Search PubMed⌕ Search

Biomedical subjects

M H Aprison

Publications and source records attributed to M H Aprison.

At least 73 records · Page 4Linked to original sources
PubMed1975

Content of amino acids in axons from the CNS of the lobster.

The contents of alanine, proline, glycine, GABA, glutamate, and aspartate were measured in four bundles of axons (designated areas A through D) from the circumesophageal connective of the lobster (Homarus americanus). The contents of these amino acids were also determined in individual axons within specific bundles and in the external sheath covering the circumesophageal connective. Within the nerve bundles the levels of aspartate were highest of the amino acids measured, ranging from 1.95 +/- 0.12 mumol/mg protein in area C to 7.55 +/- 0.54 mumol/mg protein in area B. On the other hand, GABA had the lowest value in the four bundles; its highest level was found in area C (0.083 +/- 0.006 mu mol/mg protein) and the lowest in area B (none detected). The content of glycine ranged from 1.63 +/- 0.14 (area C) to 2.52 +/- 0.32 mumol/mg protein in area A; that for glutamate ranged from 0.390 +/- 0.019 (area C) to 1.01 +/- 1.03 (area B). The contents of alanine and proline changed relatively little from bundle-to-bundle. The content of aspartate was the highest of any of the amino acids assayed in individual axons (with diameters in the range of 40 to 65 mu) dissected from areas B and C. Glycine had the next highest content followed in order by glutamate, proline, and alanine. GABA was not detected in these axons. With the exception of GABA (which could not be detected), aspartate had the lowest level (0.066 +/- 0.017) and glycine had the highest level (2.00 +/- 0.498 mumol/mg protein) in the external sheath covering the the circumesophageal connective.

Amino Acids↗
PubMed1975

Serotonergic and cholinergic mechanisms during disruption of approach and avoidance behavior.

Injections of D,L-5-hydroxytryptophan (D,L-5-HTP) into pigeons and rats working on approach schedules produce a period of behavioral depression that is temporally correlated to increased levels of total serotonin (5-?HT) in the telencephalon and diencephalon. Administration of alpha-methyl-meta-tyrosine (alpha-MMT) also results in depressed responding; however, the temporal correlation is with decreased levels of total 5-HT in brain. Our hypothesis to explain these two apparent opposite biochemical states which result in similar behavioral disruptions is that in both cases more 5-HT is released within certain key serotonergic synapses mediating this behavior. Evidence from subcellular studies supports this concept. tnot only are the levels of 5-HT significantly higher in preparations of nerve endings isolated from the telencephalon and diencephalon of pigeons given injections of D,L-5-HTP, but in vitro studies also show that low concentrations of L-5-HTP significantly increased the release of radioactive 5-HT from serotonergic nerve endings. On the other hand, L-5-HTP in much higher concentrations had no effect on the release of labeled dopamine or norephinephrine. A major metabolite of alpha-MMT, alpha-methyl meta tyramine, also caused a significant increase in the release of labeled 5-?HT from similar preparations of nerve endings. Whereas serotonin appears to be involved in the disruption of approach behavior, another series of studies have indicated that acetylcholine may play a role in excitation during avoidance behavior. Behavioral excitation observed following administration of tetrabenazine 18 hr after iproniazid pretreatment to rats working on shock-avoidance schedules was temporally correlated with lowered levels of acetylcholine in the telencephalon. Pretreatment with 0.8 mg/kg of atropine blocked excitation whereas one-eight of this dose increased the duration. Excitation in these rats was shortened by 50% following bilateral septal lesions, which lowered brain acetylcholine levels. Mechanisms to explain these neurochemical correlates of behavior are discussed.

5-Hydroxytryptophan↗