For this month’s journal club, I presented two papers ‘A possible pathway connecting the photosensitive pineal eye to the swimming central pattern generator in young Xenopus laevis tadpoles’ (1999) and ‘Responses of young Xenopus laevis tadpoles to light dimming: possible roles for the pineal eye’ (2000) both by Jamieson and Roberts.
A decrease in light intensity leads to excitation of the pineal eye which causes swimming to occur. With the use of anatomical, behavioural and physiological experiments, the authors were able to characterise this neural pathway and define its behavioural significance.
When light intensity decreases, diencephalic/mesencephalic descending (D/MD) neurons found in the midbrain, excited by pineal ganglion cells via glutamatergic synapses, project to the hindbrain and/or spinal cord to initiate swimming. Behaviourally, this leads directly to upward turns in free-swimming tadpoles, whereby, maintained activity in the pineal ganglion cells provides continuous excitatory input to the nervous system. This increases the probability of upwards swimming initiated by touch in tadpoles under low light conditions, thus, when the tadpole is disturbed by a predator, the response appears to be appropriate for escape.
Given the importance of the midbrain in survival, my project will focus on characterising the midbrain circuitry to give insight on the role it plays in mediating behaviour in the young Xenopus laevis tadpole.