Structural basis for noradrenergic regulation of neural circuits in the mouse olfactory bulb.

Olfactory input is processed in the glomerulus of the main olfactory bulb (OB) and relayed to higher centers in the brain by projection neurons. Conversely, centrifugal inputs from other brain regions project to the OB. We have previously analyzed centrifugal inputs into the OB from several brain regions using single-neuron labeling. In this study, we analyzed the centrifugal noradrenergic (NA) fibers derived from the locus coeruleus (LC), because their projection pathways and synaptic connections in the OB have not been clarified in detail. We analyzed the NA centrifugal projections by single-neuron labeling and immunoelectron microscopy. Individual NA neurons labeled by viral infection were three-dimensionally traced using Neurolucida software to visualize the projection pathway from the LC to the OB. Also, centrifugal NA fibers were visualized using an antibody for noradrenaline transporter (NET). NET immunoreactive (-ir) fibers contained many varicosities and synaptic vesicles. Furthermore, electron tomography demonstrated that NET-ir fibers formed asymmetrical synapses of varied morphology. Although these synapses were present at varicosities, the density of synapses was relatively low throughout the OB. The maximal density of synapses was found in the external plexiform layer; about 17% of all observed varicosities contained synapses. These results strongly suggest that NA-containing fibers in the OB release NA from both varicosities and synapses to influence the activities of OB neurons. The present study provides a morphological basis for olfactory modulation by centrifugal NA fibers derived from the LC.

Axonal projection-specific differences in somatodendritic α2 autoreceptor function in locus coeruleus neurons.

The locus coeruleus (LC) contains the majority of central noradrenergic neurons sending wide projections throughout the entire CNS. The LC is considered to be essential for multiple key brain functions including arousal, attention and adaptive stress responses as well as higher cognitive functions and memory. Electrophysiological studies of LC neurons have identified several characteristic functional features such as low-frequency pacemaker activity with broad action potentials, transient high-frequency burst discharges in response to salient stimuli and an apparently homogeneous inhibition of firing by activation of somatodendritic α2 autoreceptors (α2AR). While stress-mediated plasticity of the α2AR response has been described, it is currently unclear whether different LC neurons projecting to distinct axonal targets display differences in α2AR function. Using fluorescent beads-mediated retrograde tracing in adult C57Bl6/N mice, we compared the anatomical distributions and functional in vitro properties of identified LC neurons projecting either to medial prefrontal cortex, hippocampus or cerebellum. The functional in vitro analysis of LC neurons confirmed their mostly uniform functional properties regarding action potential generation and pacemaker firing. However, we identified significant differences in tonic and evoked α2AR-mediated responses. While hippocampal-projecting LC neurons were partially inhibited by endogenous levels of norepinephrine and almost completely silenced by application of saturating concentrations of the α2 agonist clonidine, prefrontal-projecting LC neurons were not affected by endogenous levels of norepinephrine and only partially inhibited by saturating concentrations of clonidine. Thus, we identified a limited α2AR control of electrical activity for prefrontal-projecting LC neurons indicative of functional heterogeneity in the LC-noradrenergic system.

Inorganic mercury in human astrocytes, oligodendrocytes, corticomotoneurons and the locus ceruleus: implications for multiple sclerosis, neurodegenerative disorders and gliomas.

Neurotoxic metals have been implicated in the pathogenesis of multiple sclerosis, neurodegenerative disorders and brain tumours but studies of the location of heavy metals in human brains are rare. In a man who injected himself with metallic mercury the cellular location of mercury in his brain was studied after 5 months of continuous exposure to inorganic mercury arising from metallic mercury deposits in his organs. Paraffin sections from the primary motor and sensory cortices and the locus ceruleus in the pons were stained with autometallography to detect inorganic mercury and combined with glial fibrillary acidic protein immunohistochemistry to identify astrocytes. Inorganic mercury was found in grey matter subpial, interlaminar, protoplasmic and varicose astrocytes, white matter fibrous astrocytes, grey but not white matter oligodendrocytes, corticomotoneurons and some locus ceruleus neurons. In summary, inorganic mercury is taken up by five types of human brain astrocytes, as well as by cortical oligodendrocytes, corticomotoneurons and locus ceruleus neurons. Mercury can induce oxidative stress, stimulate autoimmunity and damage DNA, mitochondria and lipid membranes, so its location in these CNS cells suggests it could play a role in the pathogenesis of multiple sclerosis, neurodegenerative conditions such as Alzheimer's disease and amyotrophic lateral sclerosis, and glial tumours.

Copper regulates rest-activity cycles through the locus coeruleus-norepinephrine system.

The unusually high demand for metals in the brain, along with insufficient understanding of how their dysregulation contributes to neurological diseases, motivates the study of how inorganic chemistry influences neural circuitry. We now report that the transition metal copper is essential for regulating rest-activity cycles and arousal. Copper imaging and gene expression analysis in zebrafish identifies the locus coeruleus-norepinephrine (LC-NE) system, a vertebrate-specific neuromodulatory circuit critical for regulating sleep, arousal, attention, memory and emotion, as a copper-enriched unit with high levels of copper transporters CTR1 and ATP7A and the copper enzyme dopamine ß-hydroxylase (DBH) that produces NE. Copper deficiency induced by genetic disruption of ATP7A, which loads copper into DBH, lowers NE levels and hinders LC function as manifested by disruption in rest-activity modulation. Moreover, LC dysfunction caused by copper deficiency from ATP7A disruption can be rescued by restoring synaptic levels of NE, establishing a molecular CTR1-ATP7A-DBH-NE axis for copper-dependent LC function.

Chemogenetic locus coeruleus activation restores reversal learning in a rat model of Alzheimer's disease.

See Grinberg and Heinsen (doi:10.1093/brain/awx261) for a scientific commentary on this article. Clinical evidence suggests that aberrant tau accumulation in the locus coeruleus and noradrenergic dysfunction may be a critical early step in Alzheimer's disease progression. Yet, an accurate preclinical model of these phenotypes that includes early pretangle tau accrual in the locus coeruleus, loss of locus coeruleus innervation and deficits locus coeruleus/norepinephrine modulated behaviours, does not exist, hampering the identification of underlying mechanisms and the development of locus coeruleus-based therapies. Here, a transgenic rat (TgF344-AD) expressing disease-causing mutant amyloid precursor protein (APPsw) and presenilin-1 (PS1ΔE9) was characterized for histological and behavioural signs of locus coeruleus dysfunction reminiscent of mild cognitive impairment/early Alzheimer's disease. In TgF344-AD rats, hyperphosphorylated tau was detected in the locus coeruleus prior to accrual in the medial entorhinal cortex or hippocampus, and tau pathology in the locus coeruleus was negatively correlated with noradrenergic innervation in the medial entorhinal cortex. Likewise, TgF344-AD rats displayed progressive loss of hippocampal norepinephrine levels and locus coeruleus fibres in the medial entorhinal cortex and dentate gyrus, with no frank noradrenergic cell body loss. Cultured mouse locus coeruleus neurons expressing hyperphosphorylation-prone mutant human tau had shorter neurites than control neurons, but similar cell viability, suggesting a causal link between pretangle tau accrual and altered locus coeruleus fibre morphology. TgF344-AD rats had impaired reversal learning in the Morris water maze compared to their wild-type littermates, which was rescued by chemogenetic locus coeruleus activation via designer receptors exclusively activated by designer drugs (DREADDs). Our results indicate that TgF344-AD rats uniquely meet several key criteria for a suitable model of locus coeruleus pathology and dysfunction early in Alzheimer's disease progression, and suggest that a substantial window of opportunity for locus coeruleus/ norepinephrine-based therapeutics exists.

Modular organization of the brainstem noradrenaline system coordinates opposing learning states.

Noradrenaline modulates global brain states and diverse behaviors through what is traditionally believed to be a homogeneous cell population in the brainstem locus coeruleus (LC). However, it is unclear how LC coordinates disparate behavioral functions. We report a modular LC organization in rats, endowed with distinct neural projection patterns and coding properties for flexible specification of opposing behavioral learning states. LC projection mapping revealed functionally distinct cell modules with specific anatomical connectivity. An amygdala-projecting ensemble promoted aversive learning, while an independent medial prefrontal cortex-projecting ensemble extinguished aversive responses to enable flexible behavior. LC neurons displayed context-dependent inter-relationships, with moderate, discrete activation of distinct cell populations by fear or safety cues and robust, global recruitment of most cells by strong aversive stimuli. These results demonstrate a modular organization in LC in which combinatorial activation modes are coordinated with projection- and behavior-specific cell populations, enabling adaptive tuning of emotional responding and behavioral flexibility.

Locus coeruleus: From global projection system to adaptive regulation of behavior.

The brainstem nucleus locus coeruleus (LC) is a major source of norepinephrine (NE) projections throughout the CNS. This important property was masked in very early studies by the inability to visualize endogenous monoamines. The development of monoamine histofluorescence methods by Swedish scientists led to a plethora of studies, including a paper published in Brain Research by Loizou in 1969. That paper was highly cited (making it a focal point for the 50th anniversary issue of this journal), and helped to spark a large and continuing set of investigations to further refine our understating of the LC-NE system and its contribution to brain function and behavior. This paper very briefly reviews the ensuing advances in anatomical, physiological and behavioral aspects of the LC-NE system. Although its projections are ubiquitously present throughout the CNS, recent studies find surprising specificity within the organizational and operational domains of LC neurons. These and other findings lead us to expect that future work will unmask additional features of the LC-NE system and its roles in normative and pathological brain and behavioral processes. This article is part of a Special Issue entitled SI:50th Anniversary Issue.

CRH Engagement of the Locus Coeruleus Noradrenergic System Mediates Stress-Induced Anxiety.

The locus coeruleus noradrenergic (LC-NE) system is one of the first systems engaged following a stressful event. While numerous groups have demonstrated that LC-NE neurons are activated by many different stressors, the underlying neural circuitry and the role of this activity in generating stress-induced anxiety has not been elucidated. Using a combination of in vivo chemogenetics, optogenetics, and retrograde tracing, we determine that increased tonic activity of the LC-NE system is necessary and sufficient for stress-induced anxiety and aversion. Selective inhibition of LC-NE neurons during stress prevents subsequent anxiety-like behavior. Exogenously increasing tonic, but not phasic, activity of LC-NE neurons is alone sufficient for anxiety-like and aversive behavior. Furthermore, endogenous corticotropin-releasing hormone(+) (CRH(+)) LC inputs from the amygdala increase tonic LC activity, inducing anxiety-like behaviors. These studies position the LC-NE system as a critical mediator of acute stress-induced anxiety and offer a potential intervention for preventing stress-related affective disorders.

Reduction of the nitro group to amine by hydroiodic acid to synthesize o-aminophenol derivatives as putative degradative markers of neuromelanin.

Neuromelanin (NM) is produced in dopaminergic neurons of the substantia nigra (SN) and in noradrenergic neurons of the locus coeruleus (LC). The synthesis of NM in those neurons is a component of brain aging and there is the evidence that this pigment can be involved in the pathogenesis of neurodegenerative diseases such as Parkinson's disease. NM is believed to derive from the oxidative polymerization of dopamine (DA) or norepinephrine (NE) with the participation of cysteine, dolichols and proteins. However, there are still unknown aspects in the chemical structure of NM from SN (SN-NM) and LC (LC-NM). In this study, we designed a new method to synthesize o-aminophenol compounds as putative degradation products of catecholamines and their metabolites which may be incorporated into NM. Those compounds are aminohydroxyphenylethylamine (AHPEA) isomers, aminohydroxyphenylacetic acid (AHPAA) isomers and aminohydroxyethylbenzene (AHEB) isomers, which are expected to arise from DA or NE, 3,4-dihydroxyphenylacetic acid (DOPAC) or 3,4-dihydroxyphenylmandelic acid (DOMA) and 3,4-dihydroxyphenylethanol (DOPE) or 3,4-dihydroxyphenylethyleneglycol (DOPEG), respectively. These o-aminophenol compounds were synthesized by the nitration of phenol derivatives followed by reduction with hydroiodic acid (HI), and they could be identified by HPLC in HI hydrolysates of SN-NM and LC-NM. This degradative approach by HI hydrolysis allows the identification of catecholic precursors unique to SN-NM and LC-NM, which are present in catecholaminergic neurons.

Monosynaptic glutamatergic activation of locus coeruleus and other lower brainstem noradrenergic neurons by the C1 cells in mice.

The C1 neurons, located in the rostral ventrolateral medulla (VLM), are activated by pain, hypotension, hypoglycemia, hypoxia, and infection, as well as by psychological stress. Prior work has highlighted the ability of these neurons to increase sympathetic tone, hence peripheral catecholamine release, probably via their direct excitatory projections to sympathetic preganglionic neurons. In this study, we use channelrhodopsin-2 (ChR2) optogenetics to test whether the C1 cells are also capable of broadly activating the brain's noradrenergic system. We selectively expressed ChR2(H134R) in rostral VLM catecholaminergic neurons by injecting Cre-dependent adeno-associated viral vectors into the brain of adult dopamine-ß-hydroxylase (DßH)(Cre/0) mice. Most ChR2-expressing VLM neurons (75%) were immunoreactive for phenylethanolamine N-methyl transferease, thus were C1 cells, and most of the ChR2-positive axonal varicosities were immunoreactive for vesicular glutamate transporter-2 (78%). We produced light microscopic evidence that the axons of rostral VLM (RVLM) catecholaminergic neurons contact locus coeruleus, A1, and A2 noradrenergic neurons, and ultrastructural evidence that these contacts represent asymmetric synapses. Using optogenetics in tissue slices, we show that RVLM catecholaminergic neurons activate the locus coeruleus as well as A1 and A2 noradrenergic neurons monosynaptically by releasing glutamate. In conclusion, activation of RVLM catecholaminergic neurons, predominantly C1 cells, by somatic or psychological stresses has the potential to increase the firing of both peripheral and central noradrenergic neurons.

Relationship between noradrenaline release in the locus coeruleus and antiallodynic efficacy of analgesics in rats with painful diabetic neuropathy.

AIMS: In animal models of neuropathic pain, the noradrenergic descending pain inhibitory pathways from the locus coeruleus (LC) may be suppressed. However, no study has investigated the correlation between noradrenaline (NA) release in the LC and efficacy of analgesics in rats with painful diabetic neuropathy. Using microdialysis and analysis of mechanical hypersensitivity, we investigated the correlation between NA release in the LC and efficacy of morphine, tramadol, and clomipramine in rats with diabetic mellitus (DM). MAIN METHODS: In freely moving rats, basal NA concentrations in LC perfusate were quantitated 72 to 96 h after microdialysis probe implantation. Following intravenous administration of each drug, NA concentrations were expressed as a percentage of basal values. We concurrently measured the threshold to elicit a paw withdrawal response every 20 min for 80 min. KEY FINDINGS: NA concentrations in the LC perfusate were significantly higher in the tramadol and clomipramine groups compared to the morphine group. Naloxone administration did not significantly affect NA concentrations. In the morphine group, NA release in the LC was not significantly correlated with the pain threshold. In contrast, in the tramadol and clomipramine groups, NA release in the LC was significantly correlated with the pain threshold. The correlation coefficient was higher in the clomipramine group than in the tramadol group. SIGNIFICANCE: Our results suggest that the descending noradrenergic pathway can play an important role in analgesia for DM neuropathy and that there is a significant correlation between NA release in the LC and the efficacy of tramadol and clomipramine.

The norepinephrine transporter (NET) radioligand (S,S)-[18F]FMeNER-D2 shows significant decreases in NET density in the human brain in Alzheimer's disease: a post-mortem autoradiographic study.

Earlier post-mortem histological and autoradiographic studies have indicated a reduction of cell numbers in the locus coeruleus (LC) and a corresponding decrease in norepinephrine transporter (NET) in brains obtained from Alzheimer's disease (AD) patients as compared to age-matched healthy controls. In order to test the hypothesis that the regional decrease of NET is a disease specific biomarker in AD and as such, it can be used in PET imaging studies for diagnostic considerations, regional differences in the density of NET in various anatomical structures were measured in whole hemisphere human brain slices obtained from AD patients and age-matched control subjects in a series of autoradiographic experiments using the novel selective PET radioligand for NET (S,S)-[(18)F]FMeNER-D(2). (S,S)-[(18)F]FMeNER-D(2) appears to be a useful imaging biomarker for quantifying the density of NET in various brain structures, including the LC and the thalamus wherein the highest densities are found in physiological conditions. In AD significant decreases of NET densities can be demonstrated with the radioligand in both structures as compared to age-matched controls. The decreases in AD correlate with the progress of the disease as indicated by Braak grades. As the size of the LC is below the spatial resolution of the PET scanners, but the size of the thalamus can be detected with appropriate spatial accuracy in advanced scanners, the present findings confirm our earlier observations with PET that the in vivo imaging of NET with (S,S)-[(18)F]FMeNER-D(2) in the thalamus is viable. Nevertheless, further studies are warranted to assess the usefulness of such an imaging approach for the early detection of changes in thalamic NET densities as a disease-specific biomarker and the possible use of (S,S)-[(18)F]FMeNER-D(2) as a molecular imaging biomarker in AD.

Visualization of neuromelanin in the Substantia nigra and locus ceruleus at 1.5T using a 3D-gradient echo sequence with magnetization transfer contrast.

Recent technical advances have enabled the visualization of neuromelanin in the substantia nigra pars compacta (SNc) and locus ceruleus (LC) by 3-tesla (T) magnetic resonance imaging in vivo. In the present study, we successfully detected neuromelanin in the SNc and LC of 6 healthy volunteers at 1.5T using a 3D gradient echo sequence with off-resonance magnetization transfer contrast.

Dynorphin and stress-related peptides in rat locus coeruleus: contribution of amygdalar efferents.

The interaction between the stress axis and endogenous opioid systems has gained substantial attention, because it is increasingly recognized that stress alters individual sensitivity to opiates. One site at which opiates and stress substrates may interact to have global effects on behavior is within the locus coeruleus (LC). We have previously described interactions of several opioid peptides [e.g., proopiomelanocortin, enkephalin (ENK)] with the stress-related peptide corticotropin-releasing factor (CRF) in the LC. To examine further the interactions among dynorphin (DYN), ENK, and CRF in the LC, sections were processed for detection of DYN and CRF or DYN and ENK in rat brain. DYN- and CRF-containing axon terminals overlapped noradrenergic dendrites in this region. Dual immunoelectron microscopy showed coexistence of DYN and CRF; 35% of axon terminals containing DYN were also immunoreactive for CRF. In contrast, few axon terminals contained both DYN and ENK. A potential DYN/CRF afferent is the central nucleus of the amygdala (CeA). Dual in situ hybridization showed that, in CeA neurons, 31% of DYN mRNA-positive cells colocalized with CRF mRNA, whereas 53% of CRF mRNA-containing cells colocalized with DYN mRNA. Finally, to determine whether limbic DYN afferents target the LC, the CeA was electrolytically lesioned. Light-level densitometry of DYN labeling in the LC showed a significant decrease in immunoreactivity on the side of the lesion. Taken together, these data indicate that DYN- and CRF-labeled axon terminals, most likely arising from amygdalar sources, are positioned dually to affect LC function, whereas DYN and ENK function in parallel.

Glutamate signaling proteins and tyrosine hydroxylase in the locus coeruleus of alcoholics.

It has been postulated that alcoholism is associated with abnormalities in glutamatergic neurotransmission. This study examined the density of glutamate NMDA receptor subunits and its associated proteins in the noradrenergic locus coeruleus (LC) in deceased alcoholic subjects. Our previous research indicated that the NMDA receptor in the human LC is composed of obligatory NR1 and regulatory NR2C subunits. At synapses, NMDA receptors are stabilized through interactions with postsynaptic density protein (PSD-95). PSD-95 provides structural and functional coupling of the NMDA receptor with neuronal nitric oxide synthase (nNOS), an intracellular mediator of NMDA receptor activation. LC tissue was obtained from 10 alcohol-dependent subjects and eight psychiatrically healthy controls. Concentrations of NR1 and NR2C subunits, as well as PSD-95 and nNOS, were measured using Western blotting. In addition, we have examined tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of norepinephrine. The amount of NR1 was lower in the rostral (-30%) and middle (-41%) portions of the LC of alcoholics as compared to control subjects. No differences in the amounts of NR2C, PSD-95, nNOS and TH were detected comparing alcoholic to control subjects. Lower levels of NR1 subunit of the NMDA receptor in the LC implicates altered glutamate-norepinephrine interactions in alcoholism.

Effects of (-)-epigallocatechin gallate on the development of morphine-induced physical dependence.

Among the various nervous systems and signaling components involved in the development of morphine withdrawal symptoms, sensitization of the brain dopaminergic nervous system and an increase in the cAMP levels in the locus coeruleus are believed to be the most important cellular events. This study tested the effects of (-)-epigallocatechin gallate (EGCG), a major compound of green tea, on the development of morphine-induced withdrawal symptoms. All the naloxone-precipitated withdrawal symptoms in morphine-dependent animals were inhibited by an EGCG pretreatment in a dose-dependent manner, being forepaw tremor, rearing, teeth chattering, urination, and wet dog shake were more sensitive than jumping and ptosis. In addition, EGCG showed moderate inhibitory effects on the morphine-induced increase in the cAMP levels in the locus coeruleus at 100 mg/kg and the signaling of the dopamine D2 receptor at 100 microM. Effects of EGCG on the sequestration of D2 receptor were inconclusive. These results suggest that EGCG has strong pharmacological activity against the development of morphine dependence, which can be partly explained by its inhibitory effects on the morphine-induced increase in the cAMP levels in the locus coeruleus and the signaling of the dopamine D2 receptor.

Neuromelanin and iron in human locus coeruleus and substantia nigra during aging: consequences for neuronal vulnerability.

In this study a comparative analysis of iron molecules during aging was performed in locus coeruleus (LC) and substantia nigra (SN), known targets of Parkinson's Disease (PD) and related disorders. LC and SN neurons, especially the SN pars compacta, degenerate in PD and other forms of parkinsonism. Iron and its major molecular forms, such as ferritin and neuromelanin (NM), were measured in LC and SN of normal subjects at various ages. Iron levels were lower, H-ferritin/iron ratio was higher and the iron content in NM was lower in LC than in SN. Iron deposits were abundant in SN tissue, very scarse in LC tissue and completely absent in pigmented neurons of both SN and LC. In both regions H- and L-ferritins were present only in glia. This suggests that in LC neurons iron mobilization and toxicity is lower than that in SN and is efficiently buffered by NM. Ferritins accomplish the same buffering function in glial cells.

Compensatory changes in the noradrenergic nervous system in the locus ceruleus and hippocampus of postmortem subjects with Alzheimer's disease and dementia with Lewy bodies.

In Alzheimer's disease (AD), there is a significant loss of locus ceruleus (LC) noradrenergic neurons. However, functional and anatomical evidence indicates that the remaining noradrenergic neurons may be compensating for the loss. Because the noradrenergic system plays an important role in learning and memory, it is important to determine whether compensation occurs in noradrenergic neurons in the LC and hippocampus of subjects with AD or a related dementing disorder, dementia with Lewy bodies (DLB). We observed profound neuronal loss in the LC in AD and DLB subjects with three major changes in the noradrenergic system consistent with compensation: (1) an increase in tyrosine hydroxylase (TH) mRNA expression in the remaining neurons; (2) sprouting of dendrites into peri-LC dendritic zone, as determined by alpha2-adrenoreceptors (ARs) and norepinephrine transporter binding sites; and (3) sprouting of axonal projections to the hippocampus as determined by alpha2-ARs. In AD and DLB subjects, the postsynaptic alpha1-ARs were normal to elevated. Expression of alpha1A- and alpha2A-AR mRNA in the hippocampus of AD and DLB subjects were not altered, but expression of alpha1D- and alpha2C-AR mRNA was significantly reduced in the hippocampus of AD and DLB subjects. Therefore, in AD and DLB subjects, there is compensation occurring in the remaining noradrenergic neurons, but there does appear to be a loss of specific AR in the hippocampus. Because changes in these noradrenergic markers in AD versus DLB subjects were similar (except neuronal loss and the increase in TH mRNA were somewhat greater in DLB subjects), the presence of Lewy bodies in addition to plaques and tangles in DLB subjects does not appear to further affect the noradrenergic compensatory changes.

Locus coeruleus and neuronal plasticity in a model of focal limbic epilepsy.

PURPOSE: A lesion of the noradrenergic nucleus Locus Coeruleus (LC) converts sporadic seizures evoked by microinfusion of bicuculline into the anterior piriform cortex (APC) of rats into limbic status epilepticus (SE). The purpose of this study was to evaluate the chronic effects of this new model of SE on the onset of secondary epileptogenesis. We further related the loss of noradrenaline (NE) with hippocampal mossy fiber sprouting. METHODS: Male Sprague Dawley rats were treated with systemic saline or DSP-4 (a neurotoxin selective for noradrenergic terminals originating from the LC), microinfused with bicuculline into the APC three days later, and sacrificed after 45 days. Naïve and DSP-4 pretreated sham-operated rats served as respective controls. The following evaluations were performed: (a) monitoring of acute seizures and delayed occurrence of spontaneous recurrent seizures (SRS); (b) NE levels in the hippocampus, frontal and olfactory cortex; (c) occurrence of mossy fiber sprouting into the inner molecular layer of the dentate gyrus of the dorsal hippocampus. RESULTS: In 30% of rats lacking noradrenergic terminals, SE evoked from the APC was followed by SRS. Conversely, seizures evoked in intact rats did not result in chronic epileptogenesis. Seizures/SE did not modify NE levels as compared with baseline levels both in naïve and DSP-4-pretreated rats. Rats undergoing SE following DSP-4 + bicuculline developed SRS which were accompanied by hippocampal mossy fiber sprouting. CONCLUSIONS: Noradrenergic loss converts focally induced sporadic seizures into an epileptogenic SE, which is accompanied by mossy fiber sprouting within the dentate gyrus.

Patterns of neuronal activation in the rat brain and spinal cord in response to increasing durations of restraint stress.

By most accounts the psychological stressor restraint produces a distinct pattern of neuronal activation in the brain. However, some evidence is incongruous with this pattern, leading us to propose that the restraint-induced pattern in the central nervous system might depend on the duration of restraint used. We therefore determined the pattern of neuronal activation (as indicated by the presence of Fos protein) seen in the paraventricular nucleus (PVN), bed nucleus of the stria terminalis, amygdala, locus coeruleus, nucleus tractus solitarius (NTS), ventrolateral medulla (VLM) and thoracic spinal cord of the rat in response to 0, 15, 30 or 60 min periods of restraint. We found that although a number of cell groups displayed a linear increase in activity with increasing durations of restraint (e.g. hypothalamic corticotrophin-releasing factor (CRF) cells, medial amygdala neurons and sympathetic preganglionic neurons of the thoracic spinal cord), a number of cell groups did not. For example, in the central amygdala restraint produced both a decrease in CRF cell activity and an increase in non-CRF cell activity. In the locus coeruleus, noradrenergic neurons did not display Fos in response to 15 min of restraint, but were significantly activated by 30 or 60 min restraint. After 30 or 60 min restraint a greater degree of activation of more rostral A1 noradrenergic neurons was observed compared with the pattern of A1 noradrenergic neurons in response to 15 min restraint. The results of this study demonstrate that restraint stress duration determines the amount and the pattern of neuronal activation seen in response to this psychological stressor.