Biomedical subjects

A Peter Bannister

Publications and source records attributed to A Peter Bannister.

5 recordsLinked to original sources

PubMed2006

Dynamic properties of excitatory synaptic connections involving layer 4 pyramidal cells in adult rat and cat neocortex.

To investigate the properties of excitatory connections between layer 4 pyramidal cells and whether these differed between rat and cat, paired intracellular recordings were made with biocytin filling in slices of adult neocortex. These connections were also compared with those from layer 4 spiny cells to layer 3 pyramids and connections between layer 3 pyramids. Connectivity ratios for layer 4 pyramid-pyramid pairs (1:14 cat, 1:18 rat) appeared lower than for the other types of connections studied in parallel, but excitatory postsynaptic potential (EPSP) amplitudes and time course were not significantly different either between species or across types of connection. Layer 4 pyramids targeted postsynaptic basal dendrites in both species, whether the pyramidal target was in layer 4 or layer 3. Within layer 4, relationships between mean EPSP amplitude, numbers of putative contacts, and distance between connected pairs indicated a rapid decline in connectivity strength with distance, equivalent to 3.4 mV and 10 synapses per 100 microm separation, from a maximum of 4 mV and 10 synapses at 0 microm. However, a subset, of burst-firing layer 4 pyramids, appeared to make no connections with other layer 4 spiny cells. Second EPSPs were depressed by 36% in rat and 28% in cat relative to first EPSPs at interspike intervals <15 ms. Subsequent EPSPs in brief trains were further depressed. Depression was predominantly presynaptic in origin. Recovery from depression could not be described adequately by a simple exponential for individual connections; it included peaks and troughs with periodicities of 10-15 ms. Complex relationships between the first 2 interspike intervals and third EPSP amplitude were also apparent in all connections so studied. Large third EPSPs followed specific combinations of first and second interspike intervals so that increasing, or decreasing, one without changing the other resulted in a smaller third EPSP. Finally, the outputs of layer 4 spiny cells to layer 3 exhibited partial recovery from depression during longer high-frequency trains, a property not apparent in the other connections studied.

Animals↗

PubMed2005

Inter- and intra-laminar connections of pyramidal cells in the neocortex.

The flow of excitation through cortical columns has long since been predicted by studying the axonal projection patterns of excitatory neurones situated within different laminae. In grossly simplified terms and assuming random connectivity, such studies predict that input from the thalamus terminates primarily in layer 4, is relayed 'forward' to layer 3, then to layers 5 and 6 from where the modified signal may exit the cortex. Projection patterns also indicate 'back' projections from layer 5 to 3 and layer 6 to 4. More recently it has become clear that the interconnections between these layers are not random; forward projections primarily contact specific pyramidal subclasses and intracortical back projections innervate interneurones. This indicates that presynaptic axons or postsynaptic dendrites are capable of selecting their synaptic partners and that this selectivity is layer dependent. For the past decade, we and others have studied pyramidal cell targeting in circuits both within, and between laminae using paired intracellular recordings with biocytin filling and have begun to identify further levels of selectivity through the preferential targeting of electrophysiologically and/or morphologically distinct pyramidal subtypes. Presented here, therefore, is a brief overview of current thinking on the layer and subclass specific connectivity of neocortical principle excitatory cells.

Animals↗

PubMed2003

Interlaminar connections in the neocortex.

This review summarizes the local circuit, interlaminar connections in adult mammalian neocortex. These were first demonstrated with anatomical techniques, which indicate some of the exquisite spatial precision present in the circuitry. Details, such as the class(es) of neurons targeted by some of these projections, have begun to be added in studies that combine paired/triple intracellular recordings with dye-filling of connected neurons. Clear patterns are emerging from these studies, with 'forward' projections from layer 4 to 3 and from 3 to 5 targeting both selected pyramidal cells and interneurons, while 'back' projections from layer 5 to 3 and from 3 to 4 target only interneurons. To place these data in a wider context, the major afferent inputs to and efferent outputs from each of the layers are discussed first.

Afferent Pathways↗

PubMed2002

Target and temporal pattern selection at neocortical synapses.

We attempt to summarize the properties of cortical synaptic connections and the precision with which they select their targets in the context of information processing in cortical circuits. High-frequency presynaptic bursts result in rapidly depressing responses at most inputs onto spiny cells and onto some interneurons. These 'phasic' connections detect novelty and changes in the firing rate, but report frequency of maintained activity poorly. By contrast, facilitating inputs to interneurons that target dendrites produce little or no response at low frequencies, but a facilitating-augmenting response to maintained firing. The neurons activated, the cells they in turn target and the properties of those synapses determine which parts of the circuit are recruited and in what temporal pattern. Inhibitory interneurons provide both temporal and spatial tuning. The 'forward' flow from layer-4 excitatory neurons to layer 3 and from 3 to 5 activates predominantly pyramids. 'Back' projections, from 3 to 4 and 5 to 3, do not activate excitatory cells, but target interneurons. Despite, therefore, an increasing complexity in the information integrated as it is processed through these layers, there is little 'contamination' by 'back' projections. That layer 6 acts both as a primary input layer feeding excitation 'forward' to excitatory cells in other layers and as a higher-order layer with more integrated response properties feeding inhibition to layer 4 is discussed.

Action Potentials↗

PubMed2002

Synaptic connections and small circuits involving excitatory and inhibitory neurons in layers 2-5 of adult rat and cat neocortex: triple intracellular recordings and biocytin labelling in vitro.

Dual and triple intracellular recordings with biocytin labelling in slices of adult neocortex explored small circuits of synaptically connected neurons. 679 paired recordings in rat and 319 in cat yielded 135 and 42 excitatory postsynaptic potentials (EPSPs) and 37 and 26 inhibitory postsynaptic potentials (IPSPs), respectively. Patterns of connectivity and synaptic properties were similar in the two species, although differences of scale and in the range of morphologies were observed. Excitatory 'forward' projections from layer 4 to 3, like those from layer 3 to 5, targeted pyramidal cells and a small proportion of interneurons, while excitatory 'back' projections from layer 3 to 4 selected interneurons, including parvalbumin immuno-positive basket cells. Layer 4 interneurons that inhibited layer 3 pyramidal cells included both basket cells and dendrite-targeting cells. Large interneurons, resembling cells previously described as large basket cells, in layers 4 and 3 (cat), with long myelinated horizontal axon collaterals received frequent excitatory inputs from both layers. A very high rate of connectivity was observed between pairs of interneurons, often with quite different morphologies, and the resultant IPSPs, like the EPSPs recorded in interneurons, were brief compared with those recorded in pyramidal and spiny stellate cells.

Animals↗