Social influence on sexual maturation and breeding in the female Mongolian gerbil (Meriones unguiculatus)

Social factors influencing reproductive activity in laboratory groups of gerbils were investigated using the ventral scent-gland as an index of reproductive condition. Sexual maturation and breeding were suppressed in female offspring remaining with their parents. In family groups living in enclosures, daughters rarely bred in the presence of their mother but breeding activity increased after death. Intra-female aggression resulted in the re-establishment of a single breeding female in groups where more than one started to breed. In a controlled social situation in which females were caged with their mothers, sexual maturation was suppressed in the presence of their mother and the continuing presence of her second litter, but not in the presence of a non-pregnant mother or a mother whose second litter had been removed.     

Pericapsular smooth muscle cells in renal corpuscles of the Mongolian gerbil

Summary During the course of a systematic investigation of the renal corpuscles in various desert rodents (Meriones unguiculati, Meriones shawii, Psammomys obesus, and Dipodymis), a thickened Bowman's capsule was observed light microscopically in some kidneys of adult Meriones unguiculati (Mongolian gerbil). Electron microscopic studies show that this unusual finding may depend on the presence of one or two layers of typical smooth muscle cells adjacent to the outer surface of the basal lamina. In the kidneys of other species of desert rats examined, no pericapsular smooth muscle cells were observed.     

Recessive yellow in the Mongolian gerbil (Meriones unguiculatus)

A new autosomal recessive coat color mutant in the Mongolian gerbil (Meriones unguiculatus) is described: recessive yellow. On the dorsal side the mutant has a rich yellow to ginger color. Ventrally it shows the typical creamy white belly of a wild-type Mongolian gerbil. The dorsal yellow hairs have short black tips, and a light olive green base. A clear demarcation line between dorsal and ventral color is present. Crosses between recessive yellow animals and multiple homozygous recessive tester animals (a/a; c^chm/c^chm; g/g; p/p) resulted only in animals of an agouti (wild-type) phenotype, showing that the new allele is not allelic with any of the known coat color mutations in the Mongolian gerbil. Molecular studies showed that the new mutant is caused by a missence mutation at the extension (E) locus. On a non-agouti background (a/a; e/e) mutant animals look like a dark wild-type agouti. In contrast to wild-type agouti it shows yellow pigmentation and dark ticking at the ventral side, resulting in the absence of a demarcation line. Since black pigment is present in both the agouti and non-agouti variant (A/A; e/e and a/a; e/e), we conclude that recessive yellow in the Mongolian gerbil is non-epistatic to agouti. Additionally we describe a second mutation at the same locus leading to a similar phenotype, however without black pigment and diminishing yellow pigment during life. Fertility and viability of both new mutants are within normal range. The extension (E) gene is known to encode the melanocortin 1 receptor (MC1R). Interestingly, this is the only gene that is known to account for substantial variation in skin and hair color in humans. Many different mutations are known of which some are associated with higher skin cancer incidence.     

Innervation of the pineal gland in the Mongolian gerbil (Meriones unguiculatus)

Summary Parasympathetic stimulation of parotid glands has been studied in vivo, a) in normal resting glands, b) 72 h after post-ganglionic sympathectomy and c) after adrenergic degranulation of the acinar cells.Morphological results in each gland were compared with a similarly pretreated, but not parasympathetically stimulated, contralateral gland from the same animal.On parasympathetic stimulation of glands with densely granulated acinar cells (groups a- and b-) a variable, but usually relatively small, tendency for vacuole formation occurred in some cells. After prior degranulation of the cells (group c-) the tendency for vacuole formation was greatly accentuated. This indicates that the pre-existing metabolic state of the cells can influence the responses to stimulation of a single nerve. Dilatation of rough endoplasmic reticulum and nuclear changes were also more prominent after parasympathetic stimulation of previously degranulated acinar cells, and this suggests that parasympathetic impulses may have strong activating effects on resynthesis under these conditions. It is also likely that parasympathetic stimulation induced some, albeit small, degree of degranulation and, since this occurred in the absence of sympathetic nerves (group b-) it was probably the consequence of a direct cholinergic effect. The present results therefore indicate that the concept of an absolute dichotomy between parasympathetic and sympathetic responses is not tenable in this tissue.Analyses of saliva for amylase and peroxidase gave complex results but indicate that the two enzymes are not necessarily secreted in parallel. The morphological results support the idea that some enzyme molecules may have entered the saliva without being prepackaged into secretory granules, but could have passed directly from dilated cisterns of rough endoplasmic reticulum into intra-cellular vacuoles, and this tendency was most apparent after para-sympathetic stimulation of previously degranulated cells.Travel grants from the Wellcome Trust to J.R. Garrett are gratefully acknowledged. This work has been helped by the technical assistance of Mr. P.S.A. RowleyM.R.C. Research Assistant     

Comparing Individual and Group-Negotiated Knowledge Structures in an Introductory Biology Course for Majors

One of the key agendas for the emerging field of disciplinary-based education research is the evaluation of the trajectory of disciplinary knowledge development from novice to expert. However, with the ongoing promotion of student-centered and collaborative undergraduate science classrooms, it is unknown how peer discourse during these exercises might influence (promote or hinder) student construction of expert knowledge. This study documented the knowledge structures of n = 13 undergraduate biology students in a first semester biology course for majors across four instructional units. Participants constructed both individual and group-negotiated concept maps and map complexity, propositional stream similarity, and propositional accuracy were used as measures of quality of knowledge structure. Results indicated that on individually-constructed maps, in general, students had moderate quality knowledge structures when compared to experts. Individual map complexity seemed to increase over time, but stream similarity and propositional accuracy were more dependent on content unit. Group-constructed maps were consistently more accurate than individually-constructed maps. Results are discussed in the context of the use of collaborative concept mapping as a means to develop disciplinary expertise in biology.     

Persistent infection with Strongyloides venezuelensis in the Mongolian gerbil (Meriones unguiculatus)

To examine the fate of Strongyloides venezuelensis. Mongolian gerbils (Meriones unguicalatus) were orally infected with 1,000 L3 larvae per animal. Altogether, 50 gerbils divided into 5 groups of 10 each were monitored for a period of 570 days to document the kinetics of faecal egg output, adults worm population, morphological development, fecundity, and hematological changes including peripheral blood eosinophilia. This study chronicled a life long parasitism of S. venezuelensis in the gerbil host, and showed that S. venezuelensis infection was quite stable throughout the course of infection and the worms maintained their normal development as evidenced by their body dimension. A progressive loss of body condition of the infected gerbils was observed as the level of infection advanced. However, no detectable pathological changes were observed in the gastrointestinal tract. The present findings indicate that an immunocompetent host, such as the Mongolian gerbil, can serve as a life long carrier model of S. venezuelensis if the worms are not expelled within 570 days after infection.     

The regulation of precopulatory behavior by ovarian hormones in the female Mongolian gerbil

The hormonal regulation of precopulatory behavior in the female Mongolian gerbil was studied using two groups (N = 6) of sexually experienced females. A novel testing procedure was used which involved females living continuously with test males for several days. The test males showed either full sexual behavior (copulating males, C) or only precopulatory behavior (noncopulating males, NC). Experiment 1 investigated changes during the estrous cycle and following ovariectomy in females. Experiment 2 studied the effects of hormonal treatment of these ovariectomized females with 6 micrograms estradiol benzoate (EB) followed by 0.4 mg progesterone (P) or by 0.04 ml arachis oil. When tested with NC males, females displayed a greater range of precopulatory behavior. The patterns could be classified into three groups according to the manner of response to ovariectomy and hormone treatment. Group I patterns (approach, leave, and olfactory investigation of the male's head) were affected by neither ovariectomy nor EB treatment relative to Day 3 levels (Day 3, day preceding estrus; Day 4, estrus), but they were increased to estrous levels by EB and P. Group II patterns (darting, foot-stomping, and the present and piloerection postures) appeared only during estrus, did not appear after ovariectomy, and reappeared only after sequential EB and P treatment. Group III patterns (investigation of the male's anogenital area, allogrooming, ventral gland marking, and sand-rolling) were reduced relative to both estrus and Day 3 levels by ovariectomy and increased above Day 3 levels by EB alone; EB and P treatment further increased Group III patterns to the level of estrus. It is suggested that female precopulatory behavior patterns differ in their responsiveness to ovarian hormones. Estrogen appears to affect those patterns associated with the earliest stages of estrus (Group III).     

Learning-induced dynamic receptive field changes in primary auditory cortex of the unanaesthetized Mongolian gerbil

Learning-induced changes of the spectro-temporal characteristics of primary auditory cortex (AI) units were studied by response plane analysis of recordings from the AI in unanaesthetized Mongolian gerbils. Using response planes obtained prior to and after auditory discrimination training bins of significant change were identified and their spectro-temporal distribution was studied. Bins of significant changes were generally found to be distributed over the entire spectro-temporal receptive field but occurred most frequently within the first 100 ms of response in the spectral neighbourhood (1.5 octaves) of the frequency of the reinforced conditioned stimulus. Training-induced response decreases occurred early after 10 ms for reinforced conditioned tones and tones in the frequency neighbourhood. Response increases occurred so early only for non-reinforced tones in the neighbourhood of the reinforced frequency and occurred later (after 40 ms) for the reinforced tones. The results are discussed in the light of dynamic disinhibition. Accepted: 13 August 1997     

Functional correlates of characteristic frequency in single cochlear nerve fibers of the Mongolian gerbil

Summary Single-unit recordings obtained from the auditory nerve of the Mongolian gerbil, Meriones unguiculatus, revealed functional differences in the response properties of neurons tuned to low and high frequencies. The distribution of neural thresholds displayed a distinct rise for auditory nerve fibers with characteristic frequencies] (CFs) between 3–5 kHz. This frequency band also marked abrupt changes in both the distribution of spontaneous discharge rates and the shape of the neural tuning curve. For neurons of all CFs, spontaneous firing rates were inversely related to neural threshold but unrelated to sharpness of neural tuning. The range of CF thresholds encountered, even when data from many animals were combined, rarely exceeded 20 dB, suggesting that cochlear nerve responses obtained from this species display little inter-animal variability. These results are compared with similar data from other species and discussed in terms of recent studies on sound communication and cochlear anatomy in gerbils.Abbreviations CF characteristic frequency - SR spontaneous discharge rate     

Pinealocytes contacting the cerebrospinal fluid of the suprapineal recess in the Mongolian gerbil (Meriones unguiculatus)

Summary The pineal system of the Mongolian gerbil (Meriones unguiculatus) was investigated by light and electron microscopy, special attention being paid to the sites of contact with the ventricular system. The results reveal that the pineal system of this species has a specific topographical relationship to the suprapineal recess of the third ventricle. The dorsal side of the proximal part of the pineal system forms the floor and the caudal wall of this recess. Here, a consistent and relatively large area lacks an ependymal lining, enabling pinealocytes to come into direct contact with the cerebrospinal fluid (CSF). This area is assumed to be the morphological correlate of a close functional interrelationship between the pineal tissue and the CSF.     

Field-specific responses in the auditory cortex of the unanaesthetized Mongolian gerbil to tones and slow frequency modulations

Responses of multi-units in the auditory cortex (AC) of unanaesthetized Mongolian gerbils to pure tones and to linearly frequency modulated (FM) sounds were analysed. Three types of responses to pure tones could be clearly distinguished on the basis of spectral tuning properties, response latencies and overall temporal response pattern. In response to FM sweeps these three types discharged in a temporal pattern similar to tone responses. However, for all type-1 units the latencies of some phasic response components shifted systematically as a function of range and/or speed of modulation. Measurements of response latencies to FMs revealed that such responses were evoked whenever the modulation reached a particular instantaneous frequency (F_i). Effective F_i was: (1) independent of modulation range and speed, (2) always reached before the modulation arrived at a local maximum of the frequency response function (FRF) and consequently differed for downward and upward sweeps, and (3) was correlated with the steepest slope of that FRF maximum. The three different types of units were found in discrete and separate fields or regions of the AC. It is concluded that gross temporal response properties are one of the key features distinguishing auditory cortical regions in the Mongolian gerbil. Accepted: 13 August 1997     

Ultracytochemical evidence for the presence of GERL in pinealocytes of the Mongolian gerbil (Meriones unguiculatus)

Summary Ultracytochemical reactions for the demonstration of acid phosphatase, glucose-6-phosphatase and thiamine pyrophosphatase, as well as zinc iodide-osmium tetroxide impregnation, revealed the existence of GERL (Golgi apparatus — Endoplasmic Reticulum — Lysosomes) in pinealocytes of the Mongolian gerbil (Meriones unguiculatus). The spatial arrangement of this structure was studied on thick sections using a goniometric stage. Although it was not possible to determine whether GERL in pinealocytes belongs to the Golgi apparatus or to endoplasmic reticulum, it can be concluded that its presence in studied cells signifies that they are considerably more active synthetically than has been believed to date.     

冷暴露长爪沙鼠下丘脑-垂体-肾上腺轴对产热的调节

为探讨下丘脑 -垂体 -肾上腺轴在野生小哺乳动物产热中的调节作用 ,对正常及肾上腺去除的长爪沙鼠进行了冷暴露研究。正常雄性长爪沙鼠在急性冷暴露 ( 4± 1℃ ,1天 )条件下 ,下丘脑促肾上腺皮质激素释放激素的合成和释放没有显著变化 ,肾上腺皮质酮含量增加 4 5 8% ,差异显著 ,血清皮质酮水平有增加趋势 ;慢性冷暴露 ( 4± 1℃ ,3周 )后 ,肾上腺皮质酮含量增加到对照的 2 14倍 ,血清皮质酮含量维持较高水平。肾上腺去除的长爪沙鼠冷暴露 3周后 ,褐色脂肪组织 (BAT)产热 (细胞色素C氧化酶活力、线粒体GTP结合数量 )增加 ,下丘脑促甲状腺激素释放激素的合成和释放、血清三碘甲腺原氨酸水平以及血清去甲肾上腺素的浓度均有增加的趋势。表明冷暴露条件下长爪沙鼠肾上腺皮质酮的合成和释放增加 ,从而抑制BAT的产热 ,皮质酮对BAT产热的抑制部分是通过抑制下丘脑 -垂体 -甲状腺轴激素的合成和分泌以及抑制交感神经系统的活动而实现的。     

Characterization of the follicles in the intermediate lobe of the pituitary gland of the Mongolian gerbil (Meriones unguiculatus)

Summary The Mongolian gerbil (Meriones unguiculatus) contains abundant follicles throughout the intermediate lobe (IL) of the pituitary gland in the adult animal. The mode of follicle formation, the nature of the follicle building cells and the distribution of follicles were investigated in semithin sections of the gerbil IL. The sections were stained conventionally, or immunohistochemically with antibodies directed against -melanocyte stimulating hormone (- MSH). Follicular cells were constantly -MSH-negative, and resembled the marginal cells lining the hypophyseal cleft with regard to their cytological and immunohistochemical properties. Moreover, follicular cells appeared to be derived from strands of marginal cells that regularly invaginated deep into the IL. Both follicular and marginal cells often made up cellular clusters. This process coincided with follicle formation and the generation or transport of the colloidal content found inside follicles and the hypophyseal cleft. Although the non-secretory cells of the IL obviously constituted one major source of pituitary colloid in the gerbil, -MSH-positive secretory cells, which occasionally were found to be discharged into the cleft cavity, might contribute to the colloidal contents.     

Alloparents in the Mongolian gerbil: impact on long-term reproductive performance of breeders and opportunities for independent reproduction

The presence of alloparents in cooperatively breeding groupsmay enhance the reproductive performance of the breeding pairbut tests of this hypothesis in mammalian cooperative breedershave typically examined short periods in the reproductive lifespan of breeders. The present experiment was designed to evaluatethe long-term effects of the presence of alloparents on reproductiveperformance under laboratory conditions in Mongolian gerbils(Mertones unguiculalus), and to evaluate the possibility thatalloparents may attempt independent reproduction during theirtenure as alloparents. Pairs were established with either 0or 4 alloparents and breeding performance was monitored overa 13.5-month period. The presence of alloparents did not enhancereproductive rates in breeding pairs, and neither enhanced nordelayed developmental rates in offspring. Variation in littersize, offspring survival, pup growth, and interbirth intervaldid not vary significantly as a function of the breeding females'reproductive tenure. Seven of 49 female alloparents of breedingage in family groups produced offspring. Alloparent breedingwas associated with long interbirth intervals in the breedingadult female. Neonatal survival in litters born to alloparentswas higher in litters that were temporally synchronized withlitters produced by the older breeding female than in asynchronouslyproduced litters. Under the conditions in this experiment, then,few indirect benefits accrue to helpers as a consequence oftheir alloparental effort, and immediate (the opportunity forindependent reproductive attempts) and delayed (parental skillsacquisition) direct benefits may account for helping behaviorin this species.     

Postnatal development of GABA- and glycine-like immunoreactivity in the cochlear nucleus of the Mongolian gerbil (Meriones unguiculatus)

The maturation of the morphological substrate for inhibitory interactions was investigated in the cochlear nucleus of the gerbil with immunocytochemistry for gamma aminobutyric acid (GABA) and glycine on alternating vibratome sections. The patterns of immunostaining obtained with both antibodies in the adult closely conformed to the general mammalian scheme. Qualitative analyses revealed an age-related increase in staining intensity and in the relative numbers of immunolabelled cells after birth up to the age of 3–4 weeks. As early as birth and in all subdivisions of the cochlear nucleus, a few labelled cells and puncta in the sections were stained either with the GABA or the glycine antibody. Immunoreactive puncta and cells were, however, far less abundant than in the adult, and the staining intensity of cells was only weak. The most strikingly GABA-immunolabelled cells at birth were the Golgi cells of the granule-cell domains. The numbers of weakly GABA- and glycine-immunostained cells of the dorsal cochlear nucleus clearly increased between birth and the third postnatal week. At approximately the onset of hearing (postnatal day 12–14), some cells of the dorsal cochlear nucleus and small cells of the ventral cochlear nucleus gained adult-like GABA-staining properties. Almost adult-like labelling intensity was observed in glycine-immunoreactive cells of the deep dorsal cochlear nucleus and in some small cells of the ventral cochlear nucleus. Puncta staining to both antibodies appeared adult-like throughout the cochlear nucleus. About 2 weeks after the onset of hearing (at the latest), adult-like staining of all subsets of immunoreactive cells occurred throughout the cochlear nucleus in all specimens. Received: 25 March 1997 / Accepted: 15 March 1998     

Development of the nasolacrimal apparatus in the Mongolian gerbil (Meriones unguiculatus), with notes on network topology and function

The nasolacrimal apparatus (NLA) is a multicomponent functional system comprised of multiple orbital glands (up to four larger multicellular exocrine structures), a nasal chemosensory structure (vomeronasal organ: VNO), and a connecting duct (nasolacrimal duct: NLD). Although this system has been described in all tetrapod vertebrate lineages, albeit not always with all three main components present, considerably less is known about its ontogeny. The Mongolian gerbil (Meriones unguiculatus) is a common lab rodent in which the individual components of the adult NLA have been well studied, but as yet nothing is known about the ontogeny of the NLA. In this study, serial sections of 15 fetal and three adult Mongolian gerbil heads show that the development of the NLA falls into three fetal stages: inception (origin of all features), elongation (lengthening of all features), and expansion (widening of all features). No postnatal or juvenile specimens were observed in this study, but considerable growth evidently occurs before the final adult condition is reached. The development of the orbital glands and the VNO in the Mongolian gerbil is largely consistent with those in other mammals, despite a slight nomenclatural conundrum for the anterior orbital glands. However, the Mongolian gerbil NLD follows a more circuitous route than in other tetrapods, due mainly to the convoluted arrangement of the narial cartilages, the development of a pair of enlarged incisors as well as an enlarged infraorbital foramen. The impact of these associated features on the ontogeny and phylogeny of the NLA could be examined through the approach of network science. This approach allows for the incorporation of adaptations to specific lifestyles as potential explanations for the variation observed in the NLA across different tetrapod clades. J. Morphol. 276:1005–1024, 2015. © 2015 Wiley Periodicals, Inc.     

The presence of substance P-immunoreactive nerve fibres in the organum vasculosum laminae terminalis of the Mongolian gerbil (Meriones unguiculatus)

Summary Serial frontal and sagittal sections through the organum vasculosum laminae terminalis (OVLT) of the male Mongolian gerbil (Meriones unguiculatus) were incubated with an antibody against substance P and stained by the indirect peroxidase anti-peroxidase technique. A high density of nerve fibres with large-sized terminals exhibiting substance P-immunoreactivity was observed in the OVLT in close relation to the blood vessels both in the internal and the external zone of the organ. In addition, a few fibres penetrated into the ependyma covering the organ. These results indicate that substance P is released into the bloodstream from the OVLT and in addition might influence the ependymal cells bordering the organ towards the third ventricle.This study was supported in part by the Carlsberg Foundation     

Genetic aspects of the organization of legumin genes in pea

We have compared physical and genetic maps of the region around the legJ gene in pea. In this vicinity there are four B-type legumin genes, arranged as two close pairs. The detection of a recombination event within this gene cluster allows the orientation of this group of genes within the surrounding linkage group to be determined. The relationship between physical and genetic distances in this region is discussed, as are the implications of this for relating physical and genetic maps elsewhere in the pea genome.     

Flow threshold for enhanced phorbol ester binding in the ischemic gerbil brain

The correlation between regional phorbol ester binding and cerebral blood flow (CBF) was evaluated in the gerbil brain after 2-hour unilateral common carotid artery occlusion [³H]phorbol 12, 13-dibutyrate (PDBu) was used as a specific ligand for estimating the translocation of protein kinase C (PKC), and CBF was determined by the [¹⁴C]iodoantipyrine method. A quantitative autoradiographic method permitted concurrent measurement of these two parameters in the same brain. In the ischemia group of the animals, statistically significant, inverse correlations were noted between the CBF and PDBu binding in the hippocampus (CA₁ and CA₃ regions and dentate gyrus), the caudate-putamen and lateral nuclei of the thalamus. In these regions, the PDBu binding increased progressively as CBF fell below 35–40 ml/100 g/min. On the other hand, the PDBu binding in the cerebral cortices did not show any significant changes even when CBF was decreased to below 35 ml/100 g/min. The above data suggest that (1) the translocation of PKC to the cell membrane may be regionally specific in response to ischmia and may remain in the regions particularly vulnerable to ischemia such as the hippocampus, caudate-putamen and lateral nuclei of the thalamus in the early ischemic phase; (2) the threshold of CBF below which PKC begins to translocate to the cell membrane in the above regions, may be 35–40 ml/100 g/min in 2-hour ischemia.