Fos expression induced by changes in arterial pressure is localized in distinct,longitudinally organized columns of neurons in the rat midbrain periaqueductal gray

The distribution of neurons expressing Fos within the periaqueductal gray (FAG) following pharmacologically induced high or low blood pressure was examined to determine (1) if PAG neurons are responsive to changes in arterial pressure (AP) and (2) the relationship of these cells to the functionally defined hypertensive and hypotensive columns in PAG. Changes in AP differentially induced robust Fos expression in neurons confined to discrete, longitudinally organized columns within PAG. Increased AP produced extensive Fos-like immunoreactivity within the lateral PAG, beginning at the level of the oculomotor nucleus. At the level of the dorsal raphe, Fos expression induced by increased AP shifted dorsally, into the dorsolateral division of PAG; this pattern of Fos labeling was maintained throughout the caudal one-third of PAG. Double-labeling for Fos and nicotinamide adenine dinucleotide phosphate diaphorase confirmed that Fos-positive cells induced by increased AP were located in the dorsolateral division of PAG at these caudal levels. Fos positive cells were codistributed, but not colocalized, with nicotinamide adenine dinucleotide phosphate diaphorase-positive cells. Decreased AP evoked a completely different pattern of Fos expression. Fos-positive cells were predominantly located within the ventrolateral PAG region, extending from the level of the trochlear nucleus through the level of the caudal dorsal raphe. Double-labeling studies for Fos and serotonin indicated that only 1–2 double-labeled cells per section were present. Saline infusion resulted in very few Foslike immunoreactive cells, indicating that volume receptor activation does not account for Fos expression in PAG evoked by changes in AP. These results indicate that (1) substantial numbers of PAG neurons are excited by pharmacologically induced changes in AP and (2) excitatory barosensitive PAG neurons are anatomically segregated based on their responsiveness to a specific directional change in AP. © 1995 Wiley-Liss, Inc.     

大鼠导水管周围灰质注射谷氨酸可使Barrington核神经元表达Fos

形态学研究已发现大鼠内侧视前区（ＭＰＯ）和导水管周围灰质（ＰＡＧ）发出大量轴突,投射至与排尿反射密切相关的Ｂａｒｒｉｎｇｔｏｎ 核。本研究试图通过注射谷氨酸钠到ＭＰＯ或ＰＡＧ后,观察Ｂａｒｒｉｎｇｔｏｎ 核内的Ｆｏｓ表达情况,来了解以上两通路的性质。将谷氨酸钠注射到ＭＰＯ后,只有少量Ｆｏｓ阳性神经元出现在Ｂａｒｒｉｎｇ－ｔｏｎ 核。而将谷氨酸钠注射到ＰＡＧ后,Ｂａｒｒｉｎｇｔｏｎ 核内出现大量的Ｆｏｓ阳性神经元。此结果提示,ＰＡＧ可能对大鼠脑桥排尿反射活动具有兴奋性调节作用。     

Nitric oxide synthase and glutamate receptor immunoreactivity in the rat spinal trigeminal neurons expressing Fos protein after formalin injection

Although recent studies implicated glutamate receptors and nitric oxide in nociception, much still needs to be known about their localisation in neurons involved in nociceptive transmission from the orofacial region. In this study, c-fos expression indicated by Fos immunohistochemistry in the caudal spinal trigeminal nucleus induced by subcutaneous injection of formalin into the lateral face of the rat was used as a marker for nociceptive neurons. The study sought to determine whether Fos-positive neurons express nitric oxide synthase, glutamate N-methyl-D-aspartate type receptor subunit 1, and glutamate alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid type receptor subunit 2/3; and whether they project to the thalamus. After formalin injection, many Fos-positive nuclei appeared in the superficial laminae of the ipsilateral trigeminal nucleus. Confocal laser scanning microscope revealed that almost all neurons with Fos immunofluorescent nuclei were colocalised with N-methyl-D-aspartate receptor 1, 94% with glutamate receptor 2/3 and 14% with nitric oxide synthase. Some of them were closely related to neurons labelled by nitric oxide synthase. Lastly, some of the Fos-positive neurons were labelled by tetramethylrhodamine-dextran injected into the trigeminothalamic tract or the thalamic region. The results suggested that activation of N-methyl-D-aspartate receptor 1 and glutamate receptor 2/3 upon glutamate release in response to noxious stimulation to the orofacial region might mediate c-fos expression in neurons involved in nociception. The expression of Fos in the neurons could also be mediated by nitric oxide produced from the same, as well as neighbouring neurons, when nociceptive stimulation persisted. Fos-positive neurons in the spinal trigeminal nucleus may project to the thalamus, relaying orofacial nociception to the higher sensory centre.     

Astrocytic Fos expression in the rat posterior pituitary following LPS administration

Systemic lipopolysaccharide (LPS) administration has been shown to cause profound Fos expression in multiple regions of the brain. In the present experiment, Fos expression in the hypothalamic supraoptic nucleus (SON), posterior pituitary, and anterior pituitary was investigated using quantitative immunohistochemistry. In the SON and anterior pituitary, a large number of Fos-positive cells were observed by restraint stress, hyperosmotic administration (1.5, 3, and 9% NaCl), and LPS administration (5, 25, and 125 microg/kg). In the posterior pituitary, LPS administration caused a significant increase in the number of Fos-positive nuclei in a dose-dependent manner, whereas restraint stress and hyperosmotic stimulation (1.5 and 3% NaCl) did not increase the number of Fos-positive cells and 9% NaCl administration induced weak Fos immunoreactivity. Moreover, a dual-labeling study using a confocal microscope revealed that Fos-positive cells in the posterior pituitary were astrocytes using MAP2, an astrocytic marker in the posterior pituitary. Here, we demonstrated that the astrocytes of the posterior pituitary expressed Fos in response to LPS administration, which suggests that Fos expression participates in the activation of astrocytes during acute-phase responses with LPS administration.     

Increased c-fos expression in spinal neurons after irritation of the lower urinary tract in the rat.

This study utilized neuronal c-fos expression to examine the spinal pathways involved in processing nociceptive and non-nociceptive afferent input from the lower urinary tract (LUT) of the urethane-anesthetized rat. C-fos protein was detected immunocytochemically in only a small number of cells (< 2 cells/L6 section) in control animals. However, chemical irritation with 1% acetic acid or mechanical stimulation of the LUT markedly increased the number of c-fos-positive neurons (56-180 cells/L6 section) in four regions of the caudal lumbosacral (L6-S1) spinal cord: medial dorsal horn (MDH), lateral dorsal horn, dorsal commissure (DCM), and sacral parasympathetic nucleus (SPN). Only small numbers of c-fos-positive cells were detected in rostral lumbar segments, a region that is thought to receive nociceptive input from the LUT via afferent pathways in sympathetic nerves. The distribution of c-fos-positive cells in the L6 spinal cord varied according to the stimulus (i.e., urethral catheter, bladder distension, or chemical irritation). Distension of the urinary bladder increased the number of c-fos-positive cells mainly in DCM and SPN regions of the cord. In contrast, irritation of the LUT increased c-fos expression largely in DCM and MDH areas. Spinal cord transection (T8 level) did not alter the c-fos expression induced by a catheter or chemical irritation, indicating that gene expression was mediated by spinal pathways. Denervation experiments showed that c-fos expression was induced by activation of afferent pathways in the pelvic and pudendal nerves. These results suggest that neurons in several regions of the spinal cord are involved in processing afferent input from different parts of the LUT. Neurons in the DCM appear to have an important role since they respond to both nociceptive and non-nociceptive inputs and to visceral (pelvic nerve) and somatic (pudendal nerve) afferent pathways. Thus, these neurons may be involved in the mechanisms of visceral-somatic referred pain.     

Nociception-driven decreased induction of Fos protein in ventral hippocampus field CA1 of the rat

To test the hypothesis that the hippocampus field CA1 is recruited in nociceptive intensity-dependent fashion in the formalin model of inflammatory pain, we determined the effect of injection of formalin (0.625-2.5%) on the induction of Fos protein along the length of the hippocampus. Compared to injection of saline, injection of formalin (0.625-2.5%) evoked a concentration-dependent increase in nociceptive behavior and a significant linear increase in the number of Fos-positive cells in the spinal cord, especially in the deeper laminae. Injection of saline also increased induction of Fos along the length of hippocampus. On the other hand, injection of formalin decreased the number of Fos-positive cells in whole CA1, CA3 and dentate gyrus, with a greater significant effect in the posterior-ventral regions of the hippocampus. Indeed, a formalin concentration-dependent decrease was observed in the ventral CA1. A systematic pattern of change in Fos induction was not observed in the medial septum region. Of the regions examined, only the formalin-induced changes in Fos cell counts in the posterior and ventral CA1 were tightly correlated with the changes observed in the spinal cord. The foregoing findings suggest that nociceptive information is processed in distributed fashion by the hippocampus, and at least the ventral CA1 is implicated in nociceptive intensity-dependent integrative functions.     

Laryngeal afferent stimulation enhances Fos immunoreactivity in periaqueductal gray in the cat.

The main functions of the larynx are protection of the airways, respiration, and vocalization. Previous studies have suggested a link between the mechanisms controlling vocalization and afferent feedback from the larynx. We inquired whether stimulation of the laryngeal afferents that run in the internal branch of the superior laryngeal nerve (ISLN) activates neurons of the periaqueductal gray (PAG), a midbrain region implicated in vocalization. We counted the number of neurons expressing Fos, the protein product of the immediate early gene c-fos, in the PAG. The counts were done both in experimental cats after electrical stimulation of the ISLN and nonstimulated controls. We also investigated the possible presence of nitric oxide synthase, an enzyme that synthesizes nitric oxide, in PAG neurons that respond to laryngeal afferent stimulation by double labeling for reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase and Fos. Fos expression was significantly greater (P < or = 0.00714) in the lateral and dorsolateral regions of the PAG in the experimental group than in the controls. The Fos-immunoreactive neurons did not contain NADPH-diaphorase, a marker for nitric oxide synthase. Our study suggests that laryngeal afferent stimulation activates neurons in discrete longitudinal columns of the PAG including the regions that have previously been shown to be involved in vocalization, and that these neurons do not contain nitric oxide synthase.     

Neuronal expression of fos protein in the forebrain of diabetic rats

We sought to identify the areas that have altered neuronal activity within the hypothalamus of diabetic rats by mapping neuronal expression of c-fos protein (Fos) and Fos-related antigens. After a standard PAP immunocytochemical protocol, Fos-like immunoreactivity was observed in the paraventricular nucleus (PVN), supraoptic nucleus (SON), median preoptic area (MnPO), anterior hypothalamus (AH) and posterior hypothalamus (PH) of control (vehicle; n=6) and diabetic rats (Sprague-Dawley rats injected with STZ 65 mg/kg/ip 4 weeks prior to the experiment; n=6). Blood glucose levels were significantly elevated in the diabetic group (370+/-8 mg/dl) compared to control group (104+/-3 mg/dl). Diabetic rats had a significantly higher number of Fos-positive cells in PVN (2.5x), SON (7x) and MnPO (2x) compared to the control rats. However, diabetic rats had significantly fewer Fos-positive cells in the AH (0.3x) and no difference was observed in the PH between the diabetic and control rats. Despite the elevated number of Fos-positive cells in the diabetic rats, dehydration (water withdrawal for 24 h) or hypertonic challenge (1.5 ml of 0.1 M NaCl i.p. injection) produced a further increase in the number of Fos-positive cells in the PVN, SON and MnPO. Dehydration did not alter the number of Fos-positive cells in the AH or PH, but hypertonic challenge produced a significant increase in the Fos-positive cells in both the AH and PH of diabetic rats. This study demonstrates that: (1) there is increased basal neuronal activity in the PVN, SON and MnPO, a decrease in neuronal activity in the AH and no change in neuronal activity in the PH as indicated by Fos staining in diabetic rats; and (2) dehydration or hypertonic challenge produces a further increase in the number of Fos-positive cells in the PVN, SON, and MnPO which is comparable to control rats. These data support the conclusion that vasopressin producing neurons in the PVN and SON and autonomic areas within the lamina terminalis and hypothalamus are activated during diabetes and may contribute to the elevated levels of vasopressin and autonomic dysfunction during diabetes.     

Neural circuitry controlling vasopressin-stimulated scent marking in Syrian hamsters (Mesocricetus auratus)

In Syrian hamsters, arginine vasopressin (AVP) plays a critical role in the control of a form of scent marking called flank marking. Microinjection of AVP into the medial preoptic-anterior hypothalamus (MPOA-AH), lateral septal nucleus (LS), bed nucleus of the stria terminalis (BNST), and the periaqueductal gray (PAG) stimulates high levels of flank marking. Microinjection of an antagonist of the V_1a-AVP receptor into sites such as the MPOA-AH inhibits expression of flank marking. The purpose of the present study was to investigate the neural circuit controlling flank marking by localizing the induction of Fos protein in response to the microinjection of AVP, a V_1a-AVP antagonist (AVPA) or saline into the MPOA-AH. Immediately after microinjection, hamsters were placed in a clean cage and their behavior was videotaped for 10 minutes. Ninety minutes after the behavioral experiment hamsters were perfused and their brains removed for subsequent immunocytochemical localization of Fos protein. The number of Fos-positive neurons was significantly greater in the BNST, PAG, and central amygdala (Ce) following the microinjection of AVP than following the microinjection of either AVPA or saline. In AVP-injected animals, the number of Fos-labeled cells in the Ce, PVN, and PAG increased with increased frequency of either flank marking or flank gland grooming. These data support the hypothesis that neurons within the MPOA-AH, BNST, and PAG play an important role in the control of flank marking and suggest that the Ce may be a previously unrecognized part of this neural circuit. © 1996 Wiley-Liss, Inc.     

Fos induction in the rat deep cerebellar and vestibular nuclei following central administration of colchicine: a qualitative and quantitative time-course study

The present study was conducted to demonstrate Fos expression at four levels (anterior, prefastigial, postfastigial, posterior) of the cerebellar-vestibular nuclear complex in rats exposed to 1, 6, 24, and 48h of colchicine treatment using a light microscopic avidin biotin peroxidase (ABC) immunohistochemistry. Intracerebroventricular administration of colchicine (60microg per 10microl saline) elicited a continuous increase in the number of Fos-positive cells in the main cerebellar (fastigial, interpositus, dentatus) and vestibular (superior, medial, lateral, spinal, Y) nuclei. One and six hours after colchicine treatment, intensive Fos labeling was observed only in the pyriform cortex and the hypothalamic paraventricular nucleus, respectively, and there was no Fos immunolabeling in any of the cerebellar or vestibular structures investigated. On the other hand, moderate number of Fos-positive cells was visible in each of the cerebellar and vestibular nuclei 24h after colchicine treatment. Exposure of the animals to 48h of colchicine treatment induced an additional, more than 50%, rise in the accumulation of Fos-positive profiles in almost all the cerebellar and vestibular nuclei. In addition, at this time-point, a characteristic pattern of Fos distribution appeared almost in all of the cerebellar and vestibular nuclei, however, the numerical incidence of Fos-positive profiles in paired structures along the neuroaxis was bilaterally symmetric. The present data demonstrate for the first time that the central administration of colchicine causes a persistent and, in comparison with other brain areas, time-delayed activation of certain population of neurons in both cerebellar and vestibular nuclei. We assume that the delayed Fos activation in these structures indicate that the cerebellar and vestibular nuclei are not the primary targets of the central effect of colchicine and their activation seems to be rather a result of a postponed functional consequences of the central action of colchicine probably related to the coordination of motor performance.     

Time course of Fos and Fras expression in the hypothalamic supraoptic neurons during chronic osmotic stimulation

The Fos family comprises Fos and several subtypes of Fos-related proteins (Fras) such as FosB, Fra-1, Fra-2, DeltaFosB, and chronic Fras. Changes in the expression of Fos family proteins with time are not well elucidated, particularly during chronic stimulation. In the present experiments, we investigated quantitatively the time course changes in Fos, FosB and Fras immunoreactivity in the magnocellular neurons of the supraoptic nucleus (SON) during acute and chronic osmotic stimulation. A small number of Fos- and FosB-positive neurons were observed in the SON of control rats, while many Fras-positive neurons were seen in control animals. Significant increases in the numbers of Fos-, FosB-, and Fras-positive neurons were observed 2 h after acute osmotic stimulation by intraperitoneal (i.p.) injection of 3% NaCl solution. Although the number of Fos-positive neurons returned to the control level 4 h after i.p. injection, a significant number of FosB- and Fras-positive neurons were still observed 8 h after i.p. injection. During chronic osmotic stimulation by giving 2% NaCl solution for 2 and 5 days, a large number of Fos-positive neurons were observed, but the cessation of chronic osmotic stimulation by normal water drinking immediately decreased the number of Fos-positive neurons to the control level within 2 h. The number of FosB-positive neurons was increased with period of chronic osmotic stimulation, and a significant number were observed 2-8 h after the cessation of the stimulation. The number of Fras-positive neurons was also significantly higher during chronic osmotic stimulation, and this number was significantly high 2-8 h after the cessation of the stimulation. RT-PCR analysis demonstrated the persistent expression of c-fos mRNA in the SON during chronic osmotic stimulation. These results suggest that c-fos mRNA and Fos protein are constitutively elevated during chronic osmotic stimulation and the time course changes in Fos are different from those seen in FosB and Fras.     

Proximal colon distention increases Fos expression in the lumbosacral spinal cord and activates sacral parasympathetic NADPHd-positive neurons in rats

Fos expression induced by nociceptive mechanical distention of the proximal colon was examined in the lumbosacral spinal cord in freely moving rats equipped with a chronic balloon in the proximal colon. Fos protein in lumbosacral neurons was detected immunocytochemically, and colocalization with nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) activity was determined histochemically at 1 hour after distention. Distention of the proximal colon (10 ml, 30 seconds on/off for 10 minutes, about 90 mm Hg) increased the number of Fos-positive cells in the lumbar 6 (L6) and sacral 1 and 2 (S1, S2) segments, whereas no change was observed in the L1–L5 and S3 segments compared with the sham distended group or with animals that received no treatment. In L6–S2 segments, Fos-positive neurons were increased by two-fold in laminae I-VII (mainly in laminae I and outer II) and area X (surrounding the central canal) and by nine-fold in the sacral parasympathetic nucleus. Results of time course studies indicate that the maximal increase in Fos expression observed at 1 hour after distention returns to basal levels within 4 hours. In the S1 segment, distention of the proximal colon increased the percentage of NADPHd/Fos-positive neurons selectively in the parasympathetic nucleus by 40% compared with less than 4% in the sham distention group; the number and pattern of NADPHd-stained cells were not modified. These results indicate that noxious distention of the proximal colon for a short duration in awake rats selectively activates neurons in the L6-S2 segments of the dorsal horn mainly in laminae involved in nociceptive and autonomic processing. The marked activation of NADPHd-positive neurons in the sacral parasympathetic nucleus suggests a possible role of nitric oxide in the visceroautonomic reflexes induced by distention of the proximal colon. J. Comp. Neurol. 390:311–321, 1998. © 1998 Wiley-Liss, Inc.     

Predatory hunting and exposure to a live predator induce opposite patterns of Fos immunoreactivity in the PAG

Considering the periaqueductal gray's (PAG) general roles in mediating motivational responses, in the present study, we compared the Fos expression pattern in the PAG induced by innate behaviors underlain by opposite motivational drivers, in rats, namely, insect predation and defensive behavior evoked by the confrontation with a live predator (a cat). Exposure to the predator was associated with a striking Fos expression in the PAG, where, at rostral levels, an intense Fos expression was found largely distributed in the dorsomedial and dorsolateral regions, whereas, at caudal levels, Fos-labeled cells tended to be mostly found in the lateral and ventrolateral columns, as well as in the dorsal raphe nucleus. Quite the opposite, insect predation was associated with increased Fos expression predominantly in the rostral two thirds of the lateral PAG, where the majority of the Fos-immunoreactive cells were found at the oculomotor nucleus levels. Remarkably, both exposure to the cat and insect predation upregulated Fos expression in the supraoculomotor region and the laterodorsal tegmental nucleus. Overall, the present results clearly suggest that the PAG activation pattern appears to reflect, at least partly, the animal's motivational status. It is well established that the PAG is critical for the expression of defensive responses, and, considering the present findings, it will be important to investigate how the PAG contributes to the expression of the predatory behavior, as well.     

Fos-like immunoreactivity in the periaqueductal gray of rats exposed to a natural predator

In the present study we examined, in rats exposed to a predator (cat), the distribution of neurons expressing Fos along the continuum formed by the central gray surrounding the caudal pole of the third ventricle and the periaqueductal gray (PAG). After the predatory encounter, a distinct cluster of Fos-immunoreactive cells was observed in the precommissural nucleus. In the rostral two-thirds of the PAG, Fos expression was mostly seen in the dorsomedial and dorsolateral regions. In contrast, at caudal levels of the PAG, most of the Fos-labelled neurons were distributed in the lateral and ventrolateral PAG. These results are discussed and compared with the pattern of the PAG activation after fear conditioned to a context or elicited by aversive foot shock.     

Bladder contractility-related neurons in Barrington's nucleus: axonal projections to the spinal cord in the cat

Barrington's nucleus projects directly to the sacral parasympathetic nucleus. The purpose of this study was to clarify whether neurons in Barrington's nucleus that increase their firing during bladder contractions project to the spinal cord and, if so, to which level(s) the axon reaches. Single units were recorded in Barrington's nucleus of cat with glass microelectrodes, and the termination level of descending axons was determined by antidromic stimulation of the spinal cord. Thirty-nine neurons projecting to the spinal cord were located in rostral parts of the dorsolateral pontine tegmentum, medial and ventral to the mesencephalic trigeminal tract. This finding is consistent with previous neuronal tracing studies. All neurons increased their firing rates during contraction associated with micturition. In 19 examined neurons, the most caudal level of the descending axon distributed between the L7 and the S3 level. Stimulation of the axon at this most caudal level resulted in antidromic spike latencies ranging between 19.5 msec and 45.0 msec. These antidromic latencies were much smaller than previously reported orthodromic conduction times between neurons in Barrington's nucleus and sacral preganglionic neurons innervating the bladder. The mean conduction velocity of the descending axon from the cell body to the border between Th13 and the L1 ranged between 7.2 m/sec and 27.7 m/sec. The decrease of the mean conduction velocity was observed at the lumbar as well as at the sacral segments, suggesting that axons issue collaterals to the lumbar level as well as to the sacral level.     

Striatal c-fos Induction by Cocaine or Apomorphine Occurs Preferentially in Output Neurons Projecting to the Substantia Nigra in the Rat

Fluorogold or rhodamine-labelled latex beads were injected in the substantia nigra (SN) or the globus pallidus (GP) in order retrogradely to label striatal output neurons that project to the two target structures. Ten days later, striatal c-fos was induced by systemic administration of cocaine (five normal rats; 25 mg/kg cocaine i.p. 2 h before killing) or apomorphine (five unilaterally dopamine-denervated rats; 0.25 mg/kg apomorphine s. c. 2 h before killing), and detection of the Fos protein in the striatum was achieved by immunofluorescence. Sections through the caudate-putamen that displayed good labelling from both SN and GP were selected for a quantitative analysis: the number of retrogradely labelled cells that exhibited Fos immunoreactivity, as well as the total number of retrogradely labelled cells located within a grid (0.16 mm² in size) were counted manually at 25 x magnification. Cocaine induced a proportionally higher c-fos expression in striate-nigral compared to striate-pallidal neurons, whereas apomorphine activated Fos almost exclusively in striate-nigral neurons. The present findings are consistent with the idea that striatal c-fos induction by dopaminergic agents is primarily mediated by an interaction with D1 -receptors, which are thought to be selectively localized on neurons projecting to SN.     

Fos expression in rat pontine tegmental neurons following activation of the medial preoptic area

Fos immunohistochemistry was used to map the distribution of pontine neurons excited by activation of the medial preoptic area (MPO). Although we have previously shown that Barrington's nucleus receives a very dense focal input from the MPO, electrical stimulation of the preoptic area unexpectedly induced very little Fos expression in Barrington's neurons. These results suggest that the MPO→Barrington's projection utilizes a transmitter(s) that does not involve transduction of the Fos protein; alternatively, MPO afferents to Barrington's nucleus may be inhibitory in nature. As Barrington's nucleus plays a critical role in micturition, MPO projections to Barrington's nucleus may regulate voiding reflexes during sexual behavior. Interestingly, while the locus coeruleus (LC) proper receives only a sparse projection from the MPO, extensive Fos expression was present in LC. The finding of Fos immunoreactive LC neurons suggests that the excitatory influence of MPO may regulate LC neuronal activity and NE release during reproductive behaviors.     

The ontogeny of the neuroendocrine response to endotoxin.

During development, the hypothalamic-pituitary-adrenal (HPA) axis is normally hyporesponsive between postnatal days (pnd) 4 and 14. This interval has been designated as the stress-hyporesponsive period (SHRP). Recent evidence indicates that the neonate can respond to selective stimuli, i.e., exposure to immune signals. The purpose of this study was to investigate the neural correlates of the neonatal stress axis in response to a stimulus that activates the pituitary-adrenal hormones. Thus, lipopolysaccharide (LPS) was administered to neonates at three ages (pnd 6, 12, and 18) during or after the SHRP. In an effort to understand the neonatal hypothalamic paraventricular nucleus (PVN) response to an endotoxin, we measured c-fos immunoreactivity and corticotrophin-releasing hormone (CRH) gene expression. At all ages tested, there was an increase in ACTH and corticosterone (CORT) following LPS compared to controls. During the SHRP, LPS treatment resulted in a marked increase in Fos-positive cells in the PVN, whereas a saline injection had no effect. However, at pnd 18, both LPS and a saline injection elicited equivalent PVN Fos expression. In contrast to the effect on Fos, LPS and a saline injection decreased CRH mRNA at pnd 6 and 12. Outside the SHRP, LPS resulted in an increase in CRH gene expression relative to saline-injected controls. Thus, while the LPS-induced activation of Fos protein and plasma hormones were concordant, CRH mRNA did not positively correlate with the peripheral response. This suggests that the SHRP is not absolute, and the brain is responsive to some stimuli during this period.     

Localization of the neurons active during paradoxical (REM) sleep and projecting to the locus coeruleus noradrenergic neurons in the rat

Locus coeruleus (LC) noradrenergic neurons are active during wakefulness, slow their discharge rate during slow wave sleep, and stop firing during paradoxical sleep (PS). A large body of data indicates that their inactivation during PS is due to a tonic GABAergic inhibition. To localize the neurons responsible for such inhibition, we first examined the distribution of retrogradely and Fos double-immunostained neurons following cholera toxin b subunit (CTb) injection in the LC of control rats, rats selectively deprived of PS for 3 days, and rats allowed to recover for 3 hours from such deprivation. We found a significant number of CTb/Fos double-labeled cells only in the recovery group. The largest number of CTb/Fos double-labeled cells was found in the dorsal paragigantocellular reticular nucleus (DPGi). It indeed contained 19% of the CTb/Fos double-labeled neurons, whereas the ventrolateral periaqueductal gray (vlPAG) contained 18.3% of these neurons, the lateral paragigantocellular reticular nucleus (LPGi) 15%, the lateral hypothalamic area 9%, the lateral PAG 6.7%, and the rostral PAG 6%. In addition, CTb/Fos double-labeled cells constituted 43% of all the singly CTb-labeled cells counted in the DPGi compared with 29% for the LPGi, 18% for the rostral PAG, and 10% or less for the other structures. Although all these populations of CTb/Fos double-labeled neurons could be GABAergic and tonically inhibit LC neurons during PS, our results indicate that neurons from the DPGi constitute the best candidate for this role.