Enhancement of phase-locking in rodents. II. An axonal recording study in chinchilla.

The trapezoid body (TB) contains axons of neurons residing in the anteroventral cochlear nucleus (AVCN) that provide excitatory and inhibitory inputs to the main monaural and binaural nuclei in the superior olivary complex (SOC). To understand the monaural and binaural response properties of neurons in the medial and lateral superior olive (MSO and LSO), it is important to characterize the temporal firing properties of these inputs. Because of its exceptional low-frequency hearing, the chinchilla (Chinchilla lanigera) is one of the widely used small animal models for studies of hearing. However, the characterization of the output of its ventral cochlear nucleus to the nuclei of the SOC is fragmentary. We obtained responses of TB axons to stimuli typically used in binaural studies and compared these responses to those of auditory nerve (AN) fibers, with a focus on temporal coding. We found enhancement of phase-locking and entrainment, i.e., the ability of a neuron to fire action potentials at a certain stimulus phase for nearly every stimulus period, in TB axons relative to AN fibers. Enhancement in phase-locking and entrainment are quantitatively more modest than in the cat but greater than in the gerbil. As in these species, these phenomena occur not only in low-frequency neurons stimulated at their characteristic frequency but also in neurons tuned to higher frequencies when stimulated with low-frequency tones, to which complex phase-locking behavior with multiple modes of firing per stimulus cycle is frequently observed.NEW & NOTEWORTHY The sensitivity of neurons to small time differences in sustained sounds to both ears is important for binaural hearing, and this sensitivity is critically dependent on phase-locking in the monaural pathways. Although studies in cat showed a marked improvement in phase-locking from the peripheral to the central auditory nervous system, the evidence in rodents is mixed. Here, we recorded from AN and TB of chinchilla and found temporal enhancement, though more limited than in cat.

Epistatic Effects Between Amino Acid Insertions and Substitutions Mediate Toxin resistance of Vertebrate Na+,K+-ATPases.

The recurrent evolution of resistance to cardiotonic steroids (CTS) across diverse animals most frequently involves convergent amino acid substitutions in the H1-H2 extracellular loop of Na+,K+-ATPase (NKA). Previous work revealed that hystricognath rodents (e.g., chinchilla) and pterocliform birds (sandgrouse) have convergently evolved amino acid insertions in the H1-H2 loop, but their functional significance was not known. Using protein engineering, we show that these insertions have distinct effects on CTS resistance in homologs of each of the two species that strongly depend on intramolecular interactions with other residues. Removing the insertion in the chinchilla NKA unexpectedly increases CTS resistance and decreases NKA activity. In the sandgrouse NKA, the amino acid insertion and substitution Q111R both contribute to an augmented CTS resistance without compromising ATPase activity levels. Molecular docking simulations provide additional insight into the biophysical mechanisms responsible for the context-specific mutational effects on CTS insensitivity of the enzyme. Our results highlight the diversity of genetic substrates that underlie CTS insensitivity in vertebrate NKA and reveal how amino acid insertions can alter the phenotypic effects of point mutations at key sites in the same protein domain.

Cochlear tuning and the peripheral representation of harmonic sounds in mammals.

Albert Feng was a prominent comparative neurophysiologist whose research provided numerous contributions towards understanding how the spectral and temporal characteristics of vocalizations underlie sound communication in frogs and bats. The present study is dedicated to Al's memory and compares the spectral and temporal representations of stochastic, complex sounds which underlie the perception of pitch strength in humans and chinchillas. Specifically, the pitch strengths of these stochastic sounds differ between humans and chinchillas, suggesting that humans and chinchillas may be using different cues. Outputs of auditory filterbank models based on human and chinchilla cochlear tuning were examined. Excitation patterns of harmonics are enhanced in humans as compared with chinchillas. In contrast, summary correlograms are degraded in humans as compared with chinchillas. Comparing summary correlograms and excitation patterns with corresponding behavioral data on pitch strength suggests that the dominant cue for pitch strength in humans is spectral (i.e., harmonic) structure, whereas the dominant cue for chinchillas is temporal (i.e., envelope) structure. The results support arguments that the broader cochlear tuning in non-human mammals emphasizes temporal cues for pitch perception, whereas the sharper cochlear tuning in humans emphasizes spectral cues.

Clinical, pathologic, and immunohistochemical features of pituitary tumors in 4 chinchillas.

Pituitary tumors are rare in chinchillas. This report describes the clinical, gross, histologic, and immunohistochemical characteristics of pituitary tumors in 4 chinchillas. The affected chinchillas were females between 4 and 18 years of age. Clinically, neurologic signs were most commonly reported and included depression, obtundation, seizure, head-pressing, ataxia, and possible blindness. Computed tomography scanning of 2 chinchillas revealed solitary intracranial extra-axial masses in the region of the pituitary gland. Two pituitary tumors were confined to the pars distalis; the other 2 invaded the brain. Based on their microscopic appearances and lack of distant metastases, all 4 tumors were diagnosed as pituitary adenomas. Immunohistochemically, all pituitary adenomas were weakly to strongly positive for growth hormone, most consistent with the diagnosis of somatotropic pituitary adenomas. To the authors' knowledge, this is the first detailed report of the clinical, pathologic, and immunohistochemical features of pituitary tumors in chinchillas.

Myocardial protein aggregates in pet guinea pigs.

A retrospective study of guinea pigs submitted for necropsy revealed intracytoplasmic inclusions in the cardiomyocytes of 26 of 30 animals. The inclusions were found with approximately the same frequency in male and female guinea pigs and were slightly more common in older animals. In most cases, the animals did not have clinical signs or necropsy findings suggestive of heart failure, and the cause of death or reason for euthanasia was attributed to concurrent disease processes. However, the 4 guinea pigs with the highest inclusion body burden all had pulmonary edema, sometimes with intra-alveolar hemosiderin-laden macrophages, suggestive of heart failure. The inclusions were found in both the left and right ventricular myocardium, mainly in the papillary muscles, but were most common in the right ventricular free wall. No inclusions were detected in the atrial myocardium or in skeletal muscle. The inclusions did not stain with Congo red or periodic acid-Schiff. Electron microscopy revealed dense aggregates of disorganized myofilaments and microtubules that displaced and compressed the adjacent organelles. By immunohistochemistry, there was some scattered immunoreactivity for desmin and actin at the periphery of the inclusions and punctate actin reactivity within the aggregates. The inclusions did not react with antibodies to ubiquitin or cardiac myosin, but were variably reactive for alpha B crystallin, a small heat shock chaperone protein. The inclusions were interpreted as evidence of impaired proteostasis.

Mass spectrometry imaging of blast overpressure induced modulation of GABA/glutamate levels in the central auditory neuraxis of Chinchilla.

Acoustic trauma damages inner ear neural structures including cochlear hair cells which result in hearing loss and neurotransmitter imbalances within the synapses of the central auditory pathway. Disruption of GABA/glutamate levels underlies, tinnitus, a phantom perception of sound that persists post-exposure to blast noise which may manifest in tandem with acute/chronic loss of hearing. Many putative theories explain tinnitus physiology based on indirect and direct assays in animal models and humans, although there is no comprehensive evidence to explain the phenomenon. Here, GABA/glutamate levels were imaged and quantified in a blast overpressure model of chinchillas using Fourier transform ion cyclotron resonance mass spectrometry imaging. The direct measurement from whole-brain sections identified the relative levels of GABA/glutamate in the central auditory neuraxis centers including the cochlear nucleus, inferior colliculus, and auditory cortex. These preliminary results provide insight on the homeostasis of GABA/glutamate within whole-brain sections of chinchilla for investigation of the pathomechanism of blast-induced tinnitus.

Concomitant Congenital Diaphagmatic Hernia (CDH) and bilateral bacterial glomerulonephritis in a pet chinchilla (Chinchilla lanigera).

BACKGROUND: The domestic chinchilla has been descended from Chinchilla lanigera (long-tailed Chinchilla) or Chinchilla chinchilla (short-tailed Chinchilla). Both species of chinchilla are currently listed as endangered by the IUCN Red List of Threatened Species. Over the past 20 years, they have spread as pets and overall knowledge about their care is improving. The present case report describes a congenital diaphragmatic hernia in a Chinchilla lanigera. CASE PRESENTATION: A 1-year-old, 420 g female chinchilla (Chinchilla lanigera) was presented for clinical examination due to 2 days haematuria episodes and anorexia. A complete haematological analysis was performed, showing a moderate neutrophilia and severe renal involvement. X-rays showed severe intestinal meteorism affecting mostly the cecum, and a soft tissue density mass with translucent areas located in the caudal thorax, making it hard to distinguish the cardiac silhouette. A barium swallow (barium sulfate) was performed and after 20 min, radiograms were performed again, showing part of the stomach dislocated in thorax. Ultrasound was also carried out, confirming the partial stomach herniation into the thoracic cavity and a severe nephropathy. The patient was euthanized according to the owner's wish and a complete necropsy was performed. The diagnosis was congenital diaphragmatic hernia concomitant to a severe bilateral bacterial glomerulonephritis. DISCUSSION AND CONCLUSIONS: Diaphragmatic hernias can be either congenital or acquired. About CDHs in pet chinchillas, literature is still lacking. In this patient there was no history of previous traumas. No scar tissue or thickening involved margins of the pathological diaphragm window at the necropsy, supporting the hypothesis of a congenital defect. Glomerulonephritis most often results from immune-mediated mechanisms, generally after the deposition of soluble immune complexes within the glomeruli. This mechanism is favoured by a prolonged antigenemia that could occur during specific viral infections, chronic bacterial infections, chronic parasitism, autoimmune diseases and neoplasia. Few cases of nephritis are described in chinchillas (Chinchilla lanigera), mostly related to bacterial sepsis or less commonly involving fungi. The evidence of bacterial aggregates in kidneys at the histopathology, confirmed the infective aetiology. No relationship between the diaphragmatic hernia and glomerulonephritis was found in this report.

Comparison of the structure of chinchilla sperm isolated from semen and from the tail of the epididymis.

Sperm cells isolated from the tail of the epididymis and from the semen of the same individuals were analysed. The use of silver nitrate to stain sperm cells isolated from the tail of the epididymis made it possible to identify structures that were not visible in the sperm from semen. Silver nitrate very clearly distinguished the acrosomal and distal parts of the sperm head. Following silver nitrate staining, the sperm isolated from the tail of the epididymis were characterized by dark 'collars' in the distal part of the head. These 'collars' are not visible in the sperm cells isolated from semen. The results of the study indicate differences in the dimensions of sperm isolated from the tail of the epididymis and sperm in semen. Sperm isolated from the tail of the epididymis had smaller heads, despite their longer length, and had longer midpieces and tails than ejaculate sperm. Silver nitrate staining is a simple and fast technique. Silver nitrate makes it possible to identify the acrosome and post-acrosomal region of the sperm head and to clearly identify the midpiece. Therefore, it can be successfully used to supplement routine techniques for evaluating sperm morphology or as an independent technique.

A Protein E-PilA Fusion Protein Shows Vaccine Potential against Nontypeable Haemophilus influenzae in Mice and Chinchillas.

PE-PilA is a fusion protein composed of immunologically relevant parts of protein E (PE) and the majority subunit of the type IV pilus (PilA), two major antigens of nontypeable Haemophilus influenzae (NTHi). Here we report on the preclinical evaluation of PE-PilA as a vaccine antigen. The immunogenic potential of the PE and PilA within the fusion was compared with that of isolated PE and PilA antigens. When injected intramuscularly into mice, the immunogenicity of PE within the fusion was equivalent to that of isolated PE, except when it was formulated with alum. In contrast, in our murine models PilA was consistently found to be more immunogenic as a subentity of the PE-PilA fusion protein than when it was injected as an isolated antigen. Following immunization with PE-PilA, anti-PE antibodies demonstrated the same capacity to inhibit the binding of PE to vitronectin as those induced after PE immunization. Likewise, PE-PilA-induced anti-PilA antibodies inhibited the formation of NTHi biofilms and disrupted established biofilms in vitro These experiments support the immunogenic equivalence between fused PE-PilA and isolated PE and PilA. Further, the potential of PE-PilA immunization against NTHi-induced disease was evaluated. After intranasal NTHi challenge, colonization of the murine nasopharynx significantly dropped in animals formerly immunized with PE-PilA, and in chinchillas, signs of otitis media were significantly reduced in animals that had received anti-PE-PilA antibodies. Taken together, our data support the use of PE-PilA as an NTHi vaccine antigen.

Mandible strength and geometry in relation to bite force: a study in three caviomorph rodents.

The monophyletic group Caviomorpha constitutes the most diverse rodent clade in terms of locomotion, ecology and diet. Caviomorph species show considerable variation in cranio-mandibular morphology that has been linked to the differences in toughness of dietary items and other behaviors, such as chisel-tooth digging. This work assesses the structural strength of the mandible of three caviomorph species that show remarkable differences in ecology, behavior and bite force: Chinchilla lanigera (a surface-dwelling species), Octodon degus (a semi-fossorial species) and Ctenomys talarum (a subterranean species). Finite element (FE) models of the mandibles are used to predict the stresses they withstand during incisor biting; the results are related to in vivo bite forces and interspecific variations in the mandibular geometries. The study concludes that the mandible of C. talarum is better able to withstand strong incisor bites. Its powerful adducting musculature is consistent with the notorious lateral expansion of the angular process and the masseteric crest, and the enhanced cortical bone thickness. Although it has a relatively low bite force, the mandible of O. degus also shows a good performance for mid-to-strong incisor biting, in contrast to that of C. lanigera, which exhibits, from a mechanical point of view, the worst performance. The mandibles of C. talarum and O. degus appear to be better suited to withstand stronger reaction forces from incisor biting, which is consistent with their closer phylogenetic affinity and shared digging behaviors. The contrast between the low in vivo bite force of C. lanigera and the relatively high estimations that result from the models suggests that its adductor musculature could play significant roles in functions other than incisor biting.

Oviduct morphology and estrogen receptors ERα and ERß 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 ERß 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 ERß throughout the oviduct epithelium. Both ERα and ERß 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.

Comparison of the characteristics of chinchilla epidydimal semen after collection, storage at 5°C and cryopreservation.

The aim of the study was to compare the characteristics of chinchilla epididymal sperm: fresh, stored at liquid state and cryopreserved. Epididymal spermatozoa obtained from 11 males were assessed for subjective motility, concentration, motility parameters measured by CASA, viability, morphology, membrane integrity, acrosome integrity, mitochondrial potential, lipid peroxidation, chromatin structure, apoptotic changes and capacitation. Then half of the spermatozoa were stored at 5°C for 30 hr, and the second half was cryopreserved. After storage and thawing the same parameters as in fresh semen were assessed. Fresh semen showed good quality, with low levels of lipid peroxidation, chromatin fragmentation and capacitation. CASA evaluation showed significantly lower values for MOT, PMOT, RAPID, VCL, VAP and VSL after both storage at liquid state and cryopreservation (p < 0.05). Cold storage did not induce membrane and acrosome damage (p > 0.05), conversely to cryopreservation (p < 0.05). After storage, there was a drop in high mitochondrial potential in live cells (p < 0.05) and an increase in the percentage of non-apoptotic, capacitated cells (p < 0.05). These changes were not seen after cryopreservation (p > 0.05). Lipid peroxidation in live cells and chromatin structure remained unchanged both after storage and cryopreservation (p > 0.05). The study showed that examined methods of semen preservation exerted different patterns of changes in spermatozoa and that sperm quality after both of them allowed for further use of preserved spermatozoa in artificial reproductive techniques.

Tonometer validation and intraocular pressure reference values in the normal chinchilla (Chinchilla lanigera).

OBJECTIVES: To determine accuracy and precision of three commonly used tonometers (TonoVet® and TonoLab® (ICare Oy, Finland)-rebound tonometers, and Tono-Pen VET™ (Reichert, NY)-applanation tonometer) in normal chinchillas, and to establish a normal intraocular pressure (IOP) reference range in this species. METHODS: The anterior chambers of three chinchilla eyes were cannulated ex vivo and readings obtained at manometric IOPs from 5 to 80 mmHg, using each of the three tonometers in random order. Data were analyzed by linear regression, ANOVA, and Bland-Altman plots. Tonometry was performed in both eyes of 60 chinchillas (age 8 weeks-16.2 years) using the TonoVet® and relationship between age and IOP analyzed using linear regression. For all statistical tests, P < 0.05 was significant. RESULTS: Intraocular pressure values obtained using the Tono-Pen VET™ and TonoVet® (in dog calibration mode;'d') showed strong linear correlation with manometry within the physiologic and clinically relevant range of IOP (0-50 mmHg). The TonoVet® 'd' setting displayed significantly greater precision over the full range of IOP evaluated than the Tono-Pen VET™, and both TonoVet and Tono-Pen VET™ were significantly more accurate than the TonoLab® tonometer. Mean ± SD IOP (TonoVet® 'd') in chinchillas was 9.7 ± 2.5 mmHg, and the 95% reference interval was 4.7-14.7 mmHg. CONCLUSIONS: Both the Tono-Pen VET™ and TonoVet® provided clinically acceptable estimates of IOP in chinchillas. The TonoVet® provides accurate and precise IOP values, while Tono-Pen VET™ derived measurements showed greater variability. Values obtained either with the TonoLab® or TonoVet® used in the 'unspecified' calibration setting were inaccurate in this species.

Gene expression profiling analysis reveals fur development in rex rabbits (Oryctolagus cuniculus).

Fur is an important economic trait in rabbits. The identification of genes that influence fur development and knowledge regarding the actions of these genes provides useful tools for improving fur quality. However, the mechanism of fur development is unclear. To obtain candidate genes related to fur development, the transcriptomes of tissues from backs and bellies of Chinchilla rex rabbits were compared. Of the genes analyzed, 336 showed altered expression in the two groups (285 upregulated and 51 downregulated, P ≤ 0.05, fold-change ≥2 or ≤0.5). Using GO and KEGG to obtain gene classes that were differentially enriched, we found several genes to be involved in many important biological processes. In addition, we identified several signaling pathways involved in fur development, including the Wnt and MAPK signaling pathways, revealing mechanisms of skin and hair follicle development, and epidermal cell and keratinocytes differentiation. The obtained rabbit transcriptome and differentially expressed gene profiling data provided comprehensive gene expression information for SFRP2, FRZB, CACNG1, SLC25A4, and SLC16A3. To validate the RNA-seq data, the expression levels of eight differentially expressed genes involved in fur development were confirmed by qRT-PCR. The results of rabbit transcriptomic profiling provide a basis for understanding the molecular mechanisms of fur development.

Adrenergic and cholinergic innervation of the atrioventricular valves in chinchilla (Chinchilla laniger).

The arrangement of autonomic fibres was studied in the cardiac atrioventricular valves of small chinchillas. The dissected valves were stained entirely using the modified histochemical acetylcholine esterase technique (AChE) and the SPG-De la Torre method. Double immunocytochemical staining was also used for the expression of vesicular acetylcholine transporter (VAChT) and dopamine beta hydroxylase (DBH). The study showed the presence of both cholinergic and adrenergic fibres, forming a kind of network on all cusps of both valves. The adrenergic network is always more strongly represented than the cholinergic network. The cholinergic nerve network of the "parietal" part formed mainly the parallel arrangement. As we move towards the free parts of the cusps, the arrangement becomes netted and radiant. The adrenergic fibres formed only the netted arrangement, which was the most dense in the peripheral (parietal) part of the cusps. Some of the fibres in the vicinity of tendinous cords extended as far as the papillary muscles. Double immunocytochemical tests confirmed the presence and distribution of DBH- and VAChT-positive fibres. Some fibres (especially within the tendinous cords) show VAChT and DBH colocalisation.

ModA2 Phasevarion Switching in Nontypeable Haemophilus influenzae Increases the Severity of Experimental Otitis Media.

Several human-adapted bacterial pathogens use a phasevarion (ie, a phase-variable regulon) to rapidly and reversibly regulate the expression of many genes, which include known virulence factors, yet the influence of phasevarion-mediated regulation in pathogenesis remains poorly understood. Here we examine the impact of the nontypeable Haemophilus influenzae (NTHI) ModA2 phasevarion on pathogenesis and disease severity in a chinchilla model of experimental otitis media. Chinchillas were challenged with NTHI variant populations that were either inoculated ON and remained ON, inoculated OFF and shifted ON, or inoculated OFF and remained OFF, within the middle ear. We show that populations that shift from OFF to ON within the middle ear induce significantly greater disease severity than populations that are unable to shift. These observations support the importance of phasevarion switching in NTHI pathogenesis and the necessity to considered phasevarion regulation when developing methods to treat and prevent infection.

Suppression Measured from Chinchilla Auditory-Nerve-Fiber Responses Following Noise-Induced Hearing Loss: Adaptive-Tracking and Systems-Identification Approaches.

The compressive nonlinearity of cochlear signal transduction, reflecting outer-hair-cell function, manifests as suppressive spectral interactions; e.g., two-tone suppression. Moreover, for broadband sounds, there are multiple interactions between frequency components. These frequency-dependent nonlinearities are important for neural coding of complex sounds, such as speech. Acoustic-trauma-induced outer-hair-cell damage is associated with loss of nonlinearity, which auditory prostheses attempt to restore with, e.g., "multi-channel dynamic compression" algorithms.Neurophysiological data on suppression in hearing-impaired (HI) mammals are limited. We present data on firing-rate suppression measured in auditory-nerve-fiber responses in a chinchilla model of noise-induced hearing loss, and in normal-hearing (NH) controls at equal sensation level. Hearing-impaired (HI) animals had elevated single-fiber excitatory thresholds (by ~ 20-40 dB), broadened frequency tuning, and reduced-magnitude distortion-product otoacoustic emissions; consistent with mixed inner- and outer-hair-cell pathology. We characterized suppression using two approaches: adaptive tracking of two-tone-suppression threshold (62 NH, and 35 HI fibers), and Wiener-kernel analyses of responses to broadband noise (91 NH, and 148 HI fibers). Suppression-threshold tuning curves showed sensitive low-side suppression for NH and HI animals. High-side suppression thresholds were elevated in HI animals, to the same extent as excitatory thresholds. We factored second-order Wiener-kernels into excitatory and suppressive sub-kernels to quantify the relative strength of suppression. We found a small decrease in suppression in HI fibers, which correlated with broadened tuning. These data will help guide novel amplification strategies, particularly for complex listening situations (e.g., speech in noise), in which current hearing aids struggle to restore intelligibility.

Histological and morphometric study of the epididymus of Chinchilla lanigera Grey under controlled conditions in captivity.

Chinchilla lanigera, native to the Andean Mountains of Perú, Chile, Bolivia and Argentina, is a specimen of great economic importance because of its fur. In mammals, spermatozoa originate in testes and are transported to the epididymis, where they undergo morphological and biochemical modifications known as sperm maturation, a basic step in the acquisition of their fertilizing ability. The aim of this work is the macroscopic and microscopic analysis of the epididymis of Chinchilla lanigera Grey and its sectorization based on a histomorphological study. The epididymis presents a clear segmentation into four regions: initial segment, caput, corpus and cauda. The epithelium lining the seminiferous tubules is pseudostratified, with principal cells with stereocilia and basal, clear, apical, narrow and halo cells. The histological analysis showed that principal and basal cells are the prevailing populations in all regions, also revealing narrow cells and the absence of clear cells in the initial segment. Each segment presents its different histological and morphometric characteristics, which supports the idea of the specific behaviour of each region, giving a segment-specific character to the process of sperm maturation in this species. No significant differences were found in the morphometric measurements or in the histological evaluation of the epididymis of samples collected in April and October. The fact that no differences were found between the samples collected during the two periods when the reproductive ability in nature is different suggests the importance of external factors in the control of the reproductive cycle of Chinchilla lanigera.

Retention of solute and particle markers in the digestive tract of chinchillas (Chinchilla laniger).

The chinchilla (Chinchilla laniger) is a herbivorous hystricomorph South American rodent for which no mean digesta retention times have been reported so far. Six animals (mean body mass ± standard deviation: 513 ± 99 g) on a diet of grass hay and lucerne-based pellets were given a pulse dose of a solute (cobalt-EDTA) and a particle (chromium-mordanted fibre, <2 mm) marker with subsequent frequent faecal collection. Dry matter intake was 45.2 ± 8.0 g/kg(0.75) /day. Mean retention times were 22.2 ± 5.3 h for solutes and 25.4 ± 5.2 h for particles, with the difference being not significant within individuals. This indicates the presence of a 'mucus-trap' colonic separation mechanism, which is in accord with morphological descriptions of the typical colonic furrow in chinchillas. Corresponding to a strategy of colonic digesta separation and caecotroph formation, secondary marker excretion peaks indicated coprophagic events that were spaced approximately 12 h apart. Given that these retention times appear longer than measures reported for rabbits (Oryctolagus cuniculus) or guinea pigs (Cavia procellus), it would be interesting to compare the digestive efficiency of chinchillas on high levels of dietary fibre to other species.

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.