Extracellular Recordings Of Spontaneous Activity Research Articles

Functional and directed connectivity of the cortico-limbic network in mice in vivo

Higher cognitive processes and emotional regulation depend on densely interconnected telencephalic and limbic areas. Central structures of this cortico-limbic network are ventral hippocampus (vHC), medial prefrontal cortex (PFC), basolateral amygdala (BLA) and nucleus accumbens (NAC). Human and animal studies have revealed both anatomical and functional alterations in specific connections of this network in several psychiatric disorders. However, it is often not clear whether functional alterations within these densely interconnected brain areas are caused by modifications in the direct pathways, or alternatively through indirect interactions. We performed multi-site extracellular recordings of spontaneous activity in three different brain regions to study the functional connectivity in the BLA–NAC–PFC–vHC network of the lightly anesthetized mouse in vivo. We show that BLA, NAC, PFC and vHC are functionally connected in distinct frequency bands and determined the influence of a third brain region on this connectivity. In addition to describing mutual synchronicity, we determined the strength of functional connectivity for each region in the BLA–NAC–PFC–vHC network. We find a region-specificity in the strength of feedforward and feedback connections for each region in its interaction with other areas in the network. Our results provide insights into functional and directed connectivity in the cortico-limbic network of adult wild-type mice, which may be helpful to further elucidate the pathophysiological changes of this network in psychiatric disorders and to develop target-specific therapeutic interventions.

Effects of extremely low frequency magnetic fields on neuronal development of P19 embryonal carcinoma cells

AbstractModulation of pluripotent stem cell differentiation by several environmental factors, such as physical stimulation, is an important theme in tissue engineering. In this study, we report the effects of extremely low frequency magnetic field (ELF‐MF) exposure on the neuronal differentiation ability of P19 embryonal carcinoma cells (P19 cells). Here, the embryoid bodies (EBs) formed during the induction process were exposed to two types of ELF‐MFs (1 or 10 mT, 50 Hz, sinusoidal). After the induction process, the effects on the development of neuronal cells were evaluated by phase‐contrast image analysis, immunohistochemical staining (MAP2, GFAP), and the extracellular recording of spontaneous activity in which microelectrode arrays (MEAs) were used. Results show that MAP2 positive cells and spike frequencies increased by 10 mT ELF‐MF exposure, but the percentage of neurite outgrowth decreased at the early stages of differentiation. In contrast, clear differences were not seen in 1 mT ELF‐MF exposed cells. These results suggest that the neuronal differentiation and network properties were affected by 10 mT ELF‐MF exposure and that the intensity of the magnetic field was one of the important factors in the neuronal development of P19 cells. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Differences in in vitro cerebellar neuronal responses to hypoxia in eider ducks, chicken and rats

Ducks are well-known to be more tolerant to asphyxia than non-diving birds, but it is not known if their defences include enhanced neuronal hypoxia tolerance. To test this, we compared extracellular recordings of spontaneous activity in the Purkinje cell layer of 400 mum thick isolated cerebellar slices from eider ducks, chickens and rats, before, during and after 60 min hypoxia (95%N(2)-5%CO(2)) or chemical anoxia (hypoxia + 2 mM NaCN). Most slices rapidly lost activity in hypoxia, with or without recovery after rinse and return to normoxia (95%O(2)-5%CO(2)), but some maintained spontaneous activity throughout the insult. Proportions of 'surviving' (i.e. recovering or active) duck slices were significantly higher than for chickens in anoxia, and relative activity levels were higher for ducks than for chickens during hypoxia, anoxia and recovery. Survival of rat slices was significantly poorer than for birds under all conditions. Results suggest that (1) duck cerebellar neurons are intrinsically more hypoxia-tolerant than chicken neurons; (2) avian neurons are more hypoxia-tolerant than rat neurons, and (3) the enhanced hypoxic tolerance of duck neurons largely depended on efficient anaerobiosis since it mainly manifested itself in chemical anoxia. Mechanisms underlying the observed differences in neuronal hypoxic responses remain to be elucidated.

In vitro extracellular recording of spontaneous activity of the intergeniculate leaflet neurons

In the view of importance of intergeniculate leaflet in circadian rhythms processes and lack of information about electrophysiological properties of isolated intergeniculate leaflet (IGL) neurons, we carried out extracellular recordings of the spontaneous activity of rat IGL cells in vitro. Unlike other structures of visual thalamus, IGL neurons have the ability to generate a robust spontaneous neuronal activity when maintained in vitro. We have observed that in a standard incubation fluid IGL neurons display at least three distinct firing patterns: continuously irregular—with a wide variety of firing rates, tonic—with a very stable level of activity, and phasic (slow bursts)—with intermittent silent periods. Our study is the first electrophysiological demonstration of IGL neuronal activity in vitro.

Age-related alterations in noradrenergic input to the hippocampal formation: structural and functional studies in intraocular transplants

Intrinsic versus extrinsic determinants of age-related alterations in hippocampal noradrenergic transmission were investigated using intraocular allografts in rats. Three groups of animals were examined: young hippocampal transplants in young hosts, old transplants in old hosts and young transplants in old hosts. Postsynaptic sensitivity to noradrenaline (NA) was measured by extracellular recordings of spontaneous activity and superfusion with known concentrations of catecholamines in the anterior chamber of the eye. Hill plots demonstrated that the dose-response relationships of NA-induced depressions were linear and parallel in the 3 groups. Aged hippocampal grafts displayed a highly significant subsensitivity to NA of one order of magnitude. The EC 50 for this group was 203.1 μM as compared to 29.2 in young grafts. Young intraocular grafts in old hosts responded similarly to transplants in young hosts, with an EC 50 of 32.4 μM for the depressant actions of NA. Collaterals of the host iris sympathetic ground plexus invaded the hippocampal grafts. The density of this noradrenergic innervation was estimated by immunohistochemistry for tyrosine hydroxylase. A slightly increased density and fluorescence intensity of the noradrenergic fibers were observed in the old transplants as compared to the young transplants in young and old hosts. This was correlated with a significantly ( P < 0.01) increased content of NA in old transplants, as measured with high performance liquid chromatography. The old transplants also contained a large number of autofluorescent lipofuchsin granules, which were absent in the young transplants, regardless of the recipient age. Taken together, these results suggest the existence of alterations in pre- as well as postsynaptic noradrenergic mechanisms in the aging hippocampus. These changes were dependent on transplant age rather than host age, thus suggesting an involvement of intrinsic rather than extrinsic determinants in this model system.

Morphologic and functional abnormalities that develop in kitten purkinje neurons during maintenance for months after maturation in organotypic cultures

The morphologic and functional properties of the Purkinje cells (P-cells) grown for 10–11 weeks in organotypic cultures from newborn kitten cerebella were studied and compared to cultures which had been grown for 4–5 weeks under the same standard conditions. Electrophysiological and morphological data were obtained from HRP iontophoretically labeled neurons and were quantified by means of computerized techniques. Extracellular recordings of spontaneous activity showed that the 10–11-week-old P-cells had a pacemaker-like firing rate whereas the P-cells aged 4–5 weeks in vitro displayed a bursting activity. The qualitative morphological data evidenced abnormal swellings both on dendritic and axonal processes of the 10–11-week-old P-cells which were not present on the 4–5-week-old P-cells. The quantitative data revealed a significant decrease in the overall size of the dendritic network of the 10–11-week-old P-cells mainly due to a reduction in the total dendritic length and in the total number of dendritic segments, whereas the individual segment lengths remained almost unchanged. Dendritic spine counts showed no decrease in the dendritic density of these older P-cells. Such data suggest that the changes observed in 10–11-week-old cultured P-cells may be compared to the age-related changes occurring in vivo and that such in vitro models could be useful tools in the study of the pathology of aging. However, alternative factors other than senescence are discussed since they may account for some degenerative changes observed in the older cultured P-cells.