Non-adrenergic Non-cholinergic Inhibitory Nerves Research Articles

Role of the enteric nervous system in the elongated sigmoid colon of patients with sigmoid volvulus.

To clarify the physiologic function of the enteric nervous system (ENS) in the elongated sigmoid colon (ESC) of patients with sigmoid volvulus (SV), we examined the enteric nerve responses in lesional and normal longitudinal muscle strips (LMS) derived from patients with ESC and patients who underwent colon resection for colonic cancers. Thirty preparations of LMS were taken from the lesional sigmoid colons of 10 ESC patients with SV (8 men and 2 women, aged 53 to 80 years, mean 66.2 years). Forty preparations of LMS were taken from the normal sigmoid colons (NSC) of 20 patients with colonic cancer (12 men and 8 women, aged 55 to 76 years, mean 62.3 years). A mechanographic technique was used to evaluate in vitro muscle responses to electrical field stimulation (EFS) before and after treatment with various autonomic nerve blockers. Response to EFS before blockade of the adrenergic and cholinergic nerves was as follows: NSC and ESC significantly demonstrated relaxation reaction rather than contraction reaction (P = 0.0253, P < 0.0001, respectively). ESC showed relaxation reaction more than NSC (P = 0.1138). Response to EFS after blockade of the adrenergic and cholinergic nerves was as follows: NSC and ESC significantly demonstrated relaxation reaction via nonadrenergic noncholinergic (NANC) inhibitory nerves rather than contraction reaction via NANC excitatory nerves (P < 0.0001, P < 0.0001, respectively). ESC with SV significantly showed relaxation reaction more than NSC (P = 0.0092). An increased response of relaxation mediated NANC inhibitory nerves may play a role in impaired motility in the ESC of patients with SV.

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

Substance P and vasoactive intestinal peptide in rat small-bowel isografts

Background It is established that substance P (SP) is released by stimulation of nonadrenergic noncholinergic (NANC) excitatory nerves and vasoactive intestinal peptide (VIP) by stimulation of NANC inhibitory nerves. To evaluate the function of peptidergic nerves such as SP and VIP in small-bowel isografts, we examined the enteric nerve responses to SP and VIP in the isografted rat jejunum, using the normal rat jejunum as a control. Methods Orthotopic entire small bowel transplantation (SBT) with portocaval drainage was performed from Lewis rats to Lewis rats. Grafted tissue specimens were obtained 130 days after SBT (n = 9). As controls, normal segments of the jejunum were obtained from untransplanted Lewis rats (n = 22). A mechanograph was used to evaluate in vitro jejunal responses to electrical field stimulation of the enteric nervous system before and after treatments with various autonomic nerve blockers and neuropeptides (SP and VIP). Results SP concentration-dependently mediated the contraction reaction of NANC excitatory nerve in the isografted jejunum and to a lesser extent in the normal jejunum. In addition, there were significant diferences in the percentages showing contraction at 1 × 10 −8 and 1 × 10 −6g/mL SP between the normal and isografted jejunal muscle strips ( P < .05, respectively). VIP concentration dependently mediated the relaxation reaction of NANC inhibitory nerve in the normal jejunum and to a lesser extent in the isografted jejunum. In addition, there was a significant difference between the relaxation frequencies of the normal and those of isografted jejunal muscle strips at 1 × 10 −6 g/mL SP ( P < .01). Conclusions Contraction reactions of SP were observed in both the normal and isografted jejunum but were increased in the isografted jejunum. Relaxation reactions of VIP were also observed in both the normal and isografted jejunum but were decreased in the isografted jejunum. The increase of the effects of SP via NANC excitatory nerves and the decrease of the effects of VIP in mediating NANC inhibitory nerves may be largely related to the peristaltic abnormalities seen in the isografted LEW rat jejunum.

Physiological studies on vasoactive intestinal peptide in rat small bowel isografts

Background Vasoactive intestinal peptide (VIP) is released by stimulation of nonadrenergic noncholinergic (NANC) inhibitory nerves. In order to evaluate the function of VIP in jejunal isografts, we examined the enteric nerve responses in isografted rat jejunum compared with normal jejunum. Methods Orthotopic entire small bowel transplantation (SBT) with portocaval drainage was performed from Lewis rats to Lewis rats. Grafted tissue specimens were obtained 130 days after SBT ( n = 8). As controls, normal segments of the jejunum were obtained from nontransplanted Lewis rats ( n = 20). A mechanograph was used to evaluate in vitro jejunal responses to electrical field stimulation (EFS) of the adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers and VIP. Results The isografted jejunum was more strongly innervated by excitatory nerves, especially NANC excitatory nerves, than the normal jejunum ( P < .05). VIP mediated relaxation reactions of NANC inhibitory nerves in the normal but to a lesser extent in the isografted jejunum ( P < .05). Conclusions The increased NANC excitatory nerves and the decreased effects of VIP in mediating NANC inhibitory nerves may largely relate to the peristaltic abnormalities seen in the isografted LEW rat jejunum.

Physiologic studies on nitric oxide in rat small bowel isografts.

The enteric nervous system (ENS), especially the nonadrenergic noncholinergic (NANC) inhibitory nerves, is an important factor in intestinal peristalsis. Recently, it was established that nitric oxide (NO) is released after stimulation of NANC inhibitory nerves. Inhibitory nerves such as NANC inhibitory nerves in the ENS are more easily damaged than excitatory nerves by reperfusion or ischemic injuries during small bowel transplantation (SBT). To evaluate the effects of reperfusion and ischemic injuries to the ENS in the transplanted small bowel, we examined the ENS responses, including the effects of NO in the isografted rat jejunum, using the nontransplanted jejunum as a control. To avoid potentially confounding immune phenomena, we used syngeneic Lewis (LEW) rats. Orthotopic entire SBT with portocaval drainage was performed from LEW rats to LEW rats. Isografted muscle strips were obtained from 8 LEW rats 130 days after SBT (n = 24). As controls, normal muscle strips of the jejunum were obtained from 20 nontransplanted LEW rats (n = 60). A mechanograph was used to evaluate in vitro jejunal responses to electrical field stimulation of the adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers, N(G)-nitro-Ll-arginine ( L-NNA), and L-arginine. The results indicated that excitatory nerves, especially NANC excitatory nerves, were more dominant in the isografted jejunum than in the normal jejunum (p < 0.01). NANC inhibitory nerves were found to act on the normal jejunum and to a lesser extent on the isografted jejunum (p < 0.05). NO mediates the relaxation reaction of NANC inhibitory nerves in the normal jejunum and to a lesser extent in the isografted jejunum. These results indicated that the intrinsic intestinal innervation contains excitatory and inhibitory nerves and that the former, especially NANC excitatory nerves, are more dominant in the isografted jejunum than in the normal jejunum. In addition, reduction of the action of NANC inhibitory nerves such as that by NO may be largely related to impaired motility in the isografted jejunum. Thus over a long period of time (more than 130 days after SBT) transplanted small bowel dysmotility may be influenced by reperfusion or ischemic injury to the ENS (especially NANC inhibitory nerves) via NO in the transplanted jejunum after syngeneic SBT.

The role of nitric oxide (NO) in the human internal anal sphincter.

Nitric oxide (NO) has recently been shown to be a neurotransmitter in nonadrenergic noncholinergic (NANC) inhibitory nerves in the human gut. To clarify the physiological significance of NO in the human internal anal sphincter (IAS), we investigated enteric nervous responses in normal IAS muscle strips above the dentate line, obtained from patients with rectal cancer. Normal IAS muscle strips above the dentate line, obtained from ten patients who underwent rectal amputation for low rectal cancers were used. The subjects consisted of eight men and two women, aged from 46-72 years (mean age, 54.2 years). A mechanographic technique was used to evaluate in-vitro IAS muscle responses to electrical field stimulation (EFS) of adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers, N(G)-nitro-L-arginine (L-NNA) and L-arginine. Excitatory nerves were mainly involved in the regulation of enteric nerve responses to EFS in the baseline condition of the study, and NANC inhibitory nerves acted on the normal IAS. L-NNA concentration-dependently inhibited the relaxation in response to EFS in the human IAS, and this inhibitory effect in the IAS was reversed by L-arginine. These findings suggest that NANC inhibitory nerves play important roles in regulating relaxation of the human IAS, and that NO plays an important role as a neurotransmitter in NANC inhibitory nerves of the human IAS.

Characterization of non‐adrenergic, non‐cholinergic inhibitory responses of the isolated guinea‐pig trachea: differences between pre‐ and post‐ganglionic nerve stimulation

1 Differences in the mechanism of non-adrenergic, non-cholinergic (NANC) inhibitory responses to preganglionic- and post-ganglionic nerve stimulation were investigated in the guinea-pig isolated trachea. 2 Stimulation of the vagus nerve at frequencies above 4 Hz elicited NANC relaxation of the trachealis muscle. Responses to low frequencies of stimulation (4-8 Hz) were abolished by the nitric oxide (NO) synthase inhibitor L-NOARG (10 microM), while a L-NOARG resistant component was observed at higher stimulus frequencies. The L-NOARG-resistant component of NANC inhibitory responses to higher frequencies of vagus nerve stimulation were significantly attenuated by the proteinase alpha-chymotrypsin (2 U/ml), suggesting that a neuropeptide such as VIP may contribute to NANC responses. 3 When postganglionic nerves were stimulated by electrical field stimulation (EFS), responses were readily elicited at frequencies below 4 Hz. Like responses to vagus nerve stimulation, responses to low frequency (<4 Hz) EFS were abolished by L-NOARG while a L-NOARG-resistant component was apparent at higher stimulus frequencies. 4 The L-NOARG-resistant component of NANC inhibitory responses to EFS was sensitive to alpha-chymotrypsin only if stimuli were delivered in either long trains at a low frequency (4 Hz for 10-30 s) or short trains of high frequency (16 Hz for 2.5-7.5 s). 5 Responses to preganglionic nerve stimulation were approximately 35% of the amplitude of responses to EFS in the same preparations. 6 In conclusion, responses to preganglionic and postganglionic NANC inhibitory nerve stimulation in the guinea-pig trachea differ in maximum amplitude, frequency-response characteristics and the contributions of cotransmitters. We suggest that these differences may be explained by filtering of preganglionic input to postganglionic NANC neurons. These results have implications in all studies where EFS is considered to be representative of physiological stimulation of post-ganglionic nerve stimulation.

Distribution of nitric oxide synthase in stomach wall in rats.

It has been shown that neuronal nicotinamide adenene dinucleotide phosphate-diaphorase (NADPH-d) may correspond to the neuronal nitric oxide synthase (NOS), and may be used as a marker for NOS in the central and peripheral nervous system. Thus, NADPH-d histochemistry provides us with a mean to specifically identify neurons producing nitric oxide (NO)[1,2]. Recent pharmacological and physiological-stu-dies demonstrated that NO is a neurotransmitter in the non-adrenergic non-cholinergic (NANC) in-hibitory nerves in the mammalian gastrointestinal tract. It may play a very important role in then euronal regulation of gut. NOS activity is present in neurons and fibers of the major enteric nerve layer in intestine[3]. However, there have been far fewer studies of NOS activity in stomach wall. If NO is a transmitter of NANC in hibitory nerves, it should be present in neurons innervating the muscularis. What proportion of nerves produce NO? What is the pattern of innervation of these neurons? To answer these questions, we examined the distribution and morphological feature of NOS positive neurons in the stomach wall with improved whole mount preparation technique.

Effects of suramin on electrical and mechanical activities in antrum smooth muscle of the guinea-pig stomach.

The effects of suramin on electrical and mechanical responses produced by adenosine triphosphate (ATP), acetylcholine and transmural nerve stimulation were observed in antrum smooth muscle isolated from the guinea-pig stomach. Suramin (>10(-6) M) inhibited the non-adrenergic non-cholinergic inhibitory junction potential, with no alteration of the resting membrane potential, slow wave and the ATP-induced responses (hyperpolarization and inhibition of slow waves). The amplitude, but not the frequency, of spontaneous rhythmic contraction was inhibited by suramin (>10(-5) M), with no alteration of electrical responses of the membrane. Transmural nerve stimulation elicited cholinergic excitatory and non-adrenergic non-cholinergic inhibitory responses on the spontaneous contraction, and suramin inhibited only the latter. Suramin did not alter the ATP-induced inhibition of spontaneous contraction. The contractions produced by low concentrations (<10(-7) M), but not high concentrations (10(-6) - 10(-5) M), of acetylcholine were inhibited by suramin. It is concluded that in smooth muscle of the guinea-pig antrum, suramin inhibits contractions produced spontaneously and by low concentrations of acetylcholine, with no relation to the electrical responses of the membrane. Parallel inhibition by suramin of the electrical and mechanical responses elicited by excitation of non-adrenergic non-cholinergic inhibitory nerves may not be causally related to the inhibition of ATP-receptors.

Role of non-adrenergic non-cholinergic inhibitory nerves in the colon of patients with ulcerative colitis.

The cause of impaired colonic motility in patients with ulcerative colitis (UC) is unknown. The non-adrenergic non-cholinergic (NANC) inhibitory nervous system is one of the most important factors in the enteric nervous system of human gut. To assess the physiological significance of NANC inhibitory nerves in the colon of patients with UC, we investigated the enteric nerve responses of colonic tissues from patients with this disease. Colonic tissues were obtained from the lesional sigmoid colons of six patients with UC. Normal sigmoid colonic tissues obtained from ten patients with colonic cancer were used as controls. A mechanographic technique was used to evaluate in-vitro muscle responses to the electrical field stimulation (EFS) of adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers. NANC inhibitory nerves were found to act on both normal colon and the lesional colon of patients with UC, but colon with UC was more strongly innervated by NANC inhibitory nerves than was the normal colon. These findings suggest that NANC inhibitory nerves play an important role in the impaired motility observed in the colon of patients with UC.

Role of nitric oxide in the colon of patients with ulcerative colitis.

The cause of impaired motility, such as diarrhea and toxic megacolon, in patients with ulcerative colitis (UC) is unknown. Nitric oxide (NO) has been shown to be a neurotransmitter in the nonadrenergic noncholinergic (NANC) inhibitory nerves in the human gut. To assess the physiologic significance of NO in the colon of patients with UC, we investigated enteric nerve responses on lesional and normal bowel segments derived from patients with ulcerative colitis (n = 6) and patients who underwent colon resection for colonic cancers (n = 10). A mechanographic technique was used to evaluate in vitro muscle responses to electrical field stimulation (EFS) of adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers, including NG-nitro-L-arginine (L-NNA) and L-arginine. The results showed that (1) NANC inhibitory nerves were found to act on both normal colon and UC colon; (2) the colon with UC was more strongly innervated by NANC inhibitory nerves than the normal colon; (3) L-NNA concentration-dependently inhibited the relaxation in response to EFS in the colon of both normal and UC colon; and (4) this inhibitory effect in the colon of both normal and UC patients was reversed by L-arginine; (5) NO acts more strongly in the UC colon than the normal colon. These findings suggest that NANC inhibitory nerves play an important role in the impaired motility observed in patients with UC and that NO plays an important role as a neurotransmitter in NANC inhibitory nerves of human colon.

Contribution of Nitric Oxide and Sensory Transmitters to Non-adrenergic, Non-cholinergic Innervation of Nasal Blood Vessels

The possible contribution of a non-adrenergic, non-cholinergic (NANC) vasodilator mechanism in human nasal mucosa was studied using an in vitro muscle tension measuring technique. Strips of the nasal mucosa were suspended in a Magnus tube filled with Krebs solution and aerated with 95% O 2 . Isometric changes in tension were detected on administration of various drugs under electric stimulation and recorded with a transducer. The relaxing reaction under electrical train pulse stimulation with pretreatment of blockers of the autonomic nerves was suppressed by nitric oxide synthase inhibitor (L-NAME) and antagonists to the receptors of sensory nerve transmitters (Spantide, hCGRP8-37). This result suggests that nitric oxide, substance P and CGRP may be mediators in the NANC inhibitory nerve system.

The role of motilin and cisapride in the enteric nervous system of the lower esophageal sphincter in humans.

To assess the pharmacophysiological significance of the enteric nervous system and the responses of the human lower esophageal sphincter (LES) to motilin and cisapride, the mechanical responses of esophageal tissues from six patients with esophageal cancer and seven patients with gastric cancer were investigated. Circular muscle reactions were recorded to evaluate the in vitro esophageal responses to electrical field stimulation (EFS), motilin, and cisapride, evoking the adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers. The findings of this study revealed that: cholinergic nerves are mainly involved in the regulation of enteric nerves in the steady state, while non-adrenergic non-cholinergic (NANC) inhibitory nerves also exist; motilin may act both via nerves and also directly on the LES smooth muscle; and cisapride releases acetylcholine from the end of the postganglionic fiber of the cholinergic nerve in human LES thereby inducing contraction of the LES. These results suggest that cholinergic and NANC inhibitory nerves play an important role in human LES, and that motilin and cisapride is clinically useful for improving the impaired LES of patients with gastroesophageal reflux.

Relationship between nitric oxide and non-adrenergic non-cholinergic inhibitory nerves in human lower esophageal sphincter.

Nitric oxide (NO) has recently been shown to be a neurotransmitter in the non-adrenergic non-cholinergic (NANC) inhibitory nerves in the gastrointestinal tract. To clarify the the role of NO in the human lower esophageal sphincter (LES), enteric nerve responses in lower esophageal tissue specimens obtained from patients with esophageal cancer (n = 7) and patients with gastric cancer (n = 6) were investigated. A mechanographic technique was used to evaluate in vitro LES muscle responses to electrical field stimulation (EFS) of adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers, including NG-nitro-L-arginine (L-NNA) and L-arginine. Findings were: (1) Cholinergic nerves were those mainly involved in the regulation of enteric- nerve responses to EFS in the steady state, and NANC inhibitory nerves acted on the LES; (2) L-NNA concentration-dependently inhibited the relaxation in response to EFS in the LES; and (3) this inhibitory effect in the LES was reversed by L-arginine. These findings suggest that cholinergic and NANC inhibitory nerves play important roles in regulating contraction and relaxation of the human LES, and that NO plays an important role as a neurotransmitter in NANC inhibitory nerves of the human LES.

Properties of junction potentials in gastric smooth muscle of the rat.

In isolated smooth muscles of the rat stomach, the properties of electrical responses of the membrane elicited by transmural nerve stimulation were studied. The smooth muscle membranes were quiescent in the fundus and spontaneously active with slow waves and often action potentials superimposed on top of the slow wave in the antrum and pylorus. The maximum membrane potentials were larger in the antrum (-50 to -55 mV) than in the fundus (-40 to -45 mV). Transmural nerve stimulation elicited an excitatory junction potential (e.j.p.) which was followed by an inhibitory junction potential (i.j.p.) in the fundus, and an i.j.p. alone in the antrum. The e.j.p. was inhibited by atropine, indicating that this potential was cholinergic in nature. The amplitude of the e.j.p. was increased by apamin or nitroarginine, and the latter was more potent than the former. The i.j.p. was inhibited by apamin or nitroarginine, and was resistant to adrenergic and cholinergic blocking agents, and therefore this potential was non-adrenergic non-cholinergic (NANC) in nature. The inhibitory actions of nitroarginine on the i.j.p. were antagonized by L-arginine, suggesting the involvement of nitric oxide (NO) in this junctional transmission. The results indicate that smooth muscles of the rat stomach receive cholinergic excitatory and NANC inhibitory nerves, and that endogenous NO may either be partly responsible for the generation of the i.j.p. or may modulate the junctional transmissions.

Functional role and histological demonstration of nitric‐oxide‐mediated inhibitory nerves in dog sphincter of Oddi

Nitric oxide (NO) plays an important physiological role in regulating gastrointestinal motility. Involvement of endogenous NO was evaluated in the response to non-adrenergic, non-cholinergic (NANC) nerve stimulation of the dog sphincter muscle of Oddi. Transmural electrical stimulation (TES), nicotine (10(-5) M) and K+ (10 mM) produced only a relaxation in the sphincter muscle strips contracted with substance P, which was not potentiated by atropine. The TES-induced relaxation was abolished by tetrodotoxin (3 x 10(-7) M) and oxyhaemoglobin (1.6 x 10(-5) M), but not affected by atropine (10(-7) M), propranolol (10(-7) M), phentolamine (10(-7) M), indomethacin (10(-6) M), cholecystokinin (CCK, 10(-8) M) and vasoactive intestinal polypeptide (VIP, 10(-8) M). The relaxation was also abolished by treatment with NG-nitro-L-arginine (L-NA, 10(-5) M), an NO synthase inhibitor. Nicotine produced a transient relaxation, which was abolished by tetrodotoxin, hexamethonium (10(-5) M) and L-NA, but not affected by atropine and NG-nitro-D-arginine (D-NA, 10(-5) M). The addition of K+ elicited a transient relaxation, which was abolished by tetrodotoxin and L-NA. The inhibitory effects of L-NA were antagonized by L-arginine (10(-3) M). The presence of neurons containing nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase was histochemically demonstrated in the sphincter of Oddi. These findings may indicate that TES, nicotine and K+ liberate NO from NANC inhibitory nerve which is involved in the relaxation of the dog sphincter of Oddi. The muscular tone does not seem to be regulated by cholinergic nerves under the experimental conditions used.

A role of nitric oxide in Hirschsprung's disease

Nitric oxide (NO) has recently been shown to be a neurotransmitter in the nonadrenergic noncholinergic (NANC) inhibitory nerves in the gastrointestinal tract. To clarify the significance of NO in Hirschsprung's disease (HD), enteric nerve responses in colonic tissue obtained from HD patients were investigated. Colonic tissue specimens were obtained from four patients with HD and from 11 patients without constipation who were used as controls. A mechanograph was used to evaluate in vitro colonic responses to electrical field stimulation (EFS) of the adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers, and N G-nitro-L-arginine (L-NNA) and L-arginine with the following results: (1) NANC inhibitory nerves were found to act on normal human colon, but had no effect on aganglionic colon; (2) L-NNA concentration dependently inhibited the relaxation in response to EFS in the normal colon, but had no effect on aganglionic colon; and (3) this inhibitory effect was reversed by L-arginine in the normal colon, but had no effect on the aganglionic colon. Nitric oxide mediates the relaxation reaction of NANC inhibitory nerves in the human colon, but the effect of NO was absent in aganglionic colon. The loss of action by NO may be implicated in the impaired motility observed in aganglionic colon.

Nitric Oxide: Role as a Relaxant Agonist and Transmitter of Nonadrenergic Noncholinergic Inhibitory Nerves in Guinea Pig Trachea

Nitric oxide (NO) has been proposed as an inhibitory neurotransmitter in guinea pig trachea. Studies were undertaken to examine the relaxant actions of NO and its possible role as a transmitter of nonadrenergic noncholinergic inhibitory (NANCI) nerves and as a modulator of contractile responses in guinea pig trachea.

Functional innervation of bovine ophthalmic artery.

To investigate the functional innervation pattern in smooth muscle of bovine ophthalmic artery, we studied the effect of electrical stimulation and various drugs on the mechanical responses of this muscle using isometric tension recording methods. Electrical stimulation evoked phasic contractions which were abolished by guanethidine and tetrodotoxin (TTX), suggesting that the responses were neurogenic in origin. Phentolamine (10(-5) M) and 10(-5) M timolol did not affect this contractions, but 10(-5) M phentolamine and 10(-6) M prazosin markedly reduced the amplitude of contraction evoked by exogenously applied phenylephrine (10(-5) M). Electrical stimulation applied during sustained contraction evoked by 5-hydroxytryptamine in the presence of guanethidine and atropine evoked relaxation which was markedly suppressed by TTX. These results indicate that bovine ophthalmic artery is innervated by adrenergic nerve fibers, and an unidentified neurotransmitter, other than noradrenaline, may play an important role in the excitatory neuroeffector transmission, and that the tissue is also innervated by non-adrenergic non-cholinergic inhibitory nerve fibers.

Nervous regulation of the tone of the retractor penis muscle in the goat.

The nervous control of the retractor penis muscle (rp) was investigated in the anaesthetized goat. Also, isolated field stimulated strips of the muscle were studied. The noradrenaline (NA) and acetylcholine (ACh) content of the rp was determined, and histochemistry for adrenergic and acetylcholinesterase (AChE) positive nerves was performed. The muscle exhibited spontaneous activity that persisted after section of all nerves. There was, however, also a tendency of the activity to follow the general vasomotor tone, which disappeared after section of the sympathetic chains. The excitatory adrenergic nerves which innervate the muscle come from the sympathetic chains and run along the pudendal, the hypogastric and the pelvic nerves. The rp has a dense network of adrenergic fibres and is very sensitive to excitatory adrenergic stimulation. It has a fairly large NA content, which is higher in old goats (5.95 +/- 0.42 micrograms g-1) than in young goats (2.87 +/- 0.78 micrograms g-1). Inhibitory non-adrenergic non-cholinergic (NANC) innervation reaches it via the pelvic and the hypogastric nerves. The maximum inhibitory response is reached at low frequencies (2-4 Hz). Cholinergic prejunctional inhibition of the excitatory response to sympathetic chain stimulation was effected by simultaneous stimulation of the hypogastric nerves. In vitro experiments confirmed the presence of endogenous cholinergic muscarinic suppression of the excitatory adrenergic neurotransmission. Significant amounts of ACh (0.81 +/- 0.18 micrograms g-1) are present in the muscle, and it contains strongly AChE positive nerve fibres and nerve cell bodies. It is concluded that the goat rp is innervated by sympathetic adrenergic excitatory nerves and parasympathetic NANC inhibitory nerves. It further has a direct sympathetic inhibitory NANC innervation, and an indirect inhibitory cholinergic innervation which at least in part is sympathetic.