SL65.0155

SL65.0155 is one of the most important experimental demonstrations that 5-HT4 partial agonism enhances cognition, and it helped cement the receptor as a target for Alzheimer's disease and other memory disorders. It is a selective, orally active 5-HT4 partial agonist that shows behavioural efficacy at strikingly low doses in the range of hundredths of a milligram per kilogram in rodents.

In a model of temporal-lobe damage, intradentate colchicine lesions that destroyed dentate granule cells produced a clear associative learning deficit in an olfactory discrimination task; a single low dose of SL65.0155 given before training enabled complete recovery of associative learning in the lesioned animals, suggesting 5-HT4 activation can compensate for hippocampal-circuit damage relevant to pathological ageing ^[1].

Beyond memory, SL65.0155 improved attention. In the five-choice serial reaction time task, a standard rodent test of sustained attention, it increased the proportion of correct responses, reduced incorrect and perseverative responses, and produced benefits comparable in several respects to the reference cognitive enhancer nicotine, supporting the idea that 5-HT4 agonists may help attentional as well as mnemonic deficits ^[2]. The human relevance of the underlying mechanism has since been reinforced by studies showing that the clinical 5-HT4 agonist prucalopride improves verbal learning and memory in healthy volunteers ^[3].

SL65.0155 has not been evaluated for safety in humans and should be regarded strictly as a research compound. In rodent studies it was active and behaviourally well tolerated at very low doses, but no human tolerability, dosing, drug-interaction, or cardiac data exist. As with all brain-penetrant 5-HT4 agonists, peripheral prokinetic and serotonergic class effects are theoretically possible, and its cardiac profile has not been characterized to clinical standards.

SL65.0155 was developed by Sanofi-Synthelabo in the late 1990s and early 2000s as part of an effort to exploit the 5-HT4 receptor for cognitive disorders, and it became a widely cited pharmacological tool after academic groups demonstrated its memory- and attention-enhancing effects in rodents. It was studied alongside RS-67333 as evidence accumulated that 5-HT4 agonism could both enhance cognition and, through effects on amyloid precursor protein processing, potentially modify Alzheimer's disease. It remained an investigational tool and did not progress to an approved cognitive therapy.

In the cognitive neuroscience literature SL65.0155 is regarded as a benchmark pro-cognitive 5-HT4 partial agonist, frequently referenced for its low-dose efficacy and its ability to restore learning after hippocampal lesions. In nootropic communities it is discussed with theoretical interest as an early, potent 5-HT4 cognition enhancer, though it has never been available as a consumer product and lacks human data. Its reputation rests on a compact but influential preclinical record.