Fos-immunoreactive Neurons Research Articles

Further evidence for the involvement of the spinoparabrachial pathway in nociceptive processes: A c‐Fos study in the rat

We have analysed in briefly anaesthetised rats (1% halothane for 18 minutes) the effects of innocuous and noxious heat, applied to the hindpaw, on evoked c-Fos immunoreactivity at the levels of the parabrachial area (PB), spinal cord, and nucleus of the solitary tract (NTS). After anaesthesia recovery, animals were left to move freely for 2 hours. At the spinal level, c-Fos was expressed primarily in the ipsilateral superficial laminae, increasing with the applied temperatures in a dependent manner in the noxious range (correlation coefficient r = 0.954, n = 20). At the NTS level, no noxiously evoked c-Fos expression was observed. At the PB level, c-Fos was expressed preferentially contralaterally, increasing with the applied temperatures in a dependent manner in the noxious range (r = 0.971, n = 25). The maximum expression was observed in the outer portion of the external lateral, the lateral crescent, and the superior lateral subnuclei around the pontomesencephalic junction. This was congruent with the densest supraspinal projection of lamina I neurones of the dorsal horn. Labelling in the PB area was highly correlated (r = 0.936, n = 20) with labelling in the superficial laminae. We conclude that, under our experimental procedures, noxious heat-induced c-Fos expression at the PB level depends on the intensity of the noxious stimulation. These data further support the relevance of the recently described spino-PB pain pathway. Because of their location, the Fos-immunoreactive neurones observed in the pontine and the mesencephalic divisions of the PB area were likely PB-amygdaloid and PB-hypothalamic nociceptive neurones, respectively. J. Comp. Neurol. 383:439-458, 1997. © 1997 Wiley-Liss, Inc.

Evidence for Hypothalamic Paraventricular Nucleus as an Integrative Center of Neuroimmunomodulation

It has been well documented that the medial parvocellular subnucleus of the hypothalamic paraventricular nucleus (PVN) participates in immune regulation by releasing corticotrophin-releasing hormone (CRH), which triggers the hypothalamus-pituitary-adrenal axis, leading to immunosuppression. Little is known about other possible influences of PVN on immunomodulation. Evidence, however, has been accumulating recently, indicating possible involvement of other subnuclei of this nucleus. By using the c-fos technique, the present study investigated the neuronal groups of the PVN that were activated in response to intracerebroventricularly administered IL-1 beta. In addition to strong Fos expression in the dorsal part of medial parvocellular subnucleus of the PVN, where CRH neurons are located, two more neuronal groups were found to express Fos protein. One of which was the oxytocin-immunoreactive magnocellular neurons, mainly concentrated in the anterior and medial magnocellular subnuclei of the PVN. The magnocellular PVN subnuclei are known to project to, and release their hormones, in the posterior pituitary. Another group of Fos-immunoreactive neurons were found in the brainstem and spinal cord projecting area of the PVN. By combining retrograde tracing technique and Fos immunohistochemistry, it was proved that many of the spinal cord projecting PVN neurons were activated following IL-1 beta administration, through which the spinal cord sympathetic outflow might be regulated. The present study indicates that the hypothalamic PVN may serve as an integrative center for immunomodulation via three channels, i.e., the CRH and oxytocin neuroendocrinological and the PVN-spinal cord sympathetic neural channels.

Differential effects of haloperidol and two anxiolytic drugs, buspirone and lesopitron, on c-Fos expression in the rat striatum and nucleus accumbens

We have studied the effects of the neuroleptic haloperidol and the non-benzodiazepine anxiolytics buspirone and lesopitron on the expression of c-Fos immunoreactivity in the rat forebrain. Haloperidol and buspirone administration resulted in a significant quantitative increase in the number of Fos-immunoreactive neurons in the lateral striatum and a presumable qualitative increase in the nucleus accumbens. In contrast, lesopitron did not lead to a significant increase in the c-Fos expression in the striatum. The induction of c-Fos immunoreactivity by buspirone is compatible with an interaction of this compound with D2 dopamine receptors, as documented for haloperidol. The lack of effects after lesopitron administration suggests that, in contrast with buspirone, this compound has no dopaminergic blocking activity.

Persistent c-fos expression in the brains of mice with chronic social stress

The present study was conducted to demonstrate immunohistochemically, the sites of c- fos protein expression in the brains of mice subjected to acute and chronic social defeat stress. To induce social stress, mice were placed in situations of species-specific intermale aggression either only once or five times at 24 h intervals. Two hours after the single or fifth defeat stress, many c- fos immunoreactive neurons were observed in a variety of brain regions including the limbic system and sensory relay nuclei. The c- fos immunoreactive neurons in the brains of acute defeat mice decreased in number with time and the c- fos staining pattern of acute defeat mice became indistinguishable from that of normal control mice by 24 h after the single defeat stress. In contrast, chronic defeat stress induced persistent c- fos expression in the forebrain and brainstem even 24 h after the fifth defeat stress. In the forebrain of chronic defeat mice, the olfactory bulb, cingulate cortex, hippocampus, entire hypothalamus, septal nuclei and the amygdaloid complex, except for the central nucleus, were labeled intensely with c- fos antiserum. In the lower brainstem, nerve cells with c- fos immunoreactivity were seen mainly in ascending and descending sensory relay nuclei relevant to auditory and vestibular transmission, epicritic sensation (gracile and external cuneate nuclei), pain inhibition (central gray and raphe nuclei), and viscerosensory transmission (solitary tract nucleus). The differences in c- fos expression among the normal control, acute and chronic defeat mice were evaluated by an enumeration of the immunopositive neurons within each brain nucleus examined, and they were confirmed subsequently by statistical analysis. There was little c- fos expression in the nucleus putamen, lateral, ventral and posterior thalamic nuclei, pretectal nuclei, medial geniculate nucleus, red nucleus, substantia nigra, cerebellum, spinal cord, or cranial nerve nuclei. These findings suggest that chronic but not acute defeat stress causes persistent c- fos expression in more widespread brain regions than do any other stresses so far investigated. The present study may shed light on the central mechanisms by which behavioral abnormalities and/or chronic sociopsychological stress leads to the occurrence of abnormal behavior and/or psychosomatic disorders in experimental animals and humans.

Basal and touch-evoked fos-like immunoreactivity during experimental inflammation in the rat

Fos-immunoreactivity can readily be induced in spinal cord neurones by noxious, but to a much more limited extent, by innocuous peripheral stimuli. The present study has investigated whether low intensity stimuli and electrical stimulation of Aβ afferents elicit greater c-fos expression during the behavioural sensory hypersensitivity generated by experimental peripheral inflammation. We have examined the time-course of c-fos expression after inflammation produced by either an intra-plantar injection of the irritant turpentine oil or of complete Freund's adjuvant (CFA). In the former case, a significant initial expression in all dorsal horn laminae was followed by a gradual decrease, whereas after CFA injection, an initial expression limited to the superficial laminae subsequently extended into the deep laminae, with a decrease at 24 h and an increase in labelling at later times. Low intensity touch stimuli repeated for 10 min, when applied at 24 h and 48 h after CFA injection, elicited a significant increase in the number of Fos-immunoreactive neurons in both the superficial and deep laminae of the dorsal horn compared to non-inflamed animals. Electrical stimulation of the sciatic nerve 24 h post-CFA injection, at a strength sufficient only to activate Aβ-afferents fibres (100 μA, 50 μs, 10 min), also elicited a significant increase in labelling relative to the same stimuli applied in control animals, especially in laminae V–VI. The present results demonstrate that low intensity cutaneous stimuli elicit a significantly greater increase in c-fos expression in dorsal horn neurons during peripheral inflammation and that Aβ-afferent input contributes to this, a finding that may relate to the allodynia experienced during inflammation.

NEONATAL INHIBITION OF BRAIN ESTROGEN SYNTHESIS ALTERS ADULT NEURAL FOS RESPONSES TO MATING AND PHEROMONAL STIMULATION IN THE MALE RAT

Neonatal inhibition of brain estrogen formation in male rats by administration of the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), permanently changes aspects of their mating behavior and partner preference in adulthood. The medial preoptic area receives chemosensory inputs via a sexually dimorphic vomeronasal projection circuit, which responds to reproductively relevant pheromonal cues. The medial preoptic area also receives genital somatosensory inputs via the midbrain central tegmental field and the medial amygdala. We used Fos immunoreactivity as a marker of neuronal activation to determine whether there is a correspondence between the behavioral profiles of neonatally ATD-treated male rats and their neuronal responses in the medial preoptic area and other brain regions to somatosensory and chemosensory stimuli.Achieving eight intromissions with an estrous female led to a greater neuronal Fos immunoreactivity in the medial preoptic area of neonatally ATD-treated male rats compared with neonatally cholesterol-treated male rats. Exposure for 1.5 h to chemosensory cues derived from soiled bedding of estrous females induced Fos immunoreactivity throughout the vomeronasal pathway (i.e. medial amygdala, bed nucleus of the stria terminalis and medial preoptic area) in both ATD and cholesterol males (Experiment 2a). By contrast, exposure for 1.5 h to chemosensory cues derived from soiled bedding of sexually active males revealed clear differences between ATD and cholesterol males in neuronal Fos immunoreactive (Experiment 2b). At peripheral portions of the vomeronasal pathway (i.e. the accessory olfactory bulb and the medial amygdala), there were no differences in the number of Fos-immunoreactivity neurons between ATD and cholesterol males. However, neurons in the more central portions of the vomeronasal pathway (i.e. the bed nucleus of the stria terminalis and the medial preoptic area) showed increased Fos immunoreactivity after exposure to odors from sexually active males in ATD males as opposed to cholesterol males. Females, like ATD males, showed neuronal Fos immunoreactivity at each level of the vomeronasal pathway after being exposed to odors from sexually active males.These results suggest that the responsiveness of neurons in the central portion of the vomeronasal projection circuit to odors from sexually active males, but not estrous females, is sexually differentiated in male rats due to the neonatal action of estrogens. Copyright © 1996 IBRO. Published by Elsevier Science Ltd.

Androgen receptor immunoreactivity and mating-induced Fos expression in forebrain and midbrain structures in the male rat

The distribution of androgen receptor immunoreactive-neurons, mapped with the PG21 anti-androgen receptor antibody, was compared in male rat brains with the distribution of Fos-immunoreactive neurons induced by mating. In gonadally intact, but not in castrated male rats, substantial numbers of androgen receptor-containing neurons were present in a variety of forebrain and midbrain regions. The PG21 antibody apparently had a higher affinity for occupied than for non-occupied androgen receptors. Androgen receptor-immunoreactive regions included the medial preoptic area and other forebrain areas previously identified as containing androgen receptors, the dorsal and ventral periaqueductal gray, and a midbrain region that included the lateral part of the central tegmental field, part of the caudal zona incerta, the subparafascicular nucleus of the thalamus and the peripeduncular nucleus. Fos-expressive neurons were essentially absent in non-mated males but were present in the brains of rats which mated to ejaculation. All brain regions in which androgen receptor-immunoreactive neurons were counted also expressed Fos immunoreactivity after mating, and there was considerable overlap between the distributions of androgen receptor- and Fos-immunoreactive neurons. In a second experiment, we used immunofluorescent techniques to document the intraneuronal co-localization of Fos with androgen receptor immunoreactivity in the medial preoptic area, medial amygdala, and central tegmental field. In these regions mating-induced Fos immunofluorescence was exclusively localized in androgen receptor-immunofluorescent neurons. However, not all androgen receptor neurons were Fos expressive, suggesting that only some androgen-sensitive neurons were activated during mating. These results are consonant with the view that hormone actions on forebrain and midbrain structures influence the neuronal activity correlated with mating.

Comparison of neurons in rat medulla oblongata with fos immunoreactivity evoked by seizures, chemoreceptor, or baroreceptor stimulation.

Neurons in rat medulla oblongata with Fos immunoreactivity as a marker of synaptic excitation evoked by pentylenetetrazole-induced seizures were compared with cell populations activated by the stimulation of chemoreceptor and baroreceptor afferent pathways. Chemoreceptors were stimulated by placing rats in a hypoxic gas mixture (7% oxygen) for 2 h. Baroreceptors were activated by phenylephrine-induced hypertension. Seizures and hypoxia induced Fos immunoreactivity in neurons with similar anatomical distributions in the nucleus tractus solitarius, dorsal motor nucleus of the vagus, and ventrolateral medulla. Hypertension was associated with Fos immunoreactivity in an overlapping anatomical distribution compared to seizures and hypoxia, but in a more restricted pattern. A similar proportion of catecholaminergic cells of medulla oblongata (cells immunoreactive for catecholamine synthetic enzymes, tyrosine hydroxylase or phenylethanolamine-N-methyltransferase) had Fos immunostaining after seizures and hypoxia (P > 0.05), while significantly fewer were activated by hypertension (P < 0.05). The majority of tyrosine hydroxylase-immunoreactive cells in caudal ventrolateral medulla were activated by both seizures and hypoxia (mean per cents, 79 and 67%, respectively). Since cell populations activated by seizures and hypoxia are indistinguishable, and a majority of tyrosine hydroxylase-reactive cells in caudal ventrolateral medulla are independently activated by each stimulus, it may be inferred that some impulses originating from seizures and chemoreceptor afferent pathways converge to a common set of neurons. These observations identify neurons in rat medulla oblongata which may mediate the impact of seizures on central processing of chemoreceptor afferent activity.

Temporal-spatial pattern of c-Fos expression in the rat brain in response to indispensable amino acid deficiency. II. The learned taste aversion.

Rats rapidly become anorectic when eating an amino acid-imbalanced diet that induces a deficiency of an indispensable amino acid. Recognition of amino acid deficiency is thought to be a function of the anterior piriform cortex. However, the neuronal circuitry underlying the secondary learned aversion to such diets may involve the amygdala. In this study, Fos immunohistochemistry was employed to identify regions of the brain activated during the learned aversion phase of the response to an amino acid-imbalanced diet. c-Fos expression was examined in the brains of rats at intervals from 1 to 6 h after introduction of a diet imbalanced in threonine, a corrected (amino acid-balanced) diet or a basal (low protein) diet. The study has revealed that, within the time frame associated with the learned aversive response, Fos-immunoreactive (Fos-IR) neurons increased selectively in the central nucleus of the amygdala in animals fed a threonine-imbalanced diet. These results suggest a temporal relationship between changes in neuronal activity in the central nucleus of the amygdala and the learned aversion associated with acute amino acid deficiency.

Temporal-spatial pattern of c-fos expression in the rat brain in response to indispensable amino acid deficiency. I. The initial recognition phase.

Rats reduce their food intake after ingestion of a small amount of an amino acid imbalanced (AA-IMB) diet that induces a pronounced amino acid deficiency. Two hours after ingesting a threonine-IMB diet, just when food intake is depressed significantly, the concentration of threonine is decreased in some but not all brain areas. Neural recognition of this decrease in the limiting amino acid is thought to be the first step in the anorectic responses to AA-IMB diets. To identify the regions of the brain that may be activated upon recognition of an AA-IMB diet, we examined the temporal-spatial distribution of Fos immunoreactive neurons at intervals after introduction of either threonine-IMB or control diets. We found that Fos immunoreactivity in the anterior piriform cortex and immediately surrounding areas, along with the infralimbic cortex, was increased selectively early (by 2 h) after introduction of the AA-IMB diet, and remained elevated through 3 h. The anterior piriform cortex is believed to function in neural recognition of amino acid deficiency. Fos immunoreactivity in the AA-IMB group increased over the control diet groups somewhat later in the dorsomedial nucleus of the hypothalamus. We hypothesize that these areas in the rostral forebrain may serve as neural relays in the early phases of the anorectic responses that occur upon recognition of amino acid deficiency.

Temporal-spatial pattern of c-fos expression in the rat brain in response to indispensable amino acid deficiency I. The initial recognition phase

Rats reduce their food intake after ingestion of a small amount of an amino acid imbalanced (AA-IMB) diet that induces a pronounced amino acid deficiency. Two hours after ingesting a threonine-IMB diet, just when food intake is depressed significantly, the concentration of threonine is decreased in some but not all brain areas. Neural recognition of this decrease in the limiting amino acid is thought to be the first step in the anorectic responses to AA-IMB diets. To identify the regions of the brain that may be activated upon recognition of an AA-IMB diet, we examined the temporal-spatial distribution of Fos immunoreactive neurons at intervals after introduction of either threonine-IMB or control diets. We found that Fos immunoreactivity in the anterior piriform cortex and immediately surrounding areas, along with the infralimbic cortex, was increased selectively early (by 2 h) after introduction of the AA-IMB diet, and remained elevated through 3 h. The anterior piriform cortex is believed to function in neural recognition of amino acid deficiency. Fos immunoreactivity in the AA-IMB group increased over the control diet groups somewhat later in the dorsomedial nucleus of the hypothalamus. We hypothesize that these areas in the rostral forebrain may serve as neural relays in the early phases of the anorectic responses that occur upon recognition of amino acid deficiency.

The development of diurnal rhythmicity in fetal suprachiasmatic neurons as demonstrated by Fos immunohistochemistry

Using Fos immunohistochemistry as a marker of cellular activity, we have shown that neurons in the suprachiasmatic nucleus of fetal sheep are active by 75 days gestation. From at least 90 days gestation (term is 146 days), these neurons are more active during the day (12.00) than at night (03.00) when pregnant ewes are exposed to a 12-h light–dark cycle with lights on at 07.00. The day–night difference in Fos immunoreactivity persisted when the lighting schedule was extended by 8 h to 03.00, although neurons were now more active at 03.00 than they were in fetuses maintained on the normal light–dark cycle. When ewes were maintained in constant light from 133 to 138 days, the day–night difference in Fos immunoreactivity in the fetal suprachiasmatic nucleus was abolished, suggesting that diurnal activity of the fetal suprachiasmatic nucleus is maintained by a signal related to the external lighting regime. In a twin pregnancy where one fetus was optically enucleated at 100 days gestation, the density of Fos-immunoreactive neurons in the suprachiasmatic nucleus during the day at 138 days was similar to the unoperated twin. This suggests that the effects of dim light in the uterus on the fetal retina do not account for the high level of Fos immunoreactivity in the suprachiasmatic nucleus in the daytime. We propose that a chemical messenger of maternal origin, possibly melatonin, suppresses the activity of fetal suprachiasmatic neurons during the night, and that fetal suprachiasmatic neurons have endogenous activity which is expressed fully during the daytime.

Abnormal c- fos expression in the lateral habenula during dystonic attacks in a hamster model of idiopathic dystonia

The genetically dystonic hamster ( dt sz ), an animal model of idiopathic dystonia, displays sustained twisting movements and postures either spontaneously or in response to mild stress. In the present study the expression of c- fos immunoreactive neurons (Fos-ir), used as an indicator of neuronal activity, was investigated within various brain regions in dt sz hamsters and non-dystonic control hamsters. Under baseline condition, i.e. in the absence of dystonia, the expression of Fos-ir did not reveal any differences between dt sz hamsters and controls. However, in response to mild stress several brain regions, particularly the lateral habenula (LHb), exhibited differences in c- fos induction in dt sz hamsters and controls. Whereas in the LHb the expression of Fos-ir was markedly enhanced in controls, it showed almost no increase in dystonic hamsters, indicating impaired neuronal activity. Since the lateral habenula receives major input from the basal ganglia via the entopeduncular nucleus, the present data might indicate that basal ganglia are involved in the dystonic syndrome in mutant hamsters.

Differential distribution of fos-like immunoreactivity in the spinal trigeminal nucleus after noxious and innocuous thermal and chemical stimulation of rat cornea

Corneal afferent nerves project to two spatially distinct sites within the spinal trigeminal nucleus: the subnucleus interpolaris/caudalis transition and the subnucleus caudalis/upper cervical spinal cord transition. The role of these two regions in processing corneal input is uncertain. To determine if neurons in these regions encode different features of an applied corneal stimulus, immunoreactivity for the immediate early gene protein product, Fos, was quantified in barbiturate-anesthetized rats. Intensity was varied across thermal (thermal probe 5, 35, 42, 52 degrees C; radiant heat of approximately 45 degrees C) stimuli and compared with that seen after mustard oil (5 microliters, 20%) or mineral oil application. All stimuli increased the number of Fos-positive neurons located at the ventrolateral pole of the subnucleus interpolaris/caudalis transition compared with unstimulated controls. By contrast, only 52 degrees C thermal probe and mustard oil produced an additional peak of Fos-positive neurons within the superficial laminae at the subnucleus caudalis/cervical cord transition. Further, the magnitudes of the bimodal peaks of Fos produced by 52 degrees C thermal probe and mustard oil stimuli were different quantitatively. Mustard oil caused a greater Fos response at the subnucleus interpolaris/caudalis transition than 52 degrees C thermal probe stimulation, whereas the opposite was true at the subnucleus caudalis/cervical cord transition. Double-labeling revealed that Fos immunoreactive neurons within the spinal trigeminal nucleus were restricted to regions densely labeled for calcitonin gene-related peptide. These results indicate that select features of corneal stimuli such as modality are encoded differently by neurons in the trigeminal subnucleus interpolaris/caudalis transition compared with those located in the subnucleus caudalis/cervical cord transition. It is likely that neurons in these two brainstem regions subserve different aspects of corneal sensation.

Connectivity between brainstem autonomic structures and expression of c-fos following electrical stimulation of the central nucleus of the amygdala in rat.

Combinations of retrograde tracing with detection of Fos (the protein product of the immediate early gene c-fos) following electrical stimulation of the central nucleus of the amygdala were used to explore: (1) the connectivity of activated (Fos-positive) neurons in the ventrolateral medulla with the nucleus of the solitary tract; (2) the connectivity of activated neurons in the nucleus of the solitary tract with the ventrolateral medulla; (3) the proportion of activated catecholaminergic neurons that project to the nucleus of the solitary tract or to the ventrolateral medulla. Retrograde tracer was injected into the nucleus of the solitary tract or the ventrolateral medulla. After 5 days, stimulation for 60 min induced a statistically significant increase in the number of Fos-immunoreactive neurons in the ventrolateral medulla that project to the nucleus of the solitary tract and in the number of Fos-positive neurons in the nucleus of the solitary tract that project to the ventrolateral medulla. Of the neurons activated by stimulation of the central nucleus of the amygdala, 20% in the ventrolateral medulla and 3% in the nucleus of the solitary tract contained the retrograde tracer and were also immunopositive for tyrosine hydroxylase, the enzyme responsible for synthesis of catecholamines.

C-fos Expression in Fetal and Maternal Suprachiasmatic Nucleus (SCN) in the Sheep

Circadian rhythms (CR) are changes in physiological variables with a period close to 24 h., synchronized by environment signals. The fetal sheep presents CR of plasma prolactin and cerebospinal fluid vasopressin at 135 days of gestational age (GA, term 147 days) In adults, CR are driven by the SCN. We investigated whether the maternal and fetal sheep SCN behave as circadian oscillators. To that effect, we measured expression of c-fos (marker of cellular activity) at 135 days's GA in the SCNs of 6 maternal sheep and their fetuses (n=9) at 1200h (day) and 2400h (night). The sheep. were sacrificed with pentobarbitone and the fetuses were delivered by hysterotomy. The maternal and fetal brain were perfused with 4% paraformaldehyde in phosphate buffer 0.1 M, pH 7.4. The brains were removed, post-fixed and the SCN cut in 40μm frozen sections. Alternated sections were stained with cresyl violet of with anti-Fos antibody (Oncogene Science), developed with avidin-biotin and diaminobenzidine. We measured the density of Fos immunoreactive (Fos +) neurons bys mm2 in the SCN. Result were mean ± SE; ANOVA.

Deafness-induced plasticity in the mature central auditory system

Studies in rats and guinea pigs indicate that local changes in inhibitory transmitters may underlie deafness-induced plastic changes in electrophysiological responsiveness of cells of the mature central auditory system. Following 21 days of bilateral deafness there is an increase in evoked Fos-immunoreactive neurones in the central nucleus of the inferior colliculus (CIC) to contralateral cochlear electrical stimulation, compared with normal or 1-day deafened animals. Deafness is also associated with a dramatic reduction in the population of CIC neurones that respond with suppression of activity to electrical stimulation. Moreover, in vivo microdialysis reveals a marked decrease in gamma-aminobutyric acid (GABA) release from the CIC cells in deafened animals. The results may have general implications for the mediation of central nervous system plasticity induced by deafferentation of sensory input.

NADPH-diaphorase activity and Fos expression in brain nuclei following nitroglycerin administration

Organic nitrates are considered nitric oxide donors in that they have been shown to form nitric oxide in vitro and in vivo. Nitroglycerin is an organic nitrate which possesses peculiar activities mediated, to some extent, by the central nervous system via the noradrenergic system. Previous reports have shown that systematic nitroglycerin is able to induce Fos expression in brain nuclei which are known to contain also the nitric oxide synthesizing enzyme. Neuronal NADPH-diaphorase has been shown to be a nitric oxide synthase. Thus, in this study we used NADPH-diaphorase histochemistry to evaluate the distribution of Fos-immunoreactive cells within neurons which contain nitric oxide synthase. The data obtained showed co-localization of Fos with NADPH-diaphorase activity in numerous neurons of the paraventricular and supraoptic nuclei of the hypothalamus. In the brainstem, a few neurons were doubly labeled for Fos and NADPH-diaphorase activity, but NADPH-diaphorase positive fibers and Fos-immunoreactive neurons were consistently co-distributed in the locus coeruleus, parabrachial nucleus, nucleus tractus solitarius and spinal trigeminal nucleus caudalis. These findings demonstrate that nitroglycerin administration activates a selective group of neurons which are a source of nitric oxide or which are in close proximity with neuronal processes containing nitric oxide synthase, and suggest that the nitric oxide synthesizing pathway may be involved at various levels in the central effect of nitroglycerin.

A method to study changes in eye-related columns in the visual cortex of kittens during and following early periods of monocular deprivation.

An immunohistochemical method that exploits the rapid light-evoked expression of Fos, the protein product of the immediate early gene, c-fos, to visualize eye-related columns in the visual cortex, has been used to provide preliminary data on the relative innervation of the cortex by the two eyes of monocularly deprived kittens and the speed of the changes that occur afterward during reverse occlusion. In contrast to conventional anatomical techniques, the method allows both cellular resolution and documentation of the dimensions of eye-related columns through the depth of the cortex. In kittens monocularly deprived from near birth, Fos-immunoreactive neurones were observed in oval or circular patches, the size of which decreased as the duration of deprivation was increased from 4 to 6 weeks. Following reverse occlusion at 5 weeks of age, the size of the patches increased rapidly so that after 4 days their area had approximately tripled. In addition to providing possible insights into the anatomical underpinnings of the puzzling behavioural effects that occur following termination of short periods of reverse occlusion, the method can be used to investigate the temporal order of the anatomical effects of monocular deprivation in different cortical layers.

Fos expression in neurons projecting to the pressor region in the rostral ventrolateral medulla after sustained hypertension in conscious rabbits.

Previous studies in anaesthetized animals have shown that the baroreflex control of sympathetic vasomotor activity is mediated to a large extent by inhibitory inputs to sympathoexcitatory pressor neurons in the rostral part of the ventrolateral medulla. The aim of this study was to determine, in conscious rabbits, the distribution of neurons within the brain that have two properties characteristic of interneurons conveying baroreceptor signals to the rostral ventrolateral medulla: (i) they are activated by an increase in arterial pressure; and (ii) they project specifically to the rostral ventrolateral medulla pressor region. In a preliminary operation, an injection of the retrogradely transported tracer, fluorescent-labelled microspheres, was made into the physiologically identified pressor region in the rostral ventrolateral medulla. After a waiting period of one to eight weeks, hypertension was produced in the conscious rabbit by continuous intravenous infusion of phenylephrine at a rate sufficient to increase arterial pressure by approximately 20 mmHg, maintained for a period of 60 min. A control group of animals was infused with the vehicle solution alone. In confirmation of our previous study, hypertension produced by phenylephrine resulted in the neuronal expression of Fos (a marker of neuronal activation) in the nucleus of the solitary tract, area postrema, the intermediate and caudal parts of the ventrolateral medulla parabrachial complex, and in the central nucleus of the amygdala. Approximately 50% of the Fos-immunoreactive neurons in both the caudal and intermediate parts of the ventrolateral medulla were also retrogradely labelled from the rostral ventrolateral medulla pressor region; such double-labelled neurons were confined to a discrete longitudinal column located just ventrolateral to the nucleus ambiguus. Significant numbers of double-labelled neurons were also found in the nucleus of the solitary tract and area postrema, although these represented a much lower proportion (13-16%) of the total number of Fos-immunoreactive neurons in these regions. In the parabrachial complex, Fos-immunoreactive and retrogradely labelled neurons were largely separate populations, while in the amygdala they were entirely separate populations. In the control group of rabbits, virtually no double-labelled neurons were found in any of these regions. The results indicate that putative baroreceptor interneurons that project to the pressor region of the rostral ventrolateral medulla are virtually confined to the lower brainstem. In particular, they support the results of previous studies in anaesthetized animals indicating that neurons in the intermediate and caudal ventrolateral medulla convey baroreceptor signals to the rostral ventrolateral medulla pressor region, and extend them by demonstrating the precise anatomical distribution of these neurons.(ABSTRACT TRUNCATED AT 400 WORDS)