Cholinergic innervation and calretinin-immunoreactive neurones in the hippocampus during postnatal development of the rat brain.

Immunohistochemical study of the cholinergic innervation of the hippocampal calretinin-containing cells was conducted on 28 rat brains of postnatal ages: P0, P4, P7, P14, P21, P30 and P60. Sections with double immunostaining for vesicular acetylcholine transporter (VAChT; the marker of cholinergic cells, fibres and terminals) and calretinin were analysed using confocal laser-scanning microscope. Obtained data demonstrate that during development as well as in adult species calretinin-containing neurones in the rat hippocampus form sparse synaptic contact with VAChT-ir terminals. It seems probable that cholinergic innervation is not crucial for the functioning of CR-ir cells--probably they remain under the greater influence of a system other than the cholinergic system.