Neurotransmitter sampling and storage for capillary electrophoresis analysis

Quantitative analysis of signaling molecules from single cells and cellular materials requires careful validation of the analytical methods. Strategies have been investigated that enable single neurons and neuronal tissues to be stored before being assayed for many low-weight, biologically active molecules, such as serotonin, dopamine, and citrulline. Both metacerebral cell and pedal ganglia homogenates isolated from Pleurobranchaea californica have been studied by capillary electrophoresis with two complimentary laser-induced fluorescence detection methods. For homogenized ganglia samples, several cellular analytes (such as arginine and citrulline) are unaffected by standing at room temperature for days. Many other analytes in the biological matrix, including the catecholamines and indolamines, degrade by 20% within 10 h at room temperature. Rapidly freezing samples or preserving them with ascorbic acid preserves more than 80% of the dopamine and about 70% of the serotonin even after five days. In addition, serotonin and dopamine remain completely stable for at least five days by combining the ascorbic acid preservation and freezing at –20 °C. The timing of preservation is critical in maintaining the original composition of the biological samples. Using our optimum storage protocol of freezing the sample within 2 h after isolation, we can store frozen homogenate ganglia samples for more than four weeks before assay while still obtaining losses less than 10% of the original serotonin and dopamine. The nanoliter-volume single cell samples, however, must be analyzed within 4 h to obtain losses of less than 10% for serotonin related metabolites. Received: 23 August 2000 / Revised: 2 November 2000 / Accepted: 7 November 2000