Reactive oxygen species are not involved in the onset of age-related memory impairment in Drosophila.

Damage from reactive oxygen species (ROS) is thought to be a cause of organismal aging. Reactive oxygen species have also been proposed to be responsible for several age-associated phenotypes, including age-related memory impairment (AMI). However, it has not previously been tested whether increasing ROS affects AMI onset. Here we examined the effects of feeding hydrogen peroxide, and the ROS-generating agent, paraquat, on olfactory aversive memory in Drosophila at young ages and during AMI onset. Reactive oxygen species feeding greatly reduced fly survival, and increased oxidized proteins and transcripts of an antioxidant enzyme, catalase (Cat) and a stress-responsive chaperone, heat-shock protein 22 (Hsp22) in fly heads. However, feeding did not impair memory in young wild-type flies, nor did it exacerbate the memory deficits in flies at the onset of AMI. Strikingly ROS feeding did disrupt memory at young ages and accelerated AMI onset was observed when expression of genes involved in the defense system to ROS, including antioxidant enzymes and Hsp22, was reduced in the mushroom bodies, neural centers required for olfactory memory. These results implicate that although ROS production increases upon aging, neuronal functions required for memory processes are sufficiently protected by the defense system to ROS even at the age of AMI onset. Thus we propose that ROS production does not affect AMI onset in Drosophila.

Hypothalamic mechanisms coordinating cardiorespiratory function during exercise and defensive behaviour.

Defensive behaviour evoked by mild or moderate psychological stress as well as increased activity and arousal are part of everyday life in humans and other animals. Both defensive behaviour and exercise are associated with marked and often quite stereotyped changes in autonomic and respiratory function. These patterned responses are generated by feed-forward or "central command" mechanisms, and are also modulated by feedback from peripheral receptors. In this review we first describe the pattern of autonomic and respiratory changes associated with defensive behaviour and exercise, and then discuss the central mechanisms that generate these patterned responses in the light of recent studies, with a particular focus on the role of the dorsomedial hypothalamus (DMH). We consider the hypothesis that the cardiorespiratory changes associated with defensive behaviour and exercise may, at least in part, be driven by common central mechanisms. Finally, we discuss the possible role of the DMH in generating circadian rhythms in arterial blood pressure and heart rate, and also in generating longer-term increases in sympathetic activity in some types of hypertension.

Cardiovascular effects of angiotensin II in the rostral ventrolateral medulla: the push-pull hypothesis.

Neurons within the rostral ventrolateral medulla (RVLM) play a pivotal role in the tonic and phasic control of blood pressure. This region also contains a high density of angiotensin II type 1 (AT1) receptors. There is evidence that tonic activation of AT1 receptors in the RVLM contributes to an increased sympathetic vasomotor activity in some models of hypertension. At the same time, under certain conditions, activation of AT1 receptors in the RVLM can cause sympathoinhibition. In this review we argue that the effect of endogenous angiotensin II in the RVLM on sympathetic vasomotor activity depends upon the balance between tonic excitatory and inhibitory effects on sympathetic premotor neurons mediated by AT1 receptors within this region, and that this balance may be altered in different physiological or pathophysiological conditions.

Differential control of cardiac and sympathetic vasomotor activity from the dorsomedial hypothalamus.

1. The dorsomedial hypothalamus (DMH) plays a crucial role in mediating the cardiovascular responses to different stressors, including acute psychological stress and cold stress. Activation of neurons in the DMH evokes increases in arterial pressure and in the activity of sympathetic nerves innervating the heart, blood vessels and brown adipose tissue. The descending pathways from the DMH to the spinal sympathetic outflow include synapses with neurons in medullary nuclei and possibly other brain stem regions. 2. Recent studies from our and other laboratories have indicated that neurons in the rostral ventrolateral medulla (RVLM) and in the region of the raphe pallidus (RP) in the medulla are important components of the descending pathways that mediate the cardiovascular response to activation of the DMH. Neurons in the RP primarily mediate the sympathetic cardiac components of the DMH-evoked response, whereas the RVLM neurons primarily mediate the sympathetic vasomotor component. 3. Activation of DMH neurons not only increases heart rate and sympathetic vasomotor activity, but also resets the baroreceptor reflex such that it remains effective, without any decrease in sensitivity, over a higher operating range of arterial pressure. 4. Activation of 5-hydroxytryptamine 5-HT(1A) receptors in the medulla oblongata leads to a selective suppression of cardiac and sympathetic vasomotor components of the DMH-evoked response, but does not affect sympathetic reflex responses evoked from baroreceptors or chemoreceptors. Thus, central 5-HT(1A) receptors modulate cardiovascular responses evoked from the DMH in a highly potent but selective fashion.

Long-term regulation of arterial blood pressure by hypothalamic nuclei: some critical questions.

1. The long-term level of arterial pressure is dependent on the relationship between arterial pressure and the urinary output of salt and water, which, in turn, is affected by a number of factors, including renal sympathetic nerve activity (RSNA). In the present brief review, we consider the mechanisms within the brain that can influence RSNA, focusing particularly on hypothalamic mechanisms. 2. The paraventricular nucleus (PVN) in the hypothalamus has major direct and indirect connections with the sympathetic outflow and there is now considerable evidence that tonic activation of the PVN sympathetic pathway contributes to the sustained increased level of RSNA that occurs in conditions such as heart failure and neurogenic hypertension. The tonic activity of PVN sympathetic neurons, in turn, depends upon the balance of excitatory and inhibitory inputs. A number of neurotransmitters and neuromodulators are involved in these tonic excitatory and inhibitory effects, including glutamate, GABA, angiotensin II and nitric oxide. 3. The dorsomedial hypothalamic nucleus (DMH) also exerts a powerful influence over sympathetic activity, including RSNA, via synapses with sympathetic nuclei in the medulla and, possibly, also other brainstem regions. The DMH sympathetic pathway is an important component of the phasic sympathoexcitatory responses associated with acute stress, but there is no evidence that it is an important component of the central pathways that produce long-term changes in arterial pressure. Nevertheless, it is possible that repeated episodic activation of this pathway could lead to vascular hypertrophy and, thus, sustained changes in vascular resistance and arterial pressure. 4. Recent studies have reactivated the old debate concerning the possible role of the baroreceptor reflex in the long-term regulation of sympathetic activity. Therefore, central resetting of the baroreceptor-sympathetic reflex may be an important component of the mechanisms causing sustained changes in RSNA. However, little is known about the cellular mechanisms that could cause such resetting.

Renal sympathetic and cardiac changes associated with anaphylactic hypotension.

Severe anaphylactic reactions can result in life-threatening hypotension, but little is known about the autonomic changes that accompany the hypotensive response. The aim of this study was to determine the renal sympathetic and cardiac responses to anaphylactic hypotension, and to evaluate the contribution of sinoaortic and vagal afferent inputs in producing these responses. Rats were sensitized with bovine serum albumin (BSA) and, after 10-14 days, were anaesthesized with sodium pentobarbitone and arterial pressure, heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded. In about two thirds of the rats, injection of BSA evoked a severe and sustained hypotension, while in the remainder, there was either a more transient hypotension or else no significant change in arterial pressure. In control unsensitized rats, BSA injection had no significant effect on arterial pressure, heart rate, or RSNA. The BSA-induced hypotension in sensitized rats was associated with increases in HR and RSNA, the magnitudes of which were correlated with the magnitude of the hypotension. There were two components to the cardiac and renal sympathoexcitatory response: (1) an initial increase in HR and RSNA, which immediately followed the onset of hypotension and which was abolished by sinoaortic denervation and vagotomy, and (2) a delayed and gradual increase in HR and RSNA, which continued even while the arterial pressure was recovering and was reduced but not abolished by sinoaortic denervation and vagotomy. Thus, BSA-induced anaphylactic hypotension causes prolonged tachycardia and renal sympathoexcitation, which is only partly due to reflex effects arising from sinoaortic baroreceptors and cardiopulmonary receptors.

Descending vasomotor pathways from the dorsomedial hypothalamic nucleus: role of medullary raphe and RVLM.

The dorsomedial hypothalamic nucleus (DMH) is believed to play a key role in mediating vasomotor and cardiac responses evoked by an acute stress. Inhibition of neurons in the rostral ventrolateral medulla (RVLM) greatly reduces the increase in renal sympathetic nerve activity (RSNA) evoked by activation of the DMH, indicating that RVLM neurons mediate, at least in part, the vasomotor component of the DMH-evoked response. In this study, the first aim was to determine whether neurons in the medullary raphe pallidus (RP) region also contribute to the DMH-evoked vasomotor response, because it has been shown that the DMH-evoked tachycardia is mediated by the RP region. The second aim was to directly assess the effect of DMH activation on the firing rate of RVLM sympathetic premotor neurons. In urethane-anesthetized rats, injection of the GABA(A) receptor agonist muscimol (but not vehicle solution) in the RP region caused a modest ( approximately 25%) but significant reduction in the increase in RSNA evoked by DMH disinhibition (by microinjection of bicuculline). In other experiments, disinhibition of the DMH resulted in a powerful excitation (increase in firing rate of approximately 400%) of 5 out of 6 spinally projecting barosensitive neurons in the RVLM. The results indicate that neurons in the RP region make a modest contribution to the renal sympathoexcitatory response evoked from the DMH and also that sympathetic premotor neurons in the RVLM receive strong excitatory inputs from DMH neurons, consistent with the view that the RVLM plays a key role in mediating sympathetic vasomotor responses arising from the DMH.

Medullary and supramedullary mechanisms regulating sympathetic vasomotor tone.

AIM: Neurons in the rostral ventrolateral medulla (RVLM) that project directly to sympathetic preganglionic neurons in the spinal cord play a critical role in maintaining tonic activity in sympathetic vasomotor nerves. Intracellular recordings in vivo from putative RVLM presympathetic neurons have demonstrated that under resting conditions these neurons display an irregular tonic firing rate, and also receive both excitatory and inhibitory synaptic inputs. This paper will briefly review some recent findings on the role of glutamate, GABA and angiotensin II (Ang II) receptors in maintaining the tonic activity of RVLM presympathetic neurons. RESULTS: Based on these findings, the following hypotheses will be discussed: (1) RVLM neurons receive tonic glutamatergic excitatory inputs, which originate from both medullary and supramedullary sources; (2) at least some neurons that project to and tonically inhibit RVLM presympathetic neurons are themselves tonically inhibited by GABAergic inputs originating from neurons in the caudalmost part of the ventrolateral medulla (caudal pressor area); (3) under normal conditions, Ang II receptors in the RVLM do not contribute significantly to the tonic activity of RVLM presympathetic neurons, but may do so in abnormal conditions such as heart failure or neurogenic hypertension; (4) RVLM presympathetic neurons maintain a significant level of tonic resting activity even when glutamate, GABA and Ang II receptors on the neurons are completely blocked. Under these conditions, the tonic activity is a consequence either of the intrinsic membrane properties of the neurons (autoactivity) or of synaptic inputs mediated by receptors other than glutamate, GABA or Ang II receptors. CONCLUSION: The current evidence indicates that the resting activity of RVLM presympathetic neurons is determined by the balance of powerful tonic excitatory and inhibitory synaptic inputs. Ang II receptors also contribute to the raised resting activity of these neurons in some pathological conditions.

Functional organisation of central cardiovascular pathways: studies using c-fos gene expression.

Until about 10 years ago, knowledge of the functional organisation of the central pathways that subserve cardiovascular responses to homeostatic challenges and other stressors was based almost entirely on studies in anaesthetised animals. More recently, however, many studies have used the method of the expression of immediate early genes, particularly the c-fos gene, to identify populations of central neurons that are activated by such challenges in conscious animals. In this review we first consider the advantages and limitations of this method. Then, we discuss how the application of the method of immediate early gene expression, when used alone or in combination with other methods, has contributed to our understanding of the central mechanisms that regulate the autonomic and neuroendocrine response to various cardiovascular challenges (e.g., hypotension, hypoxia, hypovolemia, and other stressors) as they operate in the conscious state. In general, the results of studies of central cardiovascular pathways using immediate early gene expression are consistent with previous studies in anaesthetised animals, but in addition have revealed other previously unrecognised pathways that also contribute to cardiovascular regulation. Finally, we briefly consider recent evidence indicating that immediate early gene expression can modify the functional properties of central cardiovascular neurons, and the possible significance of this in producing long-term changes in the regulation of the cardiovascular system both in normal and pathological conditions.

Simplified method for estimation of microbial activity in compost by ATP analysis.

A simplified method using ATP analysis was proposed to estimate the time course of microbial activity during composting. A compost sample was suspended in distilled water and its filtrate was used to estimate the ATP content in the compost by the luciferine-luciferase fluorescence reaction. The method permitted the rapid and simple determination of ATP in the compost and was successfully applied to monitor the time course of the microbial activity in the laboratory-scale composting process. The analytical simplicity in this method greatly improved the field-applicability of the ATP analysis for the composting process monitoring.

Evidence for tonic disinhibition of RVLM sympathoexcitatory neurons from the caudal pressor area.

Previous studies in the rat have shown that a significant proportion of the tonic activity of presympathetic neurons in the rostral ventrolateral medulla (RVLM) is dependent on the tonic activity of neurons within the caudal pressor area (CPA), located in the most caudal part of the caudal ventrolateral medulla (CVLM). In this study, we determined the extent to which tonically active neurons in the CPA contribute to sympathetic vasomotor tone, and we also investigated the pharmacological mechanisms by which these neurons affect the tonic activity of RVLM presympathetic neurons. In anaesthetised rabbits, bilateral injections of the neuroinhibitory compound muscimol into the CVLM at the level of the most caudal part of the lateral reticular nucleus, which corresponds to the anatomical location of the CPA as mapped in the rat, resulted in an immediate profound hypotension and almost complete abolition of renal sympathetic nerve activity (rSNA). In contrast, microinjections into surrounding regions had little or no effect or else evoked a delayed hypotensive response. The hypotensive and sympathoinhibitory response evoked by inhibition of the CPA was greatly delayed by prior injections of the GABA receptor antagonist bicuculline into the RVLM. In contrast, injections of the glutamate receptor antagonist kynurenic acid into the RVLM did not alter the hypotensive and sympathoinhibitory response. The results indicate that neurons within the CPA tonically inhibit other neurons, which, in turn, inhibit RVLM sympathoexcitatory neurons, via a GABAergic synapse. This disinhibition of RVLM neurons by CPA neurons is essential for maintaining resting sympathetic vasomotor tone.

Central mechanisms underlying short- and long-term regulation of the cardiovascular system.

1. Sympathetic vasomotor nerves play a major role in determining the level of arterial blood pressure and the distribution of cardiac output. The present review will discuss briefly the central regulatory mechanisms that control the sympathetic outflow to the cardiovascular system in the short and long term. 2. In the short term, the sympathetic vasomotor outflow is regulated by: (i) homeostatic feedback mechanisms, such as the baroreceptor or chemoreceptor reflexes; or (ii) feed-forward mechanisms that evoke cardiovascular changes as part of more complex behavioural responses. 3. The essential central pathways that subserve the baroreceptor reflex and, to a lesser extent, other cardiovascular reflexes, have been identified by studies in both anaesthetized and conscious animals. A critical component of these pathways is a group of neurons in the rostral ventrolateral medulla that project directly to the spinal sympathetic outflow and that receive inputs from both peripheral receptors and higher centres in the brain. 4. Much less is known about the central pathways subserving feed-forward or 'central command' responses, such as the cardiovascular changes that occur during exercise or that are evoked by a threatening or alerting stimulus. However, recent evidence indicates that the dorsomedial hypothalamic nucleus is a critical component of the pathways mediating the cardiovascular response to an acute alerting stimulus. 5. Long-term sustained changes in sympathetic vasomotor activity occur under both physiological conditions (e.g. a change in salt intake) and pathophysiological conditions (e.g. heart failure). There is evidence that the paraventricular nucleus in the hypothalamus is a critical component of the pathways mediating these changes. 6. Understanding the central mechanisms involved in the long-term regulation of sympathetic activity and blood pressure is a major challenge for the future. As a working hypothesis, a model is presented of the postulated central mechanisms that result in sustained changes in sympathetic vasomotor activity that are evoked by different types of chronic stimulation.

Selective production of organic acids in anaerobic acid reactor by pH control.

The selective production of organic acids by anaerobic acidogenesis with pH control was examined using a chemostat culture. The results showed that the product spectrum in the acid reactor strongly depended on the culture pH. Under acidic and neutral conditions, the main products were butyric acid, while acetic and propionic acids were the main products under the basic condition. This phenomenon was reversible between the acidic and basic conditions, and was not affected by the dilution rate. The change in the main products was caused by the change in the dominant microbial populations, from butyric acid-producing bacteria to propionic acid-producing bacteria in the acid reactor due to the pH shift. The control of culture pH was considered to be a useful way for controlling the product spectrum in the anaerobic acid reactor.

Role of angiotensin II receptors in the regulation of vasomotor neurons in the ventrolateral medulla.

1. There is a high density of angiotensin type 1 (AT1) receptors in various brain regions involved in cardiovascular regulation. The present review will focus on the role of AT1 receptors in regulating the activity of sympathetic premotor neurons in the rostral part of the ventrolateral medulla (VLM), which are known to play a pivotal role in the tonic and phasic regulation of sympathetic vasomotor activity and arterial pressure. 2. Microinjection of angiotensin (Ang) II into the rostral VLM (RVLM) results in an increase in arterial pressure and sympathetic vasomotor activity. These effects are blocked by prior application of losartan, a selective AT1 receptor antagonist, indicating that they are mediated by AT1 receptors. However, microinjection of AngII into the RVLM has no detectable effect on respiratory activity, indicating that AT1 receptors are selectively or even exclusively associated with vasomotor neurons in this region. 3. Under normal conditions in anaesthetized animals, AT1 receptors do not appear to contribute significantly to the generation of resting tonic activity in RVLM sympathoexcitatory neurons. However, recent studies suggest that they contribute significantly to the tonic activity of these neurons under certain conditions, such as salt deprivation or heart failure, or in spontaneously hypertensive or genetically modified rats in which the endogenous levels of AngII are increased or in which AT1 receptors are upregulated. 4. Recent evidence also indicates that AT1 receptors play an important role in mediating phasic excitatory inputs to RVLM sympathoexcitatory neurons in response to activation of some neurons within the hypothalamic paraventricular nucleus. The physiological conditions that lead to activation of these AT1 receptor-mediated inputs are unknown. Further studies are also required to determine the cellular mechanisms of action of AngII in the RVLM and its interactions with other neurotransmitters in that region.

Exogenous ACC enhances volatiles production mediated by jasmonic acid in lima bean leaves.

We report the synergistic effects of exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) and jasmonic acid (JA) on production of induced volatiles by excised lima bean leaves. Application of ACC alone to leaves induced trace amounts of volatiles. ACC positively affected three JA-induced volatiles, (E)- and (Z)-beta-ocimene, and (Z)-3-hexenyl acetate. The ethylene inhibitor, silver thiosulfate, inhibited the production of these compounds. The results suggest synergistic effects of JA and ACC on inducible volatile production by lima bean leaves. Furthermore, lima bean leaves treated with JA plus ACC became more attractive to predatory mites, Phytoseiulus persimilis, than those treated with JA alone.

Neuronal nitric oxide strongly suppresses sympathetic outflow in high-salt Dahl rats.

OBJECTIVE: To investigate the effects of a selective inhibitor of neuronal nitric oxide synthase (nNOS), 7-nitroindazole, on peripheral sympathetic outflow in Dahl rats. DESIGN AND METHODS: Dahl salt-sensitive and salt-resistant rats were fed either a regular-salt (0.4% NaCl) or a high-salt (8% NaCl) diet for 4 weeks. In chronically instrumented conscious rats, renal sympathetic nerve activity (RSNA) was measured in both baroreceptor-loaded and baroreceptor-unloaded states. The baroreceptor unload was performed by decreasing arterial pressure with occlusion of the inferior vena cava. RESULTS: 7-Nitroindazole (307 micromol/kg intraperitoneally) increased resting RSNA from 24 +/- 3% to 38 +/- 6% with an increase in mean arterial pressure of 15 +/- 3 mmHg, and increased baroreceptor-unloaded RSNA from 100% to 278 +/- 16% in salt-sensitive Dahl rats receiving a high-salt diet However, 7-nitroindazole did not increase resting RSNA, but did increase baroreceptor-unloaded RSNA from 100% to 179 +/- 15%, 177 +/- 15%, and 133 +/- 4% in salt-sensitive Dahl rats receiving a regular-salt diet, salt-resistant Dahl rats receiving a high-salt diet, and salt-resistant Dahl rats receiving a regular-salt diet, respectively. The high-salt diet significantly increased the baroreceptor-unloaded RSNA more than the regular-salt diet did, in both salt-sensitive and salt-resistant rats. After administration of the vehicle for 7-nitroindazole (peanut oil), L-arginine (100 micromol/kg per min for 10 min) decreased both resting and baroreceptor-unloaded RSNA, whereas after pretreatment with 7-nitroindazole, the L-arginine-induced suppression was reversed, in Dahl salt-sensitive rats receiving a high-salt diet. CONCLUSIONS: Neuronal nitric oxide may suppress the sympathetic discharge generated before baroreflex-mediated inhibition in all rats. This neuronal nitric oxide-mediated suppression was enhanced by the salt load in both salt-resistant and salt-sensitive Dahl rats. Finally, the neuronal nitric oxide-mediated suppression in tonic peripheral sympathetic outflow may be greatly enhanced in salt-sensitive hypertension.

Short-time ultrasound of head and neck squamous cell carcinoma under radiotherapy.

To evaluate the efficacy of ultrasonography for patients with head and neck squamous cell carcinoma before and during radiotherapy (RT), consecutive patients with macroscopic lesions were examined before and during RT. Each scan was performed percutaneously in a short time (less than 5 min). The demonstration rate of primary tumors and the largest node of previously known metastatic cervical nodes were measured. Of all 190 patients, 91 primary tumors were detected (47.9%). Primary tumors in oral cavity, oropharynx, hypopharynx and cervical esophagus were determined in over 70% and, for those of nasopharynx and larynx, the demonstration rates were 30% or less. Nodal metastases were visualized in 78 of 80 patients with regional metastases (97.5%). Using the above information, 73 patients (38.4%) received the benefit of radiation therapy. Short-time sonography is a valuable modality for patients with selected sites of head and neck cancers.

Performance of a partially packed charcoal pellet bioreactor for acetic acid fermentation.

The performance of a partially packed charcoal pellet bioreactor was compared to that of a fully packed bioreactor for aerobic acetic acid production. In the fully packed charcoal pellet bioreactor, it was considered that the shortening of an actual retention time of the culture broth limited the bioreactor performance under high dilution rate and high aeration conditions. By reducing the filling ratio of charcoal pellets to 44%, which increased the actual retention time of the culture broth, the maximum productivity increased from 3.9 g/l/h in the fully packed bed bioreactor to 5.7 g/l/h in the partially packed bioreactor without affecting the operational stability.

What drives the tonic activity of presympathetic neurons in the rostral ventrolateral medulla?

1. The present review discusses the mechanisms that maintain the tonic activity of presympathetic cardiovascular neurons in the rostral part of the ventrolateral medulla. 2. Experimental evidence is reviewed that indicates that these neurons receive both tonic excitatory and tonic inhibitory synaptic inputs. The former appear to be mediated, at least in part, by glutamate receptors and the latter appear to be mediated by GABA receptors. 3. There is also evidence that these neurons have the capacity to generate action potentials in the absence of synaptic inputs. However, at present, there is not clear evidence that such an intrinsic pacemaker-like mechanism contributes to the tonic activity of these neurons under normal resting conditions. 4. These neurons are also chemosensitive and this may contribute to their tonic activation under conditions of hypoxia or hypercapnia.