Cholecystokinin inhibits evoked inhibitory postsynaptic currents in the rat nucleus accumbens indirectly through gamma-aminobutyric acid and gamma-aminobutyric acid type B receptors.
We recently reported that cholecystokinin (CCK) excited nucleus accumbens (NAc) cells and depressed excitatory synaptic transmission indirectly through gamma-aminobutyric acid (GABA), acting on presynaptic GABAB receptors (Kombian et al. [2004] J. Physiol. 555:71-84). The present study tested the hypothesis that CCK modulates inhibitory synaptic transmission in the NAc. Using in vitro forebrain slices containing the NAc and whole-cell patch recording, we examined the effects of CCK on evoked inhibitory postsynaptic currents (IPSCs) recorded at a holding potential of -80 mV throughout CCK-8S caused a reversible inward current accompanied by a concentration-dependent decrease in evoked IPSC amplitude. Maximum IPSC depression was approximately 25% at 10 microM, with an estimated EC50 of 0.1 microM. At 1 microM, CCK-8S induced an inward current of 28.3 +/- 4.8 pA (n=6) accompanied by an IPSC depression of -18.8% +/- 1.6% (n=6). This CCK-induced IPSC depression was blocked by pretreatment with proglumide (100 microM; -3.7% +/- 6.9%; n=4) and by LY225910 (100 nM), a selective CCKB receptor antagonist (4.4% +/- 2.6%; n=4). It was not blocked by SCH23390 (10 microM; -23.5% +/- 1.3%; P < 0.05; n=7) or sulpiride (10 microM; -21.8% +/- 5.1%; P <0.05; n=4), dopamine receptor antagonists. By contrast, it was blocked by CGP55845 (1 microM; -0.4% +/- 3.4%; n=5) a potent GABAB receptor antagonist, and by forskolin (50 microM; 9.9% +/- 5.2%; n=4), an adenylyl cyclase activator, and H-89 (1 microM; 6.9% +/- 3.9%; n=4), a protein kinase A (PKA) inhibitor. These results indicate that CCK acts on CCKB receptors to increase extracellular levels of GABA, which then acts on GABAB receptors to decrease IPSC amplitude.
Kombian
Samuel B
SB
Department of Applied Therapeutics, Faculty of Pharmacy, Kuwait University, Safat, Kuwait. kombian@hsc.edu.kw
Ananthalakshmi
Kethireddy V V
KV
Parvathy
Subramanian S
SS
Matowe
Wandikayi C
WC
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002766:Cholecystokinin / Q000494:pharmacology*; D045604:Extracellular Fluid / Q000187:drug effects / Q000378:metabolism; D018756:GABA Antagonists / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009434:Neural Pathways / Q000187:drug effects / Q000378:metabolism; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism*; D009924:Organ Culture Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D043887:Receptor, Cholecystokinin B / Q000037:antagonists & inhibitors / Q000378:metabolism; D018080:Receptors, GABA-B / Q000187:drug effects / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018756:GABA Antagonists; D043887:Receptor, Cholecystokinin B; D018080:Receptors, GABA-B; D005680:gamma-Aminobutyric Acid; D002766:Cholecystokinin; D000262:Adenylyl Cyclases