Molecular organization of the visual thalamus...
			Extracellular recordings from a single neuron...

Encoding Social Signals in the Olfactory Bulb
Mice, like most other mammals, convey their identity, sex, and reproductive status to other mice through chemical signals in bodily secretions, such as urine. Most mammals have two distinct systems for detecting and responding to these chemical cues: the accessory olfactory system, which is specialized to detect nonvolatile chemicals, and the main olfactory system, which detects volatile signals. In previous work, we used a miniature head-mounted microdrive that allowed us to record the activity of single neurons in the accessory olfactory bulb (AOB) of male mice during social interactions. We discovered that the neurons in this brain region exhibit unique response properties. Individual neurons are very selective and are only activated when physical contact occurs between mice of a particular strain and sex. We did not find neurons that are activated by all males or all females. In addition to the excitatory responses, we discovered that the activity of many neurons is strongly inhibited by animals of specific sex and strain. As animals within a single inbred strain of mice are essentially genetically identical, these results imply that neurons in the AOB can discriminate between the pheromones present in genetically different animals, as well as males versus females. These recordings provided the first glimpse of how pheromonal information is represented in the mammalian brain.

While several reproductive behaviors in mice rely on the accessory olfactory system (see the abstract of Catherine Dulac [HHMI, Harvard University]), animals also use volatile cues detected by their main olfactory system during social interactions. Over the past year, we have used a combination of electrophysiology, gas chromatography, and chemical synthesis to investigate how social signals present in urine are represented in the main olfactory system. This has led to the discovery of a small region of the main olfactory bulb that responds to volatile cues emitted from urine. An astoundingly complex stimulus, urine comprises hundreds or even thousands of different volatile compounds. Remarkably, urine-responsive mitral cells (the principal neurons in the olfactory bulb) are activated by just a single one of these many compounds, indicating that these neurons act as exquisitely tuned feature detectors.