Combined effects of exposure to engineered silver nanoparticles and the water-soluble fraction of crude oil in the marine copepod Calanus finmarchicus

While it is likely that ENPs may occur together with other contaminants in nature, the combined effects of exposure to both ENPs and environmental contaminants are not studied sufficiently. In this study, we investigated the acute and sublethal toxicity of PVP coated silver nanoparticles (AgNP) and ionic silver (Ag⁺; administered as AgNO₃) to the marine copepod Calanus finmarchicus. We further studied effects of single exposures to AgNPs (nominal concentrations: low 15 μg L^-1 NPL, high 150 μg L^-1 NPH) or Ag⁺ (60 μg L^-1), and effects of co-exposure to AgNPs, Ag⁺ and the water-soluble fraction (WSF; 100 μg L^-1) of a crude oil (AgNP + WSF; Ag⁺+WSF). The gene expression and the activity of antioxidant defense enzymes SOD, CAT and GST, as well as the gene expression of HSP90 and CYP330A1 were determined as sublethal endpoints. Results show that Ag⁺ was more acutely toxic compared to AgNPs, with 96 h LC₅₀ concentrations of 403 μg L^-1 for AgNPs, and 147 μg L^-1 for Ag⁺. Organismal uptake of Ag following exposure was similar for AgNP and Ag⁺, and was not significantly different when co-exposed to WSF. Exposure to AgNPs alone caused increases in gene expressions of GST and SOD, whereas WSF exposure caused an induction in SOD. Responses in enzyme activities were generally low, with significant effects observed only on SOD activity in NPL and WSF exposures and on GST activity in NPL and NPH exposures. Combined AgNP and WSF exposures caused slightly altered responses in expression of SOD, GST and CYP330A1 genes compared to the single exposures of either AgNPs or WSF. However, there was no clear pattern of cumulative effects caused by co-exposures of AgNPs and WSF. The present study indicates that the exposure to AgNPs, Ag⁺, and to a lesser degree WSF cause an oxidative stress response in C. finmarchicus, which was slightly, but mostly not significantly altered in combined exposures. This indicated that the combined effects between Ag and WSF are relatively limited, at least with regard to oxidative stress.

Rainfall triggers more deep-seated landslides than Cascadia earthquakes in the Oregon Coast Range, USA

The coastal Pacific Northwest USA hosts thousands of deep-seated landslides. Historic landslides have primarily been triggered by rainfall, but the region is also prone to large earthquakes on the 1100-km-long Cascadia Subduction Zone megathrust. Little is known about the number of landslides triggered by these earthquakes because the last magnitude 9 rupture occurred in 1700 CE. Here, we map 9938 deep-seated bedrock landslides in the Oregon Coast Range and use surface roughness dating to estimate that past earthquakes triggered fewer than half of the landslides in the past 1000 years. We find landslide frequency increases with mean annual precipitation but not with modeled peak ground acceleration or proximity to the megathrust. Our results agree with findings about other recent subduction zone earthquakes where relatively few deep-seated landslides were mapped and suggest that despite proximity to the megathrust, most deep-seated landslides in the Oregon Coast Range were triggered by rainfall.

Carbon source utilization profiles as a method to identify sources of faecal pollution in water

AIMS

Carbon source utilization profiles as a phenotypic fingerprinting methodology for determining sources of faecal pollution in water were evaluated.

METHODS AND RESULTS

Three hundred and sixty-five Enterococcus isolates were collected from known faecal sources in four different geographical regions and were identified to species with the commercial Biolog system. Discriminant analysis (DA) was used to identify the substrate-containing wells that best classified the 365 isolates by source. By using 30 of the 95 wells for the analysis, the average rate of correct classification (ARCC) by source was 92.7% for a human vs non-human two-way classification when isolates from all regions were combined into one library. Corresponding ARCCs for other classification schemes were 81.9% for a four-way classification of human vs livestock vs wildlife vs domestic pets, and 85.7% for a three-way classification without human isolates. When three individual libraries were made based on classification of sources within Enterococcus species, the ARCC was 95.3% for the Ent. faecalis library, 95.8% for the Ent. gallinarum library and 94.7% for the Ent. mundtii library. Thirty Enterococcus isolates (unknown sources) were obtained from each of three stream sites where a specific source of pollution was apparent; 90.0% of the isolates from a human-suspected source were classified as human, 86.6% were classified as livestock from a livestock-suspected site, and 93.3% were classified as wildlife from a wildlife-suspected site.

CONCLUSIONS

Phenotypic fingerprinting with carbon source utilization profiles provided levels of correct classification by sources from an Enterococcus library that were in the upper range of those reported in the literature. ARCCs for three Enterococcus species-specific libraries were very high and may be the best approach for further developing this concept and methodology. SIGNIFICANCE ANC IMPACT OF THE STUDY: The results, based on a modest Enterococcus library and a preliminary field validation test, demonstrated the potential for carbon source utilization profiles to be employed as a phenotypic method for determining sources of faecal pollution in water.

Pediatric angiosarcoma of the heart: a unique presentation and metastatic pattern

We report the seventh case of angiosarcoma of the heart in a child. The patient was a 23-month-old female who presented for lower extremity limping and underwent open surgical biopsy of the femur. Immediately postoperatively, she developed pericardial tamponade, and a bulky intracardiac mass was discovered as the underlying cause. The mass was composed of highly pleomorphic tumor cells reactive for the endothelial markers CD31, CD34, and factor VIII-related antigen (FVIII-RA). Staging evaluation revealed widespread metastases involving the brain, ovaries, and bone marrow. She died of complications of metastatic disease 8 months following initial presentation. Unusual features of this case include the young age of the patient, left-sided nature of the cardiac tumor, presentation secondary to metastatic disease, and the pattern of metastases. The literature on cardiac angiosarcoma, which is limited to six case reports in the pediatric population, is also reviewed.

Cerebrovascular adaptation in chronic hydrocephalus

This study characterizes the regional changes in vascularity, which accompanies chronic progressive hydrocephalus. Fifteen dogs underwent surgical induction of hydrocephalus and were used for histologic studies. Animals were divided into 4 groups: surgical control, short term (< or = 5 weeks), intermediate term (8 weeks), and long term (10 to 12 weeks). Vessel diameter, density, and luminal area were calculated by imaging quantification after manual vessel identification in the cortical gray, white matter, and caudate nucleus. Capillary vessel diameter decreased 23.5% to 30.2% (P < 0.01) in the caudate, but then returned to normal at 12 weeks. Capillary vessel density decreased 53.5% (P < 0.05) in the cortical gray, but then increased to 234.8% (P < 0.01) over surgical controls at 12 weeks. There was no initial decrease in capillary density in the caudate; however, the long-term group capillary density was significantly greater (172.8% to 210.5%, P < 0.01) than surgical controls. Overall, there was a short-term decrease in lumen area, with recovery in the longer term. Glial fibrillary acidic protein (GFAP) immunohistochemistry demonstrated the pattern of GFAP staining and reactive astrocytes differed in the caudate compared with the occipital cortex. This data suggest that an increase in capillary density and diameter may be an adaptive process allowing maintenance of adequate cerebral perfusion and metabolic support in the hypoxic environment of chronic hydrocephalus.

Colon and anal sphincter contractions evoked by microstimulation of the sacral spinal cord in cats

The colon and anal sphincter contractions induced by microstimulation of the S2 spinal cord were investigated by measuring the intraluminal pressure change via saline filled balloons in alpha-chlorolose anesthetized cats. Stimulation of sacral ventral roots (S1-S3) revealed that the S2 efferent outflow usually produces the largest colon response. Stimulation of the S2 ventral root or the spinal cord both indicated that 15 Hz stimulation was the optimal frequency for evoking colon contractions. Colon and anal sphincter contractions were also influenced by stimulation intensity and pulsewidth. Locations in S2 spinal cord, where microstimulation evoked a distal/proximal colon pressure response that was greater than the anal sphincter response, included the area of sacral parasympathetic nucleus (SPN), the area medial to the SPN extending to the dorsal commissure, and areas deep in the ventral horn. Anal sphincter relaxation was evoked by microstimulation in more restricted locations in S2 spinal cord, which appeared to overlap with those evoking anal sphincter contractions. These results suggest a possible method to evoke colon contraction and defecation by microstimulation of the S2 spinal cord with multiple microelectrodes.

Multimicroelectrode stimulation within the cat L6 spinal cord: influences of electrode combinations and stimulus interleave time on knee joint extension torque

During multimicroelectrode stimulation within the cat L6 spinal cord, the number of electrodes activated, their separation distance, and the stimulus interleave time all influenced isometric knee joint extension torque. The torque evoked by stimulation with a three electrode combination could be enhanced or suppressed when compared with that evoked by single or paired electrode stimulation. A similar difference was noted when comparing two electrode combination versus single electrode stimulation. Relative fatigue was not improved significantly by interleaving the stimuli from two or three microelectrodes. Compared with the extension torque response evoked by noninterleaved stimulation, torque evoked by interleaved stimulation with the two microelectrode combination was decreased when the electrode distance was 2.0 mm or less and increased when the electrode distance was 3.0 mm. Designing an optimal stimulation strategy for multimicroelectrode spinal cord stimulation will be challenging and complex if a suppression effect among these electrodes is to be avoided. To reduce muscle fatigue, an asynchronous, interleaved strategy of stimulation may be required.

Isometric torque about the knee joint generated by microstimulation of the cat L6 spinal cord

Isometric torque was generated about the knee joint by microstimulation of the cat L6 spinal cord using a single microelectrode. The torque responses varied with microstimulation location. Appreciable extension torque was generated by microstimulation in ventrolateral locations of the L6 spinal cord. Stimulation parameters (intensity, frequency and pulse-width) also influenced the extension torque. Specific stimulation parameters (100 microA intensity, 40 Hz frequency and 0.20 ms pulse-width) appear best suited for mapping the spinal cord based on knee joint torque responses. Low levels of cocontraction of the extensor and flexor could be achieved when extension torque was produced, but also varied with the stimulation locations. There are locations in the L6 ventral horn where microstimulation could evoke sustained extension for at least 4 min with only a slight change in torque. This study suggests the possibility of restoring lower limb function in patients with spinal cord injury above the lumbar level.

Penile erection produced by microstimulation of the sacral spinal cord of the cat

The sacral neural pathways mediating penile erection in the cat were studied by measuring the change in cavernous sinus pressure (CSP) elicited by stimulation of the sacral ventral roots or by microstimulation of the sacral spinal cord. Ventral root stimulation revealed that the S1 segment rather than S2 and S3 spinal segments could evoke the largest CSP responses. Microstimulation in the S1 spinal cord elicited large CSP responses but small or no bladder contractions. Maximal CSP responses were evoked by microstimulation in the middle of the S1 ventral horn, 1.6-2.8 mm below the cord surface and midway between the midline and the lateral edge of the gray matter. The area was 200-400 microm wide (medial to lateral) and extended 1-2 mm in the rostrocaudal direction. Maximal CSP responses to spinal cord microstimulation were elicited by stimulus intensities of 50-150 microA, at a pulse width of 0.2 ms and at frequencies of 3040 Hz and occurred after delay of 8-40 s. This study suggests that focal microstimulation of the sacral spinal cord might be useful in eliciting penile erectile activity in patients with spinal cord injury.

Role of spinal glutamatergic transmission in the ascending limb of the micturition reflex pathway in the rat

This study was undertaken to evaluate the role of glutamate receptors at spinal synapses on the ascending limb of the micturition reflex. In urethane-anesthetized female rats, a tungsten electrode was inserted stereotaxically into the dorsal part of the rostral pons to record field potentials which were evoked by electrical stimulation of the pelvic nerve (PLN) (1-15 V, 0.05 ms pulse duration at 100-300 Hz, 5-30 ms train duration). The effects of glutamate receptor antagonists administered intrathecally (i.t.) on the PLN-evoked field potentials in the dorsal part of the rostral brainstem were examined. PLN stimulation evoked short latency (10-22 ms) negative field potentials (85 +/- 4 microV) in a limited area of the dorsal part of the rostral pons (bregma -9.0 to -8.4, L 0.5 to 1. 5, H 4.2 to 5.4). The i.t. administration of LY215490 (0.1-30 microg), a competitive alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist, reduced the amplitude of the evoked potentials in a dose-dependent manner; 84 +/- 6%, 59 +/- 11% (P < .001), 31 +/- 10% (P < .001), 17 +/- 9% (P < .001) of control after 0.1, 1, 10, 30 microg of LY215490, respectively. The i.t. administration of MK-801 (1-100 microg), a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, also reduced the amplitude of the evoked potentials in a dose-dependent manner; 93 +/- 21%, 76 +/- 14%, 52 +/- 9% (P < .001), 39 +/- 9% (P < .001) of control after 1, 10, 30, 100 microg of MK-801, respectively. Combined administration of LY215490 (0.1 microg) and MK-801 (1 microg), in doses which individually did not elicit a significant effect, markedly reduced the amplitude of the evoked potentials (27 +/- 9% of control, P = . 0002). These results suggest that AMPA and NMDA glutamatergic synaptic mechanisms play a key role in the spinal processing of afferent input from the bladder and that these mechanisms function synergistically in the ascending limb of the spinobulbospinal micturition reflex pathway.

Mechanism of action of local anesthetics on synaptic transmission in the rat

The mechanism of action of local anesthetics on synaptic transmission and their effects on synaptic components and on electrophysiologic properties of the nerve cell body are not clear. Therefore, the effects of lidocaine and bupivacaine on pre- and postsynaptic mechanisms underlying synaptic transmission in sympathetic ganglia were studied utilizing the techniques of intracellular recording and stimulation on isolated superfused superior cervical ganglia of rats. Lidocaine and bupivacaine either depressed or completely blocked synaptic transmission in sympathetic ganglia in a dose-dependent manner. Blockade of axonal conduction in presynaptic fibers was preceded by increased latency (the latency increased from 11.2 +/- 0.9 to 16.5 +/- 1.4 ms, mean +/- SEM, P less than 0.01) when the drugs were applied to the presynaptic nerves. Application of the drugs directly to the ganglion produced alterations in postsynaptic membrane properties consisting of decreased membrane resistance (from 40 +/- 3 to 32 +/- 3 M omega, P less than 0.01), increased firing threshold (from 14 +/- 0.5 to 18 +/- 0.5 mV, P less than 0.01), and decreased action potential amplitude (P less than 0.01) and/or blockade of action potential generation. Resting postsynaptic membrane potential did not change significantly. These changes were reversible. However, even after the excitatory postsynaptic potential resulting from presynaptic nerve stimulation had fully recovered during washout of the local anesthetic, the threshold for evoking the spike potential (firing level) still remained elevated for both presynaptic and intracellular stimulation of the ganglion cell, suggesting prolonged cell depression.(ABSTRACT TRUNCATED AT 250 WORDS)

Excitatory effect of substance P in parasympathetic ganglia of cat urinary bladder

Intra-arterial administration of substance P (0.1-50 micrograms/kg) to the urinary bladder of the cat produced slow-onset and sustained bladder contractions, asynchronous firing of bladder postganglionic nerves, and facilitation of nicotinic transmission in bladder ganglia. Intracellular recording from bladder ganglia in vitro revealed that substance P depolarized ganglion cells and initiated burst of action potentials (maximal frequency 6-7 Hz). The ganglionic excitatory effect of substance P in situ was blocked by gamma-aminobutyric acid (2-20 micrograms/kg) and the substance P antagonist [D-Arg1,D-Pro2,D-Trp7.9,Leu11]substance P (0.5-20 micrograms/kg) but was not altered by atropine (10-100 micrograms/kg), hexamethonium (0.5-2 mg/kg), norepinephrine (2-20 micrograms/kg), or leucine enkephalin (0.5-20 micrograms/kg). The bladder contractions elicited by substance P were not blocked by atropine, hexamethonium, or [D-Arg1,D-Pro2,D-Trp7.9,Leu11]substance P (0.1-10 micrograms/kg) but were blocked by another substance P antagonist, [D-Pro2,D-Phe7,D-Trp9]substance P. These data indicate that substance P has a direct postsynaptic excitatory effect on neurons in the vesical parasympathetic ganglia and on bladder smooth muscle cells. The differential effects of substance P antagonists on the excitatory responses at these two sites indicate the responses were mediated by different types of tachykinin receptors.

Distribution of neurons in the major pelvic ganglion of the rat which supply the bladder, colon or penis

In male rats a large number of the postganglionic neurons which innervate the pelvic organs are located in the major pelvic ganglion. In the present study we have identified the location within this ganglion of neurons which project to either of three pelvic organs, the penis, colon or urinary bladder. Two fluorescent retrogradely-transported dyes, Fast Blue and Fluoro-Gold, were used. For most animals one dye was injected into the cavernous space of the penis, the wall of the distal colon or the wall of the urinary bladder. In a small number of animals two organs were injected, each with a different dye. One to six weeks after injection the major pelvic ganglia were fixed in buffered formaldehyde. The distribution of fluorescent dye-labelled cells was observed in whole mounts of complete ganglia and, in most cases, also in small accessory ganglia located between the ureter and the prostate. The studies showed a unique pattern of distribution for each organ-specific group of neurons. Most of the colon neurons are located in the major pelvic ganglion near the entrance of the pelvic nerve, whereas almost all of the penis neurons are near or within the penile nerve. Bladder neurons are relatively evenly distributed throughout the ganglion. These results demonstrate a distinct topographical organization of organ-specific neurons of the major pelvic ganglion of the male rat, a phenomenon which has also been observed in other peripheral ganglia.

Morphological and electrophysiological properties of pelvic ganglion cells in the rat

Intracellular recording and dye injection were used to study the morphological and electrophysiological properties of rat pelvic ganglion cells. The dye-injected cells measured on the average 37 micron by 22.5 micron and had a mean number of 1.5 primary processes (axon and dendrites). The cells received unmyelinated preganglionic inputs from either the pelvic (parasympathetic) or the hypogastric (sympathetic) nerves, but no cells received inputs from both nerves. The number of synaptic inputs to each cell varied between 1 and 5 with a mean of 2. Each cell had at least one large amplitude suprathreshold EPSP which always initiated an action potential. These properties, namely, morphological simplicity, small number of inputs, security of synaptic transmission and lack of convergence between sympathetic and parasympathetic inputs, suggest that the capacity for synaptic modulation and integration in this ganglion is minimal. Such a structure should therefore relay preganglionic information to target organs with little or no alteration.

Reflex hypotension due to regional activation of left ventricular mechanoreceptors to explain the hypotension noted in clinical myocardial ischaemia or reperfusion

To determine if regional increases in myocardial contractility, as may occur clinically in angina pectoris, myocardial infarction, or coronary thrombolysis, can initiate the reflex hypotension that sometimes accompanies these conditions, regional injections of positive inotropic agents were made into 32(3)% of the left ventricular myocardium in seven pneumonectomised dogs on total cardiac bypass. The coronary and systemic circulations were isolated and perfused separately. The systemic circulation was perfused at a constant rate so that changes in systemic pressure reflected changes in resistance. Regional injections of doses from 0.001 to 1.0 micrograms noradrenaline in a 0.1 ml volume appreciably increased regional contractility, detected visually and by strain gauge arches, whereas global contractility (left ventricular peak dP/dt) was increased much less. This caused a fall in the systemic pressure (resistance) of 14(2)% below the control value of 78(5)mm Hg, at the largest dose. The decreases in resistance were abolished by bilateral vagotomy, proving their reflex nature. The smaller (0.0001-0.01 micrograms) doses of noradrenaline and the smallest (0.25 micrograms) dose of veratridine increased regional contractility almost without increasing global contractility, indicating that the increase in regional contractility was the major cause of the reflex decrease in systemic resistance. In one animal a decrease in contractility in a control myocardial region occurred simultaneously with the experimentally produced increase in regional left ventricular contractility. This decrease may be analogous to the increase in contractility in the non-ischaemic left ventricular myocardium that occurs simultaneously with the decrease in contractility in the ischaemic region in clinical or experimental myocardial infarction. Left ventricular mechanoreceptors in the region with increased contractility probably initiate the reflex hypotension that sometimes occurs in both circumstances. Thus in angina pectoris or acute myocardial infarction the reflex hypotension probably originates in the hyperactive non-ischaemic myocardial region, whereas in coronary arterial thrombolysis it probably originates in the newly reperfused, formerly ischaemic, region.

Regulation of urinary bladder capacity by endogenous opioid peptides

Naloxone administered to chloralose or ketamine anesthetized cats reduced urinary bladder capacity. Successive cystometrograms revealed that naloxone in doses of 0.5 microgram./kg. to 15 micrograms./kg. i.v. reduced the volume necessary to evoke micturition by 10 to 50 per cent, respectively. The effect was maximal within a few minutes, remained constant for about 1/2 hour and returned to control values over the next 2 to 3 hours. Following return to control, subsequent doses of naloxone produced no further effect on capacity. In chloralose anesthetized animals naloxone also increased the frequency and amplitude of low amplitude pressure waves on the tonus limb of the cystometrogram. Intrathecal administration of naloxone to the sacral spinal cord did not significantly reduce the volume necessary to evoke micturition even at large doses, but did increase the amplitude of micturition contractions. These data, along with previous reports, suggest that mu receptors in the brainstem alter urinary bladder capacity, while delta receptors in the spinal cord modulate the magnitude of bladder contractions. Pharmacological manipulation of these receptor systems could provide a tool for the management of neurogenic bladder dysfunction.

Use of intracoronary KCl in the beating and asystolic heart to determine the mechanism of initiation of the left ventricular mechanoreceptor reflex

To provide further evidence that the veratrum alkaloids' mechanical, positive inotropic effect and not their chemical depolarising action predominates in initiating the left ventricular mechanoreceptor (including the Bezold) reflex the effect of intracoronary KCl, a chemical depolarising agent like the veratrum alkaloids, but with a negative inotropic effect, was studied in beating and verapamil-asystolic hearts. Five dogs were placed on a total cardiac bypass, pneumonectomised and their coronary and systemic circulations isolated and perfused separately, at a constant rate, so that changes in systemic pressure reflected changes in systemic resistance. Injection of 5 mmol X litre-1 KCl into the isolated coronary circulation caused cardiac asystole and a resultant reflex rise in systemic pressure (resistance) of 26 +/- 9% (p less than 0.05) above the control of 10.5 +/- 0.7 kPa (79 +/- 5 mmHg). This pressure rise, which indicates predominance of KCl's mechanical, negative inotropic over its chemical depolarising effect, was abolished by vagotomy, indicating its reflex nature. Contrariwise, in five other pneumonectomised dogs, similarly perfused on total cardiac bypass but with cardiac asystole from intracoronary verapamil, a subsequent, similar intracoronary dose of KCl now produced a fall in systemic pressure (resistance) of 8 +/- 2% (p less than 0.005) below the control of 12.8 +/- 0.5 kPa (96 +/- 4 mmHg). This pressure fall, presumably due to chemical depolarisation of the left ventricular mechanoreceptors, was also abolished by vagotomy.(ABSTRACT TRUNCATED AT 250 WORDS)

The location and morphology of preganglionic neurons and the distribution of visceral afferents from the rat pelvic nerve: a horseradish peroxidase study

Preganglionic neurons of the sacral parasympathetic nucleus (SPN) were located almost exclusively (98%) within the L6-S1 spinal cord segments. The SPN contained approximately 550 neurons of medium size (10 X 20 micron). These were mainly located in the intermediolateral gray matter and had dendrites that extended into the dorsolateral funiculus, along the lateral marginal zone of the dorsal horn, and medially into the dorsal gray commissure. Labeled dorsal root ganglion cells were almost all located (95%) in the L6 and S1 ganglia. An average of approximately 1,500 sensory neurons were found. These were small cells (17 X 25 micron) whose central processes entered Lissauer's tract from which two groups of collaterals emerged: 1) a prominent lateral pathway along the lateral margin of the dorsal horn that extended into the region of the SPN and also into the dorsal gray commissure, 2) a less prominent medial pathway extending around the dorsal margin of the dorsal horn to terminate in the dorsal gray commissure. These two collateral groups formed fiber bundles that were spaced by approximately 100 micron between centers when observed in the horizontal plane. A third afferent bundle, composed of rostrocaudally oriented fibers, was located in the sagittal plane immediately ventral to the central canal. Comparisons are made between the results in rats and the results of similar experiments performed in cats and monkeys.

The presence of leucine-enkephalin in the sacral preganglionic pathway to the urinary bladder of the cat

Leucine-enkephalin (L-ENK) nerve terminals which surround the cholinergic neurons in ganglia of the cat urinary bladder are eliminated after transection of the sacral ventral roots or the pelvic nerve. These findings, coupled with other anatomical and physiological data, suggest that L-ENK may be a cotransmitter with acetylcholine in the sacral preganglionic pathways to the urinary bladder.

Parasympathetic ganglia: naloxone antagonizes inhibition by leucine-enkephalin and GABA

Synaptic transmission in parasympathetic ganglia of the cat urinary bladder was depressed by low doses (0.1-10 micrograms i.a.) of Leu- or Met-enkephalin but only by larger doses (10 micrograms-1 mg i.a.) of morphine. Naloxone blocked the depressant effects of the opiates as well as the depression produced by GABA, but did not block the depressant effects of norepinephrine. Intracellular recording revealed that Leu-enkephalin reduced EPSP-amplitude and lowered the probability of synaptically evoked firing without altering postsynaptic membrane potential or resistance. These findings suggest that enkephalinergic inhibition in bladder ganglia is mediated at least in part by a presynaptic site of action on delta opiate receptors.

The effects of naloxone on the neural control of the urinary bladder of the cat

Naloxone in doses ranging from 0.5 to 512 micrograms/kg i.v., enhanced reflex contractions of the urinary bladder of the cat. At the lowest doses (threshold, 0.5-5 micrograms/kg) the drug increased the frequency of spontaneous bladder contractions. In large doses (10-100 micrograms/kg) the drug produced an initial tonic contraction of bladder lasting 15-40 min followed by a period of high frequency rhythmic activity. Multiunit firing in parasympathetic postganglionic nerves on the surface of the urinary bladder was also enhanced. Bursts of firing which in untreated animals occurred during large bladder contractions occurred continuously during the entire sustained contraction of the bladder following large doses of naloxone. Various evidence indicates that the site of action of naloxone is in the central nervous system. These findings suggest that the parasympathetic reflex pathway to the urinary bladder may be subject to tonic enkephalinergic inhibitory control.

The role of neuropeptides in the sacral autonomic reflex pathways of the cat

Immunohistochemical and pharmacological studies were conducted to examine the origin and function of peptidergic nerves in the sacral autonomic system of the cat. Leucine-enkephalin (L-Enk) immunoreactivity was identified in nerve terminals in peripheral ganglia on the surface of the urinary bladder and in the parasympathetic nucleus in the sacral spinal cord. In colchicine-treated animals L-Enk was also detected in sacral preganglionic neurons (sPGN) identified by retrograde transport of a fluorescent dye. L-Enk terminals in bladder ganglia are believed to arise from sPGN since the terminals were eliminated by transection of the sacral ventral roots. Pharmacological studies indicated that exogenous as well as endogenously released enkephalins have an inhibitory action at both ganglionic and spinal sites in the sacral outflow to the urinary bladder. Peptides were also associated with afferents nerves in the sacral autonomic system. The distribution of substance P, VIP and cholecystokinin in the sacral dorsal horn paralleled the distribution of visceral afferent projections as demonstrated with HRP techniques. Dye labeling combined with immunohistochemistry revealed that some dorsal root ganglion cells projecting to the pelvic viscera contain substance P or VIP.

Parasympathetic preganglionic neurons in the sacral spinal cord

Two types of preganglionic neurons have been identified in the sacral parasympathetic nucleus (SPN) of the cat. These neurons could be differentiated by various characteristics including axonal conduction velocities, morphology, location in the nucleus, organ of innervation and central reflex mechanisms controlling their activity. Neurons having myelinated axons (B-PGNs) with conduction velocities between 3.3 and 13 m/s were located in the lateral band of the SPN and innervated the urinary bladder. Neurons with unmyelinated axons (C-PGNs) with conduction velocities of 0.5-1.4 m/s were located in the dorsal band of the nucleus and innervated the large intestine. B-PGNs were excited by distention of the bladder and inhibited by distension or mechanical stimulation of the intestine, whereas C-PGNs exhibited the opposite responses to these stimuli. C-PGNs often exhibited a low level of spontaneous discharge in absence of stimulation but exhibited marked firing (3.5-10 spikes/s) during a defecation reflex elicited by mechanical stimulation of the rectum-anal canal. The excitatory responses were elicited by C-fiber afferents via a spinal reflex pathway. B-PGNs were inactive when intravesical pressure was below the threshold for inducing micturition (5 cm H2O) but raising the pressure above the threshold induced firing consisting of repetitive bursts of action potentials occurring at relatively high frequencies (15-60 spikes/s). These bursts coincided with rhythmic bladder contractions. The frequency of bladder contractions and associated bursts of PGN-firing and the mean PGN-firing rate (2-8 spikes/s) increased as intravesical pressure was increased in steps between 5 and 30 cm H2O. However, as indicated by interspike interval histograms, the frequency of firing within a burst of action potentials was unchanged. It is concluded that the micturition reflex pathway is organized as a simple on-off switching circuit and that B-PGNs receive a maximal synaptic input when intravesical pressure exceeds the micturition threshold. This circuit was triggered by vesical A delta afferents via a spinobulbospinal pathway. Transection of the spinal cord interrupted the reflex pathway and blocked micturition. However, in chronic spinal animals a spinal reflex mechanisms emerged which contributed to the recovery of bladder function. This mechanism, which was weak or non-existent in animals with an intact neuraxis, exhibited a number of important differences from the normal micturition reflex, most notably being activated by a C-fiber afferent rather than a A delta afferent limb. The mechanism underlying the emergence of C-fiber evoked bladder reflexes in spinal animals is uncertain.

Organization of the sacral parasympathetic reflex pathways to the urinary bladder and large intestine

Electrophysiological and horseradish peroxidase (HRP) techniques have provided new insights into the organization of the sacral parasympathetic reflex pathways to the large intestine and urinary bladder. The innervation of the two organs arises from separate groups of sacral preganglionic cells: (1) a dorsal band of cells in laminae V and VI providing an input to the intestine; and (2) a lateral band of cells in lamina VII providing an input to the bladder. These two groups of cells were separated by an interband region containing tract cells and interneurons. Neurons in the interband region received a visceral afferent input and exhibited firing correlated with the activity of intestine and urinary bladder. It seems reasonable therefore to consider the interband region as a third component of the sacral parasympathetic nucleus. Anterograde transport of HRP revealed that visceral afferents from the intestine and bladder projected into the parasympathetic nucleus. Most of the projections were collaterals from afferent axons in Lissauer's tract that passed in lamina I laterally and medially around the dorsal horn. These afferent collaterals were located in close proximity to preganglionic perikarya and dendrites in laminae I, V and VI. The proximity of visceral afferents and efferents in the sacral cord probably reflects the existence of polysynaptic rather than monosynaptic connections since electrophysiological studies revealed that both the defecation and micturition reflexes occurred with very long central delays (45-70 msec). The reflex pathways mediating defecation and micturition in cats with an intact neuraxis were markedly different. Defecation was dependent upon a spinal reflex with unmyelinated (C-fiber) peripheral afferent and efferent limbs. On the other hand, micturition was mediated by a spinobulbospinal pathway with myelinated peripheral afferent (A-fiber) and efferent axons (B-fiber). Transection of the spinal cord at T12-L2 blocked the micturition reflex but only transiently depressed the defecation reflex. In chronic spinal cats the micturition reflex recovered 1-2 weeks after spinalization; however, in these animals bladder-to-bladder micturition reflexes were elicited by C-fiber rather than A-fiber afferents. The C-fiber afferent-evoked reflex was weak or undetectable in animals with an intact neuraxis. Transection of the spinal cord also changed the micturition reflex in neonatal kittens (age 5-28 days). In neonates with an intact neuraxis bladder-to-bladder reflexes occurred via a long latency spinobulbospinal pathway (325-430 msec). The long latency is attributable to the slow conduction velocity in immature unmyelinated peripheral and central axons. In chronic spinal kittens (3-7 days after spinalization) the long latency reflex was abolished and a shorter latency (90-150 msec) bladder reflex was unmasked. The emergence of this spinal pathway may reflect axonal sprouting and the formation of new reflex connections within the sacral parasympathetic nucleus.

Inhibition and facilitation in parasympathetic ganglia of the urinary bladder

Neurons in vesical parasympathetic ganglia receive excitatory and inhibitory inputs from both divisions of the autonomic nervous system. Sacral parasympathetic pathways (cholinergic) provide the major excitatory input to these ganglia via activation of nicotinic receptors. Parasympathetic pathways also activate muscarinic inhibitory and excitatory receptors, which may exert a modulatory influence on transmission. Cholinergic transmission is relatively inefficient when preganglionic nerves are stimulated at low frequencies (< 1 Hz). However, excitatory postsynaptic potentials (EPSPs) and postganglionic firing markedly increase during repetitive stimulation at frequencies of 1-10 Hz. It is concluded that enhanced transmitter release accounts for the temporal facilitation and that vesical ganglia function as "high pass filters" that amplify the parasympathetic excitatory input to the detrusor muscle during micturition. Transmission in vesical ganglia is also sensitive to adrenergic inhibitory and facilitatory synaptic mechanisms elicited by efferent pathways in the hypogastric nerves. The effects of exogenous norepinephrine indicate that adrenergic inhibition is mediated by alpha receptors and reflects primarily a presynaptic depression of transmitter release although postsynaptic adrenergic hyperpolarizing and depolarizing effects have also been noted. Adrenergic facilitation is mediated by beta receptors as well as unidentified receptors. Norepinephrine also can inhibit or excite spontaneously active neurons in vesical ganglia. The existence of inhibitory and facilitatory synaptic mechanisms in vesical ganglia provides the basis for a complex ganglionic modulation of the central autonomic outflow to the bladder.

Physiology of the urinary bladder and urethra

Activation of the parasympathetic pathways to the detrusor muscle and inhibition of somatic input to the external urethral sphincter are the essential neuronal events initiating release of urine. The former occurs via a spinobulbospinal pathway, whereas the latter is produced by inhibitory mechanisms in the sacral spinal cord. The sympathetic outflow to the urinary tract promotes urine storage by increasing urethral resistance and depressing detrusor contractions. Sympathetic activity is generated at least in part by a spinal vesicosympathetic reflex pathway. Evidence indicates that the integration of sympathetic and parasympathetic inputs to the bladder can occur at the level of the peripheral autonomic ganglion as well as at levels of the effector organ. The existence of facilitatory and adrenergic inhibitory mechanisms in ganglia and the identification of spontaneously active ganglion cells raise the possibility that vesical ganglia may have a role in modulating or "filtering" the efferent neural input to the bladder.

Physiology of male sexual function

The male sexual response cycle consists of excitement, plateau, orgasm, and resolution. The initial event, penile erection, is produced by arteriolar dilatation and increased blood flow to the erectile tissue of the penis. Erection is a reflex response initiated by visual, olfactory, or imaginative stimuli impinging upon supraspinal centers or by genital stimulation that in turn activates spinal reflex mechanisms. Sacral parasympathetic and thoracolumbar sympathetic nerves provide the efferent vasodilator input to the penis. Parasympathetic nerves also stimulate secretion from the seminal vesicles and prostate and Cowper's glands during the plateau phase. The orgasmic phase is characterized by seminal emission and ejaculation and the accompanying sensations. Emission of semen into the urethra depends on sympathetic nerves that elicit contractions of smooth muscles in the vas deferens, seminal vesicles, and prostate. Rhythmic contractions of striated muscle (bulbocavernosus and ischiocavernosus) generated by efferent pathways in the pudendal nerve eject semen from the urethra.

Removal of anaesthetic waste gases. An inexpensive antipollution system for use with pipeline suction

A simple, safe, and extremely inexpensive system is described for removing anaesthetic waste gases from the operating theatre, by utilising such equipment and facilities as already exist in most modern operating departments.