Mesolimbic noradrenaline but not dopamine is responsible for organization of rat behavior in the forced swim test and an anti-immobilizing effect of desipramine.

The role of mesolimbic monoaminergic innervation in the organization of rat behavior in the forced swim test (FST) and in the anti-immobilizing action of desipramine (DMI) in the test, was examined. The results can be summarized as follows: neither 6-hydroxydopamine (60HDA)-lesions nor electrical stimulation of the ventral tegmental area (A-10) and intra-accumbens dopamine (DA) microinjections produced specific (i.e. independent from changes in rats locomotion) effects on rat behavior or on DMI action in the FST. On the other hand, 60HDA lesions to the locus coeruleus (LC) antagonized the anti-immobilizing effect of DMI. It was also shown by us that the electrostimulation of the LC produced in the FST an effect similar to that of DMI. Moreover, the intra-accumbens injections of noradrenaline (NA) mimicked the effect of DMI in the test. Similar results were obtained after local administration of adrenergic receptor agonists--phenylephrine and isoproterenol. It is concluded that NA but not DA plays a crucial role in the organization of rat behavior in the FST and in the anti-immobilizing effect of DMI. The data suggest also a direct involvement of the nucleus accumbens septi in these neural processes.