Knowledge as the reward
The mice, with antennae on their heads, acted as amateur radio operators. When they became thirsty, a light came on. The light also signaled to the scientist which neurons were communicating, and when. “These are the most rewarding moments”, recalls Zimmerman, visibly enthusiastic, “when, looking at the monitor, one suddenly understands something that one had been thinking about for a long time.”
Thanks to the work by Zimmerman’s team, it is now clear that these neurons inside the hypothalamus are flanked by two additional rapid sensory signals. The first signal encodes messages about the amount of drink – irrespective of whether it consisted of silicone oil or salt water. “This finding resulted in the question of where inside the body the nervous system identifies the actual nature of the drink”, says Zimmerman, explaining his thought process.
His team followed a hunch and also prepared the abdomens of the mice with catheters for infusions into the stomach. Lo and behold – they were right: the second signal receives its information from the intestines; it is able to discern whether the mouse had indeed been given water to drink and, if in doubt, also override the first signal (from the oral cavity) – in case the drink had been oil after all. Moreover, Zimmerman discovered that these two newly deciphered signals, which are transmitted from within the body, in fact act in an anticipatory manner, i.e., they predict the hydration level of the blood and are thus capable of prophylactically regulating thirst. This explains the fact that thirst is quenched after only a few gulps, even though it is not yet possible for the liquid to have reached the body’s metabolism.
Visible scientific pride
By now, Zimmerman’s discoveries have been incorporated into scientific textbooks. Put on the spot, he himself describes them as “groundbreaking”, his scientific pride audible. It is also visible – even though he must wear a mask throughout our Zoom interview. The mask does not bother him; handling pathogens in the laboratory on a daily basis, he is used to it. What is worse, though, is the fact that as soon as Christopher Zimmerman arrived at his new place of work at the Ivy League Princeton University in New Jersey, so did the coronavirus: all laboratories were closed, and most of the the mice had to be euthanized.
Scientist through and through – ambitious, meticulous and extremely organized – he continued to further his career despite the lockdown. He loves reading historical research literature as well as retracing the scientific questions of the time. He also acquired new skills which include the management of large datasets.
The American researcher considers his scientific life to be “extremely challenging mentally.” Taking a break from time to time and relaxing is practically a must. For him, this is best achieved in nature while hiking and climbing mountains with his wife, a fellow scientist. “She is an astronomer – that’s much cooler”, laughs Zimmerman.