Peripheral Sympathetic Neurotransmission Research Articles

Relationship between central behavioral effects and peripheral sympathetic neurotransmission functionality during acute cocaine withdrawal syndrome in adult rats

ABSTRACTBackground: Acute cocaine withdrawal syndrome (ACWS) is characterized as a set of organic alterations triggered by abrupt discontinuation of chronic cocaine consumption, usually occurring at 24–40 hours after withdrawal. However, little is known about the relationship between central and peripheral sympathetic neurotransmission during ACWS. Objective and Methods: We investigated the mechanisms involved in central and peripheral sympathetic neurotransmission and how ACWS affects the sympathetic functionality. Cocaine was administered twice daily for 5 days in Wistar rats (at least 5 in each group): on the first and second day, 15 mg/kg/i.p.; third day, 20 mg/kg/i.p.; and finally in the last two days, 30 mg/kg/i.p. Subsequently, at 1, 24, 48 and 120 h after cocaine administration the following experiments were done: (i) at the central level, behavioral tests of open-field and elevated plus maze; and (ii) at the peripheral level, tests of catecholamine release, function of α2-adrenergic receptors (α2-ARs), imidazoline receptors (I1,2-Rs), L-type voltage-gated (Cav1.2) Ca2+ channels and α1-ARs. Results: During ACWS, rats showed hypolocomotion and exacerbation of anxiogenic-effects 24 h after cocaine withdrawal. Likewise, a decrease in the catecholamine release and activity of α2-ARs/I1,2-Rs at 24–48 h after cocaine withdrawal was observed. A decrease in Cav1.2 channels and α1-ARs function at 48 h after cocaine withdrawal was observed. Conclusions: The relationship of central and peripheral sympathetic neurotransmission during ACWS possibly due to a failure in activation and/or inactivation of presynaptic α2-ARs/I1,2-Rs, may offer a potential target for attenuating ACWS.

Influence of acute treatment with sibutramine on the sympathetic neurotransmission of the young rat vas deferens

The effects of acute treatment with sibutramine on the peripheral sympathetic neurotransmission in vas deferens of young rats were still not evaluated. Therefore, we carried out this study in order to verify the effects of acute sibutramine treatment on the neuronal- and exogenous agonist-induced contractions of the young rat vas deferens. Young 45-day-old male Wistar rats were pretreated with sibutramine 6mg/kg and after 4h the vas deferens was used for experiment. The acute treatment with sibutramine was able to increase the potency (pD2) of noradrenaline and phenylephrine. Moreover, the efficacy (Emax) of noradrenaline was increased while the efficacy of serotonin and nicotine were decreased. The maximum effect induced by a single concentration of tyramine was diminished in the vas deferens from treated group. Moreover, the leftward shift of the noradrenaline curves promoted by uptake blockers (cocaine and corticosterone) and β-adrenoceptor antagonist (propranolol) was reduced in the vas deferens of treated group. The initial phasic and secondary tonic components of the neuronal-evoked contractions of vas deferens from treated group at the frequencies of 2Hz were decreased. Moreover, only the initial phasic component at 5Hz was diminished by the acute treatment with sibutramine. In conclusion, we showed that the acute treatment with sibutramine in young rats was able to affect the peripheral sympathetic nervous system by inhibition of noradrenaline uptake and reduction of the neuronal content of this neurotransmitter, leading to an enhancement of vas deferens sensitivity to noradrenaline.

Functional effects of alcohol withdrawal syndrome on peripheral sympathetic neurotransmission in vas deferens of adult rats

AimsAlcohol withdrawal syndrome (AWS) is characterized by a set of physiological modifications triggered by abrupt withdrawal and/or decreasing consumption of ethanol (EtOH), which may manifest 16–48h after ceasing consumption. The relationship between the effects of AWS and central and peripheral sympathetic neurotransmission is unknown. This study investigates the possible mechanisms on the sympathetic system during periods of AWS. Main methodsMale Wistar rats were treated with EtOH (6–10g/kg/day/v.o. 5days). Subsequently, 1h, 24h, 48h and 120h after administration of the last dose of EtOH, the animals were sacrificed, and their vas deferens (VD) were removed to perform the following evaluations: (a) concentration–effect curves of sympathetic agonist; (b) activity of α2-adrenoreceptor; (c) function of voltage-dependent calcium channels (Cav); and (d) release of endogenous catecholamines measured in real time coupled to HPLC. Key findingsThe results showed that the maximum effects of contraction were increased by agonists tested in at 24h and 48h EtOH withdrawal. The inhibitory affinity (pIC50) of guanfacine was decreased 24h EtOH withdrawal. The function of Cav was also decreased as pIC50 values dropped 24h and 48h EtOH withdrawal. The release of catecholamines increased 48h after EtOH withdrawal. It is suggested that AWS triggers hyperactivity in peripheral sympathetic neurotransmission. SignificanceThe mechanisms underlying hyperactivity are possibly explained by a failure of autoregulation from catecholamines released by α2-adrenoreceptors and/or an increase of Cav function, which may be potential targets to attenuate the symptoms of AWS at the peripheral level.

Increase of angiotensin-converting enzyme activity and peripheral sympathetic dysfunction could contribute to hypertension development in streptozotocin-induced diabetic rats

Diabetes augments the risk of hypertension. Although several factors have been implicated in the development of such hypertensive state, we designed this study to investigate blood pressure development, the activity of angiotensin-converting enzyme (ACE) in blood as well as sympathetic neurotransmission in the vas deferens of diabetic rats. We used streptozotocin (STZ)-induced diabetic rats (60 mg/kg) in order to evaluate the systolic blood pressure (SBP), ACE activity and peripheral sympathetic neurotransmission. We observed the following changes of parameters: increase of SBP, decrease of heart rate, augmentation of plasma ACE activity, enhancement of phasic and tonic vas deferens contractions elicited by electrical stimulation at 5 Hz, increase of maximal response to noradrenaline (NA) and decrease of adenosine triphosphate (ATP)-elicited contraction of vasa deferentia. The results reveal that in the development of hypertension in diabetic rats, augmentation of circulating ACE activity precedes the sympathetic dysfunction. Additionally, it seems that the purinergic and noradrenergic neurotransmission is compromised.

Beneficial effects of γ-aminobutyric acid on right ventricular pressure and pulmonary vascular remodeling in experimental pulmonary hypertension

AimsIt has been reported that activation of the sympathetic nervous system and increase in plasma norepinephrine (NE) levels are observed in patients with pulmonary hypertension (PH). γ-Aminobutyric acid (GABA) is one of the major inhibitory neurotransmitters in the central nervous system and suppresses peripheral sympathetic neurotransmission. This study investigated whether chronic treatment with GABA prevents the development of monocrotaline (MCT)-induced PH. To elucidate the relationship between the development of PH and sympathetic nerve activity, hemodynamic parameters, cardiac functions, and plasma NE concentrations as well as cardiac endothelin-1 (ET-1) contents of MCT-induced PH rats were evaluated with or without GABA treatment. Main methodsRats were injected with MCT (60mg/kg) or saline subcutaneously and these rats were randomly divided into GABA (500mg/kg/day for 4weeks)- or vehicle-treated groups, respectively. Key findingMCT-treated rats had higher right ventricular systolic pressures, right ventricle-to-left ventricle plus septum weight ratios, pulmonary arterial medial thickening, and plasma NE levels than those of saline-injected rats. MCT-induced alternations were significantly attenuated by treatment with GABA. In MCT-induced PH rats with or without GABA treatment, plasma NE levels were positively correlated with right ventricular systolic pressure. Right ventricular endothelin-1 (ET-1) contents were increased by MCT injection, but these increments were not affected by treatment with GABA. SignificanceThese results suggest that plasma NE levels play an important role in the development of MCT-induced PH in rats and that GABA exerts a preventive effect against MCT-induced PH by suppressing the sympathetic nervous system but not the cardiac ET-1 system.

Functional antagonism of amphetamine versus ethanol on adrenergic neurotransmission in vas deferens of adolescent rats

Because of the few studies that emphasize the in vivo use of amphetamine and ethanol, and their consequences on autonomic neurotransmission, we decided to study the effect of these drugs on peripheral noradrenergic neurotransmission of young animals. We used contractions of the vas deferens of adolescent rats as a model for the study of pre-treatment with both agents. The 30 to 40day old adolescent rats were pre-treated with amphetamine, at doses of 3mg/kg, or ethanol at doses of 1.2g/kg. Both agents were also used simultaneously to investigate possible interactions. The group treated with amphetamine showed a potentiation of the vas deferens contractions evoked by noradrenaline and barium (about 20%), as well as time–response contractions of calcium (about 20%). However, the response to electrical field stimulation (EFS) was not significantly changed, but the content of noradrenaline was reduced by about 50%. The group treated with ethanol showed a decrease in vas deferens contractility to noradrenaline, phenylephrine, and barium, by less than 20%. In this group, contraction by EFS was reduced by about 40% (Tonic, 2Hz) and 20% (Phasic, 5Hz), but the response to calcium was not changed. As after amphetamine, the content of noradrenaline was reduced by about 50%. In the group treated with amphetamine+ethanol all the changes described after the single treatments with amphetamine or ethanol were neutralized. It is concluded that a functional antagonism was shown between amphetamine and ethanol when administered simultaneously on peripheral sympathetic neurotransmission in vas deferens of adolescent animals.

Pravastatin normalises peripheral cardiac sympathetic hyperactivity in the spontaneously hypertensive rat

Hypertension is associated with heightened cardiac sympathetic drive whilst statins reduce angiotensin II (ATII) signalling, superoxide anion production and increase nitric oxide bioavailability, events that can potentially reduce peripheral cardiac sympathetic neurotransmission. We therefore investigated whether pravastatin alters peripheral cardiac sympathetic control in the spontaneously hypertensive rat (SHR). SHRs (16–18weeks) had significantly (p<0.05) enhanced atrial 3H-norepinephrine (3H-NE) release to field stimulation compared to normotensive WKYs. 2-week pravastatin supplementation significantly reduced 3H-NE release to levels observed in the WKY. In-vivo, pravastatin lowered resting heart rate (HR) in the SHR despite not affecting arterial blood pressure or serum cholesterol. In SHR atria/right stellate ganglion preparations, the HR response to stellate stimulation (1, 3, and 5Hz) was also significantly reduced by pravastatin whilst the HR response to exogenous NE (0.025–5μmol) remained similar. The nitric oxide synthase (NOS) inhibitor l-NAME (1mmol/l) increased 3H-NE release by similar amounts in atria from supplemented and non-supplemented SHRs, whilst Western blotting showed no difference in protein levels of nNOS, eNOS, guanylyl cyclase, or the NADPH oxidase subunits Gp91 and P40phox. Pravastatin significantly reduced cardiac ATII levels and angiotensin converting enzyme 1 and 2 expressions whilst protein levels of the ATII receptor (ATR1) remained unchanged in the SHR. Immunohistochemistry co-localised ATR1 with tyrosine hydroxylase positive neurons in the stellate ganglion. The ATR1 antagonist Losartan (5μmol) equalised release of 3H-NE to comparable levels in supplemented and non-supplemented SHRs. These results suggest 2-week pravastatin treatment reduces cardiac ATII, and prevents its facilitatory effect on NE release thus normalising cardiac sympathetic hyper-responsiveness in SHRs.

Dysrhythmias associated with cocaine overdose

Dysrhythmias associated with cocaine overdose

Angiotensin II and sympathetic activity in sodium-restricted essential hypertension.

Angiotensin II (Ang II) potentiates sympathetic neurotransmission by presynaptic facilitation of norepinephrine release. We investigated whether endogenous Ang II modulates peripheral sympathetic activity in sodium-depleted essential hypertensive patients. We evaluated the effect of intrabrachial infusion of saralasin, an Ang II antagonist (5 micrograms/100 mL forearm tissue per minute), and benazeprilat, an angiotensin-converting enzyme inhibitor (2 micrograms/100 mL forearm tissue per minute), on forearm vasoconstriction (measured by strain-gauge venous plethysmography) induced by the application of lower body negative pressure (-10 mm Hg for 5 minutes). Both saralasin and benazeprilat (n = 6 for each group) blunted the vasoconstrictor action of lower body negative pressure, suggesting that circulating Ang II modulates peripheral sympathetic activity. In addition, since beta-adrenoceptor stimulation can activate the production of vascular Ang II, the effect of saralasin and benazeprilat on lower body negative pressure application was evaluated in the presence of isoproterenol (0.09 microgram/100 mL forearm tissue per minute) and propranolol (10 micrograms/100 mL forearm tissue per minute). In two other groups of hypertensive patients, isoproterenol infusion increased the release of Ang II in the forearm vasculature (arteriovenous values measured by radioimmunoassay). Furthermore, isoproterenol potentiated lower body negative pressure-induced vasoconstriction. This facilitating effect was abolished by either saralasin or benazeprilat (n = 6 for each group). In contrast, in two further groups of patients (n = 6 for each group), in the presence of the beta-blocker propranolol saralasin and benazeprilat did not alter the vasoconstrictor action of the endogenous sympathetic stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Participation of prostaglandins and bradykinin in the effects of angiotensin II and converting enzyme‐inhibition on sympathetic neurotransmission in vivo

We investigated the mechanism(s) by which angiotensin converting enzyme (ACE)-inhibition and angiotensin (Ang) II influence peripheral sympathetic neurotransmission in canine gracilis muscle in situ, with alpha-adrenoceptors either intact or irreversibly blocked by phenoxybenzamine. ACE-inhibition by ramiprilat reduced, and subsequent infusion of Ang II (30 ng kg-1 min-1 i.v.) markedly increased arterial plasma Ang-(1-8)octapeptide levels, basal muscle perfusion pressures and mean arterial pressure. Local intra-arterial bolus injection of Ang II caused marked vasoconstriction followed by vasodilation. This vasoconstrictor response was enhanced and the ensuing vasodilation was abolished following prostaglandin synthesis inhibition by diclofenac. The vasoconstrictor response to low frequency (0.5 Hz) sympathetic nerve stimulation was also enhanced by diclofenac. The nerve stimulation-evoked noradrenaline (NA) overflow was reduced by ramiprilat when alpha-adrenoceptors were blocked (-11 +/- 3%, P < 0.05), but increased when alpha-adrenoceptors were intact (+28 +/- 14%, P < 0.05). During ACE-inhibition, effective bradykinin receptor antagonism by HOE 140 reduced stimulation-evoked NA overflow irrespective of alpha-adrenoceptor blockade (i.e. by 25 +/- 5 and 20 +/- 3% in the absence and presence of alpha-adrenoceptor blockade, respectively, P < 0.01). Diclofenac increased stimulation-evoked NA overflow in the absence of alpha-adrenoceptor blockade (+ 19 +/- 4%, P < 0.05). IV infusion of Ang II failed to enhance stimulation-evoked NA overflow both before and after diclofenac.(ABSTRACT TRUNCATED AT 250 WORDS)

C-type natriuretic peptide neuromodulates independently of guanylyl cyclase activation.

Of the four endogenous members of the natriuretic peptide family, only atrial natriuretic peptide has been demonstrated to have neuromodulatory effects. This study compares the neuromodulatory effects of atrial natriuretic peptide and a recently identified natriuretic peptide, C-type natriuretic peptide, in the rabbit isolated vas deferens. The ability of these peptides to alter cyclic nucleotide concentrations was assessed to determine the potential contribution of either cyclic AMP or cyclic GMP to the observed responses. The central hypothesis tested was that C-type natriuretic peptide modulates neurotransmission via an interaction with a guanylyl cyclase. C-type natriuretic peptide inhibited both purinergic and adrenergic neurotransmission in a concentration-dependent manner but failed to alter either cyclic GMP or cyclic AMP concentrations. Maximal inhibitory effects of C-type natriuretic peptide averaged 35 +/- 4% for purinergic and 49 +/- 7% for adrenergic neurotransmission. Atrial natriuretic peptide not only attenuated both purinergic and adrenergic neurotransmission but also increased cyclic GMP concentrations. C-type natriuretic peptide probably inhibited the release of the neurotransmitters because it failed to alter contractions to exogenously administered norepinephrine or ATP, the two putative neurotransmitters. These results suggest that the C-type natriuretic peptide receptor, guanylyl cyclase B, is not present in rabbit vas deferens and that C-type natriuretic peptide suppresses peripheral sympathetic neurotransmission independently of guanylyl cyclase activation.

Converting enzyme inhibition modulates sympathetic neurotransmission in vivo via multiple mechanisms

We investigated the mechanism(s) by which angiotensin-converting enzyme (ACE) inhibition influences peripheral sympathetic neurotransmission. Thus effects of the angiotensin II (ANG II) receptor antagonist losartan (Du Pont 753) were compared with those of the ACE inhibitor benazeprilat on sympathetic neurotransmission in canine gracilis muscle in situ, with alpha-adrenoceptors either intact or irreversibly blocked by phenoxybenzamine. Furthermore, effects of the bradykinin receptor antagonist HOE 140 and the prostaglandin synthesis inhibitor diclofenac were studied after ACE inhibition. Losartan reduced the vasoconstrictor response to exogenous ANG II by 76 +/- 4% at the dose used and lowered muscle perfusion pressures. ACE inhibition by benazeprilat reduced plasma ANG-(1-8) octapeptide levels (from 8 +/- 2 to 2 +/- 1 pM), mean arterial pressure, and muscle perfusion pressures. After ACE inhibition, both HOE 140 (at a dose that reduced the vasodilatory response to exogenous bradykinin by 80 +/- 3%) and diclofenac elevated basal perfusion pressures. Losartan reduced the nerve stimulation-evoked overflow of endogenous norepinephrine (NE) (-14 +/- 6%) and vasoconstrictor responses (alpha-adrenoceptors intact). ACE inhibition increased NE overflow when alpha-adrenoceptors were intact (+12 +/- 5%) and tended to reduce it when alpha-adrenoceptors were blocked (-12 +/- 4%). During ACE inhibition, HOE 140 reduced and diclofenac enhanced the evoked NE overflow. In the absence of ACE inhibition, neither HOE 140 nor diclofenac influenced NE overflow. Our findings indicate that ACE inhibition influences sympathetic neurotransmission via reduced ANG II formation and enhanced bradykinin and prostaglandin accumulation. The effects of ANG II on sympathetic neurotransmission are, however, small under these in vivo conditions.

Influence of angiotensin II, alpha- and beta-adrenoceptors on peripheral noradrenergic neurotransmission in canine gracilis muscle in vivo.

Interactions between angiotensin II and adrenoceptor-mediated effects on peripheral sympathetic neurotransmission were investigated in constant flow blood-perfused canine gracilis muscle in situ, without and with pretreatment by non-competitive alpha-adrenoceptor blockade. Angiotensin converting enzyme (ACE)-inhibition by benazeprilat increased nerve stimulation (2 Hz, 4 min)-evoked noradrenaline (NA) overflow (+ 21 +/- 5%) with alpha-adrenoceptors intact, but reduced NA overflow (- 18 +/- 6%) when alpha-adrenoceptors were blocked. Vasoconstrictor responses were slightly reduced by benazeprilat. Subsequent infusion of angiotensin II (Ang II, 20 and 500 ng kg-1 min-1 i.v., raising arterial concentrations from 0.6 +/- 0.2 pM to 1390 +/- 240 and 25,110 +/- 3980 pM, respectively) failed to increase NA overflow or to enhance stimulation-evoked vasoconstriction. Adrenaline (0.4 nmol kg-1 min-1 i.v.) did not change evoked NA overflow before or after benazeprilat, either with or without alpha-adrenoceptor blockade, despite high concentrations (approximately 10 nM) in arterial plasma. Following benazeprilat, propranolol reduced NA overflow (- 24 +/- 3%) only if the alpha-adrenoceptors were blocked. In conclusion, benazeprilat reduced evoked NA overflow in the presence of alpha-adrenoceptor blockade to a similar degree as previously shown in the presence of neuronal uptake inhibition in this model. However, contrasting to our previous findings, benazeprilat enhanced NA overflow and reduced the post-junctional response to nerve stimulation in the absence of alpha-adrenoceptor blockade. This could be related to bradykinin accumulation during ACE-inhibition, in addition to the reduction of Ang II generation. Our data are not compatible with facilitation of NA release by circulating Ang II even at pharmacological dose levels. Although activation of prejunctional beta-adrenoceptors may facilitate evoked NA overflow in this model, circulating adrenaline is ineffective under physiological conditions even after alpha-adrenoceptor blockade. Also, beta-adrenoceptor-mediated prejunctional effects do not seem to involve Ang II in canine skeletal muscle in vivo.

Effects of the Selective &amp;beta;&lt;sub&gt;1&lt;/sub&gt;-Adrenoceptor Antagonist, Nebivolol, on Cardiovascular Parameters in the Pithed Normotensive Rat

In the pithed rat we investigated the cardiovascular properties of d,l-nebivolol and its enantiomers. We used the increase in heart rate elicited by (-)-adrenaline and (-)-noradrenaline as a model for studying beta 1-adrenoceptors. A leftward shift of the logarithmic dose-pressor response curve of (-)-adrenaline reflects beta 2-adrenoceptor-blocking properties. The blood pressure responses of methoxamine, B-HT 920 and serotonin (5-HT) were studied in order to test whether d,l-nebivolol has alpha 1-, alpha 2- and 5-HT2-receptor-blocking properties. Furthermore, the interaction of d,l-nebivolol with the peripheral sympathetic neurotransmission was investigated in pithed rats by electrical stimulation of the spinal cord. d,l-Nebivolol and d-nebivolol (threshold concentration 10(-8) mol/kg) were demonstrated to be selective beta 1-adrenoceptor antagonists. l-Nebivolol was a factor of 1,000 less potent as beta 1-adrenoceptor blocker. Up to a dose of 10(-5) mol/kg, d,l-nebivolol appeared to have neither alpha 1-, alpha 2-, beta 2-, 5-HT2-, angiotensin II-receptor antagonistic, calcium entry blocking, converting enzyme inhibiting nor direct vasodilating properties and did not interact with the sympathetic neurotransmission in the vascular wall. An explanation for an antihypertensive effect independent of beta-adrenoceptor blockade as found in spontaneously hypertensive rats and man could not be found in this model, therefore we suggest that this blood-pressure-lowering effect does not originate from conventional peripheral mechanisms.

An examination of age-related changes in pre- and postsynaptic α-adrenoceptors in the rat isolated vas deferens

Age-related changes in pre- and postsynaptic α-adrenoceptors were investigated in prostatic and epididymal portions of vasa deferentia from young adult (2–3 month) and 24 month old Sprague-Dawley rats, using the selective α 1-agonist amidephrine and the selective α 2-agonist xylazine. Effects of agonists were assessed against the isometric contraction to single pulse field stimulation. There was no change in the pre- or postsynaptic potency of amidephrine, but the presynaptic inhibitory potency of xylazine was significantly reduced in old rats. Therefore, in old rats there is a reduced sensitivity of presynaptic α 2- but no change in pre- or postsynaptic α 1-adrenoceptors and this may result in increased peripheral sympathetic neurotransmission.

Premature development of cardiac sympathetic neurotransmission in the fetal alcohol syndrome

The development of the ability of hypoglycemia to evoke centrally-mediated reflex activation of sympathetic efferent pathways was studied in rats whose mothers received ethanol. Hypoglycemia was elicited by insulin administration, and sympathetic stimulation was assessed by measuring heart ODC activity and depletion of adrenal catecholamines. In control rats, cardiac sympathetic neurotransmission was absent at 4 days of age and matured toward the end of the first week of postnatal age. In contrast, pups from ethanol-treated mothers displayed fully functional reflex responses as early as 4 days. This acceleration appeared to be independent of nutritional or body weight-related factors. In contrast, enhanced maturation of peripheral sympathetic neurotransmission in pups born to ethanol-fed mothers was not seen in the sympatho-adrenal pathway.