Activation Of Α1 Receptors Research Articles

Small conductance calcium-activated potassium channel contributes to stress induced endothelial dysfunctions

Patients with Takotsubo syndrome displayed endothelial dysfunction, but underlying mechanisms have not been fully clarified. This study aimed to explore molecular signalling responsible for catecholamine excess induced endothelial dysfunction.Human cardiac microvascular endothelial cells were challenged by epinephrine to mimic catecholamine excess. Patch clamp, FACS, ELISA, PCR, and immunostaining were employed for the study.Epinephrine (Epi) enhanced small conductance calcium-activated potassium channel current (ISK1–3) through activating α1 adrenoceptor. Phenylephrine enhanced edothelin-1 (ET-1) and reactive oxygen species (ROS) production, and the effects involved contribution of ISK1–3. H2O2 enhanced ISK1–3 and ET-1 production. Enhancing ISK1–3 caused a hyperpolarization, which increases ROS and ET-1 production. BAPTA partially reduced phenylephrine-induced enhancement of ET-1 and ROS, suggesting that α1 receptor activation can enhance ROS/ET-1 generation in both calcium-dependent and calcium-independent ways.The study demonstrates that high concentration catecholamine can activate SK1–3 channels through α1 receptor-ROS signalling and increase ET-1 production, facilitating vasoconstriction.

Renal Function and Transporters in the Na/K-ATPase α1S/S Mouse Model of High Affnity for Cardiotonic Steroids

Genetic ablation of ATP1A1 in the mouse renal proximal tubule (RPT) revealed that Na/K-ATPase (NKA) α1 tonically inhibits sodium and water reabsorption. Mechanistically, findings in KO mouse RPT and renal epithelial cells were consistent with a prevalent role of a NKA/Src-dependent downregulation of Na+/H+ exchanger 3 (NHE3). Pharmacologically, functional activation of this pathway has been obtained in vitro and ex vivo using low concentrations of NKA archetypal ligands cardiotonic steroids (CTS). However, the physiological implication of an activation of the endogenous CTS (eCTS)/NKA/Src on renal transporters including NHE3 has not been explored. We assessed the renal impact of CTS/NKA α1 receptor activation by comparing mice expressing the naturally resistant NKA α1 and age-matched mice genetically engineered to express a mutated NKA α1 with high affnity for CTS (R111Q/D122N double substitution). Mice obtained from established colonies at the University of Cincinnati were a gift from Dr. Jerry Lingrel. CTS-sensitive (α1S/S) male mice aged 3-6 months on a C57Bl6 background and age-matched controls (α1R/R) were used. Mice were born with a normal Mendelian ratio, with no observable difference between α1S/S and α1R/R. Renal Na/K-ATPase inhibitory dose-response curve to the CTS ouabain was shifted to the left, as expected, and occurred without detectable change of total renal NKA activity, NKA α1 or β1 protein contents. Metabolic cage studies revealed that increased α1 sensitivity to CTS resulted in a significant increase in urine output in α1S/S mice compared to age-matched α1R/R controls (3.9±0.3 vs. 2.4±0.2 ml/24h; n=6, p<0.01). Consistent with an activation of the NKA/Src receptor by eCTS, western blot analyses of renal cortical preparation revealed an increased phosphorylation of NKA α1 at Y260 (Src target residue) and decreased NHE3 content (43.6 %; n=5, p<0.01). RNA-seq analysis of whole kidneys from α1S/S and α1R/R littermate mice using the Illumina NovaSeq 6000 system (Novogene) and Volcano Plot (DEG data using Python) further showed differential expression of 296 genes (147 upregulated and 149 downregulated). Gene Set Enrichment Analysis (GSEA) using the WebGestalt toolkit showed that the altered pathways were mostly involved in solute transport. Taken together, these results provide genetic evidence of the physiological role of eCTS/NKAα1 on renal function in the intact mouse. Increased affnity to eCTS is suffcient to lead to an activation of NKAα1/Src, a downregulation of NHE3, and transcriptional regulation of renal transporters associated with increased urine output. This work was supported by AHA, Predoctoral fellowship #19PRE34450095, NIH DK129937, and NIH Grant P20GM103434 to the West Virginia IDeA Network of Biomedical Research Excellence. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Anti-hypotensive effect of “Yahom Navakot” in rats with orthostatic hypotension

Background and aimYahom Navakot (YN), is a Thai traditional medicine, consisting of 54 plants, for treating fainting and dizziness. Thus, YN might relieve orthostatic hypotension (OH) symptoms, but its therapeutic action is unclear. Therefore, this study evaluated YN in OH rats, using a head-up tilt test (HUT). Experimental procedureRats were anesthetized, and OH induced via a 90oHUT, before and after administering vehicle, a YN powder suspension (10, 100 mg/kg), a YN aqueous extract (100 mg/kg), and midodrine (5 mg/kg). The systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial blood pressure (MAP), pulse pressure (PP) and heart rate (HR) were determined via the carotid artery. Plasma noradrenaline (NA) was evaluated. YN-induced vasoconstriction of isolated rat aorta rings was determined using organ bath technique. Results and conclusionBaseline BP increased with the 100 mg/kg YN powder suspension, the YN aqueous extract or midodrine, while HR decreased, compared with vehicle and control. 90oHUT rapidly reduced SBP, DPB and MAP, but increased HR, for control and vehicle-treated groups, but BP was steady with the 100 mg/kg YN powder suspension, the YN aqueous extract or midodrine. The 90oHUT-increase in HR was most pronounced with the 100 mg/kg YN powder suspension (the traditional formulation). This accords with increased plasma NA. YN also induced vasoconstriction in rat aorta via α1-receptor activation. Thus, the anti-hypotensive action of YN involved a stimulating effect on the heart and blood vessels via sympathetic activation. The results support the traditional use of YN and demonstrated the effectiveness of YN for OH prevention.

Serum Activity Against G Protein-Coupled Receptors and Severity of Orthostatic Symptoms in Postural Orthostatic Tachycardia Syndrome.

BackgroundPostural orthostatic tachycardia syndrome (POTS) is characterized by excessive heart rate increase on standing and orthostatic intolerance. Previous data indicate autoimmune involvement. We studied serum activity against G protein–coupled receptors in relation to symptoms in patients with POTS and controls using a commercial cell‐based assay.Methods and ResultsForty‐eight patients with POTS (aged 28.6±10.5 years; 44 women) and 25 healthy individuals (aged 30.7±8.6 years; 21 women) were included. The 10‐item Orthostatic Hypotension Questionnaire (OHQ) was completed by 33 patients with POTS and all controls. Human embryonic kidney 293 cells overexpressing one G protein–coupled receptor: adrenergic α1 receptor, adrenergic β2 receptor, cholinergic muscarinic type 2 receptor, and opioid receptor‐like 1 were treated with sera from all patients. Receptor response was analyzed using a β‐arrestin–linked transcription factor driving transgenic β‐lactamase transcription by fluorescence resonance energy transfer method. Receiver operating characteristic curves were constructed. G protein–coupled receptor activation was related to OHQ indices in linear regression models. Sera from patients with POTS activated all 4 receptors to a higher degree compared with controls (P<0.01 for all). The area under the curve was 0.88 (0.80–0.97, P<0.001) combining all 4 receptors. Adrenergic α1 receptor activation associated with OHQ composite score (β=0.77 OHQ points per SD of activity, P=0.009) and with reduced tolerability for prolonged standing (P=0.037) and walking for short (P=0.042) or long (P=0.001) periods. All 4 receptors were associated with vision problems (P<0.05 for all).ConclusionsOur results indicate the presence of circulating proteins activating adrenergic, muscarinic, and nociceptin receptors in patients with POTS. Serum‐mediated activation of these receptors has high predictive value for POTS. Activation of adrenergic α1 receptor is associated with orthostatic symptoms severity in patients with POTS.

α1 adrenergic receptor activation has a dynamic effect on masticatory muscle afferent fibers

Temporomandibular Disorder (TMD) patients report amplification of pain in the masticatory muscles after psychological trauma or stressful conditions. The mechanisms underlying this phenomenon are yet to be elucidated. This study combined immunohistochemistry with single cell in vivo electrophysiology recordings of masticatory muscle afferent fibers to investigate the role of α1-adrenergic receptors in muscle nociception. It was found that a subset of trigeminal afferent fibers which innervate the masseter and temporal muscles expressed α1a, α1b and α1d receptors, including a smaller number of putative nociceptors which co-expressed TrpV1 receptors. Local injection of the selective α1 adrenergic receptor agonist phenylephrine into masticatory muscle decreased and increased the mechanical activation threshold of slow and fast conducting afferent fibers, respectively. This effect was reversed by co-administration of the α1 selective antagonist terazosin. To rule out the possibility that local ischemia was responsible for the observed effect of phenylephrine on masticatory muscle afferent fibers, additional experiments were conducted where blood flow to the masticatory muscle was reduced by common carotid artery occlusion. This investigation found that muscle blood flow occlusion increased the mechanical activation threshold of the majority of masticatory muscle afferent fibers unrelated to conduction velocity. These findings suggest that under conditions of increased sympathetic tone, such as those related to stress, noradrenaline may sensitize masticatory muscle nociceptors to increase pain and desensitize muscle proprioceptors to alter muscle tone, through activation of α1 receptors.

Postnatal development of persistent inward currents in rat XII motoneurons and their modulation by serotonin, muscarine and noradrenaline.

Persistent inward currents (PICs) in spinal motoneurons are long-lasting, voltage-dependent currents that increase excitability; they are dramatically potentiated by serotonin, muscarine, and noradrenaline (norepinephrine). Loss of these modulators (and the PIC) during sleep is hypothesized as a major contributor to REM sleep atonia. Reduced excitability of XII motoneurons that drive airway muscles and maintain airway patency is causally implicated in obstructive sleep apnoea (OSA), but whether XII motoneurons possess a modulator-sensitive PIC that could be a factor in the reduced airway tone of sleep is unknown. Whole-cell recordings from rat XII motoneurons in brain slices indicate that PIC amplitude increases ∼50% between 1 and 23days of age, when potentiation of the PIC by 5HT2 , muscarinic, or α1 noradrenergic agonists peaks at <50%, manyfold lower than the potentiation observed in spinal motoneurons. α1 noradrenergic receptor activation produced changes in XII motoneuron firing behaviour consistent with PIC involvement, but indicators of strong PIC activation were never observed; in vivo experiments are needed to determine the role of the modulator-sensitive PIC in sleep-dependent reductions in airway tone. Hypoglossal (XII) motoneurons play a key role in maintaining airway patency; reductions in their excitability during sleep through inhibition and disfacilitation, i.e. loss of excitatory modulation, is implicated in obstructive sleep apnoea. In spinal motoneurons, 5HT2 , muscarinic and α1 noradrenergic modulatory systems potentiate persistent inward currents (PICs) severalfold, dramatically increasing excitability. If the PICs in XII and spinal motoneurons are equally sensitive to modulation, loss of the PIC secondary to reduced modulatory tone during sleep could contribute to airway atonia. Modulatory systems also change developmentally. We therefore characterized developmental changes in magnitude of the XII motoneuron PIC and its sensitivity to modulation by comparing, in neonatal (P1-4) and juvenile (P14-23) rat brainstem slices, the PIC elicited by slow voltage ramps in the absence and presence of agonists for 5HT2 , muscarinic, and α1 noradrenergic receptors. XII motoneuron PIC amplitude increased developmentally (from -195±12 to -304±19pA). In neonatal XII motoneurons, the PIC was only potentiated by α1 receptor activation (5±4%). In contrast, all modulators potentiated the juvenile XII motoneurons PIC (5HT2 , 5±5%; muscarine, 22±11%; α1 , 18±5%). These data suggest that the influence of the PIC and its modulation on XII motoneuron excitability will increase with postnatal development. Notably, the modulator-induced potentiation of the PIC in XII motoneurons was dramatically smaller than the 2- to 6-fold potentiation reported for spinal motoneurons. In vivo measurements are required to determine if the modulator-sensitive, XII motoneuron PIC is an important factor in sleep-state dependent reductions in airway tone.

Cocaine increases dopaminergic neuron and motor activity via midbrain α1 adrenergic signaling.

Cocaine reinforcement is mediated by increased extracellular dopamine levels in the forebrain. This neurochemical effect was thought to require inhibition of dopamine reuptake, but cocaine is still reinforcing even in the absence of the dopamine transporter. Here, we demonstrate that the rapid elevation in dopamine levels and motor activity elicited by cocaine involves α1 receptor activation within the ventral midbrain. Activation of α1 receptors increases dopaminergic neuron burst firing by decreasing the calcium-activated potassium channel current (SK), as well as elevates dopaminergic neuron pacemaker firing through modulation of both SK and the hyperpolarization-activated cation currents (Ih). Furthermore, we found that cocaine increases both the pacemaker and burst-firing frequency of rat ventral-midbrain dopaminergic neurons through an α1 adrenergic receptor-dependent mechanism within the ventral tegmental area and substantia nigra pars compacta. These results demonstrate the mechanism underlying the critical role of α1 adrenergic receptors in the regulation of dopamine neurotransmission and behavior by cocaine.

Adrenergic α1 receptor activation is sufficient, but not necessary for phrenic long-term facilitation

Acute intermittent hypoxia (AIH; three 5-min hypoxic episodes) causes a form of phrenic motor facilitation (pMF) known as phrenic long-term facilitation (pLTF); pLTF is initiated by spinal activation of Gq protein-coupled 5-HT2 receptors. Because α1 adrenergic receptors are expressed in the phrenic motor nucleus and are also Gq protein-coupled, we hypothesized that α1 receptors are sufficient, but not necessary for AIH-induced pLTF. In anesthetized, paralyzed, and ventilated rats, episodic spinal application of the α1 receptor agonist phenylephrine (PE) elicited dose-dependent pMF (10 and 100 μM, P < 0.05; but not 1 μM). PE-induced pMF was blocked by the α1 receptor antagonist prazosin (1 mM; -20 ± 20% at 60 min, -5 ± 21% at 90 min; n = 6). Although α1 receptor activation is sufficient to induce pMF, it was not necessary for AIH-induced pLTF because intrathecal prazosin (1 mM) did not alter AIH-induced pLTF (56 ± 9% at 60 min, 78 ± 12% at 90 min; n = 9). Intravenous (iv) prazosin (150 μg/kg) appeared to reduce pLTF (21 ± 9% at 60 min, 26 ± 8% at 90 min), but this effect was not significant. Hypoglossal long-term facilitation was unaffected by intrathecal prazosin, but was blocked by iv prazosin (-4 ± 14% at 60 min, -13 ± 18% at 90 min), suggesting different LTF mechanisms in different motor neuron pools. In conclusion, Gq protein-coupled α1 adrenergic receptors evoke pMF, but they are not necessary for AIH-induced pLTF.

Comparison of two different doses of dexmedetomidine infusion on post-operative pain and sedation in patients undergoing laparoscopic surgery

Background: Effective attenuation of the sympathoadrenal stress responses is an important goal in anesthesiology. Dexmedetomidine (Dex) a new generation highly selective α2 adrenoreceptor agonist might permit sedation and analgesia without the unwanted vascular effects from activation of α1 receptors. In addition, it has been shown to induce a centrally mediated reduction of sympathetic nervous system activity and decrease hemodynamic and plasma catecholamine response to stressful events. These properties theoretically make it a suitable agent for use as part of the anesthetic regimen. The aim was to study the effect of Dex infusion at two different doses on sedation and post-operative pain using Ramsay sedation score and visual analog scale (VAS) during the post-operative period for first 24 hrs. Methods: In this study, the patients were randomly divided into three different groups (control, Dex 0.3, and Dex 0.6) using computer generated random table. Post-operatively patient’s sedation pain scores were compared using Ramsay sedation score and VAS, respectively. Results: It was observed that the duration of surgery, duration of infusion and use of fentanyl (μg) was statistically insignificant in all the three groups. The mean pain in subjects of both Dex 0.3 and Dex 0.6 just after surgery till 6 hrs post-surgery were found to be significantly (p 0.05) between the three groups i.e., remains statistically the same. On comparing the mean Sedation in subjects of Dex 0.3 and Dex 0.6 just after surgery till 12 hrs post-surgery were found to be significantly (p 0.05). Conclusion: The perioperative infusion of Dex may be an attractive option during laparoscopic surgery as it, offered better control of intraoperative and post-operative hemodynamics, and decreased post-operative pain level and better sedation scores, as compared with control.

Differential Sensitivity to Psychostimulants Across Prefrontal Cognitive Tasks: Differential Involvement of Noradrenergic α1- and α2-Receptors

Psychostimulants improve a variety of cognitive and behavioral processes in patients with attention-deficit/hyperactivity disorder (ADHD). Limited observations suggest a potentially different dose-sensitivity of prefrontal cortex (PFC)-dependent function (narrow inverted-U-shaped dose-response curves) versus classroom/overt behavior (broad inverted U) in children with ADHD. Recent work in rodents demonstrates that methylphenidate (MPH; Ritalin) elicits a narrow inverted-U-shaped improvement in performance in PFC-dependent tests of working memory. The current studies first tested the hypothesis that PFC-dependent tasks, in general, display narrow dose sensitivity to the beneficial actions of MPH. The effects of varying doses of MPH were examined on performance of rats in two tests of PFC-dependent cognition, sustained attention and attentional set shifting. Additionally, the effect of pretreatment with the α₁-antagonist prazosin (.5 mg/kg) on MPH-induced improvement in sustained attention was examined. MPH produced a broad inverted-U-shaped facilitation of sustained attention and attentional set shifting. Prior research indicates α₁-receptors impair, whereas α₂-receptors improve, working memory. In contrast, attentional set shifting is improved with α₁-receptor activation, whereas α₂-receptors exert minimal effects in this task. Given the similar dose sensitivity of sustained attention and attentional set-shifting tasks, additional studies examined whether α₁-receptors promote sustained attention, similar to attentional set shifting. In these studies, MPH-induced improvement in sustained attention was abolished by α₁-receptor blockade. PFC-dependent processes display differential sensitivity to the cognition-enhancing actions of psychostimulants that are linked to the differential involvement of α₁- versus α₂-receptors in these processes. These observations have significant preclinical and clinical implications.

Apnea‐induced respiratory long‐term facilitation of genioglossus motor outflow requires noradrenergic receptor activation on hypoglossal motoneurons

The respiratory neuronal network is highly flexible and can undergo neuroplasticity, one form of which is called long-term facilitation (LTF). Current data suggests that concurrent episodic activation of serotonin 2A (5-HT2A) and α1 noradrenergic receptors underlie hypoxia-induced LTF of breathing. The aims of this study were to determine: 1) whether apnea-induced LTF of genioglossus (GG) muscle tone involves 5-HT2A and/or α1-dependent processes, and 2) if the underlying mechanisms are operating at the level of hypoglossal motoneurons. LTF was measured as a along-lasting (> 1-hour) enhancement in inspiratory GG EMG activity following repeated apneas in spontaneously breathing, anesthetized adult rats. We found that systemic administration (i.v.) of either the α1 receptor antagonist terazosin (15ug/kg; n=5), or the 5-HT2A receptor antagonist ketanserin (2 mg/kg; n=6) prevented apnea-induced LTF (p=0.343 and p=0.073 respectively). Expression of apnea-induced LTF was dependent on the activation of α1 receptors on hypoglossal motoneurons because microdialysis of terazosin (1 uM; n=6) into the hypoglossal motor pool abolished LTF (p=0.10), whereas ketanserin perfusion did not (50 uM, n=6; p= 0.001 and 100 uM, n=4; p=0.006). Our data indicates that repeated apneas result in activation of α1-dependent processes within hypoglossal motoneurons, leading to enhancement of upper airway activity. 5-HT2A receptor activation may in turn be required elsewhere in the respiratory network, upstream of motoneurons. Grant Funding Source: NSERC

Noradrenergic Regulation of GABAergic Inhibition of Main Olfactory Bulb Mitral Cells Varies as a Function of Concentration and Receptor Subtype

The main olfactory bulb (MOB) receives a rich noradrenergic innervation from the pontine nucleus locus coeruleus (LC). Previous studies indicate that norepinephrine (NE) modulates the strength of GABAergic inhibition in MOB. However, the nature of this modulation and the NE receptors involved remain controversial. The goal of this study was to investigate the role of NE receptor subtypes in modulating the GABAergic inhibition of mitral cells using patch-clamp electrophysiology in rat MOB slices. NE concentration dependently and bi-directionally modulated GABA(A) receptor-mediated spontaneous and miniature inhibitory postsynaptic currents (sIPSCs/mIPSCs) recorded in mitral cells. Low doses of NE suppressed sIPSCs and mIPSCs because of activation of alpha2 receptors. Intermediate concentrations of NE increased sIPSCs and mIPSCs primarily because of activation of alpha1 receptors. In contrast, activation of beta receptors increased sIPSCs but not mIPSCs. These results indicate that NE release regulates the strength of GABAergic inhibition of mitral cells depending on the NE receptor subtype activated. Functionally, the differing affinity of noradrenergic receptor subtypes seems to allow for dynamic modulation of GABAergic inhibition in MOB as function of the extracellular NE concentration, which in turn, is regulated by behavioral state.

Dopamine Induces a Slow Afterdepolarization in Lateral Amygdala Neurons

The amygdala and dopaminergic innervation thereunto are considered to cooperatively regulate emotional states and behaviors. The present experiments examined effects of dopamine on lateral amygdala (LA) neuron excitability by whole cell recordings. Bath application of dopamine induced slow afterdepolarization (sADP). This sADP lasted for >5 s, and its magnitude varied in a concentration-dependent manner. Co-application of the D1 receptor antagonist SKF83566 reduced its amplitude. The D1 receptor agonist SKF38393, applied alone, induced sADP of a smaller amplitude. Induction of the full sADP required 5-HT(2) and noradrenalin alpha(1) receptor activation as well. D2 receptor activation or blockade did not affect sADP induction. The calcium channel blocker cadmium or intracellular calcium chelator bis-(o-aminophenoxy)-N,N,N',N' tetraacetic acid (BAPTA) blocked induction of the sADP, which was suggested to be triggered by calcium influx. Under voltage clamp, membrane conductance decreased at the peak of sADP current (I(sADP)). I(sADP) was suppressed by cesium included in pipettes. The I-V curve of the net I(sADP) was shifted as the external concentration of potassium was raised, and the reversal potential was identical to that of potassium, suggesting that dopamine decreases potassium conductance to induce the sADP. The present sADP may serve as a positive-feedback regulator of excitability in LA neurons.

Effect of Prazosin on the Peripheral Vasculature during Rest Low, Mild, and Heavy Exercise Workloads.

INTRODUCTION: Metabolic inhibition of alpha-1 mediated vasoconstriction in exercising muscles is evident in both animal and human models. A majority of the studies investigating the role of alpha-1 receptors have infused exogenous α1-receptor agonists intra-arterially to activate these receptors. However the role of physiological activation of these receptors in humans is incompletely understood. PURPOSE: To test the hypothesis that as exercise intensity increases physiological activation of α1-receptors has a decreased role in the control of the peripheral vasculature in exercising muscles. METHODS: We compared the vasoconstrictor responses before and after oral ingestion of the α1-receptor blocker Prazosin (1mg/20kg of body weight) in healthy humans (n=5) during rest and dynamic knee-extensor exercise at roughly 40%, 60% and 80% of workloadmax. Neck pressure (NP) stimuli were used to unload carotid baroreceptors thus leading to sympathoexcitation. Ultrasound Doppler provided direct measurements of femoral blood flow (FBF) and intra-arterially measured blood pressures were used to calculate femoral vascular conductance (FVC). RESULTS: Prazosin resulted in significant increases FVC at rest when compared to the control protocol (+68 ± 6%). During exercise the Prazosin mediated increases in FVC decreased with increasing exercise intensities (+68 ± 4%, +39 ±4%, and +23 ± 6% respectively). In both conditions “functional sympatholyis” was occurring because the NP mediated vasoconstriction was attenuated in an exercise intensity dependent manner. During NP the % decreases in FVC were not significantly different between conditions. CONCLUSIONS: These data demonstrate that vasoconstriction elicited by physiological activation of ?1 -receptors with circulating endogenous agonists as a result of intense dynamic exercise is reduced as exercise intensity increases. Additionally there was a reduced response to sympathetically mediated vasoconstriction as a result of functionally unloading the carotid baroreceptors with NP stimuli in both conditions, i.e. functional sympatholysis was present. Furthermore the NP mediated vasoconstriction was attenuated to a similar degree in both conditions. Supported in part by NIH grant # HL-045547

Slow Oscillatory Firing: A Major Firing Pattern of Dopamine Neurons in the Ventral Tegmental Area

Using spectral analysis and in vivo single-unit recording in rats, the present study revealed a pronounced slow oscillation (SO) in the firing activity of about half the dopamine (DA) neurons recorded in the ventral tegmental area. DA neurons in this group tended to fire repetitive spike clusters, making them appear to be rhythmic bursting cells. However, only some of these burst-like events met the traditional "80/160 ms" burst criteria entirely. The observation that the SO could be found in nonbursting DA cells, occurred at frequencies different from those of bursts, and persisted after bursts were digitally removed from spike trains further supports the suggestion that the SO is different from the traditionally defined bursting. Interspike intervals (ISIs) had been thought to be bimodally distributed in bursting DA neurons. This study found that some nonbursting DA cells also had a bimodal ISI distribution and a significant number of bursting cells did not. In the majority of cells where less than half the spikes occurred in bursts, a bimodal ISI distribution was highly predictive of the presence of the SO. Results further showed that the generation of the SO required forebrain inputs to DA neurons but not the adrenergic alpha1 receptor activation responsible for psychostimulant-induced increases in the SO. Taken together, these results suggest that the SO is distinct from the traditionally defined bursting and represents a major firing pattern of DA neurons in the ventral tegmental area.

Postnatal changes in the noradrenergic system modulating hypoglossal motoneurons

Appropriate activation of hypoglossal (XII) motoneurons (MNs) during inspiration is essential for maintaining upper airway patency. Morphological and electrophysiological properties of XII MNs, as well as numerous modulatory systems affecting these MNs, undergo significant change postnatally. These changes must be properly coordinated to ensure that breathing continues uninterupted throughout development. We have previously described an α1 noradrenergic receptor-mediated potentiation of XII nerve activity that increases approximately 1.8-fold over the first three postnatal days and 2.5-fold over the first two postnatal weeks [1]. To examine the development of the noradrenergic system underlying this potentiation, we combined electrophysiological and immunohistochemical approaches. Mechanisms underlying the potentiating effects of α1 receptor activation were assessed using whole-cell recordings from XII MNs in rhythmically-active medullary slice preparations from P0 (postnatal day zero) and P3 mice. The development of the catecholaminergic cell phenotype and the time course over which norepinephrine (NE) immunoreactive terminals appear in the XII nucleus were examined immunohistochemically using a monoclonal antibody against tyrosine hydroxylase (TH; Boehringer Mannhiem) and a polyclonal antibody against NE (Chemicon) in mice ranging from P0 to adult. Tissue from all age groups was processed simultaneously and labelled using a stan-protocol. Images were captured using a CCD dard DAB/H2O2 camera and optical density of immunolabelling was measured using NIH Image software. Phenylephrine (PE) induced an inward current or a depolarization in all inspiratory XII MNs tested (n = 21). At a holding potential of -60 mV, currents induced by PE (100 μM) increased from 2.9 ± 0.7 pA/pF in P0 (n = 9) to 4.7 ± 1.1 pA/pF in P3 (n = 12)MNs. Application of PE did not affect input resistance (RN) in P0 MNs (n = 7) but increased RN by 11 ± 4% in P3 MNs (n = 11). PE potentiated inspiratory synaptic currents, and the magnitude of this potentiation was significantly greater in P3 (peak current 25 ± 7%; charge transfer per burst 43 ± 7%, n = 8) relative to P0 (peak 17 ± 7; charge transfer per burst 28 ± 11%, n = 6) XII MNs. Involvement of post-synaptic receptors was indicated by persistence of the responses in TTX (1 μM, n = 7). PE did not affect repetitive firing elicited by injected current in P0 MNs tested (n = 2). However, the frequency/current relationship was significantly shifted to the left in 3/5 P3 MNs. Immunohistochemical data showed that labelling for TH in the A5, A7 and LsC (Locus subCoeruleus) cell groups was already strong in P0 and increased approximately 30% by P14, before decreasing to adult levels which were similar to P0 values. Immunolabelling for NE in these cell groups was also apparent at P0. A developmental increase in NE immunolabelling was modest, except in LsC where it increased up to 140% by P7, before decreasing to adult levels (that were half those observed in P0 animals). The number of NE-positive fibers and varicosities within XII nucelus was low in P0 mice, but increased dramatically by P14 where dense innervation was present along the entire rostro-caudal extent of the nucleus. In adults, NE-positive terminals/varicosities were dense over only a limited rostro-caudal region. These data suggest that the factors contributing to the developmental increase in the noradrenergic potentiation of XII MN activity include a proliferation of NE-containing terminals within the XII nucleus and maturation of postsynaptic α1 receptor mechanisms.

Norepinephrine increases rat mitral cell excitatory responses to weak olfactory nerve input via alpha-1 receptors in vitro

A rat olfactory bulb in vitro slice preparation was used to investigate the actions of norepinephrine on spontaneous and afferent (olfactory nerve) evoked activity of mitral cells. Single olfactory nerve shocks elicited a characteristic mitral cell response consisting of distinct, early and late spiking components separated by a brief inhibitory epoch. Bath-applied norepinephrine (1 μM) increased the early spiking component elicited by perithreshold (79% increase, P<0.02), but not by suprathreshold (3% decrease, P>0.05), intensity olfactory nerve shocks. The facilitatory effect of norepinephrine was due to a reduction in the incidence of response failures to perithreshold intensity shocks. Norepinephrine also decreased the inhibitory epoch separating the early and late spiking components by 44% ( P<0.05). By contrast, norepinephrine had no consistent effect on the spontaneous discharge rate of the mitral cells. The effects of norepinephrine were mimicked by the α1 receptor agonist phenylephrine (1 μM, P<0.001). Both norepinephrine and phenylephrine modulation of mitral cell responses were blocked by the α1 adrenergic antagonist WB-4101 (1 μM). These findings are consistent with observations that the main olfactory bulb exhibits the highest density of α1 receptors in the brain. The α2 receptor agonist clonidine (100 nM) and the β receptor agonist isoproterenol (1 μM) had inconsistent effects on mitral cell spontaneous and olfactory nerve-evoked activity. These results indicate that norepinephrine increases mitral cell excitatory responses to weak but not strong olfactory nerve inputs in vitro via activation of α1 receptors. This is consistent with recent findings in vivo that synaptically released norepinephrine preferentially increases mitral cell excitatory responses to weak olfactory nerve inputs. Taken together, these results suggest that the release of norepinephrine in the olfactory bulb may increase the sensitivity of mitral cells to weak odors. Olfactory cues evoke norepinephrine release in the main olfactory bulb, and norepinephrine plays important roles in early olfactory learning and reproductive/maternal behaviors. By increasing mitral cell responses to olfactory nerve input, norepinephrine may play a critical role in modulating olfactory function, including formation and/or recall of specific olfactory memories.

Noradrenergic regulation of synaptic plasticity in the hippocampal CA1 region.

The effects of norepinephrine (NE) and related agents on long-lasting changes in synaptic efficacy induced by several patterns of afferent stimuli were investigated in the CA1 region of rat hippocampal slices. NE (10 microM) showed little effect on the induction of long-term potentiation (LTP) triggered by theta-burst-patterned stimulation, whereas it inhibited the induction of long-term depression (LTD) triggered by 900 pulses of 1-Hz stimulation. In nontreated slices, 900 pulses of stimuli induced LTD when applied at lower frequencies (1-3 Hz), and induced LTP when applied at a higher frequency (30 Hz). NE (10 microM) caused a shift of the frequency-response relationship in the direction preferring potentiation. The effect of NE was most prominent at a stimulus frequency of 10 Hz, which induced no changes in control slices but clearly induced LTP in the presence of NE. The facilitating effect of NE on the induction of LTP by 10-Hz stimulation was blocked by the beta-adrenergic receptor antagonist timolol (50 microM), but not by the alpha receptor antagonist phentolamine (50 microM), and was mimicked by the beta-agonist isoproterenol (0.3 microM), but not by the alpha1 agonist phenylephrine (10 microM). The induction of LTD by 1-Hz stimulation was prevented by isoproterenol but not by phenylephrine, indicating that the activation of beta-receptors is responsible for these effects of NE. NE (10 microM) also prevented the reversal of LTP (depotentiation) by 900 pulses of 1-Hz stimulation delivered 30 min after LTP induction. In contrast to effects on naive (nonpotentiated) synapses, the effect of NE on previously potentiated synapses was only partially mimicked by isoproterenol, but fully mimicked by coapplication of phenylephrine and isoproterenol. In addition, the effect of NE was attenuated either by phentolamine or by timolol, indicating that activation of both alpha1 and beta-receptors is required. These results show that NE plays a modulatory role in the induction of hippocampal synaptic plasticity. Although beta-receptor activation is essential, alpha1 receptor activation is also necessary in determining effects on previously potentiated synapses.

Alpha 1-adrenergic receptor subtypes. Molecular structure, function, and signaling.

The α1ARs are important mediators of sympathetic nervous system responses, particularly those involved in cardiovascular homeostasis, such as arteriolar smooth muscle constriction and cardiac contraction.1 2 In addition, α1ARs have more recently been implicated in the pathogenesis of cardiac hypertrophy, in ischemia-induced cardiac arrhythmias, and in ischemic preconditioning.1 3 Like other ARs, α1ARs are activated by the catecholamines, norepinephrine and epinephrine. They are intrinsic membrane glycoproteins and are members of the GPCR superfamily. Over the past 10 to 15 years, data initially based on functional, radioligand, and biochemical studies have accumulated, indicating that the α1ARs are a heterogeneous group of distinct but related proteins. This conclusion has been confirmed with the molecular cloning of three distinct α1-receptor subtypes, although until recently discrepancies between the properties of the cloned expressed receptors and those characterized pharmacologically and biochemically have led to confusion in the classification of α1-receptor subtypes and their coupled effector responses. As detailed in the present review, much of this confusion has now been clarified for the three cloned α1ARs. These and other recent insights into the molecular structure, function, and signaling of α1ARs, the control of α1AR-gene expression, and pharmacological evidence for additional α1AR subtypes will be reviewed here. For additional information, the reader is also referred to several previous reviews of α1ARs.4 5 6 7 Functional studies of AR responses, particularly from the laboratories of McGrath8 and Ruffolo,9 provided the initial evidence that there may be subtypes of α1ARs. These studies indicated that postjunctional responses mediated by α1ARs could not be explained adequately on the basis of a single population of receptors. This concept was further advanced …

Effects of Vasoactive Agents and their Antagonists Measured by Acoustic Rhinometry

The purpose of this study was to assess the effects of a agonists on the human nasal mucosa. Volumetric changes in the nasal cavity after application of phenylephrine (PNL), oxymetazoline (OMZ), and epinephrine (EPR) were investigated using acoustic rhinometry. The reactions of the nasal mucosa were extremely modified after pretreatment by α1 and α2 antagonists, phenoxybenzamine (POB) and yohimbine (YOH), and local anesthetic, xylocaine (XLC). Decongestion of the nasal mucosa evoked by α stimulants was considered to originate mainly from the direct activation of α1 receptors. Decongestion of the middle and posterior parts began later than the anterior part and was more gradual because of the time necessary to transport the drug particles to the posterior areas. Contralateral volume changes were probably controlled by the afferent signals from the ipsilateral side of the nose.