SFN Poster Session: For Lovers of the Superior Colliculus

Most of my first afternoon at SFN was spent in the poster session, specifically hunting for posters regarding functionality in the superior colliculus, and its non-mammalian homolog the optic tectum. Since I work in this brain region, most of my attention has been focused on findings applicable to my own research. Without going too in depth into my own research and why I spend half an hour pondering the release of nicotine into the superficial layers of the pigeon optic tectum (thanks to Macarena Faures' poster), some brief thoughts on the posters: For aficionados of the region, there are several groups who have successfully expressed channelrhodopsin (or halorhodopsin) variants in axons of retinal ganglion cells, using this technique to selectively activate (or inactivate) visual activity into the superior colliculus. Most of the posters show the success of the expression, it seems that we will have to wait until next year for the results of any experiments made possible by these technological advances. One exception is a group that uses a channelrhodopsin variant expressed in a sub-population of retinal ganglion cells to show that connectivity between RGCs and the circuitry of the superior colliculus is in place before maturation of the retinal opsin system. It’s possible that these results are not surprising, given previous research showing that wiring of RGC axons in the superior colliculus is dependant on spontaneous RGC waves. (Someone more familiar with the temporal placement of retinal waves during development should feel free to correct me here).

To turn back to the Faures poster, out of the Marin group - their discussion brings up the possibility that the neurotransmitter identity of a particular brain region, Ipc, has been incorrectly identified. The Ipc is the avian homolog of the mammalian parabigeminal nucleus, and has been classically thought to be cholinergic, due mostly to the presence of ChAT immunoreactivity. However, recent research is apparently calling into question the assumption that the Ipc released acetylcholine - at least according to a researcher in the Marin group. I'm going to withhold my judgement (although I am deeply skeptical) and wait for the proof positive combination of recordings and histochemistry. But that the question is being posed in the first place is fascinating to me - if their concerns are valid, it will highlight the difficulty of exactly characterizing any brain area based on expression of particular proteins.

On a less scientific note: of general amusement has been watching as my PI strode through the poster session, ending up huddled with about 4 other PI's, hotly debating the function of the superior colliculus.