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Atp Modulatory Actions on Hippocampal Synaptic Transmission ATP MODULATORY ACTIONS ON HIPPOCAMPAL SYNAPTIC TRANSMISSION YUANJING YANG A thesis submitted to the Department of Anatomy and Cell Biology in conforrnity with the requirements for the degree of Master of Science Queen's University Kingston, Ontario, Canada May 30,200 1 Copyright O Yuanjing Yang, 2001 National Library Bibliothèque nationale of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. me Wellington Ottawa ON K1A ON4 Ottawa ON K1A ON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence dowing the exclusive permettant a la National Lhray of Canada to Bibliothèque nationale du Canada de reproduce, loan, disûibute or seil reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thése sous paper or electronic formats. la forme de microfiche/fïlm, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fkom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. 1. ABSTRACT ATP might play a role in the establishment of Long-term potentiation (LTP) in the hippocampus, which is one of the synaptic modifications proposed to underlie the memory process. In this study, we set out to investigate the modulatory effects and mechanisms of action of ATP on synaptic transmission in these synapses. Our observations indicate that there are at least three different effects of ATP on the hippocmpal synaptic transmission, which rnight be rnediated by different purine receptors (purinoceptors). The first effect was observed at a nanomolar ATP concentration and it consisted of a transitory synaptic transmission enhancement. This ATP action rnight be mediated by a P2Y purinoceptor on which 8-cyclopentyltheophyline (CPT) appears to work as an antagonist. The second action was observed at a micromolar concentration and was characterised by inhibition of the synaptic transmission. Such an effect is mediated by a presynaptic P2Y receptor, which is CPT sensitive and appears to be incorporated in the presynaptic terminais right after the induction of LTP. The third effect was observed with a millimolar concentration of ATP and was characterised by inhibition of synaptic transmission. This inhibition appeared to have two different phases, a short-lasting and a long-lasting. The later resembles long-term depression. These observations indicate that ATP actions on hippocampal synapses are complex and that a diverse population of purinoceptors mediate its effects. 11, ACKNOWLEDGMENTS First I wish to thank Dr. Carlos Barrages-LBpez for this project and his continua1 advice and supervision throughout the research. 1 have appreciated his very patient, invaluable support, and guidance. Sincere thanks for the two years, Carlos. 1 also would like to thank Drs. Stephen C. Pang and R- David Andrew. Thanks for the encouragement, selfless help, salvation, and guidance. Your contribution to my graduate studies was immeasurabIe. A special thank you goes to my [ab-mates Rosa Espinosa-Luna, Rustum Karanjia and Xuzhi Li for the question asking-answering support and valued companionship. Thank-you to the administrative staff and other members of the Department of Anatomy and Ce11 Biology, and especialIy, Ms. Anita Lister, 1 will always remember your cornfort. VI11. RESULTS .......................................................................... 23-38 A . Field potentids in the straturn pyramidale and rnolec~rlarlayer ............ 23 B . LTP in the stratrrm pyramidale ............................................... 25 C . ATP modulation of synaptic transmission ................... ........, .... 28 1 . Effects of low concentrations of ATP and adenosine ............... 28 2 . Effects of intermediate concentrations of ATP on synaptic . * transmission .............................................................. 31 3 . Effects of large concentrations of ATP on synaptic transmission .............................................................. 36 IX . DISCUSSION ..................................................................... 39-45 The synaptic potentiation induced by a nanornolar concentration of ATP appears to be rnediated by ATP itself .......................................... 39 The synaptic potentiation induced by a nanomolar concentration of ATP appears to be mediated by P2Y-CPT sensive receptors .....................40 The synaptic potentiation induced by a nanomolar concentration of ATP is different than LTP ........................................................... 1 P2Y-CPT receptors are rapidly incorporated in the putative new synapses formed during the LTP ......................................................... 42 Activation of P2X receptors might mediate long-term depression (LTD)............................................................................ 43 X . CONCLUSIONS .................................................................... 46 XI. REFERENCES ................................................................... 47-60 iv XII. APPENDIX A (CURRICULUM VITAE) .............*.---...-.-.-. .-.- 61-62 IV, LIST OF ABBEWVIATIONS Long-Term Potentiation (LTP), Long-Term Depression (LTD), Field Excitatory Postsynaptic Potentials (fEPSPs), 8-Cyclopentyltheophyline (CPT), Pyridoxalphosphate-6-Azophenyl-2',4'-Disulfonic Acid (PPADS), Adenosine Triphosphate (ATP), Adenosine Diphosphate (ADP), Adenosine Monophosphate (AMP), Artificial Cerebrospinal Fluid (aCSF), Excitatory Postsynaptic Potentials (EPSPs), N- Methyl-D-Aspartate (NMDA), Alpha-amino-3-Hydroxy-5-Methyl-4-IsoxazoLepropionic Acid (AMPA), Persona1 Computer (PC), High Frequency Tetanic Stimulation (Tetanus), and Cornu Arnmonis (CA, Latin for Ammon's hom). V. LIST OF FIGURES Figure 1. Schematic representation of a coronal section of the rat hippocampus and dentate gyms showing the main excitatory connections ...................... 4 Figure 2. A rise in intraceIlular calcium concentration plays a central role in the induction of both long-term potentiation (LTP) and depression (LTD) in the CAL hippocampal area .................................................................. 9 Figure 3. Equipment used to record and to analyze the field potentials from rat hippocampal slices ................................................................ 1 8 Figure 4. Equipment used to superfuse and visualize hippocampal slices. ........... 19 Figure 5. Typical field potential recorded in the stratum pyramidale of CA1 hippocampal area -...........,..,,...... ,. ..................................................... 2 1 Figure 6. Field excitatory postsynaptic potentials (EPSPs) recorded in the molecular layer (A) and stratum pyramidale (B) of the CA1 have opposite polarities ..................................................................... 2 4 Figure 7. Typical field potentials recorded in the stratum pyramidale of CA1 hippocampal is stimulus dependent ........................................... 26 Figure 8. Application of a high frequency tetanic stimulation (Tetanus) increased both the population spike amplitude (A) and the slope of initial wave (Pl) of the field potentials (B) .............................................................. 2 7 Figure 9. A low ATP concentration (300 nM) transitorily increases the population spike amplitude in the CA1 area ........................ .. ......................... 29 .. Figure 10. 8-Cyclopentyltheophyline (CPT) blocks the effects of low ATP concentrations (300 nM) but it increases the amplitude of the population spike by itseIf .............................................................................. 3 O Figure Il. Low adenosine concentration (300 nM) fails to modify the evoked population spike.............................................................................. 3 O Figure 12. Adenosine also fails to change the population spike after inhibition of GABA, receptors with picrotoxin ................. ... .............................. 3 2 Figure 13. A micromolar concentration (100 PM) of ATP reversibly blocks synaptic . transmission ...... .,. ........................................................ 3 3 Figure 14. Electrically potentiated field potentials were also inhibited by a micromolar concentration (100 PM) of ATP but did not prevent the subsequent appearance of Long-term potentiation (LTP) ........................ .... ...................3 4 Figure 15. ATP-induced inhibition of electrically potentiated field potentials occurs very rapidly (< 140 seconds)........................................................ 35 Figure 16. ATP also inhibits the field potentials after total saturation of the long-term potentiation (LTP).............................................................. 3 7 Figure 17. A short application of a high ATP concentration (30 rnM) induces a Long-term synaptic depression which is partially blocked by the P2X receptor antagonist, PPADS ......................................................................... 3 8 VI. INTRODUCTION "...die mecfianisms of rnentaC aczivity are ceriain (y accom.anied moCecuhr rnoïfzztions in tzerve ceTl andpreceded6y conydéx changes in the relationsliip 6e~weenneiirons. $0 understand mental activity it is necessary to
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