Neuropeptide Y (NPY) co-exists with tyrosine hydroxylase and potentiates the adrenergic contractile response of vascular smooth muscle in the human uterine artery.

The human uterine artery was studied by immunocytochemistry and in vitro pharmacology. Nerve fibres containing immunoreactivity for neuropeptide Y (NPY) were encountered in the media, adventitia, smooth muscle layers and surrounding the vasa vasorum. Approximately 50% of the nerve fibres containing NPY also stored immunoreactivity for tyrosine hydroxylase (TH) and TH activity was found in no other fibres. Noradrenaline (NA) contracted the isolated uterine artery in a concentration dependent manner. The presence of increasing doses of NPY shifted the concentration-response curve for NA to the left. Consequently the pD2-values were increased indicating a potentiation of the adrenergic effects induced by NPY. The results demonstrate the existence of NPY in adrenergic nerve fibres surrounding the human uterine artery. A close co-operation between NPY and NA in the neuronal control of smooth muscle is suggested.     

Pharmacological characteristics of P2 receptors in human uterus

We studied contractile responses of isolated smooth muscles from human uterus induced by P2 receptor agonists. In preparations from pregnant uterus all tested P2 receptor agonists caused smooth muscle contractions. The relative activity of P2 receptor agonists decreased in the following order: a,b-methylene-ATP-uridine triphosphate-ATP. Responses induced by ATP and ADP were similar. The amplitude of contractions induced by alpha,beta-methylene-ATP significantly decreased in the presence of P2 receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid. None of tested P2 receptor agonists induced contractions of isolated myometrium from nonpregnant women. Our results indicate that pregnant human uterus contains P2 receptors mediating the contractile response.     

Postjunctional alpha 1- and alpha 2-adrenoceptors mediating contraction in isolated human groin arteries and veins

By means of selective agonists and antagonists for alpha 1- and alpha 2-receptors, the alpha-receptor subtypes in human groin arteries and veins were characterized and compared. In the arteries the alpha 1-receptor blocker prazosin caused a concentration-dependent parallel displacement of the noradrenaline (NA) concentration-response (cr) curve without reduction of maximum (pA2 = 9.86); the selective alpha 2-receptor antagonist rauwolscine in the concentration 10(-8) M caused a right-ward shift of the NA cr-curve without reduction of Emax, but 10(-7) M and 10(-6) M caused little or no further shift. In the veins, the two antagonists had the opposite effects. Rauwolscine caused a concentration-dependent right-ward shift of the NA cr-curve without depression of maximum (pA2 = 9.03); prazosin 10(-9) M significantly displaced the NA cr-curve, whereas 10(-8) M and 10(-7) M caused little or no further shift. The responses to the alpha 2-receptor agonist clonidine in the arteries were too small to allow calculations of pEC50 values; in the veins contractions were elicited in all vessel segments investigated (pEC50 = 6.24). Phenylephrine, selective for alpha 1-receptors, was significantly more potent in arteries than in veins. NA was significantly more potent in veins than in arteries. It is concluded that in human groin vessels, there is a functional predominance of alpha 1-receptors in the arteries and of alpha 2-receptors in the veins.     

Pregnancy: Atrial natriuretic peptide antagonizes the contractile effect of angiotensin II in the human uterine artery

The regulatory peptides angiotensin II (Ang II) and atrial natriureticpeptide (ANP) are believed to play important roles in the pathogenesisof pre-eclampsia. The interactions between Ang II, ANP and noradrenaline(NA) were studied in vitro on the human uterine artery. BothAng II and NA contracted the isolated vessel in a concentration-dependentway. At high doses a decrease in the contractile force inducedby Ang II but not NA was encountered. ANP inhibited the smoothmuscle activity elicited by Ang II, resulting in a dextroshiftof the concentration-response curve, and a decrease in bothE_max (the maximum contractile response) and pD2 (the negativelogarithm of the agonist concentration inducing 50% of the E_max)for Ang II. The results might indicate a specific antagonismbetween Ang II and ANP, probably at the post-receptor level.ANP did not induce any significant change in pD₂ of the concentration-responsecurve for NA. Only at the highest dose of ANP (10^–7 M)was E_max depressed. Thus, the results only indicate a weak antagonisticrelationship between NA and ANP in the human uterine artery.     

Contractile effects of noradrenaline and 5-hydroxytryptamine in human hand veins: a pharmacological receptor characterization

The postjunctional receptors mediating contractile responses to noradrenaline (NA) and 5-hydroxytryptamine (5-HT) were characterized in ring segments of human hand veins by using subtype selective agonists and antagonists. The mechanical characteristics of the preparations were also examined by length-tension measurements. The length-active wall tension curve was bell-shaped and reached a maximum at a length corresponding to a passive distending pressure of approximately 14 mmHg. (-)-Phenylephrine consistently contracted the veins and was 24 times less potent than (+/-)-NA whereas clonidine produced a contraction in only two out of 11 vessel segments. Neither prazosin nor rauwolscine competitively inhibited the contractile response to NA, and large inter-individual differences were found in the degree of inhibition produced by the antagonists. However, application of both prazosin and rauwolscine almost abolished the NA-induced contraction. Ketanserin and methergoline inhibited the contractile response to 5-HT; the former in an apparently competitive manner with a pA2 value of 8.94, whereas the latter substantially reduced the maximum 5-HT response. It is suggested that NA elicits contraction in human hand veins by acting at a mixed population of alpha 1- and alpha 2-adrenoreceptors. The contractile response to 5-HT, on the other hand, appears to be mediated predominantly by 5-HT2 receptors.     

Mechanisms underlying pre- and postjunctional effects of neuropeptide Y in sympathetic vascular control

The effects of porcine neuropeptide Y (NPY) regarding sympathetic vascular control were studied in vitro on isolated rat blood vessels. The 10(-9)M NPY enhanced (about two-fold) the contractile responses to transmural nerve stimulation (TNS), noradrenaline (NA) and adrenaline (about two-fold) in the femoral artery. Higher concentrations of NPY (greater than 10(-8)M) caused an adrenoceptor-resistant contraction per se. The TNS-evoked [3H]NA efflux was significantly reduced by NPY in a concentration-dependent manner (threshold 10(-9)M). The calcium antagonist, nifedipine, abolished the contractile effects of NPY and the NPY-induced enhancement of NA contractions but did not influence the prejunctional inhibition of [3H]NA release. Receptor-binding studies showed that the ratio of alpha 1-to alpha 2-adrenoceptors in the femoral artery was 30:1. The NPY did not cause any detectable change in the number of alpha 1-or alpha 2-adrenoceptor binding sites or in the affinity of alpha 2-binding sites, as revealed by prazosin- and clonidine-binding, respectively. The NPY also inhibited the TNS-evoked [3H]NA release (by 42-86%) in the superior mesenteric and basilar arteries and in femoral and portal veins. The NPY still depressed TNS-evoked [3H]NA secretion from the portal vein in the presence of phentolamine. The NPY caused a clear-cut contraction in the basilar artery, increased the contractile force of spontaneous contractions in the portal vein, while only weak responses were observed in the superior mesenteric artery and femoral vein. The NA-induced contraction was markedly enhanced by NPY in the superior mesenteric artery, only slightly enhanced in the portal vein and uninfluenced in the femoral vein. In conclusion, in all blood vessels tested, NPY depresses the TNS-evoked [3H]NA secretion via a nifedipine-resistant action. Furthermore, NPY exerts a variable, Ca2+-dependent vasoconstrictor effect and enhancement of NA and TNS contractions.     

Inhibition of vasoconstriction and Ca2+ currents mediated by neuropeptide Y Y2 receptors.

The effects of neuropeptide Y (NPY) and agonists selective for NPY Y1 and Y2 receptors were studied on contraction and Ca2+ currents in arterial smooth muscle. In isolated arterioles from the guinea pig small intestine, small brief constrictions were evoked by depolarising the arteriolar smooth muscle using high K+ solution applied from a micropipette. The constrictions were reduced in amplitude by the Y2-selective agonists PYY(13-36) and N-acetyl[Leu28, Leu31]NPY-(24-36) in concentrations from 20-100 nM. NPY or the Y1 selective agonist [Leu31 Pro34]NPY in concentrations from 50 pM to 100 nM increased the amplitude of the constrictions, with a maximum effect at 10 nM. Smooth muscle cells were isolated from rat small mesenteric arteries, and voltage-activated Ca2+ currents measured by whole cell patch clamping. The peak amplitude of the Ca2+ currents was decreased by N-acetyl[Leu28, Leu31]NPY-(24-36), and by NPY (100 nM). [Leu31, Pro34]NPY either had no effect or slightly increased the Ca2+ currents. We conclude that Y2 receptors on vascular smooth muscle can reduce Ca2+ currents induced by depolarisation, and thus oppose constriction caused by smooth muscle depolarisation.     

Postnatal changes in response of canine neonatal pulmonary arteries to histamine.

Postnatal development of histamine receptors in the canine pulmonary circulation was examined utilizing histamine cumulative dose-response curves of pulmonary arteries isolated from neonatal and adult dogs. The maximal contractile response to histamine was relatively low at birth (avg 0.069 g) and increased with postnatal age, reaching a maximum in the adult (avg 1.10 g). H2-receptor blockade with metiamide increased the contractile response to histamine during the first 2 wk of life (avg 0.38 g), suggesting H2-receptor dominance over H1-receptors in the newborn. Maximal developed tension, in response to KCl, gradually increased with postnatal age, suggesting progressive maturation of the smooth muscle response. In contrast to pulmonary arteries, isolated tracheal segments from puppies aged 1-5 days demonstrated large contractile responses (avg 5 g). Histamine (in microgram/g of wet wt of lung tissue) was absent in the lungs from 3rd trimester fetal dogs and rapidly increased over the first 2 wk of life, reaching a maximum in the adult. It is concluded that 1) the response of pulmonary arteries to histamine changes during the first 2 wk of life; 2) this change may reflect a decrease in H2-receptors and an increase in H1-receptors; 3) the contractile ability of pulmonary vascular smooth muscle increases with postnatal age; and 4) histamine is unavailable for physiological responses in the fetal dog pulmonary circulation.     

Differences in α2-adrenoceptor modulation of calcium channels in vascular smooth muscle cells of male and female rats

 Effects of the α₂-adrenergic agonist clonidine on current through Ca²⁺ channels was recorded from vascular smooth muscle cells isolated from tail arteries and aortae of male and female rats. The average Ba²⁺ current in control was not significantly different between males and females; however, clonidine (1 μM) enhanced Ba²⁺ current through Ca²⁺ channels in cells from females, but not from males. The greater sensitivity of vascular smooth muscle cells to clonidine may underlie different contractile responses to α₂-adrenergic agonists between males and females. Received: 20 May 1996/Received after revision and accepted: 2 August 1996     

Effects of N-ethylmaleimide and forskolin on noradrenaline release from rat hippocampal slices. Evidence that prejunctional adenosine and alpha-receptors are linked to N-proteins but not to adenylate cyclase

N-ethylmaleimide (NEM) treatment has been shown to inactivate regulatory GTP-binding N (G)-proteins in many preparations, including slices of rat hippocampus. NEM-treatment (100 microM for 15 min) has been used to examine the possible involvement of a N-protein in the prejunctional inhibitory effect of an adenosine analogue, R-PIA acting on A1-receptors, and of clonidine acting on alpha 2-adrenoceptors in this tissue. NEM treatment significantly enhanced basal overflow of [3H]NA and the overflow stimulated by low (0.3 Hz) frequency stimulation, but not the overflow stimulated by higher (1-10 Hz) frequency stimulation. The prejunctional inhibitory effect of R-PIA (1 microM) on NA release, stimulated by a 3 Hz stimulation, was abolished by NEM pretreatment, which also eliminated the dose-dependent prejunctional effect of clonidine and reduced the facilitatory effect of yohimbine. Forskolin had a small, but significant stimulatory effect on NA overflow, but did not reduce the prejunctional inhibitory effect of R-PIA. The adenylate cyclase inhibitor SQ 22, 536 did not reduce NA overflow. These results show that NEM blocks a critical step in the prejunctional action of both adenosine- and alpha 2-receptor agonists, which may be a N-protein. The possibility is discussed that the prejunctional A1- and alpha 2-receptors couple to a N-protein that controls a different effector than adenylate cyclase.     

Modulation of calcium homeostasis as a mechanism for altering smooth muscle responsiveness in asthma

Airway hyperresponsiveness remains a defining characteristic of asthma. Traditional views assert that airway smooth muscle is an important structural effector cell in the bronchi that modulates bronchomotor tone induced by contractile agonists. New evidence, however, suggests that abnormalities in airway smooth muscle functions, induced by variety of extracellular stimuli, may play an important role in the development of airway hyperresponsiveness. Studies using isolated bronchial preparations or cultured cells show that inflammatory mediators and cytokines may alter calcium homeostasis in airway smooth muscle and render the cells nonspecifically hyperreactive to agonists.     

Alterations of excitation-contraction coupling by platelet-derived growth factor in enzymatically isolated and cultured vascular smooth muscle cells

We studied stimulus-specific alterations of the excitation-contraction coupling pathway in freshly isolated contractile and subcultured non-contractile vascular smooth muscle cells. Using the calcium indicator aequorin, we detected physiological increases in cytoplasmic free calcium ([Ca²⁺]_i) in subcultured smooth muscle cells subjected to angiotensin or 33 mM potassium depolarization. These increases were qualitatively identical to those previously measured in intact vascular strips. Platelet-derived growth factor (PDGF) induced a slow, sustained [Ca²⁺]_i increase when applied to the subcultured smooth muscle cells at low picomolar concentrations. Freshly isolated, contractile vascular smooth muscle cells, prepared by a novel technique, exhibited a slow shortening of 20% of resting length in response to PDGF. PDGF also markedly potentiated smooth muscle cell shortening in response to an ED₅₀ dose of phenylephrine. This effect was PDGF concentration dependent. The time course of shortening induced by PDGF alone was consistent with the time course of the PDGF-induced [Ca²⁺]_i increase in the cultured smooth muscle cells. These data suggest that agonists which induce [Ca²⁺]_i changes in contractile smooth muscle cells may retain this ability with respect to cultured smooth muscle cells. PDGF, a peptide mitogen for proliferative smooth muscle cells, may also serve to modulate vascular tone by modestly raising [Ca²⁺]_i in contractile smooth muscle cell and, therefore, sensitizing the cells to alpha adrenergic agonists.     

Peculiarities of adrenergic regulation of smooth muscles in rabbit pulmonary arteries

Muscle tension recording was used to study adrenergic contractile reactions of pulmonary artery smooth muscles in rabbits. Stimulation of alpha-adrenoceptors induced contraction of pulmonary artery smooth muscle cells. Endothelium partially inhibited the contractile effect of alpha-adrenoceptor agonists. Activation of smooth muscle beta-adrenoceptors in pulmonary arteries produced a dual dose-dependent effect (relaxation at agonist concentrations of 10 nM-1 muM and contraction at concentrations above 10 muM). The contractile effect of beta-adrenoceptor activation in smooth muscle cells is a specific feature of pulmonary arteries probably related to peculiarities of cAMP-signaling in these cells.     

Influence of extracellular calcium and nifedipine on alpha 1- and alpha 2-adrenoceptor-mediated contractile responses in isolated rat and cat cerebral and mesenteric arteries

The influence of extracellular Ca2+ and nifedipine on contractile responses to 10 microM noradrenaline (NA) was investigated in isolated rat and cat middle cerebral (RCA, CCA) and mesenteric (RMA, CMA) arteries. In the CCA (containing predominantly alpha 2-adrenoceptors), the NA-induced contractions developed considerably more slowly than in the RCA, RMA (containing mainly alpha 1-adrenoceptors) and CMA (sensitive to both alpha 1- and alpha 2-adrenoceptor selective antagonists). The tonic component of the NA-induced contraction in the four types of artery was substantially suppressed after only short periods in Ca2+-free solution. In each type of artery, excluding the CCA, the contractile response to 124 mM K+ was more sensitive to Ca2+ deprivation than that to NA. This suggests that NA, besides mobilizing extracellular Ca2+, can also release Ca2+ from an intracellular pool in the RCA, RMA and CMA, but not in the CCA. Thus, alpha 1-adrenoceptor-mediated contractions in the RCA and RMA seem to depend on both Ca2+ influx and intracellular Ca2+ release, whereas alpha 2-adrenoceptor-mediated contractile responses in the CCA appear to rely almost entirely on Ca2+ influx. Both the maximum response and the tonic component of the NA-induced contraction were significantly more sensitive to nifedipine in the CCA than in the RCA. In comparison with the NA-induced contractions in these arteries, those in the RMA and CMA were relatively resistant to nifedipine. In the CCA exposed to NA in Ca2+-free medium, nifedipine almost abolished the contraction induced by re-addition of Ca2+, whereas in the other types of artery, Ca2+ re-application evoked a significant contraction also in the presence of the drug. The differential effects of nifedipine presumably reflect differences between the arteries, not only in the relative contribution of Ca2+ influx and intracellular Ca2+ release to the contractile activation, but also in the nifedipine sensitivity of the Ca2+ entry pathways utilized by NA. It is concluded that the mechanisms through which NA induces contraction seem to be related both to the subtype of alpha-adrenoceptor stimulated by NA and to the type of vessel studied.     

Effect of alpha1-adrenergic receptor antagonist on the noradrenaline-induced facilitation in respiratory rhythm in newborn rat pons-medulla-spinal cord preparations

We hypothesized that facilitation of respiratory rhythm by noradrenaline (NA) in rat pons-medulla-spinal cord preparations is mediated through alpha1-adrenergic receptors. In 0- to 4-day-old rats, the respiratory frequency (fR) was monitored at the C4 ventral root and trigeminal motor (VMO) outputs. fR at temperature (Te)=23 degrees C was lower than that at a higher Te (27 degrees C) and was increased by NA. At 23 degrees C, lower concentrations of NA were needed to produce the same increases in fR seen at 27 degrees C. With highest NA concentration we tested (50 microM), activity at C4 was maintained in all preparations at both Te, whereas that at VMO was maintained in 50% (27 degrees C) or 88% (23 degrees C) of the preparations. Particularly, tonic activity at C4 appeared in all preparations at both Te, but that at the VMO occurred in 0% (27 degrees C) or 18% (23 degrees C) of the preparations. Based on these results, we used the lower Te (23 degrees C) and applied a low concentration of NA (3 microM) to the preparations. We found that: (1) with the addition of NA, fR was increased without the occurrence of tonic activity and (2) NA-related fR facilitation was inhibited by pre-treatment with the alpha1-adrenergic receptor antagonist prazosin (2 microM). fR was increased by application of the alpha1-adrenergic receptor agonist phenylephrine (4 microM), and this response was inhibited by prazosin (4 microM). At Te=23 degrees C, fR facilitation by NA in newborn rat pons-medulla-spinal cord preparations was obtained by activation of alpha1-adrenergic receptors.     

A pharmacological analysis of the responses of isolated aorta from rats with adjuvant arthritis

In order to investigate whether chronic inflammation alters the reactivity of vascular smooth muscle, the effects of various agonists have been compared on isolated aortae from rats with and without arthritis. No significant differences in the EC50 values and maximal responses to 5-hydroxytryptamine (5-HT), noradrenaline (NA) and potassium chloride (KCl) were observed. When calcium was removed from Krebs solution the responses to 5-HT and NA were significantly higher in the preparations from arthritic rats. Verapamil had the same inhibitory effect on the responses of both groups. This suggests that the reactivity of the aortic smooth muscle from arthritic rats is less dependent on extracellular calcium than that of the control preparations.     

Affinity of Noradrenaline and Dopamine for Neural α-Receptors Mediating Negative Feedback Control of Noradrenaline Secretion in Human Vasoconstrictor Nerves

Isolated superfused field stimulated biopsy specimens of human peripheral arteries and veins, preincubated with ³H-(-)-noradrenaline (NA) to label the neural stores of NA, were used to study the potency of dopamine (DA) and of NA as triggers of α-adrenoceptor mediated negative feedback control of sympathetic neurotransmitter secretion, evoked by stimulation with trains of 300 shocks at 1 Hz. In this preparation DA was found to be only slightly less potent than NA in depressing both the secretion of ³H-NA, and the contractile response, evoked by nerve stimulation. DA depressed the contraction evoked by exogenous NA as well, but to a very much smaller extent. On the other hand, DA was a very weak agonist on the α-receptors of the smooth muscle; nearly 1 000 times higher concentrations of DA were required to mimick contractions evoked by exogenous NA. The results show that the neural α-receptor function involved in control of NA secretion differs considerably from the α-receptors of e.g. smooth muscle, with respect to sensitivity to DA. It seems possible that the observed depressing effect of DA on NA secretion may be of pharmacological and clinical interest; it may at least in part explain the vasodilating effect of DA infusions in man.     

Adenosine modulation of neuroeffector transmission in guinea-pig uterine smooth muscle.

Effects of adenosine and adenosine analogues on neuroeffector transmission in separate layers of the guinea-pig uterine smooth muscle during different phases of the oestrus cycle were studied. Adenosine (ADO), N6-[(R)-1-methyl-2-phenylethyl]- adenosine (R-PIA) and 5'-N-ethylcarboxamideadenosine (NECA) enhanced spontaneous contractile activity as well as contractile responses to nerve stimulation or direct muscle stimulation in the longitudinal and circular muscle layers both at the time of ovulation and implantation. The agonist potency order was R-PIA greater than or equal to NECA greater than ADO. Furthermore, in the circular muscle layer inhibitory effects were seen at time of implantation and the agonist potency for this inhibitory effect was NECA greater than R-PIA greater than or equal to ADO. 8-p-sulphophenyltheophylline (8-PSOT) antagonized both the stimulatory and inhibitory effects of the purines and 8-p-sulphophenyltheophylline applied to untreated preparations inhibited nerve-induced contractile activity. NECA inhibited stimulation-induced release of 3H in preparations incubated with [3H]noradrenaline. We suggest that adenosine and its analogues can modulate adrenergic neuroeffector transmission in guinea-pig uterine smooth muscle via action at postjunctional receptors stimulating contractile activity and prejunctional receptors inhibiting transmitter release. In the circular muscle layer postjunctional receptors inhibiting contractile activity were evident at time of implantation. Furthermore, endogenous purines exerting a stimulatory action on the neuroeffector transmission were likely formed during the present experimental conditions.     

Identification of functional alpha2- and beta-adrenergic receptors in mammalian spermatozoa

BACKGROUND: A recent study of several compounds, structurally related to amphetamine, provided evidence that mammalian spermatozoa might have adrenergic receptors able to regulate cAMP production. The present study investigated this possibility using physiological and immunochemical analyses of mouse and human spermatozoa. METHODS: Antibodies specific for different receptor subtypes were used for Western blotting of mouse and human sperm lysates and for immunocytochemical evaluation of whole mouse and human spermatozoa. Uncapacitated and capacitated mouse spermatozoa were incubated with specific agonists and antagonists for alpha2-, beta1-, beta2- and beta3-adrenergic receptors for approximately 35 min and then assessed using chlortetracycline (CTC) fluorescence. RESULTS: Western blotting revealed proteins of the correct size for all these receptors; immunolocalization indicated their presence on the head, especially acrosomal and neck regions, and flagellum of both mouse and human spermatozoa. CTC results indicated significant responses to agonists for all of the beta-receptors in uncapacitated cells, with agonist effectiveness being beta1 > beta2 > beta3; relevant antagonists blocked responses. In contrast, an agonist and antagonist for alpha2-receptors acted only on capacitated spermatozoa. CONCLUSION: These experiments provide the first good evidence that mammalian spermatozoa have both beta-adrenergic receptors, known to stimulate cAMP production by membrane-associated adenylyl cyclases (mACs), and alpha2-adrenergic receptors, known to inhibit cAMP production by mACs. Responses are capacitation state dependent and provide a mechanism for inhibiting spontaneous acrosome reactions and helping to maintain fertilizing ability. These results suggest that the use of amphetamine-related compounds, either for medical or for social reasons, might have an unexpected positive impact on fertility.     

Dopaminergic modulation of behavioral states in mesopontine tegmentum: a reverse microdialysis study in freely moving cats

STUDY OBJECTIVES: We investigated the role of dopamine (DA) in behavioral state control and, in particular, paradoxical (or rapid eye movement) sleep (PS) generation in mesopontine structures. DESIGN: Reverse microdialysis and polygraphic recordings in freely moving cats were used to assess the effects on sleep-wake states of applied DA and monoaminergic agonists and antagonists. SETTINGS: NA. PATIENTS OR PARTICIPANTS: NA. INTERVENTION: NA. MEASUREMENTS AND RESULTS: Quantitative and qualitative analysis of behavioral states and electroencephalogram showed that DA had no significant effect when applied to any part of the mesopontine tegmentum, except the peri-locus coeruleus alpha, a region located just ventromedial to the locus coeruleus, pars alpha, and critically implicated in PS generation. In this structure, DA caused a selective and dose-dependent inhibition of PS and induced PS without atonia. These effects were not mimicked by SKF-81297, a selective D1-like agonist, or selective D2-like agonists such as quinelorane, quinpirole, and 7-OH-DPAT. Instead, D2-like agonists induced a significant decrease in wakefulness and increases in both slow-wave sleep and PS. The effects of DA were mimicked, however, by application of clonidine, a selective alpha2 adrenoceptor agonist, and blocked by co-application of RX821002, a selective antagonist of alpha2 adrenoceptors. CONCLUSIONS: Our results indicate that DA inhibits PS in the peri-locus coeruleus alpha via excitation of alpha2 adrenoceptors, but application of D2-like agonists to the same region markedly decreases wakefulness and increases both slow-wave sleep and PS. This effect may be responsible for the excessive daytime sleepiness and sleep attacks induced by antiparkinsonian dopaminergic agents.