Glutamate Receptor Activity Is Required for Normal Development of Tectal Cell Dendrites In Vivo

APV slows dendritic arbor growth over 24 hr. Time-lapse in vivo confocal images of DiI-labeled tectal neurons imaged at 24 hr intervals. Images in the top rowof each set (0h) were collected at 0 hr, before drug treatment. Images in the bottom row of each set (24h) were collected 24 hr after exposure to rearing solution (CONTROL) or APV, as indicated. Three neurons from each group are shown in order of increasing dendritic branch tip numbers at the initial image from left toright.

Quantification of the effect of 24 hr APV and CNQX exposure on dendritic growth rate. Increase in TDBL over 24 hr in control, APV-treated, or CNQX-treated neurons. Thenumber of cells observed (n) under each condition is shown. *p < 0.05.

Matrix of changes in dendritic arbor morphology as a function of branch dynamics. A prototypical neuron is shown at thetop. Possible changes in TDBL are shown fromleft to right and branch tip number fromtop to bottom. Neuronal morphology can change from the prototype, without any apparent change in branch tip number or branch length or by increasing or decreasing branch length, branch tip number, or both.

APV blocks dendritic arbor growth over 4 hrin vivo. Time-lapse in vivo confocal images of DiI-labeled tectal neurons imaged at 4 hr intervals. Four cells are shown in order of increasing dendritic branch tip number at the first image from left to right. Thetop row of each set (0h) of images was collected at the beginning of the experiment before drug treatment. Thebottom row of each set (4h) of images was collected after 4 hr in rearing solution (CONTROL) or 100 μm APV.

NMDA receptor blockade slows dendritic arbor development in simple neurons. Time-lapse in vivoconfocal images of four DiI-labeled tectal neurons from control animals or animals exposed to 100 μm APV, 20 μmCNQX, or 1 μm TTX. Images in the top rowof each set (0h) were collected before drug treatment. Images in the bottom row of each set (4h) were collected after 4 hr in rearing solution (CONTROL) or drug solution, as indicated. Control neurons show increases in branch length and dynamic changes in the branch tip numbers and arrangement. Cells from the treated animals show only modest morphological changes. Growth cones are represented by dotted outlines.

Quantification of effect of activity blockade on dendritic arbor development. A, Growth rate over 4 hr in control cells and cells from animals exposed to APV, CNQX, or TTX.Number of cells observed (n) for each condition in A also applies to C andD. B, Scatterplots of changes in dendritic branch length for each neuron under the four conditions. Rate of branch tip additions (C) and retractions (D) for control and drug-treated neurons over 4 hr. E, Scatterplots of changes in dendritic branch tip number for each neuron under the four conditions. *p < 0.05.

Color-coded drawings reveal arbor dynamics. Composite line drawings were obtained by superimposing the drawings from the 4 hr time point onto the 0 hr time point. The stable branches of the arbor are shown in black, branch additions and extensions in green, and branch retractions inred. Control neurons show more branch length additions compared with retractions. APV-treated neurons show fewer additions than controls.

APV selectively decreases branch extension. Dendritic branch length increase (A) and decrease (B) of the arbor for control and drug-treated neurons. Numbers of cells (n) for each condition are shown above the bar inA. *p < 0.001.

APV and CNQX slow dendritic arbor development in more complex neurons. Time-lapse in vivo confocal images of four DiI-labeled tectal neurons from either control animals or animals exposed to 100 μm APV or 20 μmCNQX. Images in the top row of each set (0h) were collected before drug treatment. Images in thebottom row of each set (4h) were collected after 4 hr in rearing solution (Control) or drug solution, as indicated. Control neurons show modest increases in branch length and branch tip numbers and arrangement. Cells from APV- and CNQX-treated animals show decreased morphological changes. Growth cones are represented bydotted outlines.

NMDA R and AMPA R maintain dendritic arbor structure in complex neurons. A, Growth rate over 4 hr in complex neurons from control animals and those exposed to APV or CNQX. Numbers of cells observed (n) for each condition are shownabove the corresponding bars. Growth rates of each APV and control neuron (B) normalized to its initial TDBL. Simple cells show relatively greater growth rates than complex cells. Note that APV-treated neurons with TDBL <200 μm show lower growth rates than control cells. *p < 0.05.