Cellular NeurobiologyBIPN140

1st Midterm Exam Ready for PickupBy the elevator on the 3rd Floor of Pacific Hall (waiver)

Exam Depot Window at the north entrance to Pacific Hall (no waiver)Mon-Fri, 10:00 AM to 4:00 PM

1st midterm regrade: contact the IA who graded the question directly before Nov 14, 2016.

PS4 Q&A will be posted on October 27th

Nick’s Office Hour this Wednesday (Oct 26) is canceled.

Chih-Ying’s Office Hour: Monday, 1:00-2:00 PM, Bonner Hall 4146

BIPN140 Lecture 9: Neurotransmitters and Their Receptors

1. Acetylcholine

2. Glutamate

3. GABA

4. Neuropeptides

Su (FA16)

Acetylcholine (Figs. 5.4)

Acetylcholine Metabolism (Fig 6.2)

Nicotinic ACh Receptor: nAChR

Muscarinic ACh Receptors: mAChR (Fig. 6.4)

Muscarine, a poisonous alkaloid found in some mushrooms, a mAChRagonist, profound effect on the peripheral parasympathetic nervous system leading to convulsion and death

Glutamate Synthesis and Cycling between Neurons and Glia (Fig. 6.5)

Glutamate Receptors: Ionotropic & Metabotropic

AMPA

Kainic Acid

NMDA

Glutamate

Structure of the AMPA & NMDA Receptor (Fig. 6.7)

Co-agonist

Different Ionotropic Glutamate Receptor Properties (Fig. 6.6)

slower &longer-lasting

slower decay

rapid desensitization

Pharmacological Separation of Two Components of EPSC

APV: NMDA receptor antagonist

NMDA component: slower

Peak current: AMPA component

CNQX: AMPA receptor antagonist

NMDA component: slower

Pharmacological Separation of Two Components of EPSC

Synthesis and Reuptake of the Inhibitory NTs: GABA (Fig. 6.8)

GABABGABAA

GABA receptors

Excitatory Actions of GABA in the Developing Brain (Box 6D)

NKCC1KCC2

Comparison of Key Ligand-Gated Channels

Kandel et al., Principles of Neural Science, 5th Edition, Figure 10-7

Major Neurotransmitters: Neuropeptides (Fig, 6.17)

Proteolytic Processing of Pre-Propeptides (Fig. 6.16)

Rough ER

Golgi/Vesicles

Vesicles

Varieties of ionotropic NT receptors (Fig. 6.3)

Varieties of metabotropic NT receptors (Fig. 6.4)

Background: GABA, the main “inhibitory” transmitter in the brain, is actually excitatory during embryogeneis and early postnatal life because of a “reversed” Cl- gradient. The excitatory phase of GABA signaling is critical for proper neuronal development and integration into circuits, i.e. synapses forming onto the neuron. Key to the GABA switch from excitation to inhibition is the appearance of the “mature” Cl- transporter KCC2, which pumps Cl- out of the cell, and the loss of the “immature” transporter NKCC1, which pumps Cl- into the cell. The mature Cl- gradient then enables GABA to be inhibitory (Cl- rushes in when GABAA receptors are activated). What determines the timing of the transition?

• Experiments: Spontaneous nicotinic cholinergic signaling drives waves of excitation through the embryonic and early postnatal nervous system. Might this be related to the GABAergic switch? Test whether blocking nicotinic activity delays the developmental conversion of GABAergic transmission from excitation to inhibition. Methods: (1) In chick embryos block nicotinic activity receptor antagonists. (2) In mice block nicotinic activity by removing nicotinic receptor genes (knockouts). Easy test for GABA excitation: calcium fluor to “report” calcium influx (through VGCCs opened by the GABA excitation).

Chick ciliary ganglion: express both nAChRs and GABAA-R

Fig. 1. Blocking nAChR extends the period of GABAergic excitation (pharmacology)

E14 neuron (calcium imaging)

before switch after switch

To block nAChRs: treating with various antagonists at E8

EquilibriumPotential: I = 0

EquilibriumPotential (relative to AP threshold)

NKCC1: keeps intracellular Cl-

high

Linking pharmacological manipulations with molecular mechanisms

Fig. 2. Blocking nAChR extends the period of GABAergic excitation (genetics)

Mouse hippocampal neurons

7-nAChRs: relatively high calcium permeability (remember: calcium is an important signaling molecule!)

Genetic manipulation: knocking out the gene encoding 7-nAChR subunit

Calcium imaging

Results: Endogenous nicotinic activity determines when GABAergic signaling converts from excitation to inhibition. Nicotinic activity does this by increasing KCC2 and decreasing NKCC1 to make a mature chloride gradient. Also shown (in other figures): (1) Preventing the depolarizing phase of GABA signaling causes the neurons to get less innervation. (2) Interestingly, even the initial inhibitory phase of GABAergic signaling has developmental instructions if, and only if, the neurons is also getting nicotinic excitation (integration is key).