Nitric oxide synthase inhibition impairs spatial navigation learning and induces conditioned taste aversion

Area of Science:

• Neuroscience
• Cognitive Science
• Pharmacology

Background:

• Nitric oxide (NO), a free radical gas derived from L-arginine, plays a role in brain regions crucial for learning and memory.
• Previous studies showed that nitric oxide synthase (NOS) inhibition with N omega-nitro-L-arginine methyl ester (L-Name) impairs memory recall in primates, with higher doses causing gastrointestinal side effects.

Purpose of the Study:

• To investigate the impact of L-Name on spatial learning in rats using a spatial navigation task.
• To evaluate L-Name's capacity to induce conditioned taste aversion (CTA) to a novel sucrose solution.

Main Methods:

• Rats were administered L-Name (5, 20, and 50 mg/kg) in the Morris water maze task to assess cued spatial learning over three days.
• General activity levels were monitored.
• A two-bottle choice paradigm was used to assess CTA induction by L-Name.
• The effects of L-Name were also examined in conjunction with L-arginine administration.

Main Results:

• L-Name significantly impaired cued spatial learning at all tested doses (5, 20, and 50 mg/kg) without affecting general activity.
• L-Name induced a potent CTA at higher doses (20 and 50 mg/kg).
• Both learning impairment and CTA were reversed by co-administration of L-arginine, indicating NO pathway involvement.

Conclusions:

• Inhibition of NO activity by L-Name selectively impairs cognitive performance at low doses (< 20 mg/kg).
• At higher doses, learning impairment may be secondary to drug-induced malaise and gastrointestinal disturbances.
• Interpreting the role of NO in learning and memory requires careful consideration of potential side effects and the use of selective, centrally-acting compounds.