Effects of Prostaglandin D₂ on the Activity of Hypothalamic Neurons in the Rat

Abstract

The effects of electrophoretically applied prostaglandin D₂ (PGD₂) on neuronal activity in the rat lateral preoptic area (LPOA) and posterior hypothalamic area (PHA) were examined. In the LPOA, 20% of the tested neurons were excited, 26% inhibited, and 6% showed bidirectional response. The direct effects often showed desensitization after repeated applications. Neurons excited by PGD₂ were significantly sensitive (excitation) to acetylcholine (ACh). The ACh excitatory effect was sometimes (38%) attenuated, blocked, or reversed by concurrent PGD₂ application. Excitatory or inhibitory effect of noradrenaline (NA) was not related to the effects of PGD₂, however, modulation of the NA responses by PGD₂ was common (58%). Inhibition, the predominant NA response, was changed to no effect or to excitation during simultaneous PGD₂ application. Changes of the NA responses from inhibition to excitation, or from excitation to inhibition-excitation sequences were observed after PGD₂ infusion into the third cerebral ventricle at low concentrations. In 43% of the cells, neurotransmission in the LPOA following ventral noradrenergic bundle stimulation was modified by PGD₂ application. PGD₂ application tended to reduce the duration of inhibition and to extend that of excitation. The direct effects of PGD₂ in the PHA were similar to those in the LPOA. Desensitization was also observed in the PHA, but no interrelations were observed among the effects of PGD₂, ACh, and NA. Modulation of ACh and NA responses by PGD₂ was rarely seen in the PHA. Possible contributions of PGD₂ to sleep and thermoregulation are discussed.