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Results for “functional connectivity”

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At least 289 records · Page 16Linked to original sources
PubMed1997

Interneurons in area CA1 stratum radiatum and stratum oriens remain functionally connected to excitatory synaptic input in chronically epileptic animals.

Past work has demonstrated a reduction of stimulus-evoked inhibitory input to hippocampal CA1 pyramidal cells in chronic models of temporal lobe epilepsy (TLE). It has been postulated that this reduction in inhibition results from impaired excitation of inhibitory interneurons. In this report, we evaluate the connectivity of area CA1 interneurons to their excitatory afferents in hippocampal-parahippocampal slices obtained from a rat model of chronic TLE. Rats were made chronically epileptic by a period of continuous electrical stimulation of the hippocampus, which establishes an acute condition of self-sustained limbic status epilepticus (SSLSE). This period of SSLSE is followed by a development of chronic recurrent spontaneous limbic seizures that are associated with chronic neuropathological changes reminiscent of those encountered in human TLE. Under visual control, whole cell patch-clamp recordings of interneurons and pyramidal cells were obtained in area CA1 of slices taken from adult, chronically epileptic post-SSLSE rats. Neurons were activated by means of electrodes positioned in stratum radiatum. Intrinsic membrane properties, including resting membrane potential, action potential (AP) threshold, AP half-height width, and membrane impedance, were unchanged in interneurons from chronically epileptic (post-SSLSE) tissue compared with control tissue. Single stimuli delivered to stratum radiatum evoked depolarizing excitatory postsynaptic potentials and APs in interneurons, whereas paired-pulse stimulation evoked facilitation of the postsynaptic current (PSC) in both control and post-SSLSE tissue. No differences between interneurons in control versus post-SSLSE tissue could be found with respect to the mean stimulus intensity or mean stimulus duration needed to evoke an AP. A multiple linear regression analysis over a range of stimulus intensities demonstrated that a greater number of APs could be evoked in interneurons in post-SSLSE tissue compared with control tissue. Spontaneous PSCs were observed in area CA1 interneurons in both control and post-SSLSE tissue and were markedly attenuated by glutamatergic antagonists. In conclusion, our data suggest that stimulus-evoked and spontaneous excitatory synaptic input to area CA1 interneurons remains functional in an animal model of chronic temporal lobe epilepsy. These findings suggest, therefore, that the apparent decrease of polysynaptic inhibitory PSPs in CA1 pyramidal cells in epileptic tissue is not due to a deficit in excitatory transmission from Schaffer collaterals to interneurons in stratum radiatum and straum oriens.

Animals↗
PubMed2001

Anatomical and functional connections among cell groups in the gerbil brain that are activated with ejaculation.

Based on Fos expression, four areas of the gerbil brain are activated with ejaculation, i.e., the posterodorsal preoptic nucleus (PdPN), the lateral part of the posterodorsal medial amygdala (MeApd), the medial cell group of the sexually dimorphic preoptic area (medial SDA), and the parvicellular part of the subparafascicular thalamus (SPFp). The SPFp and medial SDA also express Fos earlier in the context of mating. To study connections among these areas, we injected one with FluoroGold and assessed the colocalization of FluoroGold and mating-induced Fos in the others. To determine if any of these areas activates the others, we lesioned one unilaterally and measured mating-induced Fos ipsilaterally and contralaterally in the others. Half of the SPFp cells projecting to the medial SDA, PdPN, and MeApd were activated with mating. SPFp lesions also decreased Fos expression in those areas. However, those areas do not project to the SPFp or affect its Fos expression with mating. Projections from the lateral MeApd to the medial SDA and PdPN, and from the medial SDA to the lateral MeApd, were also activated with mating, but lesions in these areas did not affect Fos expression in the others. Because 32-50% of the mating-activated cells in the SPFp participated in each SPFp projection identified, projections may have been identified for all of the mating-activated cells in the SPFp. In contrast, most of the mating-activated cells in the lateral MeApd, PdPN, and medial SDA do not participate in any projection studied, suggesting that they are either interneurons or project elsewhere.

Amygdala↗
PubMed1997

Functional connectivity of the transected brachial plexus after intercostal neurotization in monkeys.

Microsurgical reconstructions of brachial plexuses were performed on twelve monkeys by using ipsilateral intercostal nerves (T3-9). Reinnervation in individual nerves was evaluated monthly by observations of neuromuscular and electromyographic improvements. The electromyographic studies revealed reappearance of motor unit potentials. According to a motor scale ranging from 0 to 4, the mean muscle power 6 months after operation improved to 2.75 in the deltoid muscles, 2 in the biceps muscles, 1.22 in the triceps muscles, 1.13 in the flexor carpi radialis muscles, and 1.6 in the intrinsic muscles of the hands. Retrograde transport of horseradish peroxidase (HRP) from the neuromuscular junctions of the reconstructed musculocutaneous nerves 6 months after complete brachial plexus lesion in four animals demonstrated HRP-labeled neurons in the anterior horns, spinal ganglia and sympathetic ganglia of the thoracic spinal cords. It suggested that the regenerated afferent and efferent circuits in the thoracic cords innervating the transected brachial plexuses were able to generate the movements in the paralyzed upper limbs. However, as evidenced by the behavior patterns and the fact that retrograde-labeled neurons were all found in the thoracic cords, the novel movements observed in the reconstructed brachial plexuses were in synchrony with respiration. These results suggested that the plasticity of central neural networks is limited between two widely separated areas, such as between the midcervical and midthoracic motor cortical areas in the present studies, and therefore, the efforts to reconstruct neural networks, both centrally and peripherally, should aim at rebuilding situations as nearly to the original status as possible.

Animals↗
PubMed1981

The middle temporal visual area in the macaque: myeloarchitecture, connections, functional properties and topographic organization.

The location, topographic organization, and function of the middle temporal visual area (MT) in the macaque monkey was studied using anatomical and physiological techniques. MT is a small, elliptically shaped area on the posterior bank of the superior temporal sulcus which can be identified by its direct inputs from striate cortex and by its distinctive pattern of heavy myelination. Its average surface area is 33 mm2, which is less than 3% of the size of striate cortex. It contains a complete, topographically organized representation of the contralateral visual hemifield. There are substantial irregularities in the detailed pattern of topographic organization, however, and the representation is significantly more complex than that found for MT in other primates. Much of MT is devoted to the representation of central visual fields, with the emphasis on central vision being similar to that found in striate cortex. Electrophysiological recordings have confirmed previous reports of a high incidence of direction selective cells in MT. The transition in functional properties, from cells lacking direction selectivity outside MT to direction selective cells within, occurs over a distance of 0.1-0.2 mm or less along the lateral border of MT. Such a transition does not occur along the medial border, however, as the cortex medial to MT contains many cells with strong direction selectivity. Nevertheless, this region differs from MT in its myeloarchitecture, its lack of inputs from striate cortex, and the large size of its receptive fields. These results demonstrate the existence of three distinct visual areas on the posterior bank of the superior temporal sulcus which can be distinguished on the basis of both physiological and anatomical criteria.

Animals↗
PubMed2004

Nonlinear analysis of EEG during NREM sleep reveals changes in functional connectivity due to natural aging.

The spatial organization of nonlinear interactions between different brain regions during the first NREM sleep stage is investigated. This is achieved via consideration of four bipolar electrode derivations, Fp1F3, Fp2F4, O1P3, O2P4, which are used to compare anterior and posterior interhemispheric interactions and left and right intrahemispheric interactions. Nonlinear interdependence is detected via application of a previously written algorithm, along with appropriately generated surrogate data sets. It is now well understood that the output of neural systems does not scale linearly with inputs received and, thus, the study of nonlinear interactions in EEG is crucial. This approach also offers significant advantages over standard linear techniques, in that the strength, direction, and topography of the interdependencies can all be calculated and considered. Previous research has linked delta activity during the first NREM sleep stage to performance on frontally activating tasks during waking hours. We demonstrate that nonlinear mechanisms are the driving force behind this delta activity. Furthermore, evidence is presented to suggest that the aging brain calls upon the right parietal region to assist the pre-frontal cortex. This is highlighted by statistically significant differences in the rates of interdependencies between the left pre-frontal cortex and the right parietal region when comparing younger subjects (<23 years) with older subjects (>60 years). This assistance has been observed in brain-imaging studies of sleep-deprived young adults, suggesting that similar mechanisms may play a role in the event of healthy aging. Additionally, the contribution to the delta rhythm via nonlinear mechanisms is observed to be greater in older subjects.

Adult↗
PubMedDate not supplied

Statistical analysis of the functional connections between the neurons of the visual and motor cortex in different forms of conditioned reflex behavior.

The organization of interneuronal cortical connections was studied in experiments on cats with the development of delayed alimentary instrumental reflexes in response to light. The dynamics of the intra- and interstructural neuronal network at the level of the cortical projection (visual and motor) zones of the cat brain in three forms of behavior was revealed through a cross correlation analysis: the realization of the CR, in the intersignal period with the presence and absence of instrumental movements. The predominance of "informational" or "motivational" neuronal connections was observed depending upon the forms of the behavior.

Animals↗
PubMed1996

Genetic analysis of functional connectivity between substrate recognition domains of Escherichia coli glutaminyl-tRNA synthetase.

It has previously been shown that the single mutation E222K in glutaminyl-tRNA synthetase (GlnRS) confers a temperature-sensitive phenotype on Escherichia coli. Here we report the isolation of a pseudorevertant of this mutation, E222K/C171G, which was subsequently employed to investigate the role of these residues in substrate discrimination. The three-dimensional structure of the tRNA(Gln): GlnRS: ATP ternary complex revealed that both E222 and C171 are close to regions of the protein involved in interactions with both the acceptor stem and the 3' end of tRNA(Gln). The potential involvement of E222 and C171 in these interactions was confirmed by the observation that GlnRS-E222K was able to mischarge supF tRNA(Tyr) considerably more efficiently than the wild-type enzyme, whereas GlnRS-E222K/C171G could not. These differences in substrate specificity also extended to anticodon recognition, with the double mutant able to distinguish supE tRNA(CUA)(Gln) from tRNA2(Gln) considerably more efficiently than GlnRS E222K. Furthermore, GlnRS-E222K was found to have a 15-fold higher K(m) for glutamine than the wild-type enzyme, whereas the double mutant only showed a 7-fold increase. These results indicate that the C171G mutation improves both substrate discrimination and recognition at three domains in GlnRS-E222K, confirming recent proposals that there are extensive interactions between the active site and regions of the enzyme involved in tRNA binding.

Adenosine Triphosphate↗
PubMed2006

Quantifying functional connectivity: experimental assessment of boundary permeability for the natterjack toad (Bufo calamita).

Like other pond-breeding amphibians, the natterjack toad (Bufo calamita) typically presents a patchy distribution. Because the species experiences high probabilities of local population extinction, its persistence within landscapes relies on both local and landscape-scale processes [dispersal allowing the (re)colonization of habitat patches]. However, the structure and composition of the matrix surrounding local populations can alter the dispersal rates between populations. As shown previously (Landscape Ecol 19:829-842, 2004), the locomotor performances of individuals at the dispersal stage depend on the nature of the component crossed: some landscape components offer high resistance to movement (high resistance or high viscosity components) whereas others allow high efficiency of movement (low resistance components). We now examine the ability of individuals to discriminate between landscape components and select low-resistance components. Our experimental study investigates the ways in which young natterjack toads choose from among landscape components common to southern Belgium. Toadlets (the dispersal stage) were experimentally confronted with boundaries between surrogates of sandy soils, roads, forests, agricultural fields and intensive pastures. Our results show: 1 the ability of toadlets to react to boundaries between landscape components, 2 differences in permeability among boundaries, and 3 our inability to predict correctly the permeability of the boundaries from the patch-specific resistance assessed previously. Toadlets showed a preference for bare environments and forests, whereas they avoided the use of agricultural environments. This pattern could not be explained in terms of patch-specific resistance only, and is discussed in terms of mortality risks and resource availability in the various landscape components, with particular attention to repercussions on conservation strategies.

Animals↗
PubMed1988

Anatomical and functional connections of neurons of the rostral medullary raphe of the rabbit.

Single cell recordings were made from neurons in the rostral medullary raphe (RMR) of the rabbit. The recording sites were ones that had been shown to yield pressor responses from electrical stimulation and by pressure injections of glutamate. Electrical stimulation of the intermediolateral (IML) region of the spinal cord led to antidromic activation of 12 of the 100 cells studied. Eleven of these cells were located in raphe pallidus or raphe magnus, and one cell was located in raphe obscurus. These findings were consistent with the results of horseradish peroxidase (HRP) histochemistry experiments. Injections of HRP into the IML led to heavy cell body labeling in raphe pallidus and raphe magnus, but sparse labeling in raphe obscurus. Cells in the RMR could be orthodromically activated by electrical stimulation of the putative defense area of the periaqueductal (PAG) but not by stimulation of putative defense areas in the hypothalamus. Most of these cells were located in raphe pallidus or raphe magnus. Similarly, HRP injections into raphe pallidus and raphe magnus led to heavy cell body labeling in the PAG but not the hypothalamus; no cell body labeling was found in the PAG when injections were made into raphe obscurus.

Action Potentials↗