Number Of Fos-like Immunoreactive Neurons Research Articles

The Fos expression in rat brain following electrical stimulation of dura mater surrounding the superior sagittal sinus changed with the pre-treatment of rizatriptan benzoate

Fos expression in the brain was systematically investigated by means of immunohistochemical staining after electrical stimulation of the dura mater surrounding the superior sagittal sinus in conscious rats. Fos-like immunoreactive neurons are distributed mainly in the upper cervical spinal cord, spinal trigeminal nucleus caudal part, raphe magnus nucleus, periaqueductal gray, ventromedial hypothalamic nucleus, and mediodorsal thalamus nucleus. With the pre-treatment of intraperitoneal injection of rizatriptan benzoate, the number of Fos-like immunoreactive neurons decreased in the spinal trigeminal nucleus caudal part and raphe magnus nucleus, increased in the periaqueductal gray, and remained unchanged in the ventromedial hypothalamic nucleus and mediodorsal thalamus nucleus. These results provide morphological evidence that the nuclei described above are involved in the development and maintenance of the trigeminovascular headache.

Fos expression and hormone changes following electrical stimulation of the posterodorsal amygdala and the effects on food intake in conscious female rats

Previous studies have shown that lesions of the posterodorsal amygdala (PDA) produce hyperphagia and obesity in female rats. To better understand the role of the PDA in the regulation of feeding behavior, the current study examined the effects of electrical stimulation of the PDA of female rats on food intake and identified neurons activated by PDA stimulation using Fos immunohistochemistry. Hormonal levels following stimulation of the PDA were also investigated. Electrical stimulation (100 μA, 0.2 ms, 20 Hz, 10 min) of the PDA remarkably decreased 1 h food intake of rats. Following PDA stimulation, the number of Fos-like immunoreactive neurons increased in the caudal and intermediate parts of the nucleus of the solitary tract (NST), the area postrema (AP), the external lateral subnucleus of the parabrachial nucleus (PBN), the arcuate nucleus of the hypothalamus (Arc), and the central amygdaloid nucleus (CeA). The level of circulating leptin was elevated significantly by PDA stimulation as well. Together with previous studies, the results suggest that the PDA may play an important role in the regulation of feeding behavior, at least partly by modulating the circulating leptin, and that the caudal and intermediate parts of the NST, AP, external lateral PBN, Arc, and CeA probably participate in this regulation.

The Number and Location of Fos-like Immunoreactive Neurons in the Central Gustatory System Following Electrical Stimulation of the Parabrachial Nucleus in Conscious Rats

Electrical stimulation of the waist area (W) of the parabrachial nucleus (PBN) in conscious rats elicits stereotypical oromotor behaviors (Galvin et al. 2004). To identify neurons possibly involved in these behavioral responses, we used Fos immunohistochemistry to locate populations of neurons within central gustatory and oromotor centers activated by PBN stimulation. Dramatic increases in the numbers of Fos-like immunoreactive neurons were observed in the ipsilateral PBN, nucleus of the solitary tract (NST), and central amygdala. The increase in neurally-activated cells within the ventral subdivision (V) of the rostral NST is particularly noteworthy because of its projections to medullary oromotor centers. A modest increase in labeled neurons occurred bilaterally within the gustatory cortex. Although there were trends for an increase in Fos-labeled neurons in the gustatory thalamus and medullary reticular formation, most changes in labeled neurons in these areas were not statistically significant. Linear regression analysis revealed a relationship between the number of taste reactivity (TR) behaviors performed during PBN stimulation and the number of Fos-like immunoreactive neurons in the caudal PBN and V of the rostral NST. These data support a role for neurons in W of the PBN and the ventral rostral NST in the initiation of TR behaviors.

Dissociation between post-surgical pain behaviors and spinal Fos-like immunoreactivity in the rat

Previous studies have demonstrated that Fos-like immunoreactivity is increased in spinal dorsal horn neurons in several pain models, and have suggested that Fos-like immunoreactivity could be used as a marker of neurons activated by painful stimulation. In the present study, we evaluated nociceptive behaviors and spinal Fos-like immunoreactivity in a rat skin incision model of post-operative pain. In this model, evoked and non-evoked pain behaviors were observed at least for 2 days after paw surgery, an increased number of Fos-like immunoreactive neurons was observed in the spinal dorsal horn at lumbar levels 4–5 two-hour post-surgery. The number of Fos-like immunoreactive neurons was significantly greater in animals with skin–muscle incision compared to animals with skin-alone incision. Interestingly, spinal Fos-like immunoreactivity was quickly normalized in rats with paw surgery at later time points (8 and 24 h post-surgery), whereas nociceptive behaviors were still observed. Furthermore, at 24 h post-surgery, spinal Fos-like immunoreactivity induced by thermal stimulation (42, 44, 46, 48, 52 °C for 15 s) was not significantly different between sham animals and animals with surgery. In both groups, an increase in spinal Fos-like immunoreactive neurons was observed with increasing temperatures, with similar laminar distribution. Finally, systemic morphine reduced post-operative pain and Fos-like immunoreactivity in a naloxone reversible manner, with greater potency and efficacy on behavioral endpoints than on Fos-like immunoreactivity. These results demonstrate a different profile of nociceptive behaviors and spinal Fos-like immunoreactivity in the rat skin incision model, suggesting a limited potential of spinal Fos-like immunoreactivity to study post-surgical pain and its pharmacology.

Role of Thalamic Phospholipase Cβ4 Mediated by Metabotropic Glutamate Receptor Type 1 in Inflammatory Pain

Phospholipase C (PLC) beta4, one of the four isoforms of PLCbetas, is the sole isoform expressed in the mouse ventral posterolateral thalamic nucleus (VPL), a key station in pain processing. The mouse thalamus also has been shown to express a high level of metabotropic glutamate receptor type 1 (mGluR1), which stimulates PLCbetas through activation of Galphaq/11 protein. It is therefore expected that the thalamic mGluR1-PLCbeta4 cascade may play a functional role in nociceptive transmission. To test this hypothesis, we first studied behavioral responses to various nociceptive stimuli in PLCbeta4 knock-out mice. We performed the formalin test and found no difference in the pain behavior in the first phase of the formalin test, which is attributed to acute nociception, between PLCbeta4 knock-out and wild-type mice. Consistent with this result, acute pain responses in the hot plate and tail flick tests were also unaffected in the PLCbeta4 knock-out mice. However, the nociceptive behavior in the second phase of the formalin test, resulting from the tissue inflammation, was attenuated in PLCbeta4 knock-out mice. In the dorsal horn of the spinal cord where PLCbeta1 and PLCbeta4 mRNAs are expressed, no difference was found between the wild-type and knock-out mice in the number of Fos-like immunoreactive neurons, which represent neuronal activity in the second phase in the formalin test. Thus, it is unlikely that spinal PLCbeta4 is involved in the formalin-induced inflammatory pain. Next, we found that pretreatment with PLC inhibitors, mGluR1 antagonists, or both, by either intracerebroventricular or intrathalamic injection, attenuated the formalin-induced pain behavior in the second phase in wild-type mice. Furthermore, activation of mGluR1 at the VPL enhanced pain behavior in the second phase in the wild-type mice. In contrast, PLCbeta4 knock-out mice did not show such enhancement, indicating that mGluR1 is connected to PLCbeta4 in the VPL. Finally, in parallel with the behavioral results, we showed in an electrophysiological study that the time course of firing discharges in VPL corresponds well to that of pain behavior in the formalin test in both wild-type and PLCbeta4 knock-out mice. These findings indicate that the thalamic mGluR1-PLCbeta4 cascade is indispensable for the formalin-induced inflammatory pain by regulating the response of VPL neurons.

Spinal administration of lipoxygenase inhibitors suppresses behavioural and neurochemical manifestations of naloxone-precipitated opioid withdrawal.

1. This study investigated the role of spinal lipoxygenase (LOX) products in the induction and expression of opioid physical dependence using behavioural assessment of withdrawal and immunostaining for CGRP and Fos protein expression in the spinal cord. 2. Administration of escalating doses (5-50 mg kg-1; i.p.) of morphine for 5 days markedly elevated CGRP-like immunoreactivity in the dorsal horn of the rat spinal cord. Naloxone (2 mg kg-1; i.p.) challenge precipitated a robust withdrawal syndrome that depleted CGRP-like immunoreactivity and increased the number of Fos-like immunoreactive neurons in the dorsal horn. 3. Intrathecal administration of NDGA (10, 20 microg), a nonselective LOX inhibitor, AA-861 (1.5, 3 microg), a 5-LOX selective inhibitor, or baicalein (1.4, 2.8 microg), a 12-LOX selective inhibitor, concurrently with systemic morphine for 5 days or as a single injection immediately preceding naloxone challenge, blocked the depletion of CGRP-like immunoreactivity, prevented increase in the number of Fos-like immunoreactive neurons in the dorsal horn, and significantly attenuated the morphine withdrawal syndrome. 4. The results of this study suggest that activity of LOX products, at the spinal level, contributes to the expression of opioid physical dependence, and that this activity may be expressed through increased sensory neuropeptide release.

Effect of intrathecal octreotide on thermal hyperalgesia and evoked spinal c-Fos expression in rats with sciatic constriction injury.

This study was designed to determine whether intrathecal octreotide (sandostatin), a synthetic octapeptide derivative of somatostatin, relieved thermal hyperalgesia and reduced the evoked spinal c-Fos expression in rats with chronic constriction injury (CCI) of the sciatic nerve. Intrathecal catheters were implanted in rats 7 days before CCI of the sciatic nerve over the left hind limb. After confirmation of the development of thermal hyperalgesia by decreased paw withdrawal latencies (PWL) to heat stimulation 7 days after CCI, intrathecal sandostatin at 20, 40, and 80 microg was administered, respectively. Rats in the control group received saline injections intrathecally. PWLs were evaluated at 30, 60, 120, 180, and 240 min after drug administration. Detection of Fos-like immunoreactivity (Fos-LI) neurons in the dorsal horn of the spinal cord following drug administration was performed after mechanical stimulation (stroking of the hind paws) on the 14th day after CCI. The reduction of PWL was attenuated significantly in the groups that received intrathecal sandostatin at 20, 40, and 80 g when compared with the saline group. However, PWL did not return to pre-CCI values in all groups. In the 40 microg group, PWL returned up to 76% of pre-CCI values 120 min after drug administration. Stroking of the hind paw in CCI-treated (ipsilateral) limbs induced a significantly greater expression of spinal Fos-LI neurons than that of non-CCI treated (contralateral) limbs in each group. The number of Fos-LI neurons in animals receiving intrathecal sandostatin was dose-dependently reduced. Expression of Fos-LI neurons in the 80 microg group was nearly completely inhibited. These data suggest that intrathecal sandostatin significantly relieved thermal hyperalgesia behaviorally but with limited effects and dose-dependently reduced spinal Fos-LI neurons expression evoked by stroking stimulation, which may reflect mechanical allodynia in rats with sciatic constriction injury. This implies that intrathecal sandostatin was effective in the treatment of neuropathic pain.

Effect of ionotropic glutamate receptor antagonists on Fos-like immunoreactivity in the dorsal horn following transection of the rat sciatic nerve

Fos-like immunoreactivity (FLI) was investigated in the lumbar dorsal horn 2 h after transection of the rat sciatic nerve and sham operation. FLI following nerve transection was distributed through the medio-lateral extension of the superficial layer of the dorsal horn, while FLI after sham operation, tissue injury, was restricted to the lateral one-third of this layer. The number of FLI neurons in the lateral one-third was similar in the two operations, indicating that neurons expressing FLI in the medial two-thirds and in the lateral one-third of the superficial layer after nerve transection are derived from nerve injury and tissue injury, respectively. FLI in the lateral one-third, but not the medial two-thirds, after nerve transection was significantly reduced by pretreatment with NMDA and AMPA/KA receptor antagonists, indicating that there is a considerable difference in the contributions of ionotropic glutamate receptors to FLI in this layer induced by nerve injury and tissue injury.

Effects of MK-801 and morphine on spinal C-Fos expression during the development of neuropathic pain.

The purpose of this study was to investigate the expression of c-fos in the spinal cord during the development of allodynia, induced by peripheral nerve injury. Following tight ligation of the left L5 and L6 spinal nerves of Sprague- Dawley rat, the lumbar spinal cord was postfixed following perfusion. Frontal frozen sections of 40 microm were immunostained according to the peroxidase-antiperoxidase method. The allodynic threshold was checked with 8 calibrated von Frey filaments. MK-801 (0.3 mg/kg), morphine (3 mg/kg) and saline (as a placebo) were administered subcutaneously 30 min before, and 24 and 48 hrs after surgery. The tactile threshold decreased below 3 g since 2 days after surgery in the saline and morphine groups, but delayed a little in the MK-801 group. In the superficial layer the number of Fos-like immunoreactive neurones (Fos-LI) peaked at 2 hours and decreased thereafter, and reached normal levels 24 hrs following operation, for all groups. In the deep layer they were biphasic, - peaking at 2 and 24 hrs - in the saline group, but were suppressed in the morphine and MK-801 groups until 7 days following operation. The above discrepancy between the number of Fos-LI and the allodynic threshold showed that central sensitizations are not critically involved in the development of nerve injury induced tactile allodynia.

Differential contributions of NMDA and non-NMDA receptors to spinal Fos expression evoked by superficial tissue and muscle inflammation in the rat

The role of N-methyl- D-aspartate (NMDA) and non-NMDA receptors in the spinal cord in the transmission of nociceptive afferents from superficial tissue and muscle was studied by examining the effects of NMDA or non-NMDA receptor antagonists on Fos expression in the spinal dorsal horn. Muscle inflammation was induced by injection of turpentine oil into the gastrocnemius muscle, whereas superficial tissue inflammation was induced by an intraplantar injection of turpentine oil into the hindpaw. The NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (AP-5), the non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX) or normal saline were intrathecally administered 15 min before an intramuscular or intraplantar injection of turpentine oil. Muscle inflammation evoked expression of Fos-like immunoreactive neurons staining in neurons that were predominantly distributed in the middle portions of laminae I–II outer and the lateral portions of laminae V–VI of the ipsilateral dorsal horn at the spinal L 4–L 5. DNQX, but not AP-5, significantly reduced the total number of Fos-like immunoreactive neurons evoked by muscle inflammation. In contrast, superficial tissue inflammation evoked expression of Fos-like immunoreactive neurons in the medial portions of laminae I–II outer and V–VI of the ipsilateral dorsal horn at the spinal L 4–L 5 that was blocked by AP-5, but not by DNQX. Injection of normal saline did not influence the numbers of Fos-LI neurons. These results indicate that different glutamate receptors in the dorsal horn of the spinal cord may mediate nociceptive input from superficial tissue (particularly skin) and muscle. DNQX receptors may mediate transmission of nociceptive information originating in muscle, while NMDA receptors may preferentially mediate transmission of nociceptive information originating in skin.

Somatic noxious mechanical stimulation induces Fos expression in the postsynaptic dorsal column neurons in laminae III and IV of the rat spinal dorsal horn.

This study was conducted to ascertain the possible expression of Fos-like immunoreactivity (Fos-LI) in the postsynaptic dorsal column (PSDC) neurons in response to noxious mechanical stimulation of the forepaw glabrous area of normal rats. For this purpose, Fos immunohistochemistry along with Fluoro-Gold (FG) retrograde tracing was utilized. After repeated noxious pinching of the forepaw glabrous area, there was a marked increase in number of Fos-LI neurons in the dorsal horn, including Rexed's laminae III and IV, at C5-T1 spinal cord segments ipsilateral to the stimulation. Between segments C5 and T1, about 40% of the Fos-LI neurons in laminae III and IV were distributed at segment C7. In the rats subjected to the noxious pinch coupled with FG injection into the right cuneate nucleus, PSDC neurons double labeled with Fos and FG were localized in the ipsilateral laminae III and IV extending from segment C5 to T1, with about 70% of them distributed at segments C6 and C7. At segment C6 or C7, double-labeled neurons made up about 10% of the PSDC neurons that projected their axons to the cuneate nucleus. Most of the double-labeled neurons appeared fusiform with their primary dendrites projected dorso-ventrally. The present results suggest that the morphologically distinct, subclasses of PSDC neurons in spinal laminae III and IV may contribute to the central transmission of mechanical nociceptive information through the dorsal column into the cuneate nucleus.

Behavioral training-induced c-Fos expression in the rat nucleus basalis of Meynert during aging

The present study investigated the behavioral training-induced c-Fos expression in the nucleus basalis of Meynert (nbM) in differently aged rats. This study demonstrated that the c-Fos expression in nbM was significantly increased and the peak occurred at 2 h after dark-avoidance training. Although the increase of c-Fos expression was also observed after pseudotraining, the number of Fos-like immunoreactive neurons in pseudotrained rats was significantly less than that in dark-avoidance trained rats at each time-point. This result suggested that c-Fos expression might be involved in learning and memory processes. In addition, all the pseudotraining-, training- and memory arousing-induced c-Fos expression was decreased with increasing age, and the decrease was more notable in trained and memory aroused rats. This suggested that the total number of nbM neurons and/or the sensitivity of nbM neurons to experimental manipulations, especially learning and memory performance, might reduce during aging.

Expression of immediate early genes in the hippocampal formation of the black-capped chickadee ( Poecile atricapillus) during a food-hoarding task

Black-capped chickadees store food in many different locations in their home range and are able to accurately remember these locations. We measured the number of cells immunopositive for three different Immediate Early Gene products (Fra-1, c-Fos and ZENK) to map neuronal activity in the chickadee Hippocampal Formation (HF) during food storing and retrieval. Fra-1-like immunoreactivity is downregulated in the dorsal HF of both storing and retrieving chickadees compared to controls. In retrieving birds, the number of Fos-like immunoreactive neurons relates to the number of items remembered, while the number of ZENK-like immunoreactive neurons in the HF may be related to the accuracy of cache retrieval. These results imply that the brain might process complex information by recruiting more neurons into the network of active neurons. Thus, our results could help explain why food-hoarding birds have more HF neurons than non-hoarders, and why this number increases in autumn when large numbers of food items are cached.

족삼리(足三里) 봉독약침자극(蜂毒藥鍼刺戟)이 척수내(脊髓內) Fos 양성반응(陽性反應) 신경세포(神經細胞)의 활성(活性)에 미치는 영향(影響)

This study was designed to evaluate the analgesic effect of bee venom (BV) Acupuncture into different treatment points, Chok-samni (ST36) and blank loci of the gluteal muscle and back. We investigated neuronal activity in the spinal cord using the Fos immunohistochemical technique according to the pretreatment with different concentrations of BV, thirty minutes before the formalin injection. The results were summarized as follows: 1. The number of Fos-like immunoreactive (Fos-LI) neurons in L2 segment of the saline-formalin treated group was significantly increased in NECK and VENT of the spinal cord as compared with that of the room control group. However, there was no significant change in the number of the Fos-LI neurons in L2 segment of the BV-formalin treated group as compared with that of the room control group. 2. The number of Fos-LI neurons in L3-5 segment of the saline-formalin group was significantly increased in all the regions of 142 the spinal cord as compared with that of the room control group. However, the Fos-LI neurons in L3-5 segment of the BV-formalin treated group was dramatically decreased in all the regions of the spinal cord as compared with that of the saline-formalin group. Therefore, these results indicated that the BV acupuncture suppressed the nociceptive neuronal activities in L3-5 of the spinal cord induced by formalin injection. 3. There was a strong positive correlation between the formalin-induced pain behavior and the number of the Fos-LI neurons in L3-5 segment.

Hypothyroidism induces Fos-like immunoreactivity in ventral medullary neurons that synthesize TRH

Altered thyroid statuses are associated with autonomic disorders. Thyrotropin-releasing hormone (TRH) in medullary nuclei regulates vagal efferent activity. Induction of Fos-like immunoreactivity (IR) in medullary TRH-synthesizing neurons was investigated in 24-h fasted rats with different thyroid statuses. Hypo- and hyperthyroidism were induced by 6-N-propyl-2-thiouracil (PTU) in drinking water and a daily intraperitoneal injection of thyroxine (T(4); 10 microgram. 100 g(-1). day(-1)), respectively, for 1-4 wk. The numbers of Fos-like IR positive neurons in the raphe pallidus, raphe obscurus, and parapyramidal regions, which were low in euthyroid rats (0-2/section), increased remarkably as the hypothyroidism progressed and were negatively correlated with serum T(4) levels. At the 4th wk, Fos-like IR positive neurons were 10- to 70-fold higher compared with euthyroid controls. Simultaneous T(4) replacement (2 microgram. 100 g(-1). day(-1)) prevented the increases of Fos-like IR in PTU-treated rats. Hyperthyroidism did not change the number of Fos-like IR neurons in the raphe nuclei but reduced it in the parapyramidal regions. Double immunostaining revealed that most of the Fos-like IR induced by hypothyroidism was located in the prepro-TRH IR positive neurons. The selective and sustained induction of Fos-like IR in TRH-synthesizing neurons in ventral medullary nuclei by hypothyroidism indicates that these neurons play a role in the autonomic disorders observed in altered thyroid statuses.

Effects of U-69,593, a κ-opioid receptor agonist, on carrageenin-induced peripheral oedema and Fos expression in the rat spinal cord

In an attempt to study the anti-inflammatory and the antinociceptive effects of a κ 1-opioid receptor agonist (U-69,593: trans-3,4-dichloro- N-methyl- N-[7-(1-pyrrolidinyl)cycloexil]benzene acetamide methanesulfonate), we used a combination of the measurement of peripheral oedema (with a calliper) and Fos immunodetection in the carrageenin model of inflammation. The intraplantar injection of carrageenin-induced the development of a peripheral oedema, associated with an increase in Fos-like immunoreactivity at the level of the dorsal horn of the spinal cord. U-69,593 administered intravenously (i.v.) 10 min before carrageenin administration over the dose range 0.75, 1.5 and 3 mg/kg, reduced both paw and ankle oedema in a non dose-dependent manner. The maximal decrease was observed at the highest dose and did not exceed 21% and 20% for the paw and the ankle respectively. These effects were κ-opioid receptor specific since the anti-inflammatory effect of 1.5 mg/kg i.v. of U-69,593 was antagonised by a specific κ-opioid receptor antagonist nor-binaltorphimine. Pre-treatment with U-69,593 strongly decreased the number of Fos-like Immunoreactive neurones of the spinal cord in a dose-dependent, antagonist reversible manner; maximal effect was 65%. The disparate results between the anti-inflammatory effects and the depressive effects on Fos expression suggest that anti-inflammatory effects of κ-opioid receptor agonist are of minor importance for the antinociceptive effects of this compound.

Distribution of Fos-Like Immunoreactivity in the Medullary Reticular Formation of the Rat after Gustatory Elicited Ingestion and Rejection Behaviors

The distribution of neurons in the medullary reticular formation (RF) activated by the ingestion of sucrose or rejection of quinine was examined using standard immunohistochemical techniques to detect the expression of the Fos protein product of the immediate-early gene c-fos. Double-labeling techniques were used to gain further insight into the possible functional significance of RF neurons exhibiting Fos-like immunoreactivity (FLI). Compared with sucrose and unstimulated controls, quinine elicited significantly more FLI neurons in three specific RF subdivisions: parvocellular reticular nucleus (PCRt), intermediate reticular nucleus (IRt), and dorsal medullary reticular nucleus (MdD). Moreover, the number of FLI neurons in the RF of quinine-stimulated animals was significantly correlated with the degree of oromotor activity. Thus, the distinct distribution of FLI neurons throughout the RF after quinine may reflect the activation of a specific oral rejection circuit. The double-labeling results indicated a high degree of segregation between FLI neurons and premotor projection neurons to the hypoglossal nucleus (mXII) retrogradely labeled with Fluorogold. Thus, although there were a significant number of double-labeled neurons in the RF, the major concentration of premotor projection neurons to mXII in IRt were medial to the preponderance of FLI neurons in the PCRt. In contrast, there was substantial overlap between FLI neurons in the RF and labeled fibers after injections of the anterograde tracer, biotinylated dextran into the rostral (gustatory) portion of the nucleus of the solitary tract. These results support a medial (premotor)/lateral (sensory) functional topography of the medullary RF.

Effects of Intrathecal Monoamine Antagonists on the Nociceptive c-Fos Expression in a Lesioned Rat Spinal Cord

Effects of intrathecal (i.t.) administration of monoamine antagonists on formalin-induced neuronal c-Fos expression in two sides of the lumbar dorsal horn were observed in rats with unilateral transection of the dorsolateral funiculus at T11-12 level. The results showed that: 1) pretreated with i.t. normal saline (control) and then an equal volume of formalin was injected into the two hindpaws, the number of Fos-like immunoreactive neurons were 44% lower on the side of lumbar dorsal horn with intact dorsolateral funiculus (57 ± 3.1 vs. 103 ± 3.8). 2) Pretreatment with i.t. phentolamine (a non-selective aL-adrenoceptor antagonist) caused an increase of Fos-like immunoreactive neurons on the intact side so showing only a reduction rate of 23% to the lesioned side (p <. 01); 3) pretreatment with i.t. cyproheptadine (a 5-HT-receptor antagonist) caused a similar reduction rate of 21% (p <. 01) of Fos-like immunoreactive neurons on the intact side; and 4) combined i.t. pretreatment with phentolamine and cyproheptadine caused a reduction of Fos-like immunoreactive neurons of only 4% on the intact side, namely, the differences in the number of Fos-like immunoreactive neurons on two sides of the lumbar spinal cord owing to the unilateral dorsolateral funiculus lesion were nearly abolished by i.t. coinjection of phentolamine and cyproheptadine. The results indicate that 1) peripheral noxious inputs can provoke a spinally-descending inhibitory effect on the spinal nociceptive transmission via the dorsolateral funiculus and 2) the descending fibers in dorsolateral funiculus exert their action mainly through the release of either norepinephrine or 5-HT at the spinal level.

An Opioidergic Cortical Antinociception Triggering Site in the Agranular Insular Cortex of the Rat that Contributes to Morphine Antinociception

We report an anatomically defined opioid-responsive site in the rostral agranular insular cortex (RAIC) of the rat and characterize the antinociception produced by morphine acting within this region. Immunohistochemistry for the mu-opioid receptor identified a discretely localized cluster of densely labeled dendrite-like processes in the agranular insular cortex. The antinociceptive effect of morphine microinjected unilaterally into this area was evaluated using the formalin test. Antinociception was observed in both ipsilateral and contralateral hindpaws. Local pretreatment with naltrexone in the RAIC blocked the antinociception of local morphine injection, confirming that morphine was acting at an opioid receptor. Unilateral injection of naloxone methiodide into the RAIC reversed the behavioral antinociception of systemic morphine bilaterally in the formalin test. Evidence for a descending inhibitory mechanism acting on spinal nociceptive neurons was obtained by monitoring noxious stimulus-induced c-fos expression in rats having undergone formalin testing and by electrophysiological recording of single units in the lumbar dorsal horn after localized application of morphine into the RAIC. A significant reduction in the number of Fos-like immunoreactive neurons was found ipsilateral to the formalin stimulus in nociresponsive areas of the dorsal horn after on-site injections of morphine into the RAIC. Electrophysiological recording of nociresponsive dorsal horn neurons demonstrated a naloxone-reversible reduction in noxious thermal stimulus-evoked firing after morphine injection into this same area. These results suggest that the RAIC contributes to opioid-receptor-mediated antinociception after either local or systemic morphine administration and that these effects may be associated with an increased descending inhibition of dorsal horn neurons.

Intraplantar morphine depresses spinal c-Fos expression induced by carrageenin inflammation but not by noxious heat.

1. We have studied the effects of intraplantar administration of the same doses of morphine on intraplantar carrageenin (6 mg 150 microliters-1 of saline) and noxious heat (52 degrees C for 15 s) induced spinal c-Fos expression and inflammation. 2. Intraplantar carrageenin, in awake rats, induced numerous Fos-like immunoreactive (Fos-LI) neurones in the dorsal horn of L4-L5 lumbar segments of the spinal cord and extensive peripheral oedema. At 1 h 30 min, Fos-LI neurones were preferentially located in the superficial laminae (74 +/- 2%) whereas at 3 h, Fos-LI neurones were observed both in the superficial (45 +/- 2%) and deep (37 +/- 1%) laminae of the spinal dorsal horn. 3. Intraplantar morphine dose-dependently reduced c-Fos expression induced 1 h 30 min after carrageenin (r = 0.605, P < 0.02), these effects were completely blocked by intraplantar methiodide naloxone (20 micrograms) (121 +/- 22% of control carrageenin expression). The systemic injection of the highest dose of intraplantar morphine (50 micrograms) had no significant effect on the number of Fos-LI neurones (88 +/- 9% of control carrageenin expression). None of the drugs influenced unilateral peripheral oedema observed 1 h 30 min after carrageenin. 4. In the second series of experiments, intraplantar morphine dose-dependently reduced the number of superficial and deep Fos-LI neurones induced 3 h after carrageenin (r = 0.794, P < 0.0004 and r = 0.698, P < 0.004, respectively). Furthermore, the effects of the highest dose of intraplantar morphine were completely blocked by co-administration of intraplantar methiodide naloxone (20 micrograms). 5. In addition, intraplantar morphine dose-dependently reduced the ankle (r = 0.747, P < 0.002) and paw (r = 0.682, P < 0.005) oedema observed 3 h after carrageenin, with the effect of the highest dose of intraplantar morphine being completely blocked by co-administration of methiodide naloxone (98 +/- 4% and 102 +/- 8% of control paw and ankle oedema, respectively). 6. Brief noxious heat stimulation, in urethane anaesthetized rats, induced, 2 h after the stimulation, numerous Fos-LI neurones in the dorsal horn of L3-L4 lumbar segments of the spinal cord but no detectable peripheral oedema. Fos-LI neurones were preferentially located in superficial laminae (94 +/- 2%) of the spinal dorsal horn. None of the drugs influenced the noxious heat induced c-Fos expression. 7. Such results illustrate that peripheral effects of morphine preferentially occur during inflammatory states and outline the interest of extending clinical investigations of the possible use of local injection of morphine in various inflammatory pain states.