Identification of Mauthner-initiated response patterns in goldfish: Evidence from simultaneous cinematography and electrophysiology

Summary

• 1. This paper demonstrates that the Mauthner (M-) cell action potential is correlated with the onset of C-type fast-start responses beginning with a contraction of the contralateral body musculature. We made extracellular recordings from individual M-cells with chronically implanted microelectrodes in six goldfish while the animals were free to swim in an aquarium (19–23 °C). Fast-start responses were elicited by dropping a ball into the aquarium from above the fish. The behavior was filmed at 500 frames/s with a high-speed cine camera (Fig. 31).

• 2. In 45 responses, the M-cell action potential (M-spike) fired 7.4 ms ±6.7 (±SD) after the ball hit the water. The M-spike was followed after 8.1 ms±1.6 by the first stage of a C-type fast-start response that began with an initial contraction of the body on the side opposite the monitored M-cell (Figs. 5 A and 6). This is consistent with neuroanatomical and physiological evidence that the M-cell excites contra-lateral motor neurons. No M-spike was recorded in 18 trials when the C-start began with an initial contraction on the same side as the monitored M-cell (Fig. 7B1, 7B2). Presumably, such responses were initiated by the unmonitored M-cell on the opposite side of the brain. There was also no M-spike when the fish did not respond to the stimulus (ten trials).

• 3. M-initiated C-starts fell into two different response categories differentiated by the turns taken during the second stage of the motor pattern. In most cases (83%) the animal continued in the trajectory of its initial turn (Fig. 5 A). In 17% of the responses the second stage turn was in a direction opposite that taken initially, so that the animal darted forward (Fig. 5B).

• 4. The maximum mean displacement speed of three fish in 21 trials was 18 body lengths/s as measured from the rostrum. This occurred at about 16 ms after the response began (Fig. 9A). The maximum mean angular velocity of the head was 3,500 deg/s. This occurred at 10 ms after the response began (Fig. 9C). These values correspond to the pronounced lateral movement of the head during the initial stage of the response.

• 5. The M-initiated first stage was Stereotypic in terms of the trajectory taken (Fig. 8) and the mechanical performance of the animal (Fig. 9 B and D). In contrast, the turning performance during the second stage was variable from trial to trial (Figs. 8, 9B and D).

• 6. M-initiated responses were directed away from the stimulus. The M-cell on the side closest to the ball was the one that usually fired (85% of the trials) so that the initial turn was away from the stimulus. During 87% of the second stage responses, the animal oriented away from the stimulus (Fig. 10).