CNS Pharmacology Dr. Pond Flashcards
Where is the nucleus located?
Neuron cell
Cell body
What are the Processes (extensions) of a neural cell?
Dendrites: receive signals
Axon: send signals to other cells (communicate)
What is the part of the neuron where the action potential originates?
-sending signals through the axon starts with the action potential
-the action potential is elicited in the “Initial segment” or axon hillock
What are breaches of the axon called?
-Axon collateral
At which part of the neuron do chemicals get released to communicate with other neurons?
Axon terminals
Different forms of Neurons in reference to axon and dendrites?
-Multipolar: 3 or more processes coming off the cell bodies
-> Motor neuron (muscle), but many others
-Bipolar: 2 processes: 1 axon, 1 dendrites
-> retina, olfactory cortex
-Pseudounipolar: 1 process coming off the cell body, but it branches in two different directions: 1 axon, 1 dendrite
-> dorsal root ganglion, sensory (afferent) neurons (pain neurons)
What are the different Glia cells?
-Astrocytes: regulate neuronal microenvironment, since neurons are very excitable (through ions), the concentration of ions and chemicals must be regulated, part of the BBB
-Microglial cells: resident immune cells in the CNS, since the BBB exclude leucocytes, these cells act as immune cells in the brain
-Myelinating cells: Oligodendrocytes (myelinate axons in the CNS (brain and spinal cord) and Schwann cells (myelinate cells in the periphery)
What is the purpose of myelinating cells?
-lipid region that doesn’t conduct electrical signal
-the signal skips myelinated part -> fast conduction
Which cells form and circulate cerebrospinal fluid?
Ependymal cells
they have beads that circulate the fluid in the ventricular space
Function of the ATP pump
takes 3 Na(+) from inside to the extracellular space
-> thereby using ATP (hydrolyze to ADP)
takes potassium from outside to inside
inside: net negative
outside: net positive
-the pump is constitutive (always on) - creating a gradient: a lot Na outside and lots of potassium inside
-Primary active transporter
Which channels transport ions through facilitated diffusion?
Ion channels (ions can’t cross the membrane since the membrane is lipophilic and nonpolar)
-transport down the gradient
-no energy required
What are the different typed gated channels?
-mechanical
-chemical/ligand: opens when a ligand binds to the channel
-voltage-gated: net positive outside and net negative inside -> when the charge of the membrane changes -> opening of the gate
How do ion channels transport specific ions?
Because they are charge-specific (consisting of amino acids), depending on the charge they will transport specific chemicals
-either cation channel (+) or anion channel (-)
or size-specific:
-they may conduct sodium but not potassium
What does it mean when the membrane is polarized?
-net charge inside is more negative than outside
-Depolarization: movement of membrane potential back to 0
-Overshoot: membrane potential moves beyond 0 to the positive
-Repolarization: bringing the membrane potential back to resting (negative membrane potential = -70mV)
-Hyperpolarization: taking membrane potential more negative than resting -70 mV
Why do we see over-repolarization?
K channels are slow to close
Which ion channels cause depolarization?
Na (+) channels (Na moves inside)
also overshoot
Which channels cause Repolarization?
-Potassium channel (moves out)
-Chloride channel (moves in?)
Which channels are involved in the action potential?
-voltage-gated Na-channel
open - inactivate rapidly - shut closed
-voltage-gated K-channel
open - close slowly
What is the purpose of the deactivated state of the Na channel?
-as the membrane depolarizes the Na channel opens and the inside of the membrane becomes positive
-after inactivation, the Na channel stays shut for a while: to make sure the membrane potential stays positive and the action potential doesn’t spread but move from axon hillock to axon terminal in one direction;
-and to ensure the refractory period
What is the Equilibrium potential?
The potential that is desired by specific ions
E(Na): +72 mV - when Na channel open, it tries to get the membrane potential to +72 mV by Na moving in - during depolarization
E(K): -89.7 by K moving out - during repolarization
E(Cl-): -89.2 by Cl moving in - during repolarization
What is the absolute (ARP) and relative refraction period (RRP) phase?
absolute: no action potential can fire no matter how strong the stimulus is, bc there are no enough open Na channels
relative: some Na channels open again, it is still hard to elicit the action potential -> the action potential is weak
Which channels are located in the terminal axon?
high-treshhold Ca2+ channels (strong depolarization (+) needed)
How does signal transduction in the synapsis work?
action potential moves from axon hillok to axon terminal -> open Ca2+ channel -> Ca2+ binds to proteins on the vesicles that contains neurotransmitter
it facilitates the fusion of vesicles and the axon membrane -> release of NT at synaptic cleft
What are the receptors on the postsynaptic neuron that receive Neurotransmitter?
-ionotropic receptors (ligand-gating ion channels)
-> the Neurotransmitter is the ligand -> causes opening of the ion channel and ions to move through the channel
-Metabotropic receptors (G-protein-coupled)
NT binds -> alpha subunit of the G-protein (alpha, beta, gamma) cleaves and binds to:
effector protein -> opening/close ion channel
OR
ion channels for -> opening/close ion channel
How does ion channel opening occur with an effector protein?
-effector protein: enzyme
f.e. adenylate cyclase -> converts ATP to cAMP
cAMP (second messenger) opens/closes the ion channel
How fast do channels on the postsynaptic neurons open upon activation?
ion channels: ACTION is fat but brief
metabotropic: Action is slow and long-lasting due to activation through second messenger
What are ways the postsynaptic neurons respond to neurotransmitters?
NT causes ion channels to open which causes
Excitatory Postsynaptic Potential (EPSP) - elicited by depolarization events
or
Inhibitory Postsynaptic Potential (IPSP) - elicited by repolarization events
Which ions cause EPSP?
Na -> depolarization towards treshhold -> EPSP
K and Cl cause IPSP
What type of postsynaptic potential is caused by closing K channels?
K usually moves out causing repolarization
-> when K channel closes it causes depolarization
-> EPSP
A single EPSP is enough to trigger an action potential. T/F
False, multiple are required
-Temporal summation: 2 EPSP fire with a short gap
-Spatial summation: 2 EPSP in same area combined (same space)
-Spatial summation of EPSP and IPSP -> cancel out
Presynaptic inhibition/facilitation
-axoaxonic synapsis (dominantly in
spinal cord)
-presynaptic axon communicate with postsynaptic dendrite + another postsynaptic axon connected to the first postsynaptic axon
the presynaptic neuron is influenced by the other axon -> axon releases GABA and block Ca channel on the the other presynaptic neuron
-> blocking Ca channel causes lower NT release and reduced signal transduction to the next postsynaptic neuron
Which NT has an inhibitory/facilitation effect on the presynaptic neuron (axoaxonic)
inhibitory: GABA
facilitation: Serotonin
What is the purpose of axoaxonic inhibition/facilitation?
it is homoeostatic
since NT gets released and diffuses uncontrolled and may over-induce neurons
Which of the Neurotransmitters are called Monoamines?
-Dopamine, Norepinephrine, Noradrenaline, Serotonin
-Catecholamine = Noradrenaline, Norepinephrine, Dopamine are
-all have a single amine group
Catecholamines are derived from which amino acids?
Tyrosine
Serotonin is derived from Tryptophane
GABA is derived from which amino acid?
Glutamate
What is the main excitatory NT?
Glutamate
-seen all over the CNS
-synthesized from Glutamine via Glutaminase in the presynaptic neuron -> Glutamate is then stored in the vesicle (vesicle glutamate transporter vGLUT)
-
How is Glutamate turned off?
Reuptake from synaptic cleft by Glutamate transporter into Astrocytes
-converted back into Glutamine
-released back to the presynaptic neuron
What are the Glutamate receptors?
3 ionotropic receptors
-AMPA (Na transport): uniformly distributed in the brain - often next to NMDA receptors
-NMDA (Na and Ca transport): uniformly distributed in the brain - often next to AMP receptors
-Kainate (Na transport): HIP, cerebellum, spinal cord
Why are NMDA receptors considered ligand and voltage-gated?
Glutamate binds as a ligand
-Mg blocks the channel until the membrane charge changes
-the membrane changes when Na moves in through the AMPA receptor -> as depolarization occurs, Mg will move away from the NMDA-r -> the NMDA-r will allow Ca2+ and Na to move in
How does Ca2+ influx influence Glutamate receptors on the membrane?
-Ca2+ (2nd messenger) activates specific pathways that will add more AMPA receptors
-more AMPA receptors will cause more Na to enter and a greater chance for depolarization
-> this will again makes it more likely for Mg2+ to be lifted from NMDA receptors and allow for more Ca2+ and Na+ influx
POSITIVE FEEDBACK
What important role are NMDA and AMPA receptors believed to play?
Learning and Memory
What is the major role of Glycin receptors?
Glycin receptor
-major inhibitory!
-Chloride channel -> Cl causes hyperpolarization
-IPSP
-brain stem, spinal cord
What is the major inhibitory Neurotransmitter?
GABA
-40% of brain neurons
How is GABA recycled/removed?
-it derived from Glutamate
GABA is taken up by Gliacell (astrocyte) -> converted to Glutamate -> Glutamine
Glutamine is transferred back to the presynaptic neuron and converted to Glutamate -> GABA
-also there is a transporter that transports GABA or Glutamate or Glutamine back to the presynaptic neuron (favors Glutamine)
Which ions pass through the GABA receptors?
Chloride
-inhibitory -> IPSP
-hyperpolraization
Drugs targeting GABA(a) receptor
-Benzodiazepines
-Barbiturates
-Alcohol
How is Acetylcholine synthesized?
-in the presynaptic neuron
Acetyl (from Acetyl-CoA) combined with choline
Role of GABA (b)
-metabotropic -> act via second messenger
-inhibitory
-decrease adenylate cyclase activity
-controls K(+) channels = IPSP (postsynaptic neuron)
-controls Ca2+ channels: closing -> decrease NT release on presynaptic neuron
-can be found on pre or postsynaptic neuron
GABA (c): control Cl(-) channels = IPSP
How is Acetylcholine recycled from the synaptic cleft?
Acetylcholine esterase cleaves Acetylcholine to Acetyl group and choline
-> Choline moves back to the presynaptic neuron and is reused to form new Acetylcholine
What are the major cholinergic pathways?
-Nuclei of the basal forebrain
projects throughout the cortex (learning)
projects throughout the limbic areas (memory)
-Nuclei of the brain stem
projects throughout
thought to control the REM sleep
What are the subtypes of Acetylcholine receptors?
-Nicotinic receptors (ion channels)
influx of Na(+) and efflux of K(+)
-> still EPSP bc more Na(+) coming in than K(+) going out
-Muscarinic receptors (metabotropic)
M1: tend to close K(+) channels -> EPSP (depolarization)
M2: tend to open K(+) channels -> IPSP (hyperpolarization)
Synthesis of Catecholamines
from Tyrosine -> Dopa -> Dopamine -> Norepinephrine -> Epinephrine
How are Catecholamines and Monoamines removed/recycled?
Dopamine transporter: reuptake of dopamine from the synaptic cleft back to the presynaptic neuron
COMT: extracellular degradation of catecholamines (dopamine, norepinephrine)
Monoamine oxidase (MAO): intracellular degradation of dopamine, norepinephrine, serotonin
80% of dopamine is taken up by dopamine transporter back to the presynaptic neuron
20% is degraded by COMT
Where does the Nigrostriatal pathway lead to?
Neurons from the substantia nigra to caudate-putanem (striatum)
motor control, death of these neurons results in Parkinson’s disease
Where does the Tuberoinfundibular pathway lead to?
from the Hypothalamus to the pituitary gland
Hormonal regulation
Maternal behavior (nurturing) - dopamine inhibits prolactin release (for milk production)
Where do the Mesolimbic and mesocortical pathways lead to?
from the ventral tegmental area (VTA, midbrain) to the limbic areas or prefrontal cortex
Memory
Motivation and emotional response
Reward and desire
Addiction
possibly misregulated in schizophrenia
How do Dopamine receptors affect cAMP?
D1 and D5: increase adenylate cyclase activity -> increase cAMP
D2, D3, D4: decrease adenylate cyclase activity -> decrease cAMP
Are dopamine receptors metabotropic or ionotropic?
metabotropic
How is Norepinephrine synthesized?
Tyrosine -> Dopa -> Dopamine -> Norepinephrine
80% reuptake by NET
20% degraded by COMT
Where do Norepinephrine neurons lead to?
Noradrenergic pathways
major nucleus is called: locus coeruleus
-runs through the brainstem and midbrain
controlling and arousing
-regulates many behavioral & physiological processes
sleeping, waking, attention, appetite, emotions
Are the Noradrenergic receptors depolarizing or hyperpolarizing?
-Beta-1 (b1)
-Beta-2 (b2)
-Alpha-1 (a1)
-> depolarizing by closing K(+) channels
-Alpha-2 (a2)
-> hyperpolarizing by increasing K(+) conducance
How is the amount of Norepinephrine regulated?
Feedback inhibition with alpha-2 receptors
Feedback Excitation with ß-2 receptors
How is Serotonin recycled?
-Reuptake by SERT
-some degraded by MAO
Where do Serotonin neurons lead to?
stems from the Raphe nuclei, concentrated in the upper brainstem
-> projects throughout the brain, spinal cord, cerebellum
mood, appetite, sleep, temperature, arousal
Are Serotonin receptors metabotropic or ionotropic?
-All are metabotropic except for 5-HT3
5-HT3 is a Na/K channel
Role of Serotonin receptors
-5-HT1A: presynaptic/postsynaptic - inhibitory
-5-HT1D: mostly presynaptic - inhibitory
-5-HT2A: mostly postsynaptic - excitatory
Histaminergic pathways
The tuberomammillary nucleus of the hypothalamus
-> project throughout the brain: cerebral cortex, corpus callosum, cerebellum, pons, medulla, spinal cord
How is histamine synthesized/recycled?
-Synthesized from histidine by histidine decarboxylase
-loaded into vesicles by VMAT
-degraded by histamine methyltransferase, diamine oxidase (gut)
Which peptides affect the activity of individual
neurons?
-opioid peptides, orexins (hypocretins), POMC, neuropeptide Y, substance P, neurotensin, and somatostatin
-often released with low MW transmitters (Monoamines: dopamine, norepinephrine, epinephrine, serotonin)
Opioid peptides and their receptors
-mu (μ) receptors –β endorphin (preferentially)
-delta (δ) receptors – enkephalins
-kappa (κ) receptors – dynorphin
What are the two Endocannabinoids?
-anandamide
-2-arachidonylglycerol
How do Endocannabinoids affect NT in the brain?
-suppress release of neurotransmitter GABA
-Synthesized in response to Ca2+
-Activate cannabinoid receptors (CB1- brain and
CB2- periphery)
