R15

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R15 is a neuron in the Abdominal Ganglion of Aplysia californica.

R15 in Aplysia Abdominal Ganglion. Adapted from Kupfermann et al (1974).

Basic Information

  • R15, which has also been referred to as the "Br cell", the "parabolic burster", and "Oberon", is an endogenously bursting neurosecretory cell in Aplysia (Adams & Benson 1985; Alevizos, Weiss, & Koester 1991a). It is known to synthesize three different peptides: R15α1, R15β, and R15γ (Alevizos, Weiss, & Koester 1991b). R15 may be involved in regulation of water balance. Injection of crude homogenates of R15 or R15α1 cause water retention. There is also evidence that R15 is involved in egg-laying behavior and respiratory pumping (Alevizos, Weiss, & Koester 1991a, 1991c; Levitan, Kramer, & Levitan 1987).

Identification

Anatomy

  • R15 is located in the abdominal region of Aplysia, more specifically the parietovisceral ganglion (Adams & Benson 1985; Alevizos, Weiss, & Koester 1991a).
  • It is always seen on the dorsal surface and is usually the largest cell of the right caudal quarter, measuring from 300 to 500μm (Adams & Benson 1985).
  • R15 innervates the pericardium, the mesentery of the hepatopancreas, and the large hermaphroditic duct (Alevizos, Weiss, & Koester 1991c).

Electrophysiology

Membrane potential and current flows during simulation of bursting in R15. Left Column: extended time scale to illustrate bursting. Right Column: traces were triggered at 0mV to illustrate the current flows during action potential generation. From Adams & Benson, 1985.
  • Action potentials in R15 have been found to be followed by two slow currents that outlast the currents created during the action potentials, one depolarizing and one hyperpolarizing. The slower kinetics of the hyperpolarizing current indicate that these currents may be somewhat responsible for the cell’s bursting activity. The faster depolarizing current increases the rate of fire until the slower current depolarizes the cell (Adams 1985; Adams & Levitan 1985).
  • Activity in R15 has been shown to increase the frequency of bursting in the R25/L25 network that triggers respiratory pumping (Alevizos, Weiss, & Koester 1991a).
  • R15 has been shown to be excited by the neuroendocrine bag cells, which initiate egg laying; Release of the neuropeptide egg laying hormone (ELH) augments the endogenous bursting pacemaker activity of neuron R15. Increasing levels of cyclic AMP in the cell by applying serotonin or the adenylate cyclase activator forskolin together with a phosphodiesterase inhibitor, mimics and occludes this action. The excitatory effects of the bag cells on the R25/L25 network may also be mediated in part by R15 (Alevizos, Weiss, & Koester 1991a; Levitan, Kramer, & Levitan 1987).
  • R15 activates anterograde peristaltic movements in the segment of the large hermaphroditic duct through which eggs move during egg-laying (Alevizos, Weiss, & Koester 1991c).
  • R15 is inhibited when the semi-intact animal is exposed to hypotonic seawater and excited when exposed to hypertonic seawater (Alevizos, Weiss, & Koester 1991a).
  • R15 excites L7, a multimodal motoneuron located in the abdominal ganglion. This excitation is likely strong enough to cause contraction only of the sheath muscle of the pleuroabdominal ganglion, which has a very low activation threshold (Alevizos, Weiss, & Koester 1991b).
  • R15 has been shown to have a circadian rhythm of spiking activity in vitro, which is affected both by the light/dark cycle the Aplysia is exposed to prior to dissection and the time the dissection takes place (Audeserk & Strumwasser 1975).

References

  1. Adams WB. Slow depolarizing and hyperpolarizing currents which mediate bursting in Aplysia neurone R15. J Physiol. 1985 Mar;360:51-68. PMID: 3989723
  2. Adams WB, Benson JA. The generation and modulation of endogenous rhythmicity in the Aplysia bursting pacemaker neurone R15. Prog Biophys Mol Biol. 1985;46(1):1-49. PMID: 2410951
  3. Adams WB and Levitan IB.Voltage and ion dependences of the slow currents which mediate bursting in Aplysia neurone R15. J Physiol. 1985 Mar;360:69-93. PMID: 2580972
  4. Alevizos A, Weiss KR, and Koester J. Synaptic actions of identified peptidergic neuron R15 in Aplysia. I. Activation of respiratory pumping. J Neurosci. 1991a May;11(5):1263-74. PMID: 2027045
  5. Alevizos A, Weiss KR, and Koester J. Synaptic actions of identified peptidergic neuron R15 in Aplysia. II. Contraction of pleuroabdominal connectives mediated by motoneuron L7. J Neurosci. 1991b May;11(5):1275-81. PMID: 2027046
  6. Alevizos A, Weiss KR, and Koester J. Synaptic actions of identified peptidergic neuron R15 in Aplysia. III. Activation of the large hermaphroditic duct. J Neurosci. 1991c May;11(5):1282-90. PMID: 2027047
  7. Audesirk G and Strumwasser F. Circadian rhythm of neuron R15 of Aplysia californica: In vivo photoentrainment. Proc Natl Acad Sci U S A. 1975 Jun;72(6):2408-2412. PMID: 16592252
  8. Kupfermann I, Carew TJ, Kandel ER. Local, reflex, and central commands controlling gill and siphon movements in Aplysia. J Neurophysiol. 1974 Sep;37(5):996-1019. PMID: 4370172
  9. Levitan ES, Kramer RH, Levitan IB. Augmentation of bursting pacemaker activity by egg-laying hormone in Aplysia neuron R15 is mediated by a cyclic AMP-dependent increase in Ca2+ and K+ currents. Proc Natl Acad Sci U S A. 1987 Sep;84(17):6307-11. PMID: 2819871