Noninvasive Ultrasound Monitoring of Embryonic and Fetal Development in Chinchilla lanigera to Predict Gestational Age: Preliminary Evaluation of This Species as a Novel Animal Model of Human Pregnancy.

Ultrasound is a noninvasive routine method that allows real-time monitoring of fetal development in utero to determine gestational age and to detect congenital anomalies and multiple pregnancies. To date, the developmental biology of Chinchilla lanigera has not yet been characterized. This species has been found to undergo placentation, long gestation, and fetal dimensions similar to those in humans. The aim of this study was to assess the use of high-frequency ultrasound (HFUS) and clinical ultrasound (US) to predict gestational age in chinchillas and evaluate the possibility of this species as a new animal model for the study of human pregnancy. In this study, 35 pregnant females and a total of 74 embryos and fetuses were monitored. Ultrasound examination was feasible in almost all chinchilla subjects. It was possible to monitor the chinchilla embryo with HFUS from embryonic day (E) 15 to 60 and with US from E15 to E115 due to fetus dimensions. The placenta could be visualized and measured with HFUS from E15, but not with US until E30. From E30, the heartbeat became detectable and it was possible to measure fetal biometrics. In the late stages of pregnancy, stomach, eyes, and lenses became visible. Our study demonstrated the importance of employing both techniques while monitoring embryonic and fetal development to obtain an overall and detailed view of all structures and to recognize any malformation at an early stage. Pregnancy in chinchillas can be confirmed as early as the 15th day postmating, and sonographic changes and gestational age are well correlated. The quantitative measurements of fetal and placental growth performed in this study could be useful in setting up a database for comparison with human fetal ultrasounds. We speculate that, in the future, the chinchilla could be used as an animal model for the study of US in human pregnancy.

Epididymis of Viscacha (Lagostomus maximus maximus): A Morphological Comparative Study in Relation to Sexual Maturity.

The morphological variations and the androgen receptor (AR) expression were studied in viscacha epididymis in relation to sexual maturity. The animals were divided into immature, pre-pubertal and adult, according to their corporal weight and testicular histology. The epididymides were studied by light microscopy, immunohistochemistry for AR and morphometric analysis. In pre-pubertal and adult animals, four well-differentiated segments (initial, caput, corpus and cauda) were observed, while in immature animals, three segments were identified (initial-caput segment, corpus and cauda). In each segment, the structural parameters and the relative cell distribution were different between the groups. The serum testosterone levels of pre-pubertal and adults showed a very significant increase related to sexual maturity. The AR expression in epithelial and fibromuscular stromal cells was different between the groups. In conclusion, the present work demonstrates that the morphological characteristics of the viscacha epididymis vary while sexual maturity is reached, the development of initial and caput is subsequent to corpus and cauda development and the androgens might play an important role during this process.

Reproductive performance and weaning success in fur-chewing chinchillas (Chinchilla lanigera).

In captive chinchillas, one of the most challenging behavioral problems is the development of a stress-related abnormal repetitive behavior (ARB) known as "fur-chewing". We investigated whether there is a relationship between the severity of fur-chewing behavior and reproductive function in male and female chinchillas. Regardless of the severity of abnormal behavior, fur-chewing males did not show significant differences in seminal quality (sperm concentration, motility and viability; integrity of sperm membrane and acrosome) and the response to the process of semen collection (the number of stimuli needed to achieve ejaculation) when compared to those with normal behavior. Also, females showing normal or fur-chewing behavior presented similar reproductive performance in terms of number of litters per female per year and litter size. However, pup survival rate was lower (p=0.05) in fur-chewing females than in normal females. These results seem to be consistent with data suggesting non-significant effects of ARBs on reproductive performance.

Reproduction in chinchilla (Chinchilla lanigera): current status of environmental control of gonadal activity and advances in reproductive techniques.

A review of the biology of reproduction of chinchilla, focusing on environmental control of the gonadal activity, is presented. Chinchilla is a South American hystricomorph rodent genus currently considered almost extinct in the wild. However, a domestic form is still widespread in breeding farms around the world. Information regarding their reproductive biology has been obtained from studies on captive animals. In the case of Chinchilla lanigera, a seasonal reproductive pattern has been frequently reported in breeding facilities, but factors that might trigger gonadal activity have not been identified. The available information on reproductive productivity in farms worldwide shows a range of 1.2 to 2.4 deliveries per female per yr (with up to 2.1 weaned young per female per yr). Indeed, as found in all rodents, chinchillas can multiply at high fecundity and fertility rates (4 to 6 follicles mature during estrous cycles). Some new research avenues are postulated to improve the control of gonadal activity by means of environmental and/or pharmacologic factors. Furthermore, reproductive techniques that have been validated in chinchilla are reviewed (noninvasive hormone monitoring, semen collection, sperm cryopreservation, estrus induction), and several technical steps are proposed to be able to achieve AI. Because domesticated chinchilla still share some genomic characteristics with their counterparts in the wild, validated reproductive techniques in chinchilla males and females might contribute to the success of breeding programs.

Postnatal development of cochlear microphonic and compound action potentials in a precocious species, Chinchilla lanigera.

The development of sound-evoked responses in Chinchilla lanigera was studied from postnatal ages P0-1 (first 24 h) to adult. Cochlear microphonic (CMs) and compound action potentials (CAPs), representing ensemble sound-evoked activities of hair cells and auditory nerve fibers, respectively, were present as early as age P0-1. The data indicate that CM thresholds and sensitivities were generally adult-like (i.e., fall into adult ranges) at birth, but suprathreshold CM amplitudes remained below adult ranges through P28. CAP thresholds reached adult-like values between P7-P14, but the suprathreshold CAP amplitude continued to increase until ∼P28. The results confirm the auditory precociousness of the chinchilla.

Concurrent development of the head and pinnae and the acoustical cues to sound location in a precocious species, the chinchilla (Chinchilla lanigera).

Sounds are filtered in a spatial- and frequency-dependent manner by the head and pinna giving rise to the acoustical cues to sound source location. These spectral and temporal transformations are dependent on the physical dimensions of the head and pinna. Therefore, the magnitudes of binaural sound location cues-the interaural time (ITD) and level (ILD) differences-are hypothesized to systematically increase while the lower frequency limit of substantial ILD production is expected to decrease due to the increase in head and pinna size during development. The frequency ranges of the monaural spectral notch cues to source elevation are also expected to decrease. This hypothesis was tested here by measuring directional transfer functions (DTFs), the directional components of head-related transfer functions, and the linear dimensions of the head and pinnae for chinchillas from birth through adulthood. Dimensions of the head and pinna increased by factors of 1.8 and 2.42, respectively, reaching adult values by ~6 weeks. From the DTFs, the ITDs, ILDs, and spectral shape cues were computed. Maximum ITDs increased by a factor of 1.75, from ~160 µs at birth (P0-1, first postnatal day) to 280 µs in adults. ILDs depended on source location and frequency exhibiting a shift in the frequency range of substantial ILD (>10 dB) from higher to lower frequencies with increasing head and pinnae size. Similar trends were observed for the spectral notch frequencies which ranged from 14.7-33.4 kHz at P0-1 to 5.3-19.1 kHz in adults. The development of the spectral notch cues, the spatial- and frequency-dependent distributions of DTF amplitude gain, acoustic directionality, maximum gain, and the acoustic axis were systematically related to the dimensions of the head and pinnae. The dimension of the head and pinnae in the chinchilla as well as the acoustical properties associated with them are mature by ~6 weeks.

Postnatal development of neuronal responses to frequency-modulated tones in chinchilla auditory cortex.

Responses to cortical neurons to frequency-modulated (FM) stimuli have been described in various adult animal models. Here, we ask whether FM coding at the cortical level is innate or if it is influenced by postnatal environmental experience. We report on the FM response properties of neurons in core auditory cortex of newborn (P3), 1-month-old (P28) and adult (>1-year-old) anesthetized chinchillas (Chinchilla laniger). Upward and downward linear FM sweeps spanning frequencies from 0.1 to 20 kHz were presented monaurally at speeds of 0.05 to 0.82 kHz/ms. Results indicated that neurons in neonatal pups were responsive to FM stimulation. While we observed a developmental increase in the selectivity of units for FM sweep direction (p<0.01, one-way ANOVA), selectivity for sweep speed appeared to be established early in development. Chinchilla pup neurons also demonstrated single-peak (single dominant response during FM sweep presentation) and multi-peak (multiple distinct responses during FM sweep) temporal response patterns to FM stimuli similar to those observed in adults. A developmental increase in the proportion of multi-peak units closely paralleled a previously reported increase in the complexity of pure tone receptive fields. We suggest that units in core auditory cortex of the chinchilla are not uniquely activated by FM sounds but that FM responses are largely predictable based on how changing frequency stimuli interact with the tonal receptive fields of neurons in the auditory cortex.

Postnatal Sertoli and Leydig cell proliferation and the establishment of puberty and sexual maturity in Chinchilla lanigera (Rodentia, Chinchillidae).

The Chilean chinchilla (Chinchilla lanigera) is threatened in its natural habitat and there is very little information concerning the reproductive biology of this species. Our main objectives were to investigate the postnatal testis development in this rodent, with emphasis on Sertoli and Leydig cell proliferation and the establishment of puberty and sexual maturity. Forty-four animals from one day to 30 months of age had their testis and epididymis prepared (time of collection for animals from 5 to 30 months of age, May-November in the southern hemisphere) for histological and stereological analyses. Both Sertoli and Leydig cell proliferation occurred up to two months after birth and their total number per testis were stable thereafter. Based on spermatid release from the seminiferous epithelium and the presence of sperm in the epididymis, puberty in chinchilla took place at around three months of age. However, testis weight and tubular diameter and epithelium height appeared to stabilise only after the animals reached 17 months of age, indicating that the establishment of full sexual maturity in this species takes a relatively long period of time. This particular finding indicates that chinchilla might represent an interesting experimental model to investigate the mechanisms that regulate the establishment of this important event of reproductive physiology in mammals.

Tone responses in core versus belt auditory cortex in the developing chinchilla.

Single-unit responses to tone pip stimuli were isolated from numerous microelectrode penetrations of core primary auditory cortex (AI) and a dorsocaudal (DC) belt region in the ketamine-anesthetized chinchilla (laniger). Results are reported at postnatal day 3 (P3), P15, P30, and from adult animals. The AI core could be distinguished from the DC belt on the basis of its strict tonotopic organization, evident in all chinchillas studied (including the youngest). Averaged by age group and compared to their core counterparts, belt neurons generally had similar absolute (spike rate) thresholds and onset latencies (at a given sound pressure level), but lower maximum spike rates, broader tuning bandwidths, and more complex (multipeaked) receptive fields. Most notably, the fraction of complex belt units in the near-newborn (P3) group was high (approximately 50%), and did not systematically increase with age, while that of complex core units was approximately 10% at P3 and increased steadily to about 40% in adulthood. These results provide further evidence to support the hypothesis that, at least to some extent, core and belt auditory cortex may constitute parallel processing streams which represent different aspects of complex acoustic stimuli.

Tone frequency maps and receptive fields in the developing chinchilla auditory cortex.

Single-unit responses to tone pip stimuli were isolated from numerous microelectrode penetrations of auditory cortex (under ketamine anesthesia) in the developing chinchilla (laniger), a precocious mammal. Results are reported at postnatal day 3 (P3), P15, and P30, and from adult animals. Hearing sensitivity and spike firing rates were mature in the youngest group. The topographic representation of sound frequency (tonotopic map) in primary and secondary auditory cortex was also well ordered and sharply tuned by P3. The spectral-temporal complexity of cortical receptive fields, on the other hand, increased progressively (past P30) to adulthood. The (purported) refinement of initially diffuse tonotopic projections to cortex thus seems to occur in utero in the chinchilla, where external (and maternal) sounds are considerably attenuated and might not contribute to the mechanism(s) involved. This compares well with recent studies of vision, suggesting that the refinement of the retinotopic map does not require external light, but rather waves of (correlated) spontaneous activity on the retina. In contrast, it is most probable that selectivity for more complex sound features, such as frequency stacks and glides, develops under the influence of the postnatal acoustic environment and that inadequate sound stimulation in early development (e.g., due to chronic middle ear disease) impairs the formation of the requisite intracortical (and/or subcortical) circuitry.

Development of the middle ear in neonatal chinchillas. I. Birth to 14 days.

Measures of middle-ear function in humans show large differences among neonates, infants, and adults. In contrast, hearing sensitivity is essentially mature at birth. Hypotheses that have been proposed to explain the developmental changes in middle-ear function include: (i) contaminating effects of the immature neonatal ear-canal wall and (ii) persistent fetal tissue in the ear canal, tympanic membrane (TM), and middle-ear space. To better understand the relationships between middle-ear function, hearing sensitivity and the structure of the middle ear, 30 chinchillas, aged 1-14 days, were studied. Middle-ear function was assessed by multifrequency tympanometry with probe tones ranging from 226 to 2,000 Hz. Hearing sensitivity was measured by auditory brainstem response using clicks and 1, 2, 4, and 8 kHz tone bursts. Structural characteristics were analyzed from temporal bone histologic preparations. At all frequencies, the acoustic admittance of the neonatal car is very low and tympanometric patterns are complex and irregular, compared to adult animals. The admittance is essentially constant from 1 to 14 days, indicating that developmental changes occur over a much wider age span than that investigated here. Hearing sensitivity of the chinchilla appears to be mature at birth. Histologic analysis indicated that there were no age-related changes in TM thickness, TM diameter, distance from TM to promontory, and stapes footplate diameter. There were small increases in bone thickness, middle-ear area, mastoid bulla area, and in the perimeters of the middle ear and mastoid bulla. There were no significant amounts of loose mesenchyme or other fetal tissue in the middle-ear space.

Quantitation of synaptic vesicle antigen in rabbit superior colliculus during normal development and after neonatal visual cortical lesion.

Radioimmunoassay of a synaptic vesicle-associated antigen (SV Ag) using monoclonal antibodies was used to study synapse formation in the rabbit superior colliculus (SC). Normal postnatal development was compared with development following unilateral neonatal visual cortex lesion. Neonatal lesion of the visual cortex prevents the cortical innervation of the SC, which normally accounts for 35% of the total SV Ag levels in the rabbit SC. Following such lesions, a small but significant increase in SV Ag levels over that in normally innervated SC was observed. These observations suggest that competition between retinotectal and corticotectal inputs may be required for normal development of synaptic connections in the SC.

[Growth and reproduction of the chinchilla-age at vaginal opening, oestrous cycle, gestation period, litter size, sex ratio, and diseases frequently encountered (author's transl)].

The paper deals with observations on growth and reproduction of the chinchilla in recent 4 years started from 1966 at this laboratory. There were large variations in age of vaginal opening (less than 71 days-308 days) with an average of 173.2+/-57.6 days in 45 females. The average length of 100 oestrus cycles in 24 females was 35.7+/-7.9 (15-62) days. The mean period of 5 gestations in 5 females was 110.4 (108-112) days. Eighty-one out of 123 litters were born between March and August during 3 years, and parturition never occurs in December. The most suitable season for reproduction of chinchillas may be from January to April, and a summer anoestrous seems to be present in August to early September as reported by Weir. The litter size ranged from 1 to 4 with a mode of 2 (46.3%) and an average of 1.90+/-0.76. More male kids were produced at birth at this laboratory, and sex ratio was 133.7 (98 females and 131 males). In 1973, 37 chinchillas gave birth to 71 kids with an average litter size of 1.92, and 59 of them were successfully weaned (1.59 per litter). Of these kids, 50 (1.35 per liter) attained 240 days of age (adulthood). Among 91 subjected to investigation for causes of death, 23 (25.3%) were dead during newborn period, and 9 and 5 adults were dead of malocclusion (9.9%) and the prolapse of rectum respectively.