L11 - drug induced neural behavioural plasticity

Neural plasticity

Structural and functional changes in neurons or synapses following experiences such as learning, development, injury or drug exposure.

What are dendritic spines and why are they important?

→ Small structures on dendrites containing the postsynaptic density (PSD).
→ Spine head size correlates with the number of AMPA receptors.
→ Greater spine density generally indicates greater synaptic connectivity/input.

What effect does repeated cocaine exposure have on dendritic spines in the nucleus accumbens (NAc)?

It increases spine density, suggesting cocaine reorganises patterns of synaptic connectivity.

How does the environment affect cocaine-induced plasticity?

→ Cocaine given in a novel environment produces more robust sensitisation and increased spine density compared with the home environment.
→ This shows that drug effects are influenced by “set and setting.”

Why is drug self-administration useful compared with passive drug injections?

→ Self-administration includes instrumental/operant learning: an action, such as lever pressing, leads to a drug reward.
→ This better models the learning involved in addiction behaviour in humans

What did comparing amphetamine and sucrose self-administration show?

→ Amphetamine, but not sucrose, altered dendritic morphology in NAc neurons.
→ Therefore, drug-taking itself, rather than instrumental learning alone, produces the synaptic reorganisation.

AMPAR/NMDAR ratio

→ A measure of synaptic strength.
→ A higher AMPAR/NMDAR ratio = stronger synapse, associated with increased AMPAR-mediated transmission.

How does repeated cocaine affect synaptic strength in the nucleus accumbens?

→ After long-term withdrawal, repeated cocaine increases AMPAR/NMDAR ratios and therefore synaptic strength.
→ A single cocaine injection does not produce this increase in the NAc.

How do cocaine-induced synaptic changes differ between the VTA and nucleus accumbens?

→ VTA: Both single and repeated cocaine injections increase AMPAR/NMDAR ratios, but the effect is transient.
→ NAc: Increased synaptic strength requires repeated cocaine + long-term withdrawal.
→ This supports the idea that the VTA is involved in initiating sensitisation, while longer-term adaptations occur in the NAc.