Figure 7

Long-term developmental exposure to TNF-α results in altered tectal circuitry. (A) Sample retinotectal synaptic currents in response to minimal and maximal electrical stimulation of the optic nerve. (B) The number of retinotectal (RT) inputs innervating a single tectal cell was estimated by dividing the maximal response by the minimal response. TNF-α-treated tadpoles show an increased number of retinotectal inputs per cell, consistent with lack of developmental refinement. (C) Maximal stimulation of the optic chiasm results in a prolonged barrage of polysynaptic activity driven by local intratectal circuits. The first peak of the response is the monosynaptic retinotectal input. Two sample traces are shown for both control and TNF-α reared tectal neurons. Notice that the duration and distribution of the recurrent activity is longer and slower in the TNF-α reared tadpoles. (D) Quantification of the time course of the polysynaptic activity. Synaptic charge was measured over the first three 50-ms bins following the onset of the response. Data were plotted as percent of the total synaptic charge during the entire time period. Grouped data were then fitted to a line using linear regression. Neurons from TNF-α reared tadpoles show significantly slower decay of the polysynaptic response, indicating increased intratectal interconnectivity. Asterisk indicates p < 0.05. For P-values see Results.