Transient receptor potential vanilloid type 4 is expressed in vasopressinergic neurons within the magnocellular subdivision of the rat paraventricular nucleus of the hypothalamus.

Changes in plasma osmolality can drive changes in the output from brain centres known to control cardiovascular homeostasis, such as the paraventricular nucleus of the hypothalamus (PVN). Within the PVN hypotonicity reduces the firing rate of parvocellular neurons, a neuronal pool known to be involved in modulating sympathetic vasomotor tone. Also present in the PVN is the transient receptor potential vanilloid type 4 (TRPV4) ion channel. Activation of TRPV4 within the PVN mimics the reduction in firing rate of the parvocellular neurons but it is unknown if these neurons express the channel. We used neuronal tracing and immunohistochemistry to investigate which neurons expressed the TRPV4 ion channel protein and its relationship with neurons known to play a role in plasma volume regulation. Spinally projecting preautonomic neurons within the PVN were labelled after spinal cord injection of FluoroGold (FG). This was followed by immunolabelling with anti-TRPV4 antibody in combination with either anti-oxytocin (OXT) or anti-vasopressin (AVP). The TRPV4 ion channel was expressed on 63% of the vasopressinergic magnocellular neurosecretory cells found predominantly within the posterior magnocellular division of the PVN. Oxytocinergic neurons and FG labelled preautonomic neurons were present in the same location, but were distinct from the TRPV4/vasopressin expressing neurons. Vasopressinergic neurons within the supraoptic nucleus (SON) were also found to express TRPV4 and the fibres extending between the SON and PVN. In conclusion within the PVN, TRPV4 is well placed to respond to changes in osmolality by regulating vasopressin secretion, which in turn influences sympathetic output via preautonomic neurons.

Vagal afferents, sympathetic efferents and the role of the PVN in heart failure.

Sympatho-excitation is a characteristic of cardiovascular disease including heart failure (HF). The paraventricular nucleus of the hypothalamus (PVN) is an important site for central integration of sympathetic outflow. Atrial volume receptors (AVRs) in the wall of the right atrium transduce cardiovascular variables (pressure/volume) into an input that is integrated centrally, in for example, the PVN. Descriptions of the location and structure of the AVRs as well as the molecular mechanism initiating transduction remain scarce, nevertheless preautonomic neurons of the PVN have been consistently identified as making a significant contribution to the sympatho-excitation evident in HF. Furthermore, excitatory and inhibitory interactions within the PVN determine sympathetic tone. A nitric oxide dependent GABAergic inhibition sets the prevailing sympathetic output from the PVN, which in HF becomes dysregulated. Inflammation and oxidative stress have been recognised as possible triggers to the disinhibition. The actions of proinflammatory cytokines and reactive oxygen species in relation to the signalling pathways, which are important in generating sympathetic tone are discussed, as well as the contribution these might make to abnormal control of the sympathetic nervous system in cardiovascular disease.

Expression of transient receptor potential channels TRPC1 and TRPV4 in venoatrial endocardium of the rat heart.

The atrial volume receptor reflex arc serves to regulate plasma volume. Atrial volume receptors located in the endocardium of the atrial wall undergo mechanical deformation as blood is returned to the atria of the heart. The mechanosensitive channel(s) responsible for regulating plasma volume remain to be determined. Here we report that the TRP channel family members TRPC1 and TRPV4 were expressed in sensory nerve endings in the atrial endocardium. Furthermore, TRPC1 and TRPV4 were coincident with the nerve ending vesicle marker synaptophysin. Calcitonin gene-related peptide was exclusively confined to the myo- and epicardium of the atria. The small conductance Ca(2+)-activated K(+) channels (SK2 and SK4) were also present, however there was no relationship between SK and TRP channels. SK2 channels were expressed in nerves in the epicardium, while SK4 channels were in some regions of the endocardium but appeared to be present in epithelial cells rather than sensory endings. In conclusion, we have provided the first evidence for TRPC1 and TRPV4 channels as potential contributors to mechanosensation in the atrial volume receptors.

The histamine H4 receptor is functionally expressed on neurons in the mammalian CNS.

BACKGROUND AND PURPOSE: The histamine H4 receptor is the most recently identified of the G protein-coupled histamine receptor family and binds several neuroactive drugs, including amitriptyline and clozapine. So far, H4 receptors have been found only on haematopoietic cells, highlighting its importance in inflammatory conditions. Here we investigated the possibility that H4 receptors may be expressed in both the human and mouse CNS. METHODS: Immunological and pharmacological studies were performed using a novel anti-H4 receptor antibody in both human and mouse brains, and electrophysiological techniques in the mouse brain respectively. Pharmacological tools, selective for the H4 receptor and patch clamp electrophysiology, were utilized to confirm functional properties of the H4 receptor in layer IV of the mouse somatosensory cortex. RESULTS: Histamine H4 receptors were prominently expressed in distinct deep laminae, particularly layer VI, in the human cortex, and mouse thalamus, hippocampal CA4 stratum lucidum and layer IV of the cerebral cortex. In layer IV of the mouse somatosensory cortex, the H4 receptor agonist 4-methyl histamine (20 micromol x L(-1)) directly hyperpolarized neurons, an effect that was blocked by the selective H4 receptor antagonist JNJ 10191584, and promoted outwardly rectifying currents in these cells. Monosynaptic thalamocortical CNQX-sensitive excitatory postsynaptic potentials were not altered by 4-methyl histamine (20 micromol x L(-1)) suggesting that H4 receptors did not act as hetero-receptors on thalamocortical glutamatergic terminals. CONCLUSIONS AND IMPLICATIONS: This is the first demonstration that histamine H4 receptors are functionally expressed on neurons, which has major implications for the therapeutic potential of these receptors in neurology and psychiatry.

Irrigated crop production is associated with less malaria than traditional agricultural practices in Tanzania.

There is concern that crop irrigation that results in increased numbers of vector mosquitoes will lead to a rise in malaria in local communities. We evaluated the level of malaria experienced in 3 communities in northern Tanzania with different agricultural practices: rice irrigation, sugar-cane irrigation and traditional maize cultivation. Five cross-sectional surveys were used to measure the prevalence of infection with falciparum malaria in 1-4 years old children in each community over a period of 12 months. Active case detection was also carried out to record clinical episodes of malaria during the study period. Information on antimalarial measures was also recorded. Results from the cross-sectional surveys showed that the overall prevalence of malaria parasites was less near the rice irrigation (12.5%) and sugar-cane (16.9%) schemes than the savannah village (29.4%). There were also significantly fewer clinical episodes of malaria in the rice village (15 cases/1000 child-weeks at risk [cwar]) than either the sugar-cane (36 cases/1000 cwar) or savannah (40 cases/1000 cwar) villages. Overall, rice irrigation was associated with less malaria than alternative agricultural practices, despite the considerable numbers of vectors produced in the paddies. This finding supports other studies that indicate that irrigation in much of sub-Saharan Africa will not lead to increased malaria. Nonetheless, African governments planning irrigation projects need effective policies to encourage local communities to use personal protection measures, such as insecticide-treated bednets, and to ensure that these communities have access to effective antimalarial drugs and efficient health services.

A malaria control trial using insecticide-treated bed nets and targeted chemoprophylaxis in a rural area of The Gambia, west Africa. 7. Impact of permethrin-impregnated bed nets on malaria vectors.

The impact of permethrin-impregnated bed nets on malaria vectors was studied in 6 pairs of villages during the rainy season in 1989. In each pair, the residents of one village had their nets treated whilst those of the other remained untreated. Routine collections of mosquitoes were made outdoors in the early evening using human-biting collections, and indoors with insecticide sprays, light traps and by searches under bed nets. Mosquitoes of the Anopheles gambiae complex, An. gambiae sensu stricto, An. arabiensis and An. melas, were present in large numbers for 5 months of the study period. These mosquitoes were susceptible to permethrin as judged by bioassay results. Outdoor human-biting rates in the early evening in communities with treated bed nets were similar to those in communities with untreated nets. In villages with treated bed nets most biting occurred outdoors in the early evening with little taking place under impregnated nets. The insecticidal activity of permethrin-impregnated bed nets, dipped by the local population, provided good individual protection against mosquitoes throughout the rainy season and bed nets remained effective even when washed up to 3 times. There was little to suggest that the use of insecticide-treated nets reduced the survival of mosquito populations in villages with impregnated nets. The absence of the expected village-wide effects of net impregnation may have resulted from the circulation of mosquitoes between villages with treated and untreated nets. The proportion of mosquitoes which fed on humans did not differ significantly between villages with treated and untreated nets.(ABSTRACT TRUNCATED AT 250 WORDS)

A malaria control trial using insecticide-treated bed nets and targeted chemoprophylaxis in a rural area of The Gambia, west Africa. 3. Entomological characteristics of the study area.

Baseline entomological surveillance was carried out in a rural area of The Gambia during the rainy season in 1988, one year before the implementation of a malaria control programme using insecticide-impregnated nets and targeted chemoprophylaxis in villages with a primary health care (PHC) system. Mosquito collections took place in 6 pairs of settlements each with untreated bed nets; within each pair there was a large PHC village with a resident village health worker (VHW) and traditional birth attendant (TBA) and a smaller non-PHC village without either a VHW or a TBA. The most common vectors in the study area were Anopheles gambiae sensu stricto and, to a lesser extent, An. arabiensis. These mosquitoes were found in appreciable numbers for at least 4 months of the year (geometric mean/bedroom/night = 32.5, 95% confidence interval 18.2-57.3). Numbers of mosquitoes collected in PHC villages or non-PHC villages were not significantly different. Greater numbers of mosquitoes were found in villages closer to the River Gambia than in those further away. Evidence for DDT resistance due to elevated glutathione S-transferase activity was found in one of the 12 villages, but there was no evidence of resistance to organophosphate or carbamate insecticides as suggested by the low esterase levels and carbamate sensitive acetylcholinesterase.

A malaria control trial using insecticide-treated bed nets and targeted chemoprophylaxis in a rural area of The Gambia, west Africa. 6. The impact of the interventions on mortality and morbidity from malaria.

The effects of insecticide-impregnated bed nets on mortality and morbidity from malaria have been investigated during one malaria transmission season in a group of rural Gambian children aged 6 months to 5 years. Sleeping under impregnated nets was associated with an overall reduction in mortality of about 60% in children aged 1-4 years. Mortality was not reduced further by chemoprophylaxis with Maloprim given weekly by village health workers throughout the rainy season. Episodes of fever associated with malaria parasitaemia were reduced by 45% among children who slept under impregnated nets. The addition of chemoprophylaxis provided substantial additional benefit against clinical attacks of malaria; 158 episodes were recorded among 946 children who slept under impregnated nets but who also received chemoprophylaxis. Chemoprophylaxis reduced the prevalence of splenomegaly and parasitaemia at the end of the malaria transmission season by 63% and 83% respectively. Thus, insecticide-impregnated bed nets provided significant protection in children against overall mortality, mortality attributed to malaria, clinical attacks of malaria, and malaria infection. The addition of chemoprophylaxis provided substantial additional protection against clinical attacks of malaria and malaria infection but not against death.

The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children.

Anthropometric measurements were made and serum iron and ferritin levels determined in a group of Gambian children at the beginning of the rainy season and these findings were related to the malaria experience of the children during the following malaria transmission season. Susceptibility to malaria was not correlated with prior weight-for-age, height-for-age, weight-for-height or serum albumin, or with serum iron, serum iron binding capacity nor serum ferritin. Thus, our findings do not provide any support for the view that poor nutritional status, as assessed by anthropometric measurements, or iron deficiency protect against malaria infection. Children who developed a clinical attack of malaria accompanied by a high level of parasitaemia tended to have a higher mean weight-for-age at the beginning of the rainy season than did children who had a clinical attack accompanied by a low level of parasitaemia, but the difference between groups was not statistically significant. However, they had a significantly higher mean serum ferritin level (P less than 0.01).

The effect of insecticide-treated bed nets on mortality of Gambian children.

Insecticide treatment of bed nets ("mosquito nets") may be a cheap and acceptable method of reducing the morbidity and mortality caused by malaria. In a rural area of The Gambia, bed nets in villages participating in a primary health-care (PHC) scheme were treated with permethrin at the beginning of the malaria transmission season. Additionally, children aged 6 months to 5 years were randomised to receive weekly either chemoprophylaxis with maloprim or a placebo throughout the malaria transmission season. We measured mortality in children in PHC villages before and after the interventions described, and compared this with mortality in villages where no interventions occurred (non-PHC villages). About 92% of children in PHC villages slept under insecticide-treated bed nets. In the year before intervention, mortality in children aged 1-4 years was lower in non-PHC villages. After intervention, the overall mortality and mortality attributable to malaria of children aged 1-4 in the intervention villages was 37% and 30%, respectively, of that in the non-PHC villages. Among children who slept under treated nets, we found no evidence of an additional benefit of chemoprophylaxis in preventing deaths. Insecticide-treated bed nets are simple to introduce and can reduce mortality from malaria.

A comparison of two DNA probes, one specific for Plasmodium falciparum and one with wider reactivity, in the diagnosis of malaria.

The sensitivity and specificity of 2 probes for the detection of malarial infection was studied. 399 blood samples from Gambian children were tested in a deoxyribonucleic acid (DNA) hybridization assay, and the results compared with the microscopical findings from thick blood films. 8 additional pure Plasmodium malariae and 14 pure P. vivax samples were also assayed. One probe, containing a 21 base pair tandem repeat and highly specific for P. falciparum, detected this species in all except 2 of 74 samples with a parasitaemia of 250 per microliter or more; the overall sensitivity of the probe was 76%. The other probe, a 6 kilobase pair organelle DNA, is conserved in all Plasmodium species so far tested. Its sensitivity for P. falciparum was lower than the 21 base pair repeat, but it detected P. vivax and P. malariae at low levels of parasitaemia, and thus could be useful in field studies.

Sporozoite antibodies and malaria in children in a rural area of The Gambia.

Sporozoite antibody levels were measured in a group of children aged one to nine years resident in a rural area of The Gambia, using an ELISA to the repeat peptide (NANP)40. The prevalence and titre of antibodies varied with age but not with sex or ethnic group. Significant variations in prevalence were recorded within a group of adjacent villages. Children who were seropositive at the beginning of the dry season had higher spleen and parasite rates both at this time and at the end of the subsequent rainy season than did seronegative children, suggesting that they were exposed more frequently to infection. However, seropositive children had fewer episodes of fever accompanied by high levels of parasitaemia than did seronegative children, suggesting that they had a greater degree of clinical immunity. No differences were found in seroprevalence rates or in mean antibody titres between children who slept under conventional or Permethrin treated bed nets and those who did not, even though bed nets significantly reduced the number of bites by vector mosquitoes.

Lack of an association between acute gastroenteritis, acute respiratory infections and malaria in young Gambian children.

The incidence of acute gastrointestinal and acute respiratory infections was measured in 2 groups of approximately 750 Gambian children aged 3-59 months during a 3-year period. One group of children was partially protected against malaria by fortnightly chemoprophylaxis with Maloprim whilst children in the other group were infected much more frequently. Mortality from acute gastroenteritis and from acute respiratory infections was similar in the 2 groups. The proportions of children in each group who complained of gastrointestinal or severe respiratory symptoms on morbidity surveillance were also similar. Thus, no evidence was found to suggest that malaria plays either a direct or indirect role in causing acute gastrointestinal or respiratory infections in young children in The Gambia.

Responses of Anopheles gambiae complex mosquitoes to the use of untreated bednets in The Gambia.

Population dynamics of the Anopheles gambiae complex of malaria vector mosquitoes were studied in four small hamlets in The Gambia. Bednets were used to reduce man/vector contact in two of the hamlets. High densities of An. gambiae, sensu lato, were present for only 3-8 weeks during the rainy season, depending on the position of the hamlet within the study area. The proportions of blood-fed mosquitoes caught indoors (83.0%) and existing from houses (11.6%) were lower in hamlets where bednets were used than in hamlets without (96.5% and 33.1% respectively). Fewer of the blood-fed mosquitoes had fed on man in houses where people slept under bednets (68.2%) than in those without (81.5%). However, the average number of infective bites received by children was still greater than one a year in hamlets where bednets were used. Consequently bednets are considered unlikely to be an effective malaria control measure so long as they are untreated with insecticide.

An ELISA test for detecting chloroquine in urine.

Two ELISA tests for detecting chloroquine in urine have been developed using polyclonal and monoclonal antibodies which react with the 7-chloro-4-amino-quinoline part of the chloroquine molecule and thus recognize chloroquine, its metabolites, and amodiaquine. The ELISAs were sensitive and specific and did not cross-react with other commonly used antimalarials. In a field trial the chloroquine ELISA performed better than the Dill Glazko or Haskins colorimetric tests. A small proportion of urines gave an apparently false positive reaction when tested at a dilution of 1:10, but not when tested at higher dilution.