Pleural Ventral Cluster

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The pleural ventrocaudal (VC) cluster in Aplysia is comprised of mechanoafferent cells that have receptive fields over the body surface.

Basic information

The Sensory Neurons (SN) in this cluster have been widely studied in Aplysia with regard to learning and memory.

Identification

Two green sensory neurons in the pleural ganglion that are monosynapticaly connected to a red tail motor neuron in the pedal ganglion. From Marinesco and Carew, 2002.
Somatotopic organization of sensory neurons in the VC cluster. From Walters et al., 2004.
Characteristic single spike in sensory neuron when depolarizing current is injected.--Tbalmer2 13:54, 8 December 2008 (EST)

Anatomy:

  • Homogenous cluster of ~200 40-80µm cells on the ventrocaudal surface of pleural ganglion, overlying the root of the pedal-pleural connective (Walters et al, 1983a)
  • Distinctive group of orange, dark rimmed neurons
  • Only 20 of these 200 cells are tail mechanoafferent neurons
  • contain Sensorin-A mRNA (Walters et al., 2004)


Electrophysiology:

Taken from(Walters et al., 1983a)

  • No spontaneous activity
  • Vrest = 42.3 +- 4.6 mV
  • Intracellular current injection causes 66.3 +- 9.2 mV action potential
  • Often have axons in pedal nerve p9
    • Tail nerve shock evokes antidromic spikes in ~10% of VC cells (Marinesco & Carew, 2002)
  • They respond to mechanical stimulation of the tail, but not NaCl
  • Sensitization/facilitation mimicked by 5-HT (Walters et al, 1983b)
    • Depolarizing pulse every 60s causes one action potential
    • After 10e-4 M 5-HT was perfused into the chamber, the brief depolarizing test pulse elicited multiple spikes (Walters et al, 1983b, fig 10)
  • Monosynaptic connections to identified motor neurons in pedal ganglia (p5-7)
    • These motor neurons also have axons in p9
    • Strong connection between the two: stimulation of the tail normally only activates a few VC neurons and will cause the motor neurons to contract the tail
    • Stimulated mechanosensory neurons and the synapse to motor neuron showed synaptic depression
    • Heterosynaptic plasticity of this SN->MN synapse is mediated by 5-HT. See figure at right. (Byrne & Kandel, 1996)
  • There is a topographic relationship (somotopic organization or “sensory aplunculus”) between VC soma position and RF position. See figure at right (Walters et al., 2004)
    • More medial VC cell has more posterior RF


References

  • Walters ET, Byrne JH, Carew TJ, Kandel ER (1983) Mechanoafferent neurons innervating tail of Aplysia. I. Response properties and synaptic connections. J Neurophysiol 50:1522-1542.
  • Walters ET, Byrne JH, Carew TJ, Kandel ER (1983) Mechanoafferent neurons innervating tail of Aplysia. II. Modulation by sensitizing stimulation. J Neurophysiol 50:1543-1559.
  • Byrne JH, Kandel ER (1996) Presynaptic facilitation revisited: state and time dependence. J Neurosci 16:425-435.
  • Marinesco S, Carew TJ (2002) Serotonin release evoked by tail nerve stimulation in the CNS of aplysia: characterization and relationship to heterosynaptic plasticity. J Neurosci 22:2299-2312.
  • Walters ET, Bodnarova M, Billy AJ, Dulin MF, Diaz-Rios M, Miller MW, Moroz LL (2004) Somatotopic organization and functional properties of mechanosensory neurons expressing sensorin-A mRNA in Aplysia californica. J Comp Neurol 471:219-240.