Alterations in the spontaneous activity of cells in the guinea pig pineal gland and visual system produced by pineal indoles.

The indoles serotonin (SER), melatonin (MEL), 5-methoxytryptophol (5-MTL) and 5-hydroxytryptophol (5-HTL) were administered during daytime microelectrophoretically to 240 cells in the pineal gland of the guniea-pig. The action of SER and 5-HTL was predominantly depressant on the electrical activity, MEL and 5-MTL caused an excitation in most of the units. Although MEL and 5-MTL caused fairly similar reactions on average, they appear to act on different cells. The effects of microelectrophoretically applied MEL and 5-MTL on the spontaneous or evoked activity in the visual system (retinal ganglion cells, optic tract, lateral lateral geniculate body, superior colliculus) of the guinea-pig were also investigated. Of the 76 cells tested in the visual system 25 of the ON- and OFF-cells increased the rate of discharge when the two indoles were applied. Cells in the optic layer of the superior colliculus showed no measurable response to the application of the two substances. 5-HTL caused no effect on cells in the visual system.