Activity of the enzyme choline acetyltransferase (CAT), which mediates the synthesis of the neurotransmitter, acetylcholine, was increased up to 20-fold in spinal cord (SC) cells grown in culture with muscle cells for 2 wk. This increase was directly related to the duration of co-culture as well as to the cell density of both the SC and muscle involved and was not affected by the presence of the acetylcholine receptor blocking agent, ct-bungarotoxin. Glutamic acid decarboxylase (GAD) activity was often markedly decreased in SC-muscle cultures while the activities of acetylcholinesterase and several other enzymes were little changed.Increased CAT activity was also observed when SC cultures were maintained in medium which had been conditioned by muscle cells or by undifferentiated cells from embryonic muscle. Muscle-conditioned medium (CM) did not affect the activities of SC cell GAD or acetylcholinesterase. Dilution or concentration of the CM directly affected its ability to increase SC CAT activity, as did the duration and timing of exposure of the SC cells to the CM. The medium could be conditioned by muscle cells in the presence or the absence of serum, and remained effective after dialysis or heating to 58~ Membrane filtration data were consistent with the conclusion that the active material(s) in CM had a molecular weight in excess of 50,000 daltons. We conclude that large molecular weight material that is released by muscle cells is capable of producing a specific increase in CAT activity of SC cells.Neurons and their target cells appear to interact in a complex reciprocal manner. These interactions have been most readily established in the neuromuscular system, where denervation results in numerous changes in muscle cell physiology (1, 6), in the visual system, where spatial and temporal relationships influence retinotectal innervation patterns (8, 23), and in the sympathetic nervous system, where the postganglionic axonal pathways appear to subserve bidirectionally significant regulatory processes (2,7,20). While these types of interactions may be mediated by neurotransmitters such as acetylcholine, or by larger molecules, such as nerve growth factor, the constraints imposed in vivo by the close physical association between cells whose interactions are demonstrable, militate against characterization of the trophic molecules involved. In contrast, the study of interacting cell systems in vitro obviates this difficulty and, as a result, a variety of techniques-circumfu-16
The authors found significantly fewer total platelet alpha 2-adrenergic receptor binding sites in 13 nonmedicated patients with borderline personality disorder than in 11 patients with borderline personality disorder who were receiving low doses of benzodiazepines and 18 nonpsychiatric control subjects. The two patient groups showed comparable degrees of depression as assessed by the Hamilton Rating Scale for Depression. However, nonmedicated borderline patients were considerably more anxious than medicated patients, raising the possibility that lower alpha 2-adrenergic receptor binding in borderline personality disorder is related to anxiety.
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