Karen S. Rommelfanger

Norepinephrine loss produces more profound motor deficits than MPTP treatment in mice

Although Parkinsons disease (PD) is characterized primarily by loss of nigrostriatal dopaminergic neurons, there is a concomitant loss of norepinephrine (NE) neurons in the locus coeruleus. Dopaminergic lesions induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) are commonly used to model PD, and although MPTP effectively mimics the dopaminergic neuropathology of PD in mice, it fails to produce PD-like motor deficits. We hypothesized that MPTP is unable to recapitulate the motor abnormalities of PD either because the behavioral paradigms used to measure coordinated behavior in mice are not sensitive enough or because MPTP in the absence of NE loss is insufficient to impair motor control. We tested both possibilities by developing a battery of coordinated movement tests and examining motor deficits in dopamine β-hydroxylase knockout (Dbh−/−) mice that lack NE altogether. We detected no motor abnormalities in MPTP-treated control mice, despite an 80% loss of striatal dopamine (DA) terminals. Dbh−/− mice, on the other hand, were impaired in most tests and also displayed spontaneous dyskinesias, despite their normal striatal DA content. A subset of these impairments was recapitulated in control mice with 80% NE lesions and reversed in Dbh−/− mice, either by restoration of NE or treatment with a DA agonist. MPTP did not exacerbate baseline motor deficits in Dbh−/− mice. Finally, striatal levels of phospho-ERK-1/2 and ΔFosB/FosB, proteins which are associated with PD and dyskinesias, were elevated in Dbh−/− mice. These results suggest that loss of locus coeruleus neurons contributes to motor dysfunction in PD.

α2-adrenoceptor blockade accelerates the neurogenic, neurotrophic, and behavioral effects of chronic antidepressant treatment

Slow-onset adaptive changes that arise from sustained antidepressant treatment, such as enhanced adult hippocampal neurogenesis and increased trophic factor expression, play a key role in the behavioral effects of antidepressants. α2-Adrenoceptors contribute to the modulation of mood and are potential targets for the development of faster acting antidepressants. We investigated the influence of α2-adrenoceptors on adult hippocampal neurogenesis. Our results indicate that α2-adrenoceptor agonists, clonidine and guanabenz, decrease adult hippocampal neurogenesis through a selective effect on the proliferation, but not the survival or differentiation, of progenitors. These effects persist in dopamine β-hydroxylase knock-out (Dbh−/−) mice lacking norepinephrine, supporting a role for α2-heteroceptors on progenitor cells, rather than α2-autoreceptors on noradrenergic neurons that inhibit norepinephrine release. Adult hippocampal progenitors in vitro express all the α2-adrenoceptor subtypes, and decreased neurosphere frequency and BrdU incorporation indicate direct effects of α2-adrenoceptor stimulation on progenitors. Furthermore, coadministration of the α2-adrenoceptor antagonist yohimbine with the antidepressant imipramine significantly accelerates effects on hippocampal progenitor proliferation, the morphological maturation of newborn neurons, and the increase in expression of brain derived neurotrophic factor and vascular endothelial growth factor implicated in the neurogenic and behavioral effects of antidepressants. Finally, short-duration (7 d) yohimbine and imipramine treatment results in robust behavioral responses in the novelty suppressed feeding test, which normally requires 3 weeks of treatment with classical antidepressants. Our results demonstrate that α2-adrenoceptors, expressed by progenitor cells, decrease adult hippocampal neurogenesis, while their blockade speeds up antidepressant action, highlighting their importance as targets for faster acting antidepressants.

Extrastriatal dopaminergic circuits of the Basal Ganglia.

The basal ganglia are comprised of the striatum, the external and internal segment of the globus pallidus (GPe and GPi, respectively), the subthalamic nucleus (STN), and the substantia nigra pars compacta and reticulata (SNc and SNr, respectively). Dopamine has long been identified as an important modulator of basal ganglia function in the striatum, and disturbances of striatal dopaminergic transmission have been implicated in diseases such as Parkinsons disease (PD), addiction and attention deficit hyperactivity disorder. However, recent evidence suggests that dopamine may also modulate basal ganglia function at sites outside of the striatum, and that changes in dopaminergic transmission at these sites may contribute to the symptoms of PD and other neuropsychiatric disorders. This review summarizes the current knowledge of the anatomy, functional effects and behavioral consequences of the dopaminergic innervation to the GPe, GPi, STN, and SNr. Further insights into the dopaminergic modulation of basal ganglia function at extrastriatal sites may provide us with opportunities to develop new and more specific strategies for treating disorders of basal ganglia dysfunction.

Reduced MPTP toxicity in noradrenaline transporter knockout mice

The noradrenergic neurons of the locus coeruleus (LC) are damaged in Parkinsons disease (PD). Neurotoxin ablation of the LC noradrenergic neurons has been shown to exacerbate the dopaminergic toxicity of MPTP, suggesting that the noradrenergic system protects dopamine neurons. We utilized mice that exhibit elevated synaptic noradrenaline (NA) by genetically deleting the noradrenaline transporter (NET), a key regulator of the noradrenergic system (NET KO mice). NET KO and wild‐type littermates were administered MPTP and striatal dopamine terminal integrity was assessed by HPLC of monoamines, immmunoblotting for dopaminergic markers and tyrosine hydroxylase (TH) immunohistochemistry. MPTP significantly reduced striatal dopamine in wild‐type mice, but not in the NET KO mice. To confirm that the protection observed in the NET KO mice was due to the lack of NET, we treated wild‐type mice with the specific NET inhibitor, nisoxetine, and then challenged them with MPTP. Nisoxetine conferred protection to the dopaminergic system. These data indicate that NA can modulate MPTP toxicity and suggest that manipulation of the noradrenergic system may have therapeutic value in PD.

Selective loss of noradrenaline exacerbates early cognitive dysfunction and synaptic deficits in APP/PS1 mice.

BACKGROUND Degeneration of the locus coeruleus (LC), the major noradrenergic nucleus in the brain, occurs early and is ubiquitous in Alzheimers disease (AD). Experimental lesions to the LC exacerbate AD-like neuropathology and cognitive deficits in several transgenic mouse models of AD. Because the LC contains multiple neuromodulators known to affect amyloid β toxicity and cognitive function, the specific role of noradrenaline (NA) in AD is not well understood. METHODS To determine the consequences of selective NA deficiency in an AD mouse model, we crossed dopamine β-hydroxylase (DBH) knockout mice with amyloid precursor protein (APP)/presenilin-1 (PS1) mice overexpressing mutant APP and PS1. Dopamine β-hydroxylase (-/-) mice are unable to synthesize NA but otherwise have normal LC neurons and co-transmitters. Spatial memory, hippocampal long-term potentiation, and synaptic protein levels were assessed. RESULTS The modest impairments in spatial memory and hippocampal long-term potentiation displayed by young APP/PS1 or DBH (-/-) single mutant mice were augmented in DBH (-/-)/APP/PS1 double mutant mice. Deficits were associated with reduced levels of total calcium/calmodulin-dependent protein kinase II and N-methyl-D-aspartate receptor 2A and increased N-methyl-D-aspartate receptor 2B levels and were independent of amyloid β accumulation. Spatial memory performance was partly improved by treatment with the NA precursor drug L-threo-dihydroxyphenylserine. CONCLUSIONS These results indicate that early LC degeneration and subsequent NA deficiency in AD may contribute to cognitive deficits via altered levels of calcium/calmodulin-dependent protein kinase II and N-methyl-D-aspartate receptors and suggest that NA supplementation could be beneficial in early AD.

Light and Electron Microscopic Localization of Alpha-1 Adrenergic Receptor Immunoreactivity in the Rat Striatum and Ventral Midbrain

Electrophysiological and pharmacological studies have demonstrated that alpha-1 adrenergic receptor (alpha1AR) activation facilitates dopamine (DA) transmission in the striatum and ventral midbrain. However, because little is known about the localization of alpha1ARs in dopaminergic regions, the substrate(s) and mechanism(s) underlying this facilitation of DA signaling are poorly understood. To address this issue, we used light and electron microscopy immunoperoxidase labeling to examine the cellular and ultrastructural distribution of alpha1ARs in the caudate putamen, nucleus accumbens, ventral tegmental area, and substantia nigra in the rat. Analysis at the light microscopic level revealed alpha1AR immunoreactivity mainly in neuropil, with occasional staining in cell bodies. At the electron microscopic level, alpha1AR immunoreactivity was found primarily in presynaptic elements, with scarce postsynaptic labeling. Unmyelinated axons and about 30-50% terminals forming asymmetric synapses contained the majority of presynaptic labeling in the striatum and midbrain, while in the midbrain a subset of terminals forming symmetric synapses also displayed immunoreactivity. Postsynaptic labeling was scarce in both striatal and ventral midbrain regions. On the other hand, only 3-6% of spines displayed alpha1AR immunoreactivity in the caudate putamen and nucleus accumbens. These data suggest that the facilitation of dopaminergic transmission by alpha1ARs in the mesostriatal system is probably achieved primarily by pre-synaptic regulation of glutamate and GABA release.

Localization and function of dopamine receptors in the subthalamic nucleus of normal and parkinsonian monkeys

The subthalamic nucleus (STN) receives a dopaminergic innervation from the substantia nigra pars compacta, but the role of this projection remains poorly understood, particularly in primates. To address this issue, we used immuno-electron microscopy to localize D1, D2, and D5 dopamine receptors in the STN of rhesus macaques and studied the electrophysiological effects of activating D1-like or D2-like receptors in normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated parkinsonian monkeys. Labeling of D1 and D2 receptors was primarily found presynaptically, on preterminal axons and putative glutamatergic and GABAergic terminals, while D5 receptors were more significantly expressed postsynaptically, on dendritic shafts of STN neurons. The electrical spiking activity of STN neurons, recorded with standard extracellular recording methods, was studied before, during, and after intra-STN administration of the dopamine D1-like receptor agonist SKF82958, the D2-like receptor agonist quinpirole, or artificial cerebrospinal fluid (control injections). In normal animals, administration of SKF82958 significantly reduced the spontaneous firing but increased the rate of intraburst firing and the proportion of pause-burst sequences of firing. Quinpirole only increased the proportion of such pause-burst sequences in STN neurons of normal monkeys. In MPTP-treated monkeys, the D1-like receptor agonist also reduced the firing rate and increased the proportion of pause-burst sequences, while the D2-like receptor agonist did not change any of the chosen descriptors of the firing pattern of STN neurons. Our data suggest that dopamine receptor activation can directly modulate the electrical activity of STN neurons by pre- and postsynaptic mechanisms in both normal and parkinsonian states, predominantly via activation of D1 receptors.

Attitudes on Mind Over Matter: Physician Views on the Role of Placebo in Psychogenic Disorders

Psychogenic movement disorders (PMD) mimic known movement disorders, yet cannot be attributed to an underlying neurological substrate. PMD has been reported to affect up to 15–25% of patients who visit specialized movement disorder clinics. The lack of mechanistic understanding of this disorder contributes to the hesitation of physicians to give a diagnosis of PMD, and patients often experience inordinate health care costs and multiple referrals between psychiatrists and neurologists who have differing views on the diagnosis and terminology of PMD. Given that the prognosis for PMD is poor, that the success of standard treatment for PMD is highly dependent on the patients belief in the diagnosis and treatment regimen, and that case studies suggest the efficacy of placebo for PMD, placebo therapy has recently been advocated for PMD. Recent surveys report a high percentage of physicians administering placebo therapy. Therefore, perhaps the ethical question in PMD should be, “Are we harming patients by withholding placebo treatment?” In order to determine whether placebo therapy would be a viable option for PMD, we must first rigorously assess the factors contributing to the medical contexts in which placebos are offered. We conducted in-depth interviews with neurologists and psychiatrists to assess the attitudes that contribute to ethical norms and to assess physician attitudes and practices surrounding placebo therapy to psychogenic patients. These data will serve to inform the future treatment of patients with PMD, to make recommendations for clinician training and healthcare policy, and to reframe and deepen our discussion of the value of placebo therapies.

Ethical Use of Neuroscience

and treatment of human and non-human beings (Giordano 2009).4 Given the pace and scope of neuroscientific advancement, we do not have the latitude for intellectual or ethical lassitude or passivity, and, like it or not, we must often act even though we have limited and incomplete information with which to leverage epistemological capital in enacting decisions of ethical, legal, and/or social importance (Giordano 2010b). Perhaps, then, neuroethics provides a means to assess both our moral sense and how we can— and should—use this sense and sensibility to employ neuroscience in medicine and society, lest we err in ways that are neither retractable, nor recuperable, nor forgivable. As my father, an engineer, used to tell me: “Measure twice and cut once, for all too often, there’s no turning back.”

Neuroethics and the NIH BRAIN Initiative

The Brain Research through Advancing Innovative Neurotechnologies® (BRAIN) Initiative is focused on developing new tools and neurotechnologies to revolutionize our understanding of how the brain functions in health and disease, in large part to address the growing societal impact of neurological, mental health, and substance abuse disorders. Recent advances in neurotechnology are delivering unprecedented ways to interrogate and modulate brain function, and the BRAIN Initiative is focused on translation for human medical uses over the next decade. Since its inception, the NIH component of the BRAIN Initiative has utilized an iterative model of integrating ethics into the scientific trajectory of the Initiative, most recently with the creation of a Neuroethics Division of the NIH BRAIN Initiative Multi-Council Working Group. The Division serves as a resource of expertise, to help the BRAIN Initiative navigate issues involving ethics. Here we discuss the BRAIN Initiative, and its implications and aspirations for neuroethics. We also discuss new opportunities for collaboration and for integrating stakeholder voices.