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PubMed1989

Histamine H2 receptor mediates postsynaptic excitation and presynaptic inhibition in submucous plexus neurons of the guinea-pig.

Intracellular recordings were made from submucous plexus neurons of the guinea-pig cecum maintained in vitro. Histamine (0.3-10 microM) produced a dose-dependent membrane depolarization (congruent to 13 mV with 3 microM) in about 28% of the cells tested; most of these cells showed a prominent calcium-activated potassium conductance (AH cells). The depolarization was due primarily to an inactivation of potassium conductance which is available at the resting membrane potential of -60 mV. Peak amplitude of the fast excitatory postsynaptic potential was depressed by histamine (0.1-10 microM) in a dose-dependent manner (congruent to 62% depression with 1 microM). This was observed even in those cells in which histamine did not produce any membrane depolarizations (mostly S cells). The depression of the fast excitatory postsynaptic potential resulted from the presynaptic inhibition of acetylcholine release. Histamine also reduced the amplitude of the non-cholinergic, presumably peptidergic, slow excitatory postsynaptic potential by suppressing peptide release from presynaptic nerve terminals. Peak amplitude of the adrenergic inhibitory synaptic potential was not depressed by histamine suggesting that histamine receptors are not present on presynaptic terminals of sympathetic nerve fibres. Both postsynaptic and presynaptic actions of histamine were blocked by cimetidine or ranitidine but not by pyrilamine implying that H2 receptors are involved.

Action Potentials↗
PubMed2005

Effects of ascorbic acid on the vasoactive intestinal peptide synthesis in the ileum submucous plexus of normal rats.

BACKGROUND: The aging process is a deteriorating process that attacks the gastrointestinal tract, causing changes in the number and size of neurons from the enteric nervous system. The activity of free radicals on enteric neurons is helped by the significant reduction of antioxidants. AIM: Evaluate the effect of the ascorbic acid supplementation on the neurons that produce the vasoactive intestinal peptide (VIP) in the submucous plexus of the ileum of normal rats for a period of 120 days. METHODS: Fifteen rats were divided in three groups: untreated control with 90 days, untreated control with 210 days and ascorbic acid-treated rats with 210 days. Ascorbic acid was given for 16 weeks from the 90th day of age by adding it to drinking water (1 g/L prepared fresh each day). The ileums were processed according to the immunohistochemistry technique for whole-mount preparation in order to detect the presence of VIP immunoreactive in the cellular bodies and nervous fibers in the neurons of the submucous plexus. We have verified their immunoreactivity and measured the cellular profile of 80 cellular bodies of VIP-ergic neurons from each studied group. RESULTS: The ascorbic acid supplementation did not alter physiological parameters such as water intake and food consumption of the three studied groups. We observed a significant increase of the cellular profile of VIP-ergic neurons in untreated control with 210 days when compared to untreated control with 90 days. The cellular profile of VIP-ergic neurons in ascorbic acid-treated rats with 210 days was bigger than those observed in others groups. CONCLUSION: The ascorbic acid had a neurotrophic effect on VIP-ergic neurons on the ileum after period 120 days of supplementation.

Animals↗
PubMed1995

Do vasoactive intestinal peptide (VIP)- and nitric oxide synthase-immunoreactive terminals synapse exclusively with VIP cell bodies in the submucous plexus of the guinea-pig ileum?

In the submucous plexus of the guinea-pig ileum, previous light-microscopic studies have revealed that vasoactive intestinal peptide (VIP)-immunoreactive and nitric oxide synthase (NOS)-immunoreactive terminals are found predominantly in association with VIP-immunoreactive nerve cell bodies. In this study, double-label immunohistochemistry at the light-microscopic level demonstrated co-localization of NOS-immunoreactivity and VIP-immunoreactivity in axon terminals in submucous ganglia. About 90% of nerve fibres with NOS-immunoreactivity or VIP-immunoreactivity were immunoreactive for both antigens; only about 10% of labelled varicosities contained only NOS-immunoreactivity or VIP-immunoreactivity. The VIP/NOS varicosities were more often seen in the central parts of the ganglia, close to the VIP-immunoreactive cell bodies. Ultrastructural immunocytochemistry with antibodies to VIP was used to determine if NOS/VIP terminals synapse exclusively with VIP-immunoreactive nerve cell bodies. We examined the targets of VIP-immunoreactive boutons in two submucous ganglia from different animals. Serial ultrathin sections were taken through the ganglia after they had been processed for VIP immunocytochemistry. For each cell body, the number of VIP inputs (synapses and close contacts) was determined. The number of VIP-immunoreactive synapses received by the cell bodies of submucous neurons varied from 0-4 and the number of VIP-immunoreactive close contacts varied from 3-10. There was no significant difference between VIP-immunoreactive nerve cell bodies and non-VIP nerve cell bodies in the number of VIP-immunoreactive synapses and close contacts they received. Thus, the implication from light microscopy that NOS/VIP terminals end predominantly on VIP nerve cells was not vindicated by electron microscopy.

Animals↗
PubMed2005

Topographic peculiarities of the submucous plexus in the human anorectum--consequences for histopathologic evaluation of rectal biopsies.

Chronic colorectal motility disorders are commonly encountered in the pediatric population. While most cases can be managed successfully by conservative therapy, a subgroup of patients suffers from severe constipation and requires further diagnostic procedures to identify the underlying pathologies, such as aganglionosis, hypoganglionosis or intestinal neuronal dysplasia (IND). The present study provides reference data about the quantitative distribution of nerve cells and ganglia within the submucosal plexus of the human anorectum from healthy subjects. Anorectal specimens (n = 15) obtained postmortem were divided into 6 segments beginning from the dentate line (S1 = 0-2 cm, S 2 = 2-4 cm, S3 = 4-6 cm, S4 = 6-8 cm, S5 = 8-10 cm, S6 = 10-12 cm). From each segment sections (6 microm thickness) were immunostained with a pan-neuronal marker (Protein Gene Product 9.5) to visualize the enteric nervous system. A morphometric analysis was carried out for each segment recording the number of ganglia and nerve cells of the submucous plexus. Neither ganglia nor nerve cells showed a uniform distribution pattern, but decreased continuously towards the anus. However, even the lowest segments (S1, S2) contained nerve cells and were not aganglionic. In the remaining segments ganglia with 7 or more nerve cells could be detected. The findings demonstrate segment-specific quantitative differences of the anorectal submucous plexus which should be taken into consideration for the histopathologic evaluation of rectal biopsies. Moreover, the data support the concept of a physiologic hypoganglionosis of the anal canal.

Adult↗
PubMed1983

The enteric nervous system in tissue culture. I. Cell types and their interactions in explants of the myenteric and submucous plexuses from guinea pig, rabbit and rat.

This paper describes methods for removing the ganglionated myenteric and submucous plexuses from the mammalian gut and maintaining them as explants in tissue culture. A detailed account is given of cell types, their interactions and the development of these cultures during 5 weeks in vitro. Three major cell types were identified in the cultures: neurons, glial cells and fibroblasts. The development of the plexuses in culture was studied in detail for the myenteric plexus from the guinea pig taenia coli. It followed a characteristic pattern, in which the merging of individual ganglia into a continuous monolayer of flattened neurons was accompanied and followed by the formation of an extensive outgrowth zone of flat glial cells covered by a dense mesh of outgrowing neurites. In older cultures, neuronal migration resulted in the reformation of discrete and compact aggregates, which consisted of neurons and glial cells, and were interconnected by thick neurite bundles. This arrangement resembles in many ways the original organization of enteric nervous tissue in vivo. This is the first time the enteric ganglia have been freed from the gut wall and grown in culture as explants of nervous tissue. These preparations open many new directions for investigations of the largest and most complex division of the peripheral nervous system, including studies of the molecular nature of neuronal and glial cell surfaces, analysis of cell-cell interactions, trophic factors and developmental signals.

Animals↗
PubMed1986

Synaptic inputs to immunohistochemically identified neurones in the submucous plexus of the guinea-pig small intestine.

1. Electrophysiological recordings were made from neurones in the submucous plexus of the guinea-pig small intestine, and these neurones were classified according to their synaptic inputs. 2. The neurones from which recording were made were filled during the recording period with the fluorescent dye, Lucifer Yellow, so they could be re-identified after processing for immunohistochemical localization of vasoactive intestinal peptide (VIP). 3. The presence or absence of VIP-like immunoreactivity was determined for a total of 130 neurones whose synaptic inputs had been fully characterized and eighty-two were found to be VIP reactive. After the VIP reactivity had been assessed, the preparations were reprocessed to reveal immunoreactivity for neuropeptide Y (NPY) and a further twenty-three neurones (none of which were reactive for VIP) were found to be reactive for this peptide. Of the remaining twenty-five neurones, nineteen were not reactive for either VIP or NPY and six could not be re-identified after reprocessing. 4. Electrical stimulation of internodal strands evoked excitatory synaptic potentials lasting 20-30 ms (fast responses) in all but one of the 130 neurones studied. 5. Almost all the VIP-reactive neurones (seventy-eight of eighty-two cells) exhibited inhibitory synaptic potentials, ranging in amplitude from 2 to 30 mV and lasting 150-1500 ms, but few of the VIP-negative neurones had such responses (six of forty-eight cells). No inhibitory synaptic potentials could be evoked in any of the NPY-reactive neurones. 6. Most VIP-reactive neurones (sixty-nine) had a slow excitatory synaptic potential which could be evoked by a single stimulus, lasted 5-20 s and was associated with an increase in input resistance. Only one NPY-reactive neurone had a slow excitatory potential, but such potentials were seen in nine of the nineteen VIP-negative, NPY-negative neurones. 7. In nine of the twenty-three NPY-reactive neurones a single stimulus evoked an excitatory synaptic potential (intermediate excitatory synaptic potential) lasting 500-1500 ms and associated with a fall in the input resistance. None of the VIP-negative, NPY-negative neurones exhibited the intermediate excitatory potentials but it was not possible to determine whether such potentials could be evoked in VIP-reactive neurones because the inhibitory synaptic potentials would obscure such events. 8. It is concluded that neurochemically distinct populations of submucous neurones can be distinguished physiologically on the basis of the differing combinations of types of synaptic input they receive.

Action Potentials↗
PubMed1975

Synaptic potentials recorded from neurones of the submucous plexus of guinea-pig small intestine.

1. Intracellular recordings have been made from neurones lying in the submucous plexus of guinea-pig mid small intestine. 2. Most neurones in this plexus receive an extensive excitatory input which could be abolished by tubocurarine. 3. A proportion of neurones also received a single inhibitory input which was activated by transmural stimulation. 4. Some of the characteristics of the inhibitory potentials evoked by transmural stimulation are described. 5. The observations are discussed in relation to the concept of descending excitation (Hirst, Holman & McKirdy, 1975).

Action Potentials↗
PubMed1994

ATP closes a potassium and opens a cationic conductance through different receptors in neurons of guinea pig submucous plexus.

Intracellular recordings were made to study the actions of ATP and related nucleotides on neurons from the guinea pig submucous plexus. Local application of ATP, by pressure, induced a depolarization in most AH-type neurons, which had a latency of several milliseconds, lasted for about 5 sec, appeared to reverse at about +4 mV and occurred concomitantly with a reduction in input resistance. Pressure application of ATP also depolarized the S-type neurons. In most of these cells the depolarization had two phases: the first component resembled the depolarization observed in AH cells and the second component was much slower in onset and was longer lasting (30-90 sec). The slower component was associated with an increase in input resistance, reversed polarity near the potassium equilibrium potential and was observed in isolation in 30% of S neurons. Superfusion of ATP or other analogs (0.03-10 microns) induced a slow depolarization in most of S neurons with the following rank order of potency: 2-methylthio-ATP > ATP > adenosine-5'-o-3-thiotriphosphate = ADP; alpha, beta-methylene ATP and beta, gamma-methylene ATP were inactive (10-100 microM). When whole-cell recordings were used, fast superfusion with ATP or other analogs (3-1000 microM) evoked, at negative membrane potentials, a rapidly desensitizing inward current. This current reversed polarity at about 0 mV and was much reduced in low extracellular sodium concentration. The rank order of potency of the used agonists was: ATP = adenosine-5'-o-3-thiotriphosphate = 2-methylthio-ATP > > alpha,beta-methylene ATP = beta,gamma-methylene ATP; adenosine, AMP or ADP (1 mM) were inactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1995

Localization of NADPH-diaphorase activity in the submucous plexus of the guinea-pig intestine: light and electron microscopic studies.

The localization of reduced nicotinamide adenine dinucleotide phosphate diaphorase in the submucous plexus of duodenum, jejunum, ileum, proximal colon, distal colon and rectum in the guinea-pig was examined histochemically by light and electron microscopy. The majority of reactive submucous neurons displayed features common to either Dogiel type I or type II neurons; some were closely adherent to the outer walls of lymphatic vessels. The use of 2-(2'-benzothiazolyl)-5-styryl-3-(4'-phthalhydrazidyl) tetrazolium chloride (BSPT) at the ultrastructural level showed that nicotinamide adenine dinucleotide phosphate diaphorase is a membrane-associated protein widely distributed in the cells, including the rough endoplasmic reticulum, Golgi apparatus and synaptic vesicles in the axon terminals associated with submucous neurons. On the basis of their diaphorase reactivity or the lack of it, the submucous neuronal somata and their associated terminals were observed to form several different kinds of synaptic configurations. The present quantitative analysis showed that the frequency of reactive submucous neurons in the large intestine was significantly higher than in the small intestine. Based on the ultrastructural localization of the diaphorase reaction product in positive cells, it is speculated that nitric oxide might be synthesized within the neurons. The demonstration of different synaptic configurations in the submucous ganglia suggests that the functional interaction between submucous neurons is extremely complex. Finally, the higher frequency of diaphorase reactive submucous neurons in the large intestine than in the small intestine indicates that submucous neurons in these two gut regions may not play equivalent roles.

Animals↗
PubMed2003

Actions of galanin on neurotransmission in the submucous plexus of guinea pig small intestine.

Electrophysiologic recording methods were used to study the actions of galanin on synaptic transmission in the submucous plexus of guinea pig ileum. Exposure to galanin resulted in concentration-dependent suppression of slow noradrenergic inhibitory postsynaptic potentials and fast nicotinic excitatory postsynaptic potentials in the majority of neurons. Failure of galanin to suppress nicotinic depolarizing responses to micropressure pulses of acetylcholine and failure to suppress hyperpolarizing responses to micropressure pulses of norepinephrine suggested that galanin acted at presynaptic inhibitory receptors to suppress release of acetylcholine and norepinephrine. Galanin suppressed slow excitatory postsynaptic potentials in eight of eight neurons with AH (after-hyperpolarization) type electrical behavior and in none of 26 neurons with S (synaptic) type electrical behavior. Suppression of excitatory neurotransmission in AH neurons was always associated with membrane hyperpolarization. Excitatory responses caused by experimentally applied substance P were also inhibited by galanin. Galanin-(1-16) and galanin-like peptide mimicked the inhibitory actions of galanin on neurotransmission. The selective galanin GAL2 receptor agonist [D-Trp(2)]galanin was inactive. The chimeric peptides, galanin-(1-13)-spantide I, galantide, galanin-(1-13)-neuropeptide Y(25-36) amide, galanin-(1-13)-bradykinin-(2-9)amide and galanin-(1-13)-Pro-Pro-Ala-Leu-Ala-Leu-Ala amide all produced varying degrees of suppression of the synaptic potentials. The evidence suggests that the galanin GAL1 receptor, but not the galanin GAL2 receptor, mediated the presynaptic and postsynaptic inhibitory actions of galanin.

Animals↗
PubMed2004

Effect of acetyl-L-carnitine on VIP-ergic neurons in the jejunum submucous plexus of diabetic rats.

The effect of the treatment with acetyl-L-carnitine (ALC) on neurons releasing the vasoactive intestinal polypeptide (VIP) of the submucous plexus in the jejunum of diabetic rats was the purpose of our investigation. Diabetes (DM) was induced by injecting streptozotocin endoveneously (35 mg/kg). After sacrificing the animals, the jejunum was collected and processed for VIP detection. Four groups were used: C (non-diabetic), CC (non-diabetic treated with ALC), D (diabetic), DC (diabetes treated with ALC). We analyzed the immunoreactivity and the cellular profile of 126 cell bodies. The treatment with ALC improved some aspects of DM. However, it promoted a small increase in the area of neurons from group CC, suggesting a possible neurotrophic effect. Neurons from groups D and DC showed a large increase in their cellular profile and immunoreactivity when compared to C and CC, suggesting a larger concentration of this neurotransmitter within the neurons that produce it. This observation constitutes a recurrent finding in diabetic animals, suggesting that ALC does not interfere in the pathophysiological mechanisms that unchain a higher production and/or neurotransmitter accumulation and increase the profile of the VIP-ergic neurons.

Acetylcarnitine↗
PubMed1975

Some effects of 5-hydroxytryptamine, dopamine and noradrenaline on neurones in the submucous plexus of guinea-pig small intestine.

1. Responses to the iontophoretic application of 5-hydroxytryptamine (5-HT), dopamine and noradrenaline were examined in neurones of the submucous plexus of guinea-pig small intestine. 2. Every neurone was excited by 5-HT. 3. In a proportion of cells, dopamine or noradrenaline caused an increase in membrane potential. This response was only observed in cells which received in inhibitory innervation. The responses closely resembled inhibitory synaptic potentials evoked by transmural stimulation. 4. Both inhibitory synaptic potentials and inhibitory responses to dopamine and noradrenaline were blocked by methysergide. 5. It seems possible that these two catecholamines may interact with similar receptors to those activated by inhibitory transmitter.

Animals↗
PubMed2000

Histamine H3 receptor-mediated suppression of inhibitory synaptic transmission in the submucous plexus of guinea-pig small intestine.

Conventional intracellular microelectrodes and marker injection techniques were used to study the actions of histamine on inhibitory synaptic transmission in the submucous plexus of guinea-pig small intestine. Bath application of histamine (1-300 microM) reversibly suppressed both noradrenergic and non-adrenergic slow inhibitory postsynaptic potentials in a concentration-dependent manner. These effects of histamine were mimicked by the selective histamine H(3) receptor agonist R(-)-alpha-methylhistamine but not the selective histamine H(1) receptor agonist, 6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl) heptanecarboxamide (HTMT dimaleate), or the selective histamine H(2) receptor agonist, dimaprit. The histamine H(3) receptor antagonist, thioperamide, blocked the effects of histamine. Histamine H(1) and H(2) receptor antagonists did not change the action of histamine. Hyperpolarizing responses to focal application of norepinephrine or somatostatin by pressure ejection from micropipettes were unaffected by histamine and R(-)-alpha-methylhistamine. The results suggest that histamine acts at presynaptic histamine H(3) receptors on the terminals of sympathetic postganglionic fibers and intrinsic somatostatinergic nerves in the small intestine to suppress the release of the inhibitory neurotransmitters, norepinephrine and somatostatin.

Animals↗
PubMed2004

ATP participates in three excitatory postsynaptic potentials in the submucous plexus of the guinea pig ileum.

Synaptic transmission between neurones intrinsic to the wall of the intestine involves multiple neurotransmitters. This study aimed to identify neurotransmitters responsible for non-cholinergic excitatory synaptic transmission in the submucous plexus of the guinea pig ileum. Intracellular recordings were made from secretomotor and vasodilator neurones. A single electrical stimulus to a fibre tract evoked excitatory postsynaptic potentials (EPSPs) with three different time courses - fast, slow and an EPSP with an intermediate time course (latency 96 ms, duration 1.2 s). In all neurones, blocking nicotinic receptors reduced fast EPSPs, but they were abolished in only 57 of 78 neurones. Fast EPSPs were also reduced by P2 purinoceptor blockade (5 of 27 neurones) or 5-HT(3) receptor blockade (3 of 20 neurones). The intermediate EPSP was abolished by P2 receptor blockade (13 of 13 neurones) or by the specific P2Y(1) receptor antagonist MRS 2179 (5 of 5 neurones) and was always preceded by a nicotinic or mixed nicotinic/purinergic fast EPSP. Intermediate EPSPs were observed in over half of all neurones including most non-cholinergic secretomotor neurones identified by immunoreactivity for vasoactive intestinal peptide. The slow EPSP evoked by a single pulse stimulus was also abolished by P2 receptor blockade (5 of 5 neurones) or by MRS 2179 (3 of 3 neurones). We conclude that fast EPSPs in submucous neurones are mediated by acetylcholine acting at nicotinic receptors, ATP acting at P2X receptors and 5-HT acting at 5-HT(3) receptors. Both the intermediate EPSP and the single stimulus slow EPSP are mediated by ATP acting at P2Y(1) receptors.

Acetylcholine↗
PubMed2002

Terminal ileum submucous plexus: Study of the VIP-ergic neurons of diabetic rats treated with ascorbic acid.

The aim of this study was to evaluate the effect of the ascorbic acid (AA) supplementation on the neurons that produce the vasoactive intestinal peptide (VIP) in the submucous plexus of the ileum of rat, four months after the induction of experimental diabetes mellitus with streptozotocin. Three groups of rats were used: C - control, D - diabetic, DA - diabetic receiving AA. We have measured the immunoreactivity and area of 80 cellular bodies of VIP-ergic neurons from each studied group. In the diabetic animals, we have observed hyperphagia, polydipsia, and an increase of glycemia and glycated hemoglobin. The VIP-ergic neurons have presented an increase of their immunoreactivity and the highest profiles when compared to the other groups. In the diabetic animals supplemented with AA it has been observed a small reduction in the glycemia and the water and food intake. We have also noticed smaller immunoreactivity in their VIP-ergic neurons, similar to what we have observed in the control group animals (group C).

Animals↗
PubMed1996

L-DOPA induces concentration-dependent facilitation and inhibition of presynaptic acetylcholine release in the guinea-pig submucous plexus.

Neurotransmitter- or neuromodulator-like actions of L-DOPA were investigated with intracellular recordings from submucous plexus neurons of the guinea-pig caecum. L-DOPA at 30 nM augmented the amplitude of fast EPSPs, but did not affect depolarizations elicited by puff application of acetylcholine (ACh). The augmenting effect of L-DOPA on the fast EPSPs was counteracted by L-DOPA methyl ester. The fast EPSPs were depressed by 10 microM L-DOPA, but transiently augmented after rinsing the drug. L-DOPA methyl ester did not affect the inhibitory action of L-DOPA on the fast EPSPs, but antagonized the potentiation following the inhibition. The depolarization elicited by exogenously applied ACh was inhibited by 10 microM L-DOPA. Intracellular Ca2+ concentrations ([Ca2+]i) of the neuronal soma were measured with fura-2 microfluorophotometry. The transient increase in the [Ca2+]i evoked by the somatic action potential (delta[Ca2+]AP) was facilitated by 30 nM L-DOPA, but decreased by the drug at 10 microM. It is concluded that L-DOPA at low concentrations enhances the delta[Ca2+]AP, increasing the neurotransmitter release, but at high dose diminishes the delta[Ca2+]AP, inhibiting the neurotransmission.

Acetylcholine↗
PubMed1981

The fine structure of the submucous plexus of the guinea-pig ileum. I. The ganglia, neurons, Schwann cells and neuropil.

A fine structural study was made of the ganglia, neurons, Schwann cells and neuropil of the submucous plexus of the guinea-pig ileum. The arrangement of the plexus as seen by light microscopy is briefly described. Submucous ganglia are small, containing an average of eight neurons per ganglion (compared with 43 in myenteric ganglia) and are connected with each other by fine nerve strands. The cell bodies of neurons and Schwann cells and a neuropil consisting of neuronal and Schwann cell processes from the ganglia. No other cell types or blood vessels are found within the ganglia. Ganglia are surrounded by a continuous basal lamina but lack a well-defined connective tissue investment. The glial investment of neurons is incomplete: many neurons lie directly beneath the basal lamina with no intervening Schwann cell processes, and the plasma membranes of adjacent neurons are often directly apposed over large areas. Other areas of apposition occur between the cell bodies and processes of neurons and Schwann cells. Desmosome-like membrane specializations may be seen between neurons and other neurons or Schwann cells. Submucous neurons could not be categorized according to size, shape, organelle content or types of processes. Processes emerging from nerve-cell bodies were placed into four broad categories on the basis of shape and microtubule content. Many bundles of closely apposed small nerve profiles lacking intervening Schwann processes are found in the neuropil in addition to a large number of vesiculated varicosities, some of which are directly apposed to the plasma membranes of nerve-cell bodies. A small proportion of vesiculated profiles from synapses with nerve cell bodies, their processes and profiles in the neuropil. From their structure, submucous neurons appear to form a more homogeneous population than myenteric neurons. Because of their incomplete investment they are more likely to be freely exposed to substances diffusing in the extraganglionic tissue than are neurons of sympathetic ganglia.

Animals↗