Breaking the balance: ocular BDNF-injections induce visual asymmetry in pigeons.
In pigeons, asymmetric photic stimulation around hatch induces functional visual asymmetries that are accompanied by left-right differences in tectal cell sizes. Different aspects of light-dependent neuronal differentiation are known to be mediated by the brain-derived neurotrophic factor (BDNF). Therefore, we investigated by means of single or triple BDNF- or saline-injections into the right eye of dark-incubated pigeon hatchlings if ocular BDNF enrichment mimics the effects of biased visual input. As adults, the birds were tested in a grit-grain discrimination task to estimate the degree and direction of visual lateralization followed by a morphometric analysis of retinal and tectal cells. The grit-grain discrimination task demonstrated that triple BDNF-injections enhanced visuoperceptual and visuomotor functioning of the left eye system. Morphometric analysis showed bilateral cell-type dependent effects within the optic tectum. While single-BDNF injections increased cell body sizes of calbindin-positive efferent neurons, triple-injections decreased cell sizes of parvalbumin-positive cells. Moreover, single BDNF-injections increased retinal cell sizes within the contralateral eye. Analysis of BDNF-induced intracellular signaling demonstrated enhanced downstream Ras activation for at least 24 h within both tectal halves whereas activity changes within the contralateral retina could not be detected. This points to primarily tectal effects of ocular BDNF. In sum, exogenous BDNF modulates the differentiation of retinotectal circuitries and dose-dependently shifts lateralized visuomotor processing towards the noninjected side. Since these effects are opposite to embryonic light stimulation, it is unlikely that the impact of light onto asymmetry formation is mediated by retinal BDNF.
Biopsychology, Faculty of Psychology, Institute of Cognitive Neuroscience, Ruhr-University Bochum, Bochum 44780, Federal Republic of Germany. Martina.Manns@rub.de
Martina
M
Manns
Nadja
N
Freund
Oliver
O
Leske
Onur
O
Güntürkün
D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000187:drug effects / Q000196:embryology / Q000378:metabolism; D019208:Brain-Derived Neurotrophic Factor / Q000008:administration & dosage / Q000494:pharmacology*; D064026:Calbindins; D010856:Columbidae / Q000033:anatomy & histology / Q000196:embryology / Q000502:physiology*; D004193:Discrimination Learning / Q000187:drug effects; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000196:embryology / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000187:drug effects*; D007150:Immunohistochemistry; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D013477:Superior Colliculi / Q000166:cytology / Q000187:drug effects / Q000196:embryology; D014795:Visual Pathways / Q000187:drug effects* / Q000196:embryology / Q000502:physiology; D018631:ras Proteins / Q000378:metabolism
D019208:Brain-Derived Neurotrophic Factor; D064026:Calbindins; D064030:S100 Calcium Binding Protein G; D018631:ras Proteins