Effects Of Norepinephrine Depletion Research Articles

Opposing effects of β-2 and β-1 adrenergic receptor signaling on neuroinflammation and dopaminergic neuron survival in α-synuclein-mediated neurotoxicity

BackgroundNoradrenergic neurons in the locus coeruleus (LC) are the primary source of norepinephrine (NE) in the brain and degeneration of these neurons is reported in the early stages of Parkinson’s disease (PD), even prior to dopaminergic neuron degeneration in the substantia nigra (SN), which is a hallmark of PD pathology. NE depletion is generally associated with increased PD pathology in neurotoxin-based PD models. The effect of NE depletion in other models of PD-like α-synuclein-based models is largely unexplored. In PD models and in human patients, β-adrenergic receptors’ (AR) signaling is associated with a reduction of neuroinflammation and PD pathology. However, the effect of NE depletion in the brain and the extent of NE and β-ARs signaling involvement in neuroinflammation, and dopaminergic neuron survival is poorly understood.MethodsTwo mouse models of PD, a 6OHDA neurotoxin-based model and a human α-synuclein (hα-SYN) virus-based model of PD, were used. DSP-4 was used to deplete NE levels in the brain and its effect was confirmed by HPLC with electrochemical detection. A pharmacological approach was used to mechanistically understand the impact of DSP-4 in the hα-SYN model of PD using a norepinephrine transporter (NET) and a β-AR blocker. Epifluorescence and confocal imaging were used to study changes in microglia activation and T-cell infiltration after β1-AR and β2-AR agonist treatment in the hα-SYN virus-based model of PD.ResultsConsistent with previous studies, we found that DSP-4 pretreatment increased dopaminergic neuron loss after 6OHDA injection. In contrast, DSP-4 pretreatment protected dopaminergic neurons after hα-SYN overexpression. DSP-4-mediated protection of dopaminergic neurons after hα-SYN overexpression was dependent on β-AR signaling since using a β-AR blocker prevented DSP-4-mediated dopaminergic neuron protection in this model of PD. Finally, we found that the β-2AR agonist, clenbuterol, reduced microglia activation, T-cell infiltration, and dopaminergic neuron degeneration, whereas xamoterol a β-1AR agonist showed increased neuroinflammation, blood brain barrier permeability (BBB), and dopaminergic neuron degeneration in the context of hα-SYN-mediated neurotoxicity.ConclusionsOur data demonstrate that the effects of DSP-4 on dopaminergic neuron degeneration are model specific, and suggest that in the context of α-SYN-driven neuropathology, β2-AR specific agonists may have therapeutic benefit in PD.

Biogenic amines in the hypothalamus of rats after diethyldithiocarbamate or AIMAX treatment, an alternative for norepinephrine depletion1

The objective of this study was to determine whether AIMAX (a dithiocarbamoylhydrazine derivative) is suitable for determining the effects of norepinephrine (NE) depletion on reproduction in domestic animals. Therefore, the effect of AIMAX (n = 6) on concentrations of biogenic amines in the medial basal hypothalamus (MBH) and anterior hypothalamic area (AHA) of ovariectomized (OVX) rats primed with ovarian steroids was compared to that of diethyldithiocarbamate (DDC; n = 5), a potent dopamine-beta-hydroxylase (DBH) inhibitor, which is chemically similar to AIMAX. Rats that received only ovarian steroids and saline injections served as controls (n = 6). Treatment with DDC resulted in sedation and reduced body temperature. In contrast, rats behaved normally after AIMAX treatment. AI-MAX reduced (P < .05) NE but increased (P < .05) dopamine (DA) concentrations in MBH and AHA compared with controls. Similar changes in NE and DA concentrations were observed in DDC-treated rats. However, elevated epinephrine (EPI) levels were measured in MBH and AHA of only DDC-treated rats. Serum LH concentrations were suppressed (P < .005) in both AIMAX- and DDC-treated rats compared with control animals. Because AIMAX, like DDC, suppressed hypothalamic NE content and LH secretion, AIMAX should be useful in studying effects of NE depletion on gonadotropin secretion in domestic animals.

Effect of norepinephrine depletion on audiogenic-like seizures elicited by microinfusion of an excitant amino acid into the inferior colliculus of normal rats

Infusions of an excitant amino acid, N-methyl- d-aspartate (NMDA) into the inferior colliculus (IC) render normal rats susceptible to audiogenic seizures (AGS) and/or spontaneous audiogenic-like seizures without tonic components. The excess excitant amino acid in the IC and the anticonvulsant effects of NMDA antagonists in genetically epilepsy-prone rats (GEPRs), along with innate norepinephrine (NE) deficits and anticonvulsant effects of NE agonists in these animals suggest a mutual role of excitant amino acids and NE in regulating AGS in GEPRs. Saline or 6-hydroxydopamine (6-OHDA, 4 μg/side in 2 μl) was infused bilaterally into the locus coeruleus (LC) of normal male rats and guide cannulas were implanted into the IC. Two weeks later, NMDA was infused bilaterally into the IC (0.5 μl; 10 nmol/side) and 10 min later the rats were subjected to an electric bell (110 db, 60 s) unless preceded by spontaneous tonic seizures. Tonic seizures were not observed in male rats following NMDA infusions in rats with LC infusions of saline. However, a marked increase in the incidence of tonic seizures was observed in the 6-OHDA-treated rats which were markedly depleted of brain NE as determined by HPLC. These findings indicate that a NE deficit greatly enhances the incidence of tonic convulsions and support the hypothesis that an excitant amino acid excess in the GEPR IC may act to initiate AGS, whereas the NE deficit may allow expression of the tonic components of AGS seen in some GEPRs.

Kindling-based status epilepticus: Effect of norepinephrine depletion with 6-hydroxydopamine

In two experiments, involvement of norepinephrine in the development of status epilepticus was determined. Rats, pretreated with intraventricular 6-hydroxydopamine to deplete brain norepinephrine or with the saline vehicle alone, were implanted with electrodes in both amygdalae. In the first experiment, one amygdala was kindled to stage 5 levels and then 2 weeks later was stimulated continously for 60 min in an effort to produce status epilepticus (SE), while in the second experiment such SE stimulation was applied to one amygdala without prior kindling. Although depletion of norepinephrine significantly facilitated amygdala kindling in experiment 1, it had no clear effect on the probability of developing SE (generalized, partial, or nonconvulsive) or on the distribution of gross brain pathology following spontaneous recovery from partial and nonconvulsive SE in either experiment. The significance of these results compared to other SE models was discussed.

The effects of norepinephrine depletion on cerebral blood flow in the rat

Cerebral blood flow (CBF) was measured by [ 14C]butanol indicator fractionation in 10 rats given intraventricular injections of 6-hydroxydopamine (6-OHDA) compared to 8 saline-injected controls. Rats treated with 6-OHDA displayed an 83% reduction in cortical norepinephrine (NE) levels. CBF was significantly increased in 6-OHDA-treated rats compared to controls (average whole brain blood flow of 126.0 ± 8.3 and 97.1 ± 10.6 ml·min −1·10 −2g −1 respectively, P<0.05). These studies suggest that noradrenergic innervation of the brain and cerebral microvasculature exerts a moderating effect on resting CBF.

Effect of paraventricular nucleus lesions on body weight, food intake and insulin levels

Lesions of the paraventricular nucleus of the hypothalamus (PVN) produce obesity and hyperphagia. However, the underlying mechanism is unknown. The connections of the PVN with brainstem centers for autonomic control suggest that a change in autonomic function could mediate the PVN obesity syndrome. We examined this hypothesis in a series of 3 experiments, searching specifically for changes in insulin secretion. Rats with PVN lesions were hyperphagic and hyperinsulinemic, when obese. However, hyperinsulinemia could not be detected prior to the onset of obesity or following weight reduction. Subdiaphragmatic vagotomy reversed the PVN obesity and lowered insulin levels below those of sham-vagotomized rats. Since noradrenergic innervation of the hypothalamus is implicated in feeding, hypothalamic norepinephrine (NE) was depleted by injection of 6-hydroxydopamine into the central tegmental tract, posterior to the hypothalamus. The effects of NE depletion was compared with those of PVN lesions. Loss of hypothalamic NE resulted in hyperphagia with no increase in body weight and no change in insulin. Histological analyses indicated that the posterior PVN was the most effective lesion focus for producing disturbances in body weight and food intake. Although the results of these experiments implicate the autonomic nervous system in PVN obesity, basal hyperinsulinemia does not appear to be a primary feature of the syndrome.

Does endogenous norepinephrine regulate potassium homeostasis and metabolism in rat cerebral cortex?

The role of endogenous cerebral norepinephrine (NE) as a modulator of transmembrane cation transport and energy metabolism was evaluated by monitoring extracellular potassium ion activity ([K+[o) in vivo and by measuring cortical Na+,K+-ATPase activity and oxygen consumption in vitro. Ipsilateral cortical NE was depleted by unilateral 6-hydroxydopamine (6-OHDA) lesions of the locus ceruleus (LC). The contralateral cortex was used for control measurements. NE depletion had no effect on resting levels of cortical [K+[o or on the rate of K+ removal from the extracellular space following direct cortical stimulation. There was also no effect of NE depletion on Na+,K+-ATPase activity in cortical homogenates nor on oxygen consumption of cortical slices over a wide range of K+ concentrations. These results indicate tht central NE depletion does not influence movements of cortical K+ either directly through an influence on Na+,K+-ATPase activity or indirectly through effects on oxidative metabolism. It is probable, therefore, that previously described effects of NE on cortical oxidative metabolism are mediated through changes in cerebral perfusion and/or modification of substrate availability in vivo.

Cerebral norepinephrine: influence on cortical oxidative metabolism in situ.

Unilateral lesion of the locus coeruleus and the resultant norepinephrine depletion in the ipsilateral cerebrum alters the relationship between cerebral metabolic demands and local delivery of oxygen and substrates. This effect of norepinephrine depletion is demonstrated by slower recovery of the redox ratio of cytochrome a,a3 during increased metabolic demands induced by local cortical stimulation.