Neuropeptide Y--a cotransmitter with noradrenaline and adenosine 5'-triphosphate in the sympathetic nerves of the mouse vas deferens? A biochemical, physiological and electropharmacological study

Selective tracking of FFAR3-expressing neurons supports receptor coupling to N-type calcium channels in mouse sympathetic neurons

Activation of short-chain free fatty acid receptors 3 (FFAR3) has been suggested to promote sympathetic outflow in postganglionic sympathetic neurons or hamper it by a negative coupling to N-type calcium (Ca_V2.2) channels. Heterogeneity of FFAR3 expression in sympathetic neurons, however, renders single neurons studies extremely time-consuming in wild-type mice. Previous studies demonstrated large variability of the degree of Ca_V2.2 channel inhibition by FFAR3 in a global population of rat sympathetic neurons. Therefore, we focused on a small subpopulation of mouse sympathetic neurons using an FFAR3 antibody and an Ffar3 reporter mouse to perform immunofluorescent and electrophysiological studies. Whole-cell patch-clamp recordings of identified FFAR3-expressing neurons from reporter mice revealed a 2.5-fold decrease in the Ca_V2.2-FFAR3 inhibitory coupling variability and 1.5-fold increase in the mean I_Ca²⁺ inhibition, when compared with unlabeled neurons from wild-type mice. Further, we found that the ablation of Ffar3 gene expression in two knockout mouse models led to a complete loss-of-function. Subpopulations of sympathetic neurons are associated with discrete functional pathways. However, little is known about the neural pathways of the FFAR3-expressing subpopulation. Our data indicate that FFAR3 is expressed primarily in neurons with a vasoconstrictor phenotype. Thus, fine-tuning of chemically-coded neurotransmitters may accomplish an adequate outcome.

Neuropeptide Y overflow and metabolism in skeletal muscle arterioles

The purpose of this study was to characterize neuropeptide Y (NPY) overflow and metabolism from isolated skeletal muscle arterioles of female rats. Gastrocnemius first-order arterioles were removed from young (2 months), young adult (6 months) and middle-aged (12 months) F344 female rats. Arterioles were isolated, cannulated and pressurized in a microvessel bath with field stimulation electrodes. NPY overflow from isolated arterioles was assessed at 0 s and 30 s post-field stimulation. Dipeptidyl peptidase IV (DPPIV) activity was quantified via fluorometric assay of whole vessel homogenate. In young adult and middle-aged rats, NPY overflow increased 0 s and 30 s following field stimulation. In young adult rats, DPPIV inhibition resulted in an increase in NPY overflow at 30 s, while middle-aged rats had no increase in NPY overflow with DPPIV inhibition (P <0.05). DPPIV activity was influenced by factors such as age, vessel type, and endothelium (P <0.05). The present data suggest that DPPIV plays a significant role in modulating the actions of NPY in arterioles of young adult females; however, this role appears to diminish with age.

Bretylium abolishes neurotransmitter release without necessarily abolishing the nerve terminal action potential in sympathetic terminals

BACKGROUND AND PURPOSE

The antidysrhythmic bretylium is useful experimentally because it selectively abolishes neurotransmitter release from sympathetic peripheral nerve terminals. Its mechanism of action seemed settled, but recent results from optical monitoring of single terminals now suggests a new interpretation.

EXPERIMENTAL APPROACH

Orthograde transport of a dextran-conjugated Ca(2+) indicator to monitor Ca(2+) in nerve terminals of mouse isolated vas deferens with a confocal microscope. In some experiments, local neurotransmitter release was detected by monitoring neuroeffector Ca(2+) transients (NCTs) in adjacent smooth muscles, a local measure of purinergic transmission. Sympathetic terminals were identified with catecholamine fluorescence (UV excitation) or post-experiment immunohistochemistry.

KEY RESULTS

Bretylium (10 microM) abolished NCTs at 60/61 junctions over the course of 2 h, indicating effective abolition of neurotransmitter release. However, bretylium did not abolish the field stimulus-induced Ca(2+) transient in most nerve terminals, but did increase both action potential delay (by 2+/-0.4 ms) and absolute refractory period (by 4+/-2 ms). Immunohistochemistry demonstrated that 85-96% of terminals orthogradely filled with a dextran-conjugated fluorescent probe contained Neuropeptide Y (NPY). A formaldehyde-glutaraldehyde-induced catecholamine fluorescence (FAGLU) technique was modified to allow sympathetic terminals to be identified with a Ca(2+) indicator present. Most terminals contained catecholamines (based on FAGLU) or secrete ATP (as NCTs in adjacent smooth muscle cells are abolished).

CONCLUSIONS AND IMPLICATIONS

Bretylium can inhibit neurotransmitter release downstream of Ca(2+) influx without abolishing the nerve terminal action potential. Bretylium-induced increases in the absolute refractory period permit living sympathetic terminals to be identified.

Effects of cannabinoid receptor activation on rabbit bisected vas deferens strips

1. In the present study, the effects of anandamide and WIN 55,212-2, cannabinoid receptor agonists, were investigated on electrical field stimulation (EFS)-induced biphasic twitch responses obtained from the epididymal and prostatic portions of rabbit vas deferens strips. 2. Anandamide and WIN 55,212-2 dose-dependently inhibited both the first and second phases of the EFS-induced twitch responses recorded from epididymal and prostatic portions of the vas deferens over the concentration range 10(-9) to 3 x 10(-6) mol/L. 3. The cannabinoid CB1 receptor antagonist AM 251 (10(-6) mol/L) and the cannabinoid CB2 receptor antagonist AM 630 (10(-6) mol/L) had no effect on the inhibitory action of anandamide on the biphasic twitch responses in the prostatic and epididymal portions of the rabbit vas deferens. 4. In both the prostatic and epididymal portions of the rabbit vas deferens, AM 251 significantly, but not completely, reversed the inhibitory effect of WIN 55,212-2 on the first phase of the twitch response. In contrast, AM 630 did not have any effect on the inhibitory action of WIN 55,212-2 in the rabbit vas deferens strips. 5. The inhibitory effects of anandamide or WIN 55,212-2 on EFS-induced twitch responses of both the prostatic and epididymal portions of the rabbit vas deferens were not altered in the presence of 10(-5) mol/L naloxone. 6. These results suggest that cannabinoid receptors may have a modulatory role in the regulation of sympathetic transmission in the rabbit vas deferens. However, further investigation is required to characterize the receptors involved.

ATP as a cotransmitter in sympathetic nerves and its inactivation by releasable enzymes

ATP and norepinephrine (NE) are cotransmitters released from many postganglionic sympathetic nerves. In this article, we review the evidence for ATP and NE cotransmission in the rodent vas deferens with special attention to the mechanisms involved in removing the cotransmitters from the neuroeffector junction. Although the clearance of NE is well understood (e.g., the primary mechanism being reuptake into the nerves), the clearance of ATP is just beginning to be explained. The general belief has been that ATP is metabolized by cell-fixed ecto-nucleotidases. It now seems, however, that when ATP is released from nerves as a transmitter there is a concomitant release of nucleotidases that rapidly degrade ATP sequentially to ADP, AMP, and adenosine, thereby terminating the action of ATP. In the guinea pig vas deferens, there appear to be at least two enzymes, one that converts ATP to ADP and ADP to AMP (an ATPDase) and a second enzyme that converts AMP to adenosine (an AMPase). An important feature of this process is that the transmitter-metabolizing nucleotidases are released into the synaptic space as opposed to being fixed to cell membranes. A preliminary characterization of these enzymes suggests that the releasable ATPDase exhibits some similarities to known ectonucleoside triphosphate/diphosphohydrolases, whereas the releasable AMPase exhibits some similarities to ecto-5'-nucleotidases.

Pharmacology of neuropeptide Y receptor antagonists. Focus on cardiovascular functions

Neuropeptide Y is one of the most abundant mammalian neuropeptides identified to date. The possible actions of neuropeptide Y, that is co-localized and released with noradrenaline, as a sympathetic co-transmitter has attracted much attention during the last decade. In recent years, several non-peptide antagonists with high subtype selectivity for neuropeptide Y receptors have been introduced. With them, the status of neuropeptide Y as a sympathetic transmitter has been established, and so have profound cardiovascular effects mediated by neuropeptide Y Y(1) and Y(2) receptors. Significant release of neuropeptide Y occurs especially upon stronger sympathetic activation, and recent data suggest that the importance of neuropeptide Y seems enhanced in stress-related cardiovascular disorders. The true significance of neuropeptide Y has thus started to unfold, owing to the presence of the first generation of selective neuropeptide Y receptor antagonists. This review concerns the pharmacology of these agents, what we have learnt from them, and might find out in the future.

Autoinhibitory function of the sympathetic prejunctional neuropeptide Y Y(2) receptor evidenced by BIIE0246

The significance of neuropeptide Y Y(2) receptors in sympathetic nonadrenergic transmission was investigated using the novel selective antagonist BIIE0246 ((S)-N2-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6h)-oxodibenz[b,e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]-N-[2-[1,2-dihydro-3,5 (4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]-argininamide). In anaesthetized pigs pretreated with reserpine, and after transection of sympathetic nerves (depleted of noradrenaline), electrical stimulation of renal and splanchnic sympathetic nerves evoked vasoconstriction in, and overflow of neuropeptide Y-like immunoreactivity from, kidney and spleen, respectively. In the presence of BIIE0246, the nerve-evoked overflows of neuropeptide Y-like immunoreactivity were markedly increased and the splenic vasoconstrictor response prolonged. In addition, BIIE0246 caused splenic vasodilatation per se in this model where basal levels of circulating neuropeptide Y exceed 40 pM. It is concluded that endogenous neurogenical neuropeptide Y regulates its own release via activation of sympathetic prejunctional inhibitory neuropeptide Y Y(2) receptors in both spleen and kidney in the reserpinized pig. Moreover, when circulating levels of neuropeptide Y are moderately increased, activation of neuropeptide Y Y(2) receptors seems to contribute to basal splenic vascular tone.

Development of purinergic sensitivity in sensory neurons after peripheral nerve injury in the rat

Purinoceptors are present in the cell bodies as well as in both peripheral and central terminals of many sensory neurons, where they may play a role in sensory transmission, including pain. After peripheral nerve injury at the spinal nerve level, some axotomized afferent neurons develop ongoing discharges (ectopic discharges) that originate in the dorsal root ganglion (DRG). In the present study, we attempted to determine whether or not purinergic sensitivity develops in injured sensory neurons which display ectopic discharges, as well as in silent units. The L(4) and L(5) spinal nerves were ligated in Sprague-Dawley rats. Four to 21 days after the surgery, the DRGs with attached dorsal roots and spinal nerves were removed and ectopic discharges were recorded from teased dorsal root fascicles using an in vitro recording set-up. The results showed that 75.6 and 65.1% of the chronically axotomized DRG neurons displaying ectopic discharges enhanced their activity after application of adenosine 5'-triphosphate (ATP, 1 mM) or alpha,beta-methylene ATP (mATP, 100 microM), respectively. In addition, application of these purinoceptor agonists evoked activity in 7 of 28 axotomized DRG neurons, which did not show ongoing discharges. In contrast, only 1 of 34 DRG neurons acutely isolated from normal rats (no previous spinal nerve ligation) responded to either mATP or ATP. In most of the tested units, mATP-induced enhancement of ectopic discharges was blocked by non-specific P2X receptor antagonists, PPADS or suramin. The data from the present study suggest that purinergic sensitivity develops in DRG neurons after chronic axotomy and that this purinergic sensitivity is likely to be mediated by P2X purinoceptors. This acquired purinergic sensitivity may play an important functional role in the enhancement of ectopic discharges and exacerbation of pain upon sympathetic activation in the neuropathic pain state.

Neurotransmitter release mechanisms in sympathetic neurons: past, present, and future perspectives

In 1969, Paton and Vizi described the inhibitory actions of noradrenaline on acetylcholine release from the innervation of the guinea-pig ileum longitudinal muscle. They concluded "that acetylcholine output by the nervous networks of the longitudinal strip is under the normal control of the sympathetic by a species of presynaptic inhibition mediated by <==> receptors". This work was carried out in the Pharmacology Department at Oxford University. Clearly, a period in the 'Dreaming Spires' of Oxford sufficiently inspired Sylvester to take up a life long career in scientific research. He has published more than 300 papers on a wide range of topics but clearly has a strong interest in neurotransmitter release mechanisms and recently, non-synaptic interactions between neurons. It seems fitting therefore to write a brief review on the continuing studies on neurotransmitter release mechanisms in sympathetic neurons in a volume honoring the now distinguished Professor Vizi.

Vascular pharmacology of BIIE0246, the first selective non-peptide neuropeptide Y Y(2) receptor antagonist, in vivo

BIIE0246, a recently introduced non-peptide neuropeptide Y (NPY) Y(2) receptor antagonist, was pharmacologically characterized in vivo, on vascular responses evoked in the anaesthetized pig. The NPY Y(2) receptor agonist N-acetyl[Leu(28)Leu(31)]NPY(24-36) evoked dose-dependent vasoconstriction in spleen. These vascular responses were potently and dose-dependently antagonized by BIIE0246. Significant inhibition was seen already at 1 nmol kg(-1), whereas at 100 nmol kg(-1) of BIIE0246 these responses were completely abolished. The ID(50) value for this antagonism was 2.1 nmol kg(-1). Peptide YY (PYY) evoked dose-dependent vasoconstriction in both kidney and spleen, vascular responses mediated by the NPY Y(1) receptor and both NPY Y(1) and Y(2) receptors, respectively. Only the splenic response was inhibited by BIIE0246, the effect of which reached significance at 1 nmol kg(-1). Already 30 min after the last dose of BIIE0246 there was a significant recovery of the PYY-evoked splenic vasoconstriction, and a further 60 min later, this response was no longer significantly inhibited compared to control. BIIE0246 (100 nmol kg(-1)) did not affect renal and splenic vasoconstrictor responses either to the NPY Y(1) receptor agonist [Leu(31)Pro(34)]NPY, the alpha(1)-adrenoceptor agonist phenylephrine, the P2X(1)-purinoceptor agonist alpha,beta-methylene ATP or angiotensin II, demonstrating both selectivity and specificity for the NPY Y(2) receptor in vivo. It is concluded that BIIE0246 is a highly potent and selective NPY Y(2) receptor antagonist, albeit with rather short duration of action, in vivo. BIIE0246 thus represents the first interesting tool for studies on NPY Y(2) receptor-mediated transmission in vivo.

Neuropeptide Y cotransmission with norepinephrine in the sympathetic nerve-macrophage interplay

The CNS modulates immune cells by direct synaptic-like contacts in the brain and at peripheral sites, such as lymphoid organs. To study the nerve-macrophage communication, a superfusion method was used to investigate cotransmission of neuropeptide Y (NPY) with norepinephrine (NE), with interleukin (IL)-6 secretion used as the macrophage read-out parameter. Spleen tissue slices spontaneously released NE, NPY, and IL-6 leading to a superfusate concentration at 3-4 h of 1 nM:, 10 pM:, and 120 pg/ml, respectively. Under these conditions, NPY dose-dependently inhibited IL-6 secretion with a maximum effect at 10(-10) M: (p = 0.012) and 10(-9) M: (p < 0.001). Simultaneous addition of NPY at 10(-9) M: and the alpha-2-adrenergic agonist p-aminoclonidine further inhibited IL-6 secretion (p < 0.05). However, simultaneous administration of NPY at 10(-9) M: and the beta-adrenergic agonist isoproterenol at 10(-6) M: or NE at 10(-6) M: significantly increased IL-6 secretion (p < 0.005). To objectify these differential effects of NPY, electrical field stimulation of spleen slices was applied to release endogenous NPY and NE. Electrical field stimulation markedly reduced IL-6 secretion, which was attenuated by the NPY Y1 receptor antagonist BIBP 3226 (10(-7) M, p = 0.039; 10(-8) M, p = 0.035). This indicates that NPY increases the inhibitory effect of endogenous NE, which is mediated at low NE concentrations via alpha-adrenoceptors. Blockade of alpha-adrenoceptors attenuated electrically induced inhibition of IL-6 secretion (p < 0.001), which was dose-dependently abrogated by BIBP 3226. This indicates that under blockade of alpha-adrenoceptors endogenous NPY supports the stimulating effect of endogenous NE via beta-adrenoceptors. These experiments demonstrate the ambiguity of NPY, which functions as a cotransmitter of NE in the nerve-macrophage interplay.

Central bombesin inhibits food intake and the orexigenic effect of neuropeptide Y in the neonatal chick

It is well known that central injection of bombesin (BN) suppresses feeding in mammalian and avian species, but the anorexigenic effect of central BN are still open with special reference to the chick. The dose response (0, 0.1 and 0.5 microg) of intracerebroventricular (ICV) injection of BN was examined in Experiment 1. ICV injection of BN inhibited food intake in a dose-dependent manner. Experiment 2 was done to determine whether BN interacts with the orexigenic effect of neuropeptide Y (NPY) in the neonatal chick. Central administration of NPY (2.5 microg) greatly enhanced food intake, but co-injection of BN (0.5 microg) suppressed food intake. The dose response of NPY (2.5 microg) co-injected with three levels of BN (0, 0.1 and 0.5 microg) was examined in Experiment 3. ICV injection of BN attenuated the hyperphagia by NPY in a dose-related fashion. It is suggested that central BN may interact with NPY for the regulation of feeding in the neonatal chick.

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.

Nitric oxide synthase is co-localized with vasoactive intestinal polypeptide in postganglionic parasympathetic nerves innervating the rat vas deferens

Cross-sections of the vas deferens taken from control adult male rats showed positive histochemical reactivity to acetylcholinesterase and immunoreactivity for antibodies to protein gene product 9.5, tyrosine hydroxylase, neuropeptide Y, vasoactive intestinal polypeptide, nitric oxide synthase and calcitonin gene-related peptide. Immunoreactivity to substance P was very sparse. Histochemical reactivity to acetylcholinesterase and immunoreactivity to vasoactive intestinal polypeptide and nitric oxide synthase was concentrated in the subepithelial lamina propria and inner smooth muscle layers. Complete surgical denervation resulting from transection of the nerve arising from the pelvic ganglion which supplies the vas deferens totally abolished the immunoreactivity to all of the antibodies tested as well as the histochemical reactivity to acetylcholinesterase. In sections of the prostatic end of the vas deferens taken from rats neonatally pretreated with capsaicin, immunoreactivity to calcitonin gene-related peptide and substance P was reduced by 75 and 83%, respectively. Immunoreactivity to neuropeptide Y, vasoactive intestinal polypeptide and nitric oxide synthase was similar in tissue sections taken from capsaicin-treated rats and those taken from control tissues. Pretreatment of rats with guanethidine or 6-hydroxydopamine decreased immunoreactivity to tyrosine hydroxylase and neuropeptide Y by 60-70%, but immunoreactivity to substance P, vasoactive intestinal polypeptide and nitric oxide synthase was unchanged, while immunoreactivity to calcitonin gene-related peptide and acetylcholinesterase staining was increased by guanethidine but not by 6-hydroxydopamine treatment. Triple labelling experiments showed nitric oxide synthase, vasoactive intestinal polypeptide and acetylcholinesterase all to be co-localized in some nerve fibres. These results indicate that the nitric oxide synthase contained in the nerve fibres innervating the rat vas deferens is unaffected by pretreatment of rats with capsaicin, 6-hydroxydopamine or guanethidine but is abolished by surgical denervation, of postganglionic parasympathetic, sympathetic and sensory nerves. Therefore it appears that nitric oxide synthase is co-localized with vasoactive intestinal polypeptide in the postganglionic parasympathetic nerves which innervate the rat vas deferens.

Omega-conotoxin GVIA-resistant neurotransmitter release from postganglionic sympathetic nerves in the guinea-pig vas deferens and its modulation by presynaptic receptors

1 Intracellular recording techniques were used to study neurotransmitter release mechanisms in postganglionic sympathetic nerve terminals in the guinea-pig isolated vas deferens. 2 Recently, a component of action potential-evoked release which is insensitive to high concentrations of the selective N-type calcium channel blocker omega-conotoxin GVIA termed 'residual release' has been described. Under these conditions, release of the neurotransmitter ATP evoked by trains of low frequency stimuli is abolished, but at higher frequencies a substantial component of release is revealed. 3 'Residual release' was studied with trains of 5 or 10 stimuli at stimulation frequencies of 10, 20 and 50 Hz. The alpha2-adrenoceptor agonist clonidine (30-100 nM) inhibited 'residual release', the degree of inhibition being most marked at the beginning of a train. 4 The alpha2-adrenoceptor antagonist yohimbine (1 microM) induced a marked increase in 'residual release' which was dependent on both the frequency of stimulation and the number of stimuli in a train. 5 Prostaglandin E2 (30 nM) and neuropeptide Y (100 nM) caused a rapid inhibition of 'residual release' at all stimulation frequencies examined. 6 4-Aminopyridine (100 microM) induced a powerful potential of 'residual release' and could reverse the inhibition of omega-conotoxin GVIA. 7 'Residual release' was modulated through presynaptic alpha2-adrenoceptors suggesting that (i) residual release of ATP is subject to alpha-autoinhibition through the co-release of noradrenaline, (ii) noradrenaline release can be triggered by calcium channels other than the N-type and (iii) when presynaptic receptors are activated, inhibition of transmitter release can occur by mechanisms other than modulation of calcium-entry through N-type calcium channels in postganglionic sympathetic nerves. Prostaglandin E2 and neuropeptide Y also modulated neurotransmitter release.

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.

Evidence for the presence of CB2-like cannabinoid receptors on peripheral nerve terminals

We have investigated whether there are cannabinoid CB2 receptors that can mediate cannabinoid-induced inhibition of electrically evoked contractions in the mouse vas deferens or guinea-pig myenteric plexus-longitudinal muscle preparation. Our results showed that mouse vas deferens and guinea-pig whole gut contain cannabinoid CB1 and CB2-like mRNA whereas the myenteric plexus preparation seemed to contain only cannabinoid CB1 mRNA. JWH-015 (1-propyl-2-methyl-3-( -naphthoyl)indole) and JWH-051 (1-deoxy-11-hydroxy-delta8-tetrahydrocannabinol-dimethylheptyl+ ++), which have higher affinities for CB2 than CB1 cannabinoid binding sites, inhibited electrically evoked contractions of both tissues in a concentration related manner. This inhibition was attenuated by 31.62 nM of the cannabinoid CB1 receptor selective antagonist SR141716A [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1H-pyrazole-3-carboxamide hydrochloride] only in the myenteric plexus preparation. Vasa deferentia from delta9-tetrahydrocannabinol-pretreated mice (20 mg/kg i.p. once daily for two days) showed reduced sensitivity to JWH-015 and JWH-051. The results suggest that these compounds exert their inhibitory effects through cannabinoid CB1 receptors in the myenteric plexus preparation, but mainly through CB2-like cannabinoid receptors in the vas deferens.

Exocytotic release from neuronal cell bodies, dendrites and nerve terminals in sympathetic ganglia of the rat, and its differential regulation

Stimulant-induced exocytosis has been demonstrated in sympathetic ganglia of the rat by in vitro incubation of excised ganglia in the presence of tannic acid, which stabilizes vesicle cores after their exocytotic release. Sites of exocytosis were observed along non-synaptic regions of the surfaces of neuron somata and dendrites, including regions of dendrosomatic and dendrodendritic apposition, as well as along the surfaces of nerve terminals About half the exocytoses associated with nerve terminals were parasynaptic or synaptic, and these appeared mostly to arise from the presynaptic terminal, but occasionally from the postsynaptic element. The results demonstrated that the neurons of sympathetic ganglia release materials intraganglionically in response to stimulation, that release from different parts of the neuron is subject to independent regulation, at least via cholinergic receptors, and that release is partly diffuse, potentially mediating autocrine or paracrine effects, and partly targeted toward other neurons, but that the latter mode is not necessarily, and not evidently, synaptic. Specifically, exocytosis from all locations increased significantly during incubation in modified Krebs' solution containing 56 nm potassium. Observation of the effects of cholinergic agonists (nicotine, carbachol, oxotremorine) and antagonists (atropine, AF-DX 116) showed that nicotinic and muscarinic excitation each, independently, increased the incidence of exocytosis from somata and dendrites. Exocytosis from nerve endings was not altered by nicotine, but was enhanced or, at high initial rates of exocytosis, decreased, by muscarinic stimulation. Evidence was obtained for muscarinic auto-inhibition of exocytosis from nerve terminals, occurring under basal incubation conditions, and for a muscarinic excitatory component of somatic exocytosis, elicitable by endogenous acetylcholine. The M2-selective muscarinic antagonist AF-DX 116 was found to modify the exocytotic response of the dendrites to oxotremorine, widening the range of its variation; this effect is consistent with recent evidence for the presence of M2-like muscarinic binding sites, in addition to M1-like binding, upon these dendrites [Ramcharan E. J. and Matthews M. R. (1996) Neuroscience 71, 797-832]. Over all conditions, disproportionately more sites of somatic and dendritic exocytosis were found to be located in regions of dendrosomatic and dendrodendritic apposition than would be expected from the relative extent of the neuronal surface occupied by these relationships. Such mechanisms of intraganglionic release may be expected to contribute to the regulation and integration of the behaviour of the various functionally distinctive populations of neurons in these ganglia, by autocrine, paracrine, and focal, neuroneuronal, routes of action. Similar phenomena of exocytotic soma-dendritic release might prove to subserve integrative neuroneuronal interactions more widely throughout the nervous system.

Neuropeptide Y1 receptors in the rat genital tract

Using in situ hybridization and immunohistochemistry, the expression of type 1 neuropeptide Y (NPY) receptors (Y1-Rs) has been demonstrated in the rat genital tract. In the male Y1-R mRNA and Y1-R-like immunoreactivity (LI) were found in smooth muscles of predominantly arterioles and small arteries inside testis. Fibers showing NPY-LI could not be detected within testis but only in the tunica albuginea. These Y1-Rs are suggested to mediate vasoconstriction, possibly activated by NPY released from nerves in the tunica albuginea. In the female rat Y1-R mRNA, but not Y1-R-LI was found in vascular smooth muscles of arteries in the ovary and oviduct. In the oviduct Y1-R mRNA was also detected in the non-vascular smooth muscle layer. Fibers showing NPY-LI were found around blood vessels both in the ovary and oviduct. In the female genital tract also Y1-Rs may thus be involved in regulatory mechanisms mediating, for example, vasoconstriction.

Release of peptide cotransmitters in Aplysia: regulation and functional implications

To gain insights into the physiological role of cotransmission, we measured peptide release from cell B15, a motorneuron that utilizes ACh as its primary transmitter but also contains putative peptide cotransmitters, the small cardioactive peptides (SCPs) and the buccalins (BUCs). All stimulation parameters used were in the range in which B15 fires in freely moving animals. We stimulated neuron B15 in bursts and systematically varied the interburst interval, the intraburst frequency, and burst duration. Both peptides were preferentially released when B15 was stimulated at higher intra- or interburst frequencies or with longer burst durations. Across stimulation patterns, the amount of peptide released depended on the mean frequency of stimulation and was independent of the specific pattern of stimulation. The parameters of stimulation that produce a larger release of peptides correspond to those that evoke larger contractions. Large and frequent contractions are likely to fuse or summate, thus disrupting the rhythmic behavior mediated by the muscle innervated by motorneuron B15. Because the combined effect of the SCPs and BUCs is to accelerate the relaxation and shorten the duration of muscle contractions, these peptides reduce the probability of the disruptive fusion or summation of muscle contractions. Because these cotransmitters regulate an aspect of muscle contractions that is not controlled by acetylcholine (ACh), the primary transmitter of B15, we suggest that peptides and ACh form parallel but functionally distinct lines of transmission at the neuromuscular junction. Both types of transmission may be necessary to ensure that behavior remains efficient over a wide range of conditions.

Costorage and corelease of modulatory peptide cotransmitters with partially antagonistic actions on the accessory radula closer muscle of Aplysia californica

Many neurons that contain a classical neurotransmitter also contain modulatory peptides, but it has been difficult to establish unequivocally that these peptides are functional cotransmitters. Here, we provide evidence for functional cotransmission in a neuromuscular system of Aplysia. Using immunocytochemical techniques, we localize members of two peptide families, the small cardioactive peptides (SCPs) and the buccalins (BUCs), to a single subset of dense-core vesicles in the terminals of the cholinergic motorneuron B15. We describe a new preparation and method for the direct detection of released peptides and show that the SCPs and BUCs are released when neuron B15 is intracellularly stimulated. Consistent with their subcellular localization, the SCPs and BUCs are released in a stoichiometric ratio that is constant across conditions that change the absolute amount of peptides released. Peptide release is calcium-dependent but does not require muscle contractions. Thus, the release cannot be attributed to a displacement of peptides that may be present in the extracellular space. In previous studies, we characterized the physiological firing patterns of neuron B15. Here, we simulate these firing patterns and show that peptide release occurs. Additionally, we find that significant quantities of material are released under behaviorally relevant conditions. We find that concentrations of released peptides in the muscle are in the concentration range in which exogenously applied peptides exert characterized modulatory actions on muscle contractions. Together, our findings provide strong support for the hypothesis that peptides contained in neuron B15 are functional cotransmitters.

Sensitivity to leptin and susceptibility to seizures of mice lacking neuropeptide Y

Neuropeptide Y (NPY), a 36-amino-acid transmitter distributed throughout the nervous system, is thought to function as a central stimulator of feeding behaviour. NPY has also been implicated in the modulation of mood, cerebrocortical excitability, hypothalamic-pituitary signalling, cardiovascular physiology and sympathetic function. However, the biological significance of NPY has been difficult to establish owing to a lack of pharmacological antagonists. We report here that mice deficient for NPY have normal food intake and body weight, and become hyperphagic following food deprivation. Mutant mice decrease their food intake and lose weight, initially to a greater extent than controls, when treated with recombinant leptin. Occasional, mild seizures occur in NPY-deficient mice and mutants are more susceptible to seizures induced by a GABA (gamma-aminobutyric acid) antagonist. These results indicate that NPY is not essential for certain feeding responses or leptin actions but is an important modulator of excitability in the central nervous system.

Failure of the putative neuropeptide Y antagonists, benextramine and PYX-2, to inhibit Y2 receptors in rat isolated prostatic vas deferens

1. The pharmacological activity of neuropeptide Y (NPY) and some analogues in inhibiting the twitch contractions induced by electrical stimulation (single pulses at 25 V, 0.15 Hz, 1 ms) in the prostatic portion of the rat isolated vas deferens was investigated. The rank order of agonist potency was: PYY > NPY2-36 > NPY >> NPY13-36 >> NPY18-36 >> [Leu31,Pro34]NPY = hPP, which is consistent with the activation of a Y2 receptor. 2. The putative Y1 and Y2 antagonist, benextramine (BXT), incubated at 100 microM for 10 or 60 min, was ineffective against PYY-induced inhibition of the twitch response, suggesting that the prejunctional Y2 receptor in this tissue is different from the postjunctional one reported in the literature to be sensitive to BXT blockade. 3. The putative NPY antagonist, PYX-2, incubated at 1 microM for 20 min, was completely ineffective in antagonizing PYY-induced inhibition of twitches. 4. The twitch response was totally inhibited by suramin (100 microM) but was little affected by prazosin (1 microM). Furthermore, NPY was without effect on the dose-response curve to ATP in resting conditions. Taken together, these results suggest that in our paradigm, NPY inhibits the release of a purinergic neurotransmitter which mediates contraction of the prostatic portion of the rat vas deferens.

Opposite modulation by tachykinin (NK1) and CGRP receptors of sympathetic control of mouse vas deferens motility

Electrical field stimulation of isolated mouse vas deferens elicited sympathetic twitch whose amplitude was transiently enhanced by the selective tachykinin NK1 receptor agonist, [Sar9,Met(O2)11]substance P (0.3-30 nM), but not by selective NK2 and NK3 receptor agonists. Potentiation by [Sar9,Met(O2)11]substance P was antagonized by (+/-)-CP 96,345 [(2S,3S)-cis-2-(diphenylmethyl)-N- [(2-methoxyphenyl)-methyl]-1-azabicyclo[2.2.2]octan-3-amine] (IC50 = 0.1 microM). On the other hand, electrical field stimulation-induced contractions were inhibited by calcitonin gene-related peptide, CGRP (0.1-30 nM), and this action was reduced by its antagonist, human CGRP-(8-37) (3 microM). [Sar9,Met(O2)11]substance P (3 nM) did not affect either high-K+ or noradrenaline-induced contraction, while CGRP (3 nM) significantly reduced the noradrenaline-induced motor response. Capsaicin (1 microM) inhibited sympathetic twitches, and this effect was partially antagonized by human CGRP-(8-37). In the presence of this antagonist, capsaicin induced a short-living and (+/-)-CP 96,345-sensitive twitch enhancement. These data suggest that the sympathetic control of mouse vas deferens motility can be modulated in an opposite manner by tachykinin NK1 (prejunctionally located) and by CGRP (pre- and/or postjunctionally located) receptors.

Discrimination by benextramine between the NPY-Y1 receptor subtypes present in rabbit isolated vas deferens and saphenous vein

1. In order to characterize the neuropeptide Y (NPY) Y1 receptors known to be present in rabbit isolated vas deferens and saphenous vein, the pharmacological activity of the selective NPY Y1 receptor agonists, [Leu31,Pro34] NPY and various other peptide agonists, together with the putative NPY antagonist, benextramine, were compared in the two tissues. 2. In rabbit isolated saphenous vein, cumulative dose-response curves to various NPY agonists were obtained. All the peptides tested caused contractions which developed quite slowly. The rank order of potency obtained was: PYY > NPY > [Leu31,Pro34] NPY = NPY2-36 > hPP >> NPY13-36 = NPY18-36. Incubation with benextramine (BXT) at 100 microM for 30 min irreversibly abolished the contractile response to [Leu31,Pro34] NPY but was ineffective against NPY18-36-induced contractions. 3. Cumulative dose-response curves to [Leu31,Pro34] NPY were performed in the same preparation before and after incubation with 100 microM BXT for 20 min in order to inactivate NPY Y1 receptors. The pKA (-logKA) estimation for [Leu31,Pro34] NPY was 7.60 +/- 0.30 using the operational model and 7.20 +/- 0.33 using the null method; the difference between the two methods was not statistically significant (P = 0.36). 4. Prostatic segments of rabbit vas deferens were electrically stimulated with single pulses. Immediately after stabilization of the contractile response, a cumulative dose-response curve to various NPY agonists was obtained in each tissue. The rank order of potency for twitch inhibition was: PYY> [Leu31,Pro34]NPY > NPY > hPP>NPY2- 36 >>NPY13-36>> NPY 18-36 which indicates the presence of a prejunctional NPY Y1 receptor. BXT at 100 microM incubated for 10 or 60 min did not antagonize the response to[Leu31,Pro34] NPY.5. We conclude that rabbit isolated saphenous vein contains a population of post-junctional NPY Y1 receptors irreversibly blocked by BXT, as well as a population of post-junctional NPY Y2 receptors,which are insensitive to BXT. In contrast, the rabbit isolated vas deferens express a pre-junctional NPYY1 receptor subtype which is not blocked by BXT. Tetramine disulphides such as BXT could be useful tools in classifying NPY receptors.

Characterization of kinin receptors modulating neurogenic contractions of the mouse isolated vas deferens

1. This study analyses the receptors mediating the effects of bradykinin (BK) and analogues on neurogenic twitch contractions of the mouse isolated vas deferens evoked, in the presence of captopril (3 microM), by electrical field stimulation with trains of 4 rectangular 0.5 ms pulses of supramaximal strength, delivered at a frequency of 10 Hz every 20 s. 2. BK (0.1-300 nM) induced a graded potentiation of twitches, with an EC50 (geometric mean and 95% confidence limits) of 4.5 nM (1.7-11.6) and an Emax of 315 +/- 19 mg per 10 mg of wet tissue (n = 6). Similar results were obtained in tissues challenged with Lys-BK, [Hyp3]-BK, Met,Lys-BK and the selective B2 receptor agonist [Tyr(Me)8]-BK (0.1-300 nM). 3. The selective B2 receptor antagonists, Hoe 140 (1-10 nM) and NPC 17731 (3-30 nM), caused graded rightward shifts of the curve to BK-induced twitch potentiation, yielding apparent pA2 values of 9.65 +/- 0.09 and 9.08 +/- 0.13, respectively, and Schild plot slopes not different from 1. Both antagonists (100 nM) failed to modify similar twitch potentiations induced by substance P (3 nM) or endothelin-1 (1 nM). Preincubation with the selective B1 receptor antagonist, [Leu8,des-Arg9]-BK (1 microM), increased the potentiating effect of BK on twitches at 30-300 nM. 4. In contrast to BK, the selective B1 receptor agonist, [des-Arg9]-BK (0.3-1000 nM) reduced the amplitude of twitches in a graded fashion, with an IC50 of 13.7 nM (10.4-16.1) and an Imax of 175 +/- 11 mg (n = 4). The twitch depression induced by [des-Arg9]-BK (300 nM) was not affected by Hoe140 (30nM) or NPC 17731 (100nM), but was abolished by the selective B1 receptor antagonist,[Leu8,des-Arg9]-BK (1 microM), which did not modify the twitch inhibitory effect of clonidine (1 nM) or morphine (300 nM).5. In non-stimulated preparations, BK (100 nM) also potentiated, in a Hoe 140-sensitive (10 nM)manner, the contractions induced by ATP (100 microM), but not by noradrenaline (10 microM), whereas[des-Arg9]-BK (300 nM) did not modify the contractions induced by either agonist.6. It is concluded that the mouse vas deferens expresses both B1 and B2 receptors, which modulate sympathetic neurotransmission in opposing ways. Neurogenic contractions are inhibited by stimulation of possibly prejunctional B, receptors, whereas activation of B2 receptors increases twitch contractions,in part by amplifying the responsiveness of the smooth muscle cells to the sympathetic co-transmitter ATP.

A preliminary investigation of the mechanisms underlying cannabinoid tolerance in the mouse vas deferens

Vasa deferentia taken from mice treated with delta 9-tetrahydrocannabinol (20 mg/kg i.p., once daily for 2 days) showed tolerance to the inhibitory effect of the cannabinoid, R-(+)-arachidonyl-1'-hydroxy-2'-propylamide, on electrically evoked twitches. This treatment did not induce tolerance to the inhibitory effects on the twitch response of morphine or clonidine or of selective mu-, delta- or kappa-opioid receptor agonists. Nor did it affect the contractile potencies of noradrenaline or beta,gamma-methylene-L-ATP. We suggest that cannabinoid tolerance in the vas deferens is attributable neither to downregulation of opioid receptors or alpha 2-adrenoceptors nor to an increased sensitivity of this tissue to its main contractile transmitters noradrenaline and ATP. A concentration of delta 9-tetrahydrocannabinol that inhibits electrically evoked twitches of the vas deferens (100 nM) did not alter the ability of noradrenaline or beta,gamma-methylene-L-ATP to induce contractions suggesting that delta 9-tetrahydrocannabinol inhibits the twitch response by acting prejunctionally.

New insights into the local regulation of blood flow by perivascular nerves and endothelium

Blood flow, particularly in the skin, is essential for the success of plastic surgical operations. This review describes recent studies of the perivascular nerves and vascular endothelial cells which regulate blood flow. Perivascular nerves, once considered simply adrenergic or cholinergic, release many types of neurotransmitters, including peptides, purines and nitric oxide. Cotransmission (synthesis, storage and release of more than one transmitter by a single nerve) commonly takes place. Some afferent nerves have an efferent (motor) function and axon reflex control of vascular tone by these "sensory-motor" nerves is more widespread than once thought. Endothelial cells mediate both vasodilatation and vasoconstriction. The endothelial cells can store and release vasoactive substances such as acetylcholine (vasodilator) and endothelin (vasoconstrictor). The origins and functions of such vasoactive substances are discussed. Endothelial vasoactive substances may be of greater significance in the response of blood vessels to local changes while perivascular nerves may be concerned with integration of blood flow in the whole organism. The dual regulation of vascular tone by perivascular nerves and endothelial cells is altered by aging and conditions such as hypertension, as well as by trauma and surgery. Studies of vascular tone in disease and after denervation or mechanical injury suggest possible trophic interactions between perivascular nerves and endothelial cells. Such trophic interactions may be important for growth and development of the two control systems, particularly in the microvasculature where neural-endothelial separation is small.

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.

Evoked noradrenaline release in the rabbit ear artery: enhancement by purines, attenuation by neuropeptide Y and lack of effect of calcitonin gene-related peptide

1. Adenosine (30 microM) and its analogues 5'-N-ethylcarboxaminoadenosine (5 and 30 microM) and L-phenylisopropyladenosine (5 and 30 microM), potentiated the evoked but not spontaneous release of tritiated noradrenaline in the rabbit central ear artery. 2. Prejunctional inhibition of the evoked but not spontaneous release of tritiated noradrenaline by 100 nM neuropeptide Y is greater at 2 min than at 10 min after superfusion of the peptide. 3. Calcitonin gene-related peptide (2.63 to 263 nM) did not affect the evoked or spontaneous release of tritiated noradrenaline in this preparation. 4. These results are discussed in terms of prejunctional modulation of sympathetic transmission in the rabbit central ear artery.

Some noradrenergic neurons of locus ceruleus-olfactory pathways contain neuropeptide-Y

We report a specific tracing technique for studying projections of noradrenergic neurons that contain other transmitters. Autoradiography after retrograde axonal transport of tritiated-noradrenaline ([3H]NA) was combined with immunocytochemical detection of endogenous NA or neuropeptide Y (NPY). The specificity of [3H]NA retrograde labeling was dependent on the concentration of [3H]NA injected at the terminal region. At 2 x 10(-3) M, the specificity of [3H]NA retrograde labeling was confirmed by immunodetection of endogenous NA in radiolabeled cell bodies of the locus ceruleus. Combination of autoradiography of [3H]NA retrograde labeling with immunodetection of NPY demonstrated that a some scattered locus ceruleus noradrenergic neurons (about 26%) projecting to the olfactory bulb do contain NPY.

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.

Adrenergic and nonadrenergic cotransmitters inhibit insulin secretion during sympathetic stimulation in dogs

Vascular and biochemical responses to pancreatic sympathetic nerve stimulation were investigated in the blood-perfused pancreas of anesthetized dogs. During sympathetic nerve stimulation, pancreatic perfusion pressure and norepinephrine release increased, whereas insulin secretion decreased. The latter effect did not occur after pretreatment with the alpha 2-adrenoceptor antagonist idazoxan. However, after beta-adrenoceptor blockade with propranolol, neither single administration of idazoxan nor the alpha 1-adrenoceptor antagonist prazosin or glibenclamide, a blocker of ATP-modulated K+ channels, affected the decrease in insulin secretion induced by sympathetic nerve stimulation. In contrast, the combination of glibenclamide with idazoxan markedly antagonised the decrease in insulin release evoked by the latter procedure. After depletion of catecholamines with syrosingopine, the stimulation-induced inhibition of insulin secretion remained unchanged even though no increases in pancreas perfusion pressure or norepinephrine release were observed. In this preparation, glibenclamide inhibited the decrease in insulin release by 50%. In animals pretreated with the neuronal blocking agent bretylium, all of the responses to sympathetic nerve stimulation were abolished. These results indicate that the inhibitory effects exerted by the sympathetic nervous system on insulin secretion are mediated not only by the classical neurotransmitter norepinephrine acting on alpha 2-adrenoceptors but also by a nonadrenergic cotransmitter that can maintain transmission under conditions of catecholamine deficiency. The postulated nonadrenergic cotransmitter(s) acts, at least partly, via the opening of ATP-modulated K+ channels blockable by glibenclamide, and its release can be prevented by the neuronal blocking agent bretylium.

NPY-stimulated Ca2+ mobilization in SK-N-MC cells is enhanced after isoproterenol treatment

Neuropeptide Y (NPY) receptors in the SK-N-MC human neuroblastoma cell line couple to mobilization of intracellular Ca2+ and inhibition of adenylylcyclase. Pretreatment of SK-N-MC cells with isoproterenol enhanced the NPY-stimulated Ca2+ mobilization, mainly by increasing the maximal response to NPY. The enhancement was time-(maximal after 24 h) and concentration-dependent (maximal at 10 microM isoproterenol), blocked by the beta-adrenergic antagonist propranolol, and mimicked by forskolin. Concomitant treatment with cycloheximide prevented the enhancing effect of isoproterenol, suggesting the involvement of protein synthesis. Isoproterenol treatment did not alter the number or affinity of 125I-labeled NPY binding sites, the amount of pertussis toxin substrates, or NPY-mediated inhibition of cAMP accumulation. Similarly, isoproterenol treatment had no effect on basal intracellular Ca2+ and on Ca2+ increases elicited by carbachol, caffeine, or ionomycin. We conclude that isoproterenol treatment can sensitize NPY receptor responsiveness in a way that is specific for Ca2+ mobilization mechanisms used by this hormone.

Haloperidol-induced increase in neuropeptide Y immunoreactivity in the locus coeruleus of the rat brain

The effect of haloperidol, a dopamine (preferably D2) receptor blocking agent on neuropeptide Y immunoreactivity was studied immunohistochemically in neurons of the locus coeruleus and striatum of rat brain. It was found that haloperidol given four times (5 and 2.5 mg/kg, i.p.) induced, after 24 h, a significant increase in the level of neuropeptide Y immunoreactivity in the locus coeruleus but not in the striatum. No changes in neuropeptide Y immunoreactivity in studied structures were observed after alpha-adrenergic receptor blocking agent phenoxybenzamine or serotonin-synthesis inhibitor D,L-p-chlorophenylalanine. The results suggest that the content of neuropeptide Y-immunoreactive material in nerve cell bodies of the locus coeruleus is inhibitorally controlled by monoaminergic (may be dopaminergic D2) receptors.

Postnatal development and distribution of peptide-containing nerves in the genital system of the male rat. An immunohistochemical study

The distribution and relative density of peptide-containing nerves was studied in the rat in order to assess the progression of neuronal changes during the postnatal development of the male genital system from the prepubertal age to adulthood. Testis, caput and cauda epididymis, ductus deferens, seminal vesicles, prostate and penis from 8-, 20-, 38-, and 70-day-old rats were sectioned and were immunostained with antisera to the neuropeptides calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), and to a general neuronal marker, protein gene product 9.5 (PGP 9.5). The testicular parenchyma and caput epididymis did not show any immunoreactivity. Very scattered CGRP-containing nerves were present in 8-day-old rats; numerous VIP-, CGRP-, and NPY-peptide-containing nerves were observed in the cauda epididymis, ductus deferens, accessory glands and penis of 20-day-old rats. The number of nerves increased in 35-day-old rats while no changes were observed in more adult rats. A parallel increase was seen for the immunostain for PGP 9.5. These data suggest that peptide-containing nerves appear in the genital system after birth and reach a full development before the completion of puberty. Peptide-containing nerves were visible first in the interstitial area and then spread in the muscular coat of the ducts, glands and of the blood vessels. While CGRP- and NPY-containing nerves were distributed in the vicinity of the muscle cells, VIP-containing nerves were also observed in the subepithelial regions, suggesting a possible role of this neuropeptide in the control of epithelial functions.

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.

Neuropeptide Y (NPY) metabolism by endopeptidase-2 hinders characterization of NPY receptors in rat kidney

1. Despite the observation of pharmacological responses to neuropeptide Y (NPY) in mammalian kidneys, there are species differences in the ease with which specific NPY binding sites can be demonstrated; we have investigated whether this can be explained by differential metabolism of NPY by a membrane-bound peptidase. 2. NPY receptors were identified on cell membranes isolated from the rabbit kidney (KD = 97 +/- 16 pM, Bmax = 290 +/- 30 fmol mg-1 protein), and this preparation did not degrade [125I]-NPY. However, a similar preparation of cell membranes from the rat kidney exhibited a much lower apparent receptor affinity (IC50 approximately 30 nM); these membranes rapidly degraded [125I]-NPY to fragments which did not bind NPY receptors in either tissue. 3. [125I]-NPY binding sites were revealed in the rat kidney when degradation was inhibited by insulin B chain. Chelating agents also inhibited degradation, but interfered with receptor binding. Binding sites could not be demonstrated in sections of rat kidney, even in the presence of insulin B chain. 4. The difference in degradative activity between rat and rabbit renal cell membranes, inhibition of degradation by chelating agents and insulin B chain, and insensitivity to phosphoramidon suggest that the enzyme responsible was endopeptidase-2, and this was confirmed by comparing the hydrolysis of [125I]-NPY by purified enzyme with rat renal tissue. Activity of this enzyme explains the difficulties encountered demonstrating receptors in the rat kidney. 5. Renal cell membranes from the mouse digested [125I]-NPY in a similar manner and this may be due to the closely related enzyme, meprin. NPY degradation has not previously been reported. The results suggest that NPY should be added to the list of peptides sensitive to these enzymes.

Brain neuropeptide Y: an integrator of endocrine, metabolic and behavioral processes

Neuropeptide Y (NPY), acting through various medial hypothalamic nuclei, is found to have potent effects on a variety of endocrine, physiological and behavioral systems that modulate energy balance. This peptide affects the release of various hormones, such as corticosterone, insulin, aldosterone and vasopressin, which modulate energy metabolism, as well as food intake. It also has direct impact on energy metabolism through an effect on substrate utilization and lipogenesis. Finally, NPY has a remarkably potent stimulatory effect on feeding behavior, which is characterized by a selective increase in carbohydrate ingestion that is strongest at the beginning of the active feeding cycle and is dependent upon circulating levels of corticosterone. This evidence has led to the proposal that NPY exerts anabolic effects to restore energy balance at specific times of energy depletion. Increased NPY activity may occur at the beginning of the active cycle or after a period of food deprivation. Further evidence, that chronic NPY stimulation produces profound hyperphagia and obesity and that endogenous NPY concentration is increased in genetically obese animals, strongly suggests that hypothalamic NPY may contribute to the development of eating disorders and obesity.

Peptide YY reduces effects of sympathetic nerves and neuropeptide Y on cardiac vagal action

In anesthetized dogs intravenous injection of neuropeptide Y (NPY) or stimulation of the cardiac sympathetic nerve is followed by a period of attenuation of vagal action at the heart lasting from many minutes to over an hour. Peptide YY (PYY), a related peptide (but one not reported to occur in the heart or its autonomic innervation), also inhibits cardiac vagal action but is more powerful and has a longer duration action. In 5 of 9 dogs, cardiac sympathetic nerve stimulation inhibited vagal action on the heart in control conditions, but relieved preexisting inhibition when repeated in the presence of PYY. In 3 dogs, exogenous NPY inhibited cardiac vagal action in control conditions, but failed to augment preexisting inhibition in the presence of PYY. An explanation offered for these results is that when PYY is occupying receptors on vagal nerve terminals, nerve-released NPY or exogenous NPY is either unable to produce an effect, because it cannot gain access to the receptors, or displaces PYY from at least some receptors and, being less powerful than PYY in its inhibitory action, lessens the preexisting vagal attenuation. The results reported are consistent with the proposal that the factor released from the sympathetic nerves following their stimulation and which is responsible for cardiac vagal inhibition is NPY.