QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in JEB Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hale, M. E. Search for Related Content PubMed PubMed Citation Articles by Hale, M. E.

S- and C-start escape responses of the muskellunge (Esox masquinongy) require alternative neuromotor mechanisms

Melina E. Hale

Department of Organismal Biology and Anatomy, University of Chicago, 1027 East 57th Street, Chicago, IL 60637, USA

View larger version (6K): [in a new window]   Fig. 1. Center of mass (CM; *) and electrode positions for faststarts of the muskellunge (Esox masquinongy). Horizontal lines indicate the approximate longitudinal variation in electrode positions among the study animals quantified in Table 1.

View larger version (84K): [in a new window]   Fig. 2. The initial movements of an S-start and a shallow C-start of the muskellunge (Esox masquinongy). (A—F) S-start behavior of the muskellunge. The fish bends into an S shape early in the behavior, 16-32 ms after initiation of movement (B,C) followed by the return of the tail in the opposite direction to form an L-shaped bend by 64 ms. (G—L) A shallow C-start. A comparison of S-start images B and C with C-start images H and I demonstrates the difference in caudal bending between these two response types. Time (t) is shown in milliseconds. Scale bar, 100 mm.

View larger version (28K): [in a new window]   Fig. 3. A larger-amplitude C-start of the muskellunge (Esox masquinongy). (A-F) A C-start with greater and more typical initial bending than that shown in Fig. 2. As with the shallower C-start (Fig. 2G-L), this C-start with greater curvature does not show the bending contralateral to the rostral bend evident during the S-start. Time (t) is shown in milliseconds. Scale bar, 100 mm.

View larger version (16K): [in a new window]   Fig. 4. Profiles of head angle (A), angular velocity (B) and angular acceleration (C) through S-start and C-start behaviors. Numbers on the angular acceleration plot indicate the end of the S-bend (1), the L-bend (2) and the C-bend (3).

View larger version (21K): [in a new window]   Fig. 5. Electromyographic (EMG) profiles for a typical S-start and C-start of the muskellunge. The top three panels show EMG activity on the ipsilateral side, the side of the body towards which the head moves in stage 1, and the lower three panels show contralateral EMG activity. The vertical gray lines positioned at the initiation of EMG activity provide a reference for visualizing the alignment of the activity among electrode sites.

View larger version (20K): [in a new window]   Fig. 6. Cumulative electromyographic data for S-start and C-start behaviors of the muskellunge. The lengths of the bars reflect mean duration, with standard mean error of duration shown by error bars to the right of the bars. Trials were aligned by the first kinematic movement during the responses (zero on the x-axis). Mean onset times relative to the first movement are indicated by the left margin of each bar, and the left-hand error bars indicate the standard error of the onset times. An asterisk indicates that the standard error of the mean was less than 1. The heights of the bars approximate the mean relative amplitude of the electromyographic activity.

View larger version (19K): [in a new window]   Fig. 7. A simplified diagram of the spinal cord C-start neural circuit modified from Fetcho and Faber (1988). In this diagram, the stimulus would be from the right and the fish would turn to the left. The Mauthner axon synapses with interneurons and motoneurons in the spinal cord. Directly and through excitatory interneurons (multiple known pathways indicated by a dashed line), the Mauthner cell excites motoneurons to generate the C-bend. Through commissural interneurons, it inhibits motoneuron activity on the opposite side of the body. The numbers of cells indicated in the diagram do not reflect the numbers or distributions in the fish, nor do they reflect the relative numbers of different cell types. Instead, they simply illustrate regional differences along the body.

View larger version (28K): [in a new window]   Fig. 8. Alternative neural circuit models for the S-start startle response. The left-hand circuit depicts a possible S-start mechanisms involving multiple reticulospinal pathways. Commissural and ipsilateral reticulospinal cells cause motoneuron and muscle activity regionally in the spinal cord. The right-hand circuit depicts a possible C-start model involving a combination of reticulospinal and local circuits. Anterior activity is determined through descending reticulospinal commands, while posterior activity is generated through local spinal cord circuits. The spinal cord interneurons are presumed to be the same as those used in the C-start and are depicted as such. The numbers of cells indicated in the diagrams do not reflect the numbers or distributions in the fish, nor do they reflect the relative numbers of different cell types. Instead, they simply illustrate regional differences along the body