Effect of PGE2 on preoptic and anterior hypothalamic neurons using brain slice preparation

Membrane depolarization by activation of prostaglandin E receptor EP3 subtype of putative serotonergic neurons in the dorsal raphe nucleus of the rat

A whole-cell current-clamp study using a thin slice preparation of the rat brain was carried out to elucidate the function of prostaglandin E (PGE) receptor EP3 subtype in the dorsal raphe nucleus (DR), where mRNA of this subtype is highly expressed. Bath application of PGE2 or M&B 28767, an EP3 agonist, depolarized the membrane of the large DR neurons in a concentration-dependent manner between 10(-9) and 10(-6) M. These neurons showed hyperpolarization of membrane potential to 10 or 50 microM serotonin. Neither an EP2 receptor agonist, butaprost, an EP2/EP4 receptor agonist, 11-deoxy-PGE1, nor an EP1 receptor agonist, 17-phenyl-PGE2, had any effect on large DR neurons between 10(-9) and 10(-6) M. The M&B 28767-induced depolarization was observed in a Ca(2+)-free, high Mg2+ (5 mM) solution containing 0.3 microM tetrodotoxin, and occurred equally well when intracellular Cl- was replaced by gluconate. These results suggest that direct agonist-activation of EP3 receptor depolarizes the membrane by a cationic conductance, leading to excitation of DR neurons, and indicate a physiological implication that EP3 receptor may modulate the serotonergic inhibition of neuronal activities.

Histamine receptor and its regulation of energy metabolism

In a series of studies on brain functions of histamine, probes to manipulate activities of histaminergic neuronal systems were applied to assess histaminergic function in non-obese normal, and lean and obese Zucker rats. Food intake was suppressed by both activation of H1-receptors and inhibition of H3-receptors in the ventromedial hypothalamic nucleus (VMH) and the paraventricular nucleus, each of which is a satiety center. Feeding circadian rhythm was decreased in its amplitude through histaminergic modulation in the hypothalamus. Histamine neurons in the mesencephalic trigeminal nucleus (Me5) were involved in regulation of masticatory functions, particularly eating speed, while histamine-containing neurons in the VMH controlled intake volume of meals. Energy deficiency in the brain enhanced satiation through histaminergic activation of VMH neurons, which in turn produced glycogenolysis in the hypothalamus to maintain homoestatic control of glucose supply. A very-low-calorie conventional Japanese diet, which is a fiber rich and low energy food source, enhanced satiation by increased mastication and because of the low energy supply of the diet. Hypothalamic histamine neurons were activated by high ambient temperature and also by interleukin-1 beta, an endogenous pyrogen, to maintain homeostatic thermoregulation. Behavioral and metabolic abnormalities of Zucker obese rats were mediated by a deficit in hypothalamic neuronal histamine, and the Zucker rat was evaluated as an animal model of histamine deficiency. Transplantation of the lean fetal hypothalamus into the third cerebroventricle of host obese Zuckers attenuated the abnormalities.

Temperature effects on Legionella pneumophila killing by and multiplication in phagocytes of guinea pigs

We examined the effects of temperature on the interaction between Legionella pneumophila and phagocytes of guinea pigs. The body temperatures of guinea pigs infected with a sublethal dose (1.2 x 10(4) CFU) or a lethal dose (1.0 x 10(5) CFU) of L. pneumophila elevated from 38.4 +/- 0.15 C to 40.2 +/- 0.42 C or 40.3 +/- 0.62 C, respectively. The intracellular bacterial killing by and bacterial proliferation in the phagocytes were examined at 33, 37, 40, and 42 C, using in vitro culture systems of peritoneal macrophages or polymorphonuclear leukocytes (PMN) of guinea pigs. In all the macrophages incubated at different temperatures, significant intracellular bacterial killings were observed at 4 hr after in vitro phagocytosis. After 24 hr of incubation, there was about a 100-fold increase of CFU and the number reached a maximum after 48 hr of incubation in the macrophages incubated at 42 C as well as 37 and 40 C, suggesting that macrophages support the intracellular bacterial growth in hyperthermia. In the PMN, L. pneumophila CFU 4 hr or 12 hr after the infection were significantly lower at 42 C than those at 37 C (P < 0.05), indicating that the bactericidal capacity of PMN was enhanced at 42 C compared to 37 C. However, in all the PMN incubated at different temperatures, there were about 10-fold increases of CFU 24 hr after the infection, suggesting that PMN as well as macrophages support intracellular bacterial growth in hyperthermia. The extracellular bacterial growth was examined at 33, 37, 40, and 42 C in buffered yeast extract (BYE) broth or RPMI 1640 medium containing 50% guinea pig serum as a permissive or non-permissive liquid medium for the bacterial growth, respectively. Inhibition of bacterial growth in BYE broth at 42 C, and a decrease of CFU in RPMI 1640 medium containing 50% guinea pig serum at 42 C were observed. In conclusion, hyperthermia may be beneficial by restricting extracellular bacterial survival, but it exerts no beneficial effect on the restriction of intracellular bacterial growth in phagocytes, though PMN showed enhanced initial killing at 42 C. These results suggest that fever, or hyperthermia itself, may not largely contribute as a nonspecific host defense early in the course of legionellosis.

Preoptic/anterior hypothalamic warming increases EEG delta frequency activity within non-rapid eye movement sleep

The effects of mild POAH warming and cooling on EEG frequency patterns within sustained periods of NREM sleep were examined. EEG spectral power analysis showed that POAH warming increased delta (0.5-4.0 Hz) activity, but had no effect on theta or sigma frequencies. Delta power was also increased during a 1 h recovery period, following warming. POAH cooling had no EEG effects. Since delta power is thought to be an index of sleep depth, our findings suggest that POAH thermoregulatory mechanisms participate in the regulation of the depth of NREM sleep.

Effects of hypothalamic microinjection of PGE2 on body temperature and sympathetic nervous activities in the rabbit

The febrile response and sympathetic nervous response to hypothalamic microinjections of prostaglandin E2 (PGE2) were investigated in anesthetized rabbits. Microinjection of PGE2 (500-1000 ng) caused an increase in rectal temperature of more than 0.3 degrees C in 13 of 50 loci in the preoptic and anterior hypothalamic area (PO/AH). At 8 of these 13 loci, PGE2 elicited response patterns in the sympathetic nervous system, such as an increase in cutaneous sympathetic nervous activity and decrease in renal sympathetic nervous activity. This pattern of sympathetic nervous responses was induced with a simultaneous increase in rectal temperature of more than 0.5 degrees C. The 8 loci were distributed in the preoptic area, especially in the vicinity of the supraoptic nucleus. Electrolytic lesions of this region were made bilaterally, and intracerebroventricular injection of PGE2 (8 micrograms/kg) was found to inhibit fever and sympathetic activity. The results demonstrate that the action of PGE2 is responsible for the response patterns of sympathetic twigs during fever. The preoptic area, especially in the vicinity of the supraoptic nucleus, is most sensitive to PGE2 for the patternized response of sympathetic neurons and fever.

Prostaglandin E2 excites neurons of the nucleus tractus solitarius by activating cation channels

Nucleus tractus solitarius (NTS) has a high density of prostaglandin E2 (PGE2)-binding sites. Action of PGE2 (10(-9)-10(-6) M) was tested on neurons in a NTS slice with patch-clamp recording under synaptic blockade. PGE2 raised the firing rate in approximately half of the neurons in cell-attached patch mode. In whole-cell current clamp, PGE2 depolarized membrane potential accompanied by an increase in firing rate. In whole-cell voltage clamp (-58 mV), PGE2 induced the inward current with an increase in conductance. The current was linearly related to voltage from -100 mV to -10 mV and suppressed between -10 mV and 20 mV. The current-voltage curve remained similar under low external Cl- or high internal Cl- conditions and after external Na+ was replaced by Cs+. It is concluded that PGE2 excites NTS neurons by activating cation conductance.

Fever: causes and consequences

The present review distinguishes pathogenic, neurogenic, and psychogenic fever, but focuses largely on pathogenic fever, the hallmark of infectious disease. The data presented show that a complex cascade of events underlies pathogenic fever, which in broad outline - and with frank disregard of contradictory data - can be described as follows. An invading microorganism releases endotoxin that stimulates macrophages to synthesize a variety of pyrogenic compounds called cytokines. Carried in blood, these cytokines reach the perivascular spaces of the organum vasculosum laminae terminalis (OVLT) and other regions near the brain where they promote the synthesis and release of prostaglandin (PGE2). This prostaglandin then penetrates the blood-brain barrier to evoke the autonomic and behavioral responses characteristic of fever. But then once expressed, fever does not continue unchecked; endogenous antipyretics likely act on the septum to limit the rise in body temperature. The present review also examines fever-resistance in neonates, the blunting of fever in the aged, and the behaviorally induced rise in body temperature following infection in ectotherms. And finally it takes up the question of whether fever enhances immune responsiveness, and through such enhancement contributes to host survival.

Thermal and PGE2 sensitivity of the organum vasculosum lamina terminalis region and preoptic area in rat brain slices

1. The effects of local applications of prostaglandin E2 (PGE2) on the unit activity of fifty-one neurones in the organum vasculosum lamina terminalis (OVLT) region and fifty-eight neurones in the preoptic area (POA) were investigated in small tissue slices from the rat hypothalamus containing the OVLT and POA isolated from each other. 2. Of these, thirty OVLT and twenty-eight POA neurones were warm sensitive and increased their discharge rate in response to a rise in tissue temperature. One OVLT neurone and one POA neurone were cold sensitive and showed the opposite type of responses to changes in temperature. The thermosensitivity of these neurones was still observed in a Ca2+ free-high Mg2+ solution. 3. Perfusion with PGE2 in doses between 1 and 250 nM changed the discharge rate in forty-two of fifty-one OVLT neurones and in thirty-two of fifty-eight POA neurones in a dose-dependent manner. The responses to PGE2 were not lost during synaptic blockade. The threshold dose of PGE2 to alter the discharge rate of the OVLT neurones (4.8 +/- 1.1 (S.E.M.) nM, n = 16) was significantly lower than that of the POA neurones (40.9 +/- 12.2 nM, n = 16). 4. Fifteen of forty-two OVLT neurones exhibited the responses with a slower onset (latency 5-13 min) and a longer duration (20 min to 3 h), but such responses were observed in only one of thirty-two POA neurones. 5. The responses of OVLT and POA neurones to PGE2 (50-250 nM) were reversibly blocked by a concurrent application of AH6809, a prostanoid EP1 and/or a DP receptor antagonist. 6. While there was no clear correlation between the type of thermosensitivity and the type of response to PGE2 among the POA neurones, a significantly higher incidence of inhibitory response to PGE2 was found among the warm-sensitive neurones in the OVLT region. 7. The lower threshold responses to PGE2 and the higher incidence of PGE2 responsiveness among OVLT neurones are consistent with previous findings which showed that the highest density of PGE2 receptor binding and the highest pyrogenic sensitivity to microinjected PGE2 were observed in the OVLT region. The results provide further evidence for the critical involvement of the OVLT region in mediating the febrile responses to blood-borne endogenous pyrogen through the local release of PGE2.

Effect of prostaglandin E2 on thermoresponsive neurones in the preoptic and ventromedial hypothalamic regions of rats

1. We investigated the effect of microinjection of prostaglandin E2 (PGE2) into the preoptic (POA) or the ventromedial hypothalamic (VMH) region on rectal temperature in rats. Fever was induced by microinjection of PGE2 into the POA or the VMH regions. The febrile responses induced by PGE2 injected into the VMH region were significantly greater than those induced by injection into the POA region. 2. The effect of temperature on neuronal activity in the POA and the VMH regions was investigated by using slice preparations from rats. It was revealed that there exist many thermoresponsive neurones in the VMH region as well as in the POA region, and that the proportion of thermoresponsive neurones out of the total neurones examined in the VMH region was almost identical to that in the POA region. In addition, the warm-responsive neurones in the VMH region exhibited larger thermal coefficients than those in the POA region. 3. When PGE2 was applied in a recording chamber where the tissue slice was perfused, most of the neurones in the VMH region which responded to PGE2 showed a decrease in their firing rate, while those in the POA region showed an increase in their firing rate, regardless of their thermoresponsiveness. In the POA region, PGE2 began to affect the activities of the warm-responsive neurones in the range of 5 x 10(-7) to 7 x 10(-6) M, whereas maximum responses were obtained between the concentrations of 5 x 10(-6) and 5 x 10(-5) M. In the VMH region, PGE2 began to change the activities of the warm-responsive neurones in the range of 5 x 10(-8) to 5 x 10(-7) M, and the maximum effect of PGE2 on the VMH warm-responsive neurones occurred between the concentrations of 8 x 10(-7) and 4 x 10(-5) M. 4. The present results show that neurones exhibit different responsiveness to PGE2 and different sensitivity to PGE2 between the POA and the VMH regions. Nevertheless, microinjection of PGE2 into either the POA or the VMH region produces fever. Therefore, it is suggested that fever is produced by complex neuronal networks in the central nervous system.