is in the interval of the norm compared with several studies on desert and semi-desert rodents and also on the Wistar rat. These findings revealed the adaptive morphology and physiological function in the kidney of G. tarabuli to the desert environment.

Energy requirements, length of digestive tract compartments and body mass in six gerbilline rodents of the Negev Desert.

Energy requirements of an animal are size dependent and, in this study, the average daily metabolic rate (ADMR) of six Negev Desert gerbilline rodents, ranging in body mass (mb) from 10g to over 200g, scaled to mb0.57. Although gerbilline rodents are considered 'granivores', these rodents consume substantial amounts of green vegetation and the largest gerbil is a strict herbivore. We predicted that the lengths of the compartments of the digestive tract would scale allometrically to mb0.33 and that ADMR would scale allometrically to the lengths of the compartments to the exponent of 1.73. Using log-transformed data, the length of the colon scaled to mb0.50 (r2adj = 0.74; p= 0.02), of the caecum to mb0.45 (r2adj=0.80; p= 0.01) and of the small intestine to mb0.30 (r2adj=0.59; p < 0.05). Therefore, the exponents for the colon and caecum were higher than predicted and were close to the exponent for ADMR generated for the rodents. The absolute lengths of the colon (r2adj=0.68; p= 0.03; slope = 0.99) and of the caecum (r2adj=0.79; p= 0.01; slope = 1.19) were related significantly to ADMR, but of the small intestine was not (r2adj=0.04; p=0.33; slope = 0.85). The exponents implied that the relationships were isometric and not allometric as predicted and that the rates of increase of the lengths of the intestine compartments were at the same rate as the increase in ADMR. The lengths of the colon and caecum were highly correlated between each other (r2adj=0.98; p< 0.001; slope = 1.12) and explained most of the variation in ADMR. Green vegetation could be a nutritional bottleneck for rodents as it is bulky and, consequently, limits the dietary intake, and fermentation occurs in the caecum and colon, whereas seeds, which are compact and are digested in the small intestine, would limit intake to a much lesser degree. However, when the effect of body mass was eliminated by using residuals of the variables on body mass, only the length of the small intestine was significant (r2adj=0.86; p< 0.005; slope = -1.33) and was related negatively to ADMR. Therefore, when effects of body size were removed, most of the variation in ADMR was explained by the length of the small intestine and implied that the length of the small intestine increased with a decrease in ADMR. A higher energy expenditure was related to a shorter small intestine and, therefore, by implication, a higher concentration of metabolizable energy yield of the diet. We also questioned whether there are differences in the morphology of the digestive tract due to differences in dietary consumption. The digestive tracts of the gerbils were not diverse and could be characterized as structurally homogenous. All the gerbils had a uni-locular, hemi-glandular stomach and the differences in the digestive tract among species did not seem to be of functional importance, but rather were related to the taxon. However, some important morpho-functional characteristics of the digestive tract emerged that apply to the whole group.

Applicability of vital staining and tissue clearing to vascular anatomy and melanocytes' evaluation of temporal bone in six laboratory species.

The purpose of the present study was to define the applicability of tissue clearing to the field of otology. We combined tissue clearing with vital staining perfusion via a pumping system to examine the vascular anatomy of temporal bones in laboratory animals. We used six different types of species including Korean wild mouse, mouse, Mongolian gerbil, hamsters and Guinea pigs. A mixture of Alcian blue reagent and 4% paraformaldehyde was circulated throughout the entire circulatory system of the animal via a perfusion pump system. Transparency images were obtained from the temporal bones according to the protocol of the SunHyun 3D Imaging Kit. In examining the inner surface of the tympanic membrane, flaccid part (pars flaccida) was positioned along the entire marginal area in Guinea pig. In the Guinea pig, unlike the other species, the cortical bone of the mastoid (bullae) was easily removed using cold instruments, allowing a direct approach to the enclosed structures. The distribution and pattern of cochlea melanocytes were compared among the species. "Mobius strip"-like accumulated melanocytes in vestibules were shown in both the Korean wild mouse and mouse. The collateral blood supply to the cochlea in six different species was checked in various pattern. Combining dye infusion with tissue-clearing techniques, we documented the middle ear and transparent inner ear structures in six different species. The information and associated images will help other researchers to develop hypotheses and design experimental investigations.

Associated tympanic bullar and cochlear hypertrophy define adaptations to true deserts in African gerbils and laminate-toothed rats (Muridae: Gerbillinae and Murinae).

Hearing capabilities in desert rodents such as gerbils and heteromyids have been inferred from both anatomical and ecological aspects and tested with experiments and theoretical models. However, very few studies have focused on other desert-adapted species. In this study, a refined three-dimensional morphometric approach was used on three African rodent tribes (Otomyini, Taterillini and Gerbillini) to describe the cochlear and tympanic bullar morphology, and to explore the role of phylogeny, allometry and ecology to better understand the underlying mechanism of any observed trends of hypertrophy in the bulla and associated changes in the cochlea. As a result, desert-adapted species could be distinguished from mesic and semi-arid taxa by the gross cochlear dimensions, particularly the oval window, which is larger in desert species. Bullar and cochlear modifications between species could be explained by environment (bulla and oval window), phylogeny (cochlear curvature gradient) and/or allometry (cochlear relative length, oval window and bulla) with some exceptions. Based on their ear anatomy, we predict that Desmodillus auricularis and Parotomys brantsii should be sensitive to low-frequency sounds, with D. auricularis sensitive to high-frequency sounds, too. This study concludes that in both arid and semi-arid adapted laminate-toothed rats and gerbils there is bulla and associated cochlea hypertrophy, particularly in true desert species. Gerbils also show tightly coiled cochlea but the significance of this is debatable and may have nothing to do with adaptations to any specific acoustics in the desert environment.

Principal cells of the brainstem's interaural sound level detector are temporal differentiators rather than integrators.

The brainstem's lateral superior olive (LSO) is thought to be crucial for localizing high-frequency sounds by coding interaural sound level differences (ILD). Its neurons weigh contralateral inhibition against ipsilateral excitation, making their firing rate a function of the azimuthal position of a sound source. Since the very first in vivo recordings, LSO principal neurons have been reported to give sustained and temporally integrating 'chopper' responses to sustained sounds. Neurons with transient responses were observed but largely ignored and even considered a sign of pathology. Using the Mongolian gerbil as a model system, we have obtained the first in vivo patch clamp recordings from labeled LSO neurons and find that principal LSO neurons, the most numerous projection neurons of this nucleus, only respond at sound onset and show fast membrane features suggesting an importance for timing. These results provide a new framework to interpret previously puzzling features of this circuit.

Investigation of the 2f1-f2 and 2f2-f1 distortion product otoacoustic emissions using a computational model of the gerbil ear.

In this work, a three-dimensional computational model of the gerbil ear is used to investigate the generation of the 2f1-f2 and 2f2-f1 distortion product otoacoustic emissions (DPOAEs). In order to predict both the distortion and reflection sources, cochlear roughness is modeled by introducing random inhomogeneities in the outer hair cell properties. The model was used to simulate the generation of DPOAEs in response to a two-tone stimulus for various primary stimulus levels and frequency ratios. As in published experiments, the 2f1-f2 DPOAEs are mostly dominated by the distortion component while the 2f2-f1 DPOAEs are dominated by the reflection component; furthermore, the influence of the levels and frequency ratio of the primaries are consistent with measurements. Analysis of the intracochlear response shows that the distortion component has the highest magnitude at all longitudinal locations for the 2f1-f2 distortion product (DP) while the distortion component only dominates close to the DP best place in the case of the 2f2-f1 DP. Decomposition of the intracochlear DPs into forward and reverse waves demonstrates that the 2f1-f2 DP generates reverse waves for both the distortion and reflection components; however, a reverse wave is only generated for the reflection component in the case of the 2f2-f1 DP. As in experiments in the gerbil, the group delay of the reflection component of the DPOAE is between 1× and 2× the forward group delay, which is consistent with the propagation of DP towards the stapes as slow reverse waves.

Combined oral contraceptives promote androgen receptor and oestrogen receptor alpha upregulation in the female prostate (Skene's paraurethral glands) of adult gerbils (Meriones unguiculatus).

The aim of this study was to evaluate the effects of cyproterone acetate (CPA) and ethinyloestradiol (EE) alone or in combination on the female prostate of adult gerbils. Adult females were exposed for 21 days to daily oral doses of CPA (1mgkg-1), EE (10µgkg-1) or a combination of CPA and EE. Female prostatic complexes were removed, weighed and subjected to morphological, stereological, immunohistochemical and ultrastructural analyses. CPA treatment caused epithelial atrophy and decreased prostate secretory activity. The EE treatment group showed glandular hyperplasia, a high cell-proliferation index and an increase in androgen and oestrogen receptor α (AR and ERα) immunoreactivity. Combined treatment (CPA+EE) caused adverse effects, such as an increase in cell proliferation, higher AR and ERα immunoreactivity, prostatic intraepithelial neoplasia, cell degeneration and aging. In conclusion, the CPA-only treatment promoted antiandrogenic effects on the female gerbil prostate, whereas EE-only had a potent oestrogenic activity. However, when combined, EE overlapped the effects of CPA, changing the pattern of glandular hormonal regulation and stimulating the development of prostatic lesions in female gerbils.

[Craniometrical study of the species complex of Meriones shawii-grandis (Mammalia: Rodentia) in Morocco, in Algeria and in Tunisia]. / Étude craniométrique du complexe d'espèces Meriones shawii­grandis (Mammalia : Rodentia) au Maroc, en Algérie et en Tunisie.

In North Africa, the rodents of the species complex Meriones shawii-grandis have a considerable ecological, economic and epidemiological importance. Until now, the systematics of these species was subject to discussion due to the presence of populations displaying high morphological variability. By means of an approach of traditional morphometrics based on cranial distances and by using the method of the log shape-ratio, we attempt to characterize morphologically these two taxa. The results show significant differences in size and shape between the specimens of Morocco, on the one hand, and those of Algeria and Tunisia, on the other hand. The samples of Morocco that have been molecularly typed and attributed to M. grandis have larger tooth rows and narrower skulls, as well as relatively small tympanic bullae. On the other hand, those of Algeria and Tunisia assigned to M. shawii are characterized by small tooth rows and wide skulls with well-developed tympanic bullae. The morphological distance is relatively strong between both clades (79.5%), which corresponds to the molecular distance. However, the discriminant analysis performed after molecularly-typed specimens allows the correct classification of only 91.8% of the individuals.

Morphologic features of spontaneous annular tears and disc degeneration in the aging sand rat (Psammomys obesus obesus).

The sand rat, a member of the gerbil family, is a valuable small animal model in which intervertebral disc degeneration occurs spontaneously as the animal ages. Radiographic features of cervical and lumbar degeneration resemble those in human spines. We conducted a retrospective analysis of spines of 140 animals 3-41 months old focusing specifically on the presence of annular tears that are not visible by radiography and have not been described previously in the sand rat disc. During degeneration of the nucleus pulposus, notochordal cell death occurs and granular material, which stains with Alcian blue for proteoglycans, accumulates. Lamellar architecture also deteriorates and annular tears occur that are morphologically similar to the concentric, radiating and transdiscal annular tears in human discs. These tears contain granular material that provides a "marker" that can be used to distinguish the annular tears from artefactual separations during sectioning. We observed lamellar degeneration and separation in the annulus fibrosus at 4 months with associated tears that contained granular material in the nucleus. Tears that contained granular material and displacement of the degenerating nucleus were common in cervical and lumbar discs of animals older than 9 months; some specimens showed tears at 4 and 5 months. With advanced degeneration, granular globules were displaced dorsally adjacent to and into the spinal cord area and also ventrally into regions where osteophytes formed. We present morphologic data that expand the utility of this rodent model of spontaneous age-related disc degeneration and provide novel information on annular tears and disc degeneration.

Seasonal morphophysiological variations in the prostatic complex of the Tarabul's gerbil (Gerbillus tarabuli).

Gerbillus tarabuli is a nocturnal Saharan rodent which has an annual reproductive cycle characterized by the reproductive activity in spring and a long phase of sexual quiescence in other seasons. We describe the morphology and hormonal regulation of the prostatic complex of this rodent in the two periods, based on anatomical, histological, morphometric, and immunohistochemical analyses. The organisation of this prostatic complex is similar to that reported for Meriones unguiculatus, but different from the prostate of Psammomys obesus, the rat, and the mouse. In addition to the anterior lobes, ventral lobes, and dorsal lobes, the prostatic complex of Gerbillus tarabuli, also includes dorsolateral lobe. Each lobe is composed of a fibro-muscular stroma surrounding a glandular epithelium. Dorsolateral lobes are easily distinguishable by their big volume. The prostate grows and regresses cyclically throughout the year. During the resting season, ventral lobes and anterior lobes showed atrophy, with a significant decrease in both epithelial height and supranuclear area size, and a strong thickening of the fibro-muscular compartment. In dorsal lobes, the epithelial and stromal compartments atrophied and regenerated simultaneously, whereas in dorsolateral lobe the thickness of the epithelium, the supranuclear zone and the stroma increased during resting period. Furthermore, seasonal variations were observed in the distribution and expression of both androgen receptors, and estrogens receptors. Expression patterns of all receptors were lobe-specific. In conclusion, both androgens and estrogens are involved in the homeostasis and regulation of the prostate in Gerbillus tarabuli. Dorsolateral lobe seems to be controlled by a different mechanism than other lobes.

Histological and immunohistochemical characterization of the Mongolian gerbil's mammary gland during gestation, lactation and involution.

The morphological description of normal tissues is fundamental for making comparisons and in order to identify injuries and lesions. The aim of this work was to describe the morphological characteristics of the female Mongolian gerbil's (Meriones unguiculatus) normal mammary gland, the average expression of hormone receptors, and the average proliferation rates in the epithelial cells during the periods of lactation, pregnancy and involution. Dams were euthanized on the 14th and 21st gestational days, 7 and 14days after parturition, and 3 and 5days after weaning. The dams' mammary tissues were processed and were submitted to haematoxylin and eosin staining, Periodic Acid Schiff (PAS) staining, and Gomori's Reticulin staining. Additionally, immunohistochemistry was performed for the characterization of myoepithelial cells with α-actin, the proliferation rates with proliferating cell nuclear antigen (PCNA), the estrogen hormonal receptors (ESR1 and ESR2), and progesterone receptor (PR) quantifications. It was observed that the abundant adipose tissues were replaced by glandular epithelia and there was an increase in the epithelial cell's height (from 5.97 to 32.4µm in 14th and 21st gestational days and from 20.64 to 25.4µm in 7th and 14th lactational days, respectively) and the acini diameters (from 24.88 to 69.92µm in 14th and 21st gestational days and from 139.69 to 118.59µm in 7th and 14th lactational days, respectively) with the progression of gestation and lactation. The PAS staining intensity varied throughout the glands and between the stages that were evaluated. The extracellular matrix showed different phenotypes too, with more of a presence of the Type I collagen during the early gestation and involution and with more reticular fibers (Type III collagen) during the late gestation period and lactation. The myoepithelial layers showed alterations in their distribution with thick patterns as verified by the α-actin labeling. The PCNA showed higher rates of the marked cells in 14th and 21st gestational days (40.25 and 60.28%) and in 7th and 14th lactational days (64.08 and 65.08%). The hormone receptor quantifications showed a high variation in the rates: the average PR staining decreased from 14th to 21st gestational days (from 42.3 to 8.54%), from 7th to 14th lactational days (from 59.83 to 23.18%) and from 3rd to 5th days after weaning (from 39.98 to 12.72). There were higher averages of ESR1 staining in gestational days 14 and 21(from 58.06 to 30.02%). ESR2 staining decreased during gestation (25.7 and 12.94% in 14th and 21st gestational days)and involution (from 50.97 to 30.18% in 3rd and 5th days after weaning). The Mongolian gerbils showed similar morphological characteristics when they were compared to mice and rats. However, the higher proliferation rates with a smaller involution period compared to other murine characterized this species as being adequate for mammary pathologies studies.

Paracrine Signaling in the Prostatic Stroma: A Novel Role for the Telocytes Revealed in Rodents' Ventral Prostate.

The telocytes have recently been described in the prostate gland. In mature gland, they exist in close association with the acini and their telopodes form networks whose functions remain unclear. In this chapter, our group gives a brief introduction to telocytes and explores the history that led to such a concept and then discusses hypotheses and presents new evidences about the roles exerted by telocytes in the prostate. First is given emphasis on the role that these cells possibly play in paracrine signaling employed in the differentiation of smooth muscle periacinar are then discussed other roles potentially performed by telocytes in the prostate, such as the organizational, where these cells would act in order to delimit stromal microenvironments, thereby assisting the differentiation of the prostatic anatomical components. In addition, the pacemaker function of smooth muscle cells contraction, as evidenced by the presence of caveolae and gap-type junction and, finally, the role of telocytes in prostate remodeling and the possible action as adult progenitor cells. Generally speaking, the chapter reaffirms the existence of telocytes as distinct cells of other stromal cells and the importance of this new cell type for normal metabolism and prostate development.

The Grooved Rodent Incisor Recapitulates Rudimentary Teeth Characteristics of Ancestral Mammals.

It is known from the paleontology studies of eutherian mammals that incisor numbers were reduced during evolution. The evolutionary lost incisors may remain as vestigial structures at embryonic stages. The recapitulation of the incisor patterns among mammalian species will potentially uncover the mechanisms underlying the phenotypic transition of incisors during evolution. Here, we showed that a minute tooth formed in the presumptive groove region of the gerbil upper incisor at the early developmental stages, during which multiple epithelial swellings and Shh transcription domains spatiotemporally appeared in the dental epithelium, suggests the existence of vestigial dental primordia. Interestingly, when we trimmed the surrounding mesenchyme from incisor tooth germs at or before the bud stage prior to ex vivo culture, the explants developed different incisor phenotypes ranging from triplicated incisors, duplicated incisors, to Lagomorpha-like incisors, corresponding to the incisor patterns in the eutherian mammals. These results imply that the phenotypic transition of incisors during evolution, as well as the achievement of ultimate incisors in adults, arose from differential integrations of primordia. However, when the incisor tooth germ was trimmed at the cap stage, a grooved incisor developed similar to the normal condition. Furthermore, the incisor tooth germ developed a small but smooth incisor after the additional removal of the minute tooth and a lateral rudiment. These results suggest that multiple dental primordia integrated before the cap stage, with the labial primordia contributing to the labial face of the functional incisor. The minute tooth that occupied the boundary of the 2 labial primordia might be implicated in the groove formation. This study sheds light on how rudiments incorporate into functional organs and aids the understanding of incisor evolution.

Differential morphology of the superior olivary complex of Meriones unguiculatus and Monodelphis domestica revealed by calcium-binding proteins.

In mammals, the superior olivary complex (SOC) of the brainstem is composed of nuclei that integrate afferent auditory originating from both ears. Here, the expression of different calcium-binding proteins in subnuclei of the SOC was studied in distantly related mammals, the Mongolian gerbil (Meriones unguiculatus) and the gray short-tailed opossum (Monodelphis domestica) to get a better understanding of the basal nuclear organization of the SOC. Combined immunofluorescence labeling of the calcium-binding proteins (CaBPs) parvalbumin, calbindin-D28k, and calretinin as well as pan-neuronal markers displayed characteristic distribution patterns highlighting details of neuronal architecture of SOC nuclei. Parvalbumin was found in almost all neurons of SOC nuclei in both species, while calbindin and calretinin were restricted to specific cell types and axonal terminal fields. In both species, calbindin displayed a ubiquitous and mostly selective distribution in neurons of the medial nucleus of trapezoid body (MNTB) including their terminal axonal fields in different SOC targets. In Meriones, calretinin and calbindin showed non-overlapping expression patterns in neuron somata and terminal fields throughout the SOC. In Monodelphis, co-expression of calbindin and calretinin was observed in the MNTB, and hence both CaBPs were also co-localized in terminal fields within the adjacent SOC nuclei. The distribution patterns of CaBPs in both species are discussed with respect to the intrinsic neuronal SOC circuits as part of the auditory brainstem system that underlie the binaural integrative processing of acoustic signals as the basis for localization and discrimination of auditory objects.

The distribution of mucous secreting cells in the gastrointestinal tracts of three small rodents from Saudi Arabia: Acomys dimidiatus, Meriones rex and Meriones libycus.

The proportion of mucin phenotypes (which form the protective biofilm of the gastrointestinal tract) differs between intestinal regions. This study examines the distribution of mucin secreting cells in the gastrointestinal tracts of the Eastern spiny mouse (Acomys dimidiatus), King jird (Meriones rex) and Libyan jird (Meriones libycus), which inhabit the dry and hot deserts of Saudi Arabia. Intestinal tract samples were processed to wax and tissue sections stained with Alcian Blue-Periodic Acid Schiff (AB-PAS) and High Iron Diamine-Alcian Blue (HID-AB) in order to determine different mucin phenotypes by quantitative analysis. Mixed mucin secreting cells (combined neutral and acid) was the predominant mucin secreting cell type observed throughout the gastrointestinal tract in all species. Acid mucin secreting goblet cells were mainly located in the colon. A. dimidiatus presented with significantly more total sialo than sulfomucin secreting cells while the opposite was true for both Meriones species. The distribution of mucin secreting cells is therefore similar to previously reported results for small mammals not living under arid conditions.

Identifying predation on rodent teeth through structure and composition: A case from Morocco.

Predation by nocturnal birds of prey is one of the most frequent modes leading to the concentration of rodents in fossil assemblages. This mode of accumulation leaves characteristic surface alterations on bones and teeth. In order to evaluate and characterize the effects of these pre-diagenesis alterations on rodent fossil samples, we have carried out microstructural and chemical analyses on incisors collected from present day Moroccan wild animals and owl pellets. The microstructure of both dentine and enamel was well preserved, but chemical changes were evident in pellet samples and depended on the particular tissue and the nature of the predator. The comparison of compositional data obtained from electron microprobe chemical analyses and infrared spectrometry has allowed us to assign a possible predator to an incisor extracted from a pellet of an unknown origin. This method has further implications for the understanding of taphonomy and palaeoecology of archaeological and fossil sites.

Dendritic morphology of caudal periaqueductal gray projecting retinal ganglion cells in Mongolian gerbil (Meriones unguiculatus).

In this study we investigated the morphological features of the caudal periaqueductal gray (cPAG)-projecting retinal ganglion cells (RGCs) in Mongolian gerbils using retrograde labeling, in vitro intracellular injection, confocal microscopy and three-dimensional reconstruction approaches. cPAG-projecting RGCs exhibit small somata (10-17 µm) and irregular dendritic fields (201-298 µm). Sizes of somata and dendritic fields do not show obvious variation at different distance from the optic disk (eccentricity). Dendrites are moderately branched. Morphological analysis (n = 23) reveals that cPAG-projecting RGCs ramified in sublamina a and b in the inner plexiform layer. These cells exhibit different stratification patterns based on the thickness of dendritic bands in sublaminas a and b: majority of analyzed cells (16 out of 23) have two bands of arborizations share similar thickness. The rest of analyzed cells (7 out of 23) exhibit thinner band in sublamina a than in sublamina b. Together, the present study suggests that cPAG of Mongolian gerbil could receive direct retinal inputs from two types of bistratified RGCs. Furthermore, a small subset of melanopsin-expressing RGCs (total 41 in 6 animals) is shown to innervate the rostral PAG (rPAG). Functional characteristics of these non-visual center projecting RGCs remain to be determined.

Morphology and ciliary motion of mucosa in the Eustachian tube of neonatal and adult gerbils.

The Eustachian tube is a small canal that connects the tympanic cavity with the nasal part of the pharynx. The epithelial lining of the Eustachian tube contains a ciliated columnar epithelium at the tympanic cavity and a pseudostratified, ciliated columnar epithelium with goblet cells near the pharynx. The tube serves to equalize air pressure across the eardrum and drains mucus away from the middle ear into the nasopharynx. Blockage of the Eustachian tube is the most common cause of all forms of otitis media, which is common in children. In the present study, we examined the epithelial lining of the Eustachian tube in neonatal and adult gerbils, with a focus on the morphological and functional development of ciliated cells in the mucosa. The length of the tube is ∼8.8 mm in adult gerbils. Scanning electron microscopy showed that the mucosal member near the pharyngeal side contains a higher density of ciliated cells and goblet cells than that near the tympanic side. The cilia beat frequency is 11 Hz. During development, the length of the Eustachian tube increased significantly between postnatal day 1 (P1) and P18. Scanning electron microscopy showed that the mucosa contained a high density of ciliated cells with a few goblet cells at P1. The density of ciliated cells decreased while the density of goblet cells increased during development. At P18, the mucosa appeared to be adult-like. Interestingly, the ciliary beat frequency measured from ciliated cells at P1 was not statistically different from that measured from adult animals. Our study suggests that the Eustachian tube undergoes significant anatomical and histological changes between P1 and P18. The tube is morphologically and functionally mature at P18, when the auditory function (sensitivity and frequency selectivity) is mature in this species.