Welsh and colleagues (1995) removed neurons from the suprachiasmatic nuclei (SCN) of a newborn rat and grew them in a tissue culture. They then added tetrodotoxin, a chemical that prevents action potentials that require sodium ions. When the tetrodotoxin was washed out of the cells,
A) the firing rhythm reappeared, but the phase was disrupted by the 2.5 day application of tetrodotoxin.
B) the firing rhythm reappeared, with a phase predicted by the initial cycles.
C) the neurons failed to resume their original spontaneous rhythm in the rate of their firing.
D) the researchers found that the cells had died.

Question

Quizplus · Accepted Answer

The firing rhythm of neurons from the suprachiasmatic nuclei (SCN) is intrinsic and can persist in isolation from the rest of the brain. When Welsh and colleagues removed these neurons and treated them with tetrodotoxin, which blocks action potentials, and then washed it out, the neurons resumed their firing rhythm. This demonstrates the resilience and autonomy of the SCN's circadian rhythm-generating mechanism, which can maintain its phase even after being temporarily halted.

Welsh and Colleagues (1995) Removed Neurons from the Suprachiasmatic Nuclei