Visual information in birds is to great extent processed in the optic
tectum (TeO), a prominent laminated midbrain structure. Retinal input
enters the TeO in its superficial layers, while output is limited to
intermediate and deeper layers. In addition to visual information, the
TeO receives multimodal input from the auditory and somatosensory
pathway. The TeO gives rise to a major ascending tectofugal projection
where neurons of tectal layer 13 project to the thalamic nucleus
rotundus, which then projects to the entopallium. A second tectofugal
projection system, called the accessory pathway, has however not been
studied as thoroughly. Again, cells of tectal layer 13 form an ascending
projection that targets a nucleus known as either the caudal part of the
nucleus dorsolateralis posterior of the thalamus (DLPc) or nucleus
uveaformis (Uva). This nucleus is known for multimodal integration and
receives additional input from the lateral pontine nucleus (PL), which
in turn receives projections from layer 8-15 of the TeO. Here, we
studied a particular cell type afferent to the PL that consists of
radially oriented neurons in layer 9. We characterized these neurons
with respect to their anatomy, their retinal input, and the modulation
of retinal input by local circuits. We found that comparable to other
radial neurons in the tectum, cells of layer 9 have columnar dendritic
fields and reach up to layer 2. Sholl analysis demonstrated that
dendritic arborization concentrates on retinorecipient layers 2 and 4,
with additional arborization in layers 9 and 10. All neurons recorded in
layer 9 received retinal input via glutamatergic synapses. We analyzed
the influence of modulatory circuits of the TeO by application of
antagonists to gamma-aminobutyric acid (GABA) and acetylcholine (ACh).
Our data show that the neurons of layer 9 are integrated in a network
under strong GABAergic inhibition, which is controlled by local
cholinergic activation. Output to the PL and to the accessory tectofugal
pathway thus appears to be under strict control of local tectal
networks, the relevance of which for multimodal integration is
discussed.
«
Visual information in birds is to great extent processed in the optic
tectum (TeO), a prominent laminated midbrain structure. Retinal input
enters the TeO in its superficial layers, while output is limited to
intermediate and deeper layers. In addition to visual information, the
TeO receives multimodal input from the auditory and somatosensory
pathway. The TeO gives rise to a major ascending tectofugal projection
where neurons of tectal layer 13 project to the thalamic nucleus
rotundus, which th...
»
Login
BibTeX