Effects of prostaglandin E(2 )on the electrical properties of thermally classified neurons in the ventromedial preoptic area of the rat hypothalamus

BACKGROUND: Physiological and morphological evidence suggests that activation of the ventromedial preoptic area of the hypothalamus (VMPO) is an essential component of an intravenous LPS-dependent fever. In response to the endogenous pyrogen prostaglandin E(2 )(PGE(2)), the majority of temperature insensitive neurons in the VMPO show an increase in firing rate, while warm sensitive neurons are inhibited. We have hypothesized that these PGE(2 )dependent effects on firing rate are due to changes in the inherent electrical properties of VMPO neurons, which are regulated by the activity of specific ionic currents. RESULTS: To characterize the electrical properties of VMPO neurons, whole-cell recordings were made in tissue slices from male Sprague-Dawley rats. Our results indicate that PGE(2 )dependent firing rate responses were not the result of changes in resting membrane potential, action potential amplitude and duration, or local synaptic input. However, PGE(2 )reduced the input resistance of all VMPO neurons, while increasing the excitability of temperature insensitive neurons and decreasing the excitability of warm sensitive neurons. In addition, the majority of temperature insensitive neurons responded to PGE(2 )with an increase in the rate of rise of the depolarizing prepotential that precedes each action potential. This response to PGE(2 )was reversed for warm sensitive neurons, in which the prepotential rate of rise decreased. CONCLUSION: We would therefore suggest that PGE(2 )is having an effect on the ionic currents that regulate firing rate by controlling how fast membrane potential rises to threshold during the prepotential phase of the action potential.