The other day I found an article that seemed all too perfect. Development. Neurology. Zebrafish. For those of you who don’t know, these little fishies are not only PZ’s specialty but are also currently taking over our lab (You will be missed, fishies in tank #3).
In zebrafish, the sleep-wake cycle is regulated by hypocretin neurons (HCRT). These neurons also play a major role in mammals as well and if damaged can lead to narcolepsy. The researchers labeled these neurons in zebrafish with a presynaptic marker synaptophysin (SYP) attached to a fluorescent dye. Now the researchers can look at activity across the span of a day to visually quantify changes in baseline function or artificially produced by various conditions (e.g. sleep deprivation). So, they irritated fish for several hours after normal sleeping time until the fish were nice and sleep deprived.
The sleep deprived fish showed homeostatic influences on the number of HCRT synapses. Why is this important? The fish showed that upon sleep deprivation more synapse terminals were created to maintain cellular balance. Yet, simultaneously, the natural circadian rhythm began to decrease the number of synapses from the point of initial sleep deprivation. Homeostatic effects are estimated to be a mere 17% and this result appears only after six hours of deprivation. Essentially, as the day wears on the brain winds up more and more. The circadian rhythm counteracts this by gradually resetting the system back to baseline. A portion of this study showed that as the system tries to reset, sleep deprivation will weakly offset efficacy leading to impairment in memory retainment (and overall cranky fish).
*Professor, I would have gotten that question right but the course workload created homeostatic effects which led to faulty memory retainment!*