Aplysia pedal ganglion
The paired pedal ganglia of Aplysia californica are the most caudal of the circumesophageal ganglia. The pedal ganglia are bilaterally symmetrical and are connected by two commisures and two connectives (Fig. 1).
Pedal ganglia sectors
Each pedal ganglion's dorsal surface is divided by septa into distinct clusters of cell bodies. These sectors were originally numbered and identified by Henning et al. 1979 (Fig. 2).
Sector Ia and Ib
Darkly pigmented cells lining the pedal commisure medially in each ganglion.
Latero-anterior in each ganglion. Identified cells in sector IIIa: P1
Latero-posterior in each ganglion.
Pedal ganglia motor neuron types
Several neuron types were identified in the pedal ganglion by Hening et al. 1979. These neurons may be divided in to three types, based on the portion of the animal that they control: prosegmental motor neurons, mesosegmental motor neurons, and metasegmental motor neurons. (Fig. 3)
Pedal ganglion nerves
The pedal ganglia are connected to other ganglia through large connectives: the Pedal-Pleural connective and the Cerebro-Pedal connective. In addition, there are two commissures that connect the left and right pedal ganglia: the large commissure is known simply as the Pedal Commissure, the smaller, more anterior commissure is called the parapedal commissure. The nerves leaving the pedal ganglion are numbered in an anterior to posterior fashion (P1-P10). Unlike the other nerves, P10 is a midline nerve that exits from the parapedal commissure.
Cobalt backfilling of the 9 paired nerves by Hening et al., 1979, indicates that each nerve contains axons of neurons from several cell clusters that are dispersed through the ganglion.
1. Hening, W.A., Walters, E.T., Carew, T.J., Kandel, E.R. (1979) Motorneuronal control of locomotion in Aplysia. Brain Research, 179. 231-253.
2. Moroz, L.L., Edwards, J.R., Puthanveettil, S.V., Kohn, A.B., Ha, T., Heyland, A., Knudsen, B., Sahni, A., Yu, F., Liu, L., Jezzini, S., Lovell, P., Iannucculli, W., Chen, M., Nguyen, T., Sheng, H., Shaw, R., Kalachikov, S., Panchin, Y.V., Farmerie, W., Russo, J.J., Ju, J., Kandel, E.R. (2006). Neuronal transcriptome of Aplysia: neuronal compartments and circuitry. Cell. 127. 1453-1467.
3. Walters, E.T., Byrne, J.H., Carew, T.J., Kandel, E.R. (1983a) Mechanoafferent neurons innervating tail of Aplysia. I. Response properties and synaptic connections.