Expression of c-fos-like protein as a marker for neuronal activity following noxious stimulation in the rat

Regional expression of fos-like immunoreactivity following seizures induced by pentylenetetrazole and maximal electroshock

The expression of fos-like immunoreactivity (FLI) has been used widely as a marker of neural activation following the induction of seizures in several experimental models of epilepsy. The purpose of the present study was to provide a more detailed regional analysis of FLI expression following the induction of seizures by maximal electroshock (MES) and pentylenetetrazole (PTZ). Tonic-clonic seizures, matched for duration, were induced by MES applied by earclips (40 mA, 1 s) and intraperitoneal injections of PTZ (60 mg/kg); tonic hindlimb extension was present only after MES. Two hours after the induction of seizures brain tissue was processed for FLI. High levels of FLI were induced by both convulsion-inducing processes in a range of structures, including the dentate gyrus, the caudal amygdala, parts of the cerebral cortex, the bed nucleus of stria terminalis, various thalamic nuclei, the lateral parabranchial nucleus, and the nucleus of the solitary tract. In other structures, such as the medial and rostral amygdala, the ventromedial hypothalamic nucleus, the peripeduncular area, the central gray, and parts of the pretectum and superior colliculus, significantly greater FLI was induced by MES. Only in relatively few structures, such as the reticular thalamic nucleus and arcuate nucleus of the hypothalamus, did PTZ cause a much larger expression of FLI than MES. Insofar as the c-fos technique reflects neuronal activation, the present data reveal potentially important differences in the circuitry underlying the seizures induced in two major experimental models of epilepsy.

Noradrenergic modulation of noxious heat-evoked fos-like immunoreactivity in the dorsal horn of the rat sacral spinal cord

The tail-flick withdrawal reflex commonly is used to study spinal nociceptive mechanisms; noradrenergic agonists administered intrathecally inhibit the tail-flick reflex in a dose-dependent manner. The objectives of the present study were: (1) to use fos-like immunoreactivity as a marker for neuronal activity to examine the population of neurons in the spinal cord dorsal horn that are engaged by activation of nociceptive tail afferents, and (2) to determine whether fos-like immunoreactivity can be modulated by intrathecally administered alpha adrenoceptor agonists. Neurons demonstrating heat-evoked fos-like immunoreactivity were identified bilaterally in the sacral spinal cord in superficial and deep dorsal horn laminae. Heat-evoked fos-like immunoreactivity was inhibited dose-dependently by intrathecal norepinephrine (NE). The inhibition was attenuated significantly by: (1) phentolamine (PHEN), a nonselective alpha adrenoceptor antagonist; (2) yohimbine (YOH), an alpha-2 adrenoceptor antagonist; and (3) prazosin (PRAZ), an alpha-1 adrenoceptor antagonist. Thus, both spinal alpha-1 and alpha-2 adrenoceptors mediate the inhibition of heat-evoked fos-like immunoreactivity produced by intrathecal NE. ST-91, an alpha-2 adrenoceptor agonist, also inhibited significantly the expression of fos-like immunoreactivity; the inhibition was antagonized by YOH. In the absence of noxious heat, intrathecal NE dose-dependently evoked the expression of fos-like immunoreactivity in the superficial dorsal horn, which was antagonized by PHEN and PRAZ, but not by YOH, suggesting that the effect is mediated by spinal alpha-1 adrenoceptors.

Expression of c-fos in regions of the basal limbic forebrain following intracerebroventricular corticotropin-releasing factor in unstressed or stressed male rats

Corticotropin-releasing factor has an integrative role on the behavioral, endocrine and autonomic responses to stress. Immediate-early gene (c-fos) expression was used to determine patterns of neural activity in the limbic system following i.c.v. infusion of corticotropin-releasing factor. Either 250 or 1000 pmol corticotropin-releasing factor infused into the lateral ventricle of precannulated and handled male rats resulted in marked c-fos expression 60 or 120 min later in localized regions of the basal forebrain, including the ventrolateral septum, the dorsal and medial parvicellular divisions of the paraventricular nucleus, the central nucleus of the amygdala, and dorsal bed nucleus of the stria terminalis. Pre-infusion of alpha-helical corticotropin-releasing factor (2500 pmol), a competitive corticotropin-releasing factor antagonist of corticotropin-releasing factor, had no effect on immediate-early gene expression alone but reduced that elicited by exogenous i.c.v. corticotropin-releasing factor (250 pmol)--in some areas to control levels. Fifteen minutes of restraint stress, a situation in which corticotropin-releasing factor is released endogenously, also activated c-fos expression in a pattern that resembled corticotropin-releasing factor infusions but was not identical. There was enhanced expression in the dorsal and medial areas of the paraventricular nucleus, but not its magnocellular region, and increased expression in the ventrolateral septum; however, there was no detectable response on the central amygdala. Preinfusion of alpha-helical corticotropin-releasing factor (2500 pmol) had no significant effect on stress-induced c-fos expression in the ventrolateral septum or paraventricular nucleus. This suggests that corticotropin-releasing factor release may form only a part of the central neurochemical response to restraint stress. Rats given i.c.v. corticotropin-releasing factor (250 pmol) before restraint stress showed additive effects on c-fos in the ventrolateral septum but not in the paraventricular nucleus; the central nucleus of the amygdala reacted as if corticotropin-releasing factor alone had been infused. Corticosterone levels were raised by both stress and corticotropin-releasing factor, but pretreatment with alpha-helical corticotropin-releasing factor reduced them after either procedure, which correlates with c-fos expression in the paraventricular nucleus and ventrolateral septum. These results show that corticotropin-releasing factor induces a specific pattern of c-fos expression in localized regions of the amygdala, hypothalamus and septum, which may indicate a corresponding pattern of neural activation. Restraint, one form of stress, activates c-fos in a similar but not identical manner, suggesting that corticotropin-releasing factor may not be the only neuropeptide involved in the response to this stressor.(ABSTRACT TRUNCATED AT 400 WORDS)

Hypotension preferentially induces c-fos immunoreactivity in supraoptic vasopressin neurons

Immunoreactivity to Fos protein (Fos-IR) was detected in rat hypothalamic neurons within 1 h of onset of hemorrhage by withdrawing 4-5 ml of blood, which lowered the arterial blood pressure to 50-70 mm Hg. About 70% of vasopressin (AVP)-containing neurons in the supraoptic nucleus (SON) and 20% in the paraventricular nucleus (PVN) expressed Fos-IR. In contrast, 5% of oxytocin (OXY)-containing neurons in the SON and < 1% in PVN were Fos-IR. Intravenous infusion of the vasodilating agent, nitroprusside, which lowered the blood pressure to levels comparable to that attained by hemorrhage, induced Fos-IR in greater than 65% of AVP-containing neurons in the SON, while relatively few AVP neurons in the PVN were Fos positive. These results suggest that hemorrhage or hypotension preferentially induces c-fos expression in supraoptic AVP-containing neurons.

Narine occlusion decreases basal levels of Fos protein in the cerebral cortex of the lizard Podarcis hispanica

Immunocytochemical study of cerebral cortex of the lizard Podarcis hispanica using an antibody directed to the M peptide of the rat c-Fos protein showed a distinct pattern of Fos distribution. Abundant Fos-immunoreactive neuronal nuclei were detected in the cell layers of the medial, the dorsal and the lateral cortices, whereas only a few nuclei were found in the cell layer of the dorsomedial cortex. The Fos immunoreactivity was characterized by Western blot analysis of nuclear extracts from lizard brain and showed a distinct band with an apparent molecular weight of 30,000. In band-shift assays, nuclear extracts from lizard brain were shown to contain AP-1 complexes. The basal expression of Fos immunoreactivity is related to sensory olfactory input in the cerebral cortex of the lizard since experiments with olfactory-deprived animals resulted in a complete absence of Fos immunoreactivity in the cortical areas.

Mapping of c-fos expression elicited by pure tones stimulation in the auditory pathways of the rat, with emphasis on the cochlear nucleus

C-fos expression was mapped in the auditory pathways of rats, stimulated acoustically with pure tones. In the cochlear nucleus, two clusters of c-fos-like immunoreactive neurons, located respectively in the caudal part of the dorsal cochlear nucleus and in the granular cell region, did not show clear systematic shift in their position as a function of the tones frequency. On the other hand, more rostrally in the dorsal cochlear nucleus, a cluster of c-fos-like positive neurons moved progressively from dorsal to ventral for decreasing tones frequency. In the posteroventral cochlear nucleus, another cluster of c-fos-like positive neurons was observed, whose position also varied with tones frequency. Surprisingly, no or very rare c-fos-like immunoreactive neurons were present in the anteroventral cochlear nucleus and in the superior olivary complex. In the inferior colliculus, however, c-fos-like immunoreactive neurons formed clear isofrequency contours, shifting from dorsolateral to ventromedial for increasing tones frequency. In the medial geniculate body c-fos-like immunostaining was restricted to the medial and dorsal divisions while the ventral division was free of labeling. The cause of this differential labeling along the auditory pathways is at present unknown but may eventually provide clues as to physiological differences in parallel auditory pathways.

Changing pattern of c-FOS expression in spinal cord neurons after electrical stimulation of the chronically injured sciatic nerve in the rat

Immunocytochemical technique was used to study the distribution of c-FOS protein immunoreactive cells in the spinal cord and gracile nuclei 2 h after electrical stimulation of the sciatic nerve in ketamine/xylazine/acepromazine-anesthetized adult rats. Quantitative examination of the c-fos-labeled cells in the spinal cord laminae was made in unoperated and sham operated controls, after sciatic nerve transection without electrical stimulation, and after electrical stimulation at C-fiber or A alpha/beta-fiber intensity, both in normal animals and at various survival times after chronic sciatic nerve injury (transection and ligation) or crush. Unoperated animals showed very few c-fos-labeled cells, and sham operated controls showed labeled cells located mainly outside the sciatic nerve projection territory. A small increase in number of c-fos protein positive cells was seen after sciatic nerve transection without electrical stimulation. Stimulation of the normal sciatic nerve at C-fiber intensity resulted in c-fos protein-positive cells within the sciatic projection territory in the ipsilateral dorsal horn. Labeled cells were seen in all spinal cord laminae except lamina IX, with the vast majority in lamina I and outer lamina II. No labeled cells were seen in the gracile nucleus. Stimulation at A alpha/beta fiber intensity resulted in no or only a very small number of c-fos-positive neurons. Electrical stimulation of the injured sciatic nerve at C-fiber intensity, using the uninjured contralateral side as control, resulted in significant decreases in c-fos-immunoreactive cells in lamina I plus the outer portion of lamina II at 12 and 39 days survival after injury. A non-significant decrease was seen in these laminae also after 21 days. Significant increases were seen in laminae III and IV at 21 days. Decreases in laminae V, VI and more ventral laminae were significant at 21 and 39 days after injury. At longer survival times, the difference between the normal and injured side seen weeks after injury tended to disappear. Stimulation at A alpha/beta fiber intensity 21 days after injury resulted in increases in the numbers of labeled cells in ipsilateral laminae II, III and IV and in the gracile nucleus. Sciatic nerve stimulation after crush injury resulted in more variable side differences, with tendencies for the same alterations as those noted after chronic transection-ligation.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of c-fos protein in the medulla oblongata of conscious rabbits in response to baroreceptor activation

Neuronal expression of c-fos protein (Fos) in the medulla in response to baroreceptor activation was studied in conscious rabbits. Raising arterial pressure resulted in a marked increase, compared to control animals, in Fos immunoreactivity in the nucleus tractus solitarius, area postrema and ventrolateral medulla (VLM). Fos-immunoreactive neurons in the VLM extended from the level just rostral to the obex to 3 mm more caudal. Only a small proportion of these neurons showed tyrosine hydroxylase immunoreactivity. The results indicate that baroreceptor activation induces Fos expression in circumscribed medullary regions which have previously been shown to receive excitatory baroreceptor inputs.

Fos-like immunoreactivity in the brain of homozygous diabetes insipidus Brattleboro and normal Long-Evans rats

Water deprivation induces the production of the transcription factor Fos in neurons of the neurohypophysial system. These neurons, which are located primarily in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON), produce the antidiuretic hormone vasopressin. The present immunocytochemical study has analyzed the distribution of Fos in brain regions involved in osmoregulation and compared the extent of Fos immunoreactivity (Fos-IR) in vasopressin-deficient Brattleboro and normal Long-Evans rats under stimulated and non-stimulated conditions. Rats were osmotically challenged by means of a single intraperitoneal injection of 1.5 M/L NaCl. Since Fos may be induced by the stress of handling of animals, non-injected and isotonic saline-injected rats were used as controls. Faint nuclear Fos immunostaining was found in the organum vasculosum of the lamina terminalis (OVLT), the median preoptic nucleus (MnPO), subfornical organ (SFO), and SON of non-injected and isotonic saline-injected Brattleboro but not Long-Evans rats. Hypertonic saline injection specifically induced Fos-IR in neurons located in the SFO, OVLT, MnPO, PVN, SON, hypothalamic accessory nuclei (including the nucleus circularis), and arcuate hypothalamic nucleus (Arc) in both Long Evans and Brattleboro rats. No differences in distribution of the induced immunostaining were found between the strains. Stress of handling and (isotonic saline) injection induced Fos-IR in the lateral septal nuclei, central amygdaloid nuclei, medial amygdaloid nucleus, medial preoptic area, the bed nucleus of the stria terminalis, cingulate- and piriform cortex, the lateral hypothalamic area, ventromedial hypothalamic nucleus, and the habenular nucleus. The data are consistent with a role for Fos in the regulation of vasopressin gene expression during acute hyperosmotic stimulation. In addition, this study demonstrated that during chronic osmotic stimulation, as experienced by homozygous Brattleboro rats, Fos-IR is limited but apparently present constantly and that it increased in these animals following acute osmotic challenge. Our observations suggest that c-fos regulatory controls in homozygous Brattleboro rats are different from those in Long-Evans rats.

Induction of fos expression by activity in the spinal rhythm generator for scratching

Fos expression was evaluated immunohistochemically in L7-S1 spinal segments after inducing fictive scratching in paralysed, unanaesthetized, decerebrate cats. The activity was induced by cutaneous stimulation of the pinna on one side and recorded from peripheral nerves. A cumulative duration of scratching of 60 to 90 min was effective in inducing fos expression. Most Fos-positive neurones were found in the dorsolateral part of the ventral horn and in the intermediate region of the spinal cord on the scratching side. In sham-operated animals the finding of Fos-positive neurones in these areas was very rare.

Mapping of the cochlear nucleus subregions in the rat with neuronal Fos protein induced by acoustic stimulation with low tones

To explore the mode of appearance of Fos, a gene product of proto-oncogene c-fos, in the cochlear nucleus, a pure tone was given to rats and Fos was detected by immunohistochemistry. Following low-tone stimuli applied with moderate ranges of sound intensity, neurons with Fos-label occurred band-like in the ventral subregions of the dorsal cochlear nucleus. Organization of low-to-high tones in the ventral-to-dorsal orientation became visible at the caudal level. Several other subnuclei consistently exhibited Fos with no topographic pattern. Neurons interspersed in the adjoining vestibulocochlear nerve were also found to elicit Fos. Low-tone stimuli with very high sound intensity led to a rather widespread distribution of Fos, making the tone-specific distribution less visible.

Mapping of the motor pathways in rats: c-fos induction by intracortical microstimulation of the motor cortex correlated with efferent connectivity of the site of cortical stimulation

The general goal of the present study was to investigate structural components of a neural system anatomically as well as functionally. The rat motor system, which is reasonably well understood, was selected and a new procedure was developed to combine a functional marker with axonal tracing methods (in the same animal). This was achieved by mapping c-fos induction immunocytochemically as a result of intracortical microstimulation in the distal forelimb area of the motor cortex. The anterograde tracers Phaseolus vulgaris-leucoagglutinin or biocytin were deposited at the site of intracortical microstimulation, the former three weeks and the latter two to three days before stimulation. Neuronal nuclei, labeled for the expressed c-fos protein, were present and mapped in the following structures: motor cortex; basal ganglia (caudate-putamen, globus pallidus); thalamus (reticular, ventromedial and posterior nuclei); subthalamic nucleus; substantia nigra; tectum; red nucleus; pontine nuclei; inferior olive; external cuneate nucleus; cerebellar cortex; deep cerebellar nuclei. Labeling was often bilateral but generally more substantial ipsilaterally, except in the cerebellum where it was mainly contralateral. Axonal labeling, including terminal branches and boutons, was also found in most of the above structures with the exception of the globus pallidus, deep cerebellar nuclei, cerebellar cortex and external cuneate nucleus. These expected exceptions demonstrate that activity changes in these latter structures, as revealed by c-fos labeled neurons, were induced over more than one synapse. This combined procedure might, therefore, be useful in deciding whether two structures in a given system are linked directly (monosynaptically) or indirectly (polysynaptically) to each other. In contrast to the 2-deoxyglucose technique, functional mapping by means of c-fos induction provides cellular resolution, making it possible to establish fine details of axonal contacts with target neurons: boutons in close apposition to c-fos labeled neurons were clearly observed here, for instance in the cerebral cortex, caudate-putamen, thalamus, subthalamic nucleus and pontine nuclei. Surprisingly, the ventrolateral and ventrobasalis nuclei of the thalamus contained numerous and dense axon terminals labeled with Phaseolus vulgaris-leucoagglutinin or biocytin, but the contacted neurons in the ventrolateral and ventrobasalis nuclei were not marked with c-fos. However, with respect to directly connected structures, there was, in general, a good correlation between structures with axonal labeling and those with c-fos labeled neurons.

Expression of c-fos-like immunoreactivity in brainstem after meningeal irritation by blood in the subarachnoid space

The expression of c-fos protein was examined by immunohistochemistry in serial sections of brainstem following the instillation of either autologous arterial blood (0.3 ml) or mock cerebrospinal fluid (0.3 ml) through a catheter placed in the cisterna magna, or following catheter placement alone in pentobarbital-anesthetized Sprague-Dawley rats. After injection, blood was distributed within the subarachnoid space surrounding the brainstem and in the region of the circle of Willis. c-fos protein-like immunoreactivity was present at 1 h, peaked at 2 h and decreased by 8 h. At 2 h, immunoreactivity was strongly expressed within trigeminal nucleus caudalis (lamina I, IIo), as well as within nucleus of the solitary tract, area postrema, ependyma, pia mater and arachnoid in every animal. Moderate labeling was found in parabrachial nucleus, medullary lateral reticular nucleus and central gray. Sparse labeling was present in trigeminal nucleus caudalis (lamina III-V) and trigeminal nucleus interpolaris; few or no labeled cells were detected in other parts of the trigeminal nuclear complex, thalamus, cerebral cortex, cerebellar cortex or trigeminal ganglion. The number of positive cells was not related to the volume of injectate but was related to the amount of injected blood. The density of cell labeling evoked by injecting mock cerebrospinal fluid or after catheter placement was markedly lower than after blood in all brainstem areas. The number of labeled cells was greatly reduced within trigeminal nuclear complex, parabrachial nucleus and medullary lateral reticular nucleus, but not within the nucleus of the solitary tract, area postrema or ependyma when blood was injected into adult animals in which unmyelinated C-fibers were destroyed by neonatal capsaicin treatment. Similar results were obtained after blood was instilled into the cisterna magna of rats in which meningeal afferents were chronically sectioned at the ethmoidal foramen bilaterally. We conclude that blood in the subarachnoid space is an effective stimulus for activating c-fos expression within subpopulations of brainstem neurons. Activation within trigeminal nucleus caudalis is mediated in large part by excitation of small-caliber meningeal afferents (trigeminovascular fibers), whereas c-fos expression within nucleus of the solitary tract and area postrema may reflect direct stimulation of blood or blood products, or possibly the response to autonomic activation from noxious stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Fos-like proteins in the lumbosacral spinal cord following noxious and non-noxious colorectal distention in the rat

The rat lumbosacral spinal cord was immunocytochemically stained for Fos-like immunoreactivity following repetitive colorectal distention (CRD) to 20, 40 or 80 mm Hg. Following all 3 distention pressures, Fos-like immunoreactive (Fos-ir) nuclei were observed primarily in laminae I-II, V-VII and X, although some labeled nuclei were observed in laminae III-IV. Eighty mm Hg CRD resulted in significantly more Fos-ir nuclei than 20 or 40 mm Hg CRD. Morphological examination of the colon revealed clear signs of inflammation following 80 but not 20 mm Hg CRD. Acute 20 mm Hg CRD is a non-noxious stimulus, suggesting that both noxious and non-noxious visceral stimuli can induce Fos-like immunoreactivity in the spinal cord. It is suggested that activation of neuropeptide-containing small-diameter primary afferents is necessary, although not necessarily sufficient, to induce c-fos in the rat spinal cord.

c-fos expression in rat lumbar spinal cord during the development of adjuvant-induced arthritis

A parallel clinical and behavioral study of adjuvant-induced arthritis in the rat showed four stages in the time-course of the disease: preclinical (first week), acute (weeks 2-4), post-acute (weeks 5-8) and recovery weeks 9-11) [Calvino et al. (1987) Behav. Brain Res. 24, 11-29]. As several studies have reported the expression of the proto-oncogene c-fos in spinal cord neurons following acute noxious peripheral stimuli, the aim of this study was to quantitatively assess Fos-like immunoreactivity in lumbar spinal cord neurons at various times of adjuvant-induced arthritis development, i.e. one, two, three, 11 and 22 weeks post-inoculation. The total number of Fos-like immunoreactive neurons in the lumbar enlargement correlated with the observed development of adjuvant-induced arthritis, i.e. Fos-like immunoreactivity was absent at one week, moderate at two weeks, greatly increased at three weeks, decreased at 11 weeks and returned to control values at 22 weeks. At three weeks, at the peak of Fos-like immunoreactivity distribution and acute stage of hyperalgesia, maximal labeling was observed in L3 and L4 spinal segments. In these segments, the most densely labeled region was the neck (laminae V and VI) of the dorsal horn (55%) and the ventral horn (35%) as compared to the superficial laminae (laminae I and II; 5%) and the nucleus proprius (laminae III and IV; 5%). These data indicate that c-fos expression induced by chronic inflammation is better expressed in deeper laminae than in the superficial ones, and that the number of Fos-positive cells correlates with behavioral studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Mapping of prostaglandin E2 binding sites in rat brain using quantitative autoradiography

The density of specific prostaglandin E2 (PGE2) binding sites was quantitatively mapped in the rat brain using in vitro autoradiography. The anterior wall of the third ventricle and the nucleus solitary tract were found to have a very high density of binding sites (greater than 15 fmol/mg tissue). Two thalamic nuclei (paraventricular and anteroventral nuclei) and the dorsal parabrachial nucleus contained a high density of binding sites (10-15 fmol/mg tissue). Entorhinal cortex, ventral hippocampus, amygdala, dorsomedial hypothalamus, mammillary complex, some thalamic nuclei, central gray, superior colliculus, raphe nuclei, locus coeruleus, spinal trigeminal nucleus (caudal part) and the dorsal horn of the spinal cord (laminae 1 and 2) had each a moderate density of binding sites (5-10 fmol/mg tissue). Binding tended to occur in brain regions rich in neuronal cell bodies or neuronal cell processes (dendrites and axon terminals). PGE1, whose central actions are very similar to those of PGE2, had essentially the same pattern of binding sites as did PGE2 throughout the entire brain, suggesting there are receptors common to these two PGEs. In addition to already known functions of receptors common to these two PGEs. In addition to already known functions of PGE2 in the hypothalamus, which include fever genesis, promotion of wakefulness, cardiovascular control and LH-RH release, the unique distribution of extrahypothalamic PGE2 binding sites found in this study suggests its involvement in the processing or modulation of viscerosensory, somatosensory (nociceptive and possibly thermal) and visual inputs as well as in the central integration of autonomic and limbic functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergically induced REM sleep triggers Fos-like immunoreactivity in dorsolateral pontine regions associated with REM sleep

We sought to determine the presence of Fos-like immunoreactive (Fos-LI) cells in the pontine brainstem following cholinergically induced sustained rapid-eye movement (REMc) sleep in cats. Microinjections (0.25 microliter) of vehicle (N = 2) or carbachol (2.0 micrograms/0.25 microliter; N = 4) were made into the medial pontine reticular formation. Carbachol produced a state with all the signs of natural REM sleep and with durations of 15.2-57.8 min. Compared with vehicle control animals, carbachol treated animals showed a significantly higher number of Fos-LI cells in pontine regions implicated in REM sleep generation, with longer REMc bouts associated with more Fos-LI cells than the short-duration bout. Regions with REMc-associated Fos-LI increases included: the lateral dorsal tegmental (LDT) and pedunculopontine tegmental (PPT) nuclei, where some Fos-LI cells were immunohistochemically identified as cholinergic; the locus coeruleus, where some of the Fos-LI cells were identified to be catecholaminergic; the dorsal raphe and the pontine reticular formation. These findings suggest immediate early gene activation is associated with the ubiquitous biological state of REM sleep.

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 effect of glutamate antagonists on c-fos expression induced in spinal neurons by irritation of the lower urinary tract

Chemical irritation of the lower urinary tract (LUT) of the rat increases the expression of c-fos in neurons in the dorsal horn, dorsal commissure and intermediolateral region of the spinal cord. The role of glutamatergic synapses in this response was examined using two glutamate receptor antagonists, MK-801 (an NMDA antagonist) and CNQX (an AMPA antagonist). In rats with an intact spinal cord, MK-801 (3.5 mg/kg, i.v.) administered 15 min before bladder irritation decreased (50-60%) the number of c-fos-positive cells in all regions of the cord. A smaller dose of MK-801 (0.8 mg/kg, i.v.) was ineffective. In spinal transected rats (4-7 days prior to the experiment) MK-801 (3.5 mg/kg, i.v.) decreased c-fos expression only in the medial dorsal horn. CNQX (1.2 mg/kg, i.v.) was ineffective in both preparations. These results indicate that activation of NMDA receptors at glutamate synapses in the central nervous system may play a role in the processing of nociceptive input from the LUT and may also be involved in reflex pathways mediating micturition.

Expression of c-fos and NGFI-A messenger RNA in the medulla oblongata of the anaesthetized rat following stimulation of vagal and cardiovascular afferents

Messenger RNA encoding the immediate early genes (IEGs) c-fos and NGFI-A was localized by in situ hybridization of specific 35S-labelled oligonucleotides to detect activated neurones in the medulla oblongata following unilateral electrical stimulation of the vagus (nX) and aortic depressor nerve (ADN), and following mechanical stimulation of the left carotid sinus (CS). In electrically stimulated rats, c-fos and NGFI-A mRNA was strongly expressed in the nucleus tractus solitarius (NTS) (predominantly ipsilaterally), area postrema (AP) and in a dorsal subregion of the paratrigeminal nucleus (PTN). Lower levels of c-fos and NGFI-A mRNA were seen in the ipsilateral NTS and PTN following mechanical stimulation of the left CS. In general these data correlate with the topography of innervation by the different nerve afferents, although the expression in the PTN (and in some cases the AP) would not be predicted on the basis of neuronal innervation patterns reported for the rat. Expression of these IEGs also occurred in the rostral and caudal ventrolateral medulla and inferior olive of both stimulated and sham-operated rats; presumably due to effects of the anaesthesia and surgical procedures. In conclusion the localization of the expression of c-fos and NGFI-A mRNAs represents a useful neuroanatomical technique for detecting the cell bodies of neurones that are activated by cardiovascular nerve afferents and should allow the further characterization of the neurochemical identity of these neurones.

Fos-like immunoreactivity in the rat superficial dorsal horn induced by formalin injection in the forepaw: effects of dorsal rhizotomies

As previously described at the lumbar spinal level, we found that 2 h after subcutaneous formalin injection in the distal part of the fore-limb, Fos-like immunoreactivity (FLI) was induced in the ipsilateral cervical enlargement. Not surprisingly, as the injection site corresponds to the distal part of the C6-C8 dorsal root dermatomes, maximal labelling which predominated in the superficial laminae, was observed in the C6-C8 segments and to a lesser extent in C5. Similar experiments were performed on rats which underwent various types of unilateral dorsal rhizotomies (DRh) 7 days before formalin injection. In animals with C4, C5, T1 and T2 DRh sparing C6-C8 the rostrocaudal distribution was similar to the intact one. But, in animals having C4-T2 DRh sparing one single root, C7, the segmental FLI distribution was modified: it was slightly increased in C7, decreased in C6 and significantly decreased in C8. As expected, no FLI was found in animals with C4 to T2 DRh. The spared root model provides information about the segmental distribution in the cervical spinal cord of the input brought by a single root following stimulation of the distal forelimb, i.e., maximal distribution in the entry segment, but also in the two rostral and one caudal segments.

Electroacupuncture modifies the expression of c-fos in the spinal cord induced by noxious stimulation

The present study was designed to investigate the effect of 4 Hz vs. 100 Hz electroacupuncture (EA) on c-fos expression in the spinal cord induced by noxious stimulation (NS). A second objective was to evaluate the sensitivity of these two different frequencies of EA stimulation to the opiate antagonist, naloxone. Mechanical NS was applied to the right hindpaw following 30 min of either 4 Hz or 100 Hz EA treatment and the resulting c-fos expression in the spinal cord dorsal horn was compared to that obtained in rats exposed only to the noxious stimulation. The involvement of endogenous opioids in the EA response to 4 Hz or 100 Hz stimulation frequencies was evaluated by pretreating rats with naloxone (5 mg/kg, i.p.) 10 min prior to EA. Both 4 Hz and 100 Hz EA reduced the number of c-fos-immunoreactive neurons in the spinal dorsal horn induced by noxious stimulation by 58% and 50%, respectively. The suppression of c-fos expression induced by 4 Hz EA was completely reversed by prior treatment with naloxone. On the other hand, the suppression of c-fos induced by 100 Hz EA was only partially blocked by this opiate antagonist. These data indicate that both high- and low-frequency EA are capable of inhibiting the expression of c-fos in the dorsal horn induced by NS. Low-frequency EA appears to be mediated primarily by endogenous opioid systems, while non-opioid mechanisms may be involved in mediating the analgesic effect of high frequency EA. These results support the hypothesis that EA has a direct inhibitory effect on spinal cord dorsal horn neurons and extend the results of previous studies which indicate low frequency EA is mediated by opiate sensitive circuitry, while high frequency EA is predominantly mediated by non-opioid neurotransmitters.

Odor-induced fos-like immunoreactivity in the rat olfactory bulb

We here report odor-induced mapping patterns of c-fos-like protein (Fos) immunoreactivity in the rat olfactory bulb under urethane anesthesia. Regional patterns of cells with nuclei expressing Fos, plotted on a spread-out reconstruction of the mitral cell layer, were strikingly comparable to data from the 2-deoxyglucose method, by which different foci of the most-labelled glomeruli of metabolic activity were demonstrated using different odors. Cells in the glomerular, external plexiform, and granule cell layers were also labelled.

Activity-dependent neuronal plasticity following tissue injury and inflammation

Increases in neuronal activity in response to tissue injury lead to changes in gene expression and prolonged changes in the nervous system. These functional changes appear to contribute to the hyperalgesia and spontaneous pain associated with tissue injury. This activity-dependent plasticity involves neuropeptides, such as dynorphin, substance P and calcitonin gene-related peptide, and excitatory amino acids, such as NMDA, which are chemical mediators involved in nociceptive processing. Unilateral inflammation in the hindpaw of the rat results in an increase in the expression of preprodynorphin and preproenkephalin mRNA in the spinal cord, which parallels the behavioral hyperalgesia associated with the inflammation. Cellular intermediate-early genes, such as c-fos, are also expressed in spinal cord neurons following inflammation and activation of nociceptors. Peripheral inflammation results in an enlargement of the receptive fields of many of these neurons. Dynorphin applied to the spinal cord also induces an enlargement of receptive fields. NMDA antagonists block the hyperexcitability produced by inflammation. A model has been proposed in which dynorphin, substance P and calcitonin gene-related peptide enhance excitability at NMDA receptor sites, leading first to dorsal horn hyperexcitability and then to excessive depolarization and excitotoxicity.

C-fos immunoreactivity in the brain following unilateral electrical stimulation of the dorsal periaqueductal gray in freely moving rats

C-fos immunoreactivity was used to reveal brain areas in which neurons were influenced by electrical stimulations applied to the dorsal periaqueductal gray. These stimulations were applied in freely moving rats so that the resulting behaviors could be observed. Shortly afterwards, the brains of the rats were processed for C-fos immunoreactivity. In order to determine the specificity of the brain areas thus labeled, control stimulations were applied to the ventral tegmental area of other rats. Immunoreactive cells were found surrounding the tip of the stimulation electrode within a radius of 0.5 mm. This labeled area extended further along the rostro-caudal axis than along the medio-lateral or dorso-ventral axis in the periaqueductal gray. Distally, clusters of labeled cells were found ipsilaterally in the caudal periaqueductal gray extending to the nucleus cuneiformis, and bilaterally in the locus coeruleus and supramamillary decussation. More widespread labeling was found in most hypothalamic subareas and in the lateral habenula. The labeled brain areas following ventral tegmental area stimulations were totally distinct, and comprised the medial forebrain bundle, the nucleus accumbens, the vertical limb of the diagonal band and the medial septum. The pattern of labeling produced by periaqueductal gray stimulations was therefore specific, and provided information about brain structures involved in the motivational and behavioral effects of such stimulations.

Morphine or U-50,488 suppresses Fos protein-like immunoreactivity in the spinal cord and nucleus tractus solitarii evoked by a noxious visceral stimulus in the rat

Immunohistochemical visualization of Fos protein, the nuclear phosphoprotein product of the early-immediate gene c-fos, permits identification of populations of neurons that are activated in response to a variety of stimuli. This study examined the distribution of Fos-like immunoreactive (FLI) neurons in the spinal cord and the nucleus tractus solitarii (NTS) of the caudal medulla evoked by a noxious visceral stimulus in the unanesthetized rat. It also compared the inhibition of pain behavior and Fos expression by a mu-selective opioid agonist, morphine, and a kappa-selective opioid agonist, U-50,488. Intraperitoneal injection of 3.5% acetic acid in the unanesthetized rat evoked the expression of FLI in a discrete population of spinal cord neurons, the distribution of which closely mirrored the spinal terminations of visceral primary afferents. Specifically, FLI neurons were concentrated in laminae I, IIo, V, VII, and X. Large numbers of Fos-immunoreactive neurons were also present in the NTS of the caudal medulla, most likely as a result of spinosolitary tract and vaginal afferent input. The number of labeled neurons in both the spinal cord and the NTS was significantly correlated with the number of abdominal stretches, a pain behavior measure. Both morphine (1-10 mg/kg s.c.) and U-50,488 (3-30 mg/kg s.c.) produced a dose-dependent inhibition of the pain behavior in these animals and a dose-dependent suppression of the number of FLI neurons in both the spinal cord and in the NTS; complete suppression of FLI neurons was, however, not necessary for the production of antinociception. Furthermore, although equianalgesic doses of morphine and U-50,488 reduced the number of labelled neurons in the spinal cord to a comparable extent, morphine reduced the number of immunoreactive neurons in the NTS to a greater extent than did U-50,488. These results suggest that morphine and U-50,488 have comparable effects on the transmission of visceral nociceptive messages by spinal neurons, but differentially affect the autonomic response to noxious visceral stimuli.

Fos-like protein is induced in neurons of the medulla oblongata after stimulation of the carotid sinus nerve in awake and anesthetized rats

The protooncogene c-fos is expressed rapidly, transiently and polysynaptically within neurons in response to synaptic activation and voltage-gated calcium entry into the cell. The nuclear protein product of this gene (Fos) is detectable immunohistochemically 20-90 min after cell activation and remains within the nucleus for hours after expression. The present study was undertaken to identify cells within the rat medulla oblongata that express Fos-like protein in response to stimulation of afferent fibers of the carotid sinus nerve (CSN). Direct electrical stimulation of the CSN in anesthetized animals or hypoxic stimulation in either anesthetized or awake animals resulted in a consistent and discrete distribution of Fos-like immunoreactivity (Fos-LI). Fos-LI was observed bilaterally within nucleus tractus solitarius (NTS) and the ventrolateral medulla (VLM), within area postrema and nucleus raphe pallidus, and bilaterally along the ventral medullary surface. Unstimulated animals were devoid of Fos-LI within the medulla oblongata. Furthermore, neither the surgical preparations alone nor the effects of anesthesia could account for the extent of Fos-LI observed. We believe these cells represent second- and higher-order neurons within the baroreceptor and chemoreceptor reflex pathways.

Somatotopy of spinal nociceptive processing

Relatively little is known about the spatial organization of spinal nociceptive processing. This study has employed the expression of c-fos-like protein as a marker for neuronal activity and has analyzed the patterns of immunoreactivity seen within the rodent spinal cord following noxious mechanical stimulation of various portions of one hindlimb. The results indicate that noxious mechanical stimulation induces distinct, somatotopic patterns of immunolabeling in laminae I-IV. Individual digits of a foot are represented medially in the dorsal horn over a short rostrocaudal distance, with the most lateral digit represented approximately one segment caudal to the most medial digit. Representation of the hip region is more lateral, is centered at L2, and extends rostrocaudally over many segments. The patterns of neuronal excitation seen in laminae V-IX following noxious peripheral stimulation were similar to those noted in laminae I-IV but were less tightly organized. C-fos-like immunoreactivity was noted both medially and laterally in the deeper laminae following stimulation of any portion of the hindlimb, but stimulation of different areas produced different columns of labeled cells extending from the superficial dorsal horn into lamina VII. In the rostrocaudal direction, immunolabeling in lamina V-IX was maximal at the same segmental level as in laminae I-IV, but the more ventral laminae exhibited increases in c-fos-like immunoreactivity over longer rostrocaudal distances. Experiments in spinally transected animals indicated that long, descending pathways contributed little or nothing to the pattern of immunolabeling. The results of this study imply that spinal nociceptive processing is spatially organized not only in laminae I-IV, but also in more ventral regions of the spinal cord.

Differential c-fos-like protein expression in mechanically versus chemically induced visceral nociception

The expression of c-fos-like protein has been suggested to be a marker for neuronal activity in nociceptive processing. The immunohistochemical detection of this protein was used to determine if different visceral noxious stimuli induce distinct patterns in the rat spinal cord. We have developed a mechanical visceral pain model which is based on the acute distention of the duodenum yielding a quantifiable behavioral endpoint, writhing-like activity. One hour following either intraperitoneal injection of acetic acid or the distention of the duodenum via a chronically implanted balloon catheter, the animals were processed for the immunocytochemical detection of c-fos-like protein in the spinal cord. Characteristic patterns of c-fos-like immunoreactivity were observed following each type of stimulus that differed in spinal laminar and segmental distribution, number of neurons expressing fos-like immunoreactivity and staining intensity. The chemical noxious stimulus induced c-fos bilaterally in laminae I and X predominantly in the thoraco-lumbar region of the spinal cord. In contrast, the mechanical noxious stimulus induced a greater number and more intense neuronal c-fos-like protein expression in laminae I-VI, IX and X. These data provide further evidence that there is a differential nociceptive modulation in mechanical noxious visceral stimulation.

Electrical stimulation of visceral afferent pathways in the pelvic nerve increases c-fos in the rat lumbosacral spinal cord

Electrical stimulation (20-35 Hz, 2-5 V, 1.5 h) of the pelvic nerve in urethane-anesthetized rats increased the expression of c-fos protein-immunoreactivity primarily in neurons in the L6-S1 segments of the spinal cord. The neurons were localized to areas receiving afferent input from the pelvic viscera including the superficial dorsal horn, the dorsal commissure, and lateral laminae V-VII in the region of the sacral parasympathetic nucleus. These experiments indicate that (1) electrical stimulation of abdominal nerves following surgical exposure is a useful method for tracing visceral afferent pathways and (2) afferent information from the pelvic viscera is received by neurons in specific areas of the dorsal horn.

ACTH and enkephalin axonal input to paraventricular neurons containing c-fos-like immunoreactivity

The presence of c-fos like protein in neuronal nuclei has been observed in several areas of the central nervous system. It is associated with activation of these neurons by specific stimuli, in particular stressful stimuli. The present study investigated the expression of c-fos-like immunoreactivity in the paraventricular nucleus (PVN) of the hypothalamus following stimulation of small diameter, nociceptive afferents in the hindfoot of the rat. The afferent innervation to these c-fos containing PVN neurons was examined in order to identify putative neurotransmitters which might modulate the activity of stress responsive, i.e. c-fos containing neurons in the PVN. Adrenocorticotropic releasing hormone (ACTH), enkephalin (ENK), and corticotropin releasing factor (CRF), peptides whose functions have been related to the regulation of stress behavior, were selected to investigate their potential innervation of c-fos immunolabeled neurons. Analysis of immunocytochemically double-labeled vibratome and semi-thin plastic-embedded sections revealed that ACTH and ENK immunoreactive axonal varicosities were present in close anatomical proximity to a substantial number of parvocellular PVN neurons that contained c-fos in response to noxious stimulation. Few c-fos containing PVN neurons were apposed by CRF axonal varicosities. The resulting data show that a large number of c-fos immunoreactive PVN neurons, though not the majority, is innervated by ACTH and ENK. This suggests that the activity of stress responsive, c-fos expressing neurons can substantially be modulated and regulated by ACTH and ENK and to a lesser degree by CRF.

N-methyl-D-aspartate receptor activation in the neostriatum increases c-fos and fos-related antigens selectively in medium-sized neurons

In the neostriatum a selective loss of neurons occurs following exposure to N-methyl-D-aspartate receptor agonists. One hypothesis emerging from this observation is that an excitotoxic process via N-methyl-D-aspartate receptors may contribute to the pathogenesis of Huntington's disease, which is characterized by the loss of medium-sized neurons. However, whether there is a selective distribution of N-methyl-D-aspartate receptors in specific populations of neostriatal neurons is unknown. In this study the expression of c-fos mRNA and protein was used to examine the response of neostriatal cells to N-methyl-D-aspartate receptor stimulation in the rat. After intrastriatal injection of the N-methyl-D-aspartate receptor agonist, quinolinic acid, an increase in c-fos mRNA concentrations was detected using in situ hybridization and Northern blot analysis. Western blot analysis showed that not only the c-Fos mRNA protein product but also other Fos-related antigens capable of binding to DNA were increased in response to N-methyl-D-aspartate receptor activation. The selectivity of the neuronal response to N-methyl-D-aspartate receptor activation was examined immunohistochemically at the light and ultrastructural levels. Our results indicate that N-methyl-D-aspartate receptor activation by quinolinic acid stimulates medium spiny neurons to increase c-Fos expression; to a lesser extent, medium aspiny interneurons and glial cells also respond. In contrast, negligible change in c-Fos expression is observed in large neurons. These results are consistent with other evidence that medium-sized spiny neurons are preferentially vulnerable to the toxic effects of excitatory amino acids acting at N-methyl-D-aspartate receptors. An additional implication of these findings is that activation of the N-methyl-D-aspartate receptor in medium spiny neurons leads to increased expression of candidate AP-1 transcription factors, thereby coupling the N-methyl-D-aspartate receptor and regulation of gene expression in signal transduction processes of the neostriatal medium spiny neuron.

The expression of different cytochemical markers in normal and axotomised dorsal root ganglion cells projecting to the nucleus gracilis in the adult rat

Rat lumbar dorsal root ganglion neurones projecting to the nucleus gracilis in the brainstem were retrogradely labelled with Fluoro-Gold and analysed immunocytochemically for their expression of substance P-, calcitonin gene-related peptide-, galanin-, galanin message-associated peptide-, neuropeptide Y-, nitric oxide synthase- and carbonic anhydrase-like immunoreactivity as well as affinity to Griffonia (bandeiraea) simplicifolia lectin I--isolectin B4, RT97 and to choleragenoid. The analysis was made both in uninjured rats and in rats which had been subjected to unilateral sciatic nerve transection and partial resection 3 weeks earlier. The data showed that 6% of the L4 and L5 lumbar dorsal root ganglion cells that projected to the nucleus gracilis showed substance P-like immunoreactivity. Following nerve injury, none of the nucleus gracilis-projecting dorsal root ganglion cells showed substance P-like immunoreactivity. Nineteen per cent of the investigated cell population showed calcitonin gene-related peptide-like immunoreactivity in uninjured rats, but no nucleus gracilis-projecting calcitonin gene-related peptide-positive cells were found after nerve injury. Galanin- and galanin message-associated peptide-like immunoreactivity were found in 2% and 3%, respectively, of the Fluoro-Gold-labelled cell population normally and in 22% and 14%, respectively, after injury. No neuropeptide Y-positive cells were found in the Fluoro-Gold-labelled cell population normally, but after nerve injury, 96% of this population became neuropeptide Y-positive. Nitric oxide synthase-like immunoreactivity was found in 2% of the Fluoro-Gold-labelled cells normally and in 10% after injury. Two per cent of the Fluoro-Gold-labelled cells in the normal cases were stained by Griffonia (bandeiraea) simplicifolia lectin I--isolectin B4. After injury, however, no such double labelling was found. Thirty-four per cent of the Fluoro-Gold-labelled cell population was carbonic anhydrase positive normally, and 42% after injury. Seventy-five per cent of the Fluoro-Gold-labelled cells showed RT97 immunoreactivity normally and 12% after injury. Choleragenoid-like immunoreactivity was found in 99% of the Fluoro-Gold-labelled dorsal root ganglion cells normally and 81% after injury. Immunohistochemical visualisation of choleragenoid transganglionically transported from the injured sciatic nerve combined with neuropeptide Y immunocytochemistry showed that primary afferent fibres and terminals in the nucleus gracilis contain neuropeptide Y following peripheral nerve transection. Taken together, the results indicate that peripherally axotomised nucleus gracilis-projecting neurones undergo marked alterations in their cytochemical characteristics, which may be significant for the structural and functional plasticity of this system after injury.