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Image of a Lucifer Yellow filled CPT neuron that is also serotonergic immunoreactive. The CPT projects contralaterally to the pedal ganglion via the cerebral-pedal commissure near the eye (arrow, E). Serotonin (5-HT) immunoreactivity is in red. The cluster of CPT neurons are 5-HT immunoreactive. The filled neuron is yellow due to combining the fill in green and the 5-HT immunoreactivity in red. Figure adapted from Tian et al., 2006.

The CPT neurons (cerebropleural ganglion triplets) are found in Hermissenda crassicornis.

NeuronBank Accession ID: Her0002693

CPT neuron

Figure 2: Mechanical stimulation to the foot excites the CPTs. Plot shows the CPT spike frequency in relation to the von Frey hair pressure applied to the foot. Figure adapted from Tian et al., 2006.

All anatomical data from Tian et al., 2006. The CPT neurons are a cluster of three serotonin immunopositive neurons located in the posterior-medial portion of the cerebral ganglion that contribute to reflexive foot contractions in Hermissenda. The neurons receive sensory input from mechanoreceptors and photoreceptors and output onto VP2 motor neurons that control foot movements (Tian et al., 2006). The CPTs are homologues of the Tritonia diomedea DSIs (Newcomb and Katz, 2007), Pleurobranchaea californica As1-3 (Jing and Gillette, 1999), the Aplysia californica CC9-10 (Jing et al., 2008), the Clione limacina Cr-SP neurons (Panchin et al., 1995; Satterlie and Norekian, 1995) and the CeSP neurons that have been identified in Tochuina tetraquetra, Melibe leonina, Dendronotus iris, Dendronotus frondosus, Armina californica, Triopha catalinae (Newcomb and Katz, 2007).

Neuronal Type: Interneuron


Details from Tian et al., 2006

Figure 3: Illuminating the eyes depolarizes the CPTs. CPT (top trace) is excited when the eyes are exposed to light (bottom trace). Figure adapted from Tian et al., 2006.
  • The CPTs are located in a cluster in the posterior-medial portion of the cerebral ganglion (Figure 1).
  • The CPTs project an axon contralaterally to the pedal ganglion and then through the pedal ganglia commissure (Figure 1).
  • There are 6 CPTs in the brain (3 in each cerebral ganglion).

Molecular profile

Figure 4: CPT excites foot contracting motor neurons. Triggering an action potential in CPT elicits an excitatory PSP in VP2. Overlayed traces show the consistent monosynaptic transmission latency. Figure adapted from Tian et al., 2006.
  • Neurotransmitter: Serotonin (Tian et al., 2006)


All physiology details are from Tian et al., 2006.

Synaptic Inputs

CPT receives mechanosensory input from the anterior and middle foot region (Figure 2). The CPTs also receive input from type B photoreceptors (Figure 3). The CPTs receive polysynaptic inhibitory input from the Ib interneurons (see the Ib wiki page) and are electrically coupled to other CPT neurons.

Synaptic Outputs

The CPTs excite VP2 motor neurons, which control anterior foot contraction (Figure 4).

Spiking properties

The CPTs are spontaneously active at rest and receive common synaptic input.


The CPT neurons synapse onto VP2 motor neurons which initiate anterior foot contractions. CPT neurons receive input from the eyes and foot. Thus, it appears as though the CPT neurons cause foot contractions when excited by light or foot stimulation. The CPTs do not appear to be involved in ciliary locomotion, however. Therefore, any involvement of the CPTs in locomotion appears to be relegated to turning via foot contraction.


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  2. Newcomb JM and Katz PS (2007) Homologues of serotonergic central pattern generator neurons in related nudibranch molluscs with divergent behaviors. J Comp Physiol A 193:425-443. PMID: 17180703
  3. Jing J and Gillette R (1999) Central Pattern Generator for Escape Swimming in the Notaspid Sea Slug Pleurobranchaea californica. J Neurophysiol 81:654-667. PMID: 10036268
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  5. Satterlie RA and Norekian TP (1995) Serotonergic modulation of swimming speed in the pteropod mollusc Clione limacina III. Cerebral neurons. J Exp Biol 198:917-930. PMID: 7730754
  6. Panchin YV, Popova LB, Deliagina TG, Orlovsky GN, Arshavsky YI (1995) Control of locomotion in marine mollusk Clione limacina. VIII. Cerebropedal neurons. J Neurophysiol 62:1163-1176. PMID: 7623090