Projection pattern and target selection of Clione limacina motoneurons sprouting within an intact environment

Abstract

In the pteropod mollusc Clione limacina, two groups of locomotor motoneurons, located in the pedal ganglion, innervate the dorsal and ventral muscle layers of the ipsilateral wing through the wing nerve. Separate branches of this nerve go either only to the dorsal muscle layer or only to the ventral one. In the present study, growth of novel neurites of the wing motoneurons was induced by cutting the wing nerve. In addition, all other peripheral nerves and connectives of the pedal ganglion were cut, except for the pedal commissure to the contralateral pedal ganglion. Thus, the neurites were allowed to grow only towards the contralateral pedal ganglion. We have found that the novel neurites, entering the contralateral pedal ganglion, were capable of growing everywhere inside the central nervous system (CNS) and into any peripheral nerve. However, they preferred the wing nerve. This finding suggests that the preference is caused by the guiding cues in the wing nerve or the attractive influence of the wing muscles. Because the contralateral pedal ganglion and nerves were left intact, the growth direction of the new neurites could be determined only by factors permanently existing in the CNS, rather than induced by nerve injury or muscle denervation. Within the wing nerve, the neurites could not discriminate between the nerve branches going to the dorsal and ventral muscle layers. They formed synapses on muscles of both layers, despite the fact that the muscles were innervated by their own motoneurons.

A review of the circuit-level and cellular mechanisms contributing to locomotor acceleration in the marine mollusk Clione limacina

“…The wing nerve is also connected to the pedal ganglia and carries afferent and efferent information related to the wing-like parapodia (P). Other structures identified include the sensory structures labeled OG, the olfactory organ, and ST, the statocysts (Wagner, 1885;Arshavsky et al, 1985aArshavsky et al, ,b,c, 1990Lalli and Gilmer, 1989;Hermans and Satterlie, 1992;Moroz et al, 2000;Zelenin and Panchin, 2000). the dorsal (or upstroke) movement of the parapodia, and the other group of swim interneurons controls the ventral (or downstroke) movement of the parapodia.…”

“…The wing nerve is also connected to the pedal ganglia and carries afferent and efferent information related to the wing-like parapodia (P). Other structures identified include the sensory structures labeled OG, the olfactory organ, and ST, the statocysts ( Wagner, 1885 ; Arshavsky et al, 1985a , b , c , 1990 ; Lalli and Gilmer, 1989 ; Hermans and Satterlie, 1992 ; Satterlie et al, 1995 ; Moroz et al, 2000 ; Zelenin and Panchin, 2000 ).…”

“…Also shown in Figure 1B are the statocysts (St) that make up the vestibular or statomotor system of Clione , which contribute to the ability of Clione to orient its body within the water column and, during slow swimming, maintain the vertical body orientation as depicted in Figure 1B (Satterlie et al, 1985 ; Satterlie and Spencer, 1985 ; Panchin et al, 1995a ). The wing nerve (WN) carries axons that innervate the parapodia and branches into two main branches, the anterior and posterior branches (NWA and NWP, respectively; Zelenin and Panchin, 2000 ).…”