狠狠撸

Neurotransmitters
In the 60's, people took acid to make the world weird. Now the
world is weird and people take Prozac to make it normal.

Processes Involved in Neurotransmission
? Precursors (getting the raw materials)
? Biosynthesis (making the NTs)
? Storage (vesicles - Golgi bodies)
? Transport (neurofilaments and microtubules)
? Docking
? Influx of Ca++
? Vesicle movement
? Exocytosis— (fusion and release)
? Crossing synaptic gap
? Binding postsynaptic receptors
? Reuptake mechanisms to recover NTs
? Deactivation

Role of Neurotransmitters with their detailed description

Categories of NTs
? Amino Acids
– Glutamate (Glu)
– GABA
? Biogenic Amines
– Quaternary Amines
? Acetylcholine (Ach)
– Monoamines
? Catecholamines
– Dopamine (DA)
– Norepinephrine (NE)
? Indolamines
– Serotonin (5-HT)
? Neuropeptides
– Opioid Peptides
? Enkephalins
? Endorphins
? Dynorphins
? Others (e.g. lipids, nucleosides)

Receptors
? Genetically-coded proteins embedded
in cell membrane
? Gating
– Ligand-gated - Stretch-gated
– Voltage-gated
? Effects
– Ionotropic
– Metabotropic
? Location
– Postsynaptic
– Presynaptic
? Heteroreceptor
? Autoreceptor
ionotropic
metabotropic

Ionotropic Receptors
1. Work very fast; important role in fast neurotransmission
2. Each is made of several subunits (together form the complete receptor)
3. At center of receptors is channel or pore to allow flow of neurotransmitter
4. At rest - receptor channels is closed
5. When neurotransmitter bind -- channel immediately opens
6. When ligand leaves binding site -- channel quickly closes

Metabotropic Receptors
1. Work more slowly than ionotropic receptors
2. Though it takes longer for postsynapic cell to respond, response is
somewhat longer-lasting
3. Comprise a single protein subunit, winding back-and-forth through cell
membrane seven times (transmembrane domains)
4. They do not possess a channel or pore

Theory of Drug Action
Emil Fischer’s ‘Lock and Key’ Hypothesis (1890)
? Every ‘lock’ has its own ‘key’
? If the ‘key’ is not precise, the ‘lock’ does not open
? The ‘drug’ is the key that has to fit the target specifically and
productively

Corollary of ‘Lock & Key’ Hypothesis
? Does not explain why some ‘keys’ open doors partially? …… e.g., partial agonists or
antagonists
O
O
O
H O
OH

Daniel Koshland’s ‘Induced-Fit’ Hypothesis (1958)
? At least two steps …… step 1 is initial binding and step 2 is a
change in structure of the receptor (and/or drug)
? Receptor is flexible! …… can wrap around the drug

Common Neurotransmitters Involved in Dependence
Probable functional dysregulation:
? Dopamine (DA)
? Serotonin (SER)
? Acetylcholine (ACh)
? Endorphins (END)
? Gamma-aminobutyric acid (GABA)
? Glutamate (GLU)

Drugs Associated with Neurotransmitters
Why do people have “drugs of choice”?
? Dopamine - amphetamines, cocaine, ETOH
? Serotonin - LSD, ETOH
? Endorphins - opioids, ETOH
? GABA - benzodiazepines, ETOH
? Glutamate –ETOH
? Acetylcholine - nicotine, ETOH
? Anandamide – Marijuana

Amino Acid NTs
? High concentration in brain (micromolar)
? Circuits
– Cortico-cortical
– Sensory-motor
? Point-to-point communication
? Consistently excitatory or inhibitory
– Mainly ionotropic receptors but do have metabotropic receptors
? Fast acting, short duration (1-5 ms)
? Examples: Glutamate, Aspartate, GABA, Glycine

GABA and Glutamate
.
? Because they are
structurally very similar,
various drugs affect the
presence of GLU and
GABA in the synaptic gap
and increase or decrease
action potentials.

Glutamate
? Principal excitatory NT
? Biosynthesized as byproduct of cell metabolism
? Removed by reuptake
? Elevated levels ? neurotoxic
? 4 receptor types
– NMDA
– AMPA
– Kainate
– mGluR - Metabotropic
Ionotropic

NMDA Binding Sites
? 4 outside cell
– Glutamate
– Glycine
? Obligatory co-agonist
? Inhibitory NT at its “own” receptor
– Zinc (inverse agonist)
– Polyamine (indirect agonist)
? 2 inside cell
– Magnesium (inverse agonist)
– PCP (inverse agonist)
“The specific subunit composition of each receptor
determines its overall pharmacological properties”

GABA (Gamma Aminobutyric Acid)
? Principal Inhibitory NT
? Biosynthesis:
? Removed by reuptake
? 2 receptor types
? GABAA GABAC (ionotropic; Cl- channel)
? GABAB (metabotropic; K+ channel)
Glu GABA
Glutamic Acid
Decarboxylase (GAD)
and B6

GABAa Binding Sites
? GABA
? Benzodiazepine (indirect agonist)
– Probably also site for alcohol
– Endogenous inverse agonist binds here
? Barbiturate (indirect agonist)
? Steroid (indirect agonist)
? Picrotoxin (inverse agonist)
Phosphate groups attach to the receptor inside
the cell and regulate receptor sensitivity (via
phosphorylation) to agents such as alcohol

GABAergic Drugs
Ro15-4513, a GABAa antagonist
(indirect for GABA, direct for alcohol)
reverses alcohol intoxication
? Agonists (anti-anxiety)
? Benzodiazepines
? Barbiturates
? Ethyl alcohol (ETOH)
? Antagonists
? Picrotoxin
? Inverse agonist
? Ro 15-4513

Biogenic Amines
? Medium concentration in brain (nanomolar)
? Circuits
– Single-source divergent projections
– Mainly midbrain to cortex
? Modulatory functions
– Excitatory or inhibitory as a function of receptor
? More metabotropic receptors than ionotropic, but plenty
of both
? Slow acting, long duration (10-1000 ms)
? Examples: Acetylcholine, Epinephrine, Norepinephrine,
Dopamine, Serotonin

Acetylcholine
? Mostly excitatory effects
Removal
Acetyl CoA
+
Choline
CoA
+
ACh
Choline Acetyltransferase
(ChAT)
Ach
Acetate
+
Choline
Acetylcholine
Esterase (AChE)
? 2 receptor types
? Nicotinic (ionotropic)
? Muscarinic (metabotropic)
Synthesis

Major ACh Pathways
? Dorsolateral Pons ? mid/hindbrain [REM sleep]
? Basal Forebrain ? cortex [Learning (esp. perceptual), Attention]
? Medial Septum ? Hippocampus [Memory]

Monoamines
? Catecholamines
Dopamine - DA
– Dopaminergic
Norepinephrine - NE
– Noradrenergic
Epinephrine - E
– Adrenergic ~
? Indolamines
Serotonin - 5-HT
– Serotonergic

Monoamines (DA, NE, 5-HT)
? Modulatory (can have both
excitatory and inhibitory
effects- varies by receptor)
? Recycled by reuptake
transporter
? Excess NT in terminal broken
down by
– monoamine oxidase (MAOA/B)
– catechol-O-methyltranferase -
COMT
? Axonal varicosities (bead-like
swellings) with both targeted
and diffuse release

Dopamine
? Rewarding/motivating effects
? Biosynthesis:
Tyrosine L-DOPA DA
Tyrosine
Hydroxylase
DOPA
Decarboxylase
? Dopamine reuptake transporter (DAT)
? 5 receptor types (D1–D5, all metabotropic)
? D1 (postsynaptic)
? D2 (pre autoreceptors and postsynaptic)
? Autoreceptors are release-regulating
homeostatic mechanisms

Major DA Pathways
? Nigrostriatral (Substantia Nigra ? Striatum) [Motor movement]
? Mesolimbic (VTA ? limbic system) [Reinforcement and Addiction]
? Mesocortical (VTA ? prefrontal cortex) [Working memory and planning]
? Tuberoinfundibular tract (hypothalamus ? pituitary) [neuroendocrine
regulation]

Norepinephrine
? Generally excitatory behavioral effects
? Biosynthesis:
DA NE
Dopamine
Beta-hydroxylase
? Many receptor types
(metabotropic)
? ?1, ?1-2 (postsynaptic, excitatory)
? ?2 (autoreceptor, inhibitory)

Major NE Pathway
? Locus Coeruleus ? throughout brain [vigilance and attentiveness]

Serotonin
? Varying excitatory and inhibitory
behavioral effects
? Biosynthesis:
Tryptophan 5-HTP 5-HT
Tryptophan
Hydroxylase
5-HT
Decarboxylase
? At least 14 receptor types, all metabotropic and
postsynaptic except:
? 5-HT1A,B,D (autoreceptors) – found in CNS
? 5-HT3 (inhibitory, ionotropic) – found in the intestines

Major 5-HT Pathways
? Dorsal Raphe Nuclei ? cortex, striatum
? Medial Raphe Nuclei ? cortex, hippocampus
Roles in:
Mood
Eating
Sleep and dreaming
Arousal
Pain
Aggression

? MAOIs
Iproniazid
? Reuptake blockers
– Tricyclic antidepressants
? Imipramine
? Desipramine
- SSRIs
– Cocaine & Amphetamine ~
Indirect Monoamine Agonists

Neuropeptides
? Low concentration in brain (picomolar)
? Large vesicles
? Co-localized with other transmitters
? Circuits
– Interneuronal
? Modulatory functions
? Mostly inhibitory
? Virtually all metabotropic
? Slow acting, long duration (10-1000 ms)
? Examples: Enkephalins, Endorphins, Oxytocin,
Vasopressin, Opioids

Opioids
? ?-endorphin
– made from proopiomelanocortin (POMC)
– produced in pituitary gland, hypothalamus, brain stem
? Enkephalin
– made from proenkephalin (PENK)
– produced throughout brain and spinal cord
? Dynorphin
– made from prodynorphin (PDYN)
– produced throughout brain and spinal cord

Opioids Receptors
Receptor High affinity ligands
mu ?-endorphin, enkephalins
delta enkephalins
kappa dynorphins
? Opioids act at all opioid receptors, but with
different affinities
? Distributed throughout brain and spinal
cord, especially in limbic areas
? Some overlap but quite distinct localizations

Opioid Receptors (cont.)
? Metabotropic, with either
– moderately fast indirect action on ion channels
– long-term action via changes in gene expression
? Most analgesic effects from mu receptor action
? Some analgesic effects from delta
? Many negative side effects from kappa

Endorphins
? Morphine and heroin are agonists that bind to
receptor sites, thereby increasing endorphin
activity

An Evolutionary Perspective
Nesse and Berridge, 1997
? An electrochemical brain
– Neurotransmitters have retained function for millions
of years and are found in many species - from
invertebrates to humans
? Maximization of Darwinian fitness
– Evolution created many chemically-mediated adaptive
and self-regulatory mechanisms to control emotion
and behavior
? Mismatch between ancient chemical mechanisms
and modern environments
“The problem is rooted in the fundamental design of the human nervous system”

Darwinian Fitness
– DA and opioids are part of chemically-mediated incentive
mechanisms that act as signals (motivation/reward) for a
fitness benefit
? you “like” something (opioids) or
? you “want” something (dopamine)
– Furthermore, DA plays a role in drawing
attention/highlighting significant or surprising stimuli
? Mechanisms for greater control? As a means to prioritize likes?
for anticipatory processing? facilitates learning?
– These functions become susceptible to disruption and
addiction from external chemical signals

Mismatch
– Technological inventions such as the hypodermic needle,
synthetic psychoactive drugs, video games, snacks etc are
evolutionarily novel features that create specific ecological
pressures
? They can be inherently pathogenic because they bypass the adaptive
mechanisms and act directly on neurotransmitter systems
– positive emotions are signals to approach
? drugs that artificially induce positive emotions give a false signal of a
fitness benefit
? under some circumstances this could be beneficial (increase
empathy)
– negative emotions are signals to avoid
? drugs that block negative emotions can impair useful defenses
? is there utility to anxiety? jealousy? low mood and depression
(decrease the tendency for behaviors that are dangerous or useless?
embarrassment and guilt (regulating the individual’s hierarchical role
in a group?

Drug Effects
? External drugs hijack these evolved incentive
mechanisms and most likely impair adaptation
– When exposed to drugs the wanting system motivates
persistent pursuit of drugs that no longer give pleasure
– a core feature of addiction.
– Drugs produce sensitization of incentive mechanisms

狠狠撸

Role of Neurotransmitters with their detailed description

Recommended

More Related Content

Similar to Role of Neurotransmitters with their detailed description (20)

Recently uploaded (20)

Role of Neurotransmitters with their detailed description