Reinfection with the agent of human granulocytic ehrlichiosis

1. The functional role of the paraventricular nucleus (PVN) has been examined by studying its connections with cardiovascular neurons in the medulla and spinal cord and its influence on activity in several sympathetic nerves. 2. Chemical stimulation of neurons within the PVN can elicit pressor responses and can excite reticulo-spinal vasomotor neurons in the rostral ventrolateral medulla (RVLM). 3. The PVN-RVLM excitation is blocked by kynurenic acid applied iontophoretically in the vicinity of RVLM-spinal neurons, suggesting this is a glutamate-dependent pathway. 4. Electrical stimulation of PVN neurons evoked action potentials in RVLM neurons after 27 ms with a small variability. 5. Anterograde and retrograde labelling of PVN and RVLM neurons revealed PVN terminals closely associated with RVLM-spinal neurons and showed that the PVN is connected to the spinal cord via three pathways. 6. Chemical activation of PVN neurons can produce a pattern of activation of cardiovascular neurons similar to that occurring in defence against plasma volume expansion. 7. It is concluded that the PVN connections with the RVLM and spinal cord are important to a role in defending against life-threatening disturbances.     

Sympathoexcitation from the rostral ventrolateral medulla is mediated by spinal NMDA receptors

These studies examined the role of spinal N-methyl-D-aspartic acid (NMDA) receptors in mediating sympathoexcitation evoked by stimulation of neurons in the rostral ventrolateral medulla (RVLM). In urethane-anesthetized rats, blood pressure, heart rate, and splanchnic sympathetic nerve activity (SNA) were recorded. The NMDA receptor antagonist D-2-amino-7-phosphonoheptanoic acid (D-AP7) was administered to the spinal cord via intrathecal (IT) catheter. Blockade of spinal NMDA receptors reduced arterial blood pressure, heart rate, and SNA. Spinal administration of D-AP7 markedly attenuated the pressor and sympathoexcitatory responses evoked by L-glutamate stimulation of the RVLM. The small increases in heart rate evoked by stimulation of the RVLM were not affected by IT administration of D-AP7. These results indicate that NMDA receptors in the spinal cord mediate the pressor and sympathoexcitatory responses evoked by activation of a bulbospinal pathway originating from the RVLM. Moreover, these data suggest that excitatory amino acid neurotransmitters and NMDA receptors in the spinal cord play an important role in the maintenance and regulation of SNA and cardiovascular function.     

Effect of testosterone and its metabolites upon the level of vasopressin messenger ribonucleic acid in the hypothalamus of the hyperosmotically stimulated male rat

We examined whether the selective 5-hydroxytryptamine 1A (5-HT1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) injected systemically can act directly on sympathoexcitatory neurons located in the rostral ventrolateral medulla (RVLM) to cause the hypotensive effect of this agent in rats. Microinjections of 8-OH-DPAT and buspirone into the RVLM produced a dose-dependent decrease in blood pressure. Microinjections of spiperone and pindolol, 5-HT1A antagonists, into the RVLM inhibited the depressor response to 8-OH-DPAT intravenously injected or injected into the RVLM. Microiontophoretic application of 8-OH-DPAT onto RVLM sympathoexcitatory neurons inhibited the firing of RVLM sympathoexcitatory neurons and the inhibition of unit activity by 8-OH-DPAT was blocked by microiontophoretic spiperone. Intravenous administration of 8-OH-DPAT also inhibited the firing of these neurons. Microiontophoretic application of spiperone onto the RVLM sympathoexcitatory neurons reversed the inhibitory response to intravenous 8-OH-DPAT. These results are consistent with the hypothesis that 8-OH-DPAT may exert a portion of its hypotensive effect through a direct inhibition of RVLM sympathoexcitatory neurons in rats. The receptor involved is probably the 5-HT1A type.     

Identification of C1 presympathetic neurons in rat rostral ventrolateral medulla by juxtacellular labeling in vivo

The rostral ventrolateral medulla (RVLM) contains barosensitive, bulbospinal neurons that provide the main supraspinal excitatory input to sympathetic vasomotor preganglionic neurons. However, the phenotype of the critical RVLM cells has not been conclusively determined. The goal of the current study was to identify the proportion of electrophysiologically defined, putative, presympathetic RVLM neurons that are C1 cells. We used a juxtacellular labeling technique to individually fill spontaneously active, barosensitive, bulbospinal RVLM neurons with biotinamide following electrophysiological characterization in chloralose-anesthetized rats. To determine whether these neurons could be classified as C1 cells, the biotinamide-labeled cells were processed for detection of tyrosine hydroxylase. The majority of barosensitive bulbospinal RVLM neurons were tyrosine hydroxylase immunoreactive (TH-ir; 28 of 39). All of the barosensitive bulbospinal RVLM neurons with axonal conduction velocities in the C fiber range (<1 m/second) were TH-ir (n = 16), whereas faster conducting cells (1 to 7 m/second) were either lightly TH-ir (n = 12) or not detectably TH-ir (n = 11). Adjacent respiratory-related RVLM units labeled with biotinamide were not detectably TH-ir (n = 10). To verify that TH-ir cells were indeed adrenergic, a subset of barosensitive bulbospinal cells labeled with biotinamide were examined for phenylethanolamine N-methyltransferase immunoreactivity (PNMT-ir). Three slowly conducting cells had detectable PNMT-ir, and two fast-conducting cells had no detectable PNMT-ir. These results indicate that the majority of bulbospinal RVLM neurons with putative sympathoexcitatory function are C1 cells.     

Homeodynamics versus homeostasis: periodicities superimposed on non-linear dynamic sympathetic tone generated in ventral medulla

Homeodynamics based on theories of complexity and chaos and its impact on mechanisms generating sympathetic activity are presented. Activity in rats cervical, lumbar and renal sympathetic nerves was analyzed. In time domain glutamate stimulation of neurons within medullary periambigual area (PAA) disturbed temporal pattern of respiratory-sympathetic synchronization. Divalént calcium antagonists, Co2+ and Mg2+, blockers of synaptic transmission, uncoupled respiratory oscillator and sympathetic activity. PAA neurons act as an interphase between different subsets of respiratory neurons and bulbospinal sympathoexcitatory neurons in rostral ventrolateral medulla (RVLM). In frequency domain sympathetic activity analyzed by FFT algorithm and power density spectra (PDS) exhibited periodicities at the range from 0.4 Hz to 7.5 Hz. Blockers of synaptic transmission microinjected bilaterally into RVLM reduced total power exhibited in PDS to low level of magnitude generated in spinal cord and increased total, yet non-synchronized sympathetic activity and arterial blood pressure. A two component hybrid model of generation of sympathetic activity was proposed: a tone-generating system confined mainly to intrinsic activity of RVLM pacemaker neurons responsible for chaos-like discharges and a second component-neuronal circuits superimposed on tone-generating neurons and shaping the pattern of PDS. Contribution of spinal cord oscillatory mechanism to overall power of sympathetic periodicities was discussed.     

Imidazoline receptor proteins in brains of patients with Alzheimer''s disease

Experiments have been carried out to investigate the chemical substrate in the rostral ventrolateral medulla (RVLM) underlying the depressor responses induced by activation of the greater splanchnic nerve (GSPL) afferent fibres of the rat. In anaesthetised rats with urethane and alpha-chloralose, microinjection of bicuculline, a GABA(A) receptor antagonist, into the RVLM, attenuated largely the depressor responses elicited by electrical stimulation of the GSPL afferent fibres, while strychnine or saline had no effect. In 18 RVLM neurons (including seven identified cardiovascular neurons), iontophoresis of bicuculline also significantly blocked the inhibition evoked by stimulation of the GSPL afferent inputs. We suggest that the depressor responses induced by stimulation of the GSPL afferent fibres involve a GABA(A)-receptor-mediated mechanism in the RVLM in rats.     

Classification of caudal ventrolateral pontine neurons with sympathetic nerve-related activity

This study was designed to answer three questions concerning caudal ventrolateral pontine (CVLP) neurons whose naturally occurring discharges are correlated to sympathetic nerve discharge (SND). 1) What are the proportions of CVLP neurons that have activity correlated to both the cardiac-related and 10-Hz rhythms in SND, to only the 10-Hz rhythm, and to only the cardiac-related rhythm? 2) Do CVLP neurons with activity correlated to the cardiac-related and/or 10-Hz rhythm in SND subserve a sympathoexcitatory or sympathoinhibitory function? 3) Do CVLP neurons with activity correlated to the cardiac-related and/or 10-Hz rhythm in SND project to the thoracic spinal cord? To address these issues we recorded from 476 CVLP neurons in 24 urethan-anesthetized cats. Spike-triggered averaging, arterial pulse-triggered analysis, and coherence analysis revealed that the discharges of 66 of these neurons were correlated to inferior cardiac postganglionic SND. For 39 of these neurons, we were able to determine whether their discharges were correlated to one or both rhythms. The results showed that the CVLP contained a heterogeneous population of neurons with sympathetic nerve-related activity. The discharges of 21 neurons were correlated to both the 10-Hz and cardiac-related rhythms in SND, 9 neurons had activity correlated to only the 10-Hz rhythm, and 9 neurons had activity correlated to only the cardiac-related rhythm. The firing rates of CVLP neurons with activity correlated to both rhythms or to only the 10-Hz rhythm were decreased during the inhibition of SND induced by baroreceptor reflex activation (rapid obstruction of the abdominal aorta). These neurons are presumed to exert sympathoexcitatory actions. The time-controlled collision test verified that 11 of 12 CVLP neurons with activity correlated to both rhythms were antidromically activated by stimulation of the first thoracic segment of the spinal cord. Antidromic mapping at this level showed that the site requiring the least stimulus current to elicit the longest latency response (nearest the terminal) was in the vicinity of the intermediolateral nucleus (IML). In contrast, only 1 of 13 CVLP neurons with activity correlated to only one of the rhythms in SND could be antidromically activated by spinal stimulation. These data demonstrate for the first time that there is a direct pathway from the CVLP to the IML that is comprised almost exclusively of sympathoexcitatory neurons whose discharges are correlated to both the 10-Hz and cardiac-related rhythms in SND.     

An inactive pancreatic lipase-related protein is activated into a triglyceride-lipase by mutagenesis based on the 3-D structure

The functional correlation of the depressor caudal ventrolateral medulla (CVLM) with the two pressor regions, i.e. rostral ventrolateral medulla (RVLM) and dorsomedial medulla (DM), and with another inhibitory region, i.e. the paramedian reticular nucleus (PRN), were studied in cats anesthetized intraperitoneally with chloralose (40 mg/kg) and urethane (400 mg/kg). Systemic arterial pressure (SAP), heart rate (HR) and the sympathetic vertebral nerve activity (VNA) were recorded. The correct location of CVLM, RVLM or DM was determined by their specific responses, i.e. decreases of SAP, HR and VNA, for CVLM increases of these parameters for RVLM and DM, elicited first by electrical stimulation (80 Hz, 0.5 ms, 50-100 microA) then followed by microinjection of glutamate (Glu, 0.25 M, 70 nl). The depressor action of PRN was produced by electrical stimulation only. It was found that the depressor responses caused by the CVLM stimulation were greatly reduced 2 h after lesioning either the RVLM or DM by microinjection of kainic acid (KA, 24 mM, 200 nl) ipsilateral to the side of CVLM stimulation. The CVLM responses were further reduced after the remaining side of RVLM or DM was lesioned. The reduction of the CVLM-depressor responses was more apparent after the RVLM than DM lesioning. Data suggest that the CVLM-depressor responses are mediated through inhibition of the sympathetic-pressor neurons in both RVLM and DM with predominance of the former. Lesioning the PRN by KA and/or combination with DC electrolytic lesion reduced the CVLM-induced depressor responses. In turn, lesioning the CVLM by KA reduced the PRN-induced depressor responses. The reduction in the later manipulation was more apparent in the PRN-depressor responses than the CVLM-depressor responses. Data suggest that part of the PRN depressor action is mediated through activation of the CVLM.     

Post-synaptic activity evoked in the rostral ventrolateral medullary neurones by stimulation of the defence areas of hypothalamus and midbrain in the rat

Neurones in the rostral ventrolateral medulla (RVLM) of the rat were recorded intracellularly (n = 30) and extracellularly (n = 91) in vivo. 91% of them had spontaneous activity with frequencies of 1.1-29.9 Hz. Onset latencies of the excitation induced by the stimulation of the hypothalamic and midbrain defence areas ranged from 1.5 to 44 ms and 2 to 60 ms respectively. There was no statistical difference between two groups. Excitation followed by inhibition or inhibition followed by excitation was observed in these processes. Excitatory post-synaptic potentials (EPSPs) were summated by simultaneous stimulation of both sites and the onset latency was changed with the change of stimulus intensity. It is concluded that projections from the defence areas of hypothalamus and midbrain are relayed to RVLM neurones forming excitatory and inhibitory synapses; one mechanism of the effect summation caused by both sites is via EPSPs.     

A reductant-induced oxidation mechanism for complex I

We examined whether baroreceptor activation causes a release of acetylcholine (ACh) in the rostral ventrolateral medulla (RVLM) of the rat, in order to investigate a possible connection between RVLM cholinergic systems and cardiovascular baroreflexes. Male Wistar rats were anesthetized, paralyzed and artificially ventilated. Either electrical stimulation of aortic nerve or baroreceptor activation by intravenous phenylephrine produced an increase of the release of ACh in the RVLM, whereas baroreceptor denervation and tetrodotoxin (TTX) microinfusion in the RVLM inhibited the increase in ACh release induced by phenylephrine. TTX injected in the caudal ventrolateral medulla (CVLM) inhibited the phenylephrine-induced increase of ACh release. The excitatory amino acid L-glutamate microinfused in the CVLM produced an release in ACh release in the RVLM. These results suggest that there is a connection between RVLM cholinergic systems and cardiovascular baroreflexes. It is probable that neurons in the CVLM are involved in mediating the release of ACh in the RVLM.     

Centrally acting sympathetic inhibitors for therapy of patients with hypertension

The blood pressure is maintained by the tonic vasomotor activity of efferent sympathetic neurons which are tonically regulated by the rostral ventrolateral medulla (RVLM) in the brain. The alpha 2-adrenoceptor agonist such as clonidine, guanabenz and guanfacine, acts on RVLM to decrease sympathetic neuron activity and lower blood pressure. Drug such as alpha-methyldopa, through its metabolite alpha-methylnoradrenaline, acts like clonidine as an alpha 2-adrenoceptor agonist in the brain. Clonidine and allied drugs except for alpha-methyldopa also bind to imidazoline receptors, which is believed to mediate the hypotensive action. The centrally acting antihypertensive drugs are used for treatment of moderate to severe forms of hypertension and are effective in patients with renal failure. The treatment with these drugs induces central nervous system side effect of sedation and drowsiness, which limits the clinical usefulness and are believed to be mediated by central alpha 2-adrenoceptors. The new imidazoline compounds, rilmenidine and moxonidine, which selectively act on imidazoline receptors, may be a useful antihypertensive drug without such central side effects.     

Cardiovascular effects produced by microinjection of angiotensins and angiotensin antagonists into the ventrolateral medulla of freely moving rats

In this study we determined the cardiovascular effects produced by microinjection of angiotensin peptides [Angiotensin-(1-7) and Angiotensin II] and angiotensin antagonists (losartan, L-158,809, CGP 42112A. Sar1-Thr8-Ang II, A-779) into the rostral ventrolateral medulla of freely moving rats. Microinjection of angiotensins (12.5-50 pmol) produced pressor responses associated to variable changes in heart rate, usually tachycardia. Unexpectedly, microinjection of both AT1 and AT2 ligands produced pressor effects at doses that did not change blood pressure in anesthetized rats. Conversely, microinjection of Sar1-Thr8-Ang II and the selective Ang-(1-7) antagonist, A-779, produced a small but significant decrease in MAP an HR. These findings suggest that angiotensins can influence the tonic activity of vasomotor neurons at the RVLM. As previously observed in anesthetized rats, our results further suggest a role for endogenous Ang-(1-7) at the RVLM. The pressor activity of the ligands for AT1 and AT2 angiotensin receptor subtypes at the RVLM, remains to be clarified.     

Ascending afferent regulation of rat midbrain dopamine neurons

Standard, extracellular single-unit recording techniques were used to examine the electrophysiological and pharmacological responsiveness of midbrain dopamine (DA) neurons to selected, ascending afferent inputs. Sciatic nerve stimulation-induced inhibition of nigrostriatal DA (NSDA) neurons was blocked by both PCPA (5-HT synthesis inhibitor) and 5,7-DHT (5-HT neurotoxin), suggesting mediation by a serotonergic (5-HT) system. Direct stimulation of the dorsal raphe (which utilizes 5-HT as a neurotransmitter and inhibits slowly firing NSDA neurons) inhibited all mesoaccumbens DA (MADA) neurons tested. Paradoxically, DPAT, a 5-HT1A agonist which inhibits 5-HT cell firing, enhanced sciatic nerve stimulation-induced inhibition of NSDA neurons. MADA neurons were not inhibited by sciatic nerve stimulation and, therefore, could not be tested in this paradigm. In contrast to the dorsal raphe, electrical stimulation of the pedunculopontine tegmental nucleus preferentially excited slowly firing NSDA and MADA neurons. Thus, both excitatory and inhibitory ascending afferents influence the activity of midbrain DA neurons, and intact 5-HT systems are necessary for sciatic nerve stimulation to alter DA cell activity. However, the role that 5-HT plays in mediating peripheral sensory input remains unclear.     

Neurons in the hypothalamic paraventricular nucleus that project to the rostral ventrolateral medulla are not activated by hypotension

The retrogradely-transported tracer, rhodamine-tagged microspheres was injected into the pressor region of the rostral ventrolateral medulla (RVLM) to enable detection of paraventricular neurons in the hypothalamus that project to the RVLM. The protein, Fos, was detected immunohistochemically and used to highlight neurons that were activated by hypotension (-16+/-5 mmHg) induced by diazoxide (30 mg/kg s.c.). Compared to controls, Fos production was increased by three-fold in the parvocellular paraventricular nucleus but there was no significant increase in the number of retrogradely-labelled cells that expressed Fos. The results suggest paraventricular nucleus (PVN) neurons projecting to the RVLM are not activated by hypotension.     

Microbial degradation of tetraethyl lead in soil monitored by microcalorimetry

Fos immunohistochemistry was used to stain neurons in the caudal diencephalon, midbrain and hindbrain driven by rewarding stimulation of the lateral hypothalamus (LH). Increases in Fos-like immunoreactivity were most pronounced ipsilateral to the site of stimulation and tended to be confined within discrete structures such as the posterior LH, arcuate nucleus, ventral tegmental area (VTA), central gray, dorsal raphé, pedunculopontine area (PPTg), parabrachial nucleus, and locus coeruleus. At least two of these structures, the VTA and PPTg, have been implicated in medial forebrain bundle self-stimulation.     

Brain "ouabain", a neurosteroid, mediates sympathetic hyperactivity in salt-sensitive hypertension

This review addresses recent developments in the neurobiology of an endogenous inhibitor of brain Na+, K+ - ATPase, "ouabain". "Ouabain" is present in hypothalamic and medullary neurons and mediates sympathoexcitatory and pressor responses to acute and chronic increases in cerebrospinal fluid (CSF) sodium concentration as well as mediates the sympathoexcitatory and pressor responses to high dietary sodium intake in SHR and Dahl-S rats, and sympathetic hyperactivity in the congestive heart failure. Some of these actions of "ouabain" in the CNS take place in the median preoptic nucleus and ventral part of the AV3V region. Despite recent advances in unveiling a biological role for "ouabain" its structure, biosynthetic and metabolic pathways as well as actual control mechanisms remain unresolved.     

Protein synthesis in chloroplasts. VII. Initiation of protein synthesis in isolated intact pea chloroplasts

The distribution and features of cardiovascular neurons (CVN) were studied in the brainstem of chloralose-anesthetized rats. Only neurons yielding an immediate response to carotid occulsion (CO) were considered as CVN. The criterion was deduced from the response patterns of cardiovascular afferent (carotid sinus nerve) and efferents (sympathetic and vagal nerves) during CO. Seventy-two CVN were identified and were observed to be mostly in the medullarly reticular formation and to some extent in the nucleus tractus solitarius and nucleus ambiguus. Fifty-five CVN (type A) decreased their firing rates in response to CO where 17 CVN (type B) increased their rates. Analyses of the time courses of their responses to CO revealed the convergence of the chemoreceptor and baroreceptor inputs onto some type A neurons. Electrical stimulation of the spinal cord evoked orthodromic responses in some neurons in both types. The evoked responses were blocked by CO in type A neurons whereas they were facilitated in those of type B. These results suggest that input from arterial baroreceptors, arterial chemoreceptors, and spinal ascending afferents is integrated within CVN.     

Inhibitory effects of hypothalamic arcuate nucleus or anterior pituitary stimulation on the nociceptive responses of thalamic parafascicular neurons

The effects of hypothalamic arcuate nucleus (ARC) or anterior lobe of pituitary (AL) stimulation on the nociceptive responses of thalamic parafascicular (Pf) neurons were studied in rats with electrophysiological technique. The results showed that ARC stimulation could inhibit the nociceptive discharges of Pf neurons, namely, the immediate inhibition because of its very short latency and duration. AL stimulation could also inhibit the nociceptive discharges of Pf neurons, but this inhibition was a delayed one because of its longer latency and duration. Hypophysectomy diminished the immediate inhibition due to ARC stimulation, while ARC lesion diminished the delayed inhibition due to AL stimulation. Both kinds of inhibition were blocked by dexamethasone pretreatment. The above results suggest that neuroendocrine relationship between ARC and AL is involved in pain modulation.     

Reflex sympathetic dystrophy syndrome associated with phenobarbital

Reflex sympathetic dystrophy syndrome (RSDS) is clinically characterized by pain and edema of one or more extremities, trophic skin changes and vasomotor instability. Although the pathogenesis is unknown, it could be caused by an abnormal reflex of the sympathetic nervous system. Different studies haven't yet confirmed the classical division in three clinical phases (warm, of vasomotor instability and cold). Barbiturates are the precipitating event in 10-30% of cases. We describe the clinical features of a patient with RSDS associated with phenobarbital who needed corticosteroid treatment. The Technetium diphosphate bone scan (Tc 99m DPD) is very useful because there is an increased radionuclide uptake in the involved areas during the early phases of the disease and precedes in some weeks the radiologic signs. The Magnetic Resonance Imaging (MRI) may be useful because of the early signs it shows. The patient may develop contractures and atrophy of the involved extremities in spite of the indispensable withdrawal of the drug.     

Relationship between phospholipase D activation and endothelial vasomotor dysfunction in rabbit aorta

Lysophosphatidylcholine (lysoPC) causes endothelial vasomotor dysfunction in isolated blood vessels, although the signaling pathways involved in this effect remain to be established. Although lysoPC stimulated phospholipase D (PLD) activity in cultured endothelial cells, the role of PLD in the vascular effects of lysoPC remains unclear. This study investigated the hypothesis that PLD is involved in lysoPC-induced endothelial vasomotor dysfunction in isolated rabbit aorta. LysoPC (3-30 microM) stimulated vascular PLD activity and inhibited endothelium-dependent vasorelaxation to acetylcholine within an identical concentration range. In contrast, lysoPC-induced inhibition of vasorelaxation was not prevented by the selective protein kinase C (PKC) inhibitor, GF109203X (3 microM), which suggested that this enzyme was not involved in the endothelial vasomotor dysfunction produced by lysoPC. The ability of two other lysophospholipids, lyso-platelet-activating factor (3-30 microM) and lysophosphatidylserine (10-30 microM) to induce endothelial vasomotor dysfunction was also associated closely with their ability to stimulate vascular PLD activity. Parallel stimulation of PLD activity and inhibition of acetylcholine-induced relaxation was also observed with orthovanadate (0.1-3 mM), which suggested that the association between PLD activation and endothelial vasomotor dysfunction was not a phenomenon particular to lysophospholipids. The magnitude of PLD stimulation and the extent of endothelial dysfunction induced by these diverse stimuli were highly correlated (r2 = 0.88). These observations suggest that the PLD signal transduction pathway is important in the endothelial vasomotor dysfunction produced by lysophospholipids and perhaps other agents.