Intracisternal antisense oligonucleotides to TRH receptor abolish TRH-evoked gastric motor excitation

Thyrotropin-releasing hormone (TRH) from the nucleus raphe obscurus (nROb) innervates the dorsal vagal complex (DVC) and activates gastric motor function. Assessment of the importance of TRH has been hampered by the lack of TRH receptor antagonists. To overcome this, rats were given intracisternal antisense oligonucleotides against the first 18 bases of TRH receptor mRNA, mismatch oligonucleotides, or saline. Rats were anesthetized, and L-glutamate (15 nmol), TRH (1 and 10 pmol), and saline were microinjected into the DVC and nROb while gastric motor function was monitored. Intracisternal TRH mRNA antisense oligonucleotides abolished the gastric excitatory affects of microinjection of TRH, but not L-glutamate, into the DVC, and the response to TRH recovered after 2 wk of no antisense treatment. Chemical stimulation of the nROb increased intragastric pressure in saline- and mismatch- but not antisense-treated animals. These studies demonstrate that intracisternal TRH receptor antisense oligonucleotides produce a selective and reversible "knockdown" of responsiveness to exogenous TRH in the DVC, as well as to excitation of an endogenous TRH pathway controlling gastric function. It also provides a new tool for assessment of TRH pathways in hindbrain control of gastric function.

Cyclooxygenase inhibition in the dorsal vagal complex of the rat evokes increases in gastric motor function

To characterize the involvement of brainstem cyclooxygenase (COX) in the vagal control of gastric motor function, tolmetin, a reversible COX inhibitor, was applied to the surface of the dorsal medulla oblongata or microinjected into the dorsal vagal complex (DVC) in alpha-chloralose anesthetized rats, while intragastric pressure and contractile activity of the pyloric circular and greater curvature longitudinal muscle were monitored. Tolmetin, applied to the surface of the medulla oblongata, increased intragastric pressure and stimulated contractile activity of gastric smooth muscle. Comparable gastric motor effects were observed after microinjection of tolmetin into the DVC. All the effects of tolmetin were abolished by bilateral vagotomy at the midcervical level. These results demonstrate for the first time that COX inhibition evokes vagally-mediated gastric motor effects in the DVC of the rat and support a role for COX products in gastrointestinal regulation.

Nitric oxide modulates ventilatory responses to hypoxia in the developing rat

Nitric oxide (NO) is an important excitatory neurotransmitter in the central nervous system. In the adult rat, both selective and nonselective blockers of constitutive nitric oxide synthase (NOS) induce marked ventilatory reductions during sustained hypoxia, thereby enhancing ventilatory roll-off. Since hypoxic ventilatory depression is greater in developing mammals during the late phases of hypoxic exposure, we hypothesized that limited NOS activity may play a role in the late arm of the ventilatory response. To test our hypothesis, 5-d-, 10-d-, and 15-d-old rat pups underwent a 30-min hypoxic challenge (10% O2) before and after administration of 100 mg/kg N-nitro-L-arginine methyl ester (L-NAME), a competitive NOS inhibitor. Minute ventilation (VE) was measured using whole-body plethysmography. In 5-d-old pups, early VE hypoxic responses were enhanced, and late VE were similar after administration of L-NAME. In contrast, in 15-d-old hypoxic pups, L-NAME administration was associated with smaller early VE increments and significantly larger VE reductions when compared with pretreatment conditions. The role of central nervous system NO in the development of these ventilatory changes was further assessed by Western blots of protein equivalents from the nucleus tractus solitarius (NTS), the first central relay for peripheral chemoreceptor afferent input, which revealed increasing neuronal NOS expression with age. Furthermore, NADPH-diaphorase immunohistochemical staining of neurons in the NTS revealed increased positively labeled neuronal populations within subnuclei of this structure with advancing postnatal age. Current findings suggest that NOS activity mediates both excitatory and inhibitory components of the hypoxic ventilatory response. Furthermore, in brainstem respiratory regions, NO may play a role in modulating the prominent second phase of the biphasic response to hypoxia typically seen in early postnatal life.

Evidence for a dual mechanism of gastric motor responses to intravenously administered endothelin-1 in anesthetized rats

We have recently reported that endothelin-1 (ET-1), administered intracisternally or microinjected into the DVC of rats, increases gastric motor function via vagal pathways. To determine whether circulating ET-1 acts peripherally or centrally to alter gastric motility, ET-1 (30 and 300 pmol/kg) was administered intravenously in alpha-chloralose anesthetized rats, while monitoring intragastric pressure, gastric motility, heart rate and blood pressure. Endothelin-1, at a dose of 300 pmol/kg, increased intragastric pressure, stimulated pyloric circular muscle contractile activity, and increased arterial pressure. When ET-1 (300 pmol/kg) was administered after bilateral vagotomy at midcervical level, a marked gastric motor inhibition with an increase in arterial blood pressure were observed. We conclude that the gastric motor effects of circulating ET-1 are a result of central excitatory and peripheral inhibitory actions of the peptide.

Hindbrain effects of PACAP on gastric motor function in the rat

Pituitary adenylate cyclase-activating polypeptide (PACAP)-like immunoreactive cell bodies and fibers are visualized in hindbrain nuclei that are involved in the regulation of autonomic function, yet little is known about the gastric and cardiovascular effects of this peptide in the dorsal vagal complex, nucleus raphe obscurus, and nucleus ambiguus. Therefore, multiple-barreled micropipettes were used to inject PACAP-38 (1-100 pmol) into each of these nuclei in alpha-chloralose anesthetized rats, while intragastric pressure, pyloric and greater curvature smooth muscle contractile activity, blood pressure, and heart rate were recorded. For comparison, the effect of L-glutamate (15 nmol) microinjected into the same sites on gastric motor activity was also assessed. L-Glutamate microinjected into each nucleus before PACAP-38 significantly increased intragastric pressure, both in terms of the peak increase and the total area of the response. Microinjections of PACAP-38 (10 and 100 pmol) into each of the nuclei significantly increased peak intragastric pressure, but the total area of the response was only significantly increased by the highest dose (100 pmol) in the case of the dorsal vagal complex and nucleus raphe obscurus. No consistent changes in heart rate and mean arterial blood pressure were noted after microinjection of PACAP-38 into each of the three nuclei. Bilateral vagotomy abolished the increase in intragastric pressure in response to microinjection of PACAP-38 into the dorsal vagal complex and nucleus raphe obscurus. We conclude that PACAP-38 in the dorsal vagal complex and nucleus raphe obscurus is involved in vagally mediated gastric motor excitation.

Distribution of nitric oxide synthase in rat dorsal vagal complex and effects of microinjection of nitric oxide compounds upon gastric motor function

Nitric oxide (NO) has received attention as a vagal nonadrenergic-noncholinergic (NANC) mediator of gastrointestinal relaxation. The dorsal vagal complex (DVC) is the primary hindbrain site of vagal control of the gastrointestinal tract, and yet the subnuclear distribution of NO and its physiological effects have not been analyzed in this nucleus. Therefore, this study estimates the relative number of NO synthase (NOS)-containing neurons in subnuclear regions of the DVC, identifies NOS-containing vagal abdominal preganglionic neurons in the dorsal motor nucleus of the vagus, and defines a role of NO in the DVC in control of gastric motor function. The location of NADPH-diaphorase-positive staining (a marker of NOS activity) and NOS immunoreactivity overlap in the DVC. In the dorsal motor nucleus of the vagus there are positively stained cells caudal to the obex and at its most rostral extent, but not at the intermediate level. Intraperitoneal fluorogold combined with NADPH-diaphorase activity labels approximately 5% and 15% of fluorogold-immunoreactive cells in the caudal and rostral dorsal motor nucleus of the vagus, respectively. Thus, a portion of NOS-containing neurons are preganglionic vagal neurons projecting to the abdominal viscera. In the nucleus tractus solitarius, the majority of NADPH-diaphorase-positive cells are within the centralis, medial, and ventral/ventrolateral subnuclei. Fiber/terminal staining is present in the subnucleus centralis, subnucleus gelatinosus, subpostremal zone, and the medial nucleus tractus solitarius. The presence of NOS terminal staining implicates NO in afferent control of gastric function in the DVC (e.g., vago-vagal circuits in subnucleus gelatinosus). To determine a role of NO in the DVC, NO-related agents were microinjected into the DVC in alpha-chloralose-anesthetized rats while recording indices of gastric motor function. L-Arginine, microinjected into the DVC, significantly decreases intragastric pressure (-2.2 +/- 0.4 cm2, N = 12), and this effect is abolished by vagotomy. Microinjection of an NOS inhibitor, NG-nitro-L-arginine methyl ester, increases intragastric pressure (1.9 +/- 0.7 cm2, N = 10), with the greatest effect in the DVC rostral to the obex. Overall, it was concluded that tonic release of NO in the DVC mediates gastric relaxation, at least in anesthetized animals, and NOS-containing preganglionic neurons in the dorsal motor nucleus of the vagus may be "command" NANC neurons which control a variety of gastrointestinal functions.

Contribution of acetylcholine, vasoactive intestinal polypeptide and nitric oxide to CNS-evoked vagal gastric relaxation in the rat

Several in vitro models of gastric relaxation have elucidated a role of nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) in non-adrenergic, non-cholinergic (NANC) vagally mediated gastric relaxation. However, these models do not necessarily mimic the events leading to gastric relaxation in the whole animal. We have recently described a vagally mediated gastric relaxation evoked by micro-injection of substance P (SP) into the nucleus raphe obscurus (NRO). The present study was performed to elucidate whether this CNS-stimulated in vivo gastric relaxation involved acetylcholine, NO and VIP. Atropine (1 mg kg-1 i.v.), reduces both the rapid nadir and sustained gastric relaxation evoked by SP in the NRO, and the residual responses are abolished by NG-Nitro-L-arginine methyl ester hydrochloride (L-NAME, 10 mg kg-1 i.v.), an NO synthase inhibitor. Blockade of NO synthase alone is not sufficient to abolish the effect of SP into the NRO on intragastric pressure. A VIP antagonist, [p-chloro-D-Phe6, Leu17]VIP (32 micrograms i.v.) alone, or with the addition of L-NAME, does not affect the nadir of the gastric relaxation in response to SP microinjected into the NRO; however, both antagonists reduce the CNS-evoked sustained intragastric pressure relaxation. We conclude that, in CNS-evoked gastric relaxation, inhibition of cholinergic pathways is potentially important for both the rapid nadir and sustained gastric relaxation, and both NO and VIP contribute to sustained gastric relaxation.

The inhibitory effect of substance P on gastric motor function in the nucleus raphe obscurus is mediated via nitric oxide in the dorsal vagal complex

We have previously shown that substance P (SP), microinjected into the caudal nucleus raphe obscurus (nROb) of the rat decreases intragastric pressure via a vagally mediated pathway. Recent studies from this laboratory demonstrated that nitric oxide (NO) synthase is present in the dorsal vagal complex (DVC) and NO synthase blockade in the DVC of the rat with NG-nitro-L-arginine methyl ester (L-NAME) evokes increases in intragastric pressure. Since the nROb controls gastric vagal outflow through the DVC, we tested the hypothesis that NO in the DVC is a mediator of inhibitory effects of SP on gastric motor function in the nROb. Substance P (135 pmol) was microinjected into the nROb 3-6 min after bilateral microinjections of L-NAME (45 nmol per site) into the DVC of chloralose-anesthetized rats were started. Changes in the area of the response for intragastric pressure on microinjection of SP after L-NAME did not differ from the effect of vehicle microinjected after L-NAME and were significantly lower when compared with the effect of SP microinjected after vehicle. We conclude that SP in the nROb release NO in the DVC to mediate the inhibitory effect on intragastric pressure.

Pulmonary pharmacology

This article reviews the basic principles of pharmacodynamics and pharmacokinetics, with a special emphasis on the pharmacologic considerations that must be taken into account when treating the patient with respiratory disease who is also pregnant or nursing the neonate. A description of the four classes of therapeutic agents used for COPD is given with a discussion of the scientific evidence for their safety during pregnancy. The understanding of asthma suggests that bronchodilators relieve the symptoms, while antiinflammatories suppress the disease. Direct administration to the target tissue by inhalation of the bronchodilators (beta-adrenoreceptor agonists and anticholinergics) and immunosuppressors (corticosteroids and cromolyn) leads to low systemic levels of these drugs, which reduces fetal drug exposure. Oral administration of beta-adrenoreceptor agonists, corticosteroids, and theophylline may be necessary to obtain sufficient maternal lung function and ensure adequate oxygenation of the fetus. This must be carefully weighed against the potential fetal and maternal risks involved with increased systemic levels of these drugs. A brief description of classes of drugs used for upper respiratory diseases (antihistamines, alpha-adrenergic agonists, corticosteroids, antitussives, and expectorants) and their safety during pregnancy is also given. There is concern that most alpha-adrenergic agonists increase blood pressure at therapeutic doses needed to relieve nasal congestion. Therefore, for pregnant patients requiring decongestants, opinion favors administration of pseudoephedrine, which has the most favorable therapeutic index, to reduce potential cardiovascular adverse reactions in the fetus. Intranasal administration of the newer corticosteroids, which have limited absorption, is useful for suppression of allergic rhinitis, while minimizing the risk of adverse reactions. The purpose of this article has been to provide pharmacologic/toxicologic information about commonly used respiratory drugs. This will to enable the clinician to make an educated decision regarding the choice of therapy for respiratory disorders to ensure that fetal and maternal outcomes are optimal.

Pancreatic polypeptide, microinjected into the dorsal vagal complex, potentiates glucose-stimulated insulin secretion in the rat

Specific binding sites for circulating pancreatic polypeptide (PP) have been found within the dorsal vagal complex (DVC) in the caudal medulla oblongata. Therefore, the effects of rat PP on pancreatic hormone secretion upon its microinjection into the DVC in halothane-anesthetized rats at doses of 0.4-40 pmol were investigated. At this range of doses, the changes in plasma concentrations of insulin, glucagon and glucose over basal levels did not differ from those after vehicle microinjection. In a separate series of experiments, vehicle and PP at doses of 0.4 and 4 pmol were microinjected into the right DVC 40 min after the continuous infusion of D-glucose had been started. In animals receiving continuous infusion of D-glucose, PP microinjected into the DVC (4 pmol), resulted in markedly higher insulin levels at corresponding time points compared to those with vehicle microinjected into the DVC. These data indicate, for the first time, that microinjection of PP into the DVC may potentiate glucose-stimulated insulin secretion in halothane-anesthetized rats.

The nucleus raphe obscurus controls pancreatic hormone secretion in the rat

Until recently, the dorsal vagal complex (DVC) was considered as the only brain stem regulatory center for the vagal control of the endocrine pancreas. Because the nucleus raphe obscurus (NRO) maintains anatomic connections via the DVC to the pancreas, a functional significance of these findings was investigated in the present study. Kainic acid and vehicle were microinjected into the right DVC and the NRO of alpha-chloralose-anesthetized rats, and plasma concentrations of rat insulin, glucagon, and glucose were determined before and 5, 15, 30, and 60 min after injections. Chemical stimulation of neurons in the DVC by kainic acid at a dose of 200 pmol evoked increases in concentrations of insulin, with a peak at 15 min, and glucagon, with a peak at 30 min. Microinjection of kainic acid into the NRO at a dose of 200 pmol, but not at a dose of 20 pmol, produced increases in plasma concentrations of insulin, with a peak at 30 min, and glucagon, with a peak at 60 min. Plasma glucose levels on microinjection of kainic acid into the NRO at a dose of 20 pmol were decreased, whereas no changes on microinjection of kainic acid at a dose of 200 pmol were observed. The effects of kainic acid on insulin and glucagon secretion in the NRO were abolished by bilateral vagotomy. The study demonstrates for the first time that the NRO can contribute to vagal control of pancreatic endocrine function, although the exact circuitry and neurotransmitters involved in this response remain unknown.

Serotonin and thyrotropin-releasing hormone do not augment their effects on gastric motility on their microinjection into the nucleus raphe obscurus of the rat

The existence of an interaction between serotonin (5-HT) and thyrotropin-releasing hormone (TRH) in the nucleus raphe obscurus (NRO) of the rat in their excitatory effects on gastric motor function was examined using two different approaches. First, 5-HT and TRH were microinjected into the NRO alone at two different doses and then as a mixture in the same animals. In a second group of animals, both agents were microinjected in a rapid (20-30-sec interval) sequential order. These experiments were performed in alpha-chloralose-anesthetized rats intragastric pressure and pyloric and greater curvature motility were monitored. Both 5-HT at a dose of 6 nmol and TRH at doses of 0.6 and 15 pmol evoked significant increases in intragastric pressure. Microinjection of a mixture of 5-HT at a low dose of 0.6 nmol and TRH at doses of 0.6 pmol (low) and 15 pmol (high) resulted in significant increases in intragastric pressure that did not differ from the effects of TRH microinjected alone. A mixture of 5-HT at a low dose of 0.6 nmol and TRH at a high dose of 15 pmol evoked increases in pyloric motility that did not differ from the effects of TRH alone and increases in greater curvature motility that were significantly lower than the effects of TRH alone at the same dose. Microinjection of a mixture of 5-HT at a high dose of 6 nmol and TRH at a low dose of 0.6 pmol evoked increases in intragastric pressure that did not differ from the effect of 5-HT alone. Rapid sequential microinjection of TRH at either a low dose of 0.6 pmol or the larger dose of 15 pmol after 5-HT (0.6 nmol) resulted in increases in intragastric pressure that did not differ from the response to either dose of TRH microinjected after vehicle. Similarly, the intragastric pressure response to 5-HT (0.6 nmol) given after either dose of TRH was not significantly different from the response to 5-HT after vehicle. In summary, our study demonstrates that 5-HT and TRH do not augment their excitatory effects on gastric motor function on dual or sequential micro-injections in the NRO of the alpha-chloralose-anesthetized rats.

Substance P and serotonin independently affect intragastric pressure when microinjected into the nucleus raphe obscurus of the rat

We have recently shown that microinjection of substance P (SP) into the nucleus raphe obscurus (NRO) of the rat decreases intragastric pressure, whereas microinjection of serotonin (5-HT) increases it. The purpose of the present study was to investigate whether there exists a functional interaction between SP and 5-HT in the NRO of the rat in their effects on gastric motor function. This was accomplished by microinjection of SP (135 pmol) and 5-HT (0.6 and 6 nmol) into the NRO in a rapid, sequential order in alpha-chloralose-anesthetized rats, while monitoring intragastric pressure and pyloric and greater curvature motilities. Substance P evoked significant decreases in intragastric pressure when microinjected into the NRO after vehicle and after 5-HT (at both 0.6 and 6 nmol). There was no difference in the magnitude of the SP effect after 5-HT when compared to the response after vehicle. Serotonin at a dose of 6 nmol, but not at a dose of 0.6 nmol, elicited significant increases in intragastric pressure when microinjected after vehicle or after SP, and there was no difference between the responses to 5-HT with respect to the initial treatment. We conclude that SP and 5-HT act independently in the NRO of the rat to affect intragastric pressure.

Potentiation of intrathecal DAMGO antinociception, but not gastrointestinal transit inhibition, by 5-hydroxytryptamine and norepinephrine uptake blockade

Spinally administered mu opioid agonists produce potent antinociception and inhibition of gastrointestinal transit. Blockade of 5-hydroxytryptamine (5-HT) or norepinephrine (NE) uptake potentiates intrathecal (i.t.) DAMGO antinociception. To determine whether 5-HT and NE uptake blockade will also potentiate the gastrointestinal inhibition, mice were treated with zimelidine, desipramine or saline, followed by i.t. DAMGO and tested for tailflick antinociception or inhibition of gastrointestinal transit. DAMGO produced antinociception dose-dependently (ED50 = 4.6 ng). Zimelidine (10 mg/kg, s.c., 1 hr before DAMGO) produced a 6.2-fold leftward shift in the antinociceptive dose-response curve (ED50 = 0.73 ng). Desipramine produced a 5.3-fold shift (ED50 = 1.4 ng). DAMGO also produced a dose-dependent inhibition of gastrointestinal transit (ED50 = 117 ng). However, zimelidine or desipramine treatment did not affect DAMGO inhibition of gastrointestinal transit (ED50 = 80 ng.).

The non-NMDA subtype of excitatory amino acid receptor plays the major role in control of cardiovascular function by the subretrofacial nucleus in cats

Recent studies have reported that microinjection of kynurenic acid (KYN 12.5 nmol), the nonselective Excitatory Amino acid (EAA) antagonist, into the rostral ventrolateral medulla of the cat decreases arterial blood pressure (BP) and inferior cardiac sympathetic nerve discharge. The purpose of our study was to confirm this finding and determine the subtypes of EAA receptor(s) responsible for mediating this effect. This was done by microinjecting various EAA antagonists bilaterally into the SRFN of chloralose-anesthetized animals while monitoring BP and HR. KYN (12.5 nmol; N = 5) produced a decrease in mean BP (31 +/- 9 mmHg, P < .05) with no significant change in HR. To determine the subtype of EAA receptor responsible for eliciting tonic sympathetic outflow from the SRFN, specific antagonists of N-methyl-D-aspartate (NMDA) and non-NMDA EAA receptors were tested. The NMDA receptor antagonist 3-(RS)-Carboxypiperazin-4-yl)-proyl- 1-phosphonic acid (CPP-2.25 nmol; N = 3) microinjected into the SRFN produced a small but significant decrease in BP (-13 +/- 1 mmHg; P < .05). This effect of CPP was significantly less than that seen with KYN. Two antagonists of the non-NMDA subtype of EAA receptor, 6-cyano-7-nitroquinoxaline-2,3-dione (0.05 nmol; N = 4) and gamma-D-glutamylaminomethyl sulphonic acid (2.5 nmol; N = 4), were microinjected into the SRFN. Both of these drugs produced decreases in BP (-29 +/- 4 and -23 +/- 3 mmHg, respectively; P < 0.05) similar to that observed with KYN. No significant changes in HR were noted with CPP, 6 cyano-7-nitroquinoxaline-2,3-dione or gamma-G-glutamylamino-methylsulfonate. These data indicate that a non-NMDA EAA receptor plays the major role in control of cardiovascular function by the SRFN.

TRH and substance P independently affect gastric motility in nucleus raphe obscurus of the rat

The purpose of this study was to investigate whether there exists a functional interaction between thyrotropin-releasing hormone (TRH) and substance P (SP) in the nucleus raphe obscurus (NRO) in their effects on gastric motor function. This was accomplished by microinjection of TRH (6-45 pmol) and SP (10 and 135 pmol) into the NRO alone and then either as a mixture or in rapid sequential order in alpha-chloralose-anesthetized rats, while intragastric pressure and pyloric and greater curvature motility were monitored. TRH (15 and 45 pmol) evoked significant increases in gastric motor activity, whereas SP (135 pmol) elicited decreases in intragastric pressure. SP at a dose of 10 pmol was ineffective alone in altering gastric motor function. Microinjection of a mixture of TRH (15 pmol) and SP (10 pmol) into the NRO resulted in significant increases in intragastric pressure, pyloric motility, and greater curvature motility; these changes in gastric motor function were similar to the effect of TRH (15 pmol) alone. A mixture of TRH (15 pmol) and SP (135 pmol) resulted in changes in gastric motor activity that were significantly less than the effect of TRH (15 pmol) microinjected into the NRO alone and appeared to be an additive effect of each peptide. The results of sequential microinjections of both peptides were consistent with these findings. The stimulative effect of TRH (15 and 45 pmol) on intragastric pressure, microinjected into the NRO 30 s after SP (135 pmol), did not differ from the effect of TRH microinjected at the same doses after vehicle.(ABSTRACT TRUNCATED AT 250 WORDS)

Opposing gastric motor responses to TRH and substance P on their microinjection into nucleus raphe obscurus of rats

Little is known about the functional role of putative neurotransmitters in the nucleus raphe obscurus (NRO) in the control of gastric motor function, although thyrotropin-releasing hormone (TRH) and substance P (SP) have been detected in the cell bodies and/or fibers of this nucleus. Therefore, we investigated the effects of microinjection of these peptides (in a volume of 60 nl) into the caudal NRO of alpha-chloralose-anesthetized rats while recording intragastric pressure, pyloric and greater curvature motility, and blood pressure. L-Glutamate (30 nmol) was first microinjected into the NRO to identify the "gastric" region of the NRO and elicited significant increases in intragastric pressure as well as pyloric and greater curvature motility in all 16 animals. TRH (2-45 pmol, n = 16) microinjected into the same sites increased intragastric pressure as well as pyloric and greater curvature motility, and these effects were abolished by bilateral cervical vagotomy and atropine (0.5-1.0 mg/kg iv) but not by spinal cord transection. Microinjection of SP (45-405 pmol, n = 15) into the same sites decreased intragastric pressure; however, the inhibitory effect of SP on pyloric and greater curvature motility did not attain statistical significance. The effect of SP on intragastric pressure was completely abolished by bilateral vagotomy but not by systemic administration of atropine (1 mg/kg) or spinal cord transection. Microinjections of 45 pmol TRH and 405 pmol SP just outside of the NRO did not result in changes in gastric function. No overall significant changes in blood pressure were noted after microinjection of L-glutamate, TRH, or SP into the gastric region of the NRO. We conclude that both TRH and SP affect gastric motor function in the caudal NRO via a vagally mediated pathway; TRH apparently activates vagal cholinergic pathways, but the mechanism of SP-evoked gastric motor inhibition remains to be further investigated.

Immunocytochemical localization of the neuropeptide-synthesizing enzyme PC1 in AtT-20 cells

The subtilisin-like enzyme PC1 (also known as PC3) cleaves the neuropeptide precursor proopiomelanocortin at paired basic residues in transfection experiments, thus providing evidence for a critical role in precursor processing. While mRNA for this enzyme is highly enriched in neuroendocrine tissues, little is known about the tissue and subcellular distribution of the PC1 protein. This study used immunocytochemical techniques to investigate the anatomical distribution of PC1, both alone and compared to met-enkephalin (MET-enk), in AtT-20 pituicytes transfected with proenkephalin cDNA. A high density of PC1 immunostaining was observed in a small region adjacent to the nucleus and in the tips of the processes of these cells. Dual-staining immunocytochemistry of whole cells illustrated that both PC1 and MET-enk immunoreactivity were present in the tips, but PC1 was concentrated in a region adjacent to the nucleus while MET-enk punctate staining was dispersed throughout the soma. This codistribution was confirmed in semithin sections of dual-stained cells cut at 1-1.5 microns through the thickness of the cells. PC1 staining resembled that of TGN38, a marker for the trans-Golgi network. When PC1 immunocytochemistry was performed in cells that were pretreated with brefeldin A, a drug that redistributes the proximal Golgi compartments to the endoplasmic reticulum, there was a complete disruption of the defined locus of PC1 immunoreactivity. Taken together, our data indicate that (1) PC1 is concentrated in a region of the cell body resembling the trans-Golgi network and (2) both the enzyme and the processed peptide are transported to the tips of the processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonin microinjected into the nucleus raphe obscurus increases intragastric pressure in the rat via a vagally mediated pathway

The purpose of the present study was to investigate the effect of microinjection of serotonin (5-HT) and selected 5-HT receptor subtype agonists and antagonists into the caudal nucleus raphe obscurus on gastrointestinal motor activity in urethane-chloralose anesthetized rats. Serotonin (0.6-18.0 nmol) dose-dependently increased intragastric pressure, and this effect was abolished by peripherally administered atropine (0.5-1.0 mg/kg, i.v.). Microinjection of a 5-HT1A receptor agonist, 8-hydroxy-N,N-dipropyl-2-amino-tetralin hydrobromide (0.06-12.0 nmol), a 5-HT1C/2 receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (4.5 and 18.0 nmol), as well as a 5-HT3 receptor agonist, 1-(m-chlorophenyl)-biguanide hydrochloride (0.6-18.0 nmol), also resulted in increases in intragastric pressure. The gastric excitatory effect of 5-HT (6.0 nmol) was markedly reduced by prior microinjection of a 5-HT1/2 receptor antagonist, methiothepin (200 nmol), into the same site, as well as by i.v. administration of a 5-HT2/1C antagonist, ketanserin (2.5 mg/kg). The effect of 5-HT (6.0 nmol) on intragastric pressure was completely blocked by i.v. administration of a mixture of the 5-HT1A receptor antagonist 1-(2-methoxyphenyl)-4-[-(2-phthalimido)butyl]piperazinehydrobromide++ + (3.5 mg/kg), ketanserin (2.5 mg/kg) and the 5-HT3 receptor antagonist 3-tropanyl-3,5-dichlorobenzoate (2.5 mg/kg). These results indicate that 5-HT activates gastric motor function in the caudal nucleus raphe obscurus via a vagally mediated pathway and that the activation of multiple 5-HT receptor subtypes is required for the gastric excitatory effect of 5-HT.

Partial characterization of a neurotransmitter pathway regulating the in vivo release of prolactin

Nicotinic cholinergic, opiate and serotonergic agonists as well as dopaminergic antagonists induce the release of pituitary prolactin. The purposes of the present studies were to determine if nicotine, morphine and the serotonin1A (5-HT1A) agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) utilize a common synaptic pathway to release prolactin and, if so, to establish the serial order of the receptors involved. We also sought to determine whether the pathway under investigation leads to the secretion of prolactin via a mechanism involving dopamine, the prolactin inhibitory factor. Male rats with indwelling jugular catheters were pretreated with saline, mecamylamine, naltrexone, methysergide or bromocriptine. In the saline-treated animals, administration of nicotine, morphine, 8-OH-DPAT and haloperidol resulted in significant increases in plasma prolactin levels. Mecamylamine pretreatment prevented the prolactin response to nicotine only. Naltrexone blocked the stimulation of prolactin release by morphine and by nicotine. Methysergide inhibited the effects of 8-OH-DPAT, morphine and nicotine but not haloperidol. Bromocriptine blocked the prolactin secretion induced by haloperidol as well as by each of the above agonists. Also, in dual-immunocytochemically stained sections, tyrosine hydroxylase-immunoreactive cells and serotonin-immunoreactive processes were detected in close anatomical proximity in the dorsomedial arcuate nucleus. These data indicate that nicotine, morphine and 8-OH-DPAT act to release prolactin via a common synaptic pathway expressing nicotinic cholinergic, opiate, and 5-HT1A receptors at synapses arranged serially in that functional order. Furthermore, the data indicate that the in vivo secretion of prolactin via this pathway may ultimately occur through the inhibition of dopamine release.

An excitatory amino acid(s) in the ventrolateral medulla is (are) required for breathing to occur in the anesthetized cat

The purpose of the present study was to identify sites(s) in the ventrolateral medulla where excitatory amino acids are involved in respiratory control. For this purpose, the respiratory effects produced by bilateral microinjection of excitatory amino acid antagonist drugs were examined while tidal volume (Vt), respiratory rate (f), arterial blood pressure and heart rate were monitored in chloralose-anesthetized cats. Microinjection of kynurenic acid (12.5 nmol) into a site approximately 3 mm rostral to obex, 4 mm lateral to midline and 1.5 mm below the ventral surface produced a decrease in Vt (-20 +/- 2 ml), an increase in f (+20 +/- 3 breaths/min) and a decrease in respiratory minute volume (-108 +/- 19 ml/min) (n = 8). These changes progressed to apnea in each animal tested. No significant changes in blood pressure or heart rate were observed. To determine the excitatory amino acid receptor subtype(s) involved, antagonists of n-methyl-D-aspartate (NMDA) (3-[(RS)-carboxypiperazin-4-yl]-propyl-1-phosphoric acid (CPP] and non-NMDA [6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)] receptors were microinjected bilaterally into this site. In the case of CPP, three doses were studied (0.25 nmol, n = 4; 0.75 nmol, n = 3; 2.25 nmol, n = 2). All three doses produced similar decreases in Vt (-12 +/- 1, P less than .05; -10 +/- 1, P less than .05; and -16 +/- 5 ml, respectively) and increases in f (+14 +/- 2, P less than .05; +10 +/- 3, P less than .05; and +12 +/- 3 breaths/min, respectively). None of these animals exhibited apnea.(ABSTRACT TRUNCATED AT 250 WORDS)

Striatal glutamic acid decarboxylase immunoreactivity is increased after dopaminergic deafferentation: densitometric analysis

Several lines of evidence suggest that dopamine exerts a chronic inhibitory action on GABAergic cells in the striatum, and striatal glutamic acid decarboxylase (GAD) mRNA levels are increased after ipsilateral dopaminergic denervation. In the present study we have used GAD immunocytochemistry to assess whether dopaminergic denervation results in an increase in GAD protein synthesis. In three 6-hydroxydopamine-lesioned animals, there was a perceptible increase in the density of GAD-immunoreactive (ir)staining on the side ipsilateral to the lesion. Computer-assisted densitometric analysis showed a significant increase in GAD-ir staining in the ipsilateral striatum compared to the contralateral (control) side. These data suggest that removal of striatal dopaminergic innervation results in an increase in the amount of immunoreactive GAD, the rate limiting enzyme in the synthesis of GABA.

Excitation of neurons in the medullary raphe increases gastric acid and pepsin production in cats

The nucleus raphe obscurus (NRO) has recently emerged as an important nucleus for excitation of gastric motor activity through projections to the dorsal motor nucleus of the vagus (DMV) [P. J. Hornby, C. D. Rossiter, R. L. White, W. P. Norman, D. H. Kuhn, and R. A. Gillis. Am. J. Physiol. 258 (Gastrointest. Liver Physiol. 21): G91-G96, 1990; and M. J. McCann, G. E. Herman, and R. C. Rogers. Brain Res. 486: 181-184, 1989]. A neurotransmitter thought to be involved in this NRO-DMV pathway is thyrotropin-releasing hormone (TRH), a peptide that excites gastric activity when microinjected into the DMV. The purpose of the present study was to determine whether gastric acid and pepsin secretion were altered by 1) activation of neurons in the NRO by microinjection of kainic cid and 2) microinjection of TRH into the DMV in chloralose-anesthetized cats. Microinjection of kainic acid into the NRO increased gastric acid secretion [baseline was 6 +/- 2 (mu eq) H+/15 min (n = 7) and increased to 8 +/- 2, 26 +/- 11 (P less than 0.05), and 21 +/- 7 mu eq/15 min (P less than 0.05) during the first, second, and third 15-min periods after microinjection, respectively]. Pepsin output also increased from a baseline of 287 +/- 67 pepsin units (PU) (n = 4) to 507 +/- 126 PU 15 min postinjection, 541 +/- 118 PU 30 min after injection (P less than 0.05), 608 +/- 92 PU 45 min after injection (P less than 0.05), and 700 +/- 156 PU 60 min postinjection (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)