Synaptic modulation of oscillatory activity of hypothalamic neuronal networks in vitro.

1. Rhythmic bursts of action potentials in neurosecretory cells are a key factor in hypothalamic neurosecretion. Rhythmicity and synchronization may be accomplished by pacemaker cells synaptically driving follower cells or by a network oscillator. 2. In this review we describe a hypothalamic cell culture which may serve as a model for a hypothalamic network oscillator. An overview is given of neurochemical phenotypes, synaptic mechanisms and their development, properties of receptors for fast synaptic transmission, and membrane properties of cells in dissociated rat embryonic hypothalamic culture. 3. Rhythmic activity spreads in the cultured network through synapses that release glutamate, activating a heteromultimeric AMPA-type receptor containing a GluR2 subunit which is associated with a high-conductance channel for Na+ and K+. Rhythmic activity is controlled by synapses that release GABA to activate GABAA receptors. The presumed function of the two receptor types is facilitated by their respective location, GABAA receptors predominating near the soma and AMPA receptors being abundant in dendrites. 4. Network oscillators may be more reliable for the presumed function than single-cell oscillators. They are controlled through synaptic modulation, which may prove to represent a process important for the release of hormones.