The Effects Of Prostaglandine2 On The Firingactivities And Thermosensitivity Of Neurons In The Lateral Parabrachial Nucleus

Prostaglandin E₂?PGE₂?,the important central mediator in febrile responses,is produced in cyclooxygenase-2/membrane associated prostaglandin E₂ synthase 1?COX-2/m PGES1?pathway.It was demonstrated that COX-2/m PGES1 complex in the preoptic-anterior hypothalamus area?PO/AH?plays a key role in PGE₂ synthesis at an early stage of fever response to LPS.The lateral parabrachial nucleus?LPB?is located in the dorsolateral pons.Recent studies have identified LPB as a crucial relay for afferent signals from the skin that promote defensive thermoregulatory responses before changes in environmental temperature affect body core temperature.Recently,LPB has also been identified as one of the brain sites mediating PGE₂-induced fever,however,it is not clear whether PGE₂ can be locally synthetized in LPB during LPS fever,If can,what are the effects of PGE₂ on firing rate,temperature sensitivity and the electrophysiological properties of LPB neurons? In this study,the RT-q PCR technique was used to detect the changes in the m RNA expression of COX-2 and m PGES1 in LPB after the i.p.injection of LPS to determine whether the PGE₂ can be locally synthetized in LPB,and then the effects of PGE₂ on firing rate,temperature sensitivity and the electrophysiological properties of LPB neurons were observed by the infrared visual patch clamp technique,to clarify electrophysiological mechanisms for pyrogenic effects of PGE₂ in the LPB,and prepare grounds for further investigating the neuronal mechanisms for PGE₂-induced fever.Part I PGE₂ synthesis in the LPB during LPS fever ObjectivesTo investigate whether the PGE₂ can be locally synthetized in the LPB during LPS fever.Materials and methodsMale SD rats?220-250g?were randomized into 1,2,4,6 hour groups.Each group was consisted of 12 rats,6 of which were injected intraperitoneally with normal saline1ml/kg?0.9%?,another 6 were injected intraperitoneally with LPS 1ml/kg?100?g/ml?.After measurements of deep body temperature,rats were killed at 1,2,4,6 hour respectively,and then the changes in the m RNA expression of COX-2 and m PGES1 inthe LPB was detected using the RT-q PCR technique.Results1.Changes in body temperatureThere was no significant change in body temperature of rats in the saline group?p>0.05?,while the body temperature of rats in the LPS group was significantly increased?P<0.05?.2.Changes in the m RNA expression of COX-2 and m PGES1 in the LPBCompared with the control group,at 1 hour,2 hour,4 hour and 6 hour after the i.p.injection of LPS,the m RNA relative expression of COX-2 and m PGES1 in LPB were significantly increased?P<0.05?.ConclusionsThe PGE₂ can be locally synthetized in the LPB during LPS fever.Part II The effects of PGE₂ on the firing activity and temperature sensitivity of LPB neurons objectivesTo investigate the effects of PGE₂ on the firing rate and temperature sensitivity of LPB warm-sensitive and temperature-insensitive neurons.Materials and methodsCoronal brainstem slices containing the LPB were prepared from SPF healthy male Sprague–Dawley rats?80–150g?and incubated for about 1 hour at 32°C.Thereafter,in the current clamp mode,after identifying the temperature sensitivity of LPB neurons,PGE₂ was perfused to observe the effects of PGE₂ on the firing rate and temperature sensitivity of LPB neurons.ResultsUsing the current clamp mode,41 neurons that perfusion PGE₂ were recorded in LPBel,LPBc and LPBd.Of these neurons,9 were found in LPBel,17 in LPBc,and 15 in LPBd,13 were warm-sensitive neurons,18 were moderate-slopetemperature-insensitive neurons,and 10 were low-slope temperature-insensitive neurons.At 32 ?,36 ? and 39 ?,the firing rate of the three types of LPB neurons were significantly increased by perfusion PGE₂?P<0.05?;compared with the effects of PGE₂ on the firing rate of neurons in the three LPB subnuclei,at 36?,the effect of PGE₂ on the firing rate of the LPBel neurons was more obvious than that of LPBd neurons?P<0.05?.At 32 ?,there was no significant effect on the firing amplitude of the three types of LPB neurons by perfusion PGE₂?P >0.05?;at 36 ? and 39 ?,PGE₂ significantly reduced the firing amplitude of the warm-sensitive neurons?P<0.05?,PGE₂ had no effect on the firing amplitude of the moderate-slope temperature-insensitive neurons and the low-slope temperature-insensitive neurons?P >0.05?.At 32 ?,36 ? and 39 ?,the temperature sensitivity coefficients of the three types of LPB neurons were significantly increased by perfusion PGE₂?P<0.05?;the effects of PGE₂ on the temperature sensitivity coefficients of neurons within the three LPB subnuclei were not significantly different?P >0.05?.Conclusions1.PGE₂ participates in the febrile responses of PGE₂ in LPB by increasing the firing rate and the temperature sensitivity of LPB neurons,.2.The effect of PGE₂ on the firing rate of LPBel neurons was greater than that of LPBd neurons Key wordsPart III The effects of PGE₂ on electrophysiological properties of LPB neurons ObjectivesTo determine the cellular mechanisms responsible for the effects of PGE₂ on the firing rate of LPB neurons by observing the effect of PGE₂ on electrophysiologicalproperties of the three types of LPB neurons,Materials and methodsAfter identifying the thermosensitivity of LPB neurons,the effects of PGE₂ on the resting potential,action potential duration,firing amplitude,rate of rise of the depolarizing prepotential,threshold potential and the after hyperpolarization potential amplitude were observed in whole-cell current clamp mode.ResultsAt 32?,36?and 39?,PGE₂ all increased the firing rate,and the rate of rise of the depolarizing prepotential of 11 intracellular spontaneous firing neurons in LPB?P<0.05?,however,PGE₂ had no significant effects on the resting potential,action potential duration,firing amplitude,threshold potential and the after hyperpolarization potential amplitude?P >0.05?.ConclusionsThe cellular mechanisms responsible for the effects of PGE₂ on the firing rate of LPB neurons may be related to the increase in the rate of rise of the depolarizing prepotential.