Abstract
Here we report that unique 'switching' roles of dopamine in regulating the respiratory rhythm generation. We employed medulla-spinal cord block preparation which contains intact respiratory rhythm generator. In this preparation, respiratory rhythm generator consists mainly Pre-Inspiratory (Pre-I) neurons and inspiratory (I) neurons. I neurons are pre-motor neurons and Pre-I neurons trigger I neuronal firing as a pacemaker. Optical imaging with voltage-sensitive dye revealed that application of dopamine selectively disrupted phasic Pre-I neuronal firing and slightly enhanced I neuronal firing. This dopaminergic effect for Pre-I neuron was mimicked by dopamine D4 receptor agonist, PD168077 application and the enhanced effect of I neuronal firing was mediated with D1 receptor. Dopamine depolarized Pre-I neuronal membrane potential significantly but not on I neurons under TTX perfusion. Finally, dopamine depressed I neuronal PSPs which are probably originated from Pre-I neurons. Dopamine selectively disrupts synchronized phasic Pre-I neuronal firing through dopamine D4 receptor, and enhances I neuronal network through dopamine D1 receptor. Dopamine has opposite effects for respiratory network though different type of dopamine receptors. It seems to be the switching involuntary respiration to voluntary respiration. [J Physiol Sci. 2006;56 Suppl:S138]
