From Science, Aug 2008:
"Grueneberg Ganglion Cells Mediate Alarm Pheromone Detection in Mice
Julien Brechbühl, Magali Klaey, Marie-Christine Broillet*
Alarm pheromones (APs) are widely used throughout the plant and animal kingdoms. Species such as fish, insects, and mammals signal danger to conspecifics by releasing volatile alarm molecules. Thus far, neither the chemicals, their bodily source, nor the sensory system involved in their detection have been isolated or identified in mammals. We found that APs are recognized by the Grueneberg ganglion (GG), a recently discovered olfactory subsystem. We showed with electron microscopy that GG neurons bear primary cilia, with cell bodies ensheathed by glial cells. APs evoked calcium responses in GG neurons in vitro and induced freezing behavior in vivo, which completely disappeared when the GG degenerated after axotomy. We conclude that mice detect APs through the activation of olfactory GG neurons.
Department of Pharmacology and Toxicology, University of Lausanne, Bugnon 27, CH-1005 Lausanne, Switzerland."
Science, AAAS, Cambridge CB2 1LQ, UK
In 1973, Hans Grueneberg observed the presence of a structure at the tip of the rodent nose that, he thought, belonged to the Nervus terminalis. Recently, using transgenic techniques, several groups reported the rediscovery of this structure. They named this structure the Grueneberg ganglion in memory of the original work. However, the function of these cells remains a matter of controversy. Despite the lack of typical olfactory neuronal features, the ganglion was suggested to have some olfactory function, based on the expression of olfactory marker protein and on its neural connections to the olfactory bulb of the brain. Brechbühl et al. have now identified a function for the Grueneberg ganglion cells. A combination of anatomical, surgical, and behavioral techniques was used to suggest that the Grueneberg ganglion is involved in alarm pheromone detection.
J. Brechbühl, M. Klaey, M.-C. Broillet, Grueneberg ganglion cells mediate alarm pheromone detection in mice. Science 321, 1092-1095 (2008). [Abstract] [Full Text]
Citation: P. Stern, Sensing Alarm. Sci. Signal. 1, ec302 (2008).
It doesn't surprise me anymore that recent neuroscience that I happen to be interested in usually turns out to have come from Lausanne, Switzerland. It does surprise me a little that there have been some papers about this from earlier, so it isn't exactly fresh news.
What's interesting about this is that it used to be thought that there were only two systems, the vomernasal organ (vestigial in humans) and the regular olfactory pathways, or sense of smell. It seems there are actually these three, and that in humans, the Grueneberg ganglion is still with us. It makes sense to me that as humans evolved close social ties and the capacity to relate via language and visual cues, smell (in terms of signaling pheromones) would begin to be less essential to survival. Yet there is this system still existing in humans (it would seem) that can still "smell" and respond to "alarm". I can hardly wait to hear how this turns out, how it might tie in with those whose information base is the pondering of human relations. I can already see applications in my own work - maybe those with persistent pain have alarm bells in a constant uproar - maybe the olfactory bulbs at the other end of their Greuneberg ganglia are dysregulated, or not downregulable by them for some reason. Just a stray thought. In any case it behooves us as therapists to be able to downregulate our own alarm bells, as always, no matter which part of the brain they are to be found or which exteroceptive sense might contribute to them..
Here is some additional information:
1. Mammals emit smell to signal danger. Excerpt: "Cells in the Grueneberg ganglion use their own calcium to transmit the danger warning to the brain... Only warning pheromones could trigger the warning signal."
2. Short video entitled, Smelling Fear
3. Breer H. Fleischer J. Strotmann J; The sense of smell: multiple olfactory subsystems. Cellular & Molecular Life Sciences. 63(13):1465-75, 2006 Jul.
"The mammalian olfactory system is not uniformly organized but consists of several subsystems each of which probably serves distinct functions. Not only are the two major nasal chemosensory systems, the vomeronasal organ and the main olfactory epithelium, structurally and functionally separate entities, but the latter is further subcompartimentalized into overlapping expression zones and projection-related subzones. Moreover, the populations of 'OR37' neurons not only express a unique type of olfactory receptors but also are segregated in a cluster-like manner and generally project to only one receptor-specific glomerulus. The septal organ is an island of sensory epithelium on the nasal septum positioned at the nasoplatine duct; it is considered as a 'mini-nose' with dual function. A specific chemosensory function of the most recently discovered subsystem, the so-called Grueneberg ganglion, is based on the expression of olfactory marker protein and the axonal projections to defined glomeruli within the olfactory bulb. This complexity of distinct olfactory subsystems may be one of the features determining the enormous chemosensory capacity of the sense of smell."
4. Ma M. Encoding olfactory signals via multiple chemosensory systems. Critical Reviews in Biochemistry & Molecular Biology. 42(6):463-80, 2007 Nov-Dec.
"Most animals have evolved multiple olfactory systems to detect general odors as well as social cues. The sophistication and interaction of these systems permit precise detection of food, danger, and mates, all crucial elements for survival. In most mammals, the nose contains two well described chemosensory apparatuses (the main olfactory epithelium and the vomeronasal organ), each of which comprises several subtypes of sensory neurons expressing distinct receptors and signal transduction machineries. In many species (e.g., rodents), the nasal cavity also includes two spatially segregated clusters of neurons forming the septal organ of Masera and the Grueneberg ganglion. Results of recent studies suggest that these chemosensory systems perceive diverse but overlapping olfactory cues and that some neurons may even detect the pressure changes carried by the airflow. This review provides an update on how chemosensory neurons transduce chemical (and possibly mechanical) stimuli into electrical signals, and what information each system brings into the brain. Future investigation will focus on the specific ligands that each system detects with a behavioral context and the processing networks that each system involves in the brain. Such studies will lead to a better understanding of how the multiple olfactory systems, acting in concert, offer a complete representation of the chemical world."
Breer, H., Fleischer, J., Strotmann, J. (2006). Signaling in the Chemosensory Systems. Cellular and Molecular Life Sciences, 63(13), 1465-1475. DOI: 10.1007/s00018-006-6108-5