Substance P immunoreactivity in the superior cervical ganglia of normotensive and genetically hypertensive rats

Localization of CGRP and VEGF mRNAs in the mouse superior cervical ganglion during pre- and postnatal development

The neuropeptide calcitonin gene-related peptide (CGRP) mediates inflammation and head pain by influencing the functional vascular blood supply. CGRP is a well-characterized mediator of receptor-regulated neurotransmitter release. However, knowledge regarding the role of CGRP during the development of the superior cervical ganglion (SCG) is limited. In the present study, we observed the localization of CGRP and vascular endothelial growth factor (VEGFA) mRNAs during prenatal development at embryonic day 14.5 (E14.5), E17.5 and postnatal day 1 (P1) using in situ hybridization. The antisense probe for CGRP was detected by in situ hybridization at E14.5, E17.5, and P1, and the highest levels were detected at E17.5. In contrast, the antisense probe for VEGF-A was detected by in situ hybridization in gradually increasing intensity from E14.5 to P1. The differences in the expression of these two markers revealed specific characteristics related to CGRP concentration and release compared to those of VEGF-A during development. The correlation between CGRP and VEGF-A may influence functional stress and the vascular blood supply during prenatal and postnatal development.

Neuroanatomy and Neurochemistry of Mouse Cornea

Purpose

To investigate the entire nerve architecture and content of the two main sensory neuropeptides in mouse cornea to determine if it is a good model with similarities to human corneal innervation.

Methods

Mice aged 1 to 24 weeks were used. The corneas were stained with neuronal-class βIII-tubulin, calcitonin gene–related peptide (CGRP), and substance P (SP) antibodies; whole-mount images were acquired to build an entire view of corneal innervation. To test the origin of CGRP and SP, trigeminal ganglia (TG) were processed for immunofluorescence. Relative corneal nerve fiber densities or neuron numbers were assessed by computer-assisted analysis.

Results

Between 1 and 3 weeks after birth, mouse cornea was mainly composed of a stromal nerve network. At 4 weeks, a whorl-like structure (or vortex) appeared that gradually became more defined. By 8 weeks, anatomy of corneal nerves had reached maturity. Epithelial bundles converged into the central area to form the vortex. The number and pattern of whorl-like structures were different. Subbasal nerve density and nerve terminals were greater in the center than the periphery. Nerve fibers and terminals that were CGRP-positive were more abundant than SP-positive nerves and terminals. In trigeminal ganglia, the number of CGRP-positive neurons significantly outnumbered those positive for SP.

Conclusions

This is the first study to show a complete map of the entire corneal nerves and CGRP and SP sensory neuropeptide distribution in the mouse cornea. This finding shows mouse corneal innervation has many similarities to human cornea and makes the mouse an appropriate model to study pathologies involving corneal nerves.

Modulation of tyrosine hydroxylase, neuropeptide y, glutamate, and substance p in Ganglia and brain areas involved in cardiovascular control after chronic exposure to nicotine

Considering that nicotine instantly interacts with central and peripheral nervous systems promoting cardiovascular effects after tobacco smoking, we evaluated the modulation of glutamate, tyrosine hydroxylase (TH), neuropeptide Y (NPY), and substance P (SP) in nodose/petrosal and superior cervical ganglia, as well as TH and NPY in nucleus tractus solitarii (NTS) and hypothalamic paraventricular nucleus (PVN) of normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) after 8 weeks of nicotine exposure. Immunohistochemical and in situ hybridization data demonstrated increased expression of TH in brain and ganglia related to blood pressure control, preferentially in SHR, after nicotine exposure. The alkaloid also increased NPY immunoreactivity in ganglia, NTS, and PVN of SHR, in spite of decreasing its receptor (NPY1R) binding in NTS of both strains. Nicotine increased SP and glutamate in ganglia. In summary, nicotine positively modulated the studied variables in ganglia while its central effects were mainly constrained to SHR.

Electrophysiological effects of tachykinin agonists on sympathetic ganglia of spontaneously hypertensive rats

This study investigated the cellular basis for the enhanced ganglionic responsiveness to NK1 agonists in the spontaneously hypertensive rat (SHR) in comparison to their normotensive counterpart, the Wistar-Kyoto (WKY) rat. Rats for in vivo studies were anesthetized with pentobarbital and treated with chlorisondamine (10.5 micromol/kg). Extracellular recordings from the external carotid nerve showed a greater responsiveness of decentralized SHR superior cervical ganglia (SCG) to intravenous injection of SP (32 nmol/kg). Blood pressure and heart rate were increased in SHRs, whereas WKY rats responded with a decrease in blood pressure and only slight tachycardia. Membrane properties of SCG neurons, as shown by intracellular microelectrode recordings, were similar between strains. Picospritzer application of the NK1 agonist GR-73632 (100 microM, 1 s) evoked slow depolarization and increased neuron excitability. Spontaneous firing was evoked only in some neurons. Depolarization amplitudes were similar between strains; however, the NK1 agonist depolarized a greater number of neurons in hypertensive rats. In conclusion, SHRs are more responsive to ganglion stimulation by NK1 agonists due to a greater number of responsive cells within the SCG rather than an enhanced responsiveness of individual neurons.

Increased ganglionic responses to substance P in hypertensive rats due to upregulation of NK(1) receptors

Intravenous injection of substance P (SP) increases renal nerve firing and heart rate in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats (WKYs) by stimulating sympathetic ganglia. Blood pressure is increased in SHRs but lowered in WKYs. This study assesses the role of neurokinin-1 (NK(1)) receptors in mediating the ganglion actions of SP. Rats for functional studies were anesthetized and then treated with chlorisondamine. Renal nerve, blood pressure, and heart rate responses to intravenous injection of the NK(1) receptor agonist GR-73632 were similar but less than those to equimolar doses of SP in SHRs. GR-73632 only slightly increased renal nerve firing and heart rate and lowered blood pressure in WKYs. The NK(1) receptor antagonist GR-82334 (200 nmol/kg iv) blocked the ganglionic actions of GR-73632 and the pressor response to SP in SHRs. It reduced the renal nerve and heart rate responses by 52 and 35%. This suggests that the pressor response to SP is mediated by ganglionic NK(1) receptors and that NK(1) receptors also have a prominent role in mediating the renal nerve and heart rate responses to SP. Quantitative autoradiography showed that NK(1) receptors are more abundant in the superior cervical ganglia of SHRs. RT-PCR showed increased abundance of NK(1) receptor mRNA in SHRs as well. These observations suggest that the greater ganglionic stimulation caused by SP in SHRs is due to upregulation of NK(1) receptors.

Reduced inflammation in genetically hypertensive rat airways is associated with reduced tachykinin NK(1) receptor numbers

The airways of the genetically hypertensive rat (GH) are hyperinnervated by substance P-containing sensory nerves and exhibit reduced inflammatory responsiveness to substance P and to capsaicin. The present study measured tracheal inflammation to resiniferatoxin (1.0 microgram/kg i.v.), a capsaicin analogue, which lacks the hypotensive action of capsaicin itself, alone or after the neuronal nitric oxide synthase inhibitor 1-(2-trifluoromethylphenyl)imidazole (TRIM) (50 mg/kg i.p.). The inflammatory response to resiniferatoxin alone was 50% lower in untreated GH than in control rats, a similar strain difference to that seen previously with capsaicin. Pre-treatment with TRIM had no effect on inflammation in either strain. Binding kinetics of the tachykinin NK(1) receptor antagonist [3H](S)-1-(2-[3-(3, 4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl)piperidin-3-yl]ethyl)-4- phenyl-l-azoniabicyclo[2,2,2,]octane chloride ([3H]SR140333)(0.125-16.0 nM) showed 50% reduction of B(max) in GH versus control tracheae (74+/-13 cf.165+/-26 fmol/mg protein). Our results indicate that the reduced neurogenic inflammatory responsiveness in GH rats can be attributed entirely to reduced tachykinin NK(1) receptor numbers.

Enhanced ganglionic responses to substance P in spontaneously hypertensive rats

Intravenous injection of substance P (SP) increases blood pressure in normotensive rats by stimulating sympathetic ganglia. This study compared the effects of SP to increase renal nerve firing and blood pressure in normotensive and hypertensive rats treated with chlorisondamine. The increase in renal nerve firing was greatest in spontaneously hypertensive rats (SHR), intermediate in Wistar rats, and least in Wistar-Kyoto (WKY) rats. Blood pressure was increased more in SHR than in Wistar rats. Blood pressure was not increased in WKY rats. Responses to the ganglionic stimulant 1,1-dimethyl-4-phenylpiperazinium were the same in the three strains. These results suggest that there is a selective increase in the action of SP on sympathetic ganglia of SHR and that ganglion responsiveness to SP is correlated with its effect on blood pressure.

Decreased vascular permeability response to substance P in airways of genetically hypertensive rats

1. The inbred genetically hypertensive strain (GH) of the Otago Wistar rat possesses more sensory neurons containing the neuropeptide substance P (SP) than does its genetically related control normotensive strain. 2. As SP contributes to airway inflammation by increasing microvascular permeability, we assessed the extravasation of Evans Blue dye in trachea and main bronchus of anaesthetized GH and control rats, in the presence of endogenous (capsaicin-liberated) or exogenous SP. 3. Following intravenous administration of either capsaicin (75 microg kg(-1)) or SP (3.3 nmol kg(-1)), extravasation of Evans Blue in airways from GH rats was only about 60% of that in airways of control rats. This difference was not gender-specific and responses to capsaicin were abolished by pretreatment with a selective NK1 receptor antagonist SR 140333 (360 nmol kg(-1)). 4. By contrast, the extravasation of dye caused by intravenous 5-hydroxytryptamine (0.5 micromol kg(-1)) was similar in magnitude in both GH and control strains. 5. Falls in systemic arterial blood pressure in response to exogenous SP (0.1-3 nmol kg(-1)) or acetylcholine (0.2-2 nmol kg(-1)) were also very similar between strains, but those in response to capsaicin (75 microg kg(-1)) in the GH rats were about double those in control rats. The hypotensive response to SP was abolished by SR 140333, but that to capsaicin was unaffected. 6. Our results indicate that the increased peripheral innervation density by SP-nerves in GH rats is accompanied by reduced inflammatory responses to SP. This does not involve decreased vasodilator potency of SP and is therefore probably related to altered endothelial responsiveness.

NK1 receptor antagonist blocks angiotensin II responses in renin transgenic rat medulla oblongata

Angiotensin (Ang) II increases substance P (SP) efflux from perfused slices of medulla oblongata, and a peptide antagonist of SP, [Leu11,psiCH2NH10-11]SP, blocks the acute hypotension and bradycardia caused by Ang II injected into the nucleus tractus solitarii (nTS) of Harlan Sprague-Dawley (SD) rats. We investigated whether the same relationships exist in (mRen2)27 renin transgenic (TG) rats, which have chronic elevations of medullary tissue Ang II levels. Ang II increased SP efflux (48% above control; P<0.01) from slices of medulla prepared from 8- to 12-week old male TG rats. Injections of Ang II (250 fmol in 30 nL) into the nTS of chloralose-urethane anesthetized TG rats produced a significant increase in pressure of 7+/-2 mm Hg before a 13+/-3 mm Hg fall in pressure. Ang II induced similar depressor responses in Hannover SD rats but no increase in pressure. After nTS injection of the NK1-selective SP antagonist CP-96,345 (30 pmol in 60 nL), Ang II-induced hypotension was blocked in both groups, as was the pressor component in hypertensive rats. Hypotensive and bradycardic effects of glutamate (0.6 nmol in 30 nL) injected into the nTS were not altered by CP-96,345. In vitro receptor autoradiography showed that the SP antagonist (10 or 100 microM) did not compete for 125I-Ang II binding in the dorsal medulla, a result suggesting that it did not interact directly with Ang II receptors. Thus, the nTS cardiovascular effects of Ang II are mediated by SP in both normotensive rats and a model of hypertension with altered endogenous levels of Ang II. These findings link Ang II-induced effects on SP release from brain slices of the medulla oblongata to acute cardiovascular actions of the peptide through an NK1 receptor.

Increased numbers of substance P-containing sensory neurons in a rat strain with a genetic neurotrophic defect

The GH inbred Wistar rat possesses reduced numbers of sympathetic motor neurons. In the present study, we report that substance P (SP) concentrations in superior cervical ganglion, spinal cord, iris and trachea of GH rats are about two-fold those in normal rats, and that SP-containing sensory neuron numbers are elevated in GH rats. These data suggest increased perinatal survival of SP neurons in the GH strain, due to reduced competition by sympathetic neurons for limited amounts of nerve growth factor. By contrast with the situation in iris and trachea, we found no difference between GH and normal rats in SP content of ear skin, atrium or stomach. This accords with previous findings that only some SP sensory neurons are responsive to nerve growth factor.

Neonatal nerve growth factor treatment alters the preganglionic innervation pattern of rat superior cervical ganglion

We treated rat pups with nerve growth factor (10 micrograms/animal/day s.c.) over postnatal days 1-7. Subsequent adult neuron numbers and tyrosine hydroxylase content in superior cervical ganglion were normal, but preganglionic inputs, as gauged from ganglionic choline acetyltransferase, were reduced. In parallel, intraganglionic axon terminals containing calcitonin gene-related peptide, but not those containing substance P, were increased in number. We postulate that neonatal nerve growth factor stimulates sprouting of ingrowing axons that have entered the ganglion soon after birth and that this represses subsequent establishment of cholinergic preganglionic synapses.

Neuropeptide Y in rat sympathetic neurons is altered by genetic hypertension and by age

We have used immunocytochemistry to quantitate neuronal neuropeptide Y in superior cervical ganglia of a strain of normotensive Wistar-Otago rats and a related genetically hypertensive strain over the age range 1-60 weeks. The numbers of neuropeptide Y-immunoreactive cells and total ganglionic cell numbers were both greater in ganglia of young normotensive than in those of hypertensive rats. Between 10 and 60 weeks of age, peptide immunoreactivity and total cell numbers both fell in normotensive rat ganglia but remained constant in ganglia from hypertensive rats. Densitometric analysis showed that the concentrations of neuropeptide Y were similar in neurons of age-matched individuals of both strains, but during aging there was a substantial decline in neuronal peptide content that was similar in both strains and that was not accompanied by any decline in neuronal immunoreactivity for tyrosine hydroxylase. Our results suggest that there is a developmental abnormality of neuropeptide Y in sympathetic neurons of this strain of genetically hypertensive rat and that, furthermore, the aging process is accompanied by a selective loss of neuronal neuropeptide Y that is independent of blood pressure status.