Actions of baclofen and phaclofen upon ON- and OFF-ganglion cells in the cat retina.

The effects of the GABAB (gamma-amino butyric acidB) receptor agonist, baclofen and its antagonist, phaclofen on physiologically identified retinal ganglion cells were studied in the optically intact eye of pentobarbitone-anaesthetized cats. These results were compared with the effects of the GABAA receptor agonist, muscimol and its antagonist, bicuculline. Baclofen inhibited the total visually driven firing of both ON- and OFF-cells more effectively upon OFF- than ON-cells; this action was weaker and slower than that of muscimol. Whilst bicuculline raised the firing level of only ON-cells in the area centralis together with all peripheral cells, phaclofen raised that of all OFF-cells. Paradoxically, in OFF-cells, baclofen enhanced the driven transient component and suppressed the sustained component, whilst phaclofen raised the sustained component. Thus, GABAB receptors activated by tonically released GABA may modulate the sustained and transient excitatory inputs to OFF-cells.