The Chemistry of Behavior (Chapter 3)
The Blood-Brain Barrier:
Molecules can’t slip b/w the cells and go in/out of the capillaries (only in the nervous system)
Very few things actually get into the brain
Some lipid solubility - pretty much everything has to have an active transport system (glucose, amino acids, vitamins, hormones)
1st internal mechanism of protection for the brain
Circumventricular organs::not protected by the BBB
Area postrema::neg. molecules coming into brain and brain stem - the first poison detection center, causes vomiting/diarrhea
Nourishing Vertebrate Neurons:
Glucose, lactate, acetate - brain uses more sugar than any cells/organs
Sperm and cancer also really attracted to sugar
Using glucose requires oxygen, crosses in using a transport system
Korsakoff’s Syndrome::”alcoholic’s disease” - thiamine deficiency; neurons in the midline structures start to die (also seen in anorexic patients)
History:
1st NT discovered by Otto Loewi (1921) - acetylcholine using frog hearts
Acetylcholine works on skeletal muscles, tissue, internal organs
Activating vagus nerve lowers heart rate
Two Classes of Receptors:
Ionotropic receptors::open ion channels
Quick activity; a few ms
GABA receptors open chloride channels (hyperpolarization)
Glutamate receptors open sodium and calcium channels (depolarization)
Metabotropic receptors::2nd mess, metabolic change occurs
Slow, long lasting (30ms - s, m, etc.)
G-protein coupled
Can open surrounding ion channels or alter prod. of proteins
Basic Rules of Neurotransmitters:
Must by synthesized by a presynaptic neuron and stored in vesicles
Must be released in response to an action potential reaching the terminal
Receptor must recognize the NT somewhere
Must be some kind of a change to the cell when received by receptor
Blocking release interferes w/ability of presynaptic cell to affect postsynaptic cell
Neurotransmission in 4 Steps:
Synthesis (axon terminal or cell body)
Release
Receptor action
Inactivation
Activation and Deactivation:
Receptor-site activation
Post-synaptic effects
Depolarization, hyperpolarization, modulating effects
Pre-synaptic effects
Autoreceptors::a way of giving feedback to the neuron about the status of the external environment; guides overall production in Cell A
NT deactivation
Diffusion - they float away where they have no effect (automatic)
Degradation - degrade/fall apart over time (automatic)
Transporters (reuptake)::presynaptic, reabsorb the NT and recycle it so it can be used again
Glial cell help - astrocytes pull excess NTs and safely give to cell A
Types of Synapses:
Type I::excitatory
Type II::inhibitory
PSD::pre or post synaptic density
How Drugs Work:
Agonists::increase effectiveness of the NT targeted
Antagonists::decrease effectiveness of the NT targeted
Pharmacologists need to know Effective Dose of potential drugs - start w/animal models
Need to know Toxic Dose (TD50) or Lethal Dose (LD50)
Therapeutic Index (TI)::difference between ED and LD can have wide or narrow variability
Amino Acid NTs:
GABA::gamma-aminobutyric acid
Primary inhibitory NT (opens chloride channels and causes hyperpolarization; oval shaped vesicles on cell body)
Valium, Xanax → Benzodiazepenes (opens chloride channels for longer periods of time)
Alcohol (agonist) - loss of coordination and balance (cerebellum)
As you turn up GABA, glutamate is negatively effected (“brain mush”)
Glutamate:
Makes GABA - in every cell in our body, but very specialized in neurons
Primary excitatory NT (round vesicles, Type I synapses)
Learning and memory
Alcohol (antagonist) - loss of memories (hippocampus), poor decisions (PFC)
If turned up too high, can become neurotoxic::kills other neurons
Quaternary Amine NTs:
Acetylcholine (ACh)::highly tied to learning and memory (hippocampus and basal ganglia); fast acting at the neurotransmitter junction and degrades very quickly
Synthesized from Acetyl Coenzyme A and Coline (thru diet)
Acetylcholinesterase (AChE)::enzyme, breaks down ACh
Cholingeric Drugs:
Curare, Botex, Sarin/Soman/Tabun - neuromuscular junction
Curare and Botox are paralytics bc they block the ability of ACh to bind to the muscle - antagonists
Sarin/Soman/Tabun - nerve gases and AChE-I agonists
Nicotine - agonist, causing brain fog because ACh receptors are being removed
Alzheimer’s Disease - shrinkage in the hippocampus, tau protein chains start to disintegrate and break, neurons die or retract; plaque forming in synapse makes it hard for ACh and glutamate
Neuromuscular Junction:
Axons of motor neurons synapse onto receptor proteins that form clusters on various muscles throughout the body
Monoamine NTs - Catecholamines:
Dopamine
Motion and control, reward (feelings of pleasure)
Drugs
Cocaine, methylphenidate - dopamine agonists and block reuptake
Adderall, amphetamines - dopamine agonists and increase release of DA
MDMA - at low doses releases DA
Wellbutrin - dopamine reuptake inhibitor, helps people w/depression
Diseases (Parkinson’s on left end of continuum, schizophrenia at right end)
Parkinson’s - tremors, inability to initiate movement, DA neurons in substantia nigra are dying and can’t stimulate the basal ganglia in the mesostriatal pathway - treat w/a dopamine agonist (L-Dopa)
Schizophrenia - delusions and hallucinations, flight of ideas, disorganized behavior, overstimulation of dopamine in mesolimbocortical pathway - treat w/a dopamine antagonist (anti-psychotics)
Norepinephrine (NE)
Attention, vigilance, arousal, alertness
SNRIs (Effexor, Remeron, Cymbalta, Meridia) - good for mild/mod depression
NRIs (Atomoxetine - Strattera) - ADHD nonstimulant
Epinephrine (Epi)
Mainly in body, small amounts in brain - aka “adrenaline rush”
Cardiac meds (beta blockers)
Catecholamine Synthesis
Phenylanine and tyrosine part of our diet - essential amino acid, foods high in protein (soy based products, eggs, nuts/seeds, seafood, meat)
Turning up phenylanine/tyrosine can increase dopamine, and maybe increase NE and Epi
Monoamine NTs - Indoleamines:
Serotonin (5-HT)
Synthesized from tryptophan
Emotional states, impulse control, dreaming, OCD, anxiety, dep, over-eating, aggression
SSRIs - Prozac, Paxil, Lexapro, Celexa, Zoloft
Psychedelics - LSD, psilocybin - interaction b/w 5-HT and DA
Ecstasy - MDMA
Serotonin Synthesis
Tryptophan::essential amino acid (foods high in protein - wild game, seeds/nuts, cheeses, seafood/fish, meat)
Peptide NTs:
Opiate Drugs
Opioid receptor activation::inhabit VTA GABA neurons and increase DA activity
Blocks locus coeruleus activity in brain which thereby decreases response to stress, impairs memory, decreases arousal
Cannabis
Delta-a-tetrahydrocannabinol (THC) and cannabidol (CBD)
THC - pain relief, lower BP, relief of nausea, decreased eye pressure in glaucoma, immunosuppressive actions (Schedule I drug)
Many, many cannabinoid receptors in the brain
Decrease glutamate activity in brain regions
Disrupts attention, STM impairments, altered sensory awareness
Not lethal, very few receptors in brain stem
The Chemistry of Behavior (Chapter 3)
The Blood-Brain Barrier:
Molecules can’t slip b/w the cells and go in/out of the capillaries (only in the nervous system)
Very few things actually get into the brain
Some lipid solubility - pretty much everything has to have an active transport system (glucose, amino acids, vitamins, hormones)
1st internal mechanism of protection for the brain
Circumventricular organs::not protected by the BBB
Area postrema::neg. molecules coming into brain and brain stem - the first poison detection center, causes vomiting/diarrhea
Nourishing Vertebrate Neurons:
Glucose, lactate, acetate - brain uses more sugar than any cells/organs
Sperm and cancer also really attracted to sugar
Using glucose requires oxygen, crosses in using a transport system
Korsakoff’s Syndrome::”alcoholic’s disease” - thiamine deficiency; neurons in the midline structures start to die (also seen in anorexic patients)
History:
1st NT discovered by Otto Loewi (1921) - acetylcholine using frog hearts
Acetylcholine works on skeletal muscles, tissue, internal organs
Activating vagus nerve lowers heart rate
Two Classes of Receptors:
Ionotropic receptors::open ion channels
Quick activity; a few ms
GABA receptors open chloride channels (hyperpolarization)
Glutamate receptors open sodium and calcium channels (depolarization)
Metabotropic receptors::2nd mess, metabolic change occurs
Slow, long lasting (30ms - s, m, etc.)
G-protein coupled
Can open surrounding ion channels or alter prod. of proteins
Basic Rules of Neurotransmitters:
Must by synthesized by a presynaptic neuron and stored in vesicles
Must be released in response to an action potential reaching the terminal
Receptor must recognize the NT somewhere
Must be some kind of a change to the cell when received by receptor
Blocking release interferes w/ability of presynaptic cell to affect postsynaptic cell
Neurotransmission in 4 Steps:
Synthesis (axon terminal or cell body)
Release
Receptor action
Inactivation
Activation and Deactivation:
Receptor-site activation
Post-synaptic effects
Depolarization, hyperpolarization, modulating effects
Pre-synaptic effects
Autoreceptors::a way of giving feedback to the neuron about the status of the external environment; guides overall production in Cell A
NT deactivation
Diffusion - they float away where they have no effect (automatic)
Degradation - degrade/fall apart over time (automatic)
Transporters (reuptake)::presynaptic, reabsorb the NT and recycle it so it can be used again
Glial cell help - astrocytes pull excess NTs and safely give to cell A
Types of Synapses:
Type I::excitatory
Type II::inhibitory
PSD::pre or post synaptic density
How Drugs Work:
Agonists::increase effectiveness of the NT targeted
Antagonists::decrease effectiveness of the NT targeted
Pharmacologists need to know Effective Dose of potential drugs - start w/animal models
Need to know Toxic Dose (TD50) or Lethal Dose (LD50)
Therapeutic Index (TI)::difference between ED and LD can have wide or narrow variability
Amino Acid NTs:
GABA::gamma-aminobutyric acid
Primary inhibitory NT (opens chloride channels and causes hyperpolarization; oval shaped vesicles on cell body)
Valium, Xanax → Benzodiazepenes (opens chloride channels for longer periods of time)
Alcohol (agonist) - loss of coordination and balance (cerebellum)
As you turn up GABA, glutamate is negatively effected (“brain mush”)
Glutamate:
Makes GABA - in every cell in our body, but very specialized in neurons
Primary excitatory NT (round vesicles, Type I synapses)
Learning and memory
Alcohol (antagonist) - loss of memories (hippocampus), poor decisions (PFC)
If turned up too high, can become neurotoxic::kills other neurons
Quaternary Amine NTs:
Acetylcholine (ACh)::highly tied to learning and memory (hippocampus and basal ganglia); fast acting at the neurotransmitter junction and degrades very quickly
Synthesized from Acetyl Coenzyme A and Coline (thru diet)
Acetylcholinesterase (AChE)::enzyme, breaks down ACh
Cholingeric Drugs:
Curare, Botex, Sarin/Soman/Tabun - neuromuscular junction
Curare and Botox are paralytics bc they block the ability of ACh to bind to the muscle - antagonists
Sarin/Soman/Tabun - nerve gases and AChE-I agonists
Nicotine - agonist, causing brain fog because ACh receptors are being removed
Alzheimer’s Disease - shrinkage in the hippocampus, tau protein chains start to disintegrate and break, neurons die or retract; plaque forming in synapse makes it hard for ACh and glutamate
Neuromuscular Junction:
Axons of motor neurons synapse onto receptor proteins that form clusters on various muscles throughout the body
Monoamine NTs - Catecholamines:
Dopamine
Motion and control, reward (feelings of pleasure)
Drugs
Cocaine, methylphenidate - dopamine agonists and block reuptake
Adderall, amphetamines - dopamine agonists and increase release of DA
MDMA - at low doses releases DA
Wellbutrin - dopamine reuptake inhibitor, helps people w/depression
Diseases (Parkinson’s on left end of continuum, schizophrenia at right end)
Parkinson’s - tremors, inability to initiate movement, DA neurons in substantia nigra are dying and can’t stimulate the basal ganglia in the mesostriatal pathway - treat w/a dopamine agonist (L-Dopa)
Schizophrenia - delusions and hallucinations, flight of ideas, disorganized behavior, overstimulation of dopamine in mesolimbocortical pathway - treat w/a dopamine antagonist (anti-psychotics)
Norepinephrine (NE)
Attention, vigilance, arousal, alertness
SNRIs (Effexor, Remeron, Cymbalta, Meridia) - good for mild/mod depression
NRIs (Atomoxetine - Strattera) - ADHD nonstimulant
Epinephrine (Epi)
Mainly in body, small amounts in brain - aka “adrenaline rush”
Cardiac meds (beta blockers)
Catecholamine Synthesis
Phenylanine and tyrosine part of our diet - essential amino acid, foods high in protein (soy based products, eggs, nuts/seeds, seafood, meat)
Turning up phenylanine/tyrosine can increase dopamine, and maybe increase NE and Epi
Monoamine NTs - Indoleamines:
Serotonin (5-HT)
Synthesized from tryptophan
Emotional states, impulse control, dreaming, OCD, anxiety, dep, over-eating, aggression
SSRIs - Prozac, Paxil, Lexapro, Celexa, Zoloft
Psychedelics - LSD, psilocybin - interaction b/w 5-HT and DA
Ecstasy - MDMA
Serotonin Synthesis
Tryptophan::essential amino acid (foods high in protein - wild game, seeds/nuts, cheeses, seafood/fish, meat)
Peptide NTs:
Opiate Drugs
Opioid receptor activation::inhabit VTA GABA neurons and increase DA activity
Blocks locus coeruleus activity in brain which thereby decreases response to stress, impairs memory, decreases arousal
Cannabis
Delta-a-tetrahydrocannabinol (THC) and cannabidol (CBD)
THC - pain relief, lower BP, relief of nausea, decreased eye pressure in glaucoma, immunosuppressive actions (Schedule I drug)
Many, many cannabinoid receptors in the brain
Decrease glutamate activity in brain regions
Disrupts attention, STM impairments, altered sensory awareness
Not lethal, very few receptors in brain stem