Chapter 44, Problem 1Q

Summary Introduction

To review:

The effect of light (shown for 1 second) on the nerve cell membrane potential and on the rate of firing of the hypocretin (Hcrt) neurons, and the response of channelrhodopsin-2 (ChR2) protein to the light exposure.

Introduction:

The sleeping process involves interactions between anterior hypothalamus (sleep promoting region) and posterior hypothalamus (region responsible for wakefulness). Hypocretin is released from the lateral hypothalamus and plays an important role in wakefulness. The loss of Hcrt is related to narcolepsy.

The Hcrt cells are targeted genetically by ChR2 protein to deliver the light, deep inside the brain of freely moving mice. The photo stimulation of the brain awakes the sleeping mice.

Explanation of Solution

When the light is reflected on the Hcrt neurons, they get activated and fire an action potential. The Hcrt cells are genetically modified, created by the fusion of ChR2 proteins to the cells. On exposing the ChR2 expressing hcrt cells to the light, the ChR2 protein gets activated, which then leads to activation of these cells.

As Hcrt cells are involved in the wakefulness, the mice get awakened from the sleeping situation. A 1 second of light exposure is similar to the 1 Hertz (Hz) of light frequency. More latency is observed between the awakened and the sleeping states of mice when exposed to the light only for a second.

Conclusion

Thus, the membrane potential of the nerve cell changes on getting exposed to the light. The ChR2 expressing hypocretin neurons get activated because of photoactivation of the ChR2 protein, as a result, the hcrt neurons fire action potentials.