Date of Award

1980

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Pharmaceutical Sciences

First Advisor

Paul T. Carroll

Abstract

Mouse forebrain minces were incubated in a Krebs or a lithium high K+ (L.K.) Krebs medium, cytoplasmic (S 3 ) and crude vesicular (P 3 ) fractions prepared and the levels of choline and acetylcholine (ACh) in each, determined. ACh levels were depleted by 70% in the P3 fraction of L.K. Krebs as compared to Krebs, incubated minces; while, s3 ACh levels were not significantly altered by the lithium incubation. Lithium treatment lowered the s3 choline content by 29%, with no significant effect upon P3 choline levels, when compared to s3 and P3 fractions of contralateral minces incubated in Krebs media. Minces, depleted of P3 ACh, were subsequently incubated in Krebs containing paraoxon (0. luM) and 0. lmN concentrations of either 14c choline or 14c homocholine. Depletion of P3 ACh resulted in an enhanced transport of extracellular 14c choline (84%) and 14c homocholine (76%), into this fraction but not into the s3 fraction. Furthermore, the depleted P3 fraction was repleted with newly synthesized 14c ACh or 14c acetylhomocholine (14c AHc). The ratio of 14c ACh to the total ACh in the repleted P3 fraction (0.63), exceeded that attained in the s3 fraction, (0.35). Additionally, the ratio of 14c AHc to ACh in the repleted P3 fraction (7.26), was greater than that attained in the s3 fraction (0.44). Similar results were obtained when mouse brain hippocampal minces were depleted of P3 ACh and subsequently incubated in Krebs containing 14c homocholine (0. lmM). The ratio of 14c AHc to ACh in the repleted P3 fraction (1 .50), exceeded that ratio attained in the s3 fraction. Incubation of depleted forebrain minces in Krebs containing the preformed products 14c ACh or 14c AHc, in 0. lmM concentrations, did not result in an increased transport, or the repletion of the P3 fraction with labeled product. However, depletion of P3 ACh in hippocampal minces, did result in a greater accumulation of preformed 14c AHc into the repleted fraction, resulting in a higher ratio of 14c AHc to ACh in the repleted P3 fraction (0. 17), as compared to the P3 fraction of nondepleted minces, (0. 11). The amount of preformed 14c AHc transported into the repleted P3 fraction was insufficient, however, to replace lost transmitter. These results indicate that depletion of P3 transmitter stores, occurs independently of the cytoplasm with newly synthesized product formed from extracellular precursor.

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