Layer-Specific Intracortical Amplification Shortens the Lifetime of Thalamocortical Repetition Suppression in Auditory Cortex

Neural adaptation in sensory cortex serves important sensory functions, and is altered by various neurophsychiatric diseases. Although adaptation is a widely studied phenomenon, much remains unknown about its underlying mechanisms on a cortical circuit level. Here, we investigated repetition suppression as fundamental aspect of adaptation by layer-specific current source density analyses of synaptic mass activities in primary auditory cortex of anesthetized Mongolian gerbils (Meriones unguiculatus). We disentangled different synaptic contributions to repetition suppression in different cortical layers, and separated thalamocortical from intracortical inputs by cortical silencing with GABAA-agonist muscimol. We systematically varied stimulus onset intervals and employed statistically robust model fitting based on bootstrapping to determine the full suppression kinetics of different synaptic responses in the steady state. Whereas thalamocortical input to granular and infragranular layers was governed by longer lasting repetition suppression, most likely reflecting depression of thalamocortical synapses, intracortical amplification in granular layers shortened the lifetime of suppression by re-enhancing granular responses mainly through synchronization of synaptic events. With increasing latency, the shorter lasting suppression kinetics observed in granular layers at early latencies (<100ms) passed on to deeper layers replacing the longer lasting infragranular suppression kinetics. Granular circuit dynamics can therefore actively shape neural adaptation across cortical layers.

Speech Sound Discrimination by Mongolian Gerbils

The present study establishes the Mongolian gerbil (Meriones unguiculatus) as a model for investigating the perception of human speech sounds. We report data on the discrimination of logatomes (CVCs - consonant-vowel-consonant combinations with outer consonants /b/, /d/, /s/ and /t/ and central vowels /a/, /aː/, /ɛ/, /eː/, /ɪ/, /iː/, /ɔ/, /oː/, /ʊ/ and /uː/, VCVs - vowel-consonant-vowel combinations with outer vowels /a/, /ɪ/ and /ʊ/ and central consonants /b/, /d/, /f/, /g/, /k/, /l/, /m/, /n/, /p/, /s/, /t/ and /v/) by young gerbils. Four young gerbils were trained to perform an oddball target detection paradigm in which they were required to discriminate a deviant CVC or VCV in a sequence of CVC or VCV standards, respectively. The experiments were performed with an ICRA-1 noise masker with speech-like spectral properties, and logatomes of multiple speakers were presented at various signal-to-noise ratios. Response latencies were measured to generate perceptual maps employing multidimensional scaling, which visualize the gerbils' internal representations of the sounds. The dimensions of the perceptual maps were correlated to multiple phonetic features of the speech sounds for evaluating which features of vowels and consonants are most important for the discrimination. The perceptual representation of vowels and consonants in gerbils was similar to that of humans, although gerbils needed higher signal-to-noise ratios for the discrimination of speech sounds than humans. The gerbils' discrimination of vowels depended on differences in the frequencies of the first and second formant determined by tongue height and position. Consonants were discriminated based on differences in combinations of their articulatory features. The similarities in the perception of logatomes by gerbils and humans renders the gerbil a suitable model for human speech sound discrimination.

Micro-CT Study of Mongolian Gerbil Humeral Bone After Prolonged Spaceflight Based on a New Algorithm for Delimitation of Long-Bone Regions

The Mongolian gerbil displays unique physiological and anatomical features that make this species an attractive object for biological experiments in space. However, until recently, the Mongolian gerbil has remained a novel, mostly unstudied animal model in investigating bone loss in weightlessness (G0). After 12 days of orbital Foton-M3 mission, the humerus of Mongolian gerbils has been studied here via micro-computed tomography (micro-CT) to quantify bone morphometric parameters. The samples from the flight group, delayed synchronous ground-control group, and basal control group were investigated, and main morphometric parameters were reported in the article. The accurate selection of a region of interest is an essential step for a correct assessment of bone parameters. We proposed a new, easy and efficient method for delimiting the bone’s basic regions in the humerus. It is based on quantitative estimation of X-ray attenuation in the cortical bone as a function of humerus bone length. The micro-CT analysis of the basic bone regions revealed a difference in bone morphometric parameters between the flight and control gerbils. The most significant bone loss was observed in the cortical part of the proximal humeral zone in the flight group. No statistically significant changes of volume fraction in the cancellous tissue of proximal and distal epiphyses and metaphyses were observed. A statistically significant increase in both cancellous bone volume and bone X-ray attenuation in the flight group was detected in the proximal part of the diaphyses. We assume that enhanced calcium deposition in the diaphyseal cancellous tissue occurred due to a bone response to G0 conditions.

Bioinformatics analysis of an animal model of diet-induced nonalcoholic fatty liver disease with rapid progression

Nonalcoholic fatty liver disease (NAFLD) develops rapidly in high-fat diet (HFD) fed Mongolian gerbil ( Meriones unguiculatus). Here, we aim to explore the gene expression characteristics of Mongolian gerbil to better understand the underlying mechanism in this animal model. Mongolian gerbils were fed with normal diet or HFD for different periods. High-throughput sequencing was carried out on the hepatic mRNA and bioinformatics analysis was further performed. Eight hub genes Cd44, App, Cdc42, Cd68, Cxcr4, Csf1r, Adgre1, and Fermt3, which were involved in inflammation, fibrosis, and HCC were obtained. Four significant independent poor prognostic factors for HCC (GPC1, ARPC1B, DAB2, and CFL1) were screened out. qRT-PCR result showed that the above genes expressed high levels in different periods of modeling process. The findings of this study provide useful information for further studies on Mongolian gerbil NAFLD model.

Cryptosporidium sciurinum n. sp. (Apicomplexa: Cryptosporidiidae) in Eurasian Red Squirrels (Sciurus vulgaris)

Cryptosporidium spp. are common protozoan pathogens in mammals. The diversity and biology of Cryptosporidium in tree squirrels are not well studied. A total of 258 Eurasian red squirrels (Sciurus vulgaris) from 25 and 15 locations in the Czech Republic and Slovakia, respectively, were examined for Cryptosporidium spp. oocysts and specific DNA at the SSU, actin, HSP70, TRAP-C1, COWP, and gp60 loci. Out of 26 positive animals, only juveniles (9/12) were microscopically positive (18,000 to 72,000 OPG), and molecular analyses revealed the presence of Cryptosporidium sp. ferret genotype in all specimens. Oocysts obtained from naturally-infected squirrels measured 5.54–5.22 μm and were not infectious for laboratory mice (BALB/c and SCID), Mongolian gerbils, Guinea pigs, Southern multimammate mice, chickens, or budgerigars. None of naturally infected squirrels showed clinical signs of disease. The frequency of occurrence of the ferret genotype in squirrels did not vary statistically based on host age, gender or country of capture. Phylogenetic analysis of sequences from six loci revealed that Cryptosporidium sp. ferret genotype is genetically distinct from the currently accepted Cryptosporidium species. Morphological and biological data from this and previous studies support the establishment of Cryptosporidium sp. ferret genotype as a new species, Cryptosporidium sciurinum n. sp.

Ecology and social behaviour of the Mongolian gerbil: a generalised review

The present review provides a compilation of the published data on the ecology and social behaviour of Mongolian gerbils. Behavioural observations in the wild show that the Mongolian gerbil is a diurnal social rodent living in extended family groups. Seasonal breeding is typical of Mongolian gerbils in their natural habitat. Social monogamy seems to be characteristic of the Mongolian gerbil reproductive strategy, which however does not exclude facultative polygyny and promiscuity. A typical feature of the space use system in this species is territoriality. Social relationships in family groups may be defined as a subordination hierarchy. The hierarchy order is primarily determined by the age of the animals and maintained chiefly by the subordinates’ behaviour patterns. The complex social organisation in the Mongolian gerbil is characterised by cooperation in different activities. Cooperation appears to enhance the survival of family groups of this species under the extreme climatic conditions of Central Asia.

Thalamocortical and intracortical contributions to stimulus-evoked and oscillatory activity in rodent primary auditory cortex

Intracortical, horizontal connections seem ideally suited to contribute to cortical processing by spreading information across cortical space and coordinating activity between distant cortical sites. In sensory systems experiments have implicated horizontal connections in the generation of receptive fields and have in turn led to computational models of receptive field generation that rely on the contribution of horizontal connections. Testing the contribution of horizontal connections at the mesoscopic level has been difficult due to the lack of a suitable method to observe the activity of intracortical horizontal connections. Here, we develop such a method based on the analysis of the relative residues of the cortical laminar current source density reconstructions. In the auditory cortex of Mongolian gerbils, the method is then tested by manipulating the contribution of horizontal connections by surgical dissection. Our results indicate that intracortical horizontal connections contribute to the frequency-tuning of mesoscopic cortical patches. Futhermore, we dissociated a type of cortical gamma oscillation based on horizontal connections between mesoscopic patches from gamma oscillations locally generated within mesoscopic patches. The data further imply that global and local coordination of activity during sensory stimulation occur in a low and high gamma frequency band, respectively. Taken together the present data demonstrate that intracortical horizontal connections play an important role in generating cortical feature tuning and coordinate neuronal oscillations across cortex.

Salicylate-Induced Changes in Hearing Thresholds in Mongolian Gerbils Are Correlated With Tinnitus Frequency but Not With Tinnitus Strength

Tinnitus is an auditory phantom percept without external sound sources. Despite the high prevalence and tinnitus-associated distress of affected patients, the pathophysiology of tinnitus remains largely unknown, making prevention and treatments difficult to develop. In order to elucidate the pathophysiology of tinnitus, animal models are used where tinnitus is induced either permanently by noise trauma or transiently by the application of salicylate. In a model of trauma-induced tinnitus, we have suggested a central origin of tinnitus-related development of neuronal hyperactivity based on stochastic resonance (SR). SR refers to the physiological phenomenon that weak subthreshold signals for given sensors (or synapses) can still be detected and transmitted if appropriate noise is added to the input of the sensor. The main objective of this study was to characterize the neurophysiological and behavioral effects during salicylate-induced tinnitus and compare these to the conditions within the trauma model. Our data show, in line with the pharmacokinetics, that hearing thresholds generally increase 2 h after salicylate injections. This increase was significantly stronger within the region of best hearing compared to other frequencies. Furthermore, animals showed behavioral signs of tinnitus during that time window and frequency range as assessed by gap prepulse inhibition of the acoustic startle reflex (GPIAS). In contrast to animals with noise trauma-induced tinnitus, salicylate-induced tinnitus animals showed no correlation between hearing thresholds and behavioral signs of tinnitus, indicating that the development of tinnitus after salicylate injection is not based on SR as proposed for the trauma model. In other words, salicylate-induced tinnitus and noise trauma-induced tinnitus are not based on the same neurophysiological mechanism.