A GABA_A receptor is activated on a neuron, but the chloride reversal potential happens to equal the resting membrane potential — so no net Cl⁻ current flows. Is the neuron inhibited?
ANo — if no net current flows, the receptor activation has no functional effect on the neuron
BYes — the open channels still increase membrane conductance, making it harder for simultaneous excitatory inputs to drive depolarization (shunting inhibition)
CNo — GABA_A receptors can only inhibit when the chloride reversal potential is more negative than the resting potential
DYes — but only indirectly, because GABA also activates GABA_B receptors that open K⁺ channels
This is the shunting inhibition mechanism — one of the key insights of GABAergic neuroscience. Even when no net Cl⁻ current flows (because V_rest ≈ E_Cl), the open channels dramatically increase membrane conductance. According to Ohm's law, a larger conductance means that the same excitatory current produces a smaller voltage change. Think of it as opening a drain while someone tries to fill a bathtub: the water level (membrane potential) rises more slowly even if no water flows out. Shunting inhibition is particularly powerful for controlling integration: it doesn't need to hyperpolarize the cell to prevent it from firing.
Question 2 Multiple Choice
Benzodiazepines (e.g., Valium, Xanax) produce sedation and reduce anxiety. Based on your understanding of GABAergic transmission, which mechanism best explains these effects?
ABenzodiazepines block GABA reuptake transporters, keeping more GABA in the synapse and prolonging inhibitory signaling
BBenzodiazepines act as direct agonists at GABA_B receptors, causing slow K⁺-channel mediated hyperpolarization
CBenzodiazepines are positive allosteric modulators of GABA_A receptors, increasing the frequency of chloride channel opening in response to GABA and thereby enhancing inhibitory tone throughout the brain
Benzodiazepines bind to an allosteric site on the GABA_A receptor (between the α and γ subunits) and increase the *frequency* of chloride channel opening in response to GABA — they potentiate, rather than replace, GABA's action. This broadly enhances inhibitory tone across the brain, reducing anxiety, inducing sedation, and raising the seizure threshold. Barbiturates act similarly but increase channel *duration* rather than frequency, and at high doses can open channels without GABA — which is why they have a much lower therapeutic index than benzodiazepines. Alcohol also enhances GABA_A function, explaining overlapping sedative effects.
Question 3 True / False
GABAergic inhibition primarily functions to reduce neural activity and plays little role in generating oscillatory patterns in the brain.
TTrue
FFalse
Answer: False
GABAergic interneurons are essential rhythm generators in the brain. Fast-spiking basket cells (which release GABA) fire in rapid synchronized bursts that impose precise timing on pyramidal neuron populations, generating gamma oscillations (30–80 Hz) associated with attention, working memory, and sensory processing. Inhibition doesn't just silence neurons — it creates windows during which excitatory neurons can fire together coherently and prevents them from firing at other times. This temporal patterning is how inhibition sculpts neural codes rather than simply suppressing them. Loss of GABAergic interneurons disrupts oscillatory activity and is implicated in conditions like schizophrenia.
Question 4 True / False
GABA_B receptors, unlike GABA_A receptors, produce inhibitory effects through G-protein signaling, which means their effects develop more slowly but can last longer than GABA_A-mediated inhibition.
TTrue
FFalse
Answer: True
GABA_B receptors are metabotropic: they couple to Gi/o proteins, which inhibit adenylyl cyclase, open inwardly rectifying K⁺ channels (GIRK) on the postsynaptic membrane (causing slow hyperpolarization), and inhibit voltage-gated Ca²⁺ channels presynaptically (reducing further neurotransmitter release). This G-protein cascade takes tens of milliseconds to develop and produces effects lasting hundreds of milliseconds — much slower than GABA_A's millisecond-timescale chloride channel opening. The brain thus has two temporal scales of inhibition: fast GABA_A for millisecond precision (spike timing control) and slow GABA_B for sustained dampening (modulating overall excitability over longer windows).
Question 5 Short Answer
Explain how GABAergic inhibition can be described as 'sculpting' neural activity rather than simply suppressing it.
Think about your answer, then reveal below.
Model answer: GABAergic interneurons don't uniformly silence all activity — they impose precise spatial and temporal patterns. By firing in synchronized bursts, they create brief windows during which pyramidal neurons can fire together (as in gamma oscillations), then clamp activity between windows. This temporal gating organizes which neurons fire, when they fire, and in what sequence — the structure that underlies neural computation. Inhibition defines patterns through selective timing, not just amplitude reduction.
Consider that removing GABAergic inhibition entirely doesn't produce more processing — it produces seizures. The nervous system requires inhibition not as a brake but as the mechanism that gives neural activity its shape. Basket cells synchronize pyramidal neurons into gamma-band oscillations that coordinate information across cortical areas. Chandelier cells control action potential initiation timing. Somatostatin interneurons regulate dendritic computation. Each class of interneuron performs a different sculptural function. This is why GABA dysregulation underlies so many neurological and psychiatric conditions: schizophrenia (interneuron loss), epilepsy (insufficient inhibition), and anxiety (GABA system underactivity).