Development of seizures in the Mongolian gerbil (Meriones unguiculatus).

Studied the frequency of occurrence of seizures in 102 male and 126 female Mongolian gerbils. Frequency was a function of age but not sex. Seizures lst appeared at 2 mo. of age, and at 6 mo. their frequency was still increasing. The trigger appeared to be increased, possibly stressful, stimulus input. Early stimulation in the form of weekly tests, from 1 wk. to 4 mo. of age, delayed appearance and sharply curtailed occurrence of seizures. Results were due not only to habituation but also to the early stimulation which has been shown to affect emotional reactivity and general arousal level. It is suggested that gerbils might provide an effective model for the study of epilepsy in humans. (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of cochlear function in the neonate Mongolian gerbil (Meriones unguiculatus).

Studied auditory sensitivity and changes of selected structures of the external, middle, and inner ear in 31 Mongolian gerbil neonates. Data demonstrate an improvement in sensitivity to sound associated with postnatal changes in the morphology of the ear. Cochlear potentials and a concomitant reflex response to sound were observed 14 days after birth. At this state of postnatal development the organ of Corti appeared mature, the external auditory canal was open, but mesenchyme was present within the tympanic bulla. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex difference in the control of scent-marking behavior in the Mongolian gerbil (Meriones unguiculatus).

Investigated the importance of the gonadal hormones in the control of the scent-marking behavior of 51 adult female Mongolian gerbils. Gonadectomy did not lead to the decrease in marking which had been expected from previous studies with males. The 2nd experiment was a longitudinal study of the development of scent marking in 36 female Ss. Ss were ovariectomized or given sham operations at 22 days of age. Gonadal hormones were not required for the development of marking. In both experiments morphological measures of the ventral sebaceous scent gland and the presence of the vaginal orifice were affected by gonadectomy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Population density and social, territorial, and physiological measures in the gerbil (Meriones unguiculatus).

Conducted 2 experiments with 80 male and 80 female Mongolian gerbils reared from weaning to adulthood in 4 same-sex and 4 mixed-sex density conditions. Ventral gland marking was greatly affected by density and less so by sex in both same-sex and mixed-sex groups. In same-sex but not mixed-sex groups crowding depressed several social interaction measures as well as body, ventral gland, and testis weights. In the mixed-sex groups, paired males and females had heaviest adrenal glands, ventral glands, and marking scores, as well as the highest reproductive rate. Mixed-sex crowding did not depress either social or physiological measures as much as did same-sex crowding. Effects of crowding are discussed in the framework of an information overload concept. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Embryonic and fetal hemopoiesis in the Mongolian gerbil (Meriones unguiculatus)

A study of the development of hemopoiesis in the Mongolian gerbil (Meriones unguiculatus) was conducted in order to determine the temporal sequence, the organs involved and the cytology of blood cell formation in this species. Hemopoiesis in the intrauterine life of the gerbil can be divided into four phases based on the site of blood cell formation: (1) the vitelline phase, (2) the hepatic phase, including thymic histogenesis, (3) the splenic phase and (4) the medullary phase, with the development of secondary lymphoid tissues. At the onset of each of these phases a blast-like cell was identifiable in each hemopoietic organ which, because of its morphology and its presumed multipotentiality was classified as a "lymphoid cell". In the yolk sac phase (gestational day 12) two generations of erythrocytes, a primitive and a definitive, are formed. The liver is by day 15 erythropoietic and megakaryopoietic, but later, a few granulocytes are also found in its extravascular compartment. The thymus is exclusively lymphopoietic from the appearance of its earliest cells on day 15. Splenic hemopoiesis is initiated with the presence of lymphoid cells (day 20) followed later by the appearance of morphologically identifiable blood cell lines. Early normoblastic and granulocytic activity begins in the marrow cavities on day 23, though the marrow is not considered to be a source of circulating blood cells during fetal life. Lymph node histogenesis occurs during the last four days of gestation, first in the cervical region and then in other parts of the body. The finding of undifferentiated lymphoid cells in all organs at the initiation of hemopoiesis and in the peripheral blood throughout gestation is discussed in light of the migratory theory of hemopoiesis.     

Functional organization of auditory cortex in the mongolian gerbil (Meriones unguiculatus). II. Tonotopic 2-deoxyglucose

The tonotopic organization of the auditory cortex in the Mongolian gerbil was mapped with 2-deoxyfluoro-D-glucose (2DG) using narrow-band frequency-modulated tones of different centre frequency (FM tones) and tones periodically alternating between two different frequencies (alternating tones) as stimuli. Continuous tone bursts of a constant frequency and repetition rate were used in initial experiments. Continuous tones produced 2DG patterns similar to those observed in animals that were not specifically stimulated. With tone bursts of constant frequency and repetition rate variable patterns were observed, some of which could be interpreted only in retrospect in the light of results obtained with FM tones and alternating tones. These stimuli, in contrast, produced differential metabolic responses which in conjunction with 2DG data from monaural animals and electrophysiological data made it possible to distinguish a primary auditory field AI with its dorsal region Ald, an anterior auditory field AAF, a ventral field V, a dorsoposterior field DP and a ventroposterior field VP, a dorsal field D, and in addition an anteroventral field AV. In the largest field (AI) and the smaller rostrally adjacent field AAF, frequency-specific dorsoventral bands of labelling (isofrequency contours) were mapped quantitatively. Bands shifted as a function of frequency relative to each other and to an independent spatial reference line in the lateral hippocampus. Spatial analysis of the single bands obtained with FM tones, and of the double bands obtained with alternating tones in both fields, revealed roughly mirror-imaged tonotopic maps of AI and AAF. In AI the progression from low to high frequencies was from caudal to rostral and in AAF the gradient was reversed, leading to a common high-frequency border of the two fields. In AI, the spatial resolution for frequencies below 16 kHz was in similar intervals per octave and higher for frequencies below 1 kHz. AI showed a somewhat higher spatial resolution for frequencies (at least below 1 kHz) as well as longer isofrequency contours than AAF. The 2-deoxyglucose patterns provided average tonotopic maps and topological data on various fields, as well as reliable landmarks in the gerbil's auditory cortex.     

Dopamine and the regulation of cell proliferation in gerbil (Meriones unguiculatus) pyloric mucosa

The epithelium of the digestive system mucosa consists of a highly dynamic cell population. The conditions under which mitotic activity in the gastrointestinal epithelium is regulated is as yet poorly understood. Nevertheless, it is assumed that some biogenic amines might be involved. Having demonstrated that dopaminergic cells occur in the stomach of gerbils (Meriones unguiculatus), in the present study we examined the influence of dopamine antagonist haloperidol on the proliferation of epithelial cells in the mucosa of the stomach. Proliferating cells were detected immunocytochemically and quantified after in-vivo labeling with 5-bromo-2'-desoxyuridine in both haloperidol- and saline-treated animals. The results show that acute doses of haloperidol significantly increases the proliferation rate in the pyloric mucosa, suggesting that dopamine plays a probable modulatory role in the regulation of mitotic activity. These findings are discussed with regard to the role of paraneurons in regulating epithelial mitosis.     

Response map properties of units in the dorsal cochlear nucleus of barbiturate-anesthetized gerbil (Meriones unguiculatus)

The response map scheme introduced by Evans and Nelson (1973) and modified by others, including Davis et al. (1996) for use with gerbils, has been used primarily for classifying units recorded in the cochlear nucleus of unanesthetized decerebrate preparations. Units lacking spontaneous activity (SpAc) have been classified as either type I/III or type II units based on the relative strength of their responses to broad-band noise compared to their responses to best-frequency (BF) tones. The relative noise index (rho), a ratio of these responses after SpAc is subtracted out, provides a convenient measure of this relative strength. In this paper, responses of 320 units recorded in the dorsal cochlear nucleus (DCN) of barbiturate-anesthetized gerbils to short-duration BF tones and broad-band noise were recorded. Since 87.5% of these units lacked SpAc, their response maps resembled those of type II and type I/III units. Units were characterized by rho and the normalized slope (m) of a best line fit to the BF rate versus level plot starting from the sound level corresponding to the first inflection point of the rate curve (typically its maximum value or the start of its sloping saturation). The distributions of rho and m values do not form distinct clusters as they do for units in the decerebrate preparation. Thus, the criteria developed for classifying DCN units in the decerebrate preparation do not appear appropriate for units in the barbiturate-anesthetized preparation. Deposits of horseradish peroxidase were used to locate 52 units. Most of the low SpAc units, 56% with poor noise responses (5/9) and nearly 70% with strong noise responses (25/36), and nearly all of the high SpAc units (6/7), were located either within or below the fusiform cell layer.     

Effects of olfactory bulbectomy and peripheral deafferentation on reactions to crowding in gerbils (Meriones unguiculatus).

Conducted tests of 90 male weanling Mongolian gerbils which sustained either olfactory bulbectomies, surgical ablation of olfactory receptors, or sham operations, and lived in 1 of several density conditions for 2 mo. Differential density conditions significantly affected only sham Ss. All anosmic Ss showed deficiencies in social-interaction tests. Only bulbectomized crowded Ss showed extreme aggression in the home cage. Olfaction is shown to be an important factor mediating deleterious effects of crowding. However, since the presence of the bulbs in receptor-ablated Ss was sufficient to control home-cage aggression, that displayed by bulbectomized crowded Ss cannot be attributed to mere anosmia but rather to loss of a nonolfactory, limbic function of the bulbs. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Morphometric studies on the effects of dehydration on the renin-immunopositive cells in the kidney of the Mongolian gerbil (Meriones unguiculatus)

Labeling of mitochondrial F1-ATPase with 8-azido-ATP or 8-azido-ADP under turnover conditions with Mg(2+)-ATP resulted in the identification of one exchangeable non-catalytic site whose occupation with a ligand does not influence the ATPase activity of F1 when measured at Vmax. With 8-azido-ADP two exchangeable non-catalytic sites could be labeled, but at one of them the bound ligand exchanges, at least partly, during the illumination under turnover conditions. After labeling an exchangeable non-catalytic site under turnover conditions with 8-azido-ATP or with 8-azido-ADP, F1-ATPase kept the ability to bind NAP3-2N3ADP at the slowly exchangeable noncatalytic site, thereby inhibiting the ATPase activity by 45%, as recently described (Edel et al. (1992) Biochim. Biophys. Acta 1101, 329-338). Covalent modification of the low-affinity non-catalytic site with 8-nitreno-AT(D)P increased the Km of ATP and abolished the negative cooperativity of ATP hydrolysis. This site can therefore be marked as a regulatory site, whose occupation with a nucleotide decreases the affinity of the catalytic sites for ATP.     

Associations between the discriminative stimulus and the reinforcer in instrumental learning.

In three experiments we examined whether reinforcement of a response in the presence of a discriminative stimulus (S{d}) resulted in associations between the S{d} and the reinforcer. In Experiments 1 and 2, animals were given food pellets contingent on responding in the presence of one S{d}, and sucrose contingent on responding in the presence of a different S{d}. Next, they were trained to make two new instrumental responses, one reinforced with pellets and one with sucrose. Finally, those responses were tested in the presence of S{d}s. The presence of S{d}-reinforcer associations was inferred from the preferential enhancement of the S{d} of performance of the instrumental response trained with the same reinforcer. In Experiment 3 we compared the transfer obtained with an S{d} and a Pavlovian excitor (CS+). Both stimuli showed preferential transfer on the basis of reinforcer identity, but the level of enhancement was lower for the CS+. These results show that the S{d} provides information about the identity of the reinforcer earned by a response in the normal course of instrumental learning. Several ways in which that knowledge might be encoded are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Laboratory studies of antipredator behavior in the Mongolian gerbil (Meriones unguiculatus): factors affecting response attenuation with repeated presentations

A series of experiments was conducted to study the properties of the attenuation of responding to repeated presentation of overhead visual transients in the gerbil (Meriones unguiculatus). Results suggest that this attenuation consists of habituation to the repeated association of a potentially threatening sensory stimulus with an increasingly familiar spatial context. The results of these experiments further suggest that the likelihood of eliciting fleeing is a conjoint function of the degree of risk posed by an overhead sensory transient and the degree of safety that is to be gained by fleeing. Results are discussed in the context of the ecology of predator recognition and the structural organization of the rodent visual system.     

Prefrontal control of trace versus delay eyeblink conditioning: Role of the unconditioned stimulus in rabbits (Oryctolagus cuniculus).

The conditioned eyeblink (EB) response was studied with trace conditioning procedures in rabbits (Oryctolagus cuniculus) with lesions to the medial prefrontal cortex (mPFC) or sham lesions. Three experiments were performed in which either periorbital shock or a corneal airpuff served as the unconditioned stimulus (US) in separate groups of sham or mPFC-lesioned rabbits. Acquisition of the EB conditioned response (CR) was faster and reached a higher asymptote with the eyeshock US than with the airpuff US. However, mPFC lesion-induced trace conditioning deficits were obtained only in the groups that received the airpuff US. All rabbits showed normal delay conditioning and extinction. These results suggest that mPFC mediates trace EB conditioning when emotional arousal is low. However, in circumstances when emotional arousal may be high (i.e., during exposure to aversive periorbital shock), other structures (such as amygdala) may be activated to permit learning even in the absence of input from mPFC. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Passive avoidance learning in the earthworm (Lumbricus terrestris).

7 earthworms learned rapid approach to an earth goal at the end of a straight runway in 20 trials. Significant inhibition of approach occurred in 1 trial with aversive stimulation (saline goal). After 5 saline trials, readaptation to earth resulted in significant decreases in runway-approach time. A replication (69 Ss indicated that passive avoidance could be retained for 24 hr but not over 240 hr. Demonstration of 1-trial learning may be accounted for by the selection of salient stimuli that are particularly relevant in a cue-to-consequence relationship. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chemical sympathectomy and two-way escape and avoidance learning in the rat.

Reports 6 studies with male hooded Wistar rats on the effects of 2,4,5-trihydroxyphenylethylamine (6-hydroxydopamine) on 2-way escape and avoidance learning. Ss were tested on either escape or avoidance learning at 80 days of age after chemical sympathectomy at birth or 40 or 80 days of age. Neonatal and chronic sympathectomy (at 40 days), but not acute sympathectomy (at 80 days), resulted in depressed escape learning. Avoidance learning was affected by neonatal sympathectomy and partially by acute sympathectomy. Results have implications for the role of the autonomic nervous system in escape-avoidance learning. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Periodicity coding in the primary auditory cortex of the Mongolian gerbil (Meriones unguiculatus): two different coding strategies for pitch and rhythm?

Periodic envelope or amplitude modulations (AM) with periodicities up to several thousand Hertz are characteristic for many natural sounds. Throughout the auditory pathway, signal periodicity is evident in neuronal discharges phase-locked to the envelope. In contrast to lower levels of the auditory pathway, cortical neurons do not phase-lock to periodicities above about 100 Hz. Therefore, we investigated alternative coding strategies for high envelope periodicities at the cortical level. Neuronal responses in the primary auditory cortex (AI) of gerbils to tones and AM were analysed. Two groups of stimuli were tested: (1) AM with a carrier frequency set to the unit's best frequency evoked phase-locked responses which were confined to low modulation frequencies (fms) up to about 100 Hz, and (2) AM with a spectrum completely outside the unit's frequency-response range evoked completely different responses that never showed phase-locking but a rate-tuning to high fms (50 to about 3000 Hz). In contrast to the phase-locked responses, the best fms determined from these latter responses appeared to be topographically distributed, reflecting a periodotopic organization in the AI. Implications of these results for the cortical representation of the perceptual qualities rhythm, roughness and pitch are discussed.     

In utero cocaine, discriminative avoidance learning with low-salient stimuli and learning-related neuronal activity in rabbits (Oryctolagus cuniculus).

Daily injections of cocaine administered to pregnant rabbits (Oryctolagus cuniculus) throughout gestation were associated with neural and behavioral changes during development and in adulthood, including altered neuron structure and function in areas receiving dopaminergic projections and retarded Pavlovian eyeblink conditioning with low-salient conditional stimuli. Studies of discriminative avoidance learning have shown changes in learning-related cingulothalamic neuronal activity, but no behavioral learning impairment in cocaine-exposed offspring. Here, low-salient stimuli were used during discriminative avoidance conditioning. Impairments early in behavioral acquisition were found, as well as alterations of anterior cingulate and medial prefrontal cortical, medial dorsal thalamic, and amygdalar neuronal response profiles and learning-related neuronal activity. These results elucidate the neural processes, impaired by prenatal cocaine, that support conditioning with low-salient stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal modulation of cingulo-thalamic neuronal activity and discriminative avoidance learning in rabbits

Two experiments assessed the effects of 1) combined subicular complex and posterior cingulate cortical lesions on training-induced neuronal activity (TIA) in the anterior ventral (AV) and medial dorsal (MD) thalamic nuclei; 2) hippocampal (Ammon's horn and dentate gyrus) lesions on TIA in cingulate cortex and in the AV and MD thalamic nuclei. The rabbits acquired a conditioned avoidance response (CR), stepping in an activity wheel upon hearing a 0.5-s tone (CS+), in order to prevent a foot-shock scheduled 5 s after tone onset. No response was required after a different, safety-predictive tone (CS-). In experiment 1 the combined subicular and cingulate cortical lesions enhanced thalamic TIA during acquisition and increased CR incidence in the first session of acquisition. These results confirmed the hypothesis that subicular and cingulate cortical efferents are not essential for thalamic TIA or for avoidance learning. Hippocampal lesions (experiment 2) also enhanced thalamic TIA. However, unlike subicular lesions, hippocampal lesions enhanced posterior cingulate cortical TIA as well, especially during extinction training. Hippocampal lesions did not affect CR performance. The results suggested that subicular excitatory efferents are responsible for incrementing cingulate cortical TIA, which is viewed as subserving associative attention. Activity from hippocampus downregulates the cue-elicited neuronal activity of the cingulo-thalamic circuits by suppressing the excitatory influence of the subiculum. The hippocampal influence reduces cingulo-thalamic cue-elicited activation in particular circumstances, such as the onset of CR extinction, when an expected reinforcer is omitted.     

Organization of escape movements from overhead threats in the Mongolian gerbil (Meriones unguiculatus).

Mongolian gerbils were presented with overhead visual stimuli in different environmental situations. The organization of escape movements was investigated with video-based image analysis methods. In Exp 1, gerbils in an open field established a home base and organized their escape trajectories with reference to both the home base and the location of the stimulus. In Exp 2, gerbils were provided pairs of refuges. They used these refuges as home bases and organized their responses with reference to the home base. In Exp 3, pairs of gerbils were tested in a field with refuges. Gerbils organized their escape movements with reference to their distance to the home base in relation to the distance of the other member of the pair to the home base. The results of these experiments suggest that escape movements in gerbils can be characterized as orienting to safety rather than to fleeing from risk. (PsycINFO Database Record (c) 2010 APA, all rights reserved)