Forebrain GABAergic projections to locus coeruleus in mouse

Abstract

The noradrenergic locus coeruleus (LC) regulates arousal, memory, sympathetic nervous system activity and pain. Forebrain projections to LC have been characterized in rat, cat and primates, but not systematically in mouse. We surveyed mouse forebrain LC projecting neurons by examining retrogradely labeled cells following LC iontophoresis of fluorogold and anterograde LC labeling after forebrain injection of biotinylated dextran-amine or viral tracer. Similar to other species, the central amygdalar nucleus (CAmy), anterior hypothalamus, paraventricular nucleus, and posterior lateral hypothalamic area (PLH) provide major LC inputs. Using mice expressing green fluorescent protein in GABAergic neurons we found that more than one.third of LC projecting CAmy and PLH neurons are GABAergic. LC colocalization of biotinylated dextran-amine, following CAmy or PLH injection, with either green fluorescent protein or GAD65/67-ir confirmed these GABAergic projections. CAmy injection of adeno.associated virus encoding channelrhodopsin-2-Venus showed similar fiber labeling and association with GAD65/67-ir and tyrosine hydroxylase-ir (TH-ir) neurons. CAmy and PLH projections were densest in a peri-coerulear zone, but many fibers entered the LC proper. Close apposition between CAmy GABAergic projections and TH-ir processes suggests CAmy GABAergic neurons may directly inhibit noradrenergic principal neurons. Direct LC neuron targeting was confirmed by anterograde transneuronal labeling of LC TH-ir neurons following CAmy or PLH injection of a herpes virus that expresses red fluorescent protein following activation by Cre recombinase in mice that express Cre recombinase in GABergic neurons. This description of GABAergic projections from CAmy and PLH to the LC clarifies important forebrain sources of inhibitory control of CNS noradrenergic activity.

Pain exacerbates chronic mild stress-induced changes in noradrenergic transmission in rats

“…Although the absolute number of TH-IR neurons increased in CMS animals, our electrophysiological data revealed a decrease in their activity, a finding that should be confirmed in further studies measuring noradrenaline levels in the LC and projection areas (frontal cortex and spinal cord) in basal and evoked conditions (after a painful or stressful event). Furthermore, we detected no changes in NAT or α2-adrenoceptor expression, indicating that the changes observed in spontaneous activity are probably caused by another neurotransmitter, possibly GABA (Bravo et al, 2013;Dimitrov et al, 2013).…”

Angiotensin Type-2 Receptors Influence the Activity of Vasopressin Neurons in the Paraventricular Nucleus of the Hypothalamus in Male Mice

“…Additionally, liquid-phase radioimmunoassay (RIA) was used to determine that anti-OT-NP (PS-38) is highly-specific for the OT-NP complex and does not cross-react with AVP-NP, while the anti-AVP-NP (PS-41) reacts with AVP-NP exclusively. Furthermore, as in (21,24), the specificity of the rabbit polyclonal antibody against FluoroGold (FG) was corroborated by the lack of staining on sections originating from mice without FG treatment. Unless otherwise stated, all secondary antibodies were purchased from Jackson Immunoresearch (Westgorve, PA), raised in donkey and used at a 1:500 dilution.…”

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

“…6E). This non-selective retrograde tracing approach revealed known inputs into the LC from the cortex, hypothalamus, and central amygdala - a source of extrahypothalamic CRH (Bouret et al, 2003; Dimitrov et al, 2013; Reyes et al, 2008) (Fig. 6F, Fig.…”