Connections of eye-saccade-related areas within mesencephalic reticular formation with the optic tectum in goldfish.
Physiological studies demonstrate that separate sites within the mesencephalic reticular formation (MRF) can evoke eye saccades with different preferred directions. Furthermore, anatomical research suggests that a tectoreticulotectal circuit organized in accordance with the tectal eye movement map is present. However, whether the reticulotectal projection shifts with the gaze map present in the MRF is unknown. We explored this question in goldfish, by injecting biotin dextran amine within MRF sites that evoked upward, downward, oblique, and horizontal eye saccades. Then, we analyzed the labeling in the optic tectum. The main findings can be summarized as follows. 1) The MRF and the optic tectum were connected by separate axons of the tectobulbar tract. 2) The MRF was reciprocally connected mainly with the ipsilateral tectal lobe, but also with the contralateral one. 3) The MRF received projections chiefly from neurons located within intermediate and deep tectal layers. In addition, the MRF projections terminated primarily within the intermediate tectal layer. 4) The distribution of labeled neurons in the tectum shifted with the different MRF sites in a manner consistent with the tectal motor map. The area containing these cells was targeted by a high-density reticulotectal projection. In addition to this high-density topographic projection, there was a low-density one spread throughout the tectum. 5) Occasionally, boutons were observed adjacent to tectal labeled neurons. We conclude that the organization of the reticulotectal circuit is consistent with the functional topography of the MRF and that the MRF participates in a tectoreticulotectal feedback circuit.
Luque
Maria A
MA
Lab. Neurobiologia de Vertebrados, Dept. Fisiologia y Zoologia, Universidad de Sevilla, 41012 Sevilla, Spain.
Perez-Perez
Maria P
MP
Herrero
Luis
L
Torres
Blas
B
D000818:Animals; D001710:Biotin / Q000031:analogs & derivatives / Q000378:metabolism; D001931:Brain Mapping; D003911:Dextrans / Q000378:metabolism; D006054:Goldfish / Q000033:anatomy & histology / Q000502:physiology; D009434:Neural Pathways / Q000033:anatomy & histology*; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D010784:Photomicrography / Q000379:methods; D012154:Reticular Formation / Q000166:cytology / Q000502:physiology*; D012438:Saccades / Q000502:physiology*; D013477:Superior Colliculi / Q000033:anatomy & histology*
D003911:Dextrans; C076397:biotinylated dextran amine; D001710:Biotin