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CC3 is a cerebral-abdominal interneuron in Aplysia californica.

Basic information

Neuronal processes of CC3 in various ganglia in Aplysia. (Xin 2001)
  • Alias- CB1
  • Neurotransmitter: Serotonin

CC3 (CB-1) is a designation that considers the previous identification of a serotonergic neuron in the B cluster of the cerebral ganglion. Upon review of the similarities in morphological and physiological character, it was concluded that CC3 is likely to be CB-1. Further evidence was found in there being no neuron in the B cluster that was immunopositive for serotonin. CC3 is the only cerebral-abdominal interneuron (CAI) in the cerebral ganglion C cluster that is immunopositive for serotonin. The staining pattern resembles that of Tritonia, another gastropod mollusk. Of the C cluster serotonergic cells, it is the largest and most posterior.



  • CC3 has a bilaterally symmetric soma. It is a bipolar neuron; one axon extends ipsilaterally to the cerebral-pleural connective, while the other axon goes to the contralateral cerebral-pleural connective.
  • CC3 nerves branch in the pedal ganglia, sending projections out pedal nerve 3 and to the abdominal ganglia.
Stained dorsal view of the right anterior and middle region of the cerebral ganglion A: soma and bifurcating axon. B: cells revealed immunopositive for serotonin. (Xin 2001)


  • Stimulation of the lip results in excitation to CC3. Firing of CC3 produces effects on neurons that project to abdominal and pedal ganglion nerves. The genital nerve of the abdominal ganglion is the most strongly affected by CC3 firing; of the pedal ganglion, the strongest response is recorded in pedal nerve 3.
  • Indirect inhibition of the left upper quadrant cells (LUQ) of the abdominal ganglion stems from the inhibitory action of CC3 on interneuron L10. CC3 synapses with L10 which then goes on to inhibit the LUQ cells. The left upper quadrant cells mediate closing of the renal pore, while L10 stimulates opening of the renal pore.
  • CC3 firing causes firing in L11, pedal nerve 3, cerebral-buccal connectives, and the genital nerve (Xin et al., 2001).
  • CC3 fires irregularly when buccal nerve 2 rhythmic activity is evoked.


  • CC3 excites serotonergic neuron RB-he and other neurons in an organized network of serotonergic arousal. The actions of the serotonergic cerebral neurons to excite other serotonergic neurons in Aplysia californica suggest homology to the patterns of general arousal in Pleurobranchaea and Tritonia.


1. Hawkins RD. Localization of potential serotonergic facilitator neurons in Aplysia by glyoxylic acid histofluorescence combined with retrograde fluorescent labeling. J Neurosci 9: 4214-4226, 1989 Abstract

2. Jing J, and Gillette R. Central pattern generator for escape swimming in the Notaspid sea slug Pleurobranchaea californica. J Neurophysiol 81: 654-667, 1999 Abstract

3. Mackey SL, Kandel ER, and Hawkins RD. Identified serotonergic neurons LCB1 and RCB1 in the cerebral ganglia of Aplysia produce presynaptic facilitation of siphon sensory neurons. J Neurosci 9: 4227-4235, 1989 Abstract

4. Marinesco S, Kolkman KE, Carew TJ (2004) Serotonergic modulation in aplysia. I. Distributed serotonergic network persistently activated by sensitizing stimuli. J Neurophysiol. 92:2468-86

5. Nolen TG, Carew TJ. (1994) Ontogeny of serotonin-immunoreactive neurons in juvenile Aplysia california: implications for the development of learning. Behav Neural Biol. 61:282-95

6. Sudlow LC, Jing J, Moroz LL, and Gillette R. Serotonin immunoreactivity in the central nervous system of the marine molluscs Pleurobranchaea californica and Tritonia diomedea. J Comp Neurol 395: 466-480, 1998 Abstract

7. Wright WG, Jones K, Sharp P, Maynard B (1995) Widespread anatomical projections of the serotonergic modulatory neuron, CB1, in Aplysia. Invert Neurosci. 1:173-83

8. Xin Y, Koester J, Jing J, Weiss KR, and Kupfermann I. (2001) Cerebralabdominal interganglionic coordinating neurons in Aplysia. J Neurophysiol 85: 174–186. Full text (html)