The Dopaminergic Control of Movement-Evolutionary Considerations

Evolutionary innovations in the primate dopaminergic system

The human brain has evolved unique capabilities compared to other vertebrates. The mechanistic basis of these derived traits remains a fundamental question in biology due to its relevance to the origin of our cognitive abilities and behavioral repertoire, as well as to human-specific aspects of neuropsychiatric and neurodegenerative diseases. Comparisons of the human brain to those of nonhuman primates and other mammals have revealed that differences in the neuromodulatory systems, especially in the dopaminergic system, may govern some of these behavioral and cognitive alterations, including increased vulnerability to certain brain disorders. In this review, we highlight and discuss recent findings of human- and primate-specific alterations of the dopaminergic system, focusing on differences in anatomy, circuitry, and molecular properties.

From emotional arousal to executive action. Role of the prefrontal cortex

Emotional arousal is caused by the activity of two parallel ascending systems targeting mostly the subcortical limbic regions and the prefrontal cortex. The aversive, negative arousal system is initiated by the activity of the mesolimbic cholinergic system and the hedonic, appetitive, arousal is initiated by the activity of the mesolimbic dopaminergic system. Both ascending projections have a diffused nature and arise from the rostral, tegmental part of the brain reticular activating system. The mesolimbic cholinergic system originates in the laterodorsal tegmental nucleus and the mesolimbic dopaminergic system in the ventral tegmental area. Cholinergic and dopaminergic arousal systems have converging input to the medial prefrontal cortex. The arousal system can modulate cortical EEG with alpha rhythms, which enhance synaptic strength as shown by an increase in long-term potentiation (LTP), whereas delta frequencies are associated with decreased arousal and a decrease in synaptic strength as shown by an increase in long-term depotentiation (LTD). It is postulated that the medial prefrontal cortex is an adaptable node with decision making capability and may control the switch between positive and negative affect and is responsible for modifying or changing emotional state and its expression.

Parkinson's Disease: Cells Succumbing to Lifelong Dopamine-Related Oxidative Stress and Other Bioenergetic Challenges

The core pathological event in Parkinson's disease (PD) is the specific dying of dopamine (DA) neurons of the substantia nigra pars compacta (SNc). The reasons why SNc DA neurons are especially vulnerable and why idiopathic PD has only been found in humans are still puzzling. The two main underlying factors of SNc DA neuron vulnerability appear related to high DA production, namely (i) the toxic effects of cytoplasmic DA metabolism and (ii) continuous cytosolic Ca2+ oscillations in the absence of the Ca2+-buffer protein calbindin. Both factors cause oxidative stress by producing highly reactive quinones and increasing intra-mitochondrial Ca2+ concentrations, respectively. High DA expression in human SNc DA neuron cell bodies is suggested by the abundant presence of the DA-derived pigment neuromelanin, which is not found in such abundance in other species and has been associated with toxicity at higher levels. The oxidative stress created by their DA production system, despite the fact that the SN does not use unusually high amounts of energy, explains why SNc DA neurons are sensitive to various genetic and environmental factors that create mitochondrial damage and thereby promote PD. Aging increases multiple risk factors for PD, and, to a large extent, PD is accelerated aging. To prevent PD neurodegeneration, possible approaches that are discussed here are (1) reducing cytoplasmic DA accumulation, (2) blocking cytoplasmic Ca2+ oscillations, and (3) providing bioenergetic support.

Unravelling the functional development of vertebrate pathways controlling gaze

Animals constantly redirect their gaze away or towards relevant targets and, besides these goal-oriented responses, stabilizing movements clamp the visual scene avoiding image blurring. The vestibulo-ocular (VOR) and the optokinetic reflexes are the main contributors to gaze stabilization, whereas the optic tectum integrates multisensory information and generates orienting/evasive gaze movements in all vertebrates. Lampreys show a unique stepwise development of the visual system whose understanding provides important insights into the evolution and development of vertebrate vision. Although the developmental emergence of the visual components, and the retinofugal pathways have been described, the functional development of the visual system and the development of the downstream pathways controlling gaze are still unknown. Here, we show that VOR followed by light-evoked eye movements are the first to appear already in larvae, despite their burrowed lifestyle. However, the circuits controlling goal-oriented responses emerge later, in larvae in non-parasitic lampreys but during late metamorphosis in parasitic lampreys. The appearance of stabilizing responses earlier than goal-oriented in the lamprey development shows a stepwise transition from simpler to more complex visual systems, offering a unique opportunity to isolate the functioning of their underlying circuits.

High-resolution analysis of individual Drosophila melanogaster larvae uncovers individual variability in locomotion and its neurogenetic modulation

Neuronally orchestrated muscular movement and locomotion are defining faculties of multicellular animals. Due to its simple brain and genetic accessibility, the larva of the fruit fly Drosophila melanogaster allows one to study these processes at tractable levels of complexity. However, although the faculty of locomotion clearly pertains to the individual, most studies of locomotion in larvae use measurements aggregated across animals, or animals tested one by one, an extravagance for larger-scale analyses. This prevents grasping the inter- and intra-individual variability in locomotion and its neurogenetic determinants. Here, we present the IMBA (individual maggot behaviour analyser) for analysing the behaviour of individual larvae within groups, reliably resolving individual identity across collisions. We use the IMBA to systematically describe the inter- and intra-individual variability in locomotion of wild-type animals, and how the variability is reduced by associative learning. We then report a novel locomotion phenotype of an adhesion GPCR mutant. We further investigated the modulation of locomotion across repeated activations of dopamine neurons in individual animals, and the transient backward locomotion induced by brief optogenetic activation of the brain-descending 'mooncrawler' neurons. In summary, the IMBA is an easy-to-use toolbox allowing an unprecedentedly rich view of the behaviour and its variability of individual larvae, with utility in multiple biomedical research contexts.

Dopaminergic System in Promoting Recovery from General Anesthesia

Dopamine is an important neurotransmitter that plays a biological role by binding to dopamine receptors. The dopaminergic system regulates neural activities, such as reward and punishment, memory, motor control, emotion, and sleep-wake. Numerous studies have confirmed that the dopaminergic system has the function of maintaining wakefulness in the body. In recent years, there has been increasing evidence that the sleep-wake cycle in the brain has similar neurobrain network mechanisms to those associated with the loss and recovery of consciousness induced by general anesthesia. With the continuous development and innovation of neurobiological techniques, the dopaminergic system has now been proved to be involved in the emergence from general anesthesia through the modulation of neuronal activity. This article is an overview of the dopaminergic system and the research progress into its role in wakefulness and general anesthesia recovery. It provides a theoretical basis for interpreting the mechanisms regulating consciousness during general anesthesia.

Phosphorylation Signals Downstream of Dopamine Receptors in Emotional Behaviors: Association with Preference and Avoidance

Dopamine regulates emotional behaviors, including rewarding and aversive behaviors, through the mesolimbic dopaminergic pathway, which projects dopamine neurons from the ventral tegmental area to the nucleus accumbens (NAc). Protein phosphorylation is critical for intracellular signaling pathways and physiological functions, which are regulated by neurotransmitters in the brain. Previous studies have demonstrated that dopamine stimulated the phosphorylation of intracellular substrates, such as receptors, ion channels, and transcription factors, to regulate neuronal excitability and synaptic plasticity through dopamine receptors. We also established a novel database called KANPHOS that provides information on phosphorylation signals downstream of monoamines identified by our kinase substrate screening methods, including dopamine, in addition to those reported in the literature. Recent advances in proteomics techniques have enabled us to clarify the mechanisms through which dopamine controls rewarding and aversive behaviors through signal pathways in the NAc. In this review, we discuss the intracellular phosphorylation signals regulated by dopamine in these two emotional behaviors.