Tachykinins produce fast and slow depolarizations in sympathetic neurons of rat coeliac-superior mesenteric ganglia

Tachykininergic synaptic transmission in the coeliac ganglion of the guinea-pig

1. The responses of coeliac ganglion neurones of the guinea-pig to electrical stimulation of the mesenteric nerves and applications of tachykinin receptor agonists were investigated by use of intracellular recording techniques. 2. Ganglion neurones were classified into three groups based on firing patterns in response to a depolarizing current pulse: phasic (38% of the population), tonic (39%) and atypical (23%). In the majority of phasic neurones (91%) a long after-hyperpolarization (LAH) lasting 5-8 s followed action potentials induced by a train of depolarizing current pulses. In contrast, LAH was rarely observed in tonic neurones (5%). 3. In most of tonic neurones (90%) slow excitatory post-synaptic potentials (e.p.s.ps) lasting 3-10 min were evoked by repetitive electrical stimulation of the mesenteric nerves. Prolonged depolarizations were also evoked in most tonic neurones by applications of substance P (SP), neurokinin A (NKA) or senktide, a tachykinin NK3 receptor agonist. 4. In most of phasic neurones (73%), mesenteric nerve stimulation did not induce an obvious depolarization but induced a prolonged inhibition of LAH lasting 3-10 min. Bath-applied tachykinin receptor agonists similarly induced an inhibition of LAH without causing depolarization in most of the phasic neurones. 5. GR 71251 (5 microM), a tachykinin NK1 receptor antagonist, partially depressed the nerve-evoked slow e.p.s.ps in tonic neurones and the nerve-evoked LAH inhibition in phasic neurones. 6. Capsaicin (0.1-5 microM) induced a prolonged depolarization in tonic neurones and an inhibition of LAH in phasic neurones. 7. A mixture of peptidase inhibitors potentiated the depolarization and the LAH inhibition evoked by nerve stimulation, SP and NKA, but not those evoked by senktide. 8. It is concluded that tonic neurones respond to repetitive mesenteric nerve stimulation preferentially with slow e.p.s.ps and that phasic neurones respond preferentially with LAH inhibition. The present study further suggests that SP and NKA, released from axon collaterals of primary afferent neurones, produce slow e.p.s.ps in tonic neurones and the LAH inhibition in phasic neurones via NK1 receptors.

Selective association of nerve fibres immunoreactive for substance P or bombesin with putative cholinergic neurons of the male rat major pelvic ganglion

The male rat major pelvic ganglion contains both sympathetic and parasympathetic neurons that supply the lower urinary and digestive tracts, and the reproductive organs. The aim of this study was to describe the distribution and identify potential targets of sensory and intestinofugal axons in this ganglion. Two putative markers of these projections were chosen, substance P for primary sensory axons and bombesin for myenteric intestinofugal projections. Varicose substance P-immunoreactive axons were associated only with non-noradrenergic (putative cholinergic) somata, and most commonly with those that contained vasoactive intestinal peptide. Immunoreactivity for substance P was also present in a small group of non-noradrenergic somata, many of which were immunoreactive for enkephalins, neuropeptide Y or vasoactive intestinal peptide. Bombesin immunoreactivity was found only in preterminal and terminal (varicose) axons, the latter of which were exclusively associated with non-noradrenergic somata that contain neuropeptide Y-immunoreactivity. Some varicose axons containing either substance P- or bombesin-immunoreactivity were intermingled with clumps of small, intensely fluorescent cells. These studies indicate that substance P- and bombesin-immunoreactive axons are likely to connect with numerically small, but discrete, populations of pelvic neurons.

Different responses to opioids measured in terminals and somas of Edinger-Westphal neurons

Neurotransmitter receptors on the axon terminals of a neuron can be located a considerable distance away from comparable receptors on the cell body or dendrites of the same neuron. We examined the effects of activating either nerve terminal receptors or those located on or near the somas of chick Edinger-Westphal neurons. Cell body responses were measured via intracellular recording in a brain slice preparation. To measure nerve terminal responses, intracellular recordings were obtained from the large, calyciform nerve endings in intact ciliary ganglia, which emanate from neurons of the lateral Edinger-Westphal nucleus. Cell bodies of Edinger-Westphal neurons responded to leucine-enkephalin with a dose-dependent hyperpolarization that was associated with a decrease in input resistance. In spontaneously active Edinger-Westphal somas, leucine-enkephalin caused marked inhibition of suprathreshold and subthreshold activity, indicating that, as with a number of other central neurons, the major effect of opioids was to reduce excitability. The response to opioids was sensitive to naloxone (1 microM) and was a direct effect, since it was not blocked by either 0.5 microM tetrodotoxin or 100 microM cadmium. More selective mu ([D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin) and delta ([D-Ser2]-leucine-enkephalin-Thr and [D-Pen2,5]-enkephalin) opioid agonists produced effects similar to those of leucine-enkephalin. Opioids produced strikingly different effects in the nerve terminals of Edinger-Westphal neurons, where the major effect was a depolarization associated with a decrease in input resistance. The effects of opioids in the terminals were reduced in a low sodium buffer, indicating that they were dependent on the presence of extracellular sodium.(ABSTRACT TRUNCATED AT 250 WORDS)

Light- and electron-microscopic study of synaptic connections in the paracervical ganglion of the female rat: special reference to calcitonin gene-related peptide-, galanin- and tachykinin (substance P and neurokinin A)-immunoreactive nerve fibers and terminals

Nerve fibers and varicosities in the pelvic paracervical ganglia (PG) are immunoreactive for the neuropeptides calcitonin gene-related peptide, galanin, and the tachykinins substance P and neurokinin A. Many of these fibers and varicosities are capsaicin-sensitive, originate in dorsal root ganglia and, thus, are considered to be primary afferent fibers. Numerous immunoreactive varicosities are pericellular to principal neurons in the PG. The present study examines the ultrastructure of calcitonin gene-related peptide-, galanin-, substance P-, and neurokinin A-immunoreactive nerve fibers and varicosities in the ganglia to determine their relationships to principal neurons and their synaptic connectivity. Paracervical ganglia of female rats were processed for light-microscopic immunohistochemistry using antisera against synapsin I, as a nerve terminal marker, and microtubule-associated protein-2 to define soma and dendrites. The rationale for performing this co-immunohistochemical analysis was to reveal the relationship between nerve endings and principal neurons. Synapsin I endings were predominantly axosomatic with fewer being axodendritic. Other ganglia were processed for electron-microscopic immunohistochemistry using both standard immunogold and peroxidase-anti-peroxidase procedures. Unmyelinated fibers and varicosities immunoreactive for calcitonin gene-related peptide, galanin, and the tachykinins were routinely observed in the interstitium between neuron somas. Numerous immunoreactive axon profiles were present in small groups that were ensheathed by Schwann cells. Immunoreactive fibers and varicosities were also observed within the satellite-cell sheath of the neuron soma and often intimately associated with the membrane of the soma, somal protrusions, or with the proximal part of a dendrite. Membrane specializations, indicative of synaptic contacts, between the fibers and the principal neurons were observed. It is suggested that these peptide-immunoreactive sensory fibers and varicosities are involved in regulation of activity in the PG.

Substance P opens cation channels and closes potassium channels in rat locus coeruleus neurons

Whole-cell recordings were made from neurons of the rat locus coeruleus in a tissue slice removed from rat brain. Substance P caused an inward current in cells voltage-clamped at -60 mV. The effect of substance P was concentration-dependent (30 nM-3 microM) and was mimicked by similar concentrations of substance K and neuromedin K. The inward current resulted predominantly from an increase in membrane cation conductance; in potassium-free solutions it reversed polarity at about 12 mV. Substance P also reduced the conductance of an inwardly rectifying potassium current; this action was studied with low external sodium concentration. It is concluded that substance P excites rat locus coeruleus neurons by activating an intracellular transduction pathway leading to both cation conductance increase and potassium conductance decrease.

An after-depolarization following action potentials and its modulation by substance P in rat sympathetic neurons

Sympathetic neurons in rat coeliac-superior mesenteric ganglia (C-SMG) displayed an after-depolarization (ADP) following action potentials and after-hyperpolarization. The ADP had amplitudes of 3-10 mV and lasted for 2-6 s, during which membrane resistance and excitability of C-SMG neurons increased. The reversal potential of ADP was dependent on external K+ concentrations. The ADP was suppressed in a solution containing Cd2+ or zero Ca2+. The ADP thus appears to be produced by inhibition of certain K+ channels via a Ca(2+)-dependent process. Substances P (SP) depolarized ganglion cells and increased the ADP, leading to a long-lasting increase in membrane excitability of rat C-SMG neurons.

Fast and slow depolarizations produced by substance P and other tachykinins in sympathetic neurons of rat prevertebral ganglia

Using intracellular recording, we examined the effects of three mammalian tachykinins, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB), on sympathetic neurons of isolated rat coeliac-superior mesenteric ganglia (C-SMG). The 3 tachykinins elicited two distinct depolarizing responses in ganglion cells: fast depolarization with time-to-peak of 1-2 sec and duration of 5-10 sec, and slow depolarization with time-to-peak of about 20 sec and duration of 120-140 sec. Both fast and slow responses persisted in a solution containing low Ca2+ and high Mg2+ or tetrodotoxin, which indicates that the tachykinins directly act on ganglion cells to produce fast and slow depolarizations. The two types of tachykinin-induced responses exhibited clearly distinguishable properties. The membrane conductance was increased during the fast response, but not significantly changed, slightly decreased or sometimes increased during the slow response. Within certain range of membrane potential, the amplitude of fast response increased upon membrane hyperpolarization and decreased upon depolarization of ganglion cells. In contrast, the amplitude of slow response associated with membrane conductance decrease was increased with membrane depolarization and decreased with hyperpolarization. The fast response was markedly suppressed in a Na(+)-deficient solution, a solution containing nominally zero Ca2+ (plus 0.1 mM EGTA in some cases), and in a solution containing Cd2+ or Mn2+, whereas the slow response was not affected in these solutions and was augmented in some cells in K(+)-free solution. Thus it seems that the increase in Ca(2+)-dependent cationic conductance underlies the fast response and that the slow response is produced at least in part by suppression of certain K+ channels. The fast response progressively decreased in amplitude upon repeated application of the peptides with short intervals, whereas the slow response was rather augmented by repeated application. Lowering the temperature markedly depressed the slow response, while the fast response remained almost unaffected. It is therefore likely that the fast and slow depolarizations are mediated by two different subtypes of tachykinin receptors or a single class of receptors linked with two different intracellular mechanisms. Measurement of tachykinins in several sympathetic ganglia by combined use of HPLC and radioimmunoassay revealed that the highest amount of SP occurs in the C-SMG where the content of SP (136.0 pmol/g protein) was higher than those of NKA (44.3) and NKB (18.7). SP thus appears to function as a major tachykinin in rat C-SMG.

Effects of tachykinins on myenteric neurones of the guinea-pig gastric corpus: involvement of NK-3 receptors

Responses of gastric myenteric neurones evoked by the mammalian tachykinins substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) were investigated using conventional intracellular recording methods. Application of the tachykinins caused a long lasting depolarization of the membrane potential which was associated with increased spike discharge and augmented excitability of the cells. The responses slowly desensitized. Additionally, cross desensitization occurred between SP, NKA and NKB. Both the NK-1 receptor agonist [Sar9,MetO2(11)]SP and the NK-2 receptor agonist [beta-Ala8]NKA(4-10) had no effect on the electrical properties of the neurones. Only the NK-3 receptor agonist [MePhe7]NKB mimicked the excitatory response observed during SP, NKA and NKB applications. [MePhe7]NKB-induced desensitization abolished the response to SP, NKA and NKB. However, long lasting applications of [Sar9,MetO2(11)]SP or [beta-Ala8]NKA(4-10) had no effect on the SP, NKA or NKB responses. The excitatory effect of SP, NKA and NKB remained unchanged during application of the tachykinin analogues [D-Arg1,D-Trp7,9,Leu11]SP and [Tyr5,D-Trp6,8,9,Arg10]NKA(4-10). The results indicate that SP, NKA and NKB act as excitatory neuromodulators within the enteric nervous system of the stomach. The effects of SP, NKA and NKB appeared to be mediated by activation of NK-3 receptors.

Substance P modulates the time course of nicotinic but not muscarinic catecholamine secretion from perfused adrenal glands of rat

1. Substance P (SP) and acetylcholine (ACh) are contained within the splanchnic nerve terminals in the adrenal gland and can be released in response to stress. In the rat, the release of aCh brings about secretion of catecholamines (CA) by acting on nicotinic and muscarinic receptors on the adrenal chromaffin cells. 2. In the present study, we have used a rat isolated adrenal gland preparation to investigate the effects of SP, perfused at different concentrations, on CA secretion evoked by 10(-5) M nicotine and 10(-4) M muscarine. 3. In the first 10 min stimulation period (S1), in the absence of SP, nicotine (10(-5) M) evoked substantial and equal secretion of noradrenaline (NA) and adrenaline (Ad). In a second 10 min stimulation period (S2), carried out 18 min after S1, the nicotinic response was desensitized. In contrast, the muscarinic response, which preferentially evoked Ad secretion in S1 (Ad/NA: 8.7/1), was well maintained in S2. 4. SP present in S1 had no effect on desensitization of the subsequent nicotinic response in S2. 5. At low concentrations (10(-7)-10(-10) M), SP changed the time course of nicotine-induced CA secretion during S1 by enhancing CA secretion in the first 4 min and inhibiting CA secretion thereafter. The maximal effect occurred at 10(-9) M SP. 6. At a higher concentration (10(-5) M), SP inhibited total nicotinic CA secretion throughout S1 and produced a biphasic secretion of CA (depressed in the presence of SP and enhanced after wash out of SP). Pre-exposure of adrenal glands to SP (10-' to 10- M) for 10min produced marked inhibition of the nicotine-induced CA secretion. 7. In contrast to the effect of SP on the nicotinic response, SP from 10- to 10-SM had no effect on muscarinic CA secretion. 8. This difference in sensitivity of the nicotinic and muscarinic responses to SP points to a diversity of mechanisms available for control of adrenal catecholamine secretion. In addition to the ability of SP to increase or decrease the total amount of adrenal CA secretion, dependent on the concentration of SP, the present study shows that SP can change the time-course of nicotinic CA secretion. These results with the rat adrenal gland perfused in vitro suggests both a quantitative and temporal role for SP as a novel modulator of adrenal CA secretion.

Substance P mediates synaptic transmission between rat myenteric neurones in cell culture

1. Whole-cell patch-clamp recordings were made from pairs of neurones in cell cultures of rat myenteric neurones. In some pairs, action potentials evoked in the first neurone evoked a slow excitatory postsynaptic potential (EPSP) in the second neurone. 2. Action potentials at a frequency of at least 5 Hz were required to evoked slow EPSPs. In one group of cells, the slow EPSP followed a series of nicotinic fast EPSPs; in another group, fast EPSPs did not precede the slow EPSP. 3. The slow EPSPs were 2-16 mV in amplitude and were accompanied by decreased resting potassium conductance. 4. Most (17/28) neurones in which action potentials evoked only slow EPSPs in a follower cell contained substance P (SP)-like immunoreactivity; they were not immunoreactive for 5-hydroxytryptamine (0/15) or vasoactive intestinal peptide (0/22). 5. Postsynaptic responses to SP, neurokinin A and a synthetic tachykinin [( pGlu6, Pro9]SP6-11) mimicked the slow EPSPs. The non-tachykinin peptide vasoactive intestinal polypeptide (VIP), which was not found in neurones that evoked only slow EPSPs, also mimicked the slow EPSPs. Responsiveness to SP decreased significantly during slow EPSPs. 6. Desensitization to either SP or VIP reduced or prevented the slow EPSPs and also responses to each other. Two proposed antagonists of SP receptors, [D-Arg1, D-Pro2,D-Trp7,9,Leu11]substance P and [D-Arg1,D-Trp7,9,Leu11]substance P, did not affect the slow EPSPs significantly. 7. Antisera against SP reversibly blocked or reduced slow EPSPs evoked by eight of thirteen presynaptic neurones that evoked slow EPSPs without evoking fast EPSPs. All eight of the presynaptic neurones that evoked anti-SP-sensitive slow EPSPs contained SP-like immunoreactivity. None of the presynaptic neurones that evoked anti-SP-insensitive slow EPSPs contained detectable SP-like immunoreactivity. Normal sera and anti-VIP antisera did not alter the slow EPSPs detectably. 8. It is concluded that subsets of myenteric neurones release an SP-like transmitter to evoke slow EPSPs. These neurones appear to lack a 'classical' neurotransmitter that evokes fast EPSPs.