A new approach to the analysis of complex dose-response relationships: a multivariate study of octopamine action on the leech Leydig neurone.

Octopamine (OA) hyperpolarizes leech Leydig neurones but response amplitudes and thresholds vary. Associations between response, OA dose and other variables [initial resting potential, action potential (AP) frequency and amplitude, temperature, microelectrode resistance, position of ganglion along nerve cord, animal, treatment order] were examined using canonical correlation. A complex response was expressed by summing changes in membrane potential and AP frequency over 2 min of OA treatment. Only dose and ganglion position influenced this response. One significant canonical variate related dose to immediate changes in membrane potential and summed changes in AP frequency throughout the OA effect. Response to OA was greater in cells in posterior ganglia.