Biological Basis for Understanding Psychopharmacology Study Notes
Intracranial Regulation and Functional Brain Dynamics
Intracranial regulation (ICR) encompasses the normal and abnormal processes of intracranial function. In both community and inpatient settings, nurses care for individuals experiencing a wide range of ICR issues. Optimal ICR functioning is fundamentally dependent on a consistent supply of blood to deliver oxygen and essential nutrients, with carbohydrates serving as the primary source of fuel for the brain. Any alterations in these basic physiological processes can result in mental disturbances and physical manifestations. Psychotropic agents used to treat mental disease, while effective, can also cause undesired effects such as sedation, excitement, motor disturbances, sexual dysfunction, and weight gain. Psychiatric-mental health nursing aims to understand the neurobiology of psychiatric disorders to manage symptoms and reduce the risk of relapse. Because all brain functions are carried out by the interactions of neurons, mental disturbances are frequently associated with alterations in various brain functions including monitoring the external world, regulating skeletal muscles, initiating basic drives like hunger and thirst, and mediating conscious sensation and emotions.
Anatomy and Specific Functions of Brain Structures
The brain's architecture is genetically programmed but exhibits plasticity throughout life, a process of adapting and changing as gray matter shrinks or thickens and connections are pruned or forged. The cerebrum, or cerebral cortex, is divided into four lobes. The frontal lobe facilitates conscious movement, problem-solving, and speech production. The most anterior part, the prefrontal cortex (PFC), moderates social behaviors, personality, and goal setting. The parietal lobes manage tactile sensation and spatial awareness. The occipital lobe is responsible for vision and visual processing, while the temporal lobe handles hearing, language reception, and comprehension. The brainstem, consisting of the midbrain, pons, and medulla, regulates vital life functions. Projections known as the reticular activating system (RAS) set levels of consciousness and regulate the sleep-wake cycle. The cerebellum contributes to motor control and cognitive processing, and its dysfunction can lead to positive symptoms like hallucinations in schizophrenia or movement abnormalities in lithium toxicity.
The Limbic System: The Emotional Brain
Lying deep within the cerebrum are pockets of gray matter including the hippocampus, the amygdala, and the basal ganglia. The hippocampus and amygdala, along with the hypothalamus and thalamus, constitute the limbic system, often called the ‐emotional brain.‐ The hippocampus interacts with the PFC for memory formation, while the amygdala processes fear and anxiety. Chronic stress can cause hippocampal shrinkage, potentially leading to depression and cognitive impairment. Amygdala hyperactivity is seen in trauma and paranoia, while hypoactivity may predict a capacity to respond to antidepressants. The subcortical basal ganglia play a major role in motor responses via the extrapyramidal motor system, utilizing the neurotransmitter dopamine to maintain muscle tone. Structural changes in the striatum can occur rapidly with drugs like haloperidol, leading to extrapyramidal symptoms (EPSs) such as acute EPS or late-developing tardive dyskinesia (TD). Movement regulation also involves the diaphragm for breathing and the muscles of the throat and mouth for speech, meaning psychotropic drugs can affect respiration and speech patterns.
Homeostasis, Hormonal Regulation, and the Autonomic System
The thalamus acts as a filter for sensory information before it reaches the cortex, and disrupted filtering is linked to schizophrenia. The hypothalamus maintains homeostasis, regulating temperature, blood pressure, libido, and circadian rhythms. It secretes neurohormones like corticotropin-releasing hormone (CRH) in response to stress, which triggers the release of cortisol. This system is often disrupted in depression and anxiety. The hypothalamic neurohormone dopamine also inhibits prolactin; blocking dopamine with first-generation antipsychotics leads to hyperprolactinemia, causing amenorrhea or gynecomastia. The hypothalamus also controls the autonomic nervous system, divided into the sympathetic (fight-or-flight) and parasympathetic (calm) systems. Sympathomimetic drugs like amphetamines increase synaptic levels of dopamine and norepinephrine, improving focus in attention-deficit/hyperactivity disorder (ADHD) at low doses. Lisdexamfetamine is a ‐prodrug‐ requiring intestinal enzymes to become active, which helps prevent its abuse.
Neuroimaging: Visualizing Structure and Function
Neuroimaging provides a view of an interconnected brain. Computed tomography (CT) uses X-ray slices to detect anatomical details like lesions or ventricle abnormalities in schizophrenia. Magnetic resonance imaging (MRI) uses magnetic fields to produce cross-sectional images with higher resolution than CT, while functional MRI (fMRI) detects blood flow to active brain regions without radioactive isotopes. Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) use ionizing radiation to localize functions. PET scans show decreased metabolism in depression and schizophrenia and increased metabolism in obsessive-compulsive disorder (OCD). PET and SPECT also visualize neurotransmitter-receptor interactions, such as dopamine system dysregulation in schizophrenia or serotonin transporter blockade by antidepressants. Researchers use the striatal connectivity index (SCI) from fMRI to predict responses to antipsychotic treatment in first-episode schizophrenia.
Cellular Transmission and Neurotransmitters
The brain contains over 100 \text{billion} interconnected neurons that initiate signals through neurotransmission. Electrical signals are converted at synapses into chemical signals via the release of neurotransmitters from the presynaptic axon terminal. These molecules diffuse across the synapse to bind with receptors on the postsynaptic neuron. Insufficient transmission can result from deficient neurotransmitter release or decreased receptors, while excessive transmission can result from over-release or increased receptor responsiveness. Neurotransmitters are eventually destroyed by enzymes such as acetylcholinesterase (AChE) for acetylcholine, or monoamine oxidase (MAO) for monoamines like norepinephrine, dopamine, and serotonin. Alternatively, molecules are taken back into the presynaptic cell through cellular reuptake. Psychotropic drugs target these processes by acting as agonists (promoting activity) or antagonists (blocking activity).
Specific Neurotransmitter Systems and Pathophysiology
Dopamine is central to cognition, motivation, and movement, and its activity is increased by drugs like cocaine. The dopamine hypothesis suggests that excess dopamine activity induces psychosis, while blocking it treats schizophrenia symptoms. Acetylcholine (ACh) balances dopamine and is vital for memory; ACh deficiency is noted in Alzheimer’s disease, which is treated with AChE inhibitors like donepezil. Norepinephrine (NE) regulates mood and arousal; low levels lead to sedation/depression, while high levels cause hyperarousal. Prazosin blocks ̑_1-receptors to treat nightmares in PTSD. Serotonin () regulates mood and sleep. High serotonin levels can cause serotonin syndrome, featuring restlessness, fever, and seizures. Histamine blockade ( receptors) results in sedation and weight gain. ̓-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter; increasing its effectiveness reduces anxiety. Glutamate is the primary excitatory neurotransmitter; excessive glutamate can cause neurotoxicity and cell death in neurodegenerative conditions, which can be mitigated by NMDA receptor antagonists like memantine.
Psychotropic Drug Interactions and Pharmacogenetics
Pharmacotherapeutic efficacy is often modified by drug interactions. Pharmacokinetic interactions occur when one drug alters the absorption or metabolism of another, often through the inhibition or induction of cytochrome () enzymes. Inhibitors increase drug toxicity risks, while inducers decrease efficacy. Pharmacodynamic interactions occur when drugs act on the same or related receptors, such as the additive sedative effect of combining benzodiazepines with antihistamines. Pharmacogenetic testing, such as GeneSight technology, focuses on genes and pharmacodynamic genes to determine individual metabolic responses to medications for conditions like ADHD, PTSD, and bipolar disorder.
Antidepressant Drug Classes and Mechanisms
Antidepressant theories include the monoamine hypothesis (deficiency of dopamine, NE, or serotonin) and the monoamine receptor hypothesis (increased receptor sensitivity due to low neurotransmitter levels). Selective serotonin reuptake inhibitors (SSRIs) like fluoxetine and sertraline inhibit serotonin reuptake. Vortioxetine is a multimodal SSRI with agonist and antagonist activities. Serotonin-norepinephrine reuptake inhibitors (SNRIs) like venlafaxine block both transporters. Mirtazapine is a serotonin-norepinephrine disinhibitor (SNDI) that blocks presynaptic ̑_2-receptors. Bupropion is a norepinephrine-dopamine reuptake inhibitor (NDRI) also used for smoking cessation. Tricyclic antidepressants (TCAs) block NE and serotonin reuptake but are ‐dirty drugs‐ due to side effects like anticholinergic actions, sedation, and cardiotoxicity in overdose. Monoamine oxidase inhibitors (MAOIs) prevent monoamine breakdown but require a low-tyramine diet to avoid hypertensive crises. Tyramine is found in aged/fermented foods, and dietary restrictions must continue for after stopping MAOIs.
Anxiolytic, Sedative-Hypnotic, and Mood Stabilizing Agents
Buspirone reduces anxiety without the addictive potential of benzodiazepines. Benzodiazepines like diazepam and alprazolam promote GABA activity by binding to the receptor complex; however, they carry risks of tolerance, withdrawal, and dementia. They can cause life-threatening respiratory depression when combined with other CNS depressants like alcohol or opioids. ‐Z-hypnotics‐ like zolpidem are selective for receptors with ̑_1-subunits for sleep without muscle-relaxant effects. Lithium, a mood stabilizer with a low therapeutic index, requires blood monitoring; its levels are sensitive to kidney function and sodium balance. When sodium is depleted, the kidneys retain lithium, risking toxicity. Anticonvulsant mood stabilizers include valproate (risk of hepatotoxicity and birth defects), lamotrigine (risk of Stevens-Johnson syndrome), and carbamazepine (requires monitoring for blood dyscrasias).
Antipsychotic Medications: Generations and Side Effects
First-generation antipsychotics (FGAs), or neuroleptics, serve as dopamine receptor antagonists (DRAs) targeting receptors to reduce positive symptoms. They often cause EPSs, parkinsonism, and the life-threatening neuroleptic malignant syndrome (NMS), characterized by muscle rigidity and high fever. High-potency agents like haloperidol cause more EPS, while low-potency chlorpromazine is more sedating. Second-generation antipsychotics (SGAs), or atypicals, are serotonin-dopamine antagonists (SDAs) and are preferred due to fewer EPSs. Clozapine is highly effective but can cause agranulocytosis, necessitating regular absolute neutrophil count (ANC) monitoring. Olanzapine is associated with significant weight gain and metabolic syndrome, requiring monitoring of and fasting glucose. Risperidone can result in hyperprolactinemia and gynecomastia. Quetiapine carries a high risk for somnolence and metabolic syndrome. Ziprasidone must be taken with at least 350\text{calories} to enhance bioavailability and carries a warning for prolongation. Aripiprazole is a dopamine-serotonin stabilizer and partial agonist. Newer agents like cariprazine and brexpiprazole act as partial agonists to potentially address negative symptoms.
Psychoneuroimmunology and Cultural Considerations
Psychoneuroimmunology (PNI) studies the interaction between the immune system, behavior, and health. Chronic inflammation releases cytokines that can impair hippocampal neuroplasticity and neurogenesis, leading to cognitive decline. Cross-cultural psychopharmacology examines how ethnic variations and genetic predispositions influence drug responses. Genes are considered ‐plastic‐ because their regulation responds to internal neurotransmitters and external cues like psychotropic drugs or psychotherapy. Providing safe, effective nursing care requires empowering patients through informed decision-making and monitoring both integrated treatment effects and cultural preferences for alternative therapies.
Questions & Discussion
What are the nursing priorities for a patient with a cerebellar abscess? The priority diagnosis is the risk for falls related to the loss of balance and equilibrium. This is because the cerebellum is the primary center for maintaining equilibrium and skeletal muscle coordination. In the case of a patient starting risperidone, which nursing intervention is essential? The nurse must assess sitting, standing, and lying blood pressure daily because the drug's blockage of ̑_1\text{receptors} can cause orthostatic hypotension. Why would systematic measurement of and glucose levels be most important for a patient on olanzapine compared to aripiprazole or ziprasidone? Olanzapine has a much higher propensity for causing significant weight gain and metabolic syndrome, whereas ziprasidone and aripiprazole are considered relatively weight-neutral. Regarding the use of trazodone for sleep in a non-depressed patient: The nurse should explain that in low doses, trazodone helps relieve insomnia by utilizing its sedative-hypnotic properties through histamine receptor antagonism, whereas much higher doses are required for it to exert its antidepressant effects. Finally, which patient diagnosis is most likely to present with difficulty in problem-solving? A 52-year-old with schizophrenia who has been on long-term haloperidol, as chronic schizophrenia and long-term neuroleptic use are associated with cognitive deficits and alterations in the prefrontal cortex functions such as decision making and insight.