| Summary: | 碩士 === 國立清華大學 === 分子醫學研究所 === 97 === For crayfish (Procambarus clarkii), the brain is not necessary for some specific behaviors elicited by certain external stimuli. How do the neural network coordinate and/or integrate with two stimuli which evoke incompatible behaviors? In this study, we will investigate the possible regulatory mechanism by examining the incompatible behaviors elicited by light and touch .
Crayfish walks backward when abruptly exposed to light but moves forward when its tail fan is stimulated by mechanical stimulation. Based on our observation, if light and touch were given simultaneously, crayfishes usually moved forward, which is in line with the behavior caused by simply touching the tail fan.
Crayfish still have photonegative behavior while deprived of vision. Its photosensitivity comes from a pair of caudal photoreceptors (CPR). The light sensor of CPR is at the last abdominal ganglion. CPR will produce high-frequency impulses when suddenly exposed to light in the dark and then lead the crayfish to walk backward to the shadow. The backward walking is usually accompanied by the abdominal and tail flexion. CPR will also be regulated by mechanoreceptor neuron (MRN), which senses mechanical stimulation such as water flow and touch.
We measure the spike rates by the electrophysiological technique. Our results supported that the mechanical stimulation on the tail fan can inhibit the high-frequency impulses evoked by CPR via MRN. It implies that mechanical stimulation on the tail suppresses the CPR-induced backward walking by MRN inhibiting CPR.
Another research suggested that MRN could regulate the spike rates of CPR by acetylcholine. Activating nicotinic and muscarinic acetylcholine receptors could also depress the light-evoked high frequency impulses of CPR.
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