Intracellular recordings from the paraventricular nucleus in slices of rat hypothalamus.

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Abstract
The electrical activity of neurons (35) in the lateral area of the paraventricular nucleus (PVN) was recorded intracellularly in vitro from slices of rat hypothalamus. Spontaneously occurring action potentials were observed in 24 of the neurons. The temporal pattern of action potentials was generally slow and irregular; occasionally some cells fired bursts of action potentials. Depolarizations with a fast rising phase and slow decay occurred spontaneously in most cells. These depolarizations exhibited a wide range of amplitudes in each cell (up to 33 mV), showed temporal summation and could serve as pre-potentials for spontaneously occurring action potentials These depolarizations were presumably excitatory post-synaptic potentials (EPSP). Depolarizing current injection could evoke action potentials. Extracellular stimuli dorsolateral to the fornix column occasionally elicited action potentials which had a short and invariant latency and which could respond to stimulation rates of 100 Hz. In some cases, extracellular stimuli in the same area evoked depolarizations which had long and variable latency and were similar to those occurring spontaneously. These 2 types of responses probably represent antidromic and orthodromic activation, respectively. Intracellular injections of horseradish peroxidase suggest that these recordings were obtained primarily, but not exclusively, from magnocellular neuroendocrine cells. This is consistent with previous anatomical studies on the location of magnocellular elements in PVN.