Galanin-immunoreactive cells and their relation to calcitonin gene-related peptide-, substance P- and somatostatin-immunoreactive cells in rat lumbar dorsal root ganglia

Noradrenaline regulates substance P release from rat dorsal root ganglion neurons in vitro

OBJECTIVE

To determine whether activation and/or inhibition of α-adrenoreceptors influences substance P (SP) release from dorsal root ganglion (DRG) primary sensory neurons in vitro.

METHODS

DRGs were dissected from 15-day embryonic Wistar rats. DRG neurons were dissociated and cultured for 2 d and then exposed to noradrenaline (NA) alone (1×10(-4) mol/L), or along with the α1-adrenoreceptor antagonist prazosin (1×10(-6) mol/L) or the α2-adrenoreceptor antagonist yohimbine (1×10(-5) mol/L) for 4 d. Then, RT-PCR was used to determine the levels of preprotachykinin (PPT) mRNA encoding for SP and Western blot to assess the protein levels of SP. Basal and capsaicin (CAP)-evoked SP release were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

CAP-evoked SP release was sensitized by NA and this effect was inhibited by pre-incubation with prazosin but not with yohimbine. The levels of PPT mRNA, SP peptide, and basal SP release did not change significantly in any of the experimental conditions.

CONCLUSION

NA may significantly increase CAP-evoked SP release through activation of α-adrenoreceptors, which may contribute to noradrenergic pain modulation.

Immunohistochemical characterization of TH13-L2 spinal ganglia neurons in sheep (Ovis aries)

Spinal ganglia (SG) neurons are commonly classified according to various specific features. The most widespread classification based on morphological and ultrastructural features subdivides SG neurons into light and small dark neurons. Using immunohistochemical, histochemical and lectin methods, it is possible to further subdivide the small dark neurons into two subpopulations: peptidergic and nonpeptidergic neurons. The majority of studies on SG neurons were carried out on mice and rats; there are few or no studies on large mammals. In this study, some of the widely used neuronal markers, neurofilament 200 kDa (NF200), substance P (SP), calcitonin gene-related peptide (CGRP) and isolectin B4 (IB4), were employed to characterize neuronal nitric oxide synthase (nNOS)-immunoreactivity (-IR) in sheep (Ovis aries) SG (Th13-L2) neurons. The majority of the SG neurons were IB4-labeled (79 +/- 10%), followed by NF200- (45 +/- 4%), NOS- (44 +/- 10%), SP- (42 +/- 5%) and CGRP-IR (35 +/- 7%) neurons. The triple staining experiments showed that a higher percentage (75 +/- 16%) of NOS-IR neurons bound both IB4 and CGRP, or both IB4 and SP (49 +/- 6%). The IB4 marker showed an unexpected staining pattern; in fact, IB4-labeled neurons largely colocalized with NF200, usually considered a marker of light SG neurons, and with CGRP and SP. For this reason, IB4 cannot be employed in sheep to differentiate between light and dark neurons, or between peptidergic and nonpeptidergic neurons. These results suggest the importance of being cautious when comparing data among different species.

Development of galanin-containing nerve fibres in rat tibia

Galanin exerts tonic inhibition of nociceptive input to the central nervous system. Recently, this peptide was demonstrated in several neuronal and non-neuronal structures in bones and joints. In this study, the time of appearance and topographic localization of galanin-containing nerve fibres in bone were studied in rats from gestational day 16 (GD16) to postnatal day 21 (PD21). The tibia was chosen as a model of developing long bone and indirect immunofluorescence combined with confocal laser scanning microscopy was used to identify galanin-immunoreactive (GAL-IR) nerve fibres. The earliest, sparse GAL-IR fibres were observed on GD21 in the perichondrium of both epiphyses and in the periosteum of the diaphysis. From PD1 onwards, GAL-IR fibres were also seen in the bone marrow cavity and in the region of the inter-condylar eminence of the knee joint. Intramedullary GAL-IR fibres in proximal and distal metaphyses appeared around PD1. Some of them accompanied blood vessels, although free fibres were also seen. GAL-IR fibres located in the cartilage canals of both epiphyses were observed from PD7, in the secondary ossification centres from PD10 and in the bone marrow of both epiphyses from PD14. The time course and localization of galanin-containing nerve fibres resemble the development of substance P- and CGRP-expressing nerve fibres, thus suggesting their sensory origin.

Regulation of galanin and galanin receptor 2 expression by capsaicin in primary cultured dorsal root ganglion neurons

Galanin is a 29-amino-acid neuropeptide expressed in dorsal root ganglion (DRG) neurons which is thought to play a role in modulation of nociception in neuropathic states. Activation of galanin receptor 2 (GalR2) plays a pronociceptive role and enhances capsaicin-induced nociception in the periphery. GalR2 and vanilloid receptor 1 (VR1) are co-expressed in DRG neurons. Capsaicin evokes acute pain via activation of VR1 expressed in primary sensory neurons. It is not known to what extent galanin and its receptor GalR2 expression is regulated by capsaicin in DRG neurons. Effects of acute (4 h) or chronic (4 d) treatment with capsaicin at different concentrations (0.01, 0.1, 1 micromol/L) on galanin and GalR2 expression in primary cultured DRG neurons were investigated in the present study. Our results showed that acute exposure of high concentration capsaicin (1 micromol/L) increased galanin expression, whereas chronic exposure of low concentration capsaicin (0.01, 0.1 micromol/L) promoted galanin expression. Only chronic exposure of 0.1 micromol/L concentration capsaicin could elevate GalR2 expression, whereas capsaicin did not have this effect at any other conditions in this experiment. These results indicated that certain concentrations or exposure time of capsaicin stimulation may be relevant to upregulation of galanin and its receptor GalR2 expression in DRG cultures suggesting a response to peripheral neuronal stimulation. And also, capsaicin-induced GalR2 expression may be also modulated by capsaicin-induced galanin expression. The possible significance of the neurotransmission of nociceptive information involved in galanin or GalR2 expression caused by capsaicin is still to be clarified.

Behavioral and immunohistological assessment of painful neuropathy induced by a single oxaliplatin injection in the rat

In clinical use, a single infusion of oxaliplatin, widely used to treat metastatic colorectal cancer, induces specific sensory neurotoxicity signs triggered or aggravated by exposure to cold. To study the pathophysiology of these symptoms, we developed and characterized an animal model that reproduces the effects of a single intraperitoneal oxaliplatin administration (3, 6 and 12 mg/kg). Significant allodynia and hyperalgesia to cold stimuli were rapidly observed from 24 h to day 5 with a maximum lowering of 76% at t+30 h versus control. Other behavioral assessments revealed rapid persistent mechanical allodynia, but no thermal hyperalgesia or allodynia to heat and no hyperalgesia to mechanical stimuli. An immunohistochemical study in the superficial layers of the spinal dorsal horn revealed a marked increase in substance P immunoreactivity versus controls (12% versus 4%), whereas calcitonin gene-related peptide (CGRP) immunoreactivity was unchanged. This new animal model for the first time closely mimics the effects observed in humans after a single oxaliplatin infusion, especially onset and highly intense sensory disturbances, hypersensitivity to cold with allodynia and hyperalgesia signs. This model may help to elucidate the mechanisms of this thermal hypersensitivity, especially the possible involvement of small-diameter A-fibers in cold allodynia symptoms. These selective effects may clue up the mechanistic basis for the acute oxaliplatin neuropathy leading to a better understanding of the clinical condition and to optimize its treatment.

Corticotropin-Releasing Factor Immunoreactivity Increases in the Cerebellar Climbing Fibers in the Novel Ataxic Mutant Mouse, Pogo

The ataxic pogo mouse (pogo/pogo) is a novel neurological mutant, which was derived as an inbred strain (KJR/MsKist) from a Korean wild mouse. The pathological manifestations include a difficulty in maintaining a normal posture, the failure of inter-limb coordination and an inability to walk straight. In this study, we examined the distribution of corticotropin-releasing factor (CRF) immunoreactive cerebellar climbing fibres and their projections to tyrosine hydroxylase (TH) immunoreactive Purkinje cells in the cerebellum of the pogo mutant mouse using immunohistochemistry. In the pogo/pogo mouse, a subset of climbing fibres was stained more intensely for CRF than in the control. Moreover, ataxic pogo mouse, neurons of the inferior olivary nucleus projecting climbing fibres were also more intensely stained for CRF than in the control. In the pogo/pogo mouse, TH immunoreactivity was located in the Purkinje cells, whereas no TH expression was found in the control. Double immunostaining for CRF and TH in the pogo/pogo cerebellum revealed that the distribution of TH-immunoreactive Purkinje cells corresponded to terminal fields of CRF-immunoreactive climbing fibres but not to the CRF-immunoreactive mossy fibres. Therefore, we suggest that an increase of CRF level may alter the function of targeted Purkinje cells and that it is related to the ataxic phenotype in the pogo mutant mouse.

Post-natal changes of cyclin-dependent kinase 5 activator expression in the developing rat cerebellum

cDNA of cyclin-dependent kinase 5 (Cdk5) was cloned based on its primary sequence homology to Cdc2 and Cdk2. Cdk5 requires the neuronal Cdk5 activators such as p35 or p39(nck5ai) (p39) for its activity. In this study, we examined post-natal changes in the p39 expression pattern during the development of the rat cerebellum. p39 began to express in somata and dendrites of Purkinje cells at post-natal day 3 (PD3). In particular, at PD12, parasagittal bands (stripes) with p39 immunoreactivity were weakly observed. At PD21, p39-immunoreactive stripes were developed when compared with the PD12 group. At this age stage, p39 immunoreactivity became weak in somata of Purkinje cells, not forming stripes. At PD28, a series of parasagittal bands were more distinct than those of the PD21 group, and p39 immunoreactivity disappeared in Purkinje cells, not forming p39 immunoreactive stripes. In the adults, p39 immunoreactivity in Purkinje cells was similar to that found in the PD28 group which showed that parasagittal bands were very narrow, and became progressively more slender. Therefore, we suggest that the post-natal changes of p39 expression in Purkinje cells in the cerebellum is an autonomous characteristic of Purkinje cells with a role of Cdk5 activators.

Origin and Chemical Coding of Primary Afferent Neurones Supplying the Prostate of the Dog

Retrograde tracing technique combined with the double-fluorescent immunohistochemistry were used to investigate the distribution and chemical coding of primary afferent neurones supplying the canine prostate. After the injection of Fast Blue (FB) into the prostatic tissue retrogradely-labelled (FB(+)) primary afferent neurones were localized in bilateral L(1)-Ca(1) dorsal root ganglia (DRG). Statistical analysis using anova test showed that there are two major sources of afferent prostate innervation. The vast majority of prostate-supplying primary afferent neurones were located in bilateral L(2)-L(4) DRG (56.9 +/- 0.6%). The second source of the afferent innervation of canine prostate were bilateral S(1)-Ca(1) DRG (40.6 +/- 1.0%). No statistically significant differences were found between average number of FB(+) neurones localized in the left and right DRG (49.5 +/- 1.7 and 50.5 +/- 1.7%, respectively). Immunohistochemistry revealed that FB(+) primary afferent neurones contain several neuropeptides in various combinations. In the prostate-supplying neurones of lumbar and sacro-caudal DRG the immunoreactivity to substance P (SP) and calcitonin gene-related peptide (CGRP) was found most frequently (50 +/- 3.7 and 37.3 +/- 1.9%, respectively). Both in the lumbar and sacro-caudal DRG, considerable population of FB(+) neurones immunoreactive neither to SP nor CGRP were also found (23 +/- 2.6 and 32.8 +/- 2.3%, respectively). In the lumbar DRG 10.7 +/- 1.1% of SP-immunoreactive FB(+) neurones also contained galanin (GAL). In 9.2 +/- 2.2% of the prostate-supplying primary afferent neurones located in the sacro-caudal DRG the co-localization of SP and GAL was also reported. Results of the retrograde tracing experiment demonstrated for the first time sources of afferent innervation of the canine prostate. Double immunohistochemistry revealed that many of the prostate-supplying primary afferent neurones express some of sensory neuropeptides which presumably may be involved in nociception and some pathological processes like inflammation or nerve injury.

Changes of Calbindin D-28k Immunoreactivity in the Hippocampus after Adrenalectomy in the Seizure Sensitive Gerbil

Calbindin D-28k (CB), a calcium-binding protein, containing neurons in the hippocampus plays an important role in hippocampal excitability in epilepsy. In the present study, we investigated changes of CB immunoreactivity after adrenalectomy (ADX) in the hippocampus and dentate gyrus of the seizure sensitive gerbil, which is susceptible to seizure to identify roles of CB in epileptogenesis. The changes of the CB immunoreactivity after ADX were significant in the hippocampal CA1 region. By 24 h after ADX, CB-immunoreactive CA1 pyramidal cells and CB immunoreactivity increased. At this time, well-stained dendrites projected to the stratum radiatum. Thereafter, the CB immunoreactivity decreased time dependently by 96 h after ADX. In the dentate gyrus, the changes of CB-immunoreactive neurons were mainly observed in the granule cell layer. The number and immunoreactivity of CB-immunoreactive neurons was high at 24 h after ADX, thereafter, those decreased by 96 h after ADX. These results suggest that glucocorticoid has an important role in modulating the seizure activity and CB serves an inhibitory function, which regulates the seizure activity and output signals from the hippocampus.

Chronological Alterations of P2X3 Receptor Expression in the Trigeminal Ganglion after Ischaemic Insult in the Mongolian Gerbil

P2X receptors play a role in the transduction of sensory signals like pain. Few studies have been undertaken on altered P2X(3) receptor (P2X3) expression in sensory neurones after peripheral nerve injury. In the present study, we investigated chronological alterations in P2X3 immunoreactivity and its protein content in the trigeminal ganglion after ischaemic insult in the Mongolian gerbil. In the sham-operated group, P2X3-immunoreactive neurones were found abundantly in small- and medium-sized neurones. From 1 day after ischaemic insult, the number of P2X3-immunoreactive neurones decreased significantly. At 5 days after ischaemic insult, P2X3 immunoreactivity was observed in few neurones, but its immunoreactivity was weak. However, the number of cresyl violet-positive neurones was unchanged throughout this period in all groups. These results suggest that transient trigeminal ganglion ischaemia may provoke a decrease of P2X3 expression and its protein content, and that this down-regulation of P2X3 may be related to the altered pain and thermal sensation without being associated with a transient ischaemic insult.

Age-related change of somatostatin-immunoreactive neurones in the main olfactory bulb of the rat

Somatostatin is found in the olfactory system, including the main olfactory bulb (MOB), and is thought to be one of the neuroactive substances for olfaction. However, somatostatin immunoreactivity in the olfactory system has not been determined during ageing. Hence, we examined the age-related changes of somatostatin-immunoreactive (IR) neurones in the rat MOB over a period of 2 years, at the following various ageing stages: post-natal month 1 (PM 1), PM 3, PM 6, PM 12 and PM 24. In PM 1 group, a few somatostatin-IR neurones were detected in the granule cell layer (GCL), and had slender or oval somata and short processes. At PM 3, somatostatin-IR neurones were observed in the glomerular, external plexiform and GCL. The size of somatostatin-IR somata was larger than that at PM 1. In PM 6 group, the number and size of somatostatin-IR neurones increased, and their processes became longer while running in various directions. At PM 12, somatostatin-IR neurones increased in number, and their processes became markedly longer than those at PM 6. At this stage, somatostatin-IR neurones had multipolar somata, and were the largest in size. In PM 24 group, somatostatin-IR neurones were most numerous. However, the processes of somatostatin-IR neurones were shorter than those at PM 12. This study suggests that the increased number of somatostatin-IR neurones in the MOB of aged rats may play a role to compensate for any decrease of olfactory function.

Distribution of calcitonin gene-related peptide (CGRP), substance P (SP) and galanin (GAL) immunoreactive nerve fibers in the seminal vesicle and prostate of the male sheep

Double immunohistochemistry was used to determine the occurrence and distribution pattern of nerve fibres immunoreactive to calcitonin gene-related peptide (CGRP), substance P (SP) and galanin (GAL) in seminal vesicles and prostate of the male sheep. Numerous CGRP- and SP-immunoreactive (IR) nerve fibres were found in the mucosal layer and smooth musculature of the seminal vesicles and prostate. In both glands nerve terminals immunoreactive to CGRP were more numerous than SP-IR ones. The majority of CGRP-IR nerve fibers showed colocalization of this peptide and SP. In both layers of the seminal vesicle and prostate, rare nerve terminals immunoreactive to GAL were also found. Immunoreactivity to SP was also found in all GAL-IR nerve fibers. The presence of numerous CGRP- and SP-IR nerve fibers in the seminal vesicle and prostate of the male sheep suggests that these neuropeptides may be involved in the sensory transmission and/or control of smooth muscle contractility. On the other hand, a relatively low number of GAL-IR nerve fibers of the seminal vesicle and prostate suggest that this peptide may act as an anti-nociceptive agent. It cannot be excluded that, in the seminal vesicle, GAL may also be involved in the control of the smooth muscle fiber activity. The possible role of CGRP, SP and GAL in the regulation of functions of the accessory sexual glands needs to be determined in further physiological studies.