Our long term goal is to understand the mechanisms underlying the modulation of neurotransmitter release from presynaptic nerve terminal, an important form of synaptic plasticity involved in learning and memory. Changes in synaptic function are also likely to be important cellular loci for both neurologic and psychiatric disorders. Here, we focus our attention on the role that Ca++ channel modulation plays in presynaptic inhibition in sensory neurons of the marine snail Aplysia in response to the neuropeptide FMRFamide. Presynaptic inhibition is an important mechanism for regulating synaptic transmission. In vertebrate sensory neurons, presynaptic inhibition has been postulated to play a role in modulating the perception of pain and other stimuli. In Aplysia sensory neurons, presynaptic inhibition produced by FMRFamide (a close relative of the opioid peptides) leads to behavioral inhibition. Like presynaptic inhibition in vertebrates, the presynaptic inhibition in Aplysia is associated with an increase in K+ current and a decrease in Ca2+ current. What are the biochemical mechanisms that mediate presynaptic inhibition? In Aplysia, we previously showed that an increase in K+ channel opening with FMRFamide was mediated by the 12-lipoxygenase metabolites of arachidonic acid, a novel second messenger pathway for neurons. What is the second messenger mechanism underlying inhibition of the calcium current? In vertebrates, activation of protein kinase C appears to be involved in some, but perhaps not all, cases of modulatory decreases in calcium current. In Aplysia sensory neurons, protein kinase C does not appear to be involved. Is the decrease in calcium current in Aplysia also mediated by arachidonic acid metabolites? Are other second messenger pathways involved? Does Ca2+ channel inhibition involve the parallel action of multiple second messenger pathways or might the different cascades act in series? If arachidonic acid metabolism is involved, which metabolite is implicated. Does the same metabolite modulate both K+ channel opening and calcium current inhibition or do different branches of the arachidonic acid cascade serve different modulatory functions? Whole cell calcium current and single calcium channel currents will be studied using the patch clamp technique in Aplysia sensory neurons. The effects of FMRFamide on calcium current will be compared to the action of exogenously applied arachidonic acid and arachidonate metabolites. The effects of various inhibitors of the arachidonic acid cascade will also be tested. Finally, possible roles for other modulatory pathways will be investigated.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS019569-08
Application #
3399662
Study Section
Physiology Study Section (PHY)
Project Start
1983-04-01
Project End
1992-03-31
Budget Start
1990-04-01
Budget End
1991-03-31
Support Year
8
Fiscal Year
1990
Total Cost
Indirect Cost
Name
Columbia University (N.Y.)
Department
Type
Schools of Medicine
DUNS #
064931884
City
New York
State
NY
Country
United States
Zip Code
10027
Shuster, M J; Camardo, J S; Siegelbaum, S A (1991) Comparison of the serotonin-sensitive and Ca(2+)-activated K+ channels in Aplysia sensory neurons. J Physiol 440:601-21
Volterra, A; Siegelbaum, S A (1989) Antagonistic modulation of S-K+ channel activity by cyclic AMP and arachidonic acid metabolites. Role for two G proteins. Ann N Y Acad Sci 559:219-36
Volterra, A; Siegelbaum, S A (1988) Role of two different guanine nucleotide-binding proteins in the antagonistic modulation of the S-type K+ channel by cAMP and arachidonic acid metabolites in Aplysia sensory neurons. Proc Natl Acad Sci U S A 85:7810-4
Belardetti, F; Kandel, E R; Siegelbaum, S A (1987) Neuronal inhibition by the peptide FMRFamide involves opening of S K+ channels. Nature 325:153-6
Shuster, M J; Siegelbaum, S A (1987) Pharmacological characterization of the serotonin-sensitive potassium channel of Aplysia sensory neurons. J Gen Physiol 90:587-608
Shuster, M J; Camardo, J S; Siegelbaum, S A et al. (1986) Modulation of the 'S' K+ channel by cAMP-dependent protein phosphorylation in cell-free membrane patches. Prog Brain Res 69:119-32
Belardetti, F; Schacher, S; Siegelbaum, S A (1986) Action potentials, macroscopic and single channel currents recorded from growth cones of Aplysia neurones in culture. J Physiol 374:289-313
Siegelbaum, S A; Belardetti, F; Camardo, J S et al. (1986) Modulation of the serotonin-sensitive potassium channel in Aplysia sensory neurone cell body and growth cone. J Exp Biol 124:287-306
Shuster, M J; Camardo, J S; Siegelbaum, S A et al. (1985) Cyclic AMP-dependent protein kinase closes the serotonin-sensitive K+ channels of Aplysia sensory neurones in cell-free membrane patches. Nature 313:392-5