Lower fractional dimension in Alzheimer's disease correlates with reduced locus coeruleus signal intensity

This study aimed to determine the pattern of fractional dimension (FD) in Alzheimer's disease (AD) patients, and investigate the relationship between FD and the locus coeruleus (LC) signal intensity.A total of 27 patients with AD and 25 healthy controls (HC) were collected to estimate the pattern of fractional dimension (FD) and cortical thickness (CT) using the Computational Anatomy Toolbox (CAT12), and statistically analyze between groups on a vertex level using statistical parametric mapping 12. In addition, they were examined by neuromelanin sensitive MRI(NM-MRI) technique to calculate the locus coeruleus signal contrast ratios (LC-CRs). Additionally, correlations between the pattern of FD and LC-CRs were further examined.Compared to HC, AD patients showed widespread lower CT and FD Furthermore, significant positive correlation was found between local fractional dimension (LFD) of the left rostral middle frontal cortex and LC-CRs. Results suggest lower cortical LFD is associated with LCCRs that may reflect a reduction due to broader neurodegenerative processes. This finding may highlight the potential utility for advanced measures of cortical complexity in assessing brain health and early identification of neurodegenerative processes.

Magnetic resonance imaging of noradrenergic neurons

Noradrenaline is a neurotransmitter involved in general arousal, selective attention, memory, inflammation, and neurodegeneration. The purpose of this work was to delineate noradrenergic neurons in vivo by T₁-weighted MRI with magnetization transfer (MT). In the brainstem of human and mice, MRI identified the locus coeruleus, dorsal motor vagus nucleus, and nucleus tractus solitarius. Given (1) the long T₁ and low magnetization transfer ratio for the noradrenergic cell groups compared to other gray matter, (2) significant correlation between MT MRI signal intensity and proton density, and (3) no correlation between magnetization transfer ratio (or R₁) and iron, copper, or manganese in human brain, the high MRI signal of the noradrenergic neurons must be attributed to abundant water protons interacting with any T₁-shortening paramagnetic ions in active cells rather than to specific T₁-shortening molecules. The absence of a high MRI signal from the locus coeruleus of Ear2(-/-) mice lacking noradrenergic neurons confirms that cell bodies of noradrenergic neurons are the source of the bright MRI appearance. The observation of this high signal in DBH(-/-) mice, in 3-week-old mice, and in mice under hyperoxia/hypercapnia/hypoxia together with the general absence of neuromelanin (NM) in noradrenergic neurons of young rodents further excludes that it is due to NM, dopamine β-hydroxylase, their binding to paramagnetic ions, blood inflow, or hemoglobin. Instead, these findings indicate a high density of water protons whose T₁ is shortened by paramagnetic ions as the relevant source of the high MRI signal. In the brain of APP/PS1/Ear2(-/-) mice, a transgenic model of Alzheimer's disease, MRI detected noradrenergic neuron loss in the locus coeruleus. Proton magnetic resonance spectroscopy revealed that a 60-75% reduction of noradrenaline is responsible for a reduction of N-acetylaspartate and glutamate in the hippocampus as well as for a shortening of the water proton T₂ in the frontal cortex. These results suggest that a concurrent shortage of noradrenaline in Alzheimer's disease accelerates pathologic processes such as inflammation and neuron loss.

The rostromedial tegmental nucleus is essential for non-rapid eye movement sleep

The rostromedial tegmental nucleus (RMTg), also called the GABAergic tail of the ventral tegmental area, projects to the midbrain dopaminergic system, dorsal raphe nucleus, locus coeruleus, and other regions. Whether the RMTg is involved in sleep-wake regulation is unknown. In the present study, pharmacogenetic activation of rat RMTg neurons promoted non-rapid eye movement (NREM) sleep with increased slow-wave activity (SWA). Conversely, rats after neurotoxic lesions of 8 or 16 days showed decreased NREM sleep with reduced SWA at lights on. The reduced SWA persisted at least 25 days after lesions. Similarly, pharmacological and pharmacogenetic inactivation of rat RMTg neurons decreased NREM sleep. Electrophysiological experiments combined with optogenetics showed a direct inhibitory connection between the terminals of RMTg neurons and midbrain dopaminergic neurons. The bidirectional effects of the RMTg on the sleep-wake cycle were mimicked by the modulation of ventral tegmental area (VTA)/substantia nigra compacta (SNc) dopaminergic neuronal activity using a pharmacogenetic approach. Furthermore, during the 2-hour recovery period following 6-hour sleep deprivation, the amount of NREM sleep in both the lesion and control rats was significantly increased compared with baseline levels; however, only the control rats showed a significant increase in SWA compared with baseline levels. Collectively, our findings reveal an essential role of the RMTg in the promotion of NREM sleep and homeostatic regulation.

Neuromelanin marks the spot: identifying a locus coeruleus biomarker of cognitive reserve in healthy aging

Leading a mentally stimulating life may build up a reserve of neural and mental resources that preserve cognitive abilities in late life. Recent autopsy evidence links neuronal density in the locus coeruleus (LC), the brain's main source of norepinephrine, to slower cognitive decline before death, inspiring the idea that the noradrenergic system is a key component of reserve (Robertson, I. H. 2013. A noradrenergic theory of cognitive reserve: implications for Alzheimer's disease. Neurobiol. Aging. 34, 298-308). Here, we tested this hypothesis using neuromelanin-sensitive magnetic resonance imaging to visualize and measure LC signal intensity in healthy younger and older adults. Established proxies of reserve, including education, occupational attainment, and verbal intelligence, were linearly correlated with LC signal intensity in both age groups. Results indicated that LC signal intensity was significantly higher in older than younger adults and significantly lower in women than in men. Consistent with the LC-reserve hypothesis, both verbal intelligence and a composite reserve score were positively associated with LC signal intensity in older adults. LC signal intensity was also more strongly associated with attentional shifting ability in older adults with lower cognitive reserve. Together these findings link in vivo estimates of LC neuromelanin signal intensity to cognitive reserve in normal aging.

Projection specificity in heterogeneous locus coeruleus cell populations: implications for learning and memory

Noradrenergic neurons in the locus coeruleus (LC) play a critical role in many functions including learning and memory. This relatively small population of cells sends widespread projections throughout the brain including to a number of regions such as the amygdala which is involved in emotional associative learning and the medial prefrontal cortex which is important for facilitating flexibility when learning rules change. LC noradrenergic cells participate in both of these functions, but it is not clear how this small population of neurons modulates these partially distinct processes. Here we review anatomical, behavioral, and electrophysiological studies to assess how LC noradrenergic neurons regulate these different aspects of learning and memory. Previous work has demonstrated that subpopulations of LC noradrenergic cells innervate specific brain regions suggesting heterogeneity of function in LC neurons. Furthermore, noradrenaline in mPFC and amygdala has distinct effects on emotional learning and cognitive flexibility. Finally, neural recording data show that LC neurons respond during associative learning and when previously learned task contingencies change. Together, these studies suggest a working model in which distinct and potentially opposing subsets of LC neurons modulate particular learning functions through restricted efferent connectivity with amygdala or mPFC. This type of model may provide a general framework for understanding other neuromodulatory systems, which also exhibit cell type heterogeneity and projection specificity.

Differential distribution patterns from medial prefrontal cortex and dorsal raphe to the locus coeruleus in rats

Locus coeruleus (LC) consists of a densely packed nuclear core and a surrounding plexus of dendritic zone, which is further divided into several subregions. Whereas many limbic-related structures topographically target specific subregions of the LC, the precise projections from two limbic areas, that is, medial prefrontal cortex (mPFC) and dorsal raphe (DR), have not been investigated. The goal of the present study is to identify and compare the distribution patterns of mPFC and DR afferent terminals to the LC nuclear core as opposed to specific pericoerulear dendritic regions (Peri-LC). To address these issues, anterograde tracer injections were combined with dopamine-β-hydroxylase (DBH) immunofluorescent staining to reveal the distribution patterns around the LC nuclear complex. Our data suggest that both mPFC-LC and DR-LC projections exhibit selective afferent terminal patterns. More specifically, mPFC-LC projecting fibers mainly target the rostromedial Peri-LC, whereas DR-LC projecting fibers demonstrate a preference to the caudal juxtaependymal Peri-LC. Thus, our present findings provide further evidences that afferents to the LC are topographically organized. Understanding the relationship among different inputs to the LC may help to elucidate the organizing principle which likely governs the interactions between the broad afferent sources of the LC and its global efferent targets.

Long-term implantation of deep brain stimulation electrodes in the pontine micturition centre of the Göttingen minipig

AIM

To implant deep brain stimulation (DBS) electrodes in the porcine pontine micturition centre (PMC) in order to establish a large animal model of PMC-DBS.

METHOD

Brain stems from four Göttingen minipigs were sectioned coronally into 40-mum-thick histological sections and stained with Nissl, auto-metallographic myelin stain, tyrosine hydroxylase and corticotrophin-releasing factor immunohistochemistry in order to identify the porcine PMC. DBS electrodes were then stereotaxically implanted on the right side into the PMC in four Göttingen minipigs, and the bladder response to electrical stimulation was evaluated by subsequent cystometry performed immediately after the operation and several weeks later.

FINDINGS

A paired CRF-dense area homologous to the PMC in other species was encountered in the rostral pontine tegmentum medial to the locus coeruleus and ventral to the floor of the fourth ventricle. Electrical stimulation of the CRF-dense area resulted in an increased detrusor pressure followed by visible voiding in some instances. The pigs were allowed to survive between 14 and 55 days, and electrical stimulation resulting in an increased detrusor pressure was performed on more than one occasion without affecting consciousness or general thriving. None of the pigs developed postoperative infections or died prematurely.

CONCLUSIONS

DBS electrodes can be implanted for several weeks in the identified CRF-dense area resulting in a useful large animal model for basic research on micturition and the future clinical use of this treatment modality in neurogenic supra-pontine voiding disorders.

Sleep research in space: expression of immediate early genes in forebrain structures of rats during the nasa neurolab mission (STS-90)

1. Electrophysiological and behavioural observations have shown that changes in the sleep-waking activity occur in astronauts during the space flight. Experiments performed in ground-based experiments have previously shown that the immediate early gene (IEG) c-fos, a marker of neuronal activation, can be used as a molecular correlate of sleep and waking. However, while Fos expression peaks within 2-4 hours after the stimulus and returns to baseline within 6-8 hours, other IEGs as the FRA proteins which are also synthetized soon after their induction, persist in the cell nuclei for longer periods of time, ranging from 1-2 days to weeks. 2. Both Fos and FRA expression were evaluated in several adult albino rats sacrificed at different time points of the space flight, i.e. either at FD2 and FD14, i.e. at launch and about two weeks after launch, respectively, or at R + 1 and R + 13, i.e. at the reentry and about two weeks after landing. The changes in Fos and FRA expression were then compared with those obtained in ground controls. These experiments demonstrate activation of several brain areas which varies during the different phases of the space flight. Due to their different time of persistence, Fos and FRA immunohistochemistry can provide only correlative observations. In particular, FRA expression has been quite helpful to identify the occurrence of short-lasting events such as those related either to stress or to REM-sleep, whose episodes last in the rat only a few min and could hardly be detected by using only Fos expression. 3. Evidence was presented indicating that at FD2 and FD14 Fos-labeled cells were observed in several brain areas in which Fos had been previously identified as being induced by spontaneous or forced waking in ground-based experiments. In contrast to these findings FLT rats sacrificed at R + 1 showed low levels of Fos immunostaining in the cerebral cortex (neocortex) and several forebrain structures such as the hypothalamus and thalamus. Some Fos staining was also present in limbic cortical areas, the septum, and the hippocampus. The main area of the forebrain of FLT rats sacrificed at R + 1, showing an increased expression of Fos, was the central nucleus of the amygdala (CeA) (cf. 127), as well as the noradrenergic locus coeruleus (LC) nucleus (cf. 122). At R + 13 Fos immunostaining was variable among FLT rats. However, none of these rats showed a significant number of Fos-positive cells in CeA. 4. Most of the rats studied for Fos expression were also tested for FRA expression. In particular, a scattered amount of FRA expression occurred at FD14 in different areas of the neocortex and in limbic forebrain regions (such as the cingulate, retrosplenial and entorhinal cortex). It included also the hippocampus, the lateral septum, the caudate/putamen, as well as some hypothalamic regions. At the reentry (R + 1) it was previously shown that a prominent increase in FRA expression occurred in the LC of FLT rats (cf. 122). This finding was associated with an increase in FRA expression which affected not only the nucleus paragigantocellularis lateralis of the medulla, which sends excitatory glutamatergic afferents to the LC (cf. 31 for ref.), but also structures which are known to produce corticotropin-releasing factor (CRF), a neuropeptide which activates the noradrenergic LC neurons during stress. 5. These findings which result from acceleration stress were followed by REMS episodes, which probably occurred after a long period of sleep deprivation following exposure to microgravity. It was previously shown that an increase in Fos and FRA expression occurred at the reentry in some pontine and medullary reticular structures (cf. 128), which are likely to be involved in both the descending (postural atonia) and the ascending manifestations of PS. These findings can be integrated by results of the present experiments showing that at the reentry high levels of FRA expression occurred in the hippocampus and the limbic system, i.e. in structures which are involved in the generalized pattern of EEG desynchronization and the theta activity, typical of REMS (cf. 83, 84). A prominent increase in FRA expression also affected at the reentry some components of the amygdaloid complex, particularly the CeA. as well as some related structures, such as the lateral parabrachial nucleus (cf. 122) and the nucleus of the tractus solitarius (cf. 127). These structures are known to contribute to the PGO waves, which drive the oculomotor system either directly or through the medial vestibular nuclei (128, cf. also 126). Unfortunately due to our brainstem transections we were unable to evaluate the changes in gene expression which could affect the dorsolateral pontine structures during the occurrence of REMS episodes. Further experiments are thus required to investigate the role that these pontine structures exert in determining adaptive changes following exposure to microgravity after launch as well as readaptation to the terrestrial environment after landing.

Noradrenergic projections to the song control nucleus area X of the medial striatum in male zebra finches (Taeniopygia guttata)

There is considerable functional evidence implicating norepinephrine in modulating activity in the vocal control circuit of songbirds. However, our knowledge of noradrenergic inputs to the song system is incomplete. In this study, cholera toxin subunit B (CTB) injections into area X revealed projections from the noradrenergic nuclei locus coeruleus and subcoeruleus, and injections of biotinylated dextran amines into these noradrenergic nuclei labeled fibers in area X. The nonreciprocity of this connection was demonstrated by the absence of retrogradely labeled cells in area X following injections of CTB into the locus coeruleus. Additionally, we found novel inputs to area X from the nidopallium and arcopallium, the mesencephalic central gray, and the dorsolateralis anterior (DLL) and posterior (DLP) lateralis in the thalamus. Area X can be clearly distinguished from the surrounding medial striatum based on cytoarchitectural and chemical neuroanatomical criteria. We show here that neuromodulatory inputs to area X however, exhibit a considerable degree of overlap with the surrounding area. This finding suggests that regional specificity in neuromodulator action is most likely afforded by a specialization in receptor density and enzyme distribution rather than projections from the synthesizing nuclei. Our results extend current knowledge about noradrenergic projections to specialized nuclei of the song control circuit and provide neuroanatomical evidence for the functional action of norepinephrine-modulating context-dependent ZENK expression in area X. Furthermore, the novel projections to area X from telencephalic and thalamic areas could be new and interesting nodes in the striatopallidothalamic loop spanning the songbird brain.

Characterization of neurochemically specific projections from the locus coeruleus with respect to somatosensory-related barrels

Tactile information from the rodent mystacial vibrissae is relayed through the ascending trigeminal somatosensory system. At each level of this pathway, the whiskers are represented by a unique pattern of dense cell aggregates, which in layer IV of cortex are known as "barrels." Afferent inputs from the dorsal thalamus have been demonstrated repeatedly to correspond rather precisely with this modular organization. However, axonal innervation patterns from other brain regions such as the noradrenergic locus coeruleus are less clear. A previous report has suggested that norepinephrine-containing fibers are concentrated in the center/hollow of the barrel, while other studies have emphasized a more random distribution of monoaminergic projections. To address this issue more directly, individual tissue sections were histochemically processed for cytochrome oxidase in combination with dopamine-beta-hydroxylase, the synthesizing enzyme for norepinephrine, or the neuropeptide galanin. These two neuroactive agents were of particular interest because they colocalize in a majority of locus coeruleus neurons and terminals. Our data indicate that discrete concentrations or local arrays of dopamine-beta-hydroxylase- or galanin-immunoreactive fibers are not apparent within the cores of individual barrels. As such, the data suggest that cortical inputs from the locus coeruleus are not patterned according to cytoarchitectural landmarks or the neurochemical identity of coeruleocortical efferents. While transmitter-specific actions of norepinephrine and/or galanin may not be derived from the laminar/spatial connections of locus coeruleus axons, the possibility remains that the release of these substances may mediate distinctive events through the localization of different receptor subclasses, or the contact of their terminals onto cells with certain morphological characteristics or ultrastructural components.

The physiology and processing of pain: a review

Despite the many advances in our understanding of the mechanisms underlying pain processing, pain continues to be a major healthcare problem in the United States. Each day, millions of Americans are affected by both acute and chronic pain conditions, costing in excess of $100 billion for treatment-related costs and lost work productivity. Thus, it is imperative that better treatment strategies be developed. One step toward improving pain management is through increased knowledge of pain physiology. Within the nervous system, there are several pathways that transmit information about pain from the periphery to the brain. There is also a network of pathways that carry modulatory signals from the brain and brainstem that alter the incoming flow of pain information. This article provides a review to the physiology and processing of pain.

The locus coeruleus in schizophrenia: a postmortem study of noradrenergic neurones

Despite evidence for an abnormality of noradrenergic function in schizophrenia, it remains unclear whether the number of noradrenergic neurones is normal in patients with the disorder. In postmortem, formalin-fixed tissue from 15 schizophrenic patients and 18 controls matched for age and gender, we made estimates of the number and size of tyrosine-hydroxylase-immunoreactive cells in the locus coeruleus (LC). No significant difference was detected between these groups in the cross-sectional area or diameter of immunoreactive cell profiles. Profile number was not significantly affected by gender, side of the brainstem (left or right), postmortem interval or time in formalin; however, the levels of immunoreaction product (optical density) correlated significantly with our profile counts, which were lower on average in the schizophrenic group. When optical density was included as a covariate in our comparison (a repeated-measures analysis of variance) of schizophrenic and control cases, we found no difference between these groups in the number of neurones counted. An age-related decrease in profile number was detected, but no effect of age on our estimates of cell size was apparent. Our results highlight the importance of accounting for potential confounding variables, including variations in the quality of immunostaining, in investigations of this type. The findings presented here concur with previous studies suggesting that noradrenergic dysfunction in schizophrenia is not associated with an anatomical abnormality at the level of the LC.

Reciprocal connections between subdivisions of the dorsal raphe and the nuclear core of the locus coeruleus in the rat

The interconnection between two brainstem monoaminergic nuclei, the dorsal raphe (DR) and the locus coeruleus (LC), was analyzed in the rat using retrograde tracing and immunocytochemistry. Gold-conjugated and inactivated wheatgerm agglutinin-horseradish peroxidase (WGA-apo-HRP-gold) was injected into subdivisions of the DR or rostro-caudal levels of the nuclear core of the LC, and labeled LC or DR neurons were identified by dopamine-beta-hydroxylase (DBH) or 5-hydroxytryptamine (5-HT) immunostaining, respectively. Within the LC-DR projection, the caudal principal LC projected to the caudal, ventromedial, and interfascicular DR. Mid-LC as well as caudal LC projected with an ipsilateral predominance to the lateral wing subdivision of the DR. A few rostral LC neurons projected to caudal, dorsomedial, and ventromedial DR. Within the DR-LC projection, the rostral LC received inputs mainly from the caudal, dorsomedial, and ventromedial DR. Mid-LC to caudal LC received projections from mid-DR to caudal DR, with the heaviest projection from the ipsilateral lateral wing as well as caudal DR. The DR-LC projection was substantially more robust than LC-DR and included both serotonergic and nonserotonergic components. Thus, the data demonstrate topographically ordered, reciprocal connectivity between DR and LC with particularly strong projections from DR to LC. Communication between these two brainstem monoaminergic nuclei may be critical for a variety of functions including sleep-wake regulation, vigilance, analgesia, cognition, and stress responses.

Noradrenergic mechanisms in neurodegenerative diseases: a theory

A deficiency in the noradrenergic system of the brain, originating largely from cells in the locus coeruleus (LC), is theorized to play a critical role in the progression of a family of neurodegenerative disorders that includes Parkinson's disease (PD) and Alzheimer's disease (AD). Consideration is given here to evidence that several neurodegenerative diseases and syndromes share common elements, including profound LC cell loss, and may in fact be different manifestations of a common pathophysiological process. Findings in animal models of PD indicate that the modification of LC-noradrenergic activity alters electrophysiological, neurochemical and behavioral indices of neurotransmission in the nigrostriatal dopaminergic system, and influences the response of this system to experimental lesions. In models related to AD, noradrenergic mechanisms appear to play important roles in modulating the activity of the basalocortical cholinergic system and its response to injury, and to modify cognitive functions including memory and attention. Mechanisms by which noradrenaline may protect or promote recovery from neural damage are reviewed, including effects on neuroplasticity, neurotrophic factors, neurogenesis, inflammation, cellular energy metabolism and excitotoxicity, and oxidative stress. Based on evidence for facilitatory effects on transmitter release, motor function, memory, neuroprotection and recovery of function after brain injury, a rationale for the potential of noradrenergic-based approaches, specifically alpha2-adrenoceptor antagonists, in the treatment of central neurodegenerative diseases is presented.

Neuroanatomical evidence for indirect connections between the medial preoptic nucleus and the song control system: possible neural substrates for sexually motivated song

In European starlings ( Sturnus vulgaris) as in other seasonally breeding songbirds, a major function of song during the breeding season is mate attraction, and song in this context is highly sexually motivated. Song learning, perception, and production are regulated by nuclei of the song control system, but there is no evidence that these nuclei participate in the motivation to sing. Evidence suggests that the medial preoptic nucleus (POM), a diencephalic nucleus outside of the song control system, might regulate the motivation to sing, at least in a sexual context. If the POM is involved in the regulation of sexually motivated song, then this structure must interact with the song control system. To examine possible neuroanatomical connections between the POM and song control nuclei a tract-tracing study was performed in male starlings using the antero- and retrograde tract tracer, biotinylated dextran amine (BDA). No direct connections were identified between the POM and song control nuclei; however, labeled fibers were found to terminate in a region bordering dorsal-medial portions of the robust nucleus of the archistriatum (RA). Additionally, several indirect routes via which the POM might communicate with the song control system were identified. Specifically, POM projected to dorsomedial nucleus intercollicularis (DM), mesencephalic central gray (GCt), area ventralis of Tsai (AVT), and locus ceruleus (LoC), structures projecting directly to nuclei involved in song production (DM --> vocal-patterning and respiratory nuclei; GCt, AVT, LoC --> RA and HVC, and the context in which song is sung (AVT --> area X). These results are consistent with the possibility that the POM regulates sexually motivated song through interactions with brain regions involved in vocal production.

Coeruleotrigeminal inhibition of nociceptive processing in the rat trigeminal subnucleus caudalis

It has been accepted that the descending system from the nucleus locus coeruleus (LC)/nucleus subcoeruleus (SC) plays a significant role in spinal nociceptive processing. The present study was designed to examine modulation of nociceptive processing in the caudal part of the trigeminal sensory nuclear complex, the trigeminal subnucleus caudalis which is generally considered to be involved in the relay of oral-facial nociceptive information. Experiments were performed on anesthetized Sprague-Dawley rats. The site of LC/SC stimulation was confirmed by histology using potassium ferrocyanide to produce a Prussian blue reaction product marking the iron deposited from the stimulating electrode tip. Only data from rats which had electrode placements in the LC/SC were used. Electrical stimulation was delivered at a stimulus intensity below 100 microA in the present study. Stimulation at sites inside the LC/SC produced a reduction of both spontaneous activity and responses of subnucleus caudalis neurons to somatic input, especially nociceptive input. Increasing stimulation frequency in the LC/SC resulted in an increase in inhibitory effects on nociceptive responses of subnucleus caudalis neurons. At three of nine sites outside the LC/SC, electrical stimulation was effective on descending inhibition. A significant difference in the inhibitory effects was observed when the inhibitory effects were compared between sites of stimulation inside the LC/SC and three effective sites of stimulation outside the LC/SC. These findings suggest that nociceptive processing in the subnucleus caudalis is under the control of the descending modulation system from the LC/SC. To understand the effects of repetitive stimulation with high frequency on fine unmyelinated LC/SC fibers, the existence of recurrent collateral excitation in the LC/SC may be considered.

Intracochlear injection of pseudorabies virus labels descending auditory and monoaminerg projections to olivocochlear cells in guinea pig

Pseudorabies virus was used to label transneuronally descending auditory projections following intracochlear injections. At different time points after injection, virus-infected cells were detected immunohistochemically in the central nervous system. Initially (25 h), virus was transported retrogradely to olivocochlear cells in the pons. At 32-72 h after injection, labelling occurred in higher order auditory brainstem nuclei as well as in the locus coeruleus and pontine dorsal raphe. At 90-108 h, virus-infected neurons were found bilaterally in the medial geniculate body and in layer V of the auditory cortex. Viral transneuronal labelling in the auditory cortex after intracochlear application confirms the existence of a continuous descending chain of neurons from the auditory cortex to the cochlea, via the medial and lateral olivocochlear systems. The transneuronal labelling of the locus coeruleus and pontine dorsal raphe suggests that noradrenergic and serotonergic inputs may substantially influence the activity of olivocochlear cells, and thus the cochlea.

Unilateral hindpaw inflammation induces bilateral activation of the locus coeruleus and the nucleus subcoeruleus in the rat

Several lines of evidence have shown that unilateral hindpaw inflammation produces activation of the locus coeruleus (LC) and the nucleus subcoeruleus (SC), resulting in descending modulation of nociceptive processing in the dorsal horn. However, it is unclear if the LC/SC is activated unilaterally or bilaterally following the development of unilateral hindpaw inflammation. The present study was designed to clarify this question. For the induction of unilateral hindpaw inflammation, lambda carrageenan (2.0mg in 0.15ml saline) was injected subcutaneously into the plantar surface of the left hindpaw. Four hours after carrageenan injection, in the LC/SC both ipsilateral and contralateral to the inflamed paw, the number of Fos-positive cells increased significantly in carrageenan-injected rats when compared to vehicle (saline)-injected and untreated control rats. The Fos expression in the LC/SC was equivalent bilaterally in the carrageenan-injected rats, as well as in vehicle-injected and untreated control rats. For nociceptive testing, the paw withdrawal latency, which measures cutaneous hyperalgesia in response to thermal stimuli, was determined in rats receiving a unilateral lesion of the LC/SC either ipsilateral or contralateral to the inflamed paw. Two and a half hours after the induction of inflammation, in both groups of rats with unilateral lesion, paw withdrawal latencies decreased significantly in the LC/SC-lesioned rats. However, there was no significant difference in paw withdrawal latencies between the LC/SC-lesioned rats and sham-operated rats, indicating that unilateral activation of the LC/SC is sufficient for modulating nociceptive processing in the dorsal horn. These results suggest that unilateral hindpaw inflammation induces bilateral activation of the LC/SC.

Immunocytochemical localization of the alpha3, alpha4, alpha5, alpha7, beta2, beta3 and beta4 nicotinic acetylcholine receptor subunits in the locus coeruleus of the rat

The presence of nicotinic acetylcholine receptors (nAChRs) within the locus coeruleus (LC) has been examined using a wide range of techniques. However, the expression pattern of individual nicotinic receptor subunits has not been described. Using immunocytochemistry, we demonstrate the distribution of the alpha3, alpha4, alpha5, alpha7, beta2, beta3 and beta4 nAChR subunits within the LC. Most nAChR subunits were expressed on neuronal perikarya within the LC nucleus. The alpha3, alpha4, alpha7 and beta3 immunoreactive neurons were evenly distributed in the dorsal and ventral LC whereas the alpha5, beta2 and beta4 nAChR subunits were preferentially confined to the upper dorsal section. In addition to neuronal perikarya, alpha4, alpha5 and beta2 immunoreactive fibers were observed. With the exception of the alpha3 subunit, punctate labeling was observed within and immediately surrounding the LC. These data are consistent with the presence of multiple nAChRs within the LC and extend these findings to show the distribution pattern of each nAChR subunit throughout the LC nucleus.

The locus coeruleus-noradrenergic system: modulation of behavioral state and state-dependent cognitive processes

Through a widespread efferent projection system, the locus coeruleus-noradrenergic system supplies norepinephrine throughout the central nervous system. Initial studies provided critical insight into the basic organization and properties of this system. More recent work identifies a complicated array of behavioral and electrophysiological actions that have in common the facilitation of processing of relevant, or salient, information. This involves two basic levels of action. First, the system contributes to the initiation and maintenance of behavioral and forebrain neuronal activity states appropriate for the collection of sensory information (e.g. waking). Second, within the waking state, this system modulates the collection and processing of salient sensory information through a diversity of concentration-dependent actions within cortical and subcortical sensory, attention, and memory circuits. Norepinephrine-dependent modulation of long-term alterations in synaptic strength, gene transcription and other processes suggest a potentially critical role of this neurotransmitter system in experience-dependent alterations in neural function and behavior. The ability of a given stimulus to increase locus coeruleus discharge activity appears independent of affective valence (appetitive vs. aversive). Combined, these observations suggest that the locus coeruleus-noradrenergic system is a critical component of the neural architecture supporting interaction with, and navigation through, a complex world. These observations further suggest that dysregulation of locus coeruleus-noradrenergic neurotransmission may contribute to cognitive and/or arousal dysfunction associated with a variety of psychiatric disorders, including attention-deficit hyperactivity disorder, sleep and arousal disorders, as well as certain affective disorders, including post-traumatic stress disorder. Independent of an etiological role in these disorders, the locus coeruleus-noradrenergic system represents an appropriate target for pharmacological treatment of specific attention, memory and/or arousal dysfunction associated with a variety of behavioral/cognitive disorders.

Pontine sources of norepinephrine in the cat cochlear nucleus

In the current study, the distribution of noradrenergic neurons in the pontine tegmentum that project to the cochlear nucleus was determined with retrograde tract tracing combined with neurotransmitter immunohistochemistry in the cat. Double-labeled neurons were observed in all noradrenergic cell groups, in both the dorsolateral and the ventrolateral tegmentum. Half of the double-labeled cells were located in the locus coeruleus complex. Most of these were situated in its ventral division. Most other double-labeled cells were located in peribrachial regions, especially lateral to the brachium conjunctivum. Relatively few double-labeled cells were observed in both the A4 and the A5 cell groups, 2% and 0.4%, respectively, of the total. Except for neurons in A5, which projected only contralaterally, the projections were bilateral, with an ipsilateral preponderance. The results indicate that neurons located in the ipsilateral dorsolateral tegmentum, namely, in the locus coeruleus complex and the peribrachial region, are the primary source of pontine noradrenergic afferents to the cochlear nucleus of the cat.

Opposing regulation of the locus coeruleus by corticotropin-releasing factor and opioids. Potential for reciprocal interactions between stress and opioid sensitivity

RATIONALE

Substantial clinical and preclinical findings support an association between stress and opiate abuse. To understand the mechanisms underlying this association, it is important to identify substrates of the stress response and endogenous opioid systems that interact and specific points at which stress circuits and endogenous opioid systems intersect.

OBJECTIVE

This review focuses on corticotropin-releasing factor (CRF), a critical substrate of the stress response, and its potential for interactions with endogenous opioid systems within the pontine nucleus, locus coeruleus (LC), a brain region that has been implicated as a target in response to stress and opiates.

RESULTS

Evidence is reviewed supporting the hypothesis that CRF and endogenous opioids interact to co-regulate the LC. Thus, CRF- and enkephalin-immunoreactive fibers innervating LC dendritic fields overlap, and some axon terminals in this region co-localize CRF and enkephalin. CRF and opioids have opposing effects on LC neuronal discharge and on intracellular signaling mechanisms within LC neurons. Finally, a history of stress or opiate use induces plasticity in CRF-LC or opiate-LC interactions, respectively. Disruptions in the CRF/opioid balance as a result of this plasticity are proposed to result in hyperactivity or hyperresponsiveness of the LC-norepinephrine (NE) system.

CONCLUSIONS

Co-regulation of the LC-NE system by CRF and opioids may be important in acute adaptation to stress. Potential clinical consequences of an imbalance in this regulation as a result of prior stress include increased risk of opiate self administration and decreased sensitivity to opiates used in clinical settings. Conversely, chronic exposure to opiates may predispose individuals to stress-related psychiatric disorders.

Afferent sources to the ganglion of the terminal nerve in teleosts

Afferent sources to the ganglion (ggl) of the terminal nerve (TN) were studied in percomorph teleosts the tilapia and dwarf gourami. After tracer applications to the TN-ggl and the surrounding bulbus olfactorius, retrogradely labeled neurons were present in the area dorsalis telencephali pars posterior (Dp), area ventralis telencephali pars ventralis et supracommissuralis (Vv and Vs), nucleus tegmento-olfactorius of Prasada Rao and Finger (1984), and locus coeruleus. In the contralateral bulbus olfactorius labeled cells were observed, and terminals were seen in the TN-ggl. Tracer injection experiments to the possible sources of origin to the TN-ggl were then performed. Tracer applications to the nucleus tegmento-olfactorius labeled abundant terminals in the TN-ggl but labeled very few in the bulbus olfactorius proper. Retrogradely labeled neurons were present in the nucleus ventromedialis thalami, nucleus commissurae posterioris, area pretectalis pars dorsalis et ventralis, nucleus sensorius nervi trigemini, and formatio reticularis pars superius et medius. Tracer applications to the Dp or Vs/Vv labeled terminals mainly in the bulbus olfactorius proper. However, terminals to the TN-ggl were supplied from labeled axons on their way to the bulbus olfactorius. Tracer injections to the locus coeruleus labeled only a few fibers around the TN-ggl. These results suggest that the TN-ggl receives somatosensory and visual inputs from the nucleus tegmento-olfactorius and olfactory inputs from the bulbus olfactorius and telencephalic subdivisions, which receive secondary olfactory projections. The locus coeruleus may also send fibers to the TN-ggl.

The locus coeruleus: history

The author outlines the history of the locus coeruleus from its discovery to the latest research findings. Although Russel's report in Texas has been believed to be the first break-through scientific article of this neuronal structure, there were two preceding, anatomical and physiological, studies made by Japanese groups. One of the aims of this review is to shed brief light on their works, which being written in Japanese so that might have been unfamiliar to most researchers in the world.

Organization of the coeruleo-vestibular pathway in rats, rabbits, and monkeys

Inputs from locus coeruleus (LC) appear to be important for altering sensorimotor responses in situations requiring increase vigilance or alertness. This study documents the organization of coeruleo-vestibular pathways in rats, rabbits and monkeys. A lateral descending noradrenergic bundle (LDB) projects from LC to the superior vestibular nucleus (SVN) and rostral lateral vestibular nucleus (LVN). A medial descending noradrenergic bundle (MDB) projects from LC to LVN, the medial vestibular nucleus (MVN), group y and rostral nucleus prepositus hypoglossi (rNPH). There is a characteristic, specific pattern of innervation of vestibular nuclear regions across the three species. A quantitative analysis revealed four distinct innervation density levels (minimal, low, intermediate and high) across the vestibular nuclei. The densest plexuses of noradrenergic fibers were observed in the SVN and LVN. Less dense innervation was observed in the MVN, and minimal innervation was observed in the inferior vestibular nucleus (IVN). In monkeys and rabbits, rostral MVN contained a higher innervation density than the rat MVN. In monkeys, the rNPH also contained a dense plexus of fibers. Selective destruction of terminal LC projections (distal axons and terminals) by the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) resulted in a dramatic reduction of immunoreactive fibers within the vestibular nuclear complex of rats, suggesting that the source of these immunoreactive fibers is LC. Retrograde tracer injections into the vestibular nuclei resulted in labeled cells in the ipsilateral, caudal LC and adjacent nucleus subcoeruleus. It is hypothesized that the regional differences in noradrenergic innervation are a substrate for differentially altering vestibulo-ocular and vestibulo-spinal responses during changes in alertness or vigilance.

Contribution of glutamatergic systems in locus coeruleus to nucleus paragigantocellularis stimulation-evoked behavior

The role of extracellular glutamate, within the locus coeruleus, in mediation of the behavioral signs elicited by electrical stimulation of the nucleus paragigantocellularis (PGi) was investigated in conscious, opioid-naive rats. Each rat was prepared with a chronically implanted unilateral electrode within the PGi and a microdialysis guide cannula directed at the ipsilateral locus coeruleus. Opioid withdrawal-like behaviors (rearing, teeth-chattering, wet-dog shakes, etc.) and increases in extracellular glutamate concentrations within the locus coeruleus were evoked, in a frequency-dependent (0.5-50 Hz) manner, during PGi stimulation. Reverse dialysis perfusion of the locus coeruleus with the nonspecific glutamate receptor antagonist, kynurenic acid (0.1, 1 mM), reduced the intensity of stimulation-induced behaviors by roughly 50%, but had no effect on the corresponding increases in glutamate concentrations. Perfusion of the locus coeruleus with the glutamate transporter inhibitor, L-trans-pyrrolidine dicarboxylic acid, at 1, but not at 0.1, mM significantly increased glutamate levels in dialysates. Neither concentration of the transporter inhibitor altered the behavioral score. The results indicate that the opioid withdrawal-like behaviors elicited by electrical stimulation of the brainstem at the site of the PGi are positively correlated with locus coeruleus levels of glutamate, and suggest further that the behaviors are partially mediated by release of glutamate within the locus coeruleus or its immediate vicinity.

Projections of medullary and pontine noradrenergic neurons to the horizontal limb of the nucleus of diagonal band in the rat

Recent investigations in the rat have implicated a noradrenergic innervation to the horizontal nucleus of the diagonal band of Broca as a critical link in a neural circuit that conveys baroreceptor information centrally to inhibit the firing of vasopressin-secreting neurons in the hypothalamic supraoptic nucleus. In this study we used small intra-diagonal band injections of a retrograde tracer, rhodamine latex microspheres, in combination with tyrosine hydroxylase histochemistry to identify brainstem noradrenergic cells contributing to this innervation. In three cases where tracer injections were limited to the horizontal limb of the diagonal band, we observed 20-50 double-labelled neurons ipsilaterally in the dorsal part of the locus coeruleus (A6) and the caudal nucleus tractus solitarius (A2), and bilaterally in the caudal ventrolateral medulla (A1). Double-labelled neurons were also noted in the ventral tegmental area (dopaminergic A10 cell group). Although all major brainstem noradrenergic cell groups contribute fibers to the horizontal limb of the nucleus of diagonal band, data from physiological studies suggest that the noradrenergic A2 neurons in the nucleus tractus solitarius are the most likely pathway through which it receives this baroreceptor information.

Effects of lifelong ethanol consumption on rat locus coeruleus

The effects of lifelong ethanol consumption and ageing on the morphology of locus coeruleus (LC) were studied in alcohol-preferring AA (Alko Alcohol) rats of both sexes. Ethanol (12% v/v) was the only available liquid for the ethanol-consuming rats from 3 months up to 24 months of age. Young (3-month-old) and old (24-month-old) control groups were included in the measurements. The LC morphometry was performed by an unbiased disector method. In the old control rats, the total neuron number, neuronal density and the volume of the LC proper did not differ from the young controls. In the ethanol-exposed rats, the total neuron number of the LC was decreased by 30% and the LC neuronal density by 22%, compared to the age-matched controls. No gender difference was found in the vulnerability of LC neurons to ethanol-induced degeneration. The results suggest a remarkable sensitivity of the LC neurons to the ethanol-induced degeneration in both male and female rats. The possible mechanisms and functional implications of this neuronal loss are discussed.

Catecholaminergic systems in the zebrafish. III. Organization and projection pattern of medullary dopaminergic and noradrenergic neurons

To characterize the catecholaminergic systems in the zebrafish medulla, immunocytological studies were performed by using antibodies directed against tyrosine hydroxylase and dopamine-beta-hydroxylase. Catecholaminergic neurons could be categorized into three populations based on location, dendritic morphology, axonal projection pattern, and targets: an interfascicular group, a vagal area group, and an area postrema group. All groups contained both dopaminergic and noradrenergic neurons. Interfascicular neurons formed a loose longitudinal column of approximately 16-20 multipolar neurons on each side of the medulla, whose rostrocaudal extension coincided roughly with the vagal lobe. These neurons were relatively large and had dendrites that arborized throughout the reticular formation and in the vagal lobe. They also contributed axonal processes to the longitudinal catecholamine bundle. Neurons associated with structures in the vagal area were mostly dopaminergic. Some cells had a short, thin apical process that arborized into a dense plexus near the ventricular surface, and all cells had a basal dendrite that divided into two main branches: one extended caudally to terminate in the commissural nucleus of Cajal and among the postobecular catecholaminergic cell group; the other extended laterally and joined the longitudinal catecholamine bundle. The caudal extent of this cell group reached the medullospinal junction. The area postrema cell group consisted of densely packed, bipolar neurons. One process of these neurons contacted the ventricular surface in the area postrema, and one terminated in the commissural nucleus of Cajal. Collaterals from the latter innervated the superficial laminae of the vagal lobe and joined the longitudinal catecholamine bundle. The longitudinal catecholamine bundle ascended through the medulla ventral to the secondary gustatory tract. Whether some fibers extended more rostrally is not known. The majority of the terminal fields of medullary catecholaminergic neurons appeared to be restricted to the medulla and were strongly associated with sensory systems. With the exception of some cells in the vagal area, catecholamine-containing neurons in the zebrafish medulla were not obviously homologous to those in the mammalian brainstem.

The dorsal locus coeruleus is larger in male than in female Sprague-Dawley rats

Previous studies indicate that the locus coeruleus (LC) can be divided into sub-areas depending upon dominant efferent projection zones. Ascending projections to the forebrain originate within the dorsal half and projections to the spinal cord and the cerebellum course from the ventral half of the LC. Using Sprague-Dawley rats, the present study analyzed sex differences in LC volume and in ascending and descending projection zones. Horizontal sections were stained with cresyl violet or by using antibodies to tyrosine hydroxylase. It was found that the dorsal ascending projection zone is larger in the male. One of the well-defined sub-areas within the dorsal half of the LC provides noradrenergic innervation of the hippocampus, a structure that exhibits various male-dominated sex differences in the rat, and post hoc analysis localized the sex difference to this region of the LC. No difference was found in total LC volume. As well, a sex difference in shape of the LC is indicated by a longer anterior-posterior extent in males, while females have a greater dorso-ventral extent.

Corticotropin-releasing factor receptor antagonist infused into the locus coeruleus attenuates immobilization stress-induced defensive withdrawal in rats

It has been proposed that corticotropin-releasing factor (CRF) released during stress in the region of the locus coeruleus (LC) induces changes in behavior that are typical indices of anxiety. The experiments tested the ability of a CRF antagonist, alpha hCRF9-41, to attenuate stress-induced defensive withdrawal in rats. 1 microgram of alpha hCRF in 300 nl was infused bilaterally in the LC of rats 10 min prior to 30 min immobilization. The apparatus consisted of a small chamber set on one side of a 1 m open field, into which the rat was placed to start the test. Restraint induced defensive withdrawal in rats familiar with the apparatus and significantly increased latency time to emerge from the chamber, total time and mean time spent in the chamber. Infusion of alpha hCRF into the LC prior to restraint significantly decreased total and mean time spent in the chamber comparing to stressed animals. These results are consistent with anatomical, electrophysiological and neurochemical evidence that CRF receptors located in, or close to, the LC region influence behaviors induced by stress.

Evidence for divergent projections to the brain noradrenergic system and the spinal parasympathetic system from Barrington's nucleus

The present study was designed to determine whether Barrington's nucleus, which lies ventromedial to the locus coeruleus (LC) and projects to the sacral parasympathetic nucleus, is a source of afferent projections to the LC. Restricted injections of the anterograde tracer, biocytin, into Barrington's nucleus labeled varicose fibers that extended from the injection site into the LC. Consistent with this, injections of the retrograde tracers, wheatgerm agglutinin conjugated to horseradish peroxidase coupled to gold particles (WGA-Au-HRP) or fluorescein-conjugated latex beads, into the LC labeled numerous (approximately 10%) Barrington's neurons that were also retrogradely labeled by Fluoro-Gold (FG) injections in the spinal cord. Retrograde tracing from the LC combined with corticotropin-releasing hormone (CRH) immunohistochemistry revealed that at least one third of the retrogradely labeled neurons in Barrington's nucleus were CRH-immunoreactive (CRH-IR). Finally, in triple labeling studies, CRH-Barrington's neurons were consistently observed that were retrogradely labeled from both the and spinal cord. These findings implicate Barrington's nucleus as an LC afferent and a source of CRH-IR fibers in the LC. Additionally, the results suggest that some Barrington's neurons diverge to innervate both the spinal cord and the LC. This divergent innervation may serve to coregulate the sacral parasympathetic nervous system and brain noradrenergic system, thus providing a mechanism for coordinating pelvic visceral functions with forebrain activity.

Do amphibians have a true locus coeruleus?

Much controversy surrounds the identity of a locus coeruleus in amphibians because although previous studies on the isthmic region of the brain of anurans and urodeles revealed the presence of noradrenergic cell bodies they failed to demonstrate their projection to the telencephalon or the spinal cord. In the present study applications of Texas Red-conjugated dextran amines to the basal telencephalon or to the spinal cord in combination with tyrosine hydroxylase immunohistochemistry revealed that the noradrenergic cell bodies in the isthmic region of anuran (Rana perezi) and urodele (Pleurodeles waltl) amphibians project to the telencephalon as well as to the spinal cord. On the basis of location, neurotransmitter content and efferent projections, the isthmic noradrenergic cell group of amphibians is, therefore, considered homologous to the locus coeruleus of amniotes.

The neurochemical and behavioral effects of beta-amyloid peptide(25-35)

Beta-amyloid protein (A beta) fragments have been shown to be neurotoxic and/or enhance neuronal vulnerability when injected into the hippocampus. We investigated alterations in monoamine contents, including norepinephrine (NE), 5-HT and dopamine (DA) in the rat locus coeruleus (LC) one week following the injection of beta-amyloid peptide fragment 25-35 (beta (25-35)) into the left dorsal hippocampal areas CA1-3. A single treatment of beta (25-35) had no effect on any monoamine levels. Rats that received two treatments (separated by 7 days) revealed significant elevations in NE, 5-HT, and 5-HIAA as compared with the control group injected with ddH2O. However, these changes were observed in the LC on the contralateral side, whereas the injected side exhibited no significant change. These effects may result from an enhanced synthesis of NE by the contralateral LC neurons to compensate for the loss of tyrosine hydroxylase and accompanying recurrent inhibition in a small number of their population. In a second experiment, the influence of beta (25-35) on spatial learning was evaluated using a Morris water maze task. Rats received bilateral injections of beta (25-35) into hippocampal areas CA1-3. The results indicate that beta (25-35)-treated rats exhibited significantly longer latencies and swim distances to locate the submerged platform than did members of the control group.

Mild electrical stimulation of pontine tegmentum around locus coeruleus reduces rapid eye movement sleep in rats

The norepinephrinergic neurons in the locus coeruleus (LC) cease firing during REM sleep (REMS) and increase firing during REMS deprivation. Most of the earlier studies used lesion and transection techniques which could not confirm the role of LC in REMS generation and/or its maintenance, if at all. Hence, in this study it was hypothesized that if the LC REM-off neurons must cease firing before the onset of REMS, its continuous activation should eliminate or at least reduce REMS. Electrophysiological parameters characterizing sleep-wakefulness-REMS were recorded in freely moving male albino rats. In an attempt not to allow the REM-off LC neurons to cease firing, low intensity (200 microA), low frequency (2 Hz) rectangular (300 microseconds) pulses were continuously delivered to the LC bilaterally through chronically implanted electrodes, and the effects on sleep-wakefulness-REMS were investigated. Although the stimulation did not affect sleep state of the animals, it reduced REMS significantly. The effect on REMS was similar to that of REMS deprivation. Total duration of REMS was significantly reduced during stimulation and showed a rebound increase during the post stimulation period. This reduction in REMS duration was primarily due to a significant reduction in the REMS frequency/h while the mean REMS duration/episode was not affected. Thus, the results of this study suggest that the stimulated area (LC) affects REMS, most likely by suppression of REMS generation process.

Localization of dopamine-beta-hydroxylase-like immunoreactivity in the superior olivary complex of the rat

The noradrenergic (NA) innervation of the superior olivary complex (SOC) was investigated using a monoclonal antibody against dopamine-beta-hydroxylase (D beta H), the synthesizing enzyme for noradrenaline. In addition, positive labelling of D beta H in the inferior colliculus, the lateral lemniscus (LL) and the cochlear nucleus were documented. The antibody was detected using the highly specific and sensitive ABC immunocytochemical method. The specific aim of the study was to show the distribution of putative NA cells and fibres in the SOC in greater detail than had been previously reported. All investigated auditory regions contained D beta H-positive fibres in varying densities. All superior olivary and periolivary nuclei showed NA innervation by mainly fine, weakly staining fibres. Both nuclei of the LL were also found to contain D beta H-positive fibres. D beta H-positive cell bodies were found in the region of the ventral lateral lemniscus and immediately lateral and dorsal to the lateral superior olivary nucleus. Thus the NA innervation of the superior olivary complex could originate from these regions and/or the locus coeruleus.

Opiate microinjections in the locus coeruleus area of the cat enhance slow wave sleep

The effects on sleep/wakefulness states of morphine, morphiceptin (specific mu agonist), DPDPE (delta agonist) and U-50,488H (kappa agonist) microinjections in the Locus coeruleus area (LC) were studied in cats. Morphine (0.8-1.75 nmols in 50 nl of saline) and morphiceptin (1.75 nmols) in LC significantly increased the total time spent in slow wave sleep (SWS) and the mean duration of SWS episodes. Prior naloxone administration blocked the morphine hypnogenic effects. The total time spent in SWS was unaffected by delivery of equimolar doses of DPDPE or U-50,488H in LC; however, the mean duration of the SWS episodes increased significantly after U-50,488H microinjections in LC. Thus, when acting in the LC, opiates have a SWS-enhancing effect and this effect appears to be mediated by mu receptors, although kappa receptors may have a subsidiary action.

Neuronal regeneration and estrous cycle restoration after locus coeruleus-periventricular gray substance section

The locus coeruleus (LC) was anatomically separated from the periventricular gray substance (PVG) by means of knife cuts in the adult female rat presenting regular estrous cycling. This resulted in a transient suppression of the estrous cycling that lasted 10-13 days after surgery. After this period, irregular or regular cycling activity was observed. The regular cycling was restored 30-45 days after the knife cuts. Golgi impregnation of some of the brains of these rats revealed regenerative elements in the knife-cut-insulted area. Thus, blood vessels, macrophagic-like elements, and glial-like elements were observed in close relation with the knife-cut pathway. Additionally, well-defined stained neurons typical of the LC and PVG were observed in close proximity to the knife-cut pathway. Dendritic and axon projections towards the insulted area were observed. Well defined axons were seen across the knife-cut pathway. These data support, first, that the LC-PVG communication is part of a circuitry for the modulation of gonadotropic activity, and second, that in the restoration of the estrous cyclicity after the knife cut, regenerative processes leading to a LC-PVG functional reconnection occurred after the knife cut.

Perturbation of ion channel conductance alters the hypnotic response to the alpha 2-adrenergic agonist dexmedetomidine in the locus coeruleus of the rat

BACKGROUND

The alpha 2-adrenergic agonists are members of a novel class of hypnotic-anesthetic agents that selectively bind to alpha 2 adrenoceptors in the locus coeruleus (LC) to initiate their pharmacologic action. The postreceptor molecular mechanism of the hypnotic action of alpha 2-adrenergic agonists remains unknown. In this study we addressed the role of conductance through a variety of calcium and potassium ion channels in the hypnotic action of dexmedetomidine in the LC of the rat.

METHODS

Cannulas were inserted stereotactically into the LC of halothane-anesthetized rats (n = 318). After at least 48 h, rats were tested for loss of righting reflex in response to administration of the alpha 2-adrenergic agonist dexmedetomidine at a hypnotic (7.0 micrograms LC) or subhypnotic (3.5 micrograms LC) dose. To establish the mediating role of various species of calcium and potassium ion channels in the hypnotic response, rats were pretreated with the following drugs before the administration of dexmedetomidine LC:S(+)202791 (L-type calcium-channel activator), nifedipine and R(-)202791 (L-type calcium-channel blocker), SNX 111 (N-type calcium-channel blocker), SNX 230 (P-type calcium-channel blocker), quinine (calcium-activated and voltage-gated potassium-channel blocker), charybdotoxin (calcium-activated potassium-channel blocker), dendrotoxin (voltage-gated potassium-channel blocker), or glybenclamide (adenosine triphosphate-sensitive potassium-channel blocker). The drugs were used in doses not causing behavioral effects that could have confounded the interpretation of loss of righting reflex.

RESULTS

SNX 230 and the dihydropyridines nifedipine and R(-)202791 produced loss of righting reflex in the presence of a subhypnotic dose of dexmedetomidine. The hypnotic-enhancing effects of the dihydropyridines could be blocked with S(+)202791, which also diminished loss of righting reflex in response to dexmedetomidine 7.0 micrograms LC. Quinine, dendrotoxin, and charybdotoxin each attenuated the hypnotic response to dexmedetomidine 7.0 micrograms LC. The hypnotic response to dexmedetomidine was not significantly altered by SNX 111 or glybenclamide.

CONCLUSIONS

Inhibition of ion conductance through L- or P-type calcium channels and facilitation of conductance through voltage-gated or calcium-activated potassium channels may be involved in the mechanism of hypnotic action of alpha 2-adrenergic agonists. These changes in ion conductance were capable of producing membrane hyperpolarization and decreasing neuronal excitability. There was no evidence for the involvement of adenosine triphosphate-sensitive potassium channels or N-type calcium channels in the hypnotic response to dexmedetomidine.

Ontogeny of tyrosine hydroxylase levels in the neuropil close to locus caeruleus

We aimed to characterize tyrosine hydroxylase (TH) expression within the pericaerulean area (PCA) during postnatal development. Levels of TH along the caudorostral axis of the locus caeruleus (LC) showed a dramatic increase in the PCA beyond day 21. This was due to the extension of the TH-containing area, particularly organized in the ventrolateral and longitudinal directions. As dendrites of LC neurones were observed at long distances within this PCA, such an increase in TH distribution could affect functions related to the LC.

Pharmacological manipulations of the alpha 2-noradrenergic system. Effects on cognition

Electrophysiological and neurosurgical lesion studies with experimental animals have implicated the ascending dorsal noradrenergic bundle of the locus coeruleus system in cognitive process such as memory, learning and selective attention. However, it has also been suggested that noradrenaline (norepinephrine) is crucial in certain cognitive functions associated with the frontal lobes, particularly the prevention of distractibility by irrelevant stimuli. The alpha 2-receptors of the prefrontal cortex appear to be of particular importance in this respect. Studies with humans and experimental primates provide substantial support for this view. The aged primate brain is prone to degeneration of the locus coeruleus, as well as profound catecholamine depletion in the prefrontal cortex, and so is ideal for psychopharmacological investigation of the role of noradrenaline in frontal lobe function. Elderly monkeys show deficits in performance of the delayed response task, which can be reversed directly by both the mixed alpha 1/alpha 2-agonist clonidine, the more specific alpha 2-agonist guanfacine and also, indirectly, by the alpha 2-antagonist yohimbine. It is suggested that these results can be explained by an attenuation of the distracting properties of irrelevant stimuli following stimulation of noradrenergic activity. Conversely, distractibility is magnified whenever noradrenergic activity is reduced. This is supported by similar findings in psychopharmacological studies of healthy humans. The exception to this is when the locus coeruleus is likely to be firing, e.g. in times of stress or when novel stimuli are encountered. Clonidine attenuates locus coeruleus firing on such occasions, and so counteracts any beneficial (or deleterious) effects of stress on task performance. alpha 2-Adrenoceptor agents have little therapeutic value in patients with dementia of the Alzheimer's type. However, they may have some clinical use in patients who have a cognitive symptomatology similar to that of patients who have received neurosurgical excisions to the frontal lobes, e.g. deficits in working memory, executive function or focused attention, with relative sparing of episodic short term memory. Patients with Korsakoff's disease, attention deficit disorder or schizophrenia may benefit from treatment with alpha 2-agents. In particular, idazoxan has putative therapeutic effects in patients with a neurodegenerative disorder, namely dementia of frontal type.

Radioautographic evidence that the GABAA receptor antagonist SR 95531 is a substrate inhibitor of MAO-A in the rat and human locus coeruleus

The locus coeruleus (LC), a major noradrenergic nucleus in the brain, probably has a functional role in the regulation of anxiety states as well as vigilance, attention, learning and memory. LC neurons are under the inhibitory control of gamma-aminobutyric acid (GABA) via ionotropic GABAA receptors. However, to date, little is known of the receptor binding characteristics of these neurons. In the present investigation we therefore examined by receptor radioautography the localization of the binding sites for different components of the GABAA receptor complex in the rat and human LC. Both rat and human LC neurons have a high density of binding sites for the pyridazinyl-GABA derivative [3H]SR 95531 (gabazine, a GABAA receptor antagonist for low affinity GABA recognition sites). However, at the concentrations used, no binding sites in the LC were detectable for the benzodiazepine receptor antagonist [3H]flumazenil, the GABAA receptor agonist (for high affinity sites) [3H]muscimol or the ionophore ligand [35S]t-butyl bicyclophosphorothionate (TBPS). Unexpectedly, the pharmacological specificity of [3H]SR 95531 binding to the LC differed markedly from that to most brain regions (IC50 values for GABA and RU 5135 respectively in the LC were > 10(-2) and 10(-3) M; and, for example, in the dentate gyrus the most labelled structure after the LC, 8 x 10(-7) and 1.8 x 10(-9) M). These differences prompted the further characterization of [3H]SR 95531 binding in the LC, revealing a significant affinity for monoamine oxidase type A (MAO-A), which is highly concentrated in this nucleus. In a competition binding study, a reduction of up to 25% of the [3H]SR 95531 binding was observed with MAO-A but not MAO-B inhibitors, at concentrations which produce maximum but selective enzyme inhibition. Correspondingly, 2 h after the oral administration of supramaximal doses of the MAO-A inhibitors moclobemide and Ro 41-1049 (but not the MAO-B inhibitor lazabemide) the in vitro binding of [3H]SR 95531 was markedly reduced (by 77 and 82% of controls respectively). Moreover, enzyme radioautography with [3H]Ro 41-1049 revealed that SR 95531 has a significant affinity for MAO-A (IC50 values were 10(-5) and 4 x 10(-6) M in the LC and dentate gyrus respectively) but not for MAO-B ([3H]lazabemide binding). Altogether, these findings suggest that the high-affinity binding of [3H]SR 95531 to the LC mainly reflects its affinity for MAO-A, which questions its utility as a selective ligand for low-affinity GABA recognition sites in the CNS.(ABSTRACT TRUNCATED AT 400 WORDS)

Opiate withdrawal increases glutamate and aspartate efflux in the locus coeruleus: an in vivo microdialysis study

Electrophysiological studies suggest that an increase in excitatory amino acid release may occur in the locus coeruleus during opiate withdrawal. The present study examined directly by microdialysis in anesthetized rats the effect of naltrexone-precipitated opiate withdrawal on the efflux of excitatory amino acids in the locus coeruleus. A withdrawal-induced increase in glutamate and aspartate efflux was found when the microdialysis probe was located in the core of the locus coeruleus; no increase was seen in adjacent regions.

Locus coeruleus-induced modulation of forebrain electroencephalographic (EEG) state in halothane-anesthetized rat

The effects of reversible enhancement or suppression of locus coeruleus (LC) neuronal discharge activity on forebrain electroencephalographic (EEG) activity have been previously examined in two series of experiments in halothane-anesthetized rats. Unilateral enhancement of LC activity increased EEG measures of arousal in frontal cortex and hippocampus. The EEG effects of LC activation were blocked by intracerebroventricular pretreatment with the noradrenergic beta-antagonist, propranolol. Bilateral, but not unilateral, suppression of LC activity substantially increased EEG measures of sedation/anesthesia in cortex and hippocampus. In all experiments: a) EEG responses were only observed following changes in LC activity levels; b) onset of EEG responses closely followed changes in LC neuronal activity; c) recovery of EEG responses closely followed the recovery of LC neuronal activity. The present report integrates these previous results and considers their implications for the hypothesis that the LC may be an important modulator of behavioral state and/or state-dependent processes. Together, the two series of experiments yield complementary observations that have implications for LC function that are not apparent when considering each series in isolation.

Locus coeruleus activity in monkey: phasic and tonic changes are associated with altered vigilance

Impulse activity of individual neurons in the nucleus locus coeruleus (LC) was recorded from chair-restrained, unanesthetized cynomolgus monkeys. LC activity was closely related to the behavioral state of the animal. In alert waking, LC neurons displayed continuous, moderately irregular activity. In contrast, prolonged pauses in activity accompanied drowsiness. These pauses preceded eye closure and occurred 1-3 s before the onset of slow-wave EEG. At awakening, LC activation preceded by up to 3 s desynchronized EEG and eye opening. LC activity during alertness varied tonically. During behavioral agitation LC activity was higher than during goal-directed task behavior (described below). In addition to these changes in tonic activity, LC neurons were also phasically responsive to certain sensory stimuli. These cells responded selectively to unexpected, meaningful sounds. LC neurons were also recorded during a visual oddball discrimination task in which the monkey was required to selectively release a lever in response to an infrequent visual cue (target cue; CS+) to receive juice reward. LC neurons were selectively activated by CS+ cues in this task; no other task events evoked LC activity. The mean latency of CS+ response was 108 ms (90 ms for multicell recordings), more than 150 ms prior to the behavioral response (lever release). These responses became smaller in later epochs during the session, along with deteriorating task performance. It is proposed that these short-lasting stimulus-evoked LC responses may help optimize behavioral responses and increase vigilance to subsequent sensory stimuli. Together, LC may contribute both to maintaining tonic levels of vigilance and to phasically modulating the current vigilance level in a stimulus-dependent mode.

Cat and dog: higher center of micturition

The nervous control of micturition in the pontine level was studied using cats and dogs as research specimens. Two techniques for this purpose were employed: (1) electrical and chemical stimulations research and (2) nerve tracing research. This investigation suggests that two distinct pontine centers exist, the commonly known pontine micturition center (PMC) which is responsible for urine emptying, and a second, very important pontine center which functions as the urine storage facilitator (PUSFC). The PMC, which triggers bladder contractions and micturition, is located in the nucleus locus coerleus alpha (LCa). The second center (PUSFC) is located in the nucleus locus subcoerleus (LSC). Micturition is controlled by close coordinate operation of both centers in the pontine level.

The locus coeruleus and immediate-early genes in spontaneous and forced wakefulness

In this study, we mapped the expression of two immediate-early genes to examine the functional activation of the locus coeruleus and other regions of the rat brain after periods of spontaneous wakefulness or sleep and after sleep deprivation. c-fos and NGFI-A are two immediate-early genes that are rapidly induced by physiological stimuli and can be used as molecular markers of neural activation. We used immunocytochemical detection of Fos and NGFI-A proteins associated with double labeling for tyrosine hydroxylase to identify activated noradrenergic cells. We found that the expression of Fos and NGFI-A was markedly increased in the locus coeruleus and other brain areas both after spontaneous wakefulness and after short periods (3-24 h) of sleep deprivation. Several Fos-positive cells and most NGFI-A positive cells found in the locus coeruleus after periods of spontaneous wakefulness were shown to be noradrenergic. This study demonstrates that wakefulness per se, whether spontaneous or induced by total sleep deprivation, results in the functional activation of identified noradrenergic locus coeruleus cells.