Etiology of Geophagia
Anil Gupta in Geophagia, 2019
Dopaminergic pathways are the neuronal networks that connect one portion of brain with another. They are composed of axons of dopaminergic neurons in the brain. There are three main types of dopaminergic pathways: nigrostriatal, mesolimbic, and mesocortical pathways. The mesolimbic pathway is primarily implicated in reward behavior. The cell bodies of the mesolimbic pathway are located in the ventral tegmental area at the floor of the midbrain (Malenka et al. 2009). The axons descend from the ventral tegmental area to the ventral corpus striatum, which is located in the forebrain. The ventral corpus striatum is the chief component of the reward system of the brain (Yager et al. 2015). It is composed of the nucleus accumbens and olfactory tubercle (Ferré et al. 2010; Taylor et al. 2013).
Physiology of the Pain System
Sahar Swidan, Matthew Bennett in Advanced Therapeutics in Pain Medicine, 2020
The limbic system is a set of brain structures on either side of the thalamus that directs emotion, behavior, motivation, long-term memory, and olfaction. The mesolimbic pathway is part of the reward circuit. Dopaminergic neurons in the ventral tegmental area (VTA) of the midbrain project to the forebrain nucleus accumbens (NAc). Burst firing of dopaminergic neurons into the NAc serves as a reward signal and is inhibited by tonic GABA input.15 Opioids inhibit GABAergic tone on these neurons, while pain relief directly engages dopamine circuitry.15 The mesolimbic pathway has been implicated in depression, anxiety, pain sensation, anticipation of analgesia or placebo-induced analgesia, and chronic pain.16 Different types of pain can impact different aspects of the VTA and result in either activation or inhibition. In this way, dopamine release is variable based on various pain signals.16 These dopaminergic pathways are variably altered with stress as well as opioids. Dynorphin and the kappa opioid receptor can play a role in impairing dopamine release in the Na.16
Brain Mechanisms and the Disease Model of Addiction
Hanna Pickard, Serge H. Ahmed in The Routledge Handbook of Philosophy and Science of Addiction, 2019
In the brain disease model, all drugs of abuse have common direct or indirect effects on a single pathway in the brain—the brain’s reward system, i.e., the mesolimbic dopamine system. (Leshner 1997).2 The mesolimbic dopamine pathway is individuated at the molecular, cellular, structural, and functional levels; it extends from the ventral tegmentum to the nucleus accumbens, with connections to such areas in the brain as the limbic system and the orbitofrontal cortex (Hyman 1996; Ortiz et al. 1995). It is associated with motivation, decision-making, and inhibitory control and is thought to be a key detector of rewarding stimuli, as it controls responses to natural rewards such as food, sex, and social interactions. According to the disease model, drugs interact with the mesolimbic pathway to produce addictive effects and “reset” the brain’s reward system by causing sharp increases in the release of dopamine (Volkow et al. 2016; Di Chiara 2002). Such increases elicit a reward signal that triggers associative learning, leading individuals to associate certain stimuli with the drug use, e.g., the environment of drug taking, persons with whom it has been taken, etc. These environmental cues may all trigger craving for and use of the drug. Such conditioned responses become deeply ingrained, often lasting long after use has stopped.
Amantadine and memantine: a comprehensive review for acquired brain injury
Published in Brain Injury, 2020
Heather M. Ma, Ross D. Zafonte
A third proposed mechanism for increasing the level of severely injured patients’ clinical arousal and awareness is through targeted dopamine enhancement. The theoretical basis of this concept involved pharmacologically targeting three of the four major dopaminergic pathways in the brain (15): The mesolimbic pathway, associated with motivation, learning, and memory.The nigrostriatal pathway, involved in initiation and velocity of movement.The mesocortical pathway, involved in motivation or activation, planning, and temporal organization, as well as associated with cortical tone and attention.
Resistance is not futile: treatment-refractory schizophrenia – overview, evaluation and treatment
Published in Expert Opinion on Pharmacotherapy, 2019
Justin Faden, Leslie Citrome
While the etiology of schizophrenia is unclear, and there are likely many different pathophysiological pathways that lead to the symptoms of schizophrenia, the interaction between dopamine and glutamate may play a role for most patients. It has long been thought that increased dopamine activity in the mesolimbic pathway is responsible for the positive symptoms of schizophrenia. The origins of this may lie in the hypothesis that hypofunction of the N-methyl-D-aspartate (NMDA) glutamate receptor may lead to excess dopamine release in the mesolimbic pathway and in addition, inadequate release of dopamine in prefrontal cortex, causing negative symptoms and cognitive dysfunction [8,9]. This can be seen in clinical practice when observing an otherwise healthy individual that is intoxicated on the NMDA receptor antagonistic phencyclidine (PCP). Symptoms of PCP intoxication can mimic the positive, negative, and cognitive symptoms of schizophrenia.
Comparing the effectiveness of behavioral interventions in adults with co-occurring tobacco and substance use disorders: a systematic review of literature
Published in Journal of Social Work Practice in the Addictions, 2020
John Boatner, Timothy Rice, David Patterson, Phyllis Thompson
A neurobiological perspective can offer a lens from which tobacco dependence and other concomitant substance disorders are understood. For example, the neurotransmitter dopamine is known to have a direct relationship with a person’s learning and motivation via a neurobiological process that occurs in the ventral tegmental area of the mid-brain. This is where dopamine is released through the mesolimbic pathway and where the rewarding sensation of pleasure is experienced (Simpkins & Simpkins, 2013). All forms of tobacco contain the psychostimulant drug, nicotine, which acts through the dopaminergic mesolimbic pathway and elicits feelings of enhanced mood and a heightened sense of alertness (Fagerström, 2002). Nicotine, directly and indirectly, activates the dopaminergic pathway that is also influenced by any commonly misused drug, offering a neurobiological basis from which high levels of tobacco use co-occurs and can be better understood (Guydish et al., 2015). Ultimately, the pervasive release of dopamine through the mesolimbic pathway reinforces addictive behavior(s), which includes the use of tobacco and psychoactive substances.
Related Knowledge Centers
- Dopaminergic Pathways
- Forebrain
- Midbrain
- Nucleus Accumbens
- Basal Ganglia
- Brain
- Ventral Tegmental Area
- Striatum
- Olfactory Tubercle
- Motivational Salience