Cardiac nociception in rats: neuronal pathways and the influence of dermal neurostimulation on conveyance to the central nervous system

Neurostimulation for refractory angina pectoris is often advocated for its clinical efficacy. However, the recruited pathways to induce electroanalgesia are partially unknown. Therefore, we sought to study the effect of neurostimulation on experimentally induced cardiac nociception, using capsaicin as nociception-induced substance. Four different groups of male Wistar rats were pericardially infused with either saline or capsaicin with or without neurostimulation. Group StimCap was infused with capsaicin, and group StimVeh was infused with saline. Both groups were treated with neurostimulation. Group ShamCap was only infused with capsaicin without stimulation, whereas group ShamVeh was only infused with saline. Neuronal activation differences were assessed with cytochemical staining, revealing the cellular expression of c-fos. Pain behavior was registered on video and was quantitatively analyzed. In the StimCap and ShamCap groups, all animals exerted typical pain behavior, whereas in the StimVeh group only moderate changes in behavior were observed. Group ShamVeh animals were unaffected by the procedure. The upper thoracic spinal cord showed high numbers of c-fos-positive cells, predominately in laminae III and IV in both StimCap and StimVeh groups. Almost no c-fos expression was noticed in groups ShamCap and ShamVeh in these sections of the spinal cord. In groups StimCap and ShamCap a significantly higher number of c-fos-positive cells in comparison with groups StimVeh and ShamVeh were noticed in the periambigus region, the nucleus tractus solitarius, and the paraventricular hypothalamus. In the paraventricular thalamus, periaqueductal gray, and central amygdala, no significant differences were noted among the first three groups, and the c-fos concentration in these three groups was significantly higher than in group ShamVeh. It is concluded that neurostimulation does not influence capsaicin-induced cardiac nociceptive pain pulses to the central nervous system. Furthermore, capsaicin-induced cardiac pain and neurostimulation may utilize two different pathways.     

Association of serotonin-like immunoreactive axons with nociceptive projection neurons in the caudal spinal trigeminal nucleus of the rat

Serotoninergic projections to the spinal dorsal horn are implicated in the modulation of nociceptive transmission. However, morphological evidence indicating that serotoninergic projection fibers make synapses on nociceptive neurons in the medullary dorsal horn is still meager. Thus, we examined whether axonal varicosities with serotonin (5-HT)-like immunoreactivity (5-HT-LI) might make synapses on nociceptive projection neurons in the caudal spinal trigeminal nucleus (Vc) of the rat. Projection neurons were retrogradely labeled with tetramethylrhodamine-dextran amine (TMR-DA) or wheat germ agglutinin-horseradish peroxidase (WGA-HRP) that was injected into the parabrachial or thalamic region. Vc neurons in which c-fos protein-like immunoreactivity (Fos-LI) was induced by subcutaneous injection of formalin into the lip were considered nociceptive. Vc neurons in direct contact with axonal varicosities that bind isolectin I-B4 were also considered nociceptive. Triple labeling for 5-HT, TMR-DA, and Fos as well as that for 5-HT, TMR-DA, and I-B4 were done by using the immunofluorescence and fluorescence histochemical techniques. Confocal laser-scanning microscopy revealed that axonal varicosities with 5-HT-LI were in close apposition to TMR-DA-labeled neurons showing Fos-LI in lamina I and the outer part of lamina II (lamina IIo), and that both axonal varicosities with 5-HT-LI and those binding I-B4 were in close apposition to single neuronal profiles labeled with TMR-DA. The presumed nociceptive neuronal profiles in close apposition to axon terminals with 5-HT-LI were mainly those of laminae I and II neurons as well as dendrites of lamina III neurons. Electron microscopy confirmed that axon terminals with 5-HT-LI and those with I-B4 binding activity in laminae I and II made synapses on somatic and dendritic profiles that were labeled with WGA-HRP. The results indicate that serotoninergic neurons project directly on nociceptive projection neurons in the Vc. J. Comp. Neurol. 384:127-141, 1997. © 1997 Wiley-Liss, Inc.     

Stimulant-mediated c-fos induction in striatum as a function of age, sex, and prenatal cocaine exposure

Induction of the immediate-early gene c-fos by the stimulants cocaine and amphetamine (AMPH) was analyzed by Fos immunocytochemistry at different ages in the brains of prenatally cocaine-treated and control rats. Cocaine and AMPH induced c-fos in patches of striatal neurons during the first postnatal week, and thereafter produced a progressively more homogeneous pattern that was more dense medially. Quantification of Fos-immunoreactive cells in older rats revealed differences related to sex and prenatal cocaine treatment. Both cocaine and AMPH produced dose-dependent increases in the number of Fos-immunoreactive cells in striatum. Prenatal cocaine exposure resulted in increased Fos in males in response to AMPH (2 mg/kg) at P18 and cocaine (10 mg/kg) at 1–2 months. In females, prenatal cocaine treatment resulted in a reduced response to cocaine at 1–2 months. Increased c-fos induction was observed in control females compared to control males in response to low doses of stimulants; no such sex difference was observed in prenatally cocaine-treated rats. The dopamine D1 antagonist SCH23390 blocked cocaine-mediated c-fos induction in all groups. The NMDA antagonist MK-801 blocked cocaine-mediated c-fos induction in the medial striatum. In females only, MK-801 pretreatment resulted in a dramatic increase in the number of Fos-immunoreactive cells in lateral striatum. These findings indicate differences in the neural basis of c-fos induction in males and females, and changes in stimulant-mediated c-fos induction resulting from prenatal cocaine exposure.     

Sodium depletion induces Fos immunoreactivity in circumventricular organs of the lamina terminalis

Acute sodium depletion by peritoneal dialysis (PD) induces c-fos expression in the subfornical organ (SFO) and organum vasculosum laminae terminalis (OVLT), in conscious rats. Fos immunoreactive (Fos-ir) neurons detected by immunohistochemistry first appeared in these nuclei 60 min after PD, increased gradually in the next 4 h and remained high for 27 h following PD. Fos-ir cells were distributed throughout the body of SFO, being the core of the posterior sections preferentially activated, whereas Fos-ir neurons occurred around the periphery of OVLT (annular disposition). When rats were allowed to drink sodium salt (1.8% NaCl) 24 h after PD, there was a marked reversion of the c-fos expression in the OVLT and a comparatively smaller effect in the SFO. Intracerebroventricular infusion of hypertonic CSF (170 mM NaCl) from 30 min before and during 4 h after PD, significantly inhibited the c-fos expression in both nuclei.These results demonstrate that an acute body sodium deficit induces c-fos activity in SFO and OVLT neurons, indicating the special role of these structures in sodium balance regulation. They also show that the sodium-depletion-induced production of Fos in neurons of the lamina terminalis can be modulated by central or systemic reposition of sodium.     

Increased renal interstitial hydrostatic pressure causes c-fos expression in the rat''s spinal cord dorsal horn

To describe a sympathetic afferent circuit, interstitial hydrostatic pressure in the left kidney was increased in anesthetized rats for 1.5 h to activate renal mechanoreceptor afferents. Following renal afferent stimulation, the number of immunocytochemically stained cells for the immediate early gene c-fos was increased within the dorsal horn of the spinal cord. Relative to the surgical control procedure, increasing renal interstitial hydrostatic pressure produced more immunocytochemically stained cells per tissue section in laminae I and II of the dorsal horn both ipsilateral and contralateral to the stimulated kidney in the three most caudal thoracic spinal segments. Further, the number of c-fos immunocytochemically stained cells per section in the dorsal horn ipsilateral to the stimulated kidney was 28% greater than the number of stained cells contralateral to it. The staining patterns in the dorsal horns of stimulated and control animals were similar with most labeled cells in laminae I and II. These results indicate that (1) c-fos immunocytochemical staining may be useful for tracing specific sympathetic afferent pathways, (2) sensory pathways affected by increased renal interstitial hydrostatic pressure include spinal neurons located at lower thoracic levels, and (3) some of this sympathetic afferent pathway is located contralateral to the stimulated kidney. Neurons in the contralateral dorsal horn activated by renal stimulation may mediate renorenal reflexes.     

C-fos expression in the spinal cord of rats exhibiting allodynia following contusive spinal cord injury

Contusive spinal cord injury (SCI) may result in central neuropathic pain marked by allodynia-like features in the dermatomes close to the level of injury. The aim of this study was to compare the laminar distribution of activated neurons (as determined by c-fos immediate early gene expression) in the spinal cord immediately above the level of a SCI in rats with or without allodynia-like features. Non-noxious mechanical stimulation was applied to half the animals in the dermatomes corresponding to the level of injury prior to perfusion. Stimulation resulted in a significant increase in c-fos labelling in all laminae of the spinal dorsal horn in the segment immediately above the level of injury only in allodynic animals. Animals that had allodynia also demonstrated a significant increase in the level of c-fos labelling in lamina III, IV and V of the dorsal horn without stimulation. Thus, allodynia following SCI is associated with significant increases in basal and evoked c-fos expression (“neuronal activity”) in response to non-noxious mechanical stimulation. The data also suggest that allodynia-like behaviour following SCI cannot be accounted for solely by changes occurring at a spinal level.     

Activation of Extracellular Signal-Regulated Protein Kinase is Associated with Colorectal Distension-Induced Spinal and Supraspinal Neuronal Response and Neonatal Maternal Separation-Induced Visceral Hyperalgesia in Rats

The activation of extracellular signal-regulated protein kinase (ERK) is essential for pain sensation and development of hyperalgesia in chronic pathological pain. Neonatal maternal separation (NMS) could trigger behavioral hyperalgesia and upregulate central neuronal activity in rats. The present study aims to investigate whether ERK associates with the colorectal distension (CRD)-evoked neuronal response and the upregulated central sensitivity to CRD in NMS rats. Male Sprague–Dawley rat pups were either subjected to NMS or not handled (NH) from postnatal day 2 to day 14. The protein expression of phospho-ERK (p-ERK) and c-fos at the spinal and supraspinal levels of adult rats were quantified and their correlation was analyzed. Western blot analysis revealed significant NMS effect on p-ERK expression in the lumbosacral dorsal horn and thalamus. Immunohistochemistry analysis demonstrated that CRD elevated p-ERK and c-fos expression in the dorsal root ganglia (DRG), laminae I–II of the lumbosacral dorsal horn, thalamic nucleus central medial (CM), paraventricular thalamic nucleus (PV), and anterior cingulate cortex (ACC). Significant NMS effect on p-ERK and c-fos expression was observed in the DRG, and laminae I–II, III–IV, and X of the lumbosacral dorsal horn. Furthermore, a significant interactive effect of NMS and CRD on p-ERK expression was observed in laminae III–IV of the lumbosacral dorsal horn. Correlation analysis revealed the positive association between c-fos- and p-ERK-immunoreactive nuclei numbers in the DRG, lumbosacral dorsal horn, and ACC. These results demonstrate that ERK is actively involved in CRD-evoked neuronal activation in both NH and NMS rats. Moreover, ERK is associated with the upregulated central neuronal sensitivity to noxious CRD in NMS rats, which may be responsible for the behavioral hyperalgesia in NMS rat.     

Effects of hypoxia-ischemia and seizures on neuronal and glial-like c-fos protein levels in the infant rat

Unilateral carotid ligation in immature rats, followed by 2 h of hypoxia led to ischemic cell change from 2 h after the insult, on the ligated side of the brain. There was a time-dependent induction of immunoreactive c-fos protein in neurones but not glia or ependyma on the non-ligated side of the brain. Induction only occurred in rats that had seizures post hypoxia-ischemia. In the ligated hemisphere c-fos protein was induced in glial-like cells in the corpus callosum, fornix/fimbria and internal capsule and in ependymal cells lining the lateral ventricle starting from 2 h after hypoxia but subsiding by 3 days. No neuronal c-fos induction was seen in areas showing neuronal damage. MK-801 or carbamazepine, which prevented hypoxia-ischemia-induced seizures, also prevented c-fos induction in the non-ligated hemisphere while MK-801 was associated with increased c-fos induction in hippocampal neurones from the ligated side, as well as in glial-like and ependymal cells.These results suggest several processes are involved following the hypoxic-ischemic insult. Firstly, severe hypoxia-ischemia is associated with a reduction in neuronal c-fos protein levels, probably as a result of neuronal failure and death. Secondly, post hypoxic seizures cause c-fos induction in surviving neurones. Thirdly, glial-like from regions in which there is neural loss also exhibit induction of c-fos, which may be important for their subsequent proliferation or for the production of growth factors.     

The effect of stimulus duration on noxious-stimulus induced c-fos expression in the rodent spinal cord

C-fos is a proto-oncogene that is expressed within some neurons following depolarization. The protein product,fos, has been proposed as an anatomical marker for neuronal activity following noxious peripheral stimulation. However, the literature on noxious-stimulus induced fos expression contains several puzzling observations on the time course and laminar distribution of neuronal labeling within the spinal cord. This study has analyzed the effect of stimulus duration on the expression of fos-like immunoreactivity (FLI) within the spinal cord of anesthetized rats. In order to examine the time course of fos expression following brief periods of stimulation, we required a type of stimulus that was intense enough to activate nociceptors but that did not produce tissue damage. We have therefore employed pulsed, high intensity electrical stimulation, with stimulus durations ranging from 3 s to 24 h. The results indicate that stimulus duration has a profound effect upon the number of labeled cells, the intensity of neuronal labeling, the laminar pattern of FLI, and the time course of fos expression. Brief stimulation periods induce relatively few and relatively lightly labeled neurons, located predominantly within the most superficial laminae of the dorsal horn. Maximal immunoreactivity appears approximately 2 h after stimulation has ceased, and disappears within hours. Continuous stimulation produces many more labeled cells, darker labeling, and FLI within both dorsal and ventral laminar regions. Maximal FLI is seen after approximately 4.5 h of continuous stimulation, with reduction in the number of labeled cells thereafter. These data indicate that the results of any study employing c-fos as a marker for neuronal activity may be affected by the duration of the exciting stimulus.     

The medullary dorsal reticular nucleus facilitates pain behaviour induced by formalin in the rat

The influence of the dorsal reticular nucleus (DRt) on pain behaviour during the formalin test was studied in the rat by lesioning the nucleus through local application of electrical current or quinolinic acid. Animals in which the DRt was lesioned ipsilaterally to the paw injected with formalin spent less time in focused (licking, biting or scratching the injected paw) and total (focused pain behaviour plus protection of the injected paw during movements) pain behaviour, and showed paw-jerks less frequently than non-lesioned animals in both phases 1 and 2 of the test. Animals in which the DRt was lesioned contralaterally to the injected paw presented a decrease in total pain behaviour and number of paw-jerks only during phase 2. The number of superficial (laminae I–II) and deep (laminae III–VI) spinal dorsal horn cells expressing the c-fos proto-oncogene 2 h after subcutaneous injection of formalin was reduced by 34% and 50%, respectively, in animals with an ipsilateral DRt lesion as compared to non-lesioned rats. No differences in c-fos expression were observed after lesioning the DRt contralateral to the formalin injection. The results indicate that the DRt is involved in the facilitation of nociception during the formalin test by enhancing the response capacity of dorsal horn neurons to noxious stimulation. It is suggested that the pronociceptive action of the DRt is mediated by the reciprocal connections it establishes with the spinal dorsal horn [ Almeida et al. (1993 ) Neuroscience, 55, 1093].     

Induction of c-fos gene expression by spinal cord transection in the rat

Sympathetic nerve activity is maintained after high spinal injury through circuits that remain in question. We evaluated patterns of c-fos gene induction as a monitor of spinal neurons responding to high spinal cord transection in the rat. Rats were anesthetized with isofluorane. Lower cervical or upper thoracic spinal segments were exposed, immersed in warm mineral oil and transected. Spinal cords were exposed but not transected in anesthetized controls. After 2.5 h, spinalized and control rats were perfused for immunocytochemistry. Cervical and thoracolumbar spinal segments and dorsal root ganglia were sectioned coronally. Tissues were incubated in primary, polyclonal antisera raised in rabbit or sheep against a peptide sequence unique to the N-terminal domain of Fos, and processed immunocytochemically. Neurons were induced to express Fos-like immunoreactivity (FLI), bilaterally, in the spinal gray, but not in primary sensory ganglia. Spinal cord transection induced neurons to express FLI in thoracic laminae I, IIo (outer substantia gelatinosa). Vre (lateral reticulated division), VII (lamina intermedia) and X, and the intermediolateral cell column. Lamina VIII was also labeled in spinal-injured but not in control animals. Immunolabeled nuclei were prominent in lumbar segments and were concentrated in the medial third of laminae I and IIo, and in laminae VII and X. Few cells were labeled in upper cervical or sacral segments. FLI was sparse in the spinal gray of controls and expressed mainly within the dorsal root entry zone of upper thoracic segments. Patterns of c-fos gene expression were site-specific and correlated with laminae that respond predominantly to noxious stimulation and that contain sympathetic interneurons. Laminae that are responsive to non-noxious stimuli and activated by walking, IIi, nucleus proprius, medial V and layer VI were not induced to express FLI. We conclude that neurons in specific spinal laminae that process high threshold afferents and that harbor neurons with sympathetic nerve-related activity are activated selectively by spinal cord transections. We hypothesize that peripheral afferents processed by spinal-sympathetic circuit neurons may regulate sympathetic discharge in the absence of supraspinal drive.     

Effects of intracerebroventricular dizocilpine (MK801) on dehydration-induced dipsogenic responses, plasma vasopressin and c-fos expression in the rat forebrain

This study determined the interaction between glutamate receptors and dehydration-induced drinking, vasopressin (AVP) release, plasma osmolality and c-fos expression in the brain of conscious rats. The NMDA receptor antagonist dizocilpine (100 nmol infused into the cerebral ventricles) suppressed drinking following either 22 h water deprivation or intragastric injection of hypertonic saline (1.5 M), attenuated the increased plasma vasopressin induced by dehydration, but had no effects on peripheral hyperosmolality caused by either water deprivation or injections of hypertonic saline. Dizocilpine had no inhibitory effects on feeding after 24 h food deprivation. Dizocilpine also suppressed c-fos expression induced by dehydration in the median preoptic nucleus (MPN), the supraoptic and paraventricular nuclei (SON and PVN), but did not influence c-fos expression in the subfornical organ (SFO). The non-NMDA receptor antagonists CNQX (400 nmol) or DNQX (60 nmol) affected neither the animals' drinking nor c-fos expression induced by dehydration. Double staining showed that suppression of c-fos expression following dizocilpine occurred in the NMDA R1 receptor containing neurons in the hypothalamus. These results suggest that the NMDA-type glutamate receptors may be involved in dehydration induced dipsogenic and neuroendocrinological responses. They complement our earlier findings that dizocilpine also attenuated drinking and c-fos expression following intraventricular infusions of angiotensin II.     

Vomeronasal organ-mediated induction of fos in the central accessory olfactory pathways in repetitively mated female rats

Removal of the VNO significantly reduced the enhancement of lordosis and the induction of fos immunoreactivity in luteinizing hormone-releasing hormone (LHRH) neurons in ovariectomized estrogen-primed rats. There was a significant positive correlation between the two variables. In the accessory olfactory bulb (AOB) of the repetitively mated rats, the number of fos-positive cells in the granule (G) cell layer was significantly lower in the VNO-removed rats, whereas that in the mitral (M) cell layer was not significantly different between VNO-removed and VNO-sham females. The G/M ratio (calculated by dividing the mean number of fos-positive cells in the G cell layer by that in the M cell layer), taken as an estimate of the output of the AOB, was relatively larger in the VN-sham as compared with the VNO-removed rats. There were significant positive correlations between G/M ratio and the increase in LQ and between the G/M ratio and the percentage of fos-positive LHRH cells. The positive correlation between the number of fos-positive cells in the posterodorsal medial amygdala (PDMA) and the increase in LQ and that between the number of fos-positive cells in the PDMA and the percentage of fos-positive LHRH cells were significant, supporting the role of the medial nucleus of amygdala in lordosis. However, the correlation between G/M ratio and the number of fos-positive cells in the PDMA was not significant, indicating that fos immunoreactivity in the PDMA is not directly related to that in the AOB. In conclusion, the results support the involvement of the accessory olfactory system in mediating the facilitatory effects of repeated mating on lordosis in female rats and suggest that the influence of the accessory olfactory system is mediated likely through the LHRH neuronal system. Integration and filtering of sensory information may take place at various levels of the brain, such as the AOB and the medial amygdala, before being transmitted to higher brain centers controlling lordosis behavior in female rats.     

The exogenous control of transfected c-fos gene expression and angiogenesis in cells implanted into the rat brain

Previously, we established a stable transfectant, Nf-1, from normal rat kidney (NRK) fibroblasts transfected with a human metallothionein II A (hMT-IIA) promoter/human genomic c-fos fusion gene to produce c-Fos protein. Since the hMT-IIA promoter can be activated by heavy metals, the level of human c-fos gene expression can be increased by addition of heavy metals to the culture medium of Nf-1 cells and the anchorage-independent growth of Nf-1 in soft agar is markedly enhanced in the presence of transforming growth factor-β (TGF-β) and epidermal growth factor (EGF). In this study, we found that the hMT-IIA promoter can be activated by zinc, resulting in the elevation of fused c-fos gene expression in Nf-1 cells. We transplanted NRK and Nf-1 cells into the striatum of the rat brain and investigated whether expression of the human c-fos gene could be modified in the brain by exogenous zinc. After 8 weeks, we found that the Nf-1 cells could survive in the rat brain without any immunosuppression and grafts of Nf-1 induced angiogenesis when zinc was administered. Such implants enhanced the expression of c-fos mRNA by zinc. These results indicated that the transplanted cells continued expressing the c-fos transgene when the rats were given drinking water containing zinc, resulting in the promotion of cell growth and of neovascularization. This study will present a useful animal model of gene therapy by control of transgene expression in the brain.     

Induction of the c-fos proto-oncogene during opiate withdrawal in the locus coeruleus and other regions of rat brain

Opiate regulation of the nuclear proto-oncogene c-fos was studied in the locus coeruleus (LC) and other regions of rat brain by immunoblotting, northern blotting, and in situ hybridization procedures. Precipitation of opiate withdrawal in rats, which is known to increase LC firing rates 4-fold, led to a two- to three-fold increase in levels of mRNA and protein for c-fos in the LC 1–2 h after initiation of withdrawal. In contrast, levels of c-fos expression were decreased in LC from rats treated acutely or chronically with morphine but not experiencing withdrawal, conditions under which LC firing rate are depressed. Similar regulation of c-fos expression during opiate withdrawal was found in the amygdala, ventral tegmentum, nucleus accumbens, neostriatum, and cerebral cortex, but not in a number of other brain regions studied, which included the hippocampus, dorsal raphe, periaqueductal gray, and paragigantocellularis. In the LC and some other brain regions, induction of c-fos during opiate withdrawal was associated with a parallel induction of c-jun, another nuclear proto-oncogene, which, like c-fos, is expressed rapidly in brain in response to certain extracellular stimuli. The results demonstrate a novel use of c-fos in neuropharmacology, namely to map neuronal pathways and neuronal cell types activated in response to acute and chronic opiate administration and during opiate withdrawal, as well as in response to other psychotropic drug treatments.     

Induction of c-fos immunostaining in the rat brain after the systemic administration of nicotine

To search for evidence of altered neuronal gene expression in response to exposure to the highly addictive drug nicotine, rat brains were examined by immunocytochemistry for the fos protein after the systemic administration of nicotine. The drug was administered as an IV infusion over 1 h to chronically cannulated, freely behaving rats. At a dose of 2 mg/kg, the most dramatic nicotine-induced fos nuclear immunostaining was seen in central visual pathways, including the superficial superior colliculus and the medial terminal nu. of the accessory optic tract, in the interpeduncular nu. Notably, many regions with high levels of nicotine binding sites, including the medial habenula, thalamus, substantia nigra, and ventral tegmental area, failed to express the c-fos gene with this schedule of nicotine administration. A minimal increase in fos immunostaining was seen after a nicotine dose of 0.5 mg/kg, with a much greater response after 1 or 2 mg/kg. The response was seen as soon as 60 min after the beginning of the infusion, was maximal at 2–3 h, and declined thereafter, c-fos expression was substantially attenuated in the superficial gray layer of superior colliculus, medial terminal nucleus of the accessory optic tract, and the interpeduncular nucleus by pretreatment with the centrally acting nicotine antagonist mecamylamine, 5 mg/kg IP, but not with the peripherally acting antagonist hexamethonium, 4 mg/kg IP. These observations identify a subset of central nervous system neurons that respond to nicotine with altered expression of the immediate early gene c-fos. These neurons presumably undergo long-term changes in gene expression as a result of acute exposure to high doses of nicotine.     

Effect of locus coeruleus lesion on c-fos expression in the cerebral cortex caused by yohimbine injection or stress

The injection of the α-2 adrenoceptor antagonist, yohimbine, has been shown to increase c-fos immunoreactivity in the rat cerebral cortex. To determine the extent to which this response is mediated by the central noradrenergic system, the present studies examined it in rats previously given unilateral 6-OHDA lesions of the locus coeruleus. The lesions were found to produce a significant attenuation of the response. A similar effect on the c-fos immunoreactive response to restraint stress was found. It is concluded that the noradrenergic system plays a necessary role in the above c-fos responses in the cortex to yohimbine and to stress. The c-fos protein therefore appears to be involved in the effects of noradrenergic neurotransmission in the CNS.     

Increased c-fos expression in spinal neurons induced by electrical stimulation of the ureter in the rat

The spinal processing of afferent input from the ureter was examined using an immunocytochemical technique to detect the expression of c-fos, an immediate early gene. Proximal and distal sites in one ureter were electrically stimulated separately or together at intensities that elicited a pseudo-affective response (an increase in arterial pressure). Very few Fos + cells (range: 0.6–6.6 cells/half section were present in the L₁-L₂, L₅-S₂ spinal segments in sham operated control animals; however, following stimulation of the ureter, a significant increase in the numbers of Fos + cells was detected at spinal levels L₁-L₂ (mean 24.5–33.1 cells/half section) and L₆-S₁ (mean 17.4–33.0 cells/half section). In L₆-S₁,the numbers of Fos + cells were significantly greater ipsilateral (mean 25.2 cells/half section) vs. contralateral (12.3 cells/half section) to stimulation; whereas in L₁-L₂, the numbers were similar on both sides of the spinal cord. In L₁-L₂, a greater percentage of Fos + cells was present in superficial medial (MDH, 49.7%) and lateral dorsal hom (LDH, 40.8%); whereas in L₆-S₁, the cells were more numerous in sacral parasympathetic nucleus (SPN, 38.7%) and LDH (25.6%) regions. This distribution of Fos + cells varies in a number of respects from that noted in previous experiments after chemical irritation of the urinary bladder and urethra which activated neurons only in L₆-S₁ and primarily in the DCM and MDH. The results indicate that nociceptive afferent inputs from different areas of the urinary tract are processed in different regions of the spinal cord.