Coregulation of glutamate uptake and long-term sensitization in Aplysia.
In Aplysia, long-term facilitation (LTF) at sensorimotor synapses of the pleural-pedal ganglia is mediated by an increase in the release of a neurotransmitter, which appears to be glutamate. Glutamate uptake also is increased in sensory neurons 24 hr after the induction of long-term sensitization (Levenson et al., 2000b). The present study investigated whether the same signaling pathways were involved in the long-term increase in glutamate uptake as in the induction of LTF. Thus, roles for cAMP, PKA (cAMP-dependent protein kinase), MAPK (mitogen-activated protein kinase), and tyrosine kinase in the regulation of glutamate uptake were tested. We found that 5-HT increased cAMP and activated PKA in sensory neurons. Exposure of pleural-pedal ganglia to analogs of cAMP or forskolin increased glutamate uptake 24 hr after treatments. Inhibitors of PKA (KT5720), MAPK (U0126 and PD98059), and tyrosine kinase (genistein) blocked the long-term increase in glutamate uptake produced by 5-HT. In addition, bpV, a tyrosine phosphatase inhibitor, facilitated the ability of subthreshold levels of 5-HT to increase glutamate uptake. Inhibition of PKC, which is not involved in LTF, had no effect on the long-term increase in glutamate uptake produced by 5-HT. Furthermore, activation of PKC by phorbol-12,13-dibutyrate did not produce long-term changes in glutamate uptake. The results demonstrate that the same constellation of second messengers and kinases is involved in the long-term regulation of both glutamate release and glutamate uptake. These similarities in signaling pathways suggest that regulation of glutamate release and uptake during formation of long-term memory are coordinated through coregulation of these two processes.
Khabour
Omar
O
Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204-5001, USA.
Levenson
Jonathan
J
Lyons
Lisa C
LC
Kategaya
Lorna S
LS
Chin
Jeannie
J
Byrne
John H
JH
Eskin
Arnold
A
D000818:Animals; D001048:Aplysia / Q000378:metabolism / Q000502:physiology*; D001692:Biological Transport; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism; D007700:Kinetics; D017774:Long-Term Potentiation; D020935:MAP Kinase Signaling System; D008568:Memory; D009475:Neurons, Afferent / Q000201:enzymology / Q000378:metabolism*; D011493:Protein Kinase C / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D015398:Signal Transduction
D005973:Glutamine; D018698:Glutamic Acid; D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C