Branch Strength Potentiation.

Dendrites are wonderfully complicated. The review by Hausser and colleagues mentioned in this weblog recently drives this point home with avengence. I have got the impression there is a "hard core" of labs who are serious about getting to grips with dendritic properties, many of these labs were trained by Bert Sakmann or Dan Johnston. Notable amongst the latter is Jeff Magee. When Jeff was a postdoc with Dan he started to patch dendrites, and he and his lab have continued to do this for the past 10 years. As some sort of culmination of this work, they have an article in Nature (27 March 2008) using multi-site 2-photon uncaging of glutamate in which they outline a new, and important form of plasticity of hippocampal neurons. They call this Branch Strength Potentiation, or "BSP". Recently Johnston and Narayanan wrote a great (small) review about dendrites, which I found very helpful. Partly because is was short, and partly because it gave a nice historical introduction to the field. Part way through this review, they give this very helpful summary:

Are there any general conclusions that we can draw about function from what we know so far regarding all of the voltage-gated ion channels expressed in neuronal dendrites? The answer is probably no, because of the large diversity in channel types and expression patterns among different neurons. We can, however, summarize a few frequent observations. (i) Na-dependent action potentials backpropagate from the axon into the dendrites of most, but not all, neurons. In many, but not all, neurons, these action potentials decrement in amplitude with distance from the soma. (ii) Na-dependent and NMDA receptor-dependent spikes can be initiated in dendrites of some neurons under specific sets of conditions. Oftentimes these local spikes do not propagate to the soma, or if they do, they contribute only small, sharply rising signals that can influence the timing of action potentials initiated in the axon/soma region. (iii) Dendritic Ca channels are opened by both backpropagating action potentials and by locally initiated spikes and produce a rise in the concentration of intracellular Ca. (iv) Dendritic Ca channels, especially in more distal dendrites, can sustain Ca-dependent spikes or plateau potentials. These too produce a rise in intracellular Ca. (v) Dendritic Ca channels can be opened by synaptic potentials and produce a rise in intracellular Ca. (vi) Dendritic K channels regulate the amplitude backpropagating action potential in some, but not all, neurons. They can also influence the site of initiation of local spikes and the amplitude of synaptic potentials. (vii) Dendritic h channels regulate the integration and frequency-dependent tuning of temporal patterns of synaptic input and can mediate neuronal oscillations. (viii) The different types of voltage-gated channels expressed in dendrites play important roles in how each particular neuron responds to spatial and temporal patterns of inputs. (Trends in Neuroscience (2008) 31:309-316-the image I use is from Dan Johnston's webpage).