Effect of neurotensin on neurons in the periaqueductal gray: an in vitro study

The effect of neurotensin (NT) on periaqueductal gray (PAG) neurons was measured with extra- and intracellular recording methods in an in vitro preparation. Neurons excited by NT were heterogeneously distributed, being preferentially located in a region of PAG rich in NT-like fiber immunoreactivity. The majority of the responsive neurons were located in regions surrounding the aqueduct and the medial part of PAG. In 90% of the neurons, application of NT produced excitation that lasted for more than 2 min, while in the remaining cells, the excitatory effect lasted for less than 1 min. An inhibitory action of NT was rarely observed. Intracellular recordings showed that NT produced a depolarization leading to an increase in the spontaneous activity and multiple spiking with only a slight decrease in membrane resistance. The excitatory effect of NT was observed in neurons that were maintained in a solution containing cobalt. These results support the hypothesis that NT action on PAG neurons is due to the depolarization of the membrane and that this effect is mediated through a postsynaptic mechanism.