Immunohistochemistry for choline acetyltransferase
(ChAT) revealed an extensive network of cholinergic fibers
in the tectum of amphibians. The distribution of ChAT immunoreactive
fibers was not restricted to superficial retinocipient
layers, but also included deep tectal layers. The aim of
the present study was to investigate the origin of the
cholinergic inputs to the tectum of amphibians. For that
purpose, application of retrograde tracers in the tectum
of the anuran Rana perezi and the urodele Pleurodeles
waltl was combined with ChAT immunohistochemistry.
Double-labeled cells were found primarily in the nucleus
isthmi of both species. The cholinergic isthmotectal projection
is bilateral and topographically arranged and all retrogradely
labeled cells found in this nucleus were ChAT immunoreactive.
Remarkably, abundant cholinergic cells in two tegmental
nuclei, the pedunculopontine tegmental nucleus (anurans)
and the laterodorsal tegmental nucleus (anurans and urodeles),
were demonstrated to provide additional cholinergic innervation
to the tectum. We compare the present results with previously
reported studies in amphibians and other vertebrates, and
discuss the possible functional significance of the cholinergic
innervation of the amphibian tectum.
Cholinergic Projections From the Pedunculopontine Tegmental Nucleus Contact Excitatory and Inhibitory Neurons in the Inferior Colliculus
