Effects of chronic intracranial injection of low and high concentrations of guanethidine in the rat

Myenteric plexus of the hind-gut: developmental abnormalities in humans and experimental studies

Intraluminal pressure studies on patients with congenital aganglionosis showed that the aganglionic rectum contracted in an uncoordinated manner and failed to relax. Histochemical assessment of the innervation helped to explain the variable severity of the symptoms in this condition. It is concluded that (1) absence of ganglia prevents normal coordinated peristalsis and creates an obstructive element; (2) absence of reflex relaxation adds to the obstruction; (3) the degree of uncoordinated motor activity in distal aganglionic bowel probably relates to the number of cholinesterase-positive nerves in the circular muscle and adds another variable obstructive element; and (4) deficient innervation of distal ganglionic bowel probably creates a poor propulsive force and so accentuates more distal obstructive factors. Neurohistochemical and functional studies in the anorectum of cats reveal a somewhat different innervation pattern from that in humans but show that sphincteric tone is mainly due to alpha-adrenergic neural activity. Reflex relaxation of the internal anal sphincter is a complex function in which inhibitory responses override motor responses, and it involves an important non-adrenergic non-cholinergic component. The role of cholinergic nerves in the sphincter remains uncertain. Neurohistochemical assessment of full thickness biopsy specimens of rectal muscle from patients with disabling constipation shows that developmental neuronal dysplasias of the hind-gut may be divided into three main categories: (1) aganglionosis (Hirschsprung's disease), (2) hypoganglionosis and (3) hyperganglionosis, and that the different neuronal elements may be affected to differing degrees in individuals within each group. Resection of the aganglionic bowel is required in congenital aganglionosis but the combined diagnostic-therapeutic procedure of anorectal myotomy has been found beneficial in patients with hypoganglionosis.

Differential effect of guanethidine on dopamine and norepinephrine in rat peripheral tissues

The changes of dopamine (DA) and norepinephrine (NE) were investigated in rat peripheral tissues after guanethidine treatment (50 mg/kg i.p. five days each week) during one week (group 1, n = 10, five injections) and during 2.5 weeks (group 2, n = 8, 13 injections). Guanethidine greatly reduced NE levels in all the analyzed tissues but only partially depleted DA in kidney, bladder, stomach, intestine, lung and liver and in sympathetic ganglia. The differential pattern of changes between DA and NE induced by guanethidine suggests that peripheral DA is distributed in several neuronal or non-neuronal pools, whose presence, nature and contribution varies in the different tissues. Both noradrenergic cell bodies and small intensely fluorescent cells (SIF cells) can contribute to the DA in the superior cervical ganglion. Noradrenergic neurons seem to be the main sources of DA in seminal vesicles, vas deferens, heart and spleen. In addition to noradrenergic nerves, extraneuronal sources could account for a meaningful portion of DA in kidney, gastrointestinal tract, lung and liver. The bladder is the peripheral tissue where DA exhibits the highest resistance to the neurotoxin. Accordingly, these tissues may provide meaningful sources of non-precursor DA pools.

Response of noradrenaline and dopamine to hypoxia and sympathectomy: evidence for an independent dopaminergic reactivity

In order to assess the status of dopamine in the periphery, we submitted rats to sympathectomy (with guanethidine), to hypoxia, and to both, and measured the concentration and turnover of noradrenaline and dopamine in peripheral organs. Sympathectomy decreased noradrenaline content by 96-99% in all the organs tested. In contrast, dopamine content, which was decreased by 90% in the heart, was not significantly changed in the bladder or lungs. Based on dopamine decrease after guanethidine, and on dopamine:noradrenaline ratios in organs, we conclude that in the heart the dopamine is contained mostly in noradrenergic terminals. In other organs it appears to be contained in non-noradrenergic structures. These are found in: the bladder, stomach, lungs, and kidneys, in decreasing importance. We estimated the turnover of noradrenaline by measuring the decrease of its concentration after inhibition of tyrosine hydroxylase with alpha-methyl-p-tyrosine. Among the five organs studied, the turnover of noradrenaline was increased by long-term hypoxia (10% O2, 15 days) in the heart only (+140%). An increase of sympathetic activity during hypoxia was also found in the kidneys and lungs as shown by the increase in turnover of dopamine that was suppressed by sympathectomy. Hypoxia induced large increases in dopamine concentration in the stomach and the lungs (70 and 190% respectively). These increases were not abolished by sympathectomy and we propose that they are related to a chemosensory function of dopamine-containing paraganglia in the stomach and the lung.

Differential effect of guanethidine on dopamine and norepinephrine pools in urine, heart and superior cervical ganglion in the rat

The time-related changes of dopamine (DA) and norepinephrine (NE) pools were investigated in heart, superior cervical ganglion (SCG) and urine in rats treated chronically with guanethidine (50 mg/kg i.p. five days each week). The efficiency of sympathectomy was assessed by the great loss of NE in heart and superior cervical ganglion (SCG) (-96% and -76% respectively of control values on day 18) together with the ready reduction of NE and 3-methoxy-4-hydroxyphenylglycol (MHPG) in urine. The pattern of changes was quite different for DA, which was less readily affected and at a lesser extent than NE in heart and SCG thus suggesting the presence of norepinephrine-independent DA stores. Similarly the urinary excretion of free DA, free 3,4-dihydroxyphenylacetic acid (DOPAC) and free homovanillic acid (HVA) was slightly decreased only from the 9th day, whereas urinary conjugated DA remained unaltered. These results indicate that the greatest portion of urine free and conjugated DA, free DOPAC and free HVA derives from peripheral pools located outside noradrenergic neurons. Alternatively, the time-course of DA sensitivity to guanethidine suggests that a portion of urine DA may originate from DA stored independently from NE in noradrenergic neurons.

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.

Immunosuppressive agents prevent guanethidine-induced destruction of rat sympathetic neurons

Chronic administration of guanethidine to rats causes destruction of peripheral sympathetic neurons. Neuronal destruction, characterized morphologically by small cell infiltration and the reduction in the number of neurons within sympathetic ganglia, and biochemically by a marked reduction in tyrosine hydroxylase activity, occurred reproducibly by day 7 of treatment following 5 daily injections of 50 mg/kg guanethidine sulfate. Several observations in the literature suggested that guanethidine-induced destruction may occur by an immunologically mediated mechanism. Experiments were therefore designed to test the effects of immunosuppressive agents on guanethidine sympathectomy. A single exposure to either gamma-irradiation or cyclophosphamide, administered 8 h prior to the initiation of guanethidine treatment, protected against guanethidine-induced destruction in a dose-related manner and was virtually complete with either 900 rads of irradiation or with 100 or 150 mg/kg of cyclophosphamide. Cyclophosphamide afforded complete protection only if administered immediately prior to guanethidine treatment suggesting that it was acting during the proliferative phase of an immune response rather than non-specifically. Pretreatment with either irradiation or cyclophosphamide had no effect on the sympathectomy produced by treatment with either 6-hydroxydopamine or antibodies to nerve growth factor, nor did it prevent the accumulation of guanethidine within the sympathetic ganglia. Concurrent treatment with either azathioprine or dexamethazone also provided partial protection against guanethidine sympathectomy. These results strongly suggest that the destruction of sympathetic neurons induced by guanethidine occurs by an immunologically mediated mechanism.

Evidence for dopaminergic vasodilator innervation of the canine paw pad

1 In chloralose-anaesthetized dogs pretreated with guanethidine and pancuronium, electrical stimulation (0.2 to 5 Hz) of the peripheral end of the cut tibial nerve caused a frequency-dependent increase in femoral blood flow which was restricted to the paw pads. 2 This neurogenic vasodilatation was not attenuated by atropine, mepyramine plus burimamide, indomethacin or propranolol. It was, however, attenuated in a dose-dependent manner by intra-arterial administration of the dopamine receptor antagonist, ergometrine (0.05 to 0.5 mg). 3 The effect of ergometrine could not be explained by non-specific effects on axonal conduction or transmission or by vasospasm of the blood vessels of the paw-pads. 4 In dogs with intact tibial nerves, a pharmacologically similar dilator response localized to the paw-pads could be elicited by electrical stimulation of loci in the ipsilateral diencephalon and midbrain. This response was not due to inhibition of adrenergic vasomotor tone and was abolished by systemic ganglion blockade or by tibial nerve section as well as by femoral arterial administration of ergometrine. 5 It is suggested that the vasculature of the canine paw pads is innervated by a population of autonomic axons which utilize dopamine or a related substance as a transmitter substance and activation of which causes vasodilation.

Selectivity of neuronal degeneration produced by chronic guanethidine treatment

Chronic guanethidine treatment of rats produced extensive damage to sympathetic neurons of the superior cervical ganglion and pelvic plexus. No ultrastuctural changes were observed in parasympathetic cholinergic neurons in the ciliary ganglion and pelvic plexus, nor in sensory neurons in nodose and dorsal root ganglia. A total of only six nerve cell bodies free of degenerative changes were observed in sections of superior cervical ganglia from 20 rats. This suggests either that the earlier estimates of 5% cholinergic neurons in the superior cervical ganglion based on acetylcholinesterase staining are too high, or implies that sympathetic cholinergic neurons, unlike parasympathetic neurons, are damaged by chronic guanethidine treatment.

Intracranial injection of drugs: comparison of diffusion of 6-OHDA and guanethidine

Marked differences in extent of diffusion have been shown with the fluorescence histochemical method between guanethidine and 6-OHDA(64 mug in 2 mul) when injected acutely or chronically into the lateral hypothalamus, the substantia nigra or the amygdala of the rat brain. Cannulation damage up to 1 mm in diameter and attributed to the implantation of cannulae and placebo injection was observed. A further area of generalized damage occurred following the injection of drugs and was far greater for 6-OHDA (2 mm) than for guanethidien (0.3 mm). Guanethidine, but not 6-OHDA, caused specific damage to catecholamine-containing nerurons up to a distance of at least 3 mm and more from the cannula tip. These striking differences between the effects of intracranial injection of 6-OHDA and guanethidine are discussed in terms of the uptake and degradation of the two drugs and the anatomical features of the injection site; they are not explicable in terms of experimental conditions such as concentration, volume of injection, molecular weight or lipid solubility. The different patterns of damage would not easily be distinguished by biochemical analyses and the catecholamine specificity of 6-OHDA in studies of the central nervous system must be seriously questioned. Vascularization of chronically implanted cannula tracks and the presence of anatomical diffusion barriers are also discussed in relation to the diffusion of drugs injected intracranially.