Browsing by Subject "Acetylcholine -- Receptors"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Role of the nucleus basalis in conditioned responses of cortical neurons in the rat(Texas Tech University, 1985-12) Rigdon, Greg CNeurons in the rat frontal cortex demonstrate altered firing rates in response to conditioned stimuli. Experiments were designed to test the hypothesis that the basal forebrain cholinergic systera is involved in the generation of conditioned neuronal responses in the rat frontal cortex. Most of the cholinergic innervation to the frontal cortex is supplied by projections frora the nucleus basalis raagnocellularis (nBM), A two-second tone cue imraediately followed by rewarding medial forebrain bundle stimulation was used to elicit the conditioned neuronal responses in the following experiraents. Experiment One was performed to determine the effects of inhibiting the firing of neurons in the nBM region on the conditioned responses. This was presuraably accomplished by microinjecting procaine, a local anesthetic, or GABA, an inhibitory neurotransraitter, into the nBM region. Procaine antagonized the conditioned responses of 86% of the cortical single units tested and GABA antagonized the responses of 81% of the units. Experiment Two was designed to investigate the effects of blocking cholinergic receptors on the conditioned responses of frontal cortex neurons. Microinjection of atropine, a cholinergic antagonist, into the frontal cortex suppressed the conditioned responses of 21 of 24 cortical single units. The nBM region was lesioned with kainic acid, a neurotoxin, in Experiment Three. The lesion resulted in a significant decrease in choline acetyltransferase activity in the frontal cortex ipsilateral to the nBM lesion. Only 25% of the neurons recorded in the frontal cortex on the side of the nBM lesion exhibited conditioned responses. This was significantly lower than the percentage of neurons that exhibited conditioned responses (70%) in the cortex of untreated animals. The firing rates of units in the nBM region were monitored during the cue-event paradigm in Experiment Four. Of the 38 unit recordings from the nBM region, 28 (74%) exhibited conditioned responses. The results from the four experiments together provide strong evidence for a role of the basal forebrain cholinergic system in the generation of conditioned single unit responses in the frontal cortex.Item Solubilization and characterization of membrane-bound choline O-acetyltransferase in brain(Texas Tech University, 1984-05) Benishin, Christina GeorgievnaThe enzyme choline 0-acetyltransferase (EC 2.3.1.6, ChAT) catalyzes the synthesis of the neurotransmitter acetylcholine in central and peripheral cholinergic nerve tissue. Traditionally, ChAT was thought to exist exclusively as a soluble, cytoplasmic enzyme in nerve endings. However, several experimental results suggest that a form of ChAT exists which is more closely associated with the membranes of nerve endings. For example, although acetylcholine is stored in both the cytoplasm and the vesicles of nerve endings, these two pools are metabolized independently and supply acetylcholine for different modes of release. Cytoplasmic acetylcholine has never been demonstrated to be transported into synaptic vesicles, but choline formed from hydrolyzed acetylcholine may be transported into vesicles for synthesis of vesicular acetylcholine. The objective of this study was to determine whether membrane-bound forms of ChAT exist, of which one form may be more closely associated with the vesicles. Three fraction of ChAT were solubilized from a crude vesicular membrane fraction of brain, by washing the membranes with three solutions of increasing chaotrophic nature: 100 mM sodium phosphate buffer, pH 7.4 (NaP), 500 mM NaCl, and 2% Tritón DN-65. A variety of biochemical, anatomical, biophysical, developmental, and pharmacological properties of the three fractions were then examined to determine whether they differ from each other. NaP soluble ChAT, which is traditionally thought to be a soluble (cytoplasmic) enzyme, differed from the other two fractions of ChAT with respect to pH profile, heat inactivation, cardiolipin inhibition, hydrophobic chromatography on phenyl-Sepharose, and developmental pattern. NaCl soluble ChAT differed from the other two fractions with respect to K for choline, pH profile, anatomical distribution, sensitivity to septal-hippocampal lesion, heat inactivation, hydrophobic chromatography on phenyl-Sepharose, developmental pattern, and the effect of atropine administration. Tritón soluble ChAT differed from the other two fractions with respect to ability to acetylate homocholine, heat inactivation, and developmental pattern. The NaP soluble forra of ChAT may supply the cytoplasmic pool of acetylcholine, while it appears that the Tritón soluble form of ChAT may synthesize vesicular acetylcholine. The physiological role of NaCl soluble ChAT is more uncertain, but the results support the possibility that this form may be a precursor for one or both of the other two forms of ChAT.