Serotonin function in pathological gambling: Blunted growth hormone response to Sumatriptan

Pathological gambling is a disruptive behaviour and an important public health concern that is classified as an impulse control disorder, and is also conceptualized as a prototype of 'behavioural addiction'. Its phenomenology cannot be reduced to a single neurobiological dysfunction; instead, it has been conceived as a complex chain of events in which the serotonergic system (5-HT) has often been suggested as one of the most prominent involved. Acute administration of Sumatriptan, a selective 5-HT_1B/1D agonist, has been used to investigate the functional responsivity of 5-HT_1B/1D receptors in alcoholics, resulting in a blunted growth hormone response. These findings have been interpreted as being due to the down-regulation of these receptors. However, previous studies could not rule out the possibility that the changes in receptor function were induced by chronic substance exposure. Twenty-two pathological gamblers and 19 healthy control subjects were evaluated in response to double-blind administration of both a single dose of oral Sumatriptan (100 mg) and of placebo in a crossover design. All participants were screened to ensure that they were negative for lifetime alcohol and drug addiction, and had been free of substance abuse for at least 6 months. Outcome measures included growth hormone, prolactin, gambling severity, mood, craving and 'high' change scales. A blunted growth hormone response was observed in pathological gamblers compared with healthy controls after Sumatriptan administration. No statistically significant differences were found for prolactin or behavioural measures, except for an increase in anxiety over time in pathological gamblers. These results, together with those obtained in our previous serotoninergic challenge study, document the presence of a serotonergic dysfunction in pathological gamblers similar to that reported in alcoholics.