Novel tricyclic derivatives which are agonists of cholinergic receptors, and drugs in which they are present

A tricyclic pyridazine derivative having the formula:

• ##STR53## wherein:
• X represents a group (CH.sub.2).sub.n, where n is an integer equal to 2, 3 or 4, or alternatively a vinylene group or a methylvinylene group;
• R.sub.1 and R.sub.2, each independently represent hydrogen or a substituent occupying one of the free positions of the benzene ring and selected from the group consisting of halogens, a lower alkyl group, a lower alkoxy group, a hydroxyl group, a thiol group, a nitro group, an amino group, a mono- or di-(lower) alkyl amino group and a mono- or di-(lower acyl amino group;
• Y represents oxygen, sulphur or a group --NH--;
• and
• R.sub.3 represents:
• ##STR54## Alk represents a linear or branched alkylene group having from 2 to 5 carbon atoms;
• and
• R.sub.4 and R.sub.5 each independently represents hydrogen, a lower alkyl group or a lower hydroxyalkyl group, or alternatively R.sub.4 and R.sub.5 form, with the nitrogen atom to which they are bonded, an unsubstituted or lower alkyl-substituted pyrrolidin-1-yl, piperidino, morpholino, piperazin-1-yl or 2-oxomorpholino group;
• ##STR55## in which R.sub.6 represents a lower alkyl group having 1 to 4 carbon atoms;
• or ##STR56## in which R.sub.6 is as defined above;
• and salts thereof with pharmaceutically acceptable mineral or organic acids.