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H Schwegler

Publications and source records attributed to H Schwegler.

At least 37 records · Page 2Linked to original sources
PubMed1997

Coarse coding: calculation of the resolution achieved by a population of large receptive field neurons.

Electrophysiological studies in various sensory systems of different species show that many neurons involved in object localization have large receptive fields. This seems to contradict the high sensory resolution and the behavioral precision observed in localization experiments. Assuming a coarse coding mechanism, the resolution obtained by an ensemble of neurons is analytically calculated as a function of receptive field size. It is shown that particularly large receptive fields yield a high resolution.

Animals↗
PubMed1997

Dissociation of spatial reference memory, spatial working memory, and hippocampal mossy fiber distribution in two rat strains differing in emotionality.

Rats of the inbred strains DA/Han and BDE/Han were compared on two complex spatial learning tasks, a spatial reference memory task in a 16-unit multiple T-maze and a spatial working memory task in an eight-arm radial-maze. In addition, sizes of hippocampal mossy fiber terminal fields were measured. BDE rats showed marked superiority in multiple T-maze learning whereas DA rats outperformed BDE rats on the radial-maze task. DA rats had significantly larger intra- and infrapyramidal mossy fiber terminal fields (IIP-MF). This is consistent with findings from other studies suggesting that large IIP-MF are related to excellent spatial radial-maze learning, but it also indicates that size of IIP-MF is correlated with processing of a specific type of spatial information rather than with overall spatial abilities. BDE rats had more extended suprapyramidal mossy fiber projections (SP-MF) and a larger hilus. Rats of both strains differed in exploratory behaviour and emotionality: DA rats revealed little freezing and had a high rearing activity, whereas BDE rats showed frequent freezing and reared rarely. Results suggest that IIP-MF are involved with flexible expression of memory, updating environmental information and parallel processing whereas SP-MF might be linked to processing of familiar information. Presumably, emotional factors contribute to performance differences.

Animals↗
PubMed1997

The acoustic startle response in inbred Roman high- and low-avoidance rats.

To investigate the emotional reactions of two rat strains selectively bred for good and poor two-way avoidance acquisition (RHA/Verh and RLA/Verh), male animals of both strains were tested in an acoustic startle response test. They received 40 acoustic stimuli followed by 10 electric foot shocks and another 30 acoustic stimuli. RLA/Verh rats showed a significantly higher startle response compared to RHA/Verh animals, indicating a stronger emotional reaction to acoustic stimuli. In addition, the former showed a stronger response to foot shocks. Combined with earlier findings, we conclude that selection for two-way avoidance learning does not result in cognitive defects in the RLA/Verh strain but, rather, in stronger emotional reactions to fearful stimuli.

Acoustic Stimulation↗
PubMed1996

Genetic variation in the morphology of the septo-hippocampal cholinergic and GABAergic system in mice. I. Cholinergic and GABAergic markers.

In the present study, variations of cholinergic and GABAergic markers in the medial septum/vertical limb of the diagonal band of Broca (MS/vDB) and the hippocampus of eight different inbred mouse strains were investigated. By means of immunocytochemistry against the acetylcholine-synthesizing enzyme choline acetyltransferase (ChAT), the cholinergic neurons were visualized and the number of ChAT-positive neuronal profiles in the MS/vDB was counted. Cholinergic and GABAergic septo-hippocampal projection neurons were detected with a combined retrograde tracing and immunocytochemical approach. In order to quantify the cholinergic innervation of various hippocampal sub-regions, we estimated the density of acetylcholinesterase (AChE)-containing fibers as visualized by AChE histochemistry. Additionally, the densities of muscarinic receptors (mainly the subtypes M1 and M2) in different hippocampal areas of seven inbred strains were measured by means of quantitative receptor autoradiography. We found significant strain differences for the number of ChAT-positive neurons in the MS/vDB; in the numbers of cholinergic septo-hippocampal projection neurons; in the density of cholinergic fibers in hippocampal subfields CA3c, CA1, and in the dentate gyrus; and in the density of muscarinic receptors in the hippocampus. In contrast the GABAergic component of the septo-hippocampal projection did not differ between the strains investigated. The number of ChAT-reactive neurons in the MS/vDB was not correlated with either hippocampal cholinergic markers. This might be attributed to different collateralization of cholinergic neurons or to different projections of these neurons to other brain regions. These results show a strong hereditary variability within the septo-hippocampal cholinergic system in mice. In view of the role of the cholinergic system in learning and memory processes, strain differences in cholinergic markers might be helpful in explaining behavioral variation.

Animals↗
PubMed1996

Genetic variation in the morphology of the septo-hippocampal cholinergic and GABAergic systems in mice: II. Morpho-behavioral correlations.

We investigated the contribution of the septo-hippocampal cholinergic and GABAergic system to spatial and nonspatial aspects of learning and memory that had previously been found to correlate with the extent of the hippocampal intra- and infrapyramidal mossy fiber projection in different inbred mouse strains. The following cholinergic and GABAergic markers were measured in the septi and hippocampi of male mice: the number of cholinergic and parvalbumin-containing neurons in the medial septum/vertical limb of the diagonal band of Broca (MS/vDB), the number of septo-hippocampal cholinergic and GABAergic projection neurons, the density of cholinergic fibers in different hippocampal subfields, and the density of muscarinic receptors (predominantly M1 and M2) in the hippocampus. In addition, animals were behaviorally tested for spatially dependent and activity-dependent variables in a water maze and spatial and nonspatial working and reference memory in different experimental set-ups in an eight-arm radial maze. Using only those variables for which significant strain differences were obtained, we looked for covariations between behavior and neuroanatomy. The density of cholinergic fibers in the dentate gyrus was significantly correlated with activity-dependent learning in the water maze, whereas the number of septo-hippocampal cholinergic projection neurons correlated with spatial and, to a lesser extent, also with nonspatial aspects of radial maze learning. Only weak correlations were found between receptor densities and behavioral traits. From these data we conclude that variations in the septo-hippocampal cholinergic system, like variations in the mossy fiber projection, entail functional consequences for different types of maze learning in mice.

Acetylcholinesterase↗
PubMed1996

Paw preference and intra-/infrapyramidal mossy fibers in the hippocampus of the mouse.

The size of the intra-/infrapyramidal mossy fiber projections (IIP-MF) and their left/right asymmetry were assessed in 86 mice of either sex, including 26 animals from two mouse lines bred for strong or weak paw preference, 38 mice of a randomly bred F3 generation derived from an eight-way cross, and 22 mice with variably sized corpora callosa in which only the left hippocampus was measured. Prior to morphometry, all mice were tested for paw preference. In addition, we compared the strain means in paw preference as observed in nine inbred mouse strains with known differences in their IIP-MF distribution. Mice bred for strong paw preference had a 70% larger IIP-MF projection than weakly lateralized and dyscallosal mice; random-bred mice fell in-between the extremes. The individual scores of the strength of paw preference were positively correlated with the extent of the IIP-MF. Among the inbred strains, the extent of the IIP-MF was similarly correlated with the strength of paw preference. The acallosal mice showed a significant negative correlation between extent of the IIP-MF projection and test-retest reliability of paw use. The left-right asymmetry of the IIP-MF was significantly and positively correlated with the direction of paw preference in the entire sample. We conclude that size and asymmetry of the IIP-MF projection are some of the many factors influencing the direction of paw preference and its strength, albeit moderately. We hypothesize that mice with larger IIP-MF projections use a given paw more consistently, being perhaps more resistant to interferences, and that left-right asymmetries of the IIP-MF may bias and/or reinforce an initial choice of a paw. In addition, the data provide another example of correlations between IIP-MF variations and nonspatial behavior.

Animals↗
PubMed1996

Centromere and telomere movements during early meiotic prophase of mouse and man are associated with the onset of chromosome pairing.

The preconditions and early steps of meiotic chromosome pairing were studied by fluorescence in situ hybridization (FISH) with chromosome-specific DNA probes to mouse and human testis tissue sections. Premeiotic pairing of homologous chromosomes was not detected in spermatogonia of the two species. FISH with centromere- and telomere-specific DNA probes in combination with immunostaining (IS) of synaptonemal complex (SC) proteins to testis sections of prepuberal mice at days 4-12 post partum was performed to study sequentially the meiotic pairing process. Movements of centromeres and then telomeres to the nuclear envelope, and of telomeres along the nuclear envelope leading to the formation of a chromosomal bouquet were detected during mouse prophase. At the bouquet stage, pairing of a mouse chromosome-8-specific probe was observed. SC-IS and simultaneous telomere FISH revealed that axial element proteins appear as large aggregates in mouse meiocytes when telomeres are attached to the nuclear envelope. Axial element formation initiates during tight telomere clustering and transverse filament-IS indicated the initiation of synapsis during this stage. Comparison of telomere and centromere distribution patterns of mouse and human meiocytes revealed movements of centromeres and then telomeres to the nuclear envelope and subsequent bouquet formation as conserved motifs of the pairing process. Chromosome painting in human spermatogonia revealed compacted, largely mutually exclusive chromosome territories. The territories developed into long, thin threads at the onset of meiotic prophase. Based on these results a unified model of the pairing process is proposed.

Animals↗
PubMed1995

Transient postnatal thyroxine treatment leads to an increased number of cholinergic neurons in the medial septum and to a higher density of cholinergic fibers in hippocampal CA3 in rats.

Newborn male pups of Sprague-Dawley rats received daily injections of buffered L-thyroxine or saline during the first 12 days postnatally. At the age of 12 weeks, the number of immunocytochemically labeled cholinergic neuronal profiles in the medial septum/diagonal band (MS/vDB) was counted, and the density of acetylcholinesterase (AChE)-positive fibers in four hippocampal subregions was measured. Thyroxine-treated rats had more ChAT-positive neuronal profiles in the MS/vDB and a higher density of AChE-positive fibers in hippocampal CA3 as compared to controls. From this study it is concluded that transient postnatal hyperthyroidism leads to an increased cholinergic innervation of hippocampal CA3.

Animals↗
PubMed1995

Correlations between radial-maze learning and structural variations of septum and hippocampus in rodents.

Large, but non-pathological, individual differences in neuroanatomy of the brain exist in rodents, which have been shown to covary with behavioral traits. In the present review, we explore the relationship between variations in the extent of the intra- and infrapyramidal mossy fiber projection of the hippocampus and spatial and non-spatial learning capacities in mice and rats. Preliminary data concerning anatomical variation in the septo-hippocampal cholinergic system and its consequences for individual behavior are also presented. We conclude that the hippocampal intra- and infrapyramidal mossy fiber projection is intimately involved in the regulation of spatial, but not of non-spatial learning capabilities. Although lesion studies have shown that a well-functioning cholinergic system is a prerequisite for performance in spatial learning tasks, our preliminary data suggest that individual differences in the cholinergic system do not explain individual differences in learning.

Animals↗
PubMed1994

Cholinergic and GABAergic septo-hippocampal projection neurons in mice: a retrograde tracing study combined with double immunocytochemistry for choline acetyltransferase and parvalbumin.

The present experiments were directed to determine the proportions of the cholinergic and GABAergic septo-hippocampal projection neurons in NMRI mice. For the labeling of the septal neurons we used a double immunocytochemical method combined with retrograde transport of wheatgerm agglutinin apo-horseradish peroxidase-gold (WAHG) injected unilaterally into the hippocampus. Monoclonal antibodies against choline acetyltransferase (ChAT) and parvalbumin (PARV) were used as markers for cholinergic and GABAergic neurons in the medial septum/diagonal band complex (MS/DB). Both antibodies were visualized in the same section using the ABC detection system with diaminobenzidine and 4-chloro-1-naphtol as chromogens. Cholinergic and PARV-containing neurons are coexisting in the MS/DB. About 38% of all retrogradely labeled neurons were ChAT-positive whereas only 10% of all retrogradely labeled cells were immunostained for PARV. On the other hand, 40% of all ChAT-positive neurons and about 24% of all PARV-positive neurons were retrogradely labeled. No double immunolabeled neurons were detected. The proportion of GABAergic neurons may have been underestimated because immunostaining for PARV only labels a subpopulation of GABAergic neurons. The present results were compared with those of previous studies in rats. They may serve as a basis of further comparative studies in mice.

Animals↗
PubMed1994

Fluctuations in circulating cell numbers following chemotherapy or bone marrow transplant.

We study the effect of noise on the behaviour of a dynamic cell population model in which cell replication and maturation take place simultaneously. We assume that the maximum proliferative potential v fluctuates uniformly about a mean value of v, and show that a decrease in v and/or the input flux uin into the population can lead to an increase in the variance in the cellular efflux uf. We draw a qualitative correspondence between this behaviour and the commonly observed increase in the variance of circulating blood cell numbers following chemotherapy and radiotherapy, both of which lead to a decrease in v and uin, and bone marrow transplant which probably corresponds to a decrease in uin.

Blood Cells↗
PubMed1993

Covariations between hippocampal mossy fibres and working and reference memory in spatial and non-spatial radial maze tasks in mice.

Male mice from nine inbred mouse strains were tested at the age of 3 months in either a spatial or a non-spatial version of the radial maze. Only four out of eight arms contained food rewards, permitting simultaneous assessment of working and reference memory in both situations. Other animals from the same strains were processed histologically to estimate the strain-specific extents of the mossy fibre projections. No significant between-task correlations were obtained for either working or reference memory. However, measures of working and reference memory correlated with each other within tasks. This suggests that these concepts may perhaps not be validly used in the mouse. Large, positive correlations of the size of the intra- and infrapyramidal mossy fibre projection with both working and reference memory were obtained in the spatial radial maze task, but not in the non-spatial one. We conclude that heritable variations of the hippocampal intra- and infrapyramidal mossy fibre projection influence processes related to spatial learning capabilities in radial mazes.

Animals↗
PubMed1993

Are the fine-structural characteristics of mouse hippocampal mossy fiber synapses determined by the density of mossy fiber axons?

Heritable variation of mossy fiber synapses in hippocampal region CA3 was studied in the two inbred mouse strains C3H and CPB-K. Previous Timm studies had shown a larger mossy fiber projection in C3H mice. In contrast, synaptic boutons of CPB-K mice were larger in size and perimeter and were contacted by more dendritic spines than in C3H mice. These results point to an inverse relationship between the size of the mossy fiber projection and the number of spine synapses formed by an individual mossy fiber bouton. Thus, the fiber density of a projection may be crucial for the actual morphology of the synaptic contacts formed.

Animals↗
PubMed1993

Hippocampal morphology and spatially related behavior in Long-Evans and CFY rats.

Behavioral responses to novelty in an open field and spatial learning in a radial maze with four arms out of eight reinforced were tested in male and female CFY and Long-Evans rats. Subsequently, the sizes of the total hippocampi and of various hippocampal cell layers and terminal fields at the midseptotemporal level were measured in Timm-stained sections. No strain differences were found in the open field (except for defecation). In the radial maze, Long-Evans rats showed better spatial reference memory capabilities than rats of the CFY strain. The relative sizes of the intra- and infrapyramidal mossy fiber (IIP-MF) projections did not differ between the strains. Within the more variable CFY strain, a positive correlation between the size of the IIP-MF projection and radial maze performance was found. The absolute sizes of the entire hippocampi and all hippocampal layers at the midseptotemporal level were larger in the CFY strain. The size of the suprapyramidal mossy fiber projection was related to the number of granule cells and to the ratio between granule and CA3 pyramidal cells. In contrast, the size of the IIP-MF projection did not correlate with either of these variables. The results indicate that the size of the mossy fiber projection may be determined mainly by the available postsynaptic surface on the dendrites of CA3 pyramidal neurons. Furthermore, an increased number of granule cells and their larger projection to the apical dendrites of pyramidal neurons does not appear to result in physiological changes with behavioral consequences.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Hippocampal mossy fiber distribution does not correlate with two-way active avoidance performance in backcross lines derived from inbred mouse strains DBA/2 and C3H.

To elucidate the relation of genetically induced variations in two-way active avoidance performance and the extent of the hippocampal infra/intrapyramidal mossy fiber system (IIP-Mf) in inbred mouse strains DBA/2 (high performance, small IIP-Mf) and C3H (low performance, large IIP-Mf) we investigated a backcross line containing the DBA/2-derived genetic determinants for high avoidance performance in a C3H background. In the seventh backcross generation variations in performance analogous to the original strains were observed whereas the extent of mossy fibers was nearly homogeneous. This result suggests that both variables are determined by separate genetic factors at least in these strains and that differences in mossy fiber distribution are not an essential prerequisite for different active avoidance performance.

Afferent Pathways↗
PubMed1991

A genetic-correlational study of hippocampal structural variation and variation in exploratory activities of mice.

Our previous work provided evidence that hippocampal opioid peptides form an important neurochemical substrate underlying the gene-dependent exploratory behavior of mice. A prominent hippocampal opioid is dynorphin B, which resides in the mossy fibers exclusively. In order to seek support for causal relationships between dynorphinergic hippocampal mechanisms and exploration, a quantitative-genetic method was chosen. For this purpose, mice from the inbred strains C57BL/6, DBA/2, BLN, and CPB-K were used. Their hippocampal mossy fiber projections were visualized by means of immunohistochemistry, using a highly specific anti-dynorphin B antiserum. The additive-genetic correlations that were estimated suggest pleiotropic gene effects on locomotion, rearing-up, wall-leaning, and several intra- and infrapyramidal mossy fiber (iipMF) variables. Long iipMF, in particular, were found to be associated with high exploratory activity.

Animals↗
PubMed1991

Behavioural and neuroanatomical divergence between two sublines of C57BL/6J inbred mice.

Male mice of strains C57BL/6J and DBA/2J differ reproducibly in a number of behaviours displayed in an open-field. In particular, C57BL/6J mice show a higher rearing-up frequency than do DBA/2J animals. Recently, a marked drop occurred in the frequency with which this behaviour is displayed by the C57BL/6J//Nmg (N) subline, that has been separated from the original C57BL/6J line over 62 generations. Comparison of our animals with the C57BL/6J//Kun(K) subline, separated from the Jackson parent over at least 40 generations, showed a significant strain difference for rearing. Since both a positive additive-genetic correlation between rearing and the size of the intra- and infrapyramidal mossy fibre terminal field (iipMF) and a correlated response in the size of the iipMF to selection for rearing have been found previously, we expected to find smaller iipMF in N, as compared with K. After processing for Timm's stain, this predicted difference was indeed found. Skin grafting demonstrated that the two sublines were still completely histocompatible, excluding a possible genetic contamination of N. This provides very strong support for the hypothesis that both the behavioural and the neuroanatomical differences between these sublines are caused by a single spontaneous mutation in the N line and strengthens the idea of a functional relationship between the structural and the behavioural variable.

Animals↗