Michael Menaker (May 19, 1934 – February 14, 2021), was an American chronobiology researcher, and was Commonwealth Professor of Biology at University of Virginia. His research focused on circadian rhythmicity of vertebrates, including contributing to an understanding of light input pathways on extra-retinal photoreceptors of non-mammalian vertebrates, discovering a mammalian mutation for circadian rhythmicity (tau mutation in golden hamsters), and locating a circadian oscillator in the pineal gland of bird. He wrote almost 200 scientific publications.
Early life and education
Menaker grew up in New York City and attended Swarthmore College.
After graduating from Swarthmore College in 1955 with a B.A. in biology, Menaker went on to Princeton University. In the lab of Colin Pittendrigh, the father of research on biological clocks, Menaker studied the endogenous circadian rhythm of bats (Myotis lucifugus).
He graduated from Princeton University with a Ph.D. in 1960, and continued postdoctoral studies in Donald Griffin's lab at Harvard University. As he continued to study bats, his interest shifted from circadian rhythms to hibernation patterns. When Menaker joined faculty at University of Texas at Austin in 1962, he transitioned to studying circadian rhythms in the house sparrow (Passer domesticus) and the golden hamster (Mesocricetus auratus).
Academic career
Menaker has held academic positions at the University of Texas, University of Oregon, and more recently, at University of Virginia, where he has been the Commonwealth Professor of Biology since 1987. He served as Chairman of the Biology Department at Virginia from 1987 to 1993. He has mentored several experts in the field of chronobiology, including Joseph Takahashi, Chair of the Neuroscience Department at University of Texas Southwestern Medical Center; Heidi Hamm, Chair of the Pharmacology Department at Vanderbilt University; and Carl Johnson Professor of Biological Sciences at Vanderbilt University. He has authored almost 200 papers and maintained grant funding to support his research for over 60 years.
Scientific work
Discovery of extra-retinal photoreceptor(s) in the house sparrow
In 1968, Menaker provided evidence for the existence of extra-retinal photoreceptors that were sufficient for photoentrainment by measuring rhythmic locomotor behavior as the output signal of the house sparrows (Passer domesticus) circadian clock. He demonstrated that photoentrainment could occur in the absence of optic neurons, evidence for the presence of an extra-retinal photoreceptor(s) coupled to the House Sparrow circadian clock. In this experiment, bilaterally enucleated house sparrows were exposed to an artificial light-dark cycle. They were kept in constant darkness to determine their free-running period and subsequently allowed to entrain to light cues. Locomotor activity was recorded through observing perching behavior of the sparrows. He tested three possible confounding variables for entrainment: (1) temperature fluctuation, (2) post-enucleation retinal fragments remaining in the eye, and (3) ectoparasites that might transfer light information through their movements in the birds' skin. To study the effects of temperature on circadian rhythms, Menaker exposed the enucleated sparrows to an electroluminescent panel. Menaker treated sparrows with Dry-Die, an anti-parasitic agent, to eliminate any possible effects of light transferring by ectoparasites. Since the sparrows did not entrain during tests of temperature fluctuation and the sparrows remained entrained 10 months after enucleation, a point at which any excess of the functional retina would have degraded, Menaker ruled out these possible confounding variables. Menaker's lab concluded the sparrows were able to entrain to environmental light cues. These results demonstrate that retinal light receptors are not necessary for photoentrainment, indicating there is an extra-retinal photoreceptor(s) contributing to circadian locomotor activity. Menaker's findings in enucleated sparrows were consistent with Aschoff's Rule, and he concluded that the retinae and the extra-retinal receptor(s) both contribute to the photoentrainment process.