Guanethidine after twenty years: a pharmacologist's perspective

The Influence of an Adrenergic Antagonist Guanethidine (GUA) on the Distribution Pattern and Chemical Coding of Dorsal Root Ganglia (DRG) Neurons Supplying the Porcine Urinary Bladder

Although guanethidine (GUA) was used in the past as a drug to suppress hyperactivity of the sympathetic nerve fibers, there are no available data concerning the possible action of this substance on the sensory component of the peripheral nervous system supplying the urinary bladder. Thus, the present study was aimed at disclosing the influence of intravesically instilled GUA on the distribution, relative frequency, and chemical coding of dorsal root ganglion neurons associated with the porcine urinary bladder. The investigated sensory neurons were visualized with a retrograde tracing method using Fast Blue (FB), while their chemical profile was disclosed with single-labeling immunohistochemistry using antibodies against substance P (SP), calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase activating polypeptide (PACAP), galanin (GAL), neuronal nitric oxide synthase (nNOS), somatostatin (SOM), and calbindin (CB). After GUA treatment, a slight decrease in the number of FB⁺ neurons containing SP was observed when compared with untreated animals (34.6 ± 6.5% vs. 45.6 ± 1.3%), while the number of retrogradely traced cells immunolabeled for GAL, nNOS, and CB distinctly increased (12.3 ± 1.0% vs. 7.4 ± 0.6%, 11.9 ± 0.6% vs. 5.4 ± 0.5% and 8.6 ± 0.5% vs. 2.7 ± 0.4%, respectively). However, administration of GUA did not change the number of FB⁺ neurons containing CGRP, PACAP, or SOM. The present study provides evidence that GUA significantly modifies the sensory innervation of the porcine urinary bladder wall and thus may be considered a potential tool for studying the plasticity of this subdivision of the bladder innervation.

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

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

Sympathetic fibre sprouting in the skin contributes to pain-related behaviour in spared nerve injury and cuff models of neuropathic pain

Background

Cuff and spared nerve injury (SNI) in the sciatic territory are widely used to model neuropathic pain. Because nociceptive information is first detected in skin, it is important to understand how alterations in peripheral innervation contribute to pain in each model. Over 16 weeks in male rats, changes in sensory and autonomic innervation of the skin were described after cuff and SNI using immunohistochemistry to label myelinated (neurofilament 200 positive—NF200+) and peptidergic (calcitonin gene-related peptide positive—CGRP+) primary afferents and sympathetic fibres (dopamine β-hydroxylase positive—DBH+)

Results

Cuff and SNI caused an early loss and later reinnervation of NF200 and CGRP fibres in the plantar hind paw skin. In both models, DBH+ fibres sprouted into the upper dermis of the plantar skin 4 and 6 weeks after injury. Despite these similarities, behavioural pain measures were significantly different in each model. Sympathectomy using guanethidine significantly alleviated mechanical allodynia 6 weeks after cuff, when peak sympathetic sprouting was observed, having no effect at 2 weeks, when fibres were absent. In SNI animals, mechanical allodynia in the lateral paw was significantly improved by guanethidine at 2 and 6 weeks, and the development of cold hyperalgesia, which roughly paralleled the appearance of ectopic sympathetic fibres, was alleviated by guanethidine at 6 weeks. Sympathetic fibres did not sprout into the dorsal root ganglia at 2 or 6 weeks, indicating their unimportance to pain behaviour in these two models.

Conclusions

Alterations in sympathetic innervation in the skin represents an important mechanism that contributes to pain in cuff and SNI models of neuropathic pain.

Direct Vasodilators and Sympatholytic Agents

Direct vasodilators and sympatholytic agents were some of the first antihypertensive medications discovered and utilized in the past century. However, side effect profiles and the advent of newer antihypertensive drug classes have reduced the use of these agents in recent decades. Outcome data and large randomized trials supporting the efficacy of these medications are limited; however, in general the blood pressure-lowering effect of these agents has repeatedly been shown to be comparable to other more contemporary drug classes. Nevertheless, a landmark hypertension trial found a negative outcome with a doxazosin-based regimen compared to a chlorthalidone-based regimen, leading to the removal of α-1 adrenergic receptor blockers as first-line monotherapy from the hypertension guidelines. In contemporary practice, direct vasodilators and sympatholytic agents, particularly hydralazine and clonidine, are often utilized in refractory hypertension. Hydralazine and minoxidil may also be useful alternatives for patients with renal dysfunction, and both hydralazine and methyldopa are considered first line for the treatment of hypertension in pregnancy. Hydralazine has also found widespread use for the treatment of systolic heart failure in combination with isosorbide dinitrate (ISDN). The data to support use of this combination in African Americans with heart failure are particularly robust. Hydralazine with ISDN may also serve as an alternative for patients with an intolerance to angiotensin antagonists. Given these niche indications, vasodilators and sympatholytics are still useful in clinical practice; therefore, it is prudent to understand the existing data regarding efficacy and the safe use of these medications.

Corticotropin-releasing hormone and the sympathoadrenal system are major mediators in the effects of peripherally administered exendin-4 on the hypothalamic-pituitary-adrenal axis of male rats

Glucagon-like peptide-1 (GLP-1) and the GLP-1 receptor agonist, exendin-4 (Ex-4), potently stimulate hypothalamic-pituitary-adrenal (HPA) axis activity after either central or peripheral administration. Because several GLP-1 derivative drugs, including synthetic Ex-4, are currently in use to treat patients with type II diabetes mellitus, the characterization of Ex-4 effects on the HPA axis is highly relevant. Herein, the roles of CRH and AVP on these effects were investigated by administering the antagonists astressin and d(CH2)5Tyr(Me)AVP, respectively. The role of the sympathoadrenal system (SAS) was explored in bilateral adrenal enucleated and guanethidine-treated rats, whereas primary pituitary cell cultures were used to study direct effects on the corticotropes. Astressin completely abrogated (P < .05) the effects of Ex-4 central administration on ACTH secretion but only slightly reduced (by 35%) the ACTH response to Ex-4 peripheral administration. Moreover, astressin significantly (P < .05) decreased the corticosterone response to centrally but not peripherally administered Ex-4, suggesting different mechanisms depending on the route of administration. Pretreatment with d(CH2)5Tyr(Me)AVP failed to diminish either the ACTH or corticosterone response to Ex-4 and no direct effect of Ex-4 or GLP-1 was observed on pituitary cell cultures. In contrast, a significant (P < .05) reduction in the corticosterone response elicited by Ex-4 peripheral administration was observed in enucleated and guanethidine-treated rats, indicating a role of the SAS in the glucocorticoid stimulatory effects of Ex-4. Our data demonstrate that the effects of Ex-4 on the HPA axis are partially mediated by CRH and the sympathoadrenal system, and stress the relevance of Ex-4 as a corticosterone secretagogue.

Modulation of rat parasympathetic cardiac ganglion phenotype and NGF synthesis by adrenergic nerves

Cardiac function is regulated by interactions among intrinsic and extrinsic autonomic neurons, and the mechanisms responsible for organizing these circuits are poorly understood. Parasympathetic neurons elsewhere synthesize the neurotrophin NGF, which may promote postganglionic axonal associations where parasympathetic axons inhibit sympathetic transmitter release. Previous studies have shown that parasympathetic NGF content and neurochemical phenotype are regulated by sympathetic innervation. In this study we assessed contributions of sympathetic input on cardiac ganglion neuronal phenotype and NGF expression. Because cardiac ganglia are reported to contain putative noradrenergic neurons, we eliminated sympathetic input both surgically (extrinsic) and chemically (extrinsic plus intrinsic). In controls, most cardiac ganglion neurons expressed vesicular acetylcholine transporter, frequently colocalized with vesicular monoamine transporter, but lacked catecholamine histofluorescence. Most cardiac ganglion neurons expressed NGF transcripts, and 40% contained mature and 47% proNGF immunoreactivity. Guanethidine treatment for 7 days decreased numbers of neurons expressing vesicular acetylcholine transporter, NGF transcripts and NGF immunoreactivity, but did not affect proNGF or vesicular monoamine transporter immunoreactivity. Stellate ganglionectomy had comparable effects on neurochemical phenotype and mature NGF immunoreactivity, but proNGF expression was additionally reduced. These findings show that individual cardiac ganglion neurons display markers of both cholinergic and noradrenergic transmission. Sympathetic noradrenergic innervation maintains levels of cholinergic but not noradrenergic marker protein. Sympathetic innervation also promotes cardiac ganglion neuronal NGF synthesis. Because chemical blockade of all noradrenergic transmission is no more effective than extrinsic sympathectomy, local intrinsic noradrenergic transmission is not a factor in regulating ganglion neuron phenotype.

Interaction of local anaesthetic agents with the endogenous norepinephrine transporter in SH-SY5Y human neuroblastoma cells

Use of intravenous guanethidine for the treatment of complex regional pain syndrome type I is of variable efficacy. Guanethidine injection is painful, so local anaesthetic is co-administered. We hypothesize that local anaesthetic inhibits uptake of guanethidine and hence reduces its efficacy. In this study we have examined the effects of a range of local anaesthetic agents on the uptake of [3H]norepinephrine ([3H]NE) (as a surrogate for guanethidine) and the binding of [3H]nisoxetine to the NE transporter in cultured SH-SY5Y human neuroblastoma cells. All local anaesthetic agents inhibited NE uptake with a rank order cocaine>tetracaine>procaine(esters), dibucaine > bupivacaine > prilocaine > lidocaine (amides). In addition all anaesthetic agents displaced [3H]nisoxetine with a rank order cocaine > tetracaine > dibucaine > procaine > prilocaine > bupivacaine > lidocaine. There was a positive correlation between [3H]NE uptake and [3H]nisoxetine binding. Our data suggest that when local anaesthetic and guanethidine are co-administered the former may reduce uptake of the latter and hence reduce the clinical efficacy of guanethidine.

Adrenoceptor-mediated modulation of Evans blue dye permeation of rat small intestine

In the present study, we addressed the problem whether sympathoadrenal mechanisms could influence the paracellular permeation of macromolecules from the lumen to the lamina propria of the small intestine. Experiments were conducted with rats that were anesthetized with ether for 10-20 min, during which time laparotomy was performed and six consecutive loops (each of 5 cm length) of the jejunum were prepared. A 3% solution of the azo dye, Evans blue (EB; MW 960.83) in phosphate-buffered saline, was instilled into each loop at a volume of 0.3 ml, this compound serving as a marker for tight junctional permeability. Thereafter, the abdomen was closed and the rats were allowed to wake up, but were killed after 60 min. The loops were dissected, opened, and rinsed with acetylcysteine in order to remove the adherent mucus layer. Each loop was weighed and incubated with formamide for 24 hr to elute the amount of EB absorbed, which was quantitated spectrophotometrically. In the control situation, the uptake was homogenous along the loops. beta-Adrenoceptor-blocking, or -stimulating agents could influence the uptake considerably. The data obtained could indicate that noradrenergic nerves, via an activation of beta 2-adrenoceptors, may cause an increase of tight junction permeability for macromolecules, but circulatory mechanisms also must be taken into account in order to explain the observed effects.

Visceral vasodilatation and somatic vasoconstriction evoked by acid challenge of the rat gastric mucosa: diversity of mechanisms

1. Acid back-diffusion through a disrupted gastric mucosal barrier increases blood flow to the stomach without any change in systemic blood pressure. This study was undertaken to examine the gastric acid-evoked changes in blood flow in a number of visceral and somatic arterial beds and to elucidate the mechanisms which lead to the regionally diverse haemodynamic responses. 2. The gastric mucosa of urethane-anaesthetized rats was challenged with acid by perfusing the stomach with ethanol (15%, to disrupt the gastric mucosal barrier) in 0.15 M HCl. Blood flow was estimated by laser Doppler flowmetry, the hydrogen clearance method or the ultrasonic transit time shift technique. 3. Gastric acid challenge increased blood flow in the gastric mucosa and left gastric artery while blood flow in the femoral artery and skin declined. 4. Afferent nerve stimulation by intragastric administration of capsaicin enhanced blood flow in the left gastric artery but did not diminish blood flow in the femoral artery when compared with the vehicle. 5. The gastric acid-evoked dilatation of the left gastric artery was depressed by acute extrinsic denervation of the stomach, capsaicin-induced ablation of afferent neurones or hexamethonium-induced blockade of autonomic ganglionic transmission. 6. The gastric acid-induced constriction of the femoral artery was attenuated by acute extrinsic denervation of the stomach but left unaltered by capsaicin, hexamethonium, guanethidine, indomethacin, telmisartan (an angiotensin II antagonist), [d(CH2)5(1), Tyr(Me)2, Arg8]-vasopressin (a vasopressin antagonist), bosentan (an endothelin antagonist) and acute ligation of the blood vessels to the adrenal glands. 7. These data show that acid challenge of the gastric mucosa elicits visceral vasodilatation and somatic vasoconstriction via divergent mechanisms. The gastric hyperaemia is brought about by extrinsic vasodilator nerves, whereas the reduction of somatic blood flow seems to be mediated by non-neural, probably humoral, vasoconstrictor messengers that remain to be identified.

Is ovarian adrenergic innervation essential to gonadal function in adult rats?

We studied the relative importance of ovarian innervation during different phases of female rat sexual development, 30, 40, 45 and 60-day-old. Chemical sympathectomy was promoted by long term postnatal treatment with guanethidine (GD), an adrenergic neuron blocking agent. The sympathectomized rats exhibited delayed puberty and alterations in estrous cycle. Reduced circulating E2, LH and Prl levels at 30 days of age were observed, besides decreased steroidal secretory responsiveness to gonadotropins in vitro. On the other hand, normal pituitary secretory responsiveness to LHRH in vivo and plasma gonadotropin concentrations were observed in 60-day-old rats. These data reinforce the view that ovarian sympathetic innervation contributes to the regulation of the prepubertal development of the ovarian functions.

Participation of capsaicin-sensitive afferent neurons in gastric motor inhibition caused by laparotomy and intraperitoneal acid

Stimulation of somatic or visceral nociceptors causes changes in gastrointestinal motor activity and blood pressure. The present study examined the possible participation of capsaicin-sensitive afferent and noradrenergic efferent neurons in the blood pressure and gastric motor responses to laparotomy and intraperitoneal injection of capsaicin or hydrochloric acid in the rat. Gastric motor activity was measured by recording the intragastric pressure of phenobarbital-anaesthetized rats via an oesophageal catheter. Laparotomy as well as intraperitoneal injection of capsaicin (33 and 330 microM) or hydrochloric acid (30 mM) caused a transient reduction of gastric motor activity stimulated by intravenous infusion of bombesin (200 pmol/min) and a brief fall of blood pressure (depressor effect). The depressor effect of laparotomy was followed by prolonged hypertension. Defunctionalization of capsaicin-sensitive afferent neurons by systemic pretreatment of rats with capsaicin (0.4 mmol/kg) prevented the depressor effect and gastric motor inhibition elicited by laparotomy, intraperitoneal capsaicin (33 microM) or intraperitoneal hydrochloric acid (30 mM). However, the effects of 330 microM capsaicin on blood pressure and gastric motility were only partially reduced by capsaicin pretreatment. Blockade of noradrenergic sympathetic neurons by pretreating rats with guanethidine (0.225 mmol/kg) prevented the gastric motor inhibition and depressor effects of laparotomy and intraperitoneal injection of hydrochloric acid (30 mM). The inhibition of gastric motility caused by capsaicin (33 and 330 microM) was only partially reduced by guanethidine pretreatment. The secondary hypertension following the depressor effect of intraperitoneal capsaicin or hydrochloric acid was enhanced in guanethidine-pretreated rats whereas the prolonged hypertension induced by laparotomy was left unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional intravenous guanethidine blocks in algodystrophy

Five-hundred-thirteen regional intravenous guanethidine blocks were carried out in 125 cases of algodystrophy (118 adults), after failure of other treatments in 120 cases (Group I) and without previous treatments in 5 (Group II). A positive result occurred in 85 cases of Group I (71%) and in the 5 cases of Group II, after 4.5 +/- 1.7 blocks. In Group I the results did not differ significantly between upper (33 cases) and lower (87 cases) limb or in regard to sex, age, duration of disease, nature of previous treatments. The presence of psychic disorders was accompanied by less frequent (p less than 0.02) positive results. The tolerance was satisfactory in 85.6% of cases: 22 moderate side effects authorized a continuation of the blocks, 22 serious ones indicated interruption, especially one case of thrombophlebitis and another one of very transitory acute ischaemia. The risk of intolerance was significantly raised (p less than 0.02) by age. The regional guanethidine blocks seemed to be a good treatment for algodystrophy after failure of other treatments.

2-deoxy-D-glucose-induced hyperglycemia: role for direct sympathetic nervous system activation of liver glucose output

The hypothalamus plays an important integrative role in the control of peripheral metabolism, achieved by modulation of autonomic outflow to the endocrine pancreas, the liver and the adrenal medulla. This study examines the role of direct sympathetic nervous system control of hepatic glucose output during neuroglycopenia induced by the non-metabolizable glucose analogue 2-deoxy-D-glucose (2-DG). Steady-state tracer methodology was used to directly measure hepatic glucose output (Ra) in pentobarbitone-anesthetised male Wistar rats (220-320 g). Administration of 500 mg/kg 2-DG i.p. produced an increase in Ra from a control value of 7.3 +/- 0.3 mg/kg.min (n = 4) to 15.2 +/- 2.2 mg/kg.min-1 (n = 8), corresponding to an increase in plasma glucose (PG) from 6.4 +/- 0.1 mmol/l to 10.1 +/- 0.4 mmol/l. This rise was countered by the sympathetic noradrenergic blocker guanethidine (100 mg/kg i.p.), reducing Ra to 10.4 +/- 0.9 mg/kg.min-1 and PG to 6.1 +/- 0.3 mmol/l (n = 8), despite markedly lower plasma insulin (PI) levels (2-DG: PI = 94.7 +/- 18.6 mU/l (n = 7), 2-DG + guanethidine: PI = 41.4 +/- 3.3 mU/l (n = 8). Hyperglycemia and elevated liver glucose output were maintained in ADX animals treated with 2-DG, indicating an absence of adrenal-medullary influence (2-DG: Ra = 15.2 +/- 2.2 mg/kg.min-1, 2-DG + ADX = 15.6 +/- 1.0 mg/kg.min-1). Elevated Ra in the 2-DG + ADX was maintained despite markedly elevated insulin levels 349.3 +/- 72.6 mU/l (n = 7)).(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the mode of action of bretylium and guanethidine in post-ganglionic sympathetic nerve fibres

1. The effects of bretylium and guanethidine on the nerve terminal impulse and transmitter release from sympathetic postganglionic nerve terminals in the guinea-pig vas deferens have been studied in vitro using focal extracellular recording. Excitatory junction currents (EJCs) were used as a measure of transmitter release. 2. Both bretylium and guanethidine altered the configuration of the nerve terminal impulse in a manner consistent with their being local anaesthetics. 3. Bretylium (1-3 microM) only completely inhibited transmitter release when impulse propagation in the sympathetic nerve terminal was blocked. 4. In contrast, guanethidine (1-10 microM) could block transmitter release with little effect on the configuration of the nerve terminal impulse. 5. The inhibitory effects of these agents on both the nerve terminal impulse and on transmitter release were reversed by the indirectly acting sympathomimetic agent, d-amphetamine (1-10 microM). 6. Using this technique the mechanisms of action of drugs known to modify the transmitter release in sympathetic nerve terminals can be more precisely determined.

Syphilis in 1986

Symptoms of syphilis have evolved over the ages. In the 16th century, they were essentially cutaneomucous ones. While the intensity of the symptoms decreased localization of the infection in the various organs--mainly those of the cardiovascular and nervous system--gradually appeared. Over a period of years following the introduction of penicillin therapy, the cutaneous and visceral stages became less common. Reminder of the chief serological reactions and of some aspects of the experimental syphilis in the rabbit, similar to certain forms of human syphilis--a strong but late penicillin therapy has been proven ineffective in humans as well as in animals. It is to be regretted that numerous methods of using penicillin (all over the world), had been, from the beginning--except in a few cases--of a purely empirical nature. The authors emphasize--with proof to support their opinion--the failure of antibiotic therapy, which can explain the recent reappearance of hepatic and nervous localizations that had disappeared for 30 years. Despite views to the contrary the authors conclude that penicillin has in no way resolved all the problems raised by the treatment of syphilis.

Cutaneous hyperalgesia: contributions of the peripheral and central nervous systems to the increase in pain sensitivity after injury

This study assesses the contributions of the peripheral and central nervous systems in the development of hyperalgesia (increased pain sensitivity) after an injury. Experiments were carried out to examine the role of C-fiber afferents, the spinal cord and sympathetic efferents on inflammation, primary hyperalgesia and referred hyperalgesia produced in rats by a heat injury. A peripheral mechanism was indicated since both primary hyperalgesia and inflammation after a heat injury were significantly attenuated by blocking C-fiber afferents with local capsaicin. In addition, a central mechanism was indicated since the spread of hyperalgesia to the paw contralateral to a heat injury was prevented by either spinal anesthesia or the blocking of sympathetic efferents by guanethidine. A further role for central mechanisms was indicated since referred hyperalgesia--the enhancement of self-mutilation (autotomy) of a denervated limb which had previously sustained a heat injury--was reduced by spinal anesthesia or a combined blocking of C-fiber afferents and sympathetic efferents with intrathecal capsaicin + guanethidine. The results strongly suggest that referred hyperalgesia after a heat injury is dependent on increased spinal cord activity. However, autotomy in rats that did not undergo a previous injury was unaffected by either spinal anesthesia or intrathecal capsaicin. This suggests that spinal cord hyperactivity, although it plays a role in hyperalgesia following a heat injury, is not a crucial factor in producing pain and hyperalgesia after a nerve injury.

PC12 variants deficient in catecholamine transport

We have isolated PC12 cell variants deficient in transporter-mediated uptake of 3,4-dihydroxyphenylethylamine (dopamine). The variants either were obtained nonselectively, or they were selected by resistance to guanethidine or N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Dopamine uptake into guanethidine-resistant cells occurred with a decreased Vmax; the Km for dopamine and inhibition by guanethidine were normal. MPTP-resistant cells lacked the capacity to take up dopamine. Most of the variants resembled wild-type PC12 in their response to nerve growth factor and the storage and secretion of dopamine. MPTP-resistant cells exhibited several deficiencies in addition to dopamine transport, i.e., no measurable storage of dopamine or acetylcholine and no observable response to nerve growth factor. Wild-type and variant cells were compared with respect to the labeling of cell proteins with [3H]xylamine, which binds covalently to certain proteins apparently only after entering PC12 via the catecholamine transporter. When intact variant cells were used, there was markedly reduced labeling of the proteins by [3H]xylamine. Almost all of these proteins were readily labeled when cell homogenates were exposed to [3H]xylamine. However, MPTP-resistant cells were missing three of these proteins. Northern blot analysis with cDNA clones revealed that the MPTP-resistant cells had markedly reduced levels of several specific mRNA species.

Reproductive physiology and behavior in the male rat following acute and chronic peripheral adrenergic depletion by guanethidine

The effect of guanethidine, an adrenergic neuron blocking agent, on sexual behavior, penile reflexes, and spontaneous seminal emission (SSE) in the rat was studied by acute (i.e., 4 hours prior to testing) and daily IP injection of a low (5 mg/kg) and moderately high (25 mg/kg) dose of the drug. Acute low dose treatment eliminated the expulsion of a seminal plug with behavioral ejaculation without affecting sexual behavior; while acute high dose administration significantly decreased the number of intromissions preceding ejaculation and eliminated emission in copula and SSE for 3 days, with no evidence of retrograde ejaculation. Acute high dose treatment also increased the number of long flips displayed in the penile reflex test, and resulted in significant depression in plasma testosterone (T) and luteinizing hormone (LH) levels. Daily injection with the low dose eliminated emission in and ex copula for 4 weeks, without altering sexual behavior or penile reflexes. Seminal emission in copula reappeared more rapidly after stopping injections than SSE. Chronic high dose treatment was also without effect on copulatory activity. There was a partial recovery of emission in copula by the fourth week of treatment, suggesting that a nonadrenergic mechanism had assumed this function. In penile reflex tests conducted after 4 and 8 weeks, significantly fewer erections were displayed by drug-treated animals. During the period of initial recovery of emission in copula, emission during the reflex test was markedly increased, but SSE was decreased. Plasma T was significantly suppressed after two and four weeks of daily injections, but not thereafter, while plasma LH levels were not affected by the drug.

Inhibition of dopamine uptake by N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a cause of parkinsonism

N-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine has been reported to cause parkinsonism in man and monkeys, producing behavioral effects within 5 min of administration. The compound reversibly and competively inhibited (IC50 = 2 microM) dopamine uptake into PC12, a clonal line of rat pheochromocytoma cells that store and secrete dopamine and acetylcholine. Uptake of choline and 2-deoxyglucose was not affected. Prolonged exposure to the compound was lethal to PC12; survivors of this treatment lost the ability to store dopamine and acetylcholine and to extend neurites upon incubation with nerve growth factor.

Effects of peripheral antisympathetic treatments in the tail-flick, formalin and autotomy tests

The effects of peripheral adrenergic depleting agents on the threshold for non-damaging heat pain (tail-flick test), inflammatory pain associated with tissue injury (formalin test), and chronic pain or dysaesthesia associated with nerve lesions (autotomy test) were examined. Tail-flick latencies were increased by agents which deplete peripheral adrenergic transmitters--6-hydroxydopamine (6-OHDA) and guanethidine--as well as by an agent which prevents the synthesis of noradrenaline--FLA63. A combination of guanethidine and FLA63 also increased latencies, but no more than either treatment alone. Formalin pain scores were reduced by FLA63+ guanethidine and 6-OHDA, but not by guanethidine or FLA63 alone. The percentage of rats that exhibited autotomy was reduced minimally by 6-OHDA and guanethidine treatments which started the day of surgery, maximally by guanethidine treatments which started 4 days before surgery, and not at all by guanethidine treatments which started 4 days after surgery. The results obtained in the formalin and autotomy tests are interpreted in terms of the possible roles of adrenergic transmitters in stimulating and sensitizing damaged afferents immediately after injury. The tail-flick results, however, suggest that adrenergic transmitters also act in lowering thresholds of normal peripheral receptor-fibre units. The relevance of the findings to the development of chronic pain are discussed.

Regional intravenous guanethidine vs. stellate ganglion block in reflex sympathetic dystrophies: a randomized trial

Regional intravenous guanethidine blocks and stellate ganglion blocks have been compared in a randomized trial. Nineteen patients, randomly allocated to two groups of therapy and exhibiting severe reflex sympathetic dystrophy following peripheral nerve lesions, have been treated. The performance of the intravenous guanethidine block is of longer duration and superior to stellate ganglion block, as regards some early pharmacological effects (skin temperatures and amplitude of plethysmographic waves recorded before blockade and 15 min, 60 min, 24 h, 48 h after institution of the block). In fact the intravenous guanethidine group shows a persistent and significant increase of the skin temperature and of the plethysmographic traces in the blocked side 24 h and 48 h after blockade in comparison with the patients treated with stellate ganglion block. Concerning the therapeutic effects (changes in pain scores and clinical signs--hyperpathia, allodynia, vasomotor disturbances, trophic changes, oedema and limited motion), recorded at the end of treatment and 1 month and 3 months follow-up, an intravenous guanethidine block carried out every 4 days up to a total of 4 blocks is comparable with a stellate ganglion block every day up to a total of 8 blocks. The results of this study show that regional sympathetic block with guanethidine is a good therapeutic tool in the treatment of reflex dystrophies, especially on account of its negligible risks and contraindications.

The effects of vasoactive intestinal polypeptide and of adenosine 5'-triphosphate on the isolated anococcygeus muscle of the mouse

1 Vasoactive intestinal polypeptide (VIP, 0.01- MicroM) produced dose-related relaxations of the mouse anococcygeus muscle. 2 Following incubation with indomethacin (2.8 microM 1 h) adenosine 5'-triphosphate (ATP, 0.5-10 mM) produced dose-related relaxations of the mouse anococcygeus. 3 Haemolysed blood reduced inhibitory responses of the mouse anococcygeus to field stimulation but had no effect on relaxations to VIP or ATP. 4 Apamin (0.5 microM) had no effect on the relaxation of mouse anococcygeus to field stimulation, VIP, or ATP. 5 2-2'-Pyridylisatogen tosylate (PIT, 50 microM) itself reduced muscle tone but it did not abolish inhibitory responses to field stimulation, VIP, or ATP. 6 During prolonged inhibitory nerve stimulation the relaxation of the mouse anococcygeus in response to VIP was reduced greatly while that to ATP was unaffected. 7 Bundles of VIP-immunoreactive sites were detected in sections of the mouse anococcygeus treated by the peroxidase-antiperoxidase (PAP) immunocytochemical technique. 8 The results suggest that the mechanisms underlying non-adrenergic, non-cholinergic inhibitory transmission in the mouse anococcygeus are similar to those in the bovine retractor penis and unlike those in the guinea-pig taenia caeci. 9 The possibility that VIP or ATP might be involved in inhibitory neurotransmission in the mouse anococcygeus is discussed.