Localization of chromatographically characterized oxytocin and arginine-vasopressin to sensory neurones in the rat

Hormonal influences in migraine - interactions of oestrogen, oxytocin and CGRP

Migraine is ranked as the second highest cause of disability worldwide and the first among women aged 15-49 years. Overall, the incidence of migraine is threefold higher among women than men, though the frequency and severity of attacks varies during puberty, the menstrual cycle, pregnancy, the postpartum period and menopause. Reproductive hormones are clearly a key influence in the susceptibility of women to migraine. A fall in plasma oestrogen levels can trigger attacks of migraine without aura, whereas higher oestrogen levels seem to be protective. The basis of these effects is unknown. In this Review, we discuss what is known about sex hormones and their receptors in migraine-related areas in the CNS and the peripheral trigeminovascular pathway. We consider the actions of oestrogen via its multiple receptor subtypes and the involvement of oxytocin, which has been shown to prevent migraine attacks. We also discuss possible interactions of these hormones with the calcitonin gene-related peptide (CGRP) system in light of the success of anti-CGRP treatments. We propose a simple model to explain the hormone withdrawal trigger in menstrual migraine, which could provide a foundation for improved management and therapy for hormone-related migraine in women.

The role of oxytocin, vasopressin, and their receptors at nociceptors in peripheral pain modulation

Oxytocin and vasopressin are neurohypophyseal hormones with sequence similarity and play a central role in bodily homeostatic regulation. Pain is currently understood to be an important phenotype that those two neurohormones strongly downregulate. Nociceptors, the first component of the ascending neural circuit for pain signals, have constantly been shown to be modulated by those peptides. The nociceptor modulation appears to be critical in pain attenuation, which has led to a gradual increase in scientific interest about their physiological processes and also drawn attention to their translational potentials. This review focused on what are recently understood and stay under investigation in the functional modulation of nociceptors by oxytocin and vasopressin. Effort to produce a nociceptor-specific view could help to construct a more systematic picture of the peripheral pain modulation by oxytocin and vasopressin.

Oxytocin as a regulatory neuropeptide in the trigeminovascular system: Localization, expression and function of oxytocin and oxytocin receptors

BACKGROUND

Recent clinical findings suggest that oxytocin could be a novel treatment for migraine. However, little is known about the role of this neuropeptide/hormone and its receptor in the trigeminovascular pathway. Here we determine expression, localization, and function of oxytocin and oxytocin receptors in rat trigeminal ganglia and targets of peripheral (dura mater and cranial arteries) and central (trigeminal nucleus caudalis) afferents.

METHODS

The methods include immunohistochemistry, messenger RNA measurements, quantitative PCR, release of calcitonin gene-related peptide and myography of arterial segments.

RESULTS

Oxytocin receptor mRNA was expressed in rat trigeminal ganglia and the receptor protein was localized in numerous small to medium-sized neurons and thick axons characteristic of A∂ sensory fibers. Double immunohistochemistry revealed only a small number of neurons expressing both oxytocin receptors and calcitonin gene-related peptide. In contrast, double immunostaining showed expression of the calcitonin gene-related peptide receptor component receptor activity-modifying protein 1 and oxytocin receptors in 23% of the small cells and in 47% of the medium-sized cells. Oxytocin immunofluorescence was observed only in trigeminal ganglia satellite glial cells. Oxytocin mRNA was below detection limit in the trigeminal ganglia. The trigeminal nucleus caudalis expressed mRNA for both oxytocin and its receptor. K⁺-evoked calcitonin gene-related peptide release from either isolated trigeminal ganglia or dura mater and it was not significantly affected by oxytocin (10 µM). Oxytocin directly constricted cranial arteries ex vivo (pEC₅₀ ∼ 7); however, these effects were inhibited by the vasopressin V_1A antagonist SR49059.

CONCLUSION

Oxytocin receptors are extensively expressed throughout the rat trigeminovascular system and in particular in trigeminal ganglia A∂ neurons and fibers, but no functional oxytocin receptors were demonstrated in the dura and cranial arteries. Thus, circulating oxytocin may act on oxytocin receptors in the trigeminal ganglia to affect nociception transmission. These effects may help explain hormonal influences in migraine and offer a novel way for treatment.

Application of oxytocin with low-level laser irradiation suppresses the facilitation of cortical excitability by partial ligation of the infraorbital nerve in rats: An optical imaging study

The effects of current treatments for neuropathic pain are limited. Oxytocin is a novel candidate substance to relieve neuropathic pain, as demonstrated in various animal models with nerve injury. Low-level laser therapy (LLLT) is another option for the treatment of neuropathic pain. In this study, we quantified the effects of oxytocin or LLLT alone and the combination of oxytocin and LLLT on cortical excitation induced by electrical stimulation of the dental pulp using optical imaging with a voltage-sensitive dye in the neuropathic pain model with partial ligation of the infraorbital nerve (pl-ION). We applied oxytocin (OXT, 0.5 μmol) to the rat once on the day of pl-ION locally to the injured nerve. LLLT using a diode laser (810 nm, 0.1 W, 500 s, continuous mode) was performed daily via the skin to the injured nerve from the day of pl-ION to 2 days after pl-ION. Cortical responses to electrical stimulation of the mandibular molar pulp under urethane anesthesia were recorded 3 days after pl-ION. Both the amplitude and area of excitation in the primary and secondary somatosensory and insular cortices in pl-ION rats were larger than those in sham rats. The larger amplitude of cortical excitation caused by pl-ION was suppressed by OXT or LLLT. The expanded area of cortical excitation caused by pl-ION was suppressed by OXT with LLLT but not by OXT or LLLT alone. These results suggest that the combined application of OXT and LLLT is effective in relieving the neuropathic pain induced by trigeminal nerve injury.

Vasopressin and oxytocin in sensory neurones: expression, exocytotic release and regulation by lactation

The neurohormones arginine-vasopressin (AVP) and oxytocin (OT) synthesised in supraoptic and paraventricular nuclei of neurohypophysis regulate lactation, systemic water homeostasis and nociception. Using transgenic rats expressing AVP and OT tagged with fluorescent proteins we demonstrate that both neurohormones are expressed in sensory neurones both in vitro, in primary cultures, and in situ, in the intact ganglia; this expression was further confirmed with immunocytochemistry. Both neurohormones were expressed in nociceptive neurones immunopositive to transient receptor potential vannilloid 1 (TRPV1) channel antibodies. The AVP and OT-expressing DRG neurones responded to AVP, OT, 50 mM K⁺ and capsaicin with [Ca²⁺]_i transients; responses to AVP and OT were specifically blocked by the antagonists of V₁ AVP and OT receptors. Probing the extracellular incubation saline with ELISA revealed AVP and OT secretion from isolated DRGs; this secretion was inhibited by tetanus toxin (TeNT) indicating the role for vesicular release. Expression of OT, but not AVP in DRG neurones significantly increased during lactation. Together, the results indicate novel physiological roles (possibly related to nociception and mood regulation) of AVP and OT in the sensory neurones.

Oxytocin inhibits the activity of acid-sensing ion channels through the vasopressin, V1A receptor in primary sensory neurons

BACKGROUND AND PURPOSE

A growing number of studies have demonstrated that oxytocin (OT) plays an analgesic role in modulation of nociception and pain. Most work to date has focused on the central mechanisms of OT analgesia, but little is known about whether peripheral mechanisms are also involved. Acid-sensing ion channels (ASICs) are distributed in peripheral sensory neurons and participate in nociception. Here, we investigated the effects of OT on the activity of ASICs in dorsal root ganglion (DRG) neurons.

EXPERIMENTAL APPROACH

Electrophysiological experiments were performed on neurons from rat DRG. Nociceptive behaviour was induced by acetic acid in rats and mice lacking vasopressin, V1A receptors.

KEY RESULTS

OT inhibited the functional activity of native ASICs. Firstly, OT dose-dependently decreased the amplitude of ASIC currents in DRG neurons. Secondly, OT inhibition of ASIC currents was mimicked by arginine vasopressin (AVP) and completely blocked by the V1A receptor antagonist SR49059, but not by the OT receptor antagonist L-368899. Thirdly, OT altered acidosis-evoked membrane excitability of DRG neurons and significantly decreased the amplitude of the depolarization and number of action potentials induced by acid stimuli. Finally, peripherally administered OT or AVP inhibited nociceptive responses to intraplantar injection of acetic acid in rats. Both OT and AVP also induced an analgesic effect on acidosis-evoked pain in wild-type mice, but not in V1A receptor knockout mice.

CONCLUSIONS AND IMPLICATIONS

These results reveal a novel peripheral mechanism for the analgesic effect of OT involving the modulation of native ASICs in primary sensory neurons mediated by V1A receptors.

B-Afferents: A fundamental division of the nervous system mediating homeostasis?

The peripheral nervous system (PNS) has classically been separated into a somatic division composed of both afferent and efferent pathways and an autonomic division containing only efferents. J. N. Langley, who codified this asymmetrical plan at the beginning of the twentieth century, considered different afferents, including visceral ones, as candidates for inclusion in his concept of the “autonomic nervous system” (ANS), but he finally excluded all candidates for lack of any distinguishing histological markers. Langley's classification has been enormously influential in shaping modern ideas about both the structure and the function of the PNS. We survey recent information about the PNS and argue that many of the sensory neurons designated as “visceral” and “somatic” are in fact part of a histologically distinct group of afferents concerned primarily autonomic function. These afferents have traditionally been known as “small dark” neurons or B-neurons. In this target article we outline an association between autonomic and B-neurons based on ontogeny, cell phenotype, and functional relations, grouping them together as part of a common reflex system involved in homeostasis. This more parsimonious classification of the PNS, made possible by the identification of a group of afferents associated primarily with the ANS, avoids a number of confusions produced by the classical orientation. It may also have practical implications for an understanding of nociception, homeostatic reflexes, and the evolution of the nervous system.

Vaginocervical stimulation releases oxytocin within the spinal cord in rats

Vaginocervical stimulation (VS) significantly elevated the concentration of oxytocin (OT) in spinal cord superfusates of 8 intact urethane-anesthetized rats measured 10-15 min after VS (median [interquartile range]: 1.7 [1.00-3.37] pg/ml) compared to that measured 10-15 min before VS (1.1 [1.01-1.40] pg/ml). When VS was administered once (n = 8), it produced a 55% increase over baseline values; when administered a second time 45 min later (n = 6), it produced only a 22% increase over pre-VS values. The effects of estrogen on the VS-induced release of OT were then investigated using ovariectomized rats that were treated either with estradiol benzoate (EB; 10 microg/100 g bw) (n = 6) or with an oil vehicle (n = 6) subcutaneously for 3 days. The EB treatment significantly elevated the basal levels of OT released into spinal cord superfusates above vehicle control levels. Within 5-10 min after the onset of VS, OT concentrations in the superfusates were significantly higher in EB-treated than in vehicle-treated rats. The vehicle-treated rats did not show a significant elevation in OT concentration following VS. To rule out the possibility that the posterior pituitary gland was the source of this OT, the effect of hypophysectomy (HYPOX) was assessed on the VS-induced release of OT into spinal cord superfusates and plasma. The concentration of OT in spinal cord superfusates of both the HYPOX (n = 5) and intact rats (n = 6) increased significantly from 5.8 [4.4-6.5] pg/ml pre-VS to 7.9 [6.7-10.3] pg/ml immediately after VS, and from 4.4 [3.8-5] pg/ml pre-VS to 5.1 [4.6-5.7] pg/ml immediately after VS, respectively. There was no significant difference in baseline levels of OT in cerebrospinal fluid between the two groups. By contrast, plasma OT levels, while significantly elevated in response to VS from 3.42 [2.9-5.34] pg/ml baseline to 7.25 [5.33-15.77] pg/ml in the intact group, failed to respond significantly to VS in the HYPOX group (n = 5). The present findings provide evidence of a direct estrogen-dependent release of OT within the spinal cord in response to VS, presumably via descending oxytocinergic neurons.

Oxytocin mediates stress-induced analgesia in adult mice

As a neurohormone and as a neurotransmitter, oxytocin has been implicated in the stress response. Descending oxytocin-containing fibres project to the dorsal horn of the spinal cord, an area important for processing nociceptive inputs. Here we tested the hypothesis that oxytocin plays a role in stress-induced analgesia and modulates spinal sensory transmission. Mice lacking oxytocin exhibited significantly reduced stress-induced antinociception following both cold-swim (10 degrees C, 3 min) and restraint stress (30 min). In contrast, the mice exhibited normal behavioural responses to thermal and mechanical noxious stimuli and morphine-induced antinociception. In wild-type mice, intrathecal injection of the oxytocin antagonist dOVT (200 microM in 5 microl) significantly attenuated antinociception induced by cold-swim. Immunocytochemical staining revealed that, in the mouse, oxytocin-containing neurones in the paraventricular nucleus of the hypothalamus are activated by stress. Furthermore, oxytocin-containing fibres were present in the dorsal horn of the spinal cord. To test whether descending oxytocin-containing fibres could alter nociceptive transmission, we performed intracellular recordings of dorsal horn neurones in spinal slices from adult mice. Bath application of oxytocin (1 and 10 microM) inhibited excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation. This effect was reversed by the oxytocin antagonist dOVT (1 microM). Whole-cell recordings of dorsal horn neurones in postnatal rat slices revealed that the effect of oxytocin could be blocked by the addition of GTP-gamma-S to the recording pipette, suggesting activation of postsynaptic oxytocin receptors. We conclude that oxytocin is important for both cold-swim and restraint stress-induced antinociception, acting by inhibiting glutamatergic spinal sensory transmission.

Preprovasopressin mRNA is not present in dorsal root ganglia of the rat

Immunohistochemical studies on colchicine-treated rats have suggested that more than half of the neurons in dorsal root ganglia (DRG) contain vasopressin. Thus, vasopressin would be the most commonly found peptide in DRG neurons. In the present study we have reexamined the presence of vasopressin in DRG neurons, using a sensitive in situ hybridization method employing long riboprobes that will detect very small amounts of mRNA. The C3, C6, T2, T12, L2 and L5 DRG were studied. None of these ganglia contained any preprovasopressin mRNA. Yet, dense labeling for preprovasopressin mRNA was seen on simultaneously processed hypothalamic sections and a heavy preprotachykinin mRNA expression was seen in adjacent DRG sections. These findings demonstrate that vasopressin is not produced in DRG in normal rats.

Distribution of arginine-vasopressin in the trigeminal, dorsal root ganglia and spinal cord of the rat; depletion by capsaicin

We have measured arginine vasopressin in the neural lobe, the trigeminal ganglion (TG), dorsal root ganglia (DRG), spinal cord, trigeminal and sciatic nerves of the rat by radioimmunoassay. In control rats, the neural lobe contained 1600 pg/mg, the ganglia 52.5, 21.0, 8.5, 4.28, 3.85 pg/mg in the lumbar, sacral, cervical, thoracic, and trigeminal ganglion, respectively, the spinal cord contained 5.1, 4.3, 4.2 and 2.6 pg/mg in the lumbar, thoracic, sacral and cervical cord, respectively and the trigeminal and sciatic nerves contained 3.8 and 13 pg/mg. Neonatal capsaicin treatment depleted about 38-67% of AVP in the ganglia. Residual AVP amounted to 526.8, 30.55, 20.75, 12.88, 4.95, 2.74, 2.14, 7.94 and 2.53 pg/mg in the neural lobe, lumbar, thoracic, sacral, cervical DRG, lumbar, thoracic spinal cord, the sciatic and trigeminal nerves respectively. Capsaicin destroyed about 40.5% of total cells and 52% of AVP-immunoreactive neurons.

Neurotransmitters in subcortical somatosensory pathways

Investigations during recent years indicate that many different neuroactive substances are involved in the transmission and modulation of somesthetic information in the central nervous system. This review surveys recent developments within the field of somatosensory neurotransmission, emphasizing immunocytochemical findings. Increasing evidence indicates a widespread role for glutamate as a fast-acting excitatory neurotransmitter at different levels in somatosensory pathways. Several studies have substantiated a role for glutamate as a neurotransmitter in primary afferent neurons and in corticofugal projections, and also indicate a neurotransmitter role for glutamate in ascending somatosensory pathways. Other substances likely to be involved in somatosensory neurotransmission include the neuropeptides. Many different peptides have been detected in primary afferent neurons with unmyelinated or thinly myelinated axons, and are thus likely to be directly involved in primary afferent neurotransmission. Some neurons giving rise to ascending somatosensory pathways, primarily those with cell bodies in the dorsal horn, are also immunoreactive for peptides. Recent investigations have shown that the expression of neuropeptides, both in primary afferent and ascending tract neurons, may change as a result of various kinds of peripheral manipulation. The occurrence of neurotransmitters in intrinsic neurons and neurons providing modulating inputs to somatosensory relay nuclei (the dorsal horn, the lateral cervical nucleus, the dorsal column nuclei and the ventrobasal thalamus) is also reviewed. Neurotransmitters and modulators in such neurons include acetylcholine, monoamines, GABA, glycine, glutamate, and various neuropeptides.

Chromatographically identified oxytocin in the human peripheral nervous system

Immunoreactive oxytocin (OXT) detected in extracts of human coeliac ganglia and nn. vagi was characterized by high-performance liquid chromatography (HPLC). HPLC/RIA examinations demonstrated that a major part of the immunoreactive material in both investigated areas co-eluted with a reference synthetic OXT, but in the extracts of coeliac ganglia a second immunoreactive peak was also observed.

NF-L and peripherin immunoreactivities define distinct classes of rat sensory ganglion cells

Double immunofluorescence studies using antibodies against NF-L and peripherin revealed three distinct subpopulations of neurons in rat dorsal root ganglia (DRG). In the adult rat, 46% of the DRG neurons were small and peripherin-positive (NF-L-negative), and 48% were large and NF-L-positive (peripherin-negative). About 6% were both peripherin- and NF-L-positive. All of the DRG neurons reacted with antibodies to NF-M and nonphosphorylation-dependent or phosphorylation-independent antibodies to NF-H. The neuropeptides were predominantly found in the peripherin-positive small cell population. Eighty-seven percent of the peripherin-positive small cell population contained substance P immunoreactivity, while 43% of this cell population contained CGRP. In contrast, only 18-24% of the NF-L-positive large-cell population contained neuropeptides, and these were primarily in a smaller sized subpopulation. Similar patterns of antigen representation were observed in neonatal (PN2) DRG cell populations. Tissue cultures of sensory ganglion cells from PN2 DRG, in serum-free medium, stably maintained exclusively peripherin-positive neurons, with about 5% of these containing coexistent NF-L immunoreactivity. Very high levels of neuropeptide gene expression were exhibited by these postnatal neurons in culture.

Substance P-containing sensory neurons in the rat dorsal root ganglia innervate the adrenal medulla

The adrenal medulla is innervated by both cholinergic and substance P (SP)-containing fibres via the splanchnic nerve. SP has been shown to modulate catecholamine (CA) secretion in isolated chromaffin cells and in the perfused rat adrenal gland, however, the origin of SP-containing fibres is not known. In the present study, we have combined the techniques of SP immunohistochemistry and retrograde tracing with Fast blue injected into the left adrenal medulla of the rat in order to study whether SP-containing sensory neurons in the dorsal root ganglia innervate the adrenal medulla. The results showed that there were on average 281 +/- 31 SP-like immunoreactive cells in each left dorsal root ganglion, T3-T13 (range, 234 +/- 19 in T4 to 372 +/- 43 in T13, n = 8). The average total number of Fast blue-labelled cells (T3-T13) in 8 experiments was 172 +/- 26, distributed normally about a peak at T8 (33.8 +/- 6.3 cells) and T9 (33.3 +/- 6.8 cells) with the least at T3 (1.5 +/- 0.8) and T13 (5.2 +/- 2.0). No Fast blue-labelled cells were found in the right DRG. In the left DRG, the average number of cells exhibiting both SP and Fast blue labelled cells were distributed from T7 to T9. These results demonstrate that SP-containing sensory neurons in the dorsal root ganglia provide an ipsilateral innervation of the adrenal medulla in rats.

Localization of NADPH-diaphorase-containing neurons in sensory ganglia of the rat

The presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase activity was studied histochemically in the sensory ganglia of the rat. Supraspinally, the trigeminal ganglion possessed only a few cells positively stained for NADPH-diaphorase, while a large number of positive neurons was found in the nodose ganglion. In the dorsal root ganglia, the distribution of positive cells showed a peculiar pattern in relation to spinal levels. Very minor populations (less than 2% of the total ganglionic cells) exhibited positive reaction in ganglia at levels ranging from the first cervical (C1) to fourth thoracic (T4) and from the second lumber (L2) through the entire sacral levels. In the middle to lower thoracic levels (from T5 to L1), however, abundant diaphorase-positive cells were observed. From these positive neurons it was possible to trace intensely stained nerve fibers. In the lower thoracic level, for example, dense positive fibers were seen in the ramus communicans. Retrograde tracing studies revealed that diaphorase-containing neurons in the lower thoracic level project at least partly to the gastric wall and the celiac ganglion. These results indicate that the diaphorase-positive ganglionic neurons in the thoracicolumbar levels may carry autonomic visceral afferent information. Double staining with NADPH-diaphorase histochemistry and peptide immunohistochemistry revealed that NADPH-diaphorase colocalizes with calcitonin gene-related peptide and substance P in many of these visceral afferent neurons.

Oxytocinergic innervation of the rat spinal cord. An electron microscopic study

Pre- and postembedding immunocytochemical procedures were used, together with antisera raised against oxytocin or its neurophysin, to characterize oxytocinergic pathways in the rat spinal cord, at the electron microscopic level. Pre-embedding immunoperoxidase staining performed on vibratome sections revealed oxytocin- and neurophysin-positive axonal profiles and terminals scattered predominantly in laminae I and II of the dorsal horn and in the central gray (lamina X). They were also visible, but to a lesser extent, in the intermediolateral columns, at thoracic and lumbar levels. Postembedding immunogold staining performed directly on ultrathin sections of the same areas, fixed in osmium and embedded in resin, permitted to show clearly that the oxytocinergic axons made symmetrical and asymmetrical synaptic contacts onto dendritic profiles. It also allowed subcellular localization of the neuropeptide immunoreactivities which were restricted to relatively large, electron-dense vesicles in the immunopositive terminals. Oxytocinergic terminals were never seen to participate in glomerular configurations in the superficial layers of the dorsal horn nor were immunoreactive cell bodies visible in any spinal area. Our results provide direct morphological evidence that oxytocinergic pathways make synapses in several regions of the spinal cord, thus supporting the contention that oxytocin may exert neurotransmitter/neuromodulator actions in this area of the CNS.

Characterization of oxytocin immunoreactivity in human sympathetic paravertebral ganglia

Immunoreactive oxytocin (IR-OXT) detected in extracts of human lumbar sympathetic paravertebral ganglia was characterized by high-performance liquid chromatography (HPLC). The immunoreactive substance was found to elute at the same position as the reference preparation of oxytocin (OXT). The results revealed the presence of chromatographically identified OXT in human sympathetic ganglia.

Percentages of dorsal root axons immunoreactive for galanin are higher than those immunoreactive for calcitonin gene-related peptide in the rat

The present study shows that 28% of the myelinated and 27% of the unmyelinated axons in the L5 and S1 rat dorsal roots are immunolabeled for galanin. By contrast only 10% of the myelinated and 15% of the unmyelinated axons are immunolabeled for calcitonin gene-related peptide, which is the numerically predominant primary afferent peptide marker for dorsal root ganglion cells. Thus galanin, because of its presence in so many primary afferent fibers, emerges as an important primary afferent marker. In addition, since our data also show that galanin is present predominantly in unmyelinated and fine myelinated sensory axons, a hypothesis is that it is particularly concerned with the transmission of noxious information.

High levels of mRNA coding for substance P, somatostatin and alpha-tubulin are expressed by rat and rabbit dorsal root ganglia neurons

Oligonucleotide probes complementary to alpha-tubulin, preprotachykinin A (PPT A), preprosomatostatin (PPSOM), and preproarginine-vasopressin (PPAVP) mRNA were hybridized to sections of rat and rabbit brain and dorsal root ganglia (DRG) at all spinal levels. Approximately 100% of the DRG neurons in the rat and rabbit express alpha-tubulin mRNA, 20-30% express PPT A mRNA and 5-17% express PPSOM mRNA. Whereas neurons which express PPSOM mRNA are of relative uniform size, the neurons which express PPT A mRNA segregate into two broad groups. One group is composed of smaller neurons (200-2,000 microns 2) which contain an extremely dense concentration of PPT A mRNA. The second group is composed of larger neurons (2,000-3,500 microns 2) which contain a moderate concentration of PPT A mRNA. PPAVP mRNA is present in very high concentrations in the paraventricular and supraoptic nucleus of the rat hypothalamus but is not detected in any DRG neurons. In both the rat and the rabbit the density of PPT A and PPSOM mRNA is high in individual DRG neurons in comparison to PPT A and PPSOM mRNA levels contained in most forebrain neurons. These results suggest that although the level of neuropeptide present in DRG neurons is relatively low in comparison to other brain areas, the rate of sensory neuropeptide synthesis and turnover, as reflected by mRNA content, is extremely high.

Presence and actions of vasopressin-like peptides in the rabbit anterior uvea

The presence of vasopressin-like immunoreactivity (VP-IR) in the rabbit eye was demonstrated by radioimmunoassay. Trigeminal nerve denervation resulted in a significant and selective decrease in the levels of VP-IR in the iris sphincter muscle and the cornea. The isolated iris sphincter muscle contracted in response to low concentrations of [Arg8]vasopressin (AVP) and related peptides. The V1 vasopressin receptor antagonist, d(CH2)5Tyr(Me)AVP, potently inhibited the contractile responses to AVP. AVP was found to induce an increase in the accumulation of inositol phosphates in the iris sphincter muscle but not in the dilator/ciliary body preparation in vitro. The present investigation demonstrates the presence of VP-IR in the rabbit eye and that this substance may be another sensory nerve-derived mediator acting on specific target sites in the anterior uvea.

Neurotransmitter phenotype plasticity in cultured dissociated adult rat dorsal root ganglia: an immunocytochemical study

Culturing sympathetic ganglion neurons in vitro may modify phenotypic expression of some neurotransmitters. For dorsal root ganglia (DRG), contradictory results have been reported; most studies have used immature material. We have therefore performed a detailed immunocytochemical analysis of the transmitter content of cultured adult rat DRG neurons. To demonstrate possible modifications of neurotransmitter phenotypes, we have compared the results obtained with the same techniques on neurons cultured for 3 days and on freshly dissociated DRG cells. Also, the transmitter profile of cultured neurons was compared with that known from in situ studies. Out of 22 antigens studied, 20 were detected in cultured DRG neurons. All of them were expressed in small and/or intermediate-sized cells. Large neurons only contained CGRP, VIP, NPY, beta-END, ENK, and GABA. The percentage of immunostained neurons varied for the various antisera: less than 10% of cultured neurons were positive for ENK, beta-LPH, beta-END, DYN, VASO, and OXY; 10-30% for SOM, CCK, CAT, and SP; and greater than 30% for NPY, CRF, GLU, NT, VIP, GABA, GRP, CGRP, 5-HT, and TRH. In the latter two groups of transmitters (except CGRP), the proportion of immunoreactive neurons was by far larger in cultured than in freshly dissociated DRG. The most pronounced (greater than 25%) increase in the proportion of positively stained neurons after culturing was observed for the GRP, CRF, TRH, and 5-HT antisera. Serotonin was the only transmitter identified in cultured but not in freshly dissociated cells. These data indicate, on one hand, that various antigens, for example, CAT, GABA, NT, TRH, NPY, beta-LPH, and beta-END, which up to now have not been described in DRG in situ, can be detected immunocytochemically a few hours after dissociation of adult rat DRG. On the other hand, several transmitters, for example, VIP, NPY, SP, GABA, GLU, NT, GRP, CRF, TRH, and 5-HT, are expressed in a significantly higher proportion of cells in cultured than in freshly dissociated preparations. This might reflect a change in the phenotypic expression of transmitters due to the new environment generated by the culture conditions, a hypothesis that can be tested by measuring specific mRNA levels. Moreover, considering the plasticity and multipotentiality of their transmitter phenotype, cultured adult DRG neurons might represent an interesting material for autografts into the injured central nervous system.

Cytochemistry of the trigeminal and dorsal root ganglia and spinal cord of the rat

1. The primary sensory neurones have been classified into large light (LLC), type A, small dark (SDC), type B and type C cells on the basis of size, ultrastuctural and immunocytochemical characteristics. 2. Subclassifications have been described according to the configuration and spatial organization of cytoplasmic organelles. 3. Furthermore, the LLC are immunoreactive with a monoclonal antibody, RT97, directed against a neurofilament protein and the SDC are positive with anti-arginine vasopressin (AVP). 4. The majority of the neurochemical substances including substance P (SP), somatostatin (SOM), fluoride resistant acid phosphatase (FRAP), 5-hydroxytryptamine (5-HT) and glutamate were localized to the small and intermediate diameter neurones measuring 9-40 microns. 5. The cytochemistry of the dorsal horn was similar to the dorsal root ganglia (DRG). 6. There is good evidence that substance P (SP) and somatostatin (SOM) are transmitters for a proportion of nociceptive neurones but the neurotransmitters utilized by the rest of the subtypes are unknown. 7. 5-hydroxytryptamine (5-HT) and glutamate may be putative transmitters of the primary sensory neurones as they are localized in 28-30% of the SDC. 8. The wider distribution and extensive coexistence of the neuropeptides is incompatible with neurotransmitter function, but some may be neuromodulators whereas others such as arginine vasopressin (AVP) are useful markers for identifying type B neurones.

Nerve growth factor synthesis in cultured rat iris: modulation by endogenous transmitter substances

Organ cultures of rat iris show a characteristic change in the levels of both nerve growth factor (NGF) and its mRNA: a rapid but transient initial increase is followed by a smaller but persistently elevated NGF synthesis. This time course may be influenced by release of a factor(s) from degenerating nerve terminals and/or by the lack of some factor(s) repressing NGF synthesis in vivo. We therefore analyzed the influence of biogenic amine transmitter substances and putative neuropeptides on this elevation of NGF synthesis in cultured iris. The marked increase of NGF synthesis seen initially in culture was not completely mimicked by any of the substances tested. A specific increase in NGF production up to 150% of control was observed only with cGMP. We also obtained some evidence that reaction to trauma following the culture procedure could enhance NGF production: cutting of irides into small pieces increased NGF production in culture up to 250% of control and, vice versa, treatment with 1 microM dexamethasone decreased NGF production to about 60% of control. However, the sympathetic neurotransmitter norepinephrine (NE) decreased both NGF and its mRNA levels specifically in a dose-dependent manner (0.01-1 mM) to a minimum of about 25% of control. In situ hybridization with mRNA(NGF)-specific probes showed that in cultures of dissociated iris cells all cells were capable of expressing mRNA(NGF), but that 0.1 mM NE preferentially decreased expression of mRNA(NGF) in smooth muscle cells. Thus, our results indicate that the sympathetic transmitter NE is capable of downregulating NGF synthesis in the target cells of sympathetic neurons.