Neuropeptide Y neuromodulation of sympathetic co-transmission in the guinea-pig vas deferens

The Influence of an Adrenergic Antagonist Guanethidine on the Distribution Pattern and Chemical Coding of Caudal Mesenteric Ganglion Perikarya and Their Axons Supplying the Porcine Bladder

This study was aimed at disclosing the influence of intravesically instilled guanethidine (GUA) on the distribution, relative frequency and chemical coding of both the urinary bladder intramural sympathetic nerve fibers and their parent cell bodies in the caudal mesenteric ganglion (CaMG) in juvenile female pigs. GUA instillation led to a profound decrease in the number of perivascular nerve terminals. Furthermore, the chemical profile of the perivascular innervation within the treated bladder also distinctly changed, as most of axons became somatostatin-immunoreactive (SOM-IR), while in the control animals they were found to be neuropeptide Y (NPY)-positive. Intravesical treatment with GUA led not only to a significant decrease in the number of bladder-projecting tyrosine hydroxylase (TH) CaMG somata (94.3 ± 1.8% vs. 73.3 ± 1.4%; control vs. GUA-treated pigs), but simultaneously resulted in the rearrangement of their co-transmitters repertoire, causing a distinct decrease in the number of TH⁺/NPY⁺ (89.6 ± 0.7% vs. 27.8 ± 0.9%) cell bodies and an increase in the number of SOM-(3.6 ± 0.4% vs. 68.7 ± 1.9%), calbindin-(CB; 2.06 ± 0.2% vs. 9.1 ± 1.2%) or galanin-containing (GAL; 1.6 ± 0.3% vs. 28.2 ± 1.3%) somata. The present study provides evidence that GUA significantly modifies the sympathetic innervation of the porcine urinary bladder wall, and thus may be considered a potential tool for studying the plasticity of this subdivision of the bladder innervation.

The effects of varying Mg2+ ion concentrations on contractions to the cotransmitters ATP and noradrenaline in the rat vas deferens

The vas deferens responds to a single electrical pulse with a biphasic contraction caused by cotransmitters ATP and noradrenaline. Removing Mg²⁺ (normally 1.2 mM) from the physiological salt solution (PSS) enhances the contraction. This study aimed to determine the effect of Mg²⁺ concentration on nerve cotransmitter-mediated contractions. Rat vasa deferentia were sequentially bathed in increasing (0, 1.2, 3 mM) or decreasing (3, 1.2, 0 mM) Mg²⁺ concentrations. At each concentration a single field pulse was applied, and the biphasic contraction recorded. Contractions to exogenous noradrenaline 10 μM and ATP 100 μM were also determined. The biphasic nerve-mediated contraction was elicited by ATP and noradrenaline as NF449 (10 μM) and prazosin (100 nM) completely prevented the respective peaks. Taking the contractions in normal PSS (Mg²⁺ 1.2 mM) as 100%, lowering Mg²⁺ to 0 mM enhanced the ATP peak to 170 ± 7% and raising Mg²⁺ to 3 mM decreased it to 39 ± 3%; the noradrenaline peak was not affected by lowering Mg²⁺ to 0 mM (97 ± 3%) but was decreased to 63 ± 4% in high Mg²⁺ (3 mM). Contractions to exogenous ATP, but not noradrenaline, were increased in Mg²⁺ 0 mM and both were inhibited with Mg²⁺ 3 mM. Changing Mg²⁺ concentration affects the contractions elicited by the cotransmitters ATP and noradrenaline. The greatest effects were to potentiate the contraction to ATP in Mg²⁺ 0 mM and to inhibit the contraction to both ATP and noradrenaline in high Mg²⁺. Future publications should clearly justify any decision to vary the magnesium concentration from normal (1.2 mM) values.

The Influence of Tetrodotoxin (TTX) on the Distribution and Chemical Coding of Caudal Mesenteric Ganglion (CaMG) Neurons Supplying the Porcine Urinary Bladder

The treatment of micturition disorders creates a serious problem for urologists. Recently, new therapeutic agents, such as neurotoxins, are being considered for the therapy of urological patients. The present study investigated the chemical coding of caudal mesenteric ganglion (CaMG) neurons supplying the porcine urinary bladder after intravesical instillation of tetrodotoxin (TTX). The CaMG neurons were visualized with retrograde tracer Fast blue (FB) and their chemical profile was disclosed with double-labeling immunohistochemistry using antibodies against tyrosine hydroxylase (TH), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), calbindin (CB), galanin (GAL) and neuronal nitric oxide synthase (nNOS). It was found that in both the control (n = 6) and TTX-treated pigs (n = 6), the vast majority (92.6% ± 3.4% and 88.8% ± 2%, respectively) of FB-positive (FB+) nerve cells were TH+. TTX instillation caused a decrease in the number of FB+/TH+ neurons immunopositive to NPY (88.9% ± 5.3% in the control animals vs. 10.6% ± 5.3% in TTX-treated pigs) or VIP (1.7% ± 0.6% vs. 0%), and an increase in the number of FB+/TH+ neurons immunoreactive to SOM (8.8% ± 1.6% vs. 39% ± 12.8%), CB (1.8% ± 0.7% vs. 12.6% ± 2.7%), GAL (1.7% ± 0.8% vs. 10.9% ± 2.6%) or nNOS (0% vs. 1.1% ± 0.3%). The present study is the first to suggest that TTX modifies the chemical coding of CaMG neurons supplying the porcine urinary bladder.

Quantifying sympathetic neuro-haemodynamic transduction at rest in humans: insights into sex, ageing and blood pressure control

KEY POINTS

We have developed a simple analytical method for quantifying the transduction of sympathetic activity into vascular tone. This method demonstrates that as women age, the transfer of sympathetic nerve activity into vascular tone is increased, so that for a given level of sympathetic activity there is more vasoconstriction. In men, this measure decreases with age. Test-re-test analysis demonstrated that the new method is a reliable estimate of sympathetic transduction. We conclude that increased sympathetic vascular coupling contributes to the age-related increase in blood pressure that occurs in women only. This measure is a reliable estimate of sympathetic transduction in populations with high sympathetic nerve activity. Thus, it will provide information regarding whether treatment targeting the sympathetic nervous system, which interrupts the transfer of sympathetic nerve activity into vascular tone, will be effective in reducing blood pressure in hypertensive patients. This may provide insight into which populations will respond to certain types of anti-hypertensive medication.

ABSTRACT

Sex and age differences in the sympathetic control of resting blood pressure (BP) may be due to differences in the transduction of sympathetic nerve activity (SNA) into vascular tone. Current methods for dynamically quantifying transduction focus on the relationship between SNA and vasoconstriction during a pressor stimulus, which increases BP and may be contra-indicated in patients. We describe a simple analytical method for quantifying transduction under resting conditions. We performed linear regression analysis of binned muscle SNA burst areas against diastolic BP (DBP). We assessed whether the slope of this relationship reflects the transduction of SNA into DBP. To evaluate this, we investigated whether this measure captures differences in transduction in different populations. Specifically, we (1) quantified transduction in young men (YM), young women (YW), older men (OM) and postmenopausal women (PMW); and (2) measured changes in transduction during β-blockade using propranolol in YW, YM and PMW. YM had a greater transduction vs. OM (0.10 ± 0.01 mmHg (% s)(-1) , n = 23 vs. 0.06 ± 0.01 mmHg (% s)(-1) , n = 18; P = 0.003). Transduction was lowest in YW (0.02 ± 0.01 mmHg (% s)(-1) , n = 23) and increased during β-blockade (0.11 ± 0.01 mmHg (% s)(-1) ; P < 0.001). Transduction in PMW (0.07 ± 0.01 mmHg (% s)(-1) , n = 23) was greater compared to YW (P = 0.001), and was not altered during β-blockade (0.06 ± 0.01 mmHg (% s)(-1) ; P = 0.98). Importantly, transduction increased in women with age, but decreased in men. Transduction in women intersected that in men at 55 ± 1.5 years. This measure of transduction captures age- and sex-differences in the sympathetic regulation of DBP and may be valuable in quantifying transduction in disease. In particular, this measure may help target treatment strategies in specific hypertensive subpopulations.

Cotransmission in the autonomic nervous system

After some early hints, cotransmission was proposed in 1976 and then "chemical coding" later established for sympathetic nerves (noradrenaline/norepinephrine, adenosine 5'-triphosphate (ATP), and neuropeptide Y), parasympathetic nerves (acetylcholine, ATP, and vasoactive intestinal polypeptide (VIP)), enteric nonadrenergic, noncholinergic inhibitory nerves (ATP, nitric oxide, and VIP), and sensory-motor nerves (calcitonin gene-related peptide, substance P, and ATP). ATP is a primitive signaling molecule that has been retained as a cotransmitter in most, if not all, nerve types in both the peripheral and central nervous systems. Neuropeptides coreleased with small molecule neurotransmitters in autonomic nerves do not usually act as cotransmitters but rather as prejunctional neuromodulators or trophic factors. Autonomic cotransmission offers subtle, local variation in physiological control mechanisms, rather than the dominance of inflexible central control mechanisms envisaged earlier. The variety of information imparted by a single neuron then greatly increases the sophistication and complexity of local control mechanisms. Cotransmitter composition shows considerable plasticity in development and aging, in pathophysiological conditions and following trauma or surgery. For example, ATP appears to become a more prominent cotransmitter in inflammatory and stress conditions.

Shining light on wakefulness and arousal

Alterations in arousal states are associated with multiple neuropsychiatric disorders, including generalized anxiety disorders, addiction, schizophrenia, and depression. Therefore, elucidating the neurobiological mechanisms controlling the boundaries between arousal, hyperarousal, and hypoarousal is a crucial endeavor in biological psychiatry. Substantial research over several decades has identified distinct arousal-promoting neural populations in the brain; however, how these nuclei act individually and collectively to promote and maintain wakefulness and various arousal states is unknown. We have recently applied optogenetic technology to the repertoire of techniques used to study arousal. Here, we discuss the recent results of these experiments and propose future use of this approach as a way to understand the complex dynamics of neural circuits controlling arousal and arousal-related behaviors.

Purinergic cotransmission

Adenosine 5'-triphosphate (ATP) is a cotransmitter with classical transmitters in most nerves in the peripheral and central nervous systems, although the proportions vary between tissues and species and in different developmental and pathophysiological circumstances. There was early evidence that ATP was released together with acetylcholine (ACh) from motor nerves supplying skeletal muscle, although it was considered at the time as a molecule involved in the vesicular uptake and storage of ACh. Later it was shown that in the developing neuromuscular junction, released ATP acted on P2X receptor ion channels as a genuine cotransmitter with ACh. Adenosine triphosphate was shown to be released from sympathetic nerves supplying the guinea-pig taenia coli in 1971. Soon after, the possibility was raised that ATP was coreleased with noradrenaline from sympathetic nerves to guinea-pig seminal vesicle, cat nictitating membrane and guinea-pig vas deferens. Sympathetic purinergic cotransmission has also been demonstrated in many blood vessels. Parasympathetic nerves supplying the urinary bladder use ACh and ATP as cotransmitters; ATP acts through P2X ionotropic receptors, whereas the slower component of the response is mediated by the metabotropic muscarinic receptor. Adenosine triphosphate and glutamate appear to be cotransmitters in primary afferent sensory neurons. Adenosine triphosphate, calcitonin gene-related peptide and substance P coexist in some sensory-motor nerves. A subpopulation of intramural enteric nerves provides non-adrenergic, non-cholinergic inhibitory innervation of gut smooth muscle. Three cotransmitters are involved, namely ATP, nitric oxide and vasoactive intestinal polypeptide. In recent years, studies have shown that ATP is released with ACh, noradrenaline, glutamate, gamma-aminobutyric acid, 5-hyroxytryptamine and dopamine in different subpopulations of neurons in the central nervous system.

ATP release and its prejunctional modulation

We studied some properties of the release of noradrenaline and ATP in isolated sympathetically innervated tissues. Release was elicited by electric stimulation and assessed as overflow of tritiated compounds (after labelling with [3H]noradrenaline) and enzymically measured ATP, respectively. Evans blue, which inhibits ectonucleotidases, greatly increased the evoked overflow of ATP, indicating that a major part of the ATP was metabolized after release. Much of the ATP was postjunctional in origin. The neural fraction was isolated when postjunctional release was suppressed by prazosin (alpha 1-adrenoceptor antagonist) and suramin (P2 purinoceptor antagonist). Comparison of neural ATP and [3H]-noradrenaline release showed that prostaglandin E2 reduced the release of both co-transmitters to a similar extent. Activation of prejunctional alpha 2-adrenoceptors, however, preferentially reduced the release of [3H]noradrenaline, and activation of prejunctional A1 purinoceptors reduced preferentially the release of ATP. Nucleotides such as ATP depressed the release of [3H]noradrenaline through two receptors: the well-known prejunctional A1 receptors and a separate group of prejunctional P2 purinoceptors. P2 antagonists increased the release of [3H]-noradrenaline. Overall, the results indicate differential storage, release and modulation of release of the two sympathetic co-transmitters. They also indicate that postganglionic sympathetic axons possess receptors for both co-transmitters: alpha 2 and P2 autoreceptors.

Physiology and pathophysiology of purinergic neurotransmission

This review is focused on purinergic neurotransmission, i.e., ATP released from nerves as a transmitter or cotransmitter to act as an extracellular signaling molecule on both pre- and postjunctional membranes at neuroeffector junctions and synapses, as well as acting as a trophic factor during development and regeneration. Emphasis is placed on the physiology and pathophysiology of ATP, but extracellular roles of its breakdown product, adenosine, are also considered because of their intimate interactions. The early history of the involvement of ATP in autonomic and skeletal neuromuscular transmission and in activities in the central nervous system and ganglia is reviewed. Brief background information is given about the identification of receptor subtypes for purines and pyrimidines and about ATP storage, release, and ectoenzymatic breakdown. Evidence that ATP is a cotransmitter in most, if not all, peripheral and central neurons is presented, as well as full accounts of neurotransmission and neuromodulation in autonomic and sensory ganglia and in the brain and spinal cord. There is coverage of neuron-glia interactions and of purinergic neuroeffector transmission to nonmuscular cells. To establish the primitive and widespread nature of purinergic neurotransmission, both the ontogeny and phylogeny of purinergic signaling are considered. Finally, the pathophysiology of purinergic neurotransmission in both peripheral and central nervous systems is reviewed, and speculations are made about future developments.

Potentiation of sympathetic neuromuscular transmission mediated by muscarinic receptors in guinea pig isolated vas deferens

In guinea-pig isolated vasa deferentia, purinergic neurogenic contractions and responses to applied adenosine 5'-triphosphate (ATP) were potentiated by carbachol; responses to adrenergic transmission and applied noradrenaline were not. Following blockade of P2 receptors and alpha-adrenoceptors, the residual neurogenic response was massively potentiated by carbachol, suggesting the presence of a non-purinergic, non-adrenergic component. In the presence of guanethidine, carbachol had no significant effect, indicating that sympathetic transmission was the only element involved. Use of oxotremorine and selective muscarinic receptor antagonists suggested that the potentiating effect of carbachol and oxotremorine was mediated via M3 muscarinic receptors without involvement of nicotinic receptors.

Endothelin (ET)-1-induced inhibition of ATP release from PC-12 cells is mediated by the ETB receptor: differential response to ET-1 on ATP, neuropeptide Y, and dopamine levels

During sympathetic neurotransmitter release, there is evidence for differential modulation of cotransmitter release by endothelin (ET)-1. Using nerve growth factor (NGF)-differentiated PC12 cells, the effects of ET-1 on K(+)-stimulated release of ATP, dopamine (DA), and neuropeptide Y (NPY) were quantified using high-pressure liquid chromatography or radioimmunoassay. ET-1, in a concentration-dependent manner, inhibited the release of ATP, but not DA and NPY. Preincubation with the ET(A/B) antagonist, PD 142893 (N-acetyl-beta-phenyl-D-Phe-Leu-Asp-Ile-Ile-Trp), reversed the inhibitory effect of ET-1 on ATP release, which remained unaffected in the presence of the ET(A)-specific antagonist BQ123 [cyclo(D-Asp-Pro-D-Val-Leu-D-Trp)]. The ET(B) agonists, sarafotoxin 6c (Cys-Thr-Cys-Asn-Asp-Met-Thr-Asp-Glu-Glu-Cys-Leu-Asn-Phe-Cys-His-Gln-Asp-Val-Ile-Trp), BQ 3020 (N-acetyl-[Ala(11,15)]-endothelin 1 fragment 6-21Ac-Leu-Met-Asp-Lys-Glu-Ala-Val-Tyr-Phe-Ala-His-Leu-Asp-IIe-IIe-Trp), and IRL 1620 (N-succinyl-[Glu(9), Ala(11,15)]-endothelin 1 fragment 8-21Suc-Asp-Glu-Glu-Ala-Val-Tyr-Phe-Ala-His-Leu-Asp-Ile-Ile-Trp), decreased K(+)-stimulated release of ATP in a dose-dependent manner, and this effect was reversed by the ET(B) antagonists RES 701-1 [cyclic (Gly1-Asp9) (Gly-Asn-Trp-His-Gly-Thr-Ala-Pro-Asp-Trp-Phe-Phe-Asn-Tyr-Tyr-Trp)] and BQ 788 (N-[N-[N-[(2,6-dimethyl-1-piperidinyl)carbonyl]-4-methyl-l-leucyl]-1-(methoxycarbonyl)-D-tryptophyl]-D-norleucine sodium salt). Preincubation of PC12 cells with pertussis toxin reversed the ET-1-induced inhibition of the K(+)-evoked ATP release. Real-time intracellular calcium level recordings were performed on PC-12 cell suspensions, and ET-1 induced a dose-dependent decrease in the K(+)-evoked calcium levels. Nifedipine, the L-type voltage-dependent Ca(2+) channel antagonist, caused inhibition of the K(+)-stimulated ATP release, but the N-type Ca(2+) channel antagonist, omega-conotoxin GVIA, did not reverse the effect on ATP release. These data suggest that ET-1 modulates the release of ATP via the ET(B) receptor and its associated G(i/o) G-protein through attenuation of the influx of extracellular Ca(2+) through L-type channels.

Identification of neurones of the brain and spinal cord involved in the innervation of the ductus deferens using the viral tracing method

Using the viral transneuronal tracing technique cell groups of the spinal cord and brain transsynaptically connected with the ductus deferens were identified. Neurotropic (pseudorabies) virus was injected into the muscular coat of the ductus deferens and after survival times of 3, 4 and 5 days the spinal cord and brain were processed immunocytochemically. Virus-labelled neurones could be detected in the preganglionic sympathetic neurones and the dorsal commissural nucleus (upper lumbar segments) and in the sacral parasympathetic nucleus (L6-S1). Virus-infected perikarya were present in several brain stem nuclei including the gigantocellular and paragigantocellular nucleus, the lateral reticular nucleus, the nucleus of the solitary tract, the caudal raphe nuclei, the A1/C1, A2, A5 and A7 noradrenergic cell groups and the locus coeruleus. In the hypothalamus significant numbers of virus-infected neurones could be detected in the paraventricular nucleus. In most cases moderate numbers of virus-labelled cells were present in the lateral hypothalamic area, in the retrochiasmatic area, in the periventricular region and in the median preoptic area. Double-labelling immunofluorescence detection of virus-infected neurones and thyrosine hydroxylase (TH) showed colocalization of virus protein and TH in portion of neurones of the A1/C1, A2, A5 and A7 noradrenergic cell groups, in the locus coeruleus and in the hypothalamic paraventricular nucleus. The present results provide the first morphological data on the multisynaptic circuit of neurones innervating the ductus deferens.

Maturational and maintenance effects of testosterone on terminal axon density and neuropeptide expression in the rat vas deferens

Testosterone causes growth of many pelvic ganglion cells at puberty and their maintenance during adulthood. Here we have focused on two populations of pelvic ganglion cells that project to the rat vas deferens: noradrenergic neurons that innervate the smooth muscle and synthesize neuropeptide Y, and cholinergic neurons that primarily innervate the mucosa and contain vasoactive intestinal peptide. We have assessed the muscle innervation after pre- or postpubertal castration, using immunohistochemistry to determine axon density and radioimmunoassay to quantify levels of neuropeptides in tissue extracts. Our results show that androgen deprivation in each period causes substantial effects. Noradrenergic axons in the muscle increase in density after castration, partly due to organ size being smaller than age-matched controls. However, when corrected for target size, there is an overall decrease in total number of axons. This implies that androgen exposure at puberty has a direct effect on neurons to ensure that the adult pattern of innervation is attained, and that this is not simply by matching terminal field to target size. Similar effects of pre- and postpubertal castration imply that continued exposure to testosterone is necessary to maintain normal target innervation. Castration in both time periods increased the density of axons containing vasoactive intestinal peptide, however the effects of castration on the total number of these axons in the muscle were more variable. The concentration of vasoactive intestinal peptide increased substantially following either pre- or postpubertal castration although absolute amounts per vas deferens were decreased. Effects on neuropeptide Y concentration were less pronounced but the total amount per vas deferens was decreased after pre- or postpubertal castration. Our study shows that the action of testosterone (or a metabolite) on a pelvic ganglion cell soma is likely to reflect a change in its terminal field, but that these effects are not mediated simply by testosterone influencing the size of its target organ.

Effects of a selective neuropeptide Y Y2 receptor antagonist, BIIE0246, on Y2 receptors at peripheral neuroeffector junctions

1. This study investigated the effects of BIIE0246, a novel neuropeptide Y (NPY) Y2 receptor antagonist, on the inhibition of cholinergic neuroeffector transmission in rat heart and guinea-pig trachea and purinergic neuroeffector transmission in guinea-pig vas deferens produced by the NPY Y2 receptor agonist, N-acetyl [Leu28,31] NPY 24-36. 2. In pentobarbitone anaesthetized rats, supramaximal stimulation every 30 s, of the vagus nerve innervating the heart, increased pulse interval by approximately 100 ms. This response was attenuated by intravenous administration of N-acetyl [Leu28,31] NPY 24-36 (10 nmol x kg(-1)). 3. Transmural stimulation of segments of guinea-pig trachea at 1 min intervals with 5 s trains of stimuli at 0.5, 5, 10, 20 and 40 Hz evoked contractions which were reduced in force by N-acetyl [Leu28,31] NPY 24-36 (2 microM). 4. In guinea-pig vasa deferentia, the amplitude of excitatory junction potentials evoked by trains of 20 stimuli at 1 Hz was reduced in the presence of N-acetyl [Leu28,31] NPY 24-36 (1 microM). 5. In all preparations BIIE0246 attenuated the inhibitory effect of N-acetyl [Leu28,31] NPY 24-36 but had no effect when applied alone. 6. The findings support the view that the nerve terminals of postganglionic parasympathetic and sympathetic neurones possess neuropeptide Y Y2 receptors which, when activated, reduce neurotransmitter release.

Effects of neuropeptide Y on double-peaked constrictor responses to periarterial nerve stimulation in isolated, perfused canine splenic arteries

The periarterial electrical nerve stimulation readily induced a double-peaked vasoconstriction in the isolated, perfused canine splenic artery. P2X-Purinoceptors have previously been shown to be involved mainly in the 1st-phase response and alpha 1-adrenoceptors, mostly in the 2nd-one. The dose used of neuropeptide Y (NPY) (0.01-0.1 microM) given into the preparation caused a slight but insignificant vasoconstriction. The treatment with NPY at concentrations of 0.01-0.1 microM produced a parallel inhibition on the 1st- and 2nd-phase responses following nerve stimulation at the frequencies used (1-10 Hz) in a dose-dependent manner. The vasoconstrictor responses to administered ATP (0.01-1 mumol) or noradrenaline (0.03-3 nmol) were slightly but not significantly potentiated by 0.1 microM NPY. The results indicate that NPY predominantly exerts a prejunctionally inhibitory modulation on the purinergic and adrenergic transmission in peripheral sympathetic nerves innervating the canine splenic artery.

Adenosine 5'-triphosphate and neuropeptide Y are co-transmitters in conjunction with noradrenaline in the human saphenous vein

1. Human saphenous veins were used to assess the cooperative participation of adenosine 5-triphosphate (ATP), neuropeptide Y (NPY), and noradrenaline (NA) in the vasomotor responses elicited following electrical depolarization of the perivascular nerve terminals. Rings from recently dissected human biopsies were mounted to record isometric muscular contractions; the motor activity elicited in the circular muscle layer following electrical depolarization (2.5-20 Hz, 50 V, 0.5 msec) were recorded. 2. Incubation of the biopsies with either 100 nM tetrodotoxin (TTX) or 1 microM guanethidine abolished the vasomotor response elicited by electrical nerve depolarization. The independent application of either ATP or NA to vein rings induced concentration-dependent contractions. 3. Tissue incubation with 30 microM suramin or 10 nM prazosin produced 10 fold rightward displacements of the alpha,beta-methylene ATP and NA concentration-response curves respectively. NPY contracted a limited number of biopsies, the vasoconstriction elicited was completely blocked by 1 microM BIBP 3226. A 5 min incubation of the biopsies with 10-100 nM NPY synergized, in a concentration-dependent fashion, both the ATP and the ATP analogue-induced contractions. Likewise, tissue preincubation with 10 nM NPY potentiated the vasomotor responses evoked with 20-60 nM NA. 4. Neither suramin, BIBP 3226, nor prazosin was individually able to significantly modify the derived frequency-tension curves. In contrast, the co-application of 30 microM suramin and 10 nM prazosin or 30 microM suramin and 1 microM BIBP 3226, elicited a significant (P<0.01) downward displacement of the respective frequency-tension curves. 5. The simultaneous application of the three antagonists-30 microM suramin, 1 microM BIBP 3226 and 10 nM prazosin-caused a significantly greater displacement of the frequency-tension curve than that achieved in experiments using two of these antagonists. 6. Electrically-evoked vasomotor activity is blocked to a larger extent by tissue incubation with 2.5 microM chloroethylclonidine and 30 microM suramin rather than with 10 nM 5 methyl urapidil and 30 microM suramin. As a result, the alpha1-adrenoceptor involved in the vasomotor activity has tentatively been associated with the alpha1B adrenoceptor family subtype. 7. Results support the physiological role of ATP in sympathetic neurotransmission. The present results are consistent with the working hypothesis that human sympathetic vasomotor reflexes involve the coordinated motor action of ATP, NPY, and NA acting on vascular smooth muscle cells. The present results support the concept of sympathetic co-transmission in the human saphenous vein.

Transmitter release and uptake evoked by the amphibian skin alkaloid, pumiliotoxin-B (PTX-B), in the electrically stimulated mouse vas deferens preparation (MVD)

Upon electrical stimulation three transmitters are known to be released from the adrenergic nerve terminals of the isolated MVD preparation: two motor transmitters (noradrenaline (NA) and ATP) acting synergistically to provoke twitch contraction, and an inhibitory transmitter, the peptide NPY. The frog alkaloid pumiliotoxin-B (PTX-B) displayed two opposite effects on the electrically stimulated MVD: at low concentrations (0.1-0.3 microM) it caused twitch depression, at higher concentrations (0.5-2 microM) there was a potent twitch stimulation. Transmitters and/or receptors involved in the depressive effect could not be clearly identified, although interference with NPY is possible. On the other hand, the potent twitch stimulation caused by PTX-B may be due to exaggerated release of the same transmitters (NA and ATP) involved in twitch stimulation produced by electrical stimulation. Opening by PTX-B of the Na+ channels on the membrane of the adrenergic nerve terminals causes activation of the amine pump facilitating re-uptake of not only endogenous NA but also of exogenous catecholamines.

Neuropeptide Y (NPY) and peptide YY (PYY) effects in the epididymis of the guinea-pig: evidence of a pre-junctional PYY-selective receptor

1. The effects of peptide YY (PYY), neuropeptide Y (NPY) and structurally related peptides upon field stimulation-induced and phenylephrine-mediated contractile responses in the cauda epididymis of the guinea-pig were investigated. 2. Preparations of cauda epididymis responded to field stimulation with contractions which were completely attenuated by both the neurotoxin, tetrodotoxin (500 nM), and also by the alpha-adrenoceptor antagonist, phentolamine (3 microM). PYY (n=7) and the truncated peptide analogue PYY(3-36) (n=5) inhibited field stimulation-induced contractions (pIC50+s.e.mean: 8.9+/-0.2 and 9.4+/-0.2, respectively). Pancreatic polypeptide (PP, up to 1 microM, n=6), NPY (up to 100 nM, n=6) and the NPY analogues [Leu31,Pro34]NPY (n=6) and NPY(13-36) (both up to 1 microM, n=5) had no significant effect. 3. The NPY Y1 receptor antagonist BIBP3226 ((R)-N2-(diphenylacetyl)-N[(4-hydroxyphenyl)-methyl]-argininami de) at 750 nM (n=6) and 7.5 microM (n=6) did not affect the PYY-mediated inhibition of field stimulation-induced contractions (pIC50 8.9+/-0.3 and 9.0+/-0.3, respectively). In the presence of BIBP3226 (7.5 microM), NPY (n=6) inhibited field stimulation-induced contractions (pIC50 8.0+/-0.2). 4. NPY, PYY and PYY(3-36) inhibited [3H]-noradrenaline release from preparations of epididymis (pIC50 values 7.9+/-0.7, 9.6+/-0.8 and 10.0+/-0.9, respectively, all n=6). The agonists PP and [Leu31,Pro34]PYY (both up to 100 nM) were without significant effect (both n=6). 5. In preparations of cauda epididymis, stimulated with threshold concentrations of the alpha1-adrenoceptor agonist, phenylephrine (1 microM), both NPY (n=6) and PYY (n=7) elicited concentration-dependent increases in contractile force (with pEC50 values of 8.9+/-0.2 and 8.6+/-0.1, respectively). The effects of both NPY (n=6) and PYY (n=6) were antagonized by preincubation with BIBP3226 (75 nM; apparent pK(B)+/-s.e. values 8.3+/-1.0 and 8.2+/-0.6, respectively). The peptide analogues NPY(13-36) (n=5), PYY(3-36) (n=7) and [Leu31,Pro34]NPY (n=5) did not significantly augment responses to threshold concentrations of phenylephrine. 6. These results are consistent with the proposal that distinct NPY receptors mediate the (prejunctional) inhibition of field stimulation-induced contractions and the (postjunctional) potentiation of responses to phenylephrine in the cauda epididymis of the guinea-pig. The rank order of agonist potency (NPY > or = PYY >> NPY(13-36), [Leu31,Pro34]NPY and PYY(3-36) and the high potency of BIBP3226 indicate that the postjunctional receptor may be Y1-like. The rank orders of agonist potency in inhibiting field stimulation-induced contractile responses and [3H]-noradrenaline release (PYY(3-36) > or = PYY > NPY >> PP, NPY(13-36), [Leu31,Pro34]NPY and PYY(3-36) > or = PYY > NPY >> PP, [Leu31,Pro34]PYY, respectively) are consistent with the action of these peptides at a PYY-preferring receptor subtype, which may be distinct from the presently characterized NPY receptor subtypes.

Role of G-protein beta gamma subunits in the augmentation of P2Y2 (P2U)receptor-stimulated responses by neuropeptide Y Y1 Gi/o-coupled receptors

Neuropeptide Y (NPY) significantly potentiates the constrictor actions of noradrenaline and ATP on blood vessels via a pertussis toxin (PTX)-sensitive mechanism involving Gi/o (alpha beta gamma) protein subunits (Gi/o, GTP-binding proteins sensitive to PTX). In Chinese hamster ovary K1 (CHO K1) cells expressing specific receptors for these neurotransmitters, stimulation of Gi/o protein-coupled receptors for NPY and other neurotransmitters can augment the Gq/11-coupled (Gq/11, GTP-binding proteins insensitive to PTX) alpha 1B adrenoceptor- or ATP receptor-induced arachidonic acid (AA) release and inositol phosphate (IP) production (early events which may precede vasoconstriction). In this study, we have assessed the role of G beta gamma subunits in the synergistic interaction between Gi/o- (NPY Y1, 5-hydroxytryptamine 5-HT1B, adenosine A1) and Gq/11- [ATP P2Y2 (P2U)]-coupled receptors on AA release by using the specific abilities of regions of the beta-adrenergic receptor kinase (beta ARK1 residues 495-689) and the transducin alpha subunit to associate with G-protein beta gamma subunit dimers and to act as G beta gamma subunit scavengers. Transient expression of beta ARK1(495-689) in CHO K1 cells heterologously expressing NPY Y1 receptors had no significant effect on the PTX-insensitive ability of ATP to stimulate AA release. Stimulation of NPY Y1 receptors (as well as the endogenous 5-hydroxytryptamine 5-HT1B receptor and the transiently expressed human adenosine A1 receptor) resulted in a PTX-sensitive augmentation of ATP-stimulated AA release, which was inhibited by expression of both G beta gamma subunit scavengers. Expression of beta ARK1(495-689) similarly inhibited NPY Y1 receptor augmentation of ATP-stimulated IP production (a measure of phospholipase C activity), a step thought to precede the NPY Y1 receptor-augmented protein kinase C-dependent AA release previously observed in these cells. These experiments demonstrate that G beta gamma subunits, as inhibited by two different G beta gamma scavengers, significantly contribute to the synergistic interaction between NPY Y1 Gi/o- and Gq/11-coupled receptor activity, and are required for the augmentation of IP production and AA release observed in this model cell system.

Presynaptic inhibition of elicited neurotransmitter release

Activation of presynaptic receptors for a variety of neurotransmitters and neuromodulators inhibits transmitter release at many synapses. Such presynaptic inhibition might serve as a means of adjusting synaptic strength or preventing excessive transmitter release, or both. Previous evidence showed that presynaptic modulators inhibit Ca2+ channels and activate K+ channels at neuronal somata. These modulators also inhibit spontaneous transmitter release by mechanisms downstream of Ca2+ entry. The relative contribution of the above mechanisms to the inhibition of elicited release has been debated for a long time. Recent evidence at synapses where the relationship between transmitter release and presynaptic Ca2+ influx has been well characterized suggests that inhibition of presynaptic voltage-dependent Ca2+ channels plays the major role in presynaptic inhibition of elicited neurotransmitter release. In addition, modulation of the release machinery might contribute to inhibition of elicited release.

The norepinephrine tissue concentration and neuropeptide Y immunoreactivity in genitourinary organs of the spontaneously hypertensive rat

Tissue concentration of norepinephrine and neuropeptide-Y immunoreactivity (NPY-IR) were measured in the urinary bladder, urethra, prostate and corpus cavernosum of the spontaneously hypertensive rat, as well as the normotensive Wistar-Kyoto rat. The results showed significantly increased tissue norepinephrine concentrations in the urinary bladder, urethra and prostate of the spontaneously hypertensive rat when compared to those of the normotensive rat (hypertensive, n = 18: 18.3 +/- 2.1, 14.9 +/- 1.7, 22.6 +/- 2.3 vs. normotensive, n = 18: 11.2 +/- 1.9, 10.4 +/- 1.3, 16.7 +/- 2.4 nmol/g tissue, respectively, P < 0.05 in each case). No difference was noted in the cavernosal tissue (hypertensive, n = 18: 11.3 +/- 1.6 vs. normotensive, n = 18: 10.1 +/- 1.8 nmol/g tissue, P > 0.01). Correspondingly, tissue NPY-IR was significantly increased in the bladder, urethra and prostate tissue of the spontaneously hypertensive rat (hypertensive, n = 18: 39.7 +/- 5.6, 25.3 +/- 3.4, 31.5 +/- 2.8 vs. normotensive, n = 18: 27.4 +/- 3.1, 18.6 +/- 2.7, 24.2 +/- 3.2 pmol/g tissue, respectively, P < 0.05 in each case). Again, no significant difference was observed in the cavernosal tissue (hypertensive, n = 18: 15.9 +/- 2.2 vs. normotensive, n = 18: 14.8 +/- 2.6 pmol/g tissue, P > 0.01). It is therefore concluded that increased tissue concentration of norepinephrine and NPY-IR were present in the urinary bladder, urethra and prostate of the spontaneously hypertensive rat. The significance of such biochemical findings needs further investigation but may suggest increased sympathetic innervation or activity. On the contrary, no corresponding changes were observed in the corpus cavernosum of the hypertensive rat.

Changes in neuronal contribution to contractile responses of vas deferens of young and adult guinea pigs

The response characteristics of vas deferens to electrical hypogastric nerve stimulation at various frequencies was studied in guinea pigs of 2 to 15 weeks old. In 2-week-old guinea pigs the stimulation induced monophasic contraction, some of which remained after blocking alpha 1-adrenoceptor and desensitizing P2-purinoceptors with prazosin and alpha, beta-methylene ATP, respectively. In guinea pigs of 10 to 15 weeks old stimulation induced biphasic contraction, which was almost completely inhibited by both blockers. These results suggest that some unknown component other than ATP and norepinephrine is involved in the transmission at 2 weeks, and that its relative significance changes during development.

Modulatory effects of endothelin-1 on purinergic and adrenergic components of sympathetically-mediated contractile activity of rabbit saphenous artery

1. The present study has been performed to evaluate the modulatory effects of endothelin-1 (ET-1) on the purinergic and adrenergic components of sympathetically-mediated contractile responses of endothelium-free rabbit saphenous artery preparations. 2. ET-1 increased the smooth muscle tone, the pD2 value being 7.77 +/- 0.05. 3. Postjunctionally, ET-1 enhanced the responses to exogenous adenosine 5'-triphosphate (ATP) and did not influence those to exogenous noradrenaline (NA). 4. ET-1 increased the contractile responses to short-lasting and to long-lasting electrical field stimulation at a frequency of 5 or 10 Hz, showing a tendency towards decreasing the prazosin-sensitive component and increasing the mATP-sensitive component of the contractile responses. 5. In prazosin-treated preparations ET-1 increased the residual mATP-sensitive responses and this effect was more pronounced after yohimbine. 6. In mATP-treated preparations ET-1 increased the residual electrically-induced contractions and this increase was abolished after yohimbine. 7. It is suggested that ET-1 modulates co-transmission in the rabbit saphenous artery by potentiating postjunctionally the purinergic component of the contractile responses to both exogenous ATP or electrical stimulation.

Activation of P2-purinoceptors in the nucleus tractus solitarius mediate depressor responses

The purpose of the study was to examine the role of P2 purinergic receptors in mechanisms of cardiovascular control mediated by the nucleus tractus solitarius (NTS), a major integrative site in the brainstem involved in the reflex coordination of cardiorespiratory and visceral response patterns. Microinjections of ATP and its analogues were made into the subpostremal NTS of anesthetized, spontaneously breathing rats. ATP, alpha,beta-methylene ATP (alpha beta-meATP) and 2-methylthio-ATP (2-meSATP) produced significant dose-related reductions in arterial blood pressure. alpha beta-meATP was slightly more potent than ATP and 2-meSATP. Pretreatment with the P2 receptor antagonist, suramin (0.5 nmol/rat), into the same NTS site 10 min prior to agonist administration completely blocked pronounced depressor response pattern elicited by the highest dose of alpha beta-meATP (0.1 nmol/rat). The present findings suggest that endogenous ATP may serve as a fast transmitter substance in NTS-mediated mechanisms of cardiovascular control.

Mechanism of presynaptic inhibition by neuropeptide Y at sympathetic nerve terminals

Calcium influx through voltage-sensitive Ca2+ channels is the normal physiological stimulus for the activity-dependent release of neurotransmitters at synaptic contacts. It has been postulated that presynaptic inhibition of transmitter release is due to a reduction in Ca2+ influx at the nerve terminal, which could result from the direct inhibition of Ca2+ channels. Neuropeptide Y and noradrenaline act as cotransmitters at many sympathetic synapses. Both of these substances produce presynaptic inhibition and can inhibit Ca2+ currents in the soma of sympathetic neurons. Here we provide direct evidence that presynaptic inhibition produced by neuropeptide Y at sympathetic nerve terminals is associated with a reduction in Ca2+ influx and that this is due to the selective inhibition of neuronal N-type Ca2+ channels.

Further substantiation of a significant role for the sympathetic nervous system in inflammation

This study provides significant new evidence substantiating a role of the postganglionic sympathetic neuron in plasma extravasation in the knee-joint of the rat. Increased plasma extravasation produced by the potent inflammatory mediator bradykinin was mimicked by 6-hydroxydopamine, a selective stimulator of sympathetic fibers. Various treatments (chemical sympathectomy, co-perfusion with the local anesthetic lidocaine, or co-perfusion with depolarizing concentrations of potassium) similarly modulated plasma extravasation induced by both bradykinin and 6-hydroxydopamine, but not that produced by platelet activating factor. We also showed that bradykinin is able to release norepinephrine in the knee-joint, indicating action on the sympathetic postganglionic neuron. In summary, these experiments provide substantial additional evidence supporting a significant contribution of the sympathetic post-ganglionic neuron terminal to inflammatory plasma extravasation.

Effects of age and hyperlipidemia on rabbit coronary responses to neuropeptide Y and the interaction with norepinephrine

In coronary arteries from New Zealand White (NZW) rabbits up to 12 months of age, both direct vasoconstriction to neuropeptide Y (NPY) and inhibition of relaxation to norepinephrine (NE) by NPY were age dependent (p < 0.02 and p < 0.05, respectively); maximal relaxation to NE was unaffected. NPY had no significant effect on arteries from NZW rabbits at 4 months of age, while vessels from Watanabe Hereditable Hyperlipidaemic (WHHL) rabbits showed enhanced direct (p < 0.001) and indirect effects of NPY (p < 0.02). We conclude that the postsynaptic vasoconstrictor effects of NPY on the epicardial coronary artery increase with age and the presence of hyperlipidemia.

Modulation of bradykinin-induced plasma extravasation in the rat knee joint by sympathetic co-transmitters

We describe the contribution of various sympathetic post-ganglionic neuron mediators to bradykinin-induced plasma extravasation in the knee joint of the rat. Co-perfusion of the sympathetic post-ganglionic neuron mediators, norepinephrine or neuropeptide Y with bradykinin resulted in diminished plasma extravasation. In contrast, the putative sympathetic post-ganglionic neuron mediators of bradykinin-induced plasma extravasation, namely prostaglandin E2, ATP, the selective adenosine A2-receptor agonist, CGS21680 or the endothelium-derived relaxing factor (as its precursor L-arginine) all greatly enhanced bradykinin-induced plasma extravasation, but produced little or no increase in plasma extravasation administered alone. The data show that sympathetic post-ganglionic neuron-derived mediators may either inhibit or enhance plasma extravasation induced by bradykinin, and we hypothesize that differential release of mediators from the sympathetic post-ganglionic neuron terminal, in response to varying stimuli, regulates local plasma extravasation during inflammation.

Co-release of neuropeptide Y (NPY) and noradrenaline from the sympathetic nerve terminals supplying the rat vas deferens; influence of calcium and the stimulation intensity

Epididymal (E) and prostatic (P) segments of the rat vas deferens were incubated with tritium-labeled noradrenaline (NA); upon transmural electrical stimulation for 20 or 60 s (70 V, 1 ms, 3-35 Hz), the outflow of immunoreactive neuropeptide Y (ir-NPY) and NA was detected in the superfusion media. Ir-NPY was detected only following trains of 35 Hz for 60 s in both E and P. In contrast, tritium was released in a graded fashion following trains of 3, 15 or 35 Hz stimulation for 60 s in E, whereas in P it reached a plateau at frequencies larger than 15 Hz. The outflow of tritium, under present conditions, was dependent on the duration of the stimuli, while the release of ir-NPY was only evoked with stimuli of 60 s duration. In the absence of external Ca2+, neurotransmission was blocked and co-release of ir-NPY and NA was prevented.

Neuropeptide Y inhibits sympathetic neurotransmission in ipsilaterally innervated but not contralaterally reinnervated superior tarsal smooth muscle of the rat

The superior tarsal smooth muscle (STM), which elevates the upper eyelid, normally is innervated by sympathetic neurons from the ipsilateral superior cervical ganglion that are not neuropeptide Y-immunoreactive (NPY-ir). Following neonatal ganglionectomy, this target is reinnervated by sympathetic nerves from the contralateral superior cervical ganglion that are strongly NPY-ir. We examined the effects of exogenously administered NPY on STM tone, response to norepinephrine, and sympathetic neurotransmission in ipsilaterally innervated and contralaterally reinnervated STMs. NPY (2-10 micrograms/kg iv) increased blood pressure but did not alter STM tone. Similarly, contractile responses to co-administered norepinephrine were not affected. These findings imply an absence of direct and indirect postjunctional actions of NPY on STM. Contractions elicited by stimulation of the cervical sympathetic nerve (1.5 Hz) were not affected by NPY on the contralaterally reinnervated side; however, ipsilateral contractions were decreased in a dose-dependent fashion, with an inhibition of about 40% at 10 micrograms/kg. We conclude that while the STM is unresponsive to exogenously administered NPY, this peptide exerts selective inhibitory effects on the ipsilateral NPY-ir-negative but not the contralateral NPY-ir-positive innervation. This suggests that the neonatally denervated STM is reinnervated by contralateral fibers that are functionally different from the normal ipsilateral innervation in being devoid of functional prejunctional NPY receptors.

Is the neuronal ATP release from guinea-pig vas deferens subject to α2-adrenoceptor-mediated modulation?

The effects of a variety of alpha 2-adrenoceptor agonists and antagonists were studied on stimulation-evoked release of endogenous ATP, measured by the luciferin-luciferase assay, and on the release of [3H]noradrenaline from the guinea-pig vas deferens. The biphasic mechanical contraction of the guinea-pig smooth muscle was recorded concomitantly. The alpha 2-adrenoceptor agonist, xylazine (1 microM) inhibited the field stimulation-evoked (8 Hz, 0.1 ms, 480 shocks) release of ATP and [3H]noradrenaline, and both phases of the contraction. The inhibitory effect of xylazine on the release of ATP, noradrenaline and muscle contraction was prevented by the selective alpha 2-adrenoceptor antagonist, CH 38083 [7,8-(methylenedioxi)-14 alpha-alloberbanol, 1 microM]. In the presence of prazosin (0.1-1 microM) or WB 4101 [2-(2,6-dimethoxyphenoxyethyl)aminomethyl- 1,4-benzodioxane hydrochloride, 0.1-1 microM], i.e. under the condition when the effect of noradrenaline on postjunctional alpha 1-adrenoceptors was excluded, the stimulation-evoked release of [3H]noradrenaline was significantly enhanced, however, the release of endogenous ATP and also both phases of contraction were reduced. In the presence of prazosin, xylazine was able to inhibit the stimulation-evoked release of ATP. In vas deferens dissected from reserpine pretreated (2 x 5 mg/kg, i.p.) guinea-pigs, the content of noradrenaline was 0.5% of control and there was no detectable evoked release of noradrenaline. Under this condition, the release of ATP evoked by electrical stimulation was still detectable, but the amount of ATP was much smaller than that measured from control animals. Xylazine did not reduce the release of ATP. Oxymetazoline, a relatively selective alpha 2-adrenoceptor agonist failed to inhibit the release of [3H]noradrenaline.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of neuropeptide Y on adrenergic and non-adrenergic, non-cholinergic responses in the rat anococcygeus muscle

1. The effects of neuropeptide Y (NPY) were examined on adrenergic and non-adrenergic, non-cholinergic (NANC) neurotransmission in the rat anococcygeus muscle. 2. NPY (0.1-0.3 microM) greatly potentiated the contractile responses induced by field stimulation. Prazosin (0.1 microM) completely abolished the stimulation-induced responses either in the absence or presence of NPY. 3. NPY (0.1-0.3 microM) enhanced only the contractile responses to low doses of noradrenaline (NA, 0.003-0.01 microM). Responses to tyramine were unaffected by the same concentrations of NPY. 4. In superfused anococcygeus, previously loaded with [3H]-NA, NPY (0.1-0.3 microM) failed to modify the basal, as well as the stimulation-evoked, release of tritium at 2 and 4 Hz. 5. NANC relaxations induced by electrical stimulation were significantly reduced, in a concentration-related manner, by 0.1-0.3 microM NPY. 6. L-NG-nitro-arginine (L-NOARG, 30 microM) enhanced the stimulation (0.25-1 Hz)-induced motor responses. In the presence of L-NOARG (30 microM), NPY (0.1 microM) did not modify the motor responses induced by field stimulation (0.25-0.5 Hz). L-Arginine did not reverse the NPY-induced potentiation of stimulation-induced motor responses. 7. The relaxations of anococcygeus muscle induced by sodium nitroprusside (SNP, 0.01-0.3 microM) were diminished by NPY (0.1-0.3 microM). 8. Our study suggests that NPY, at concentrations devoid of contractile effect, potentiates the motor responses of rat anococcygeus muscle as a consequence, at least in part, of the inhibition of NANC relaxing responses by a different mechanism from L-NOARG.

Electrophysiological and electrochemical analysis of the secretion of ATP and noradrenaline from the sympathetic nerves in rat tail artery: effects of ?2-adrenoceptor agonists and antagonists and noradrenaline reuptake blockers

The aim of this study was to investigate whether or not nerve impulses release ATP and noradrenaline in parallel from the sympathetic nerve terminals of the rat tail artery. The extracellularly recorded excitatory junction current (EJC) was used to study, pulse by pulse, the release of ATP. An electrochemical method was used to study online the nerve stimulation-induced rise in the extracellular concentration of endogenous noradrenaline at the probe, a carbon fibre electrode (CF). This parameter, which does not directly represent noradrenaline release, but reflects release minus clearance, has been termed delta[NA]CF. The effects of a number of pharmacological agents on the EJCs were examined both at 0.1 and 2 Hz, and the effects on the EJC response to 100 pulses at 2 Hz compared with that on the delta[NA]CF response. Clonidine and xylazine were used as alpha 2-agonists, yohimbine and idazoxan as alpha 2-antagonists and desipramine and cocaine as blockers of noradrenaline reuptake. Most of these agents had unwanted side effects, especially at higher concentrations. However, clonidine and xylazine depressed at lower concentrations the EJC and delta[NA]CF responses to about the same extent; these effects were partially or completely reversed by yohimbine. Yohimbine or idazoxan did not affect the EJCs at 0.1 Hz but enhanced the EJC and delta[NA]CF responses to 100 pulses at 2 Hz to the same extent. All effects of desipramine (1 microM) seemed explainable as a result of block of noradrenaline reuptake, while cocaine (10 microM) in addition exerted an 'unspecific' depressant (probably local anesthetic) effect. Under control conditions, both agents depressed the EJC but dramatically enhanced the delta[NA]CF response to 100 pulses at 2 Hz. Addition of yohimbine prevented the depressant effect of desipramine on the EJCs completely and reduced that of cocaine, but increased their effects on the delta[NA]CF response. These results are compatible with the view that ATP and noradrenaline are released in parallel from the sympathetic nerve terminals of this tissue. The different, and under some conditions even opposite, effects of desipramine or cocaine on the EJC and delta[NA]CF responses are explainable in terms of the known post-secretory effects of these agents.

Neuropeptide Y 16-36 inhibits mucociliary activity but does not affect blood flow in the rabbit maxillary sinus in vivo

Recent investigations have shown neuropeptide Y (NPY) to be present in the rabbit maxillary sinus, and NPY is known to be released upon sympathetic nerve stimulation. To study, in vivo, the effect on mucociliary activity and blood flow, NPY 1-36 and some of its analogues were injected intra-arterially. The effects of the Y1/Y2 agonist NPY 1-36 was compared with the ones of the Y2 agonist NPY 16-36, the Y1-agonist [Leu31,Pro34]NPY and the Y1/Y2 agonist peptide YY. Mucociliary response was recorded photoelectrically and expressed as a percentage of the basal mucociliary activity immediately prior to challenge. The effect on blood flow was measured with laser Doppler flowmetry and expressed as a percentage of the mean blood flow during the 60 s preceding challenge. NPY 1-36 and NPY 16-36 both reduced mucociliary activity dose-dependently at equimolar dosages (0.024-1.2 nmol/kg). The greatest effect was seen after the highest dosage tested. NPY 1-36 reduced mucociliary activity by 14.6 +/- 1.8%, and NPY 16-36 by 13.2 +/- 1.4%. At the highest dosage tested the Y1 receptor agonist [Leu31,Pro34]NPY did not significantly reduce mucociliary activity, whereas PYY reduced mucociliary activity by 15.0 +/- 1.8%. Injections of NPY 16-36 had no effect on blood flow whereas NPY 1-36, [Leu31,Pro34]NPY and PYY all reduced blood flow dose-dependently. Maximal decrease was seen at the highest dosage tested and was 47.1 +/- 5.4%, 70.4 +/- 7.4% and 58.2 +/- 8.4%, respectively. These findings suggest the mucociliary effects to be mediated via Y2 receptors whereas blood flow is regulated via Y1 receptors.

Age and castration modulate the inhibitory action of neuropeptide Y on neurotransmission in the rat vas deferens

The potency of neuropeptide Y (NPY) to inhibit the electrically induced contractions of the epididymal half of the vas deferens diminishes markedly with age, being at least 20 times lower in the adult than in the 26-day-old rat. Castration sensitizes the epididymal segment to NPY in a testosterone-reversible manner. [Pro34]NPY was 3 times less potent than NPY in prepubertal rats and inactive in castrated adults, while NPY-(13-36) had no effect in either group. In the prostatic half, NPY and its analogs were active in rats from all ages studied; the order of potency being NPY greater than [Pro34]NPY greater than NPY-(13-36). The sensitivity of the prostatic segment from adult rats to NPY was unchanged by castration or testosterone replacement therapy. The NPY content of the ductus increases during development being higher in the prostatic than in the epididymal half at all ages studied. Castration decreases the peptide content in the two segments and the effect is prevented by testosterone administration. The present investigation demonstrated that the effect of NPY on vas deferens neurotransmission is subject to regulation by sex steroids, which affects differently the response of the two segments of the ductus.

Age-dependent modulation of neuropeptide Y on adrenergic transmission of guinea pig vas deferens

1. The effect of neuropeptide (NPY) on [3H]noradrenaline ([3H]NA) release- and on contractions evoked by field electrical stimulation (FES) was studied in vitro in vas deferens from mature and immature guinea pigs. 2. The evoked tritium overflow (which reflected [3H]NA release) was determined by liquid scintillation spectrometry. 3. Field electrical stimulation of 5 Hz (trains of 50 pulses in 20 sec intervals) evoked guanethidine-sensitive contractions. 4. NPY (0.01-1 microM) dose-dependently inhibited the evoked contractions in both groups of animals. NPY, 1 microM, almost completely inhibited the evoked contractions in mature animals, while those in immature guinea pigs were inhibited but only by 80.4 +/- 3.6%. 5. The amount of tritium overflow evoked by 5 Hz stimulation (300 pulses: 15 trains of 20 pulses in 20 sec intervals) was higher in immature guinea pigs (0.46 +/- 0.03%) compared with the amount of the evoked tritium overflow in mature guinea pigs (0.39 +/- 0.02%). 6. NPY, 1 microM, inhibited the evoked tritium overflow. The NPY inhibition was more pronounced in vas deferens of mature (45.3 +/- 2.0%) than in immature (25.1 +/- 3.5%) guinea pigs. 7. The results suggest that NPY modulation of adrenergic transmission at the prejunctional level increases with the maturity.