quiz's Flashcards
How are NT defined
1.The substance must be present within the presynaptic neuron.
2.The substance must be released in response to presynaptic depolarization, and the release must be Ca2+-dependent.
3.Specific receptors for the substance must be present on the postsynaptic cell.
Describe nitric oxide (NO), an unconventional neurotransmitter.
- Gaseous, small, uncharged molecule
- Synthesized & released by neurons
- Freely flows through cell membranes, so vesicle storage is not possible
- Laughing gas - nitrous oxide, N20 - is related to NO and mimics NO’s function of inhibition by serving as an anesthetic/pain-reliever.
Compare and contrast neurotransmitters, neuromodulators, and hormones.
Although a single molecule can be classified as a neurotransmitter, neuromodulator, and hormone, there are key differences between the three types of molecules. A neurotransmitter is a signaling molecule that is used to communicate with another neuron across the synapse. A substance is a neurotransmitter if it 1) is present in the presynaptic neuron, 2) is released in response to presynaptic depolarization, and 3) has specific receptors on the postsynaptic cell. A neuromodulator is a signaling molecule that either potentiates (increases the response of) or inhibits a nerve impulse, but is not the actual means of transmission itself like a neurotransmitter. Many brain chemicals are used as both neurotransmitters and neuromodulators, depending on the particular brain circuit/region. A hormone is a signaling molecule produced by glands, and is transported by the circulatory system to target distant organs. A hormone in the brain is known as a neurohormone (although that term is not used frequently).
Discuss the production, receptor types, roles in behavior, and related disorders for acetylcholine (Ach).
Acetylcholine is an abundant neurotransmitter both in the CNS and PNS. It plays a vital role in arousal as the pontine tegmental nuclei of the reticular formation activates the basal forebrain (a set of nuclei which include the medial septal nuclei, and the nucleus accumbens). The basal forebrain is the main cholinergic output (cholinergic means related to acetylcholine) and distributes acetylcholine throughout the brain.
Acetylcholine binds to nicotinic acetylcholine receptors (ionotropic) and muscarinic acetylcholine receptors (metabotropic), both of which are found in the CNS and PNS.
In the brain acetylcholine binding to nicotinic receptors is attributed to plasticity, attention, learning & memory. The Ach nicotinic receptors also are present at the neuromuscular junction and cause muscle contractions when activated. Acetylcholine binding to muscarinic receptors is attributed to roles in arousal, mood, and REM sleep, as well as modulation of the stability of the neuromuscular junction.
A decrease in acetylcholine is associated with myasthenia gravis and various types of dementia, such as Alzheimer’s disease.
Compare and contrast the production, roles in behavior, and related disorders of dopamine (DA) and norepinephrine (NE).
Dopamine and norepinephrine (also called noradrenaline) are related to each other molecularly (further modification to dopamine leads to norepinephrine); however, the location of the main “dispensers” in the brain differs for each. Dopamine is largely produced in the VTA (ventral tegmental area) and SN (substantia nigra) of the brain stem while norepinephrine is produced primarily by the locus coreleus (LC) in the reticular formation.
While both neurotransmitters are important for arousal (specifically norepinephrine and dopamine that originates from the VTA not the SN) dopamine plays a role in motor control (SN) and reward (VTA) while norepinephrine is vital for alertness, vigilance, and the sympathetic fight or flight response (much like its relative epinephrine/adrenaline, which plays these roles as a hormone outside the brain). In addition, the LC does not project into the basal ganglia while the SN does, which allows dopamine to have an effect on motor control.
Disorders related to decreased norepinephrine are ADHD (attention/alertness issue), depression (lower than normal arousal), and low blood pressure. Low NE may also play a role in Alzheimer’s disease and traumatic brain injuries, as both of those are associated with a loss of NE cells. Disorders related to decreased dopamine are Parkinson’s (associated with movement control in the basal ganglia), ADHD (lack of attention/focus: similar to norepinephrine), and depression (similar to norepinephrine). In contrast, disorders related to increased dopamine include schizophrenia and other psychosis (through effects in the frontal lobe) as well as addiction (through the euphoria of reward-pathway activation). Drugs like cocaine, heroin, and meth also increase dopamine in reward pathways & cause euphoria, which is a key modulator of addiction.
Discuss the production, receptor types, roles in behavior, and related disorders for serotonin (5-HT).
Serotonin serves as a neurotransmitter, neuromodulator, and hormone. Inside the brain, it is produced in the raphe nuclei, which are a part of the reticular formation in brainstem. The term “raphe” refers to a line or ridge that separates two symmetrical parts of the body, and was used in the naming of the raphe nuclei because this collection of nuclei are clustered around the midline of the brainstem. The raphe nuclei are composed of a number of nuclei that are found at most levels of the brainstem from the midbrain down to the spinal cord. Serotonin is also produced outside the brain, and it plays a role in digestion in the gut.
Serotonin acts through at least 15 different 5-HT receptors, which demonstrates that it has a large number of different functions. As a NM/NT, serotonin plays a key role in maintaining mood balance and also modulates cognition, reward, learning/memory, appetite. As serotonin in the brain impacts levels of mood, anxiety, and happiness, illicit mood-altering drugs such as Ecstasy and LSD that cause a significant rise in serotonin levels also cause elevated mood and feelings of happiness. As a hormone outside the brain, serotonin is involved in digestion, as well as vomiting, vasoconstriction, bladder control, and ejaculation latency. Finally, as a precursor to melatonin, serotonin also has a role in our sleep/wake cycle & internal clock.
Decreased serotonin can lead to a variety of disorders, including mood disorders (role in depression/anxiety), fibromyalgia (a likely autoimmune disease that causes chronic pain/fatigue; Dr. Brewer has this disease), premenstrual syndrome (PMS)/hormone dysfunction, GI issues, and obesity
Increased serotonin can cause signs and symptoms that can range from mild (shivering and diarrhea) to severe (muscle rigidity, fever and seizures). Severe serotonin syndrome can cause death if not treated. Serotonin syndrome can occur when you increase the dose of certain medications or add a new drug to medication regimen that includes drugs that increase serotonin. Some illegal drugs (e.g., ecstasy) and dietary supplements (e.g., St. John’s wort – considered to be a ‘natural prozac’) also are associated with serotonin syndrome.
Discuss the production, receptor types, roles in behavior, and related disorders for histamine.
Histamine acts as a neurotransmitter, neuromodulator, and hormone. It is produced in the tuberomammillary nucleus (TMN) of the hypothalamus and also in certain immune cells. The TMN of the hypothalamus is the only source of brain histamine, and this wake-promoting center projects widely. In animal studies, histamine is a well-studied wake-promoting substance when delivered to the basal forebrain, the preoptic area, the TMN, or intraventricularly. Its densest projections are sent to the limbic system and reward pathways.
A deficiency in histamine has been associated with schizophrenia (note that some antipsychotics act on histamine receptors), multiple sclerosis (autoimmune disease that attacks myelin), and various immune system disorders.
An increase in histamine primarily affects its immune-system roles, as histamine is also produced in immune cells call mast cells and basophils. Histamine release with allergies or an illness is associated with that generally sick feeling you get when you have the flu. Antihistamine medications help with allergies by blocking histamine release by immune cells, but have sleepiness as a side effect, since they also block histamine’s role in wakefulness in the brain.
