In a first step to unravel asymmetric influences of these nuclei, the present study investigated if the largest of the bed nuclei, the Nucleus subpretectalis displays morphological asymmetries in the pigeon. We found that the Nucleus subpretectalis in fact exhibits asymmetric cell sizes with larger cell bodies on the left side. This asymmetrical pattern was not present in dark-incubated animals indicating that cell size asymmetries within Nucleus subpretectalis are induced by asymmetric photic stimulation during embryonic development.. 
Outside of the telencephalon at P9, we found distinct label in nucleus ovoidalis (OV), nucleus spiriformis lateralis (SpL), and Nucleus subpretectalis (SP) in the midbrain, almost the entire diencephalon including nucleus dorsomedialis posterior thalami (DMP), stratum griseum et fibrosum superficiale (SGF) in optic tectum, and Purkinje cells in cerebellum.
After an injection of WGA-HRP into the Rt, labelled neurones were observed in the striatum griseum centrale (SGC) in both sides of the tectum (TO) and in the ipsilateral Nucleus subpretectalis/nucleus interstito-pretecto-subpretectalis (SP/IPS).
A key component of this pathway is the projection from the optic tectum onto the nucleus rotundus and the Nucleus subpretectalis.
After BDA injections into nucleus rotundus, retrogradely labelled neurons were observed consistently within the following neuronal groups in the midbrain and the diencephalon: (i) the stratum griseum centrale of the optic tectum; (ii) the Nucleus subpretectalis in the pretectum; (iii) the nucleus ansa lenticularis posterior, the posterior nucleus of the ventral supraoptic commissure, and the posteroventral nucleus, in the dorsal thalamus and (iv) the lateral suprachiasmatic nucleus and part of the reticular complex in the ventral thalamus.
The detailed electron microscopic analysis of the structure of the neurons in these nuclei revealed that the neurons in the Nucleus subpretectalis displayed GABA-like immunoreactivity.
Based on cytoarchitectural and HRP results, the pretectum of the adult hen was divided into the following eight nuclei: nucleus principalis pretectalis (P), Nucleus subpretectalis (SP), nucleus principalis precommissuralis (PPC), nucleus medialis pretectalis (PTM), nucleus pretectalis dorsalis (APd), nucleus area pretectalis (AP), nucleus spiriformis lateralis (SPL), and nucleus spiriformis medialis (SPM).
In addition, these HRP injections into EW resulted in labeled cells in the medial mesencephalic reticular formation (MRF) lateral and ventral to the oculomotor nucleus and in a localized area of the rostral lateral mesencephalic reticular formation (LRF) dorsolateral to Nucleus subpretectalis.
Both labelled nucleus spiriformis lateralis and nucleus geniculatus lateralis, pars ventralis especially heavily and also labelled the nucleus habenula medialis; Nucleus subpretectalis; nucleus isthmi, pars magnocellularis; nucleus reticularis gigantocellularis; nucleus reticularis lateralis; nucleus tractus solitarii; nucleus vestibularis dorsolateralis; nucleus vestibularis lateralis; nucleus descendens nervi trigemini; and the deep cerebellar nuclei.
In the third group, the lesions included Rt, GLv and Nucleus subpretectalis (SP).
In those cases in which the nucleus rotundus deficit was observed, the lesions were found to include the Nucleus subpretectalis, which, like nucleus rotundus, receives tectofugal fibers via the brachium of the superior colliculus.
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