Behavioral Neuroscience, lecture on Aplysia and its behavior
USD Department of Biology
Behavioral Neuroscience
Aplysia Behavior
Sensory Stimulation of Siphon Withdrawl
Motor Output driving Siphon Withdrawal
Conditioning & Memory
Aplysia Siphon and Gill text:Kandel pages 1248-1257
Acetylcholine (ACh)
Aplysia and Siphon Withdrawl
Siphon Withdrawl Circuitry
end     Acronyms/Abbreviations     Syllabus
Diagrams of Aplysia Learning Circuitry (Sea Snails), Syllabus

1) Diagram of ganglia and connections
Cartoon of Aplysia gangliaAbdominal ganglion

                                                                Abdominal Ganglion

Siphon-Gill Circuitry:
1) Top down (Dorsal) View
Top down view of gill-siphon withdrawl circuitry

2) Cell orientation in the circuitry
abdominal ganglionsensitization circuitryphotomicrograph of circuitryfull circuit

Tail-Siphon Circuitry:
1) Dorsal View
Top down view of tail-siphon withdrawl circuitry

Comparing the 2 Circuits:
Top down view of siphon & tail withdrawl circuitry

1) repeated benign stimulus produces a weaker response

1) Tail shock + siphon stimulus produces a stronger response

2) Short-term sensitization via presynaptic 5-HT faciliation of Glu release
Model of short-term heterosynaptic facilitation of the sensorimotor connection that contributes to short- and long-term sensitization in Aplysia. (A1) Sensitizing stimuli activate facilitatory interneurons (IN) that release modulatory transmitters, one of which is 5-HT. The modulator leads to an alteration of the properties of the sensory neuron (SN). (A2 and A3) An action potential in SN after the sensitizing stimulus results in greater transmitter release and hence a larger postsynaptic potential in the motor neuron (MN, AB) than an action potential before the sensitizing stimulus(A2). For short-term sensitization, the enhancement of transmitter release is due, at least in part, to broadening of the action potential and an enhanced flow of Ca2+ (ICa) into the sensory neuron. (B) Model of a sensory neuron that depicts the multiple processes for short-term facilitation that contribute to short-term sensitization. 5-HT released from facilitatory neurons binds to at least two distinct classes of receptors on the outer surface of the membrane and leads to the transient activation of two intracellular second messengers, DAG and cAMP, and their respective kinases (PKC and PKA). 5-HT can also activate MAPK apparently via the activation of cAMP. These three kinases affect multiple cellular processes, the combined effects of which lead to enhanced transmitter release when subsequent action potentials are fired in the sensory neuron (see text for additional details). Modified from Byrne and Kandel, (1996).

Three molecular targets involved in presynaptic faciltation

2) Long-term sensitization

LTS via persistent PKA activity

Learning Diagrams:
A model for memory and its persistence in Aplysia. Repeated pulses of 5-HT (5 × 5-HT) to one branch send a retrograde signal to the cell body activating transcription. The newly synthesized mRNAs, some of which are translationally inactive, are distributed to all synapses. One pulse of 5-HT applied to the other branch is sufficient to increase the level of CPEB (cytoplasmic polyadenylation element–binding protein). The newly synthesized CPEBs (conformation A) are the inactive conformational state of the protein. Some of the protein in conformation A, either spontaneously or in a regulated way, converts into the dominant, self-perpetuating active conformation B. Few molecules in conformation B have the ability to convert all of conformation A to that of conformation B. The protein in conformation B can activate the translationally inactive mRNAs by elongating their polyA tail. The CPEB mRNA itself has a putative CPE element. Thus, once activated, the conformation B proteins can potentially regulate the availability of the proteins in conformation A. This can lead to a self-sustaining, autoregulatory feedback loop that could contribute to the stabilization of learning-related synaptic growth and the persistence of memory storage. From Bailey, C.H., Kandel, E.R., and Si, K. Neuron 2004. 44:49–57. © 2004, Elsevier.
new synapses

Compare Learning with Memory: Learning and Memory are similar but distinct