Computed tomography and three dimensional anatomical study of the liver in the chinchilla (Chinchilla lanigera)

Few instances of neoplastic formations in the liver of chinchillas have been found, even though the species is widely used in different scientific experiments. In the present article we investigate the anatomical features of the chinchilla's liver using CT and three dimension (3D) imaging. For the trials we used 12 (six males and six females) clinically healthy chinchillas all at 18 months of age. The animals were positioned in dorsal recumbency. We used Th8 to L2 vertebrae and the sternum as bone markers for the transverse CT study. The investigated anatomical landmarks for the CT coronal study were the vertebrae, costal arch, soft abdominal wall, diaphragm, stomach and the right kidney. 3D reconstructions were accomplished with a specific imaging software. On transverse and coronal CT images, the chinchilla's liver was composed of lobus hepatis sinister lateralis, 'middle lobe'-without proper Latin term in NAV 2017, lobus hepatis dexter and lobus caudatus. The 'middle lobe' was separated into the 'left middle lobe' and the 'right middle lobe'. Lobus hepatis dexter consisted of lobus hepatis dexter medialis and lobus hepatis dexter lateralis. There was an anatomical relation between the liver, fundus ventriculi and corpus ventriculi. Proc. caudatus was in close contact with the right kidney. Vesica fellea was elongated and ellipsoid. 3D reformatted images confirmed the results obtained by transverse and coronal CT studies. The CT density of the liver in HU was 195.6 ± 73.1. The CT and 3D reconstructed images were visualized at high resolution. This data could be used as a basis for further morphological and imaging studies.

Comprehensive total evidence phylogeny of chinchillids (Rodentia, Caviomorpha): Cheek teeth anatomy and evolution

Rodents are the most diverse order of extant mammals, and caviomorph rodents, or New World hystricognaths, have a remarkable morphological disparity and a long fossil record that begins in the Eocene. Chinchilloidea is a poorly understood clade within Caviomorpha, from an evolutionary and phylogenetic perspective. It includes the extant families Chinchillidae and Dinomyidae, the extinct Neoepiblemidae and Cephalomyidae, and several extinct chinchilloids without a clear phylogenetic position, like Eoincamys, Borikenomys, Chambiramys, Ucayalimys, Incamys, Saremmys, Garridomys and Scotamys. The family Chinchillidae includes the extant Chinchilla and Lagidium, grouped in Chinchillinae, and the only living Lagostominae, Lagostomus maximus. Among extinct chinchillids, Eoviscaccia (early Oligocene-early Miocene of Argentina, Bolivia and Chile), Prolagostomus (early-middle Miocene of Argentina, Bolivia and Chile) and Pliolagostomus (early-middle Miocene of Argentina) are the only genera originally described as members of the family. Based on the study of specimens with unworn or little-worn cheek teeth, belonging to extinct and extant taxa, we propose homologies of the cheek teeth structures and perform a combined molecular and morphological phylogenetic analysis including extinct and extant taxa of all families of Chinchilloidea and all genera of Chinchillidae. Our phylogenetic analysis recovered three major lineages in the evolutionary history of Chinchilloidea. The first major lineage is composed of the extant taxa Chinchilla, Lagidium and Lagostomus, and the extinct genera Eoviscaccia, Prolagostomus, Pliolagostomus, Garridomys, Incamys, Loncolicu and Saremmys. Cephalomyid (Banderomys, Cephalomys, Litodontomys, Soriamys) and neoepiblemid (Neoepiblema, Perimys, Phoberomys, Scotamys) genera are part of the second major lineage, while dinomyids such as Dinomys, Drytomomys, Scleromys, 'Scleromys' and Tetrastylus constitute the third major lineage within Chinchilloidea. The phylogenetic position of some taxa previously considered as incertae sedis chinchilloids or without a clear suprageneric group (i.e. Incamys, Saremmys, Garridomys and Loncolicu) show that they belong to pan-Chinchillidae and conform the stem Chinchillidae along with Eoviscaccia. The euhypsodont crown Chinchillidae includes the living subfamilies Chinchillinae and Lagostominae. Dinomyidae and Eoincamys pascuali are recovered as the sisters of a major clade composed by 'Cephalomyidae'+Neopiblemidae and pan-Chinchillidae, and Chambiramys sylvaticus occupies a basal position to the same clade. Four major radiation events are identified in the evolutionary history of Chinchilloidea. The analysis of new morphological characters linked with molecular evidence as well as the addition of taxa of uncertain or unstable phylogenetic position or not considered in previous studies allowed us resolve part of the relationships within Chinchilloidea, particularly that of Chinchillidae, supporting preceding morphological hypotheses.

Analysis of glycoconjugates and morphological characterization of the descending colon and rectum of the plains viscacha, Lagostomus maximus

Herbivores exhibit specializations at the intestinal level that facilitate the bacterial fermentation. The available information on the digestive physiology of Lagostomus maximus makes this rodent an interesting model to evaluate morpho-functional adaptations to herbivory. The general objective of this work was centered on the study of the morphology and histochemistry of the descending colon and rectum of L. maximus. To do so, a comparative analysis of the morphology, ultrastructure and glycosylation pattern of both anatomical regions was carried out. Histochemical results revealed that in both sectors of the large intestine, there are goblet cells with different glycosylation pattern within a morphologically homogeneous cell population. The main difference between both intestinal segments lay in the fact that the most distal region of the large intestine showed a greater proportion of sialomucins, characterized by being slightly O-acetylated. Further specific differences were revealed by lectin histochemistry. These data allowed to perform a functional interpretation of the cell types and secreted substances, thus contributing to a better understanding of the role of mucins in the intestinal tract functioning.

Oviduct morphology and estrogen receptors ERα and ERβ expression in captive Chinchilla lanigera (Hystricomorpha: Chinchillidae)

Chinchilla lanigera is a hystricomorph rodent from South America whose reproductive biology presents particular characteristics that distinguishes it from other Rodentia species, such as low reproductive rate, seasonal breeding pattern, and long estrous cycle. Nevertheless, reproductive features in female chinchillas are still poorly investigated, with a scarce knowledge concerning the estrous cycle and the histology of reproductive organs. In this study, we investigate the morphology, histomorphometry, secretory activity, and immunolocalization of estrogen receptors ERα and ERβ in oviducts of nulliparous chinchillas, euthanized at fall season in Brazil. Follicular phase of estrous cycle of all studied animals was characterized by ovary and uterine morphology inspection, as well as vaginal cytology. Similar to other mammals, the oviduct wall of infundibulum, ampulla and isthmus was composed of mucosa, muscle, and serosa layers. Morphometric data of oviduct layers were used for identifying each oviduct segment. In the follicular phase, the oviduct was characterized by intense secretory activity, mainly in the ampulla, and expression of ERα and ERβ throughout the oviduct epithelium. Both ERα and ERβ were also detected in the connective tissue and smooth muscle cells. Our findings point out to the important role of estrogen in this female organ. Similar wide distribution of both ER proteins has been described for human Fallopian tube. Taken together, our data add to the understanding of the reproductive biology of female chinchillas, and may assist in the intensive breeding of this species and any eventual endeavor for conservation of chinchillas in the wild.

Upper molar morphology, homologies and evolutionary patterns of chinchilloid rodents (Mammalia, Caviomorpha)

Chinchilloidea are a clade of caviomorph rodents that includes seven living species, the Dinomyidae Dinomys branickii, the Chinchillidae Lagostomus maximus, two species of Chinchilla and three species of Lagidium. In addition, two extinct families are traditionally considered chinchilloids - Neoepiblemidae and Cephalomyidae. The phylogeny of the Chinchilloidea has so far not been well established and is based on partial analyses. Studying the anatomy and ontogeny of extinct and extant taxa, we propose homologies for the upper molars of Chinchilloidea for which these homologies have not been previously proposed: that is the Chinchillidae Prolagostomus, Lagostomus, Lagidium and Chinchilla, and the Neoepiblemidae Neoepiblema and Phoberomys. We identify patterns of occlusal simplification within Chinchilloidea and evaluate its importance in an evolutionary context. A phylogenetic analysis recovered Dinomyidae, Chinchillidae and Neoepiblemidae as clades. 'Cephalomyidae' have not been not recovered as a monophyletic group and 'cephalomyids' are closely related to Neoepiblemidae. Branisamys is not included within the Dinomyidae and appears to be a basal chinchilloid.

Anatomy and Disorders of the Oral Cavity of Chinchillas and Degus

Dental disease is among the most common causes for chinchillas and degus to present to veterinarians. Most animals with dental disease present with weight loss, reduced food intake/anorexia, and drooling. Degus commonly present with dyspnea. Dental disease has been primarily referred to as elongation and malocclusion of the cheek teeth. Periodontal disease, caries, and tooth resorption are common diseases in chinchillas, but are missed frequently during routine intraoral examination, even performed under general anesthesia. A diagnostic evaluation, including endoscopy-guided intraoral examination and diagnostic imaging of the skull, is necessary to detect oral disorders and to perform the appropriate therapy.

Immunocytochemical detection of calretinin in the claustrum and endopiriform nucleus of the chinchilla

Calretinin (CR) as a buffer and sensor protein plays an important role in regulatory processes of Ca²⁺ and anty-apoptotic cellular protection. In the present study, immunohistochemical peroxidase-antiperoxidase (PAP) method was used in order to determine the numbers, morphology, morphometry and distribution pattern of CR in neurons of the chinchilla's claustrum (Cl) and endopiriform nucleus (EN). In Cl and EN the presence of several classes of neurons with different immunoreactivity to CR was found. In Cl, CR-immunoreactive (IR) neurons were predominantly found in close vicinity to insular border while CR-IR neurons were evenly scattered throughout EN. In general, immunoreaction to CR was observed in neuronal cytoplasm, nucleus and in fibres-like nerve extensions. Statistical analysis showed the differences between average large diameter as well as cross-sectional area of CR-IR neurons present in Cl and EN. It is suggested, that CR acting as a calcium binding protein may play a role in neuronal network. Further co-localization studies are necessary to fully elucidate neurophysiology and neuropathology of the chinchilla's Cl and EN neurons.

The Uterus Duplex Bicollis, Vagina Simplex of Female Chinchillas

The available literature describing the morphology of the female chinchilla's uterine cervix varies and includes phrases such as 'the cervical canal,' 'a single cervix,' and 'the cervix;' alternatively, some publications describe 2 cervices. In this report, we provide an anatomically correct and definitive description of the uterine cervical morphology of the laboratory chinchilla. We further propose revised, anatomically precise nomenclature to characterize the female chinchilla reproductive tract as a whole.

Ultrasonography of the Harderian gland in the rabbit, guinea pig, and chinchilla

OBJECTIVE

To evaluate the Harderian gland in rabbits, guinea pigs, and chinchillas using B-mode ultrasound and to determine normal size and changes in size and/or location in normal and diseased eyes and orbits by ultrasonographic measurements.

PROCEDURE

Normal Harderian glands were evaluated ultrasonographically in 20 rabbits, 10 guinea pigs, and eight chinchillas. The Harderian gland was measured ultrasonographically in horizontal and vertical planes. Normal Harderian gland sizes were then compared with sizes in 27 rabbits, 13 guinea pigs, and three chinchillas that had exophthalmos.

RESULTS

Harderian glands in normal rabbits were 0.69 ± 0.07 cm (mean value ± SD) horizontally and 1.33 ± 0.14 cm vertically. Harderian glands in normal guinea pigs were 0.58 ± 0.05 cm horizontally and 0.61 ± 0.10 vertically. In normal chinchillas, the Harderian glands were 0.53 ± 0.04 cm horizontally and 0.53 ± 0.03 cm vertically. Harderian glands were significantly larger in the vertical plane in rabbits with exophthalmos (P = 0.001) and in the horizontal plane in guinea pigs with exophthalmos (P = 0.018). Harderian glands of rabbits with exophthalmos were significantly larger in both diseased and healthy glands in both planes compared with those of normal rabbits. Guinea pigs and chinchillas with exophthalmos had larger Harderian glands bilaterally in only the vertical plane.

CONCLUSIONS

Ultrasonography is a valuable diagnostic imaging technique to evaluate the Harderian gland in the rabbit, guinea pig, and chinchilla. Retrobulbar pathologic processes cause enlargement of the Harderian gland, which may be attributable to inflammation or possible obstruction of the excretory ducts.

Middle-ear velocity transfer function, cochlear input immittance, and middle-ear efficiency in chinchilla

The transfer function H(V) between stapes velocity V(S) and sound pressure near the tympanic membrane P(TM) is a descriptor of sound transmission through the middle ear (ME). The ME power transmission efficiency (MEE), the ratio of sound power entering the cochlea to power entering the middle ear, was computed from H(V) measured in seven chinchilla ears and previously reported measurements of ME input admittance Y(TM) and ME pressure gain G(MEP) [Ravicz and Rosowski, J. Acoust. Soc. Am. 132, 2437-2454 (2012); J. Acoust. Soc. Am. 133, 2208-2223 (2013)] in the same ears. The ME was open, and a pressure sensor was inserted into the cochlear vestibule for most measurements. The cochlear input admittance Y(C) computed from H(V) and G(MEP) is controlled by a combination of mass and resistance and is consistent with a minimum-phase system up to 27 kHz. The real part Re{Y(C)}, which relates cochlear sound power to inner-ear sound pressure, decreased gradually with frequency up to 25 kHz and more rapidly above that. MEE was about 0.5 between 0.1 and 8 kHz, higher than previous estimates in this species, and decreased sharply at higher frequencies.

Chinchilla middle-ear admittance and sound power: high-frequency estimates and effects of inner-ear modifications

The middle-ear input admittance relates sound power into the middle ear (ME) and sound pressure at the tympanic membrane (TM). ME input admittance was measured in the chinchilla ear canal as part of a larger study of sound power transmission through the ME into the inner ear. The middle ear was open, and the inner ear was intact or modified with small sensors inserted into the vestibule near the cochlear base. A simple model of the chinchilla ear canal, based on ear canal sound pressure measurements at two points along the canal and an assumption of plane-wave propagation, enables reliable estimates of Y(TM,) the ME input admittance at the TM, from the admittance measured relatively far from the TM. Y(TM) appears valid at frequencies as high as 17 kHz, a much higher frequency than previously reported. The real part of Y(TM) decreases with frequency above 2 kHz. Effects of the inner-ear sensors (necessary for inner ear power computation) were small and generally limited to frequencies below 3 kHz. Computed power reflectance was ~0.1 below 3.5 kHz, lower than with an intact ME below 2.5 kHz, and nearly 1 above 16 kHz.

Mapping the anatomy of respiratory syncytial virus infection of the upper airways in chinchillas (Chinchilla lanigera)

Although most viral infections of the upper respiratory tract can predispose to bacterial otitis media, human respiratory syncytial virus (HRSV) is the predominant viral copathogen of this highly prevalent pediatric polymicrobial disease. Rigorous study of the specific mechanisms by which HRSV predisposes to otitis media has been hindered by lack of a relevant animal model. We recently reported that the chinchilla, the preferred rodent host for studying otitis media, is semipermissive for upper-airway HRSV infection. In the current study, we defined the anatomy and kinetics of HRSV infection and spread in the upper airway of chinchilla hosts. Chinchillas were challenged intranasally with a fluorescent-protein-expressing HRSV. Upper-airway tissues were recovered at multiple time points after viral challenge and examined by confocal microscopy and immunohistochemistry. HRSV replication was observed from the rostral- to caudalmost regions of the nasal cavity as well as throughout the Eustachian tube in a time-dependent manner. Although fluorescence was not observed and virus was not detected in nasopharyngeal lavage fluids 14 d after infection, the latest time point examined in this study, occasional clusters of immunopositive cells were present, suggesting that the nasal cavity may serve as a reservoir for HRSV. These data provide important new information concerning the time course of HRSV infection of the uppermost airway and suggest that chinchillas may be useful for modeling the HRSV-induced changes that predispose to secondary bacterial infection.

The PilA protein of non-typeable Haemophilus influenzae plays a role in biofilm formation, adherence to epithelial cells and colonization of the mammalian upper respiratory tract

We recently described the expression of type IV pili (Tfp) by non-typeable Haemophilus influenzae (NTHI), a common respiratory tract pathogen. Prior to that report, Tfp were not thought to be produced by NTHI as they are not observed on NTHI when grown on chocolate agar or other commonly used growth media. To further characterize growth conditions permissive for the expression of NTHI Tfp, as well as determine their role in colonization and virulence, we transformed an NTHI otitis media isolate with a reporter plasmid containing the lux gene cluster driven by the pilA promoter. Transcription from the pilA promoter was demonstrated under a variety of in vitro growth conditions and, importantly, by ex vivo imaging of luciferase-producing NTHI in infected chinchillas. Luciferase-producing NTHI were also identified within a biofilm formed by NTHI in vivo. We further demonstrated a role for NTHI PilA in adherence to human respiratory epithelial cells, in colonization of the chinchilla respiratory tract as well as a requirement for PilA in biofilm development, both in vitro and in vivo. Collectively, our data demonstrate that NTHI express PilA in vivo, and that PilA plays an important role in the pathogenesis of an upper respiratory tract infection induced by NTHI.

Gross morphological features of plexus brachialis in the chinchilla (Chinchilla lanigera)

This study documents the detailed features of the morphological structure and the innervation areas of the plexus brachialis in the chinchilla (Chinchilla lanigera). The animals (5 female and 5 male) were euthanased with ketamine hydrocloride and xylazine hydrocloride combination, 60 mg/kg and 6 mg/kg, respectively. Skin, muscles and nerves were dissected under a stereo-microscope. The brachial plexus of the chinchilla is formed by rami ventrales of C5-C8, T1 and T2, and possesses a single truncus. The subscapular nerve is formed by the rami of the spinal nerves originating from C6 (one thin ramus) and C7 (one thick and 2 thin rami). These nerves innervate the subscapular and teres minor muscles. The long thoracic nerve, before joining with the brachial plexus, obtains branches from C6 and C7 in 5 cadavers (3 male, 2 female), from C7 in 4 cadavers (2 male, 2 female) and from C6-C8 in only 1 female cadaver. These nerves disperse in variable combinations to form the extrinsic and intrinstic named, nerves of the thoracic limb. An undefined nerve branch originates from the rami ventrales of C7, C8 and T1 spinal nerves enter the coracobrachial muscle.

Structures that contribute to middle-ear admittance in chinchilla

We describe measurements of middle-ear input admittance in chinchillas (Chinchilla lanigera) before and after various manipulations that define the contributions of different middle-ear components to function. The chinchilla's middle-ear air spaces have a large effect on the low-frequency compliance of the middle ear, and removing the influences of these spaces reveals a highly admittant tympanic membrane and ossicular chain. Measurements of the admittance of the air spaces reveal that the high-degree of segmentation of these spaces has only a small effect on the admittance. Draining the cochlea further increases the middle-ear admittance at low frequencies and removes a low-frequency (less than 300 Hz) level dependence in the admittance. Spontaneous or sound-driven contractions of the middle-ear muscles in deeply anesthetized animals were associated with significant changes in middle-ear admittance.

Geometry of the semicircular canals of the chinchilla (Chinchilla laniger)

The orientations of the semicircular canals determines the response of the canals to head rotations and, in turn, the brain's ability to interpret those motions. The geometry of chinchillas' semicircular canals has never been reported. Volumetric representations of three chinchilla skulls were generated using a microCT scanner. The centroids of each semicircular canal lumen were identified as they passed through the image slices and were regressed to a plane. Unit vectors normal to the plane representing canal orientations were used to calculate angles between canal pairs. Pitch and roll maneuvers required to bring any canal into the horizontal plane for physiologic investigation were calculated. The semicircular canals of the chinchilla were found to be relatively planar. The horizontal canal was found to be oriented 55.0 degrees anteriorly upward. Pairs of ipsilateral chinchilla canals were not orthogonal and contralateral synergistic pairs were not parallel. Despite this arrangement, the canal plane unit normal vectors were organized to respond with approximately equal overall sensitivity to rotations in any direction. The non-orthogonal chinchilla labyrinth may provide an opportunity to determine whether the frame of reference used by the central vestibular and oculomotor system is based on directions of afferent maximum sensitivity or prime directions.

The chinchilla microdialysis model for the study of antibiotic distribution to middle ear fluid

In cases of slow or limited penetration of an antibiotic to the site of infection such as in acute otitis media (the middle ear), plasma levels of the agent may not reflect the concentrations that are relevant in determining clinical outcome. There is a need for a model that allows prediction of the time-course of unbound, pharmacologically active drug levels in middle ear fluid (MEF). This article introduces microdialysis as a sampling tool to measure unbound antibiotic concentrations in the MEF of the chinchilla, and briefly summarizes the results of studies of MEF penetration of a cephalosporin, a macrolide, and a ketolide antibiotic using this technique. The general concurrence of preliminary results of the chinchilla studies with clinical findings suggests that the chinchilla microdialysis model may be useful in predicting efficacy in patients.

Year-round testicular volume and semen quality evaluations in captive Chinchilla lanigera

In mammals, reproductive performance is usually associated with seasons. Chinchilla lanigera, an endemic South American rodent, reproduces throughout the year in captivity but its seasonal breeding pattern is not fully understood. The present study was designed to evaluate (bi-weekly) over 1 year: (1) testicular volume variations and (2) seminal volume, sperm concentration and functional activity changes. Five animals were studied; they were individually housed indoors (22.2 +/- 1.0 degrees C) under natural photoperiod in Argentina (Córdoba, 31 degrees S-64 degrees W). Semen was obtained by electroejaculation; a total of 116 ejaculates was evaluated. Monthly values for paired testicular volume were less in the middle of the summer than in other seasons (p < 0.006), while those for seminal volume and total spermatozoa/ejaculate were not significantly different; these variables ranged between 7.2-30.9 cm(3), 10-130 microL and 0.9-432.6 x 10(6), respectively. Spermatozoa concentration was (x 10(6)/mL) 2145.9 +/- 365.3 and the pH of semen was 7.3 +/- 0.0. Spermatozoa functional activity showed no significant differences between monthly evaluations; confidence intervals were calculated for the means of: motility, 92.2-95.8%; viability, 92.2-96.1%; swollen cells (hypo-osmotic swelling test), 81.2-87.7% and viable intact acrosome, 83.5-89.0%. The present study represents the first longitudinal reproductive assessment in the chinchilla male. In conclusion, males produce spermatozoa continuously that exhibit high quality functional activity.

The effect of superior canal dehiscence on cochlear potential in response to air-conducted stimuli in chinchilla

A superior semicircular canal dehiscence (SCD) is a break or hole in the bony wall of the superior semicircular canal. Patients with SCD syndrome present with a variety of symptoms: some with vestibular symptoms, others with auditory symptoms (including low-frequency conductive hearing loss) and yet others with both. We are interested in whether or not mechanically altering the superior canal by introducing a dehiscence is sufficient to cause the low-frequency conductive hearing loss associated with SCD syndrome. We evaluated the effect of a surgically introduced dehiscence on auditory responses to air-conducted (AC) stimuli in 11 chinchilla ears. Cochlear potential (CP) was recorded at the round-window before and after a dehiscence was introduced. In each ear, a decrease in CP in response to low frequency (<2 kHz) sound stimuli was observed after the introduction of the dehiscence. The dehiscence was then patched with cyanoacrylate glue leading to a reversal of the dehiscence-induced changes in CP. The reversible decrease in auditory sensitivity observed in chinchilla is consistent with the elevated AC thresholds observed in patients with SCD. According to the 'third-window' hypothesis the SCD shunts sound-induced stapes velocity away from the cochlea, resulting in decreased auditory sensitivity to AC sounds. The data collected in this study are consistent with predictions of this hypothesis.

Ultrastructural and immunocytochemical studies of the viscacha (Lagostomus maximus maximus) pituitary pars tuberalis

The hypophyseal pars tuberalis (PT) has been the focus of numerous studies attempting to understand its physiological role in the reproductive regulation and modulation by the neuroendocrine system. Ultrastructural studies of the PT in a number of species have shown that it consists of a well-developed hypophyseal area with important secretory activity, demonstrated by the abundance of secretory granules in the cytoplasm and the marked blood irrigation. This article describes ultrastructural and immunocytochemical aspects of the PT in viscachas captured in their habitat. The cell types identified were PT-specific cells, agranulated cells, and Folliculostellate cells. PT-specific cells are divided into type I and II. Type I cells have cytoplasms with secretory granules of 150-500 nm diameter. The secretory granules of type II PT-specific cells are 65-200 nm in diameter. Both cellular types exhibit numerous nerve endings on the plasmatic membranes. Agranulated cells exhibit nuclei with lax chromatin, mitochondria, phagosomes, scarce Golgi complex, and rough endoplasmic reticulum. Folliculostellate cells exhibit an irregularly shaped and moderately condensed nucleus. All the described cellular types exhibit deposits of cytoplasmic glycogen. The immunocytochemical study revealed the presence of cells immunostained for LH-beta and FSH-beta in the PT caudal zone. ACTH was only detected in the zona tuberalis. No staining was observed with antiprolactin, anti-TSH-beta, and anti-GH sera. Folliculostellate cells exhibited staining with anti-S-100. The results demonstrate that the viscacha PT is a hypophyseal zone with specific cellular types, which exhibits evident secretory activity. The presence of nerve endings suggests neural control of the function of PT cells.

Anatomy of the nasal cavity in the chinchilla

There is currently great interest worldwide in developing noninvasive methods for the delivery of vaccines for upper respiratory tract diseases, including middle ear infection (otitis media, OM). One such noninvasive approach believed to have great potential for the prevention of diseases of the airway is to deliver vaccines by the intranasal (i.n.) route. Induction of a local, mucosal immune response in the upper respiratory tract, and particularly in the nasopharynx, would be a highly efficacious approach to prevention of OM. The chinchilla is the preferred rodent host for studying OM. However, although the anatomy of the chinchilla vomeronasal organ, inner ear, middle ear and Eustachian tube have been well-studied, to date there have been no reports in the literature of a similar complete analysis of the nasopharynx and nasal cavities of the chinchilla. In order to develop a relevant animal model of i.n. delivery as a potential immunization approach for the prevention of OM and to use these models for preclinical assessments of various vaccine candidates, it was important that we better understand the anatomy of the chinchilla nasal cavities and nasopharynx. Our anatomical studies revealed that the naso- and maxilloturbinates of the chinchilla nasal cavity more closely resemble the simple turbinates found in other rodents rather than the branched or complex turbinates seen in dogs, cats, and rabbits thus facilitating the i.n. delivery of vaccine candidates. The chinchilla nasal mucosa also contains numerous lymphoid aggregates like that of other rodents. Our findings thus suggest that we will be able to deliver i.n. vaccines effectively to chinchillas and that these vaccines will likely be able to induce specific immune responses.

A comparative study on cardiac ganglia in midday gerbil, Egyptian spiny mouse, chinchilla laniger and pigeon

Using the thiocholine method and histological techniques, the topography and morphology of cardiac ganglia in midday gerbil, Egyptian spiny mouse, chinchilla laniger and pigeon were studied. The results demonstrated that cardiac ganglia in all investigated species are embedded in epicardial fat. They formed plexo-ganglionic structures. Each of them composed of many ganglia (from seven up to 36) different in size and shape, and interconnected by fascicles of nerve fibres. Comparative analysis showed that the density of neural network and cell aggregations was different in individual species. The richest plexo-ganglionic structure was in pigeon. It was organized in three plexo-ganglia with an average of 30 ganglia. The largest one was located along the anterior interventricular sulcus. The cardiac ganglia of investigated mammals were localized mainly on the epicardium of atria; in Egyptian spiny mouse and chinchilla laniger on the ventral surface of right atrium, but in midday gerbil on the dorsal surface of left atrium. Moreover, in midday gerbil and Egyptian spiny mouse the little plexo-ganglionic structure on the ventricle were noticed. Additionally, in midday gerbil the single nerve cells might be observed between cardiac muscle of atria. It can be said that, the strongly developed cardiac plexus in pigeon is probably connected with his behaviour and functional properties of the heart. The arrangement of neurones in cardiac ganglia of all examined mammals was uniform over the whole surface of the sections, while in the pigeon, neurones were located mainly in the peripheral part of the ganglion.

Ultrastructure indicative of ion transport in tectal, Deiters, and tunnel cells: differences between gerbil and chinchilla basal and apical cochlea

Ultrastructural examination revealed an epithelium of about five tectal cells (TCs) roofing the outer tunnel (OT) in the mid to upper, but not the basal, region of gerbil and chinchilla cochlea. Structures in TCs that are apparently specialized for retrieval of K(+) released into tunnel fluid from outer hair cells (OHCs) include surface fimbriae in the gerbil and canalicular reticulum in the chinchilla. A tunnel roof of organelle-rich TCs appeared to be better equipped for ion resorption than a roof composed of organelle-poor Hensen cells (HCs). Fimbriae, filopodia, and the cell body of TCs descended to contact the third Deiters cell (DC3) in the gerbil, and the hypertrophied DC3 phalanx rose to contact TCs in the chinchilla, which suggests a solute exchange between TCs and DCs. Previously unrecognized structures that are speculated to provide ATP ligand for cochlear purinoreceptors occurred in the chinchilla DC and gerbil TC. The observation of a microtubule stalk in DCs indicated that they also function in cochlear mechanics. A newly delineated lateral tunnel cell (LTC) intervened between the DC3 and HC in both species. The apicomedial plasmalemma of all DCs fitted closely to the base of OHCs and enveloped afferent nerves. The morphologic specializations reported here provide further support for the proposed transcellular lateral flow route for K(+) currents generated by sound exposure and neural activity. The previously demonstrated expansion of Boettcher cells, outer sulcus cell roots, type Il and IV fibrocytes, and apical microvilli on HCs and Claudius cells (CCs) in the base of the cochlea is postulated here to mediate a basal parallel current that could supply the increased K(+) transport required for the basally elevated electric potential (EP).

Specific distribution pattern of nerve fibers containing catecholamine-synthesizing enzymes, neuropeptide Y (NPY) and C-terminal flanking peptide of NPY (CPON) in the pineal gland of the chinchilla (Chinchilla laniger)--an immunohistochemical study

The sympathetic nerve fibers originating from the superior cervical ganglia and supplying the pineal gland play the most important role in the control of the pineal activity in mammals. NPY and CPON are also present in the majority of the pinealopetal sympathetic neurons. In this study, immunohistochemical techniques were used to demonstrate the existence and coexistence of tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DbetaH) as well as NPY and CPON in the nerve fibers supplying the chinchilla pineal gland. Ten two-year-old female chinchillas housed in natural light conditions were used in the study. The pineals were fixed by perfusion. ABC immunohistochemical technique and immunofluorescence labelling method were employed. TH-immunoreactive (TH-IR) varicose nerve fibers were observed in the pineal gland as well as in the posterior commissural area. Within the chinchilla pineal gland, TH-IR nerve fibers were located in the capsule and connective tissue septa. Numerous varicose TH-IR branches penetrated into the parenchyma and formed a network showing the highest density in the proximal region of the gland. In the central and distal parts of the pineal parenchyma, a subtle network, composed of thin varicose nerve branches, was observed. Double immunostaining revealed that the majority of TH-IR nerve fibers was positive for DbetaH or NPY. TH- and DbetaH-positive neuron-like cells were observed in the proximal region of the gland. The pattern of pineal innervation immunoreactive to CPON was similar to the innervation containing NPY, TH and DbetaH. The chinchilla intrapineal innervation containing TH, DbetaH, NPY and CPON is characterized by the higher density in the proximal part of the gland than in the middle and distal ones. The specific feature of the chinchilla pineal is also the presence of single TH/DbetaH-immunoreactive neuron-like cells in the proximal part of the gland.

Fiber diameter distributions in the chinchilla's ampullary nerves

A morphometric study of the chinchilla's ampullary nerves was conducted to produce an unbiased accounting of the diameter distribution of their constituent fibers. Diameter analyses were determined from 1 microm plastic-embedded nerve sections taken at a plane immediately proximal to the sensory epithelium. We found these nerves to be composed of 2094+/-573 fibers, having diameters that ranged from 0.5 to 8 microm. The distributions of diameters were positively skewed, where approximately 75% of the fibers were found to have diameters less than 3.5 microm. An analysis of the spatial distribution of diameters within the nerve section revealed that the lateralmost areas of the nerve contained larger fractions of fibers within the smallest diameter quintiles, and the central area harbored greater proportions of the larger diameter quintiles. However, significant fractions of all quintiles were found in all areas. These data were integrated with available data of Fernandez et al. (1998) to produce diameter estimates of calyx, dimorphic, and bouton morphology subpopulations. In view of a general relationship between diameter, innervation locus, and an afferent's physiologic characteristics, these data provide the basis for developing a perspective for the in situ distribution of afferent response dynamics.

Temporal and spatial coding of periodicity information in the inferior colliculus of awake chinchilla (Chinchilla laniger)

Amplitude modulation responses and onset latencies of multi-unit recordings and evoked potentials were investigated in the central nucleus of inferior colliculus (ICC) in the awake chinchilla. Nine hundred and one recording sites with best frequencies between 60 and 30 kHz showed either phasic (18%), tonic (25%), or phasic-tonic (57%) responses. Of 554 sites tested for responses to modulation frequencies 73% were responsive and 57% showed clear preference for a narrow range of modulation frequencies. Well defined bandpass characteristics were found for 32% of rate modulation transfer functions (rate-MTFs) and 36% of synchronization MTFs (sync-MTFs). The highest best modulation frequency (BMF) of a bandpass rate-MTF was 600 Hz. Neurons with phasic responses to best-frequency tones showed strong phase coupling to modulation frequencies and were dominated by bandpass rate-MTFs and sync-MTFs. Most neurons with tonic responses showed bandpass tuning only for sync-MTFs. Both BMFs and onset latencies changed systematically across frequency-band laminae of the ICC. Low BMFs and long latencies were located medially and high BMFs and short latencies laterally. Latency distributions obtained with evoked potentials to clicks showed a similar gradient to the multi-unit data. These findings are in line with previous findings in different animals including humans and support the hypothesis that temporal processing results in a topographic arrangement orthogonal to the spectral processing axis, thus forming a second neural axis of the auditory system.

Skull size and cheek-tooth length in wild-caught and captive-bred chinchillas

Chinchillas are herbivorous rodents with teeth that all grow continuously. In captivity, they are commonly affected by dental disease. As the range of dental disease occurring in wild chinchillas is unknown, the dentition of museum specimens originally obtained from the wild was assessed and compared with specimens prepared from captive-bred animals. Skulls from wild-caught chinchillas showed minimal evidence of dental disease and the teeth were all short, cheek-tooth lengths averaging 5.9 mm. Cheek-tooth lengths in zoo specimens (average 6.6 mm), clinically normal (average 7.4 mm) and captive-bred animals with dental disease (average 10 mm) were significantly elongated by comparison (P<0.0001). Captive-bred specimens showed a wide range of tooth-related lesions. These results suggest that some aspect of captivity is responsible for the development of dental disease in chinchillas. It is suggested that the diet (its physical form and composition) is the main aetiological factor, and that provision of a diet closely matching that of wild chinchillas should significantly reduce the incidence of dental disease in captive animals.

Storage of Chinchilla lanigera semen at 4 degrees C for 24 or 72 h with two different cryoprotectants

The objectives of this study were to: (a) test the functional activity of Chinchilla lanigera spermatozoa suspended in either glycerol or ethylene glycol, cooled to 4 degrees C, and stored for 24 or 72 h and (b) investigate, after these cooling periods, the effects of incubating sperm at 37 degrees C (for 4 h) upon sperm functional activity. The ejaculate was mixed with the cryoprotectant medium (at 1 M final concentration) and cooled to 4 degrees C. After warming, sperm motility, sperm viability, hypoosmotic swelling test results, and acrosomal integrity were significantly higher for samples containing ethylene glycol than for those in glycerol, stored for 24 or 72 h, and then assayed after 0 or 4 h incubation at 37 degrees C. A significant reduction of sperm motility and viability was detected only when the glycerol cryoprotectant agent was employed, compared to the fresh samples. These results clearly indicate that under our experimental conditions, ethylene glycol is a better protectant for sperm storage than glycerol.

Helical structure of hair cell stereocilia tip links in the chinchilla cochlea

Outer-hair-cell stereocilia tip-link structure in the chinchilla cochlea was studied by transmission electron microscopy using tannic acid and Ruthenium red/ Alcian blue histochemical procedures. Tannic acid and Ruthenium red/Alcian blue treatments showed the tip link as a compact strand of filaments 9-12 nm thick. Fourier analysis of tip-link images showed that the strand is a three-start helical bundle of fine, coiled filaments which had an axial period of 22.5+/-1.5 nm. Each of three coiled filaments in the strand showed globular structures, 4.3+/-0.3 nm in diameter. The globular structures may correspond to individual protein subunits or they may be repeating identical domains of one polypeptide. The three filaments of the helical array may provide a rigidity to the tip link during stereocilia deflections. Alternatively, changes in the subunit or domain structure of each filament may result in a lengthening or shortening of the tip-link strand.

Representation of vowel stimuli in the ventral cochlear nucleus of the chinchilla

Responses of neurons in the ventral cochlear nucleus (VCN) of anesthetized chinchillas to six synthetic vowel sounds (/a/, /e/, /epsilon/, /i/, /o/ and /u/) were recorded at several intensity levels. Stimuli were synthesized with a fundamental frequency of 100 Hz or 181.6 Hz and had formant values at integer multiples of 100 Hz. Responses came from most neuron types in the VCN (with the exception of onset cells with an I-shaped pattern). Population studies, performed only on primary-like (PL) and chopper neurons, showed that PL neurons provide a better temporal representation than do chopper neurons. At the lowest level of stimulation, all neuron types provide an accurate rate-place representation of vowel spectra. With an increase in stimulus level, the rate-place representation of PL neurons becomes inferior to that of chopper neurons, either sustained choppers or transient choppers.

Ultrastructure and immunohistochemical identification of the extracellular matrix of the chinchilla cochlea

The molecular composition and three-dimensional organization of the extracellular matrix (ECM) was studied by immunofluorescent microscopy, transmission and scanning electron microscopy in three connective tissue structures of the cochlea: the spiral limbus, basilar membrane and spiral ligament. Type II collagen, fibronectin, tenascin, chondroitin sulfate proteoglycans, alphav and beta1 integrins were immunolocalized in the ECM of these connective tissue structures. Electron micrographs showed a continuum of cross-striated collagen fibrils having a similar diameter and axial periodicity that spread from the spiral limbus via the basilar membrane and into the spiral ligament. Some of collagen fibrils were aggregated laterally into bundles. Bundle images, and their digital Fourier transformations, showed a major 67-nm axial D-repeat characteristic for collagen fibrils. Transmission electron microscopy showed numerous proteoglycans associated with the collagen fibrils. The spiral limbus, basilar membrane and spiral ligament demonstrated regional differences in molecular composition and structural organization of their ECM. The glycoproteins fibronectin, tenascin and alphav integrin were immunolocalized mainly in the basilar membrane. Collagen fibrils of the spiral limbus and spiral ligament did not appear to be strongly oriented. However, most of the collagen fibrils in the basilar membrane were arranged into radially directed bundles. Collagen fibrils in the basilar membrane were also surrounded by a homogeneous matrix, which was immunoreactive to fibronectin and tenascin antibodies. A more complete understanding of the composition and structural organization of the ECM in these connective tissue structures in the cochlea provides a foundation upon which micromechanical models of cochlear function can be constructed.

The neonatal chinchilla cochlea: morphological and functional study

The developmental time scale of the cochlea varies from species to species. We investigate here the condition of the neonatal cochlea in the chinchilla, a species increasingly used in auditory research. We have examined the morphology of cochlear hair cells using scanning microscopy, and the development of auditory function during the first postnatal month by monitoring auditory brainstem evoked responses (ABR). We find that although there were some outer hair cell kinocilia present in middle and apical areas, the hair cells otherwise were mature at 24 hours after birth. Furthermore, cochlear auditory thresholds are adult-like at birth. However, whilst there was little change in ABR thresholds over one month, there is evidence of continued maturation of the central auditory system as shown by the shortening of the PI-P5 latency from 9.1 ms to 7.7 ms.

Use of computed tomography to investigate cheek tooth abnormalities in chinchillas (Chinchilla laniger)

Computerised tomographic scanning was used to investigate tooth structure in chinchillas (Chinchilla laniger), both cheek tooth crown and root abnormalities being common in this species. This paper describes a common form of dental disease affecting species with continuously growing teeth, with particular reference to the chinchilla, and confirms the potential role of computed tomography (CT) in its early diagnosis. CT imaging is compared with previously available methods of investigation which frequently fail to detect early pathological changes.

A regional ultrastructural analysis of the cellular and synaptic architecture in the chinchilla cristae ampullares

The chinchilla crista ampullaris was studied in 10 samples, each containing 32 consecutive ultrathin sections of the entire neuroepithelium. Dissector methods were used to estimate the incidence of various synaptic features, and results were confirmed in completely reconstructed hair cells. There are large regional variations in cellular and synaptic architecture. Type I and type II hair cells are shorter, broader, and less densely packed in the central zone than in the intermediate and peripheral zones. Complex calyx endings are most common centrally. On average, there are 15-20 ribbon synapses and 25-30 calyceal invaginations in each type I hair cell. Synapses and invaginations are most numerous centrally. Central type II hair cells receive considerably fewer afferent boutons than do peripheral type II hair cells, but have similar numbers of ribbon synapses. The numbers are similar because central type II hair cells make more synapses with the outer faces of calyx endings and with individual afferent boutons. Most afferent boutons get one ribbon synapse. Boutons without ribbon synapses were only found peripherally, and boutons getting multiple synapses were most frequent centrally. Throughout the neuroepithelium, there is an average of three to four efferent boutons on each type II hair cell and calyx ending. Reciprocal synapses are rare. Most synaptic ribbons in type I hair cells are spherules; those in type II hair cells can be spherical or elongated and are particularly heterogeneous centrally. Consistent with the proposal that the crista is concentrically organized, the intermediate and peripheral zones are each similar in their cellular and synaptic architecture near the base and near the planum. An especially differentiated subzone may exist in the middle of the central zone.

Anatomical localization of electrophysiological recording sites by co-ordinate transformation

A method for estimating the anatomical locations of the units recorded in electrophysiological mapping experiments is described. A total of three locations must be marked by dye injections or electrolytic lesions and identified in tissue sections. From those locations, equations are derived to translate, scale, and rotate the three-dimensional co-ordinates of the recording sites, so that they are correct for a second, three-dimensional co-ordinate system based on the anatomy of the mapped structure. There is no limit to the number of recording sites that can be localized. This differs from methods that require a dye injection or lesion to be made at the exact location at which a particular unit was recorded. The accuracy of the transformed co-ordinates is limited by the accuracy with which the co-ordinates can be measured: in test measurements and in the experiments for which this algorithm was developed, the computed co-ordinates were typically accurate to within 100 microns or less.

Arrangement of vestibular nerve fibers in the semicircular canal crista of the chinchilla

The topographic arrangement of vestibular nerve fibers innervating semicircular canal cristae of the chinchilla was studied using computer-aided video-microscopy and three-dimensional reconstruction. At the level 20 microns proximal to the base of the crista, bundles consisting of 30-50 nerve fibers each were identified. Nerve fibers in bundles were classified into seven categories depending on the diameter. We confirmed that large nerve fibers were more frequently found in the central bundles and small nerve fibers were more frequently found in the peripheral bundles. The central bundle might function as a physiological unit coding various types of head movements, whereas the peripheral bundle might contribute more to the detection of slow and long-lasting movements giving rise to tonus and posture changes. The canalicular nerve may code rotational acceleration of the head via function- and locus-specific nerve fiber bundles.

Neuronal and transneuronal degeneration of auditory axons in the brainstem after cochlear lesions in the chinchilla: cochleotopic and non-cochleotopic patterns

Terminal axonal degeneration in the brain following cochlear lesions was studied with the Nauta-Rasmussen method. Losses of hair cells and myelinated cochlear fibers were assessed. The cochleotopic map projected, from apex to base, on the ventral-to-dorsal axes of the cochlear nuclei. The cochleotopic correspondence was better for loss of cochlear nerve fibers and inner hair cells, than for outer hair cells. Cochlear fibers were traced to all parts of the cochlear nucleus, including the small-cell shell, also to cell-group Y and the flocculus. Terminal axonal degeneration in nuclei of the superior olivary complex, lateral lemniscus, and inferior colliculus was interpreted as transynaptic, since degenerated axons could not be traced to these locations from the cochlear nerve or trapezoid body. Moreover, biotinylated dextran amine injection in the basal turn of scala media of a normal cochlea labeled cochlear nerve fibers projecting to the high-frequency regions of the cochlear nuclei and to the flocculus, but not to more central auditory nuclei. This is the first detailed account of transynaptic degeneration in the ascending auditory pathway resulting from cochlear damage in an adult mammal. These findings are consistent with a dystrophic process depending on hair-cell loss and/or direct damage to cochlear nerve fibers.

Degeneration of axons in the brainstem of the chinchilla after auditory overstimulation

The patterns of axonal degeneration following acoustic overstimulation of the cochlea were traced in the brainstem of adult chinchillas. The Nauta-Rasmussen method for axonal degeneration was used following survivals of 1-32 days after a 105 min exposure to an octave-band noise with a center frequency of 4 kHz and a sound pressure level of 108 dB. Hair-cell and myelinated nerve-fiber loss were assessed in the cochlea. The cochleotopic pattern of terminal degeneration in the ventral cochlear nucleus correlated with the sites of myelinated fiber and inner-hair-cell loss: this correlation was less rigorous with outer-hair-cell loss, especially in the dorsal cochlear nucleus. These results are consistent with a dystrophic process with a slow time course depending on hair-cell loss and/or direct cochlear nerve-fiber damage. However, in a number of cases with no damage in the apical cochlea, fine fiber degeneration occurred with a faster course in low-frequency regions in the dorsal cochlear nucleus and, transynaptically, in a non-cochleotopic pattern in the superior olive and inferior colliculus. These findings suggest that neuronal hyperactivity plays a role in the central degeneration following acoustic overstimulation, possibly by an excitotoxic process.

Fine structure of the cell clusters in the cochlear nerve root: stellate, granule, and mitt cells offer insights into the synaptic organization of local circuit neurons

The small cell shell of the cochlear nucleus contains a complex integrative machinery which can be used to study the roles of interneurons in sensory processing. The cell clusters in the cochlear nerve root of the chinchilla provide the simplest example of this structure. Reported here are the neuronal architecture and synaptic organization of the three principal cell types and the three distinctive neuropil structures that could be characterized with the Nissl and Golgi methods and electron microscopy. Granule cells were characterized by several dendrites with claw-like terminals that received synaptic contacts from multiple excitatory mossy fiber rosettes. Given their relatively large number and their prolific parallel fiber synapses, the granule cells provide a suitable substrate for a tangential spread of excitatory activity, which could build to considerable proportions. The mitt cells had a thickened, single dendrite, its terminal branches arranged in a shape reminiscent of a baseball catcher's mitt. The dendritic mitt enclosed an enormous, convoluted mossy fiber rosette forming many excitatory synapses on just one cell. This could provide for a discrete, comparatively fast input-output relay of signals. Small stellate cells had longer, radiating dendrites that engaged the synaptic nests. These nests were strung in long strands, containing heterogeneous synapses from putative excitatory and inhibitory inputs. Given the prevalence of the synaptic nests, the small stellate cells appear to have the greatest integrative capacity. They provide the main output of the synaptic nests.

Digital-image analysis of the brain-base arteries in chinchilla, chinchilla laniger (Molina)

This paper attempts to quantitatively characterize the cerebral arterial circle in the chinchilla using a computerized image-analysis system. The sole source of the blood supply to the brain in this animal is the vertebral arteries and the basilar arteries. It was found that the diameter and volume of the basilar artery were over twofold larger than those of cerebral-circle arteries. The total length of the cerebral-circle arteries was approximately two times greater than the length of the basilar artery. A strong correlation between the parameters of the basilar artery and the total volume of the arterial circle was observed, as might be expected. These results suggest that if appropriate geometrical parameters are maintained, the brain can be adequately vascularized, even in the absence of additional blood supply.

Fine structure of the vomeronasal organ in the chinchilla (Chinchilla laniger)

Fine structure of the vomeronasal organ (VNO) was examined in the chinchilla (Chinchilla laniger) from a viewpoint of comparative anatomy. The VNO of chinchilla was a pair of tubular structure, about 6mm in length, and situated bilaterally along the base of the nasal septum. The VNO was encircled rostrally by the vomeronasal cartilage, but caudally by a bony capsule. The VNO communicated with the nasal cavity via a small pore at its rostral end, while it ended blindly at its caudal end. Its lumen was crescent to elliptical in a transverse plane, and lined medially with the vomeronasal sensory epithelium (VSE), but laterally with the vomeronasal respiratory epithelium (VRE). Jacobson's glands were tubulo-alveolar in type and distributed from the dorsolateral to the ventrolateral region of the VNO and opened with the duct to the lumen in the transitional region from the VSE to the VRE. Their secretions were periodic acid-Schiff (PAS)-positive but alcian blue (AB)-negative. The VSE consisted of sensory, supporting and basal cells. Supporting cells were characteristic of a large number of huge dense bodies in the perinuclear cytoplasm. The other ultrastructural features in sensory, supporting and basal cells of the VSE were similar to those in the previous reports. The VRE consisted of ciliated, non-ciliated and basal cells. Acinar cells of Jacobson's gland possessed two types of secretory granules. Secretory granules of one type were homogeneous and electronlucent, about 1,700nm in diameter, while granules of the other type were about 2,200nm in diameter, and various in electron density. The present findings suggest that the VNO is functionally active in the chinchilla.

Chinchillas

This article reviews the biology, physiology, husbandry, and handling of pet chinchillas. Diseases and conditions of practical clinical significance are presented.

[Husbandry-related diseases in the chinchilla]

The developing popularity of the chinchilla as a pet over recent years has increased its importance in veterinary practice. The husbandry of pet chinchillas differs significantly from that in commercial fur farms, where the veterinary input is directed towards diseases of animal groups. Veterinary advice and prophylaxis is particularly important for pet chinchillas, as there is relatively little literature about their husbandry and relevant diagnostic and therapeutic procedures. The owners of this 'new' companion animal frequently lack relevant knowledge, and many chinchillas are presented due to inadequate husbandry and feeding. Therefore this report describes the physiology, the management and feeding requirements and examination methods. A selection of the most frequent diseases caused by poor husbandry is presented.

Structural-functional correlation in chinchilla long loop of Henle thin limbs: a novel papillary subsegment

The ultrastructural characteristics of thin limb subsegments from chinchilla long loops of Henle were studied in perfusion-fixed kidneys and in isolated perfused tubules. In sections from the perfusion-fixed kidneys, we noted types I, II, III, and IV thin limb epithelia similar to those previously identified in other rodent species. Sections from the deepest 20% of the papillary tip, however, revealed only a single thin limb epithelial type, which had a combination of structural characteristics distinct from previously identified thin limb subtypes. This "papillary type" epithelium had relatively tall cells and a complex cellular organization with extensive interdigitation, numerous shallow tight junctions, and microvilli. In single-tubule studies, thin limb segments dissected from different levels of the outer and inner medulla were perfused in vitro for osmotic water permeability (Pf) measurements and were fixed for ultrastructural examination. Long-loop thin descending limbs (LDL) dissected from the outer medulla (Pf, 2,637 +/- 336 micron/s) had type II epithelium. LDL dissected from the middle of the inner medulla (Pf, 1,570 +/- 76 microns/s) had a type III epithelium. LDL segments dissected from the deepest 20% of the inner medulla had a low but nonzero Pf (68 +/- 9 micron/s) and had the same novel papillary type epithelium seen in sections from fixed kidneys. Thin ascending limbs dissected from inner 50% of the inner medulla had essentially zero Pf (8 +/- 4 micron/s) and had a type IV epithelium. Immunohistochemical localization of CHIP28 water channel protein confirmed the presence of CHIP28 in thin descending limbs throughout the outer 75% of the inner medulla, whereas labeling was essentially absent in the deep inner medulla where the low-PfLDL (novel papillary type epithelium) is located.

Seasonal changes of the blood-testis barrier in viscacha (Lagostomus maximus maximus): a freeze-fracture and lanthanum tracer study

Adult male viscachas (Lagostomus maximus maximus) were gathered from their natural habitat during the period of complete spermatogenesis (June) and during the month of maximum testicular regression (August). The testes were processed by conventional electron microscopic technique using lanthanum nitrate (electron-dense intercellular tracer) to define the intercellular spaces below the inter-Sertoli tight junctions and by freeze-fracture techniques. During complete spermatogenesis the tracer surrounds spermatogonia, preleptotene, and leptotene spermatocytes and stops at the level of the inter-Sertoli tight junctions below all germ cells displaying synaptonemal complexes (zygotene-pachytene spermatocytes) and germ cells in more advanced stages of differentiation. Conversely, during testicular regression the tracer percolates all intercellular spaces between Sertoli cells and the remaining germ cells (spermatogonia and few preleptotene and leptotene spermatocytes). During complete spermatogenesis, freeze-fracture replicas exhibit numerous inter-Sertoli tight junction strands parallel to each other and to the basal lamina. During spermatogenesis decay, the inter-Sertoli tight junctions are found to be short, tortuous, frequently interrupted, and often associated with extented membranous areas of gap junctions.

Hyperpigmentation of chinchilla stria vascularis following acoustic trauma

This report describes morphological alterations of the chinchilla stria vascularis seen 30 days after exposure to impulse noise. The observed changes included a dramatic increase in strial melanin content which occurred in 7 of 36 animals exposed to electronically synthesized impluses presented in various temporal patterns at either 135 or 150 dB peak SPL. In these animals, densely pigmented areas of stria 1.5 to 3 mm in length were found in the basal cochlear turn. Light and electron microscopic study revealed that these areas contained large numbers of melanin granules situated primarily in pale-staining cells of the middle layer of the stria. Unlike the pigment granules present in normal chinchilla stria, the melanosomes found in the noise-exposed material clearly showed ultrastructural features characteristic of eumelanin. Melanin granules were also observed in marginal and basal cells of the noise-exposed stria. In some cases, pigment granules which had apparently been expelled from the marginal cells were present in the endolymphatic space beneath Reissner's membrane and on the strial surface. These findings support the view that the melanin-bearing cells of the inner ear are capable of markedly increased activity in response to stressful conditions.

Cytoarchitecture of cochlear nucleus in the chinchilla

The morphology of the cochlear nucleus in the normal, adult chinchilla, as demonstrated by Nissl staining, was examined. The cytoarchitecture was determined from sections viewed at the light microscope level. The chinchilla cochlear nucleus was found to possess most of the features reported in other mammalian cochlear nuclei. It could easily be divided into dorsal and ventral components due to an intervening layer of granule cells, and most cell types previously reported in mammals were also found in the chinchilla cochlear nucleus. A distinct distribution pattern of cell types exists within each part.

Cytoarchitectonic atlas of the cochlear nucleus of the chinchilla, Chinchilla laniger

A detailed cytoarchitectonic atlas of the chinchilla cochlear nucleus complex was prepared in the transverse plane with the Nissl method. Subdivisions of the cochlear nucleus were defined on the basis of cell size, cell packing density, and, in some cases, on cytological features of cell types. In general, the chinchilla cochlear nucleus has an organizational plan similar to that described for other mammalian species. As in other rodents, the chinchilla has a large and well-developed dorsal cochlear nucleus consisting of three distinct layers. The ventral cochlear nucleus consists of two distinct nuclear masses, a posterior nuclear group and an anterior nuclear group, each composed of several subdivisions, which are qualitatively similar to those described for other mammals. Thus it is now possible to compare detailed observations, such as tonotopic maps, in the chinchilla with findings from the analogous cell populations in other mammals, such as the cat, with considerable precision. In the chinchilla, three cell groups, previously undescribed in mammals, have been defined and their counterparts in the cat identified.

[Morphologic aspects of the vestibular nerve of the chinchilla]

A quantitative study was made of the number of fibers, their diameters and patterns of distribution in 14 ampullar nerves of chinchilla. The nerves were processed for osmium staining, embedded in plastic and cut serially in 1-micron-thick sections for histologic evaluation. Quantitative evaluation of nerve-fiber characteristics was made with the aid of a laboratory computer and specific programs. The number of the nerve fibers ranged between 1,877 and 2,175. The diameters of the fibers could be as large as 8 microns. The fibers between 2 and 2.5 microns were the most abundant, representing 29.6% of the fiber population. The distribution of fibers in the cristae was size-dependent: 80% of the thin fibers were located at the ends of the nerves, while most of the thick fibers were distributed through the central and intermediate areas.