en Biological Sciences Biological Sciences Original Research Original Research The activities of 4-aminobutyric-2-oxoglutaric acid transaminase (GABA-T) and succinate semialdehyde dehydrogenase (SSADH) were determined in mouse hypothalamus after peripheral injections of cholecystokinin-8 (CCK-X)and/or caerulein (CLN). GABA transaminase activity was measured utilizing endogenous succinate semialdellyde dehydrogenase to convert the product of GAB A-T, succinate semialdehyde, to succinate. The concurrently formed NADH was used as an estimate of GABA-T activity. Similarly, the activity of SSADH was determined in terms of NADH. Injection of CCK-8 and/or CLN inhibited the GABA-T and SSADH activities in dose-dependent responses. The activities of GAB A-Tand SSADH were diminished by 52 and 66 percent respectively, 30 minutes after injection of CCK-8 (50 µg/kg body weight).Similarly, peripheral injection of CLN (50 µg/kg body weight) reduced the activity of GABA-T and SSADH by 56 and 65 percent respectively, in 30 minutes. Using ill vitro models, the full activities of GABA-T and/ or SSADH, after incubation with CCK-8 and/or CLN, were restored following 30 hours of dialysis at 4°C. These results indicate direct and reversible interactions between the catabolizing enzymes of GABA (GABA-T and SSADH) and the peptides CCK-8 and CLN. Caerulein. Cholecystokinin-8, Catabolism. GABA-transaminase, Succinate semialdehyde 263 268 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-622&slc_lang=en&sid=1 R YAZDANPARAST 20031947532846006135 20031947532846006135 Yes From the Institute of Biochemistry and Biophysics, University of Tehran D QUJEQ 20031947532846006136 20031947532846006136 No the Dept. Biochemistry, Tarbiat Modarres University, Tehran, Islamic Republic of Iran.