"We did this, when I was still at Harvard, in Venki Murthy's group, to overcome a problem that has limited olfactory circuit measurement in the past," says Florin Albeanu, Ph.D., a newly appointed assistant professor at CSHL who co-led the investigation. "Previously, we would have tried to insert electrodes into the olfactory bulb of the mouse. This is a bit like flying blind -- you can record the electrical activity of any cells you happen to hit, but you had no way of controlling which cells you would be recording from. Ashesh Dhawale, whom I met at a CSHL course on advanced imaging methods three years ago, and I decided to use light stimulation of the sensory neurons coupled with electrical recordings from the output neurons of the bulb to solve this problem."
The cells Albeanu, Dhawale and colleagues wanted to monitor are called mitral cells. These specialized cells are the final "broadcasting" stations for messages to the mouse's cortex that start out when neurons in the nasal epithelium sense an odor. Each sensory neuron is specialized to express a single molecular odor receptor type, from among some 1500 in a mouse's olfactory palette. Cells with the same sensitivity report their signals to a single specialized spherical unit -- literally a ball of synapses -- in the mouse's olfactory bulb. These collecting stations are called glomeruli.
The glomeruli each have about 15,000 axons feeding into them, and each, in turn, signals via primary dendrites to mitral cells. One glomerulus may be connected to as many as 30 mitral cells, all of which are also located in the olfactory bulb. Mitral cells also sport secondary dendrites, fibers which connect them laterally with one another via reciprocal synapses that link them to inhibitory local interneurons. By directly activating glomeruli in the olfactory bulb with tiny beams of light, the team was ab
|Contact: Peter Tarr|
Cold Spring Harbor Laboratory