Graded action potentials generated by neurons in rat hypothalamic slices

Preoptic neurons in rat hypothalamic slices were investigated with tight-seal whole-cell recording techniques. The main aim was to investigate the ability to generate graded, stimulus-dependent impulses. In response to rectangular current pulses, all cells generated impulses with an amplitude that to some degree depended on the stimulus strength. Stronger current steps induced impulses of larger amplitude. In 50% of the cells, a systematic variation of impulse amplitude of more than 10 mV (up to 40 mV) was recorded, implying a clear deviation from the 'all-or-nothing' principle. A clear variation in amplitude of spontaneous impulses was also recorded, in the whole-cell mode as well as from intact cells in the cell-attached mode.