INTRACELLULAR-RECORDING OF MAGNOCELLULAR PREOPTIC NEURON RESPONSES TOOLFACTORY BRAIN

The magnocellular preoptic nucleus of the rat supplies centrifugal inp ut to the olfactory bulb as well as projecting to other olfactory-rela ted areas. The extent to which the piriform and entorhinal cortices ca n influence the activity of magnocellular preoptic neurons and hence t hat of the olfactory bulb were examined using intracellular in vivo re cording. Stable recordings were obtained in 58 neurons impaled in the magnocellular preoptic nucleus. Antidromic responses occurred on stimu lating olfactory bulb (15), piriform cortex (14), or entorhinal area ( eight). Monosynaptic excitation was evoked by piriform (27 of 37 teste d) and entorhinal cortex (15 of 32 tested) stimulation with polysynapt ic inhibition occurring in seven and five neurons, respectively. Polys ynaptic as well as antidromic excitation by olfactory bulb stimulation occurred in four; a further 28 tested responded polysynaptically. No response to olfactory bulb stimulation was monosynaptic. In stable imp alements, 29 neurons discharged spontaneously in the absence of applie d current. Lucifer Yellow and Neurobiotin were used to label 16 cells. All but one had smooth dendrites with soma diameters ranging from 8 t o 24 mu m. These results provide a framework in which magnocellular pr eoptic neurons can influence olfactory processing by direct action on the olfactory bulb, which action can be boosted by positive feedback f rom the bulb through the olfactory piriform and entorhinal cortices. ( C) 1997 IBRO.