Specific tricyclic antidepressant binding sites in rat brain.

The discovery of high-affinity binding sites for psychoactive drugs such as benzodiazepines, opiates and neuroleptics has opened up new approaches to the study of these drugs and their mechanisms of action. Although most tricyclic antidepressants inhibit neuronal uptake of noradrenaline and serotonin, their mechanism of action remains unclear. Changes in the sensitivity of the beta-receptor after chronic tricyclic antidepressant treatment suggest that they modulate noradrenergic neurotransmission. Tricyclic antidepressants also act directly on cholinergic, histaminergic, alpha-adrenergic and serotonergic receptors. It is not clear, however, which, if any, of these effects are related to the primary antidepressant effect or whether they are simply responsible for some of the side effects. We have thus investigated the possibility that specific binding sites for tricyclic antidepressants exist in the central nervous system. So far, binding studies using 3H-labelled tricyclic antidepressant drugs have only detected binding to histaminergic H2 and cholinergic muscarinic receptors and low-affinity binding. We demonstrate here a population of specific high-affinity binding sites for 3H-imipramine on brain membranes which may be responsible for the antidepressant effects of these drugs.     

DNA sequence for a low-level promoter of the lac repressor gene and an 'up' promoter mutation.

The promoter for a weakly expressed constitutive gene, the lactose repressor gene (lacI), has been sequenced, along with an 'up' promoter mutation Iq. The 10-fold enhancement in I expression found in Iq is the result of a single base change at position -35. To facilitate the sequencing, the lacI gene was cloned in a small plasmid.