Dr. Colin McNamara

Dopaminergic cell firing

Light identified dopaminergic neuron action potential firing in a familiar and a novel environment

Left: Cross correlation with light pulse onset recorded after exploration of the familiar and novel environments. The peak in action potential firing at the onset of the light pulse shows the cell responds to activation by light hence the cell is highly likely a dopaminergic neuron. This is because light sensitive channels were genetically targeted to only express in dopaminergic neurons and the specificity of viral expression to dopaminergic cells was verified later.
Middle: Spike shape across the four channels of the tetrode for spikes recorded during exploration of the familiar environment in the absence of photostimulation, and (separately shown) spikes recorded at low latency (< 3 ms) to the onset of the laser pulse. Note how the shape of action potentials produced in response to the light pulse closely matches the shape produce by the cell’s spontaneous firing across all four channels of the tetrode. This is strong evidence that the recordings are due to the action potential firing of the same cell especially since the profile of the spike differed across the four channels of the tetrode.
Right: Path of the mouse over the first ten minutes of exploration in the familiar (ciculiar) and novel (rectangular) environments, with the location of the mouse at each spike occurrence superimposed. See how the cell fires more action potentials in the novel environment. Note the distance covered and hence average speed of the mouse were broadly similar between the two recordings.
Bottom: Raster plots of the cell action potential firing for the first five minutes during exploration in the familiar and novel environments. Note each row represents consecutive 30 second recordings from the same cell. See how with the increased firing there are many more times where action potentials follow in quick succession (highlighted in black). This will result in the neuron releasing significantly more dopamine onto postsynaptic target neurons.

mcnamara

Dr. Colin McNamara

Sir Henry Wellcome Postdoctoral Fellow

Colin McNamara graduated from the University of Limerick, Ireland, in 2006 with a B.Eng. (Hons.) in Computer Engineering. After graduation, Colin worked as a hardware and software development engineer for the high-performance signal processing integrated-circuit company Analog Devices. In 2011, he completed an M.Sc. in Neuroscience at the University of Oxford, which included two research projects; the first investigated dendritic spine morphology in hippocampal organotypic slice cultures (Emptage Group, Department of Pharmacology) and the second investigated pitch perception using multi-electrode extracellular recordings from ferret auditory cortex (King Group, Department of Physiology, Anatomy and Genetics). On completion of his M.Sc., Colin joined the Unit for his D.Phil. studies under the supervision of Dr David Dupret, and worked on a project focused on relating the midbrain dopaminergic system to hippocampal cell-assembly dynamics associated with spatial memory function. This project used large-scale extracellular recording combined with optogenetics. In 2015, Colin joined the Sharott Group as a Postdoctoral Neuroscientist and is investigating closed-loop Deep Brain Stimulation (DBS) approaches for the treatment of Parkinson’s disease.

Dopaminergic axons in the hippocampus

Dopaminergic axons in the hippocampus

Dopaminergic cells in the Ventral Tegmental Area (VTA)

Dopaminergic cells in the Ventral Tegmental Area (VTA)

Place cell action potential firing heat maps on the crossword maze

Place cell action potential firing heat maps on the crossword maze

Selected Publications
McNamara CG
Tejero-Cantero Á
Trouche S
Campo-Urriza N
Dupret D
2014.Nat. Neurosci., 17(12):1658-60.