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.

Urethral musculature and innervation in the female rat.

AIMS: The urethral sphincter and urethral muscle innervation are critically involved in maintaining continence, especially in the female. However, the urethral muscle type and distribution, as well as the urethral nerves are far from being well documented. Our aim was to clearly identify the distribution of urethral striated muscle, smooth muscle, and urethral nerves. METHODS: In a cohort analysis of 3-month-old female Sprague-Dawley rats, cross and longitudinal sections of female rat urethra were extensively investigated using morphological techniques. Urethras were harvested to the sections, in order to provide both global and detailed visions of the urethra. H&E, Masson's Trichrome, phalloidin and immunoflourence stains were used. The cytoarchitecture, nitrergic, and cholinergic innervations were mainly investigated. Different layers of the segments of urethra were traced to draw curve graphs that represent the thickness of each muscle layer of urethral wall. RESULTS: The results showed that the primary peak of striated muscle is in the middle urethra. The inner layer close to mucosa was found to contain longitudinal smooth muscle. Near the bladder orifice, the circular smooth muscle dominates, which becomes thinner distally throughout the rest of urethra. In the middle urethra the vast majority of the urethral muscle are circularly oriented striated muscle cells. Typical nerve endings were present in high power images to show the different characteristic features of nerve innervation. CONCLUSIONS: This study has illustrated the detailed morphological structure and innervations of the normal female rat urethra and can serve as a basis for further study of stress urinary incontinence (SUI).

Immunohistochemical Characterization of Sympathetic Chain Ganglia (SChG) Neurons Supplying the Porcine mammary Gland.

The aim of this study was to investigate the chemical coding of mammary gland-projecting SChG neurons using double-labelling immunohistochemistry. Earlier observation showed that after injection of the retrograde tracer fast blue (FB) into the second, right thoracic mamma, FB+ mammary gland-projecting neurons were found in Th1-3, Th9-14 and L1-4 right SChG. The greatest number of FB+ nerve cell bodies was observed in Th10 (approx. 843) and Th11 (approx. 567). Neurons projecting to the last right abdominal mamma were found in L1-4 SChG. The greatest number of FB+ neurons was observed in L2 (approx. 1200). Immunohistochemistry revealed that the vast majority of FB+ mammary-projecting neurons contained immunoreactivities to TH (96.97%) and/or DßH (95.92%). Many TH/DßH-positive neurons stained for SOM (41.5%) or NPY (33.2%), and less numerous nerve cells expressed VIP (16.9%). This observation strongly corresponds to the results of previous studies concerning the immunohistochemical characterization of nerve fibres supplying the porcine mammary gland.

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.

Distribution of adrenergic and cholinergic nerve fibres within intrinsic nerves at the level of the human heart hilum.

OBJECTIVES: The disbalance between adrenergic (sympathetic) and cholinergic (parasympathetic) cardiac inputs facilitates cardiac arrhythmias, including the lethal ones. In spite of the fact that the morphological pattern of the epicardiac ganglionated subplexuses (ENsubP) has been previously described in detail, the distribution of functionally distinct axons in human intrinsic nerves was not investigated thus far. Therefore, the aim of the present study was to quantitatively evaluate the distribution of tyrosine hydroxylase (TH)- and choline acetyltransferase (ChAT)-positive axons within intrinsic nerves at the level of the human heart hilum (HH), since they are of pivotal importance for determining proper treatment options for different arrhythmias. METHODS: Tissue samples containing the intrinsic nerves from seven epicardiac subplexuses were obtained from nine human hearts without cardiac pathology and processed for immunofluorescent detection of TH and ChAT. The nerve area was measured and the numbers of axons were counted using microphotographs of nerve profiles. The densities of fibres were extrapolated and compared between subplexuses. RESULTS: ChAT-immunoreactive (IR) fibres were evidently predominant (>56%) in nerves of dorsal (DRA) and ventral right atrial (VRA) ENsubP. Within both left (LC) and right coronary ENsubP, the most abundant (70.9 and 83.0%, respectively) were TH-IR axons. Despite subplexal dependence, ChAT-IR fibres prevailed in comparatively thinner nerves, whereas TH-IR fibres in thicker ones. Morphometry showed that at the level of HH: (i) LC subplexal nerves were found to be the thickest (25 737 ± 4131 µm(2)) ones, whereas the thinnest (2604 ± 213 µm(2)) nerves concentrated in DRA ENsubP; (ii) the density of ChAT-IR axons was highest (6.8 ± 0.6/100 µm(2)) in the ventral left atrial nerves and lowest (3.2 ± 0.1/100 µm(2)) in left dorsal ENsubP and (iii) the density of TH-IR fibres was highest (15.9 ± 2.1/100 µm(2)) in LC subplexal nerves and lowest (4.4 ± 0.3/100 µm(2)) in VRA nerves. CONCLUSIONS: (i) The principal intrinsic adrenergic neural pathways in the human heart proceed via both coronary ENsubP that supply cardiac ventricles and (ii) the majority of cholinergic nerve fibres access the human heart through DRA and VRA ENsubP and extend towards the right atrium, including the region of the sinuatrial node.

Coordinate regulation of noradrenergic and serotonergic brain regions by amygdalar neurons.

Based on the importance of the locus coeruleus-norepinephrine (LC-NE) system and the dorsal raphe nucleus-serotonergic (DRN-5-HT) system in stress-related pathologies, additional understanding of brain regions coordinating their activity is of particular interest. One such candidate is the amygdalar complex, and specifically, the central nucleus (CeA), which has been implicated in emotional arousal and is known to send monosynaptic afferent projections to both these regions. Our present data using dual retrograde tract tracing is the first to demonstrate a population of amygdalar neurons that project in a collateralized manner to the LC and DRN, indicating that amygdalar neurons are positioned to coordinately regulate the LC and DRN, and links these brain regions by virtue of a common set of afferents. Further, we have also characterized the phenotype of a population of these collaterally projecting neurons from the amygdala as containing corticotropin releasing factor or dynorphin, two peptides heavily implicated in the stress response. Understanding the co-regulatory influences of this limbic region on 5HT and NE regions may help fill a gap in our knowledge regarding neural circuits impacting these systems and their adaptations in stress.

Changes with aging in the dopaminergic and noradrenergic innervation of rat neocortex.

In normal aging, the mammalian cortex undergoes significant remodeling. Although neuromodulation by dopamine and noradrenaline in the cortex is known to be important for proper cognitive function, little is known on how cortical noradrenergic and dopaminergic presynaptic boutons are affected in normal aging. Using rats we investigated whether these two neurotransmitter systems undergo structural reorganization in aging, and if these changes correlated with cognitive loss. Young and aged rats were tested for cognitive performance using the Morris water maze. Following the behavioral characterization, the animals were sacrificed and the cortical tissue was processed for immunofluorescence using antibodies directed against tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) to detect and discriminate noradrenergic and dopaminergic varicosities. We observed a significant increase in dopaminergic varicosities in lamina V of the anterior cingulate cortex (ACC) of aged cognitively unimpaired rats when compared to young and aged-impaired animals. In laminae II and III of the ACC, we observed a significant decrease of dopaminergic varicosities in aged-impaired animals when compared to young or aged cognitively unimpaired animals. Changes in noradrenergic varicosities never reached statistical significance in any group or brain region. The data suggests that the remodeling of mesocortical dopaminergic fibers may participate in age-associated cognitive decline.