Expression of c-fos in studies of central autonomic and sensory systems

Identification of the location, extent, and pathway of sensory neurologic feedback after mechanical stimulation of a lateral spinal ligament in chickens

STUDY DESIGN

This study traced the location, extent, and pathway of sensory feedback after the mechanical stretching of a lateral spinal ligament in young chickens. The pathway was traced by locating the sites of Fos protein production in neuronal cell bodies at various sites in the nervous system.

OBJECTIVES

To trace the location, extent, and pathway of sensory feedback after the mechanical stretching of a lateral spinal ligament in young chickens.

SUMMARY OF BACKGROUND DATA

The innervation of ligaments is thought to form part of a protective feedback mechanism to provide stability for joints. The precise pathway and extent of the feedback for spinal ligaments is currently unknown. Such information would provide a clear focus for future studies, especially for diseases such as scoliosis where it has been suggested that there is abnormality in perception of sensory feedback.

METHODS

The intertransverse ligament on the right side at T3-T4 in 4-week-old chickens was exposed by blunt dissection. After Fos production resulting from the surgery had been stopped, the ligament was stretched mechanically and repeatedly for 60 minutes using a 300-g weight. Various areas of the nervous system then were sectioned and processed immunohistochemically to identify areas of Fos production in nerve cell bodies. The presence of Fos indicated neurons that had been stimulated by the stretching the ligament, including interneurons along the feedback pathway.

RESULTS

Fos protein was identified in nerve cell bodies in the dorsal root ganglia and intermediate gray matter of the spinal cord at the level of stimulation as well as at several spinal cord levels above and below the site of stimulation. Identification was made on the ipsilateral and the contralateral sides, although the extent of Fos production was less on the contralateral side. Fos presence also was identified in sympathetic ganglia at these sites. Nerve cell bodies in the combined nucleus cuneatus and gracilis in the medulla oblongata, the vestibular nuclei, and the thalamus also contained Fos-positive particles.

CONCLUSIONS

Stretching a single lateral ligament of the spine produces a barrage of sensory feedback from several spinal cord levels on both sides of the spinal cord. This sensory information also is transferred to higher levels in the brain, including the nucleus gracilis and cuneatus, the vestibular nuclei, and the thalamus. These sites of Fos production suggest the locations of pathways for this sensory information, which include the dorsal columns and the spinocerebellar tracts. The information obtained from this study provides a clear focus for future studies in this area, particularly for diseases such as scoliosis where it is thought that incorrect perception of sensory information from the ligaments might be a major contributing factor.

Circadian regulation of Fos-like expression in the brain of the blow fly Calliphora vicina

Expression of Fos-like immunoreactivity (FOS-lir) was examined in the brains of the blow fly Calliphora vicina for evidence of circadian regulation by photic stimuli. Fos-lir in various parts of the brain was investigated as a function of light and time of day. Immunohistochemistry demonstrated that photic stimuli have an inductive effect on c-fos expression in the various parts of the brain, but only in the neurons of the pars intercerebralis did the clear photic induction of c-fos expression occur at times when light was capable of phase-shifting circadian locomotor activity rhythms. This suggests that the c-fos gene may play a role in the photic pathway for circadian entrainment and that these neurons may be involved in the transduction of photic signals. Whether changes in c-fos expression are essential components of this pathway remains to be determined.

Differential c-fos expression in the nucleus of the solitary tract and spinal cord following noxious gastric distention in the rat

c-Fos has been used as a marker for activity in the spinal cord following noxious somatic or visceral stimulation. Although the viscera receive dual afferent innervation, distention of hollow organs (i.e. esophagus, stomach, descending colon and rectum) induces significantly more c-Fos in second order neurons in the nucleus of the solitary tract and lumbosacral spinal cord, which receive parasympathetic afferent input (vagus, pelvic nerves), than the thoracolumbar spinal cord, which receives sympathetic afferent input (splanchnic nerves). The purpose of this study was to determine the contribution of sympathetic and parasympathetic afferent input to c-Fos expression in the nucleus of the solitary tract and spinal cord, and the influence of supraspinal pathways on Fos induction in the thoracolumbar spinal cord. Noxious gastric distention to 80 mmHg (gastric distension/80) was produced by repetitive inflation of a chronically implanted gastric balloon. Gastric distension/80 induced c-Fos throughout the nucleus of the solitary tract, with the densest labeling observed within 300 microns of the rostral pole of the area postrema. This area was analysed quantitatively following several manipulations. Gastric distension/80 induced a mean of 724 c-Fos-immunoreactive nuclei per section. Following subdiaphragmatic vagotomy plus distention (vagotomy/80), the induction of c-Fos-immunoreactive nuclei was reduced to 293 per section, while spinal transection at T2 plus distention (spinal transection/80) induced a mean of 581 nuclei per nucleus of the solitary tract section. Gastric distension/80 and vagotomy/80 induced minimal c-Fos in the T8-T10 spinal cord (50 nuclei/section), but spinal transection/80 induced 200 nuclei per section. Repetitive bolus injections of norepinephrine produced transient pressor responses mimicking the pressor response produced by gastric distension/80. This manipulation induced minimal c-Fos in the nucleus of the solitary tract and none in the spinal cord. It is concluded that noxious visceral input via parasympathetic vagal afferents, and to a lesser extent sympathetic afferents and the spinosolitary tract, contribute to gastric distention-induced c-Fos in the nucleus of the solitary tract. The induction of c-Fos in the nucleus of the solitary tract is significantly greater than in the viscerotopic segments of the spinal cord, which is partially under tonic descending inhibition, but is not subject to modulation by vagal gastric afferents. Distention pressures produced by noxious gastric distention are much greater than those produced during feeding, suggesting that c-Fos induction in the nucleus of the solitary tract to noxious distention is not associated with physiological mechanisms of feeding and satiety. The large vagal nerve-mediated induction of c-Fos in the nucleus of the solitary tract following gastric distension suggests that parasympathetic afferents contribute to the processing of noxious visceral stimuli, perhaps by contributing to the affective-emotional component of visceral pain.

Noxious colorectal distention induced-c-Fos protein in limbic brain structures in the rat

Colorectal distention is a non-invasive stimulus used to study visceral pain processing in the nervous system. In this study, immunocytochemical labeling for the immediate-early gene, c-Fos, was used to map limbic brain structures involved in processing visceral pain. Rats received noxious colorectal distention while loosely restrained or loose restraint without distention (control). The brains were immunostained and the density of Fos-labeled nuclei within areas of the brain associated with limbic function were examined. Many cortical (cingulate; retrosplenial; insular; perirhinal, entorhinal) and subcortical (periaqueductal gray; locus coeruleus; lateral parabrachial area; paraventricular, anterodorsal and centromedian thalamic nuclei; lateral septal area; dorsomedial hypothalamus; cortical amygdala; subiculum) areas were labeled in the control rats, but significantly more Fos was observed in these areas following noxious colorectal distention (CRD). Additional areas were labeled following CRD but not restraint (e.g. infralimbic and prelimbic cortices; mediodorsal thalamic nucleus; central amygdaloid nucleus). The results show that noxious visceral stimuli result in Fos expression in limbic structures that exceeds that induced by restraint stress, suggesting that different pathways and circuits are recruited by stimuli which can produce similar emotional responses.

Increased ipsilateral expression of Fos following lateral hypothalamic self-stimulation

Immunohistochemical labeling of Fos protein was used to visualize neurons activated by rewarding stimulation of the lateral hypothalamic level of the medial forebrain bundle (MFB). Following training and stabilization of performance, seven rats were allowed to self-stimulate for 1 h prior to anesthesia and perfusion. Brains were then processed for immunohistochemistry. Two control subjects were trained and tested in an identical manner except that the stimulator was disconnected during the final 1 h test. Among the structures showing a greater density of labeled neurons on the stimulated side of the brains of the experimental subjects were the septum, lateral preoptic area (LPO), medial preoptic area, bed nucleus of the stria terminalis, substantia innominata (SI), and the lateral hypothalamus (LH). Several of these structures, the LPO, SI, and LH, have been implicated in MFB self-stimulation by the results of psychophysical, electrophysiological, and lesion studies.

Differential expression of c-fos messenger RNA in the rat spinal cord after mucosal and serosal irritation of the stomach

Expression of the immediate early gene c-fos is considered to be a marker for neuronal activation in the spinal cord in response to afferent input. Since the stomach is continually exposed to injurious chemicals, the present study examined whether application of acid (0.15 M HCl) and formalin (5%) to the gastric mucosa or serosal surface of the stomach stimulates c-fos transcription in the caudal thoracic spinal cord of anaesthetized rats. The spinal cord was removed 15, 45 or 120 min after exposure of the stomach to the noxious chemicals and processed for quantitative in situ hybridization autoradiography of c-fos messenger RNA. Exposure of the gastric mucosa to acid or formalin failed to increase the expression of c-fos messenger RNA in the thoracic spinal cord. Application of acid to the serosal surface of the stomach was also unable to stimulate c-fos transcription, whereas serosal application of formalin led to substantial expression of c-fos messenger RNA in the superficial but also deeper laminae of the spinal dorsal horn when examined 45 min, but not 15 or 120 min, post-stimulation. The highest expression of c-fos messenger RNA was seen when formalin was injected subcutaneously into one hindpaw and c-fos transcription was examined in the lumbar spinal cord. These data indicate that acute exposure of the gastric mucosa to chemical injury does not provide the afferent input which is necessary to cause appreciable c-fos transcription in second order neurons within the spinal cord. Stimulation of the gastric mucosa by acid and formalin was followed, however, by gastric hyperaemia in which spinal afferents releasing vasodilator peptides have been implicated. It is concluded, therefore, that acute stimulation of nociceptive afferents in the stomach causes local homoeostatic reactions but does not necessarily provide afferent input sufficient to recruit spinal nociceptive circuits.

Fos expression in rat visual cortex induced by ocular input of ultraviolet light

We used immunostaining for the cellular transcription factor Fos to assess patterns of neuronal activation in rat visual cortex during exposure to ultraviolet light. Exposure to monochromatic ultraviolet light (lambda max 360 nm: half-bandwidth 8.8 nm, 10 microW/cm2 at eye level) induced strong expression of Fos immunoreactivity in the primary visual cortex and associated cortical visual areas of dark-adapted rats. The stimulatory effect of ultraviolet light on Fos expression was related to exposure duration, was independent of stimulus novelty or phase of the circadian cycle in which exposure occurred, and it was mediated by a mechanism located in the eye. These results demonstrate that ocular input of ultraviolet light is capable of altering neuronal activity in cortical structures involved in visual processing and are consistent with the hypothesis that rodents may use ultraviolet light for vision.

Increased nerve growth factor inducible-A gene and c-fos messenger RNA levels in the rat midbrain and hindbrain associated with the cardiovascular response to electrical stimulation of the mesencephalic cuneiform nucleus

Functional neuronal connections associated with the cardiovascular response to unilateral low-intensity electrical stimulation of the mesencephalic cuneiform nucleus were examined in the halothane-anaesthetized and paralysed rat by in situ hybridization histochemistry using specific 35S-labelled oligonucleotides for detection of nerve growth factor inducible-A gene (NGFI-A) and c-fos messenger RNAs. Stimulation of the cuneiform nucleus increased mean arterial pressure and heart rate by 20 +/- 0.5 mmHg and 35 +/- 3 b.p.m., respectively, while no significant cardiovascular response was observed in animals stimulated in the inferior colliculus or in sham-operated animals. Cuneiform nucleus stimulation produced increased NGFI-A and c-fos messenger RNA levels in the Kölliker-Fuse and parabrachial nuclei ipsilaterally, and the cuneiform nucleus, dorsal periaqueductal gray and caudal ventrolateral medulla bilaterally at levels significantly greater than those in inferior colliculus-stimulated, sham-operated and naive, unoperated animals. NGFI-A, but not c-fos, messenger RNA expression was increased bilaterally in the caudal portion of the nucleus of the solitary tract and inferior olive. These results are consistent with previous neuroanatomical tract-tracing studies of afferent and efferent pathways from the cuneiform nucleus and indicate that these midbrain and hindbrain structures may be involved in the pressor and tachycardic responses associated with stimulation of the cuneiform nucleus. The ipsilateral nature of responses in certain brain areas may be explained by the absence of decussating pathways and/or the presence of multisynaptic connections which attenuate bilateral signal transmission. Characterization of these activated neuronal structures using other compatible labelling techniques should further elucidate the mechanisms by which these central nervous system structures are integrated in the cardiovascular responses to stimulation of the cuneiform nucleus.

Hypotension-induced expression of the c-fos gene in the medulla oblongata of piglets

Neural networks that mediate the reflex response to baroreceptor withdrawal were explored in Sus scrofa. Induction of c-fos was used as a monitor of synaptic activity in response to hypotension sustained by systemic administration of a peripheral vasodilator, sodium nitroprusside. Patterns of c-fos gene expression were compared between Saffan-anesthetized experimental animals and age-matched normotensive controls administered vehicle. Effects of other variables were controlled including 1 h preoperative accommodation to the novel environment, anesthesia, blood gases and pH. Identical post-stimulus survival periods were allowed for accumulation of transcript. The c-fos protein, Fos, was identified immunocytochemically with two rabbit antisera raised against amino acids 1-131 of Fos or residues 4-17 of synthetic human transcript. Fos was identified in catecholaminergic neurons labeled with an antiserum to tyrosine hydroxylase (TH). Fos was induced in the nucleus tractus solitarii (NTS) of hypotensive piglets. Neurons encoding Fos matched projection patterns of first order visceral afferents. Induction was prominent in the dorsolateral nucleus coinciding with the baroreceptor field. Indices of increased neuronal activity were evident in other baroreceptor terminal sites, e.g., medial subnucleus, the medial commissural field, the intermediate subnucleus and a ventral A2 noradrenergic area. In reticular formation c-fos protein was induced in circumscribed columns in the lateral tegmental field (LTF) extending from facial nucleus to calamus scriptorius. Catecholaminergic (TH-positive) neurons expressed Fos in the porcine C1 and A1 areas of ventrolateral medulla. Fos was also induced in a dorsal intermediate reticular zone of LTF. Minor or inconsistent differences between experimental and control were observed in nucleus raphe pallidus, rostral paramedian reticular formation, upper thoracic intermediolateral cell column, and stellate ganglia. In conclusion, baroreceptor withdrawal in young animals induced patterns of neuronal response along established cardiovascular reflex pathways.

Convergent influence of the central nucleus of the amygdala and the paraventricular hypothalamic nucleus upon brainstem autonomic neurons as revealed by c-fos expression and anatomical tracing

Combinations of anatomical tracing with detection of Fos (the protein product of the immediate early gene c-fos) consequent to the stimulation of the central nucleus of the amygdala were used to explore the possibility that the hypothalamic paraventricular nucleus participates in the activation of brainstem neurons in the nucleus of the solitary tract and ventrolateral medulla. After injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin in the paraventricular nucleus, labeled fibers and varicosities were found to impinge on catecholaminergic and non-catecholaminergic Fos-positive neurons in the brainstem. After injections of a retrograde tracer in the nucleus of the solitary tract or ventrolateral medulla, we observed that some of the Fos-positive neurons within the parvocellular paraventricular nucleus that project to the brainstem were catecholaminergic or oxytocinergic. The results indicate that direct and indirect inputs from the amygdala may influence the activity of autonomic neurons in the brainstem. The paraventricular nucleus, via its direct projections onto catecholaminergic and non-catecholaminergic neurons, may participate in activation of brainstem neurons. Activated catecholaminergic and oxytocinergic parvocellular neurons in the paraventricular nucleus may be involved in the transmission of autonomic signals from the amygdala toward the brainstem.

Changes in blood volume and pressure induce c-fos expression in brainstem neurons that project to the paraventricular nucleus of the hypothalamus

Immunohistochemistry for c-fos was combined with retrograde tracing techniques to study the effects of acute reductions in arterial blood pressure due to hemorrhage (HEM) in conscious rats on activated neurons in the brainstem nucleus of the tractus solitarius (NTS) or ventrolateral medulla (VLM) which project to the paraventricular nucleus (PVN) of the hypothalamus. In an attempt to separate blood pressure effects from those associated with changes in blood volume, a similar approach was used to study the effects of drug-evoked hypotension using peripheral infusions of sodium nitroprusside (NP). Few differences were found in patterns or numbers of activated neurons (Fos-immunoreactive) in the NTS or VLM after HEM or NP treatment; only in the NTS at the level of the area postrema were significantly higher numbers of neurons that expressed Fos found in NP rats. In addition, a large proportion of PVN-projecting neurons in the NTS and VLM was activated whereas many activated neurons in the NTS and VLM did not project to the PVN. These results show that a decrease in blood pressure leads to the activation of NTS and VLM neurons but that a change in blood volume does not activate significantly greater numbers of neurons in these areas that project to the PVN or to other targets. Whereas substantial numbers of neurons in the NTS and VLM appear to transmit cardiovascular information to the PVN, many others likely transmit this information to other central targets.

Time course of neuronal sensitivity to light in the circadian timing system of the golden hamster

The mammalian suprachiasmatic nuclei of the hypothalamus (SCN) have been identified as containing the pacemaker for circadian rhythms. Photic stimulation is known to induce the expression of the immediate early gene c-fos in the SCN of rodents during the subjective night. In order to determine the exact time course of the light sensitivity in the different cell subgroups of the SCN, we have investigated the effect of a light pulse every hour of the subjective night in golden hamsters kept in constant darkness for 3 days. Three neuronal populations inside and outside the SCN have been identified as sensitive to light at different times of the subjective night. These findings indicate (1) that there are neurons outside the SCN that are activated by light which might be part of the pacemaker system, and (2) that the switch from light-induced phase delays to phase advances as illustrated by phase-response curves is linked to the appearance of sensitivity to light in the three cell populations defined here.

Hypotension induces Fos immunoreactivity in NADPH-diaphorase positive neurons in the paraventricular and supraoptic hypothalamic nuclei of the rat

Double staining for Fos and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-D) was used to study the distribution of activated neurons that synthesize nitric oxide in the paraventricular (PVN) and supraoptic nuclei (SON) following hypotensive stimulation in conscious rats. Fos was detected in many magno- and parvocellular NADPH-D positive neurons in response to haemorrhage or drug-evoked hypotension using i.v. infusions of sodium nitroprusside. However, quantitative analysis did not reveal any differences in the number of Fos positive PVN neurons following either mode of stimulation. These results suggest that a subpopulation of hypothalamic NADPH-D positive neurons is activated following hypotensive challenge. This activation of NADPH-D neurons may occur indirectly through other CNS structures that influence the excitability of hypothalamic SON and PVN. Furthermore, the lack of a difference in activated neurons within the PVN following either haemorrhage or nitroprusside infusion suggests that while a drop in blood pressure causes activation of neurons that produce nitric oxide, a decrease in blood volume, which accompanies haemorrhage, does not.