Me and the copperheads–or why we still don’t know if snakes secrete melatonin at night

It seems this is a week of venom here at the Guest Blog! First it was Rachel Nuwer on Monday who looked at the U.S. death statistics at the hands (Okay, fangs and stingers) of venomous animals. Then yesterday David Manly explained how snakes bite and how their venom evolved (and still evolves). So, I thought I should complete a trifecta, and tell you a brief story about my one and only close encounter with venomous snakes (also recounted in a very old post of mine).

For background, I did my graduate studies in the laboratory of Dr. Herbert Underwood studying circadian biology – how animals’ brains measure the time of day and time of year. Dr. Underwood is one of the pioneers in the field and has, over the years, done research on several species of lizards and birds. By the time I joined the lab, it has somewhat shifted in focus from a comparative breadth to a more focused depth of research on circadian physiology in Japanese quail.

While most of our work was done in quail, we were also allowed to make brief forays into studies of other species, including some colaborative work on turkeys, a small study on crayfish by me, and an interesting study on three species of geckos by my lab-mate Chris Steele. Chris came to our lab from a herpetology background, so I was not surprised when he suggested we team up with another colleague of ours, Jim Green who studied the evolution of snake venom, for a small study on snakes’ circadian rhythm in melatonin synthesis and secretion.

What is important to know is that melatonin is a hormone secreted by all vertebrates (and many invertebrates and even plants) only at night. The main place where melatonin is produced in vertebrates is the pineal gland. Apart from producing melatonin, the pineal of non-mammalian vertebrates (e.g., lampreys, fish, amphibians, reptiles and birds) is also a photosensitive organ – it detects the intensity of environmental light. Light is quite capable of penetrating through the skin and skull of animals and the pineal is located on the very top of the brain, often under a spot where the skull bone is thinner and more transparent.

Detection of light directly by the pineal entrains (synchronizes) the circadian clock to the light-dark changes of the environment. In many non-mammalian vertebrates, pineal is also the place where the circadian clock is located, thus it makes sense that it is directly sensitive to light. Rhythmic secretion of melatonin then synchronizes other body functions to the day-night cycles in the environment.

In mammals, there are no photoreceptors in the pineal. There is also no circadian clock in the pineal. It serves only as a melatonin source in mammals….and in snakes – at least according to anatomy. Snakes are the only non-mammalian vertebrates that have pineal glands that, under the microscope, look like they came from mammals.

What we wanted to do is to see if snakes have melatonin at all, and if so, if it shows a daily rhythm in concentration like it does in other Vertebrates (believe it or not, nobody’s done that yet). We wanted to see if snakes, like all other vertebrates, secrete melatonin only at night. And, as this was Jim Green’s research animal, the copperheads were the only snakes we had at our disposal (once the project was greenlighted by the Animal Care committee), about ten of them, each in its own terrarium in a tiny shed outside of campus.

We needed to take blood samples at noon (hypothesizing that we would not be able to detect any melatonin in the middle of the day) and, after a few days of recovery, again at midnight (testing the notion that the snake’s pineal secretes melatonin at night). So, we went in at noon one day. Jim would pick up a snake and hold it by its head. Chris was holding the body of the snake. Jim’s advisor Hal Heatwole was taking the blood samples straight from the heart, and I was the “nurse assistant” taking care of needles, syringes, anticoagulant, test-tubes, etc. The whole experiment, sampling blood from 10 snakes, took perhaps an hour or so and worked out perfectly without any glitches.

About a week later, when we came for a repeat session at midnight, we were starkly reminded that copperheads are nocturnal animals. They were active. And I mean ACTIVE! To avoid the acute, direct effect of light on stopping all melatonin synthesis and release, we had to take samples in the dark, aided only by a very dim red pen-light, with some highly uncooperative snakes. The process took hours!

At one point one of the snakes, a large male, got loose in the room and, since the room was essentially dark I could not see where it was underneath the cages. So I said, “OK, you snake guys figure out where it is and call me back once you have it under control,” and I slid out of the door. I got teased for this act of cowardice for years afterwards.

Unfortunately, the melatonin essay did not work and we did not have enough blood volume to try with a new kit, so the study was never completed. The snakes got used in other experiments, Jim finished and defended his thesis and left town and nobody else wanted to try to do a repeat of this experiment. I hope one day someone will. Perhaps with a non-venomous snake species for a change – makes midnight sampling much safer and easier!

Image from (now sadly defunct) Backyard Jungle.

References:

Kunkel, B. W., The paraphysis and pineal region of the garter snake, The Anatomical Record, Volume 9, Issue 8, pages 607–636, August 1915

Ralph, C. L., Evolution of Pineal Control of Endocrine Function in Lower Vertebrates. Amer. Zool. (1983) 23 (3): 597-605. doi: 10.1093/icb/23.3.597

Kalsow C. M., Greenhouse S. S., Gern W., Adamus G., Hargrave P. A., Lang L. S., Donoso L. A. Photoreceptor cell specific proteins of snake pineal. J Pineal Res. 1991 Sep;11(2):49-56.

Advertisements

Comments are closed.