Flexible body dynamics of the goldfish C-start: implications for reticulospinal command mechanisms

Abstract

As a model for learning how reticulospinal networks coordinate movement, we have analyzed the function of the Mauthner (M-) neurons in the escape response of the goldfish. We used water displacements of 3-6 micron to elicit C-start escape responses. These responses consist of 2 fundamental movements that grade into each other: Stage 1 lasts 15-40 msec and rotates the body 30 degrees-100 degrees about the center of mass; stage 2 is an axial acceleration that moves the center of mass 2-6 cm. Combined, the 2 stages result in trajectory turns ranging from 15 degrees to 135 degrees. Thus, these data show that M-initiated C-starts are not fixed movement patterns. The durations of stage 1 body muscle EMGs were correlated with turn angles achieved during stage 1. Since variable stage 1 EMGs are not seen when the M-cell is triggered by itself, other circuits, independent of the M-cell, must control the extent of the initial turn, and consequently escape trajectory. Furthermore, turning angles of stages 1 and 2 were correlated, allowing escape trajectory to be predicted, on average, 26 msec after movement started. This suggests that the commands for escape trajectory should be organized by the end of stage 1. In concert with this, the time of onset of the stage 2 EMG preceded the stage 2 onset by a range with a mean of 28.4 msec, typically putting the stage 2 command at the beginning of stage 1 movement. Thus, stage 2 initiation does not require motion-dependent feedback. Our findings indicate that the Mauthner cell initiates the first of a series of motor commands that establish the initial left-right decision of the escape sequence from the side of the stimulus, whereas parallel circuits simultaneously organize the command controlling the escape angle.

Functional Role of a Specialized Class of Spinal Commissural Inhibitory Neurons during Fast Escapes in Zebrafish

“…Firing of the M-cell on the side of the escape was reported in adult goldfish (Zottoli, 1977;Eaton et al, 1988), although the occurrence frequencies were much lower (1 in 39 and 1 in 16, respectively). In such "incorrect" firings, it is likely that the other M-cell fired earlier.…”

The Contribution of Synaptic Inputs to Sustained Depolarizations in Reticulospinal Neurons

“…Similar mechanisms may occur in other vertebrates including goldfish and zebrafish. These species display a vigorous escape reaction in response to sensory stimulation involving the reticulospinal system (Eaton et al, 1988(Eaton et al, , 2001Fetcho and Faber, 1988;Gahtan et al, 2002).…”

Anthropomorphism and ‘mental welfare’ of fishes

“…Fishes show flight responses to certain types of stimuli, such as the rapid approach of a predator. The initial escape response to a sudden stimulus like a predator's attack or a hookset is typically so rapid (tens of milliseconds, Eaton et al 1988) that it does not permit any possible conscious fear-like processes that would require time-consuming, higher level activity in the brain (Esslen et al 2004, Damasio 2005. Of course, hooked fishes sometimes swim to the cover of structure, much as they would if making a response to a predator or other 'alarming' stimulus.…”