Decreased fast-start performance of zebrafish larvae lacking mauthner neurons

Summary

• 1. C-type fast-start responses to a vibrational stimulus were analyzed from high-speed cinematographic films of zebrafish (Brachydanio rerio) larvae with radiation-induced developmental deletions of one or both Mauthner cells (M-cells).

• 2. In 16 animals with one M-cell missing, quantitative comparisons were made between 40 responses on the side of the remaining M-axon with 36 responses on the side of the missing M-axon. There was an almost complete loss of strong, short-latency C-starts associated with the side of the missing M-cell (Fig. 2C and D). This difference in the distribution of types of responses was highly significant (Table 2).

• 3. However, according to available measures, a few of the responses on the side of the missing M-axon were comparable to the strong short-latency responses seen on the side of the remaining M-axon (Fig. 3B1 versus 3B2; Fig. 4B 1 versus 4B2). A few high-performance C-starts were also seen in two of three animals with no M-cells (Figs. 3C, 4C).

• 4. We conclude that in irradiated larvae, presence of the M-cell greatly enhances the probability that high performance C-starts will occur, but that comparable non-Mauthner responses can sometimes happen. Whether such non-Mauthner responses can occur in normal larvae remains to be determined.