NEUROBIOLOGY Dendritic Balancing Act

Neurons receive multiple excitatory (E) and inhibitory (I) inputs, which must be integrated to yield the proper level and pattern of neuronal activity (action potentials). A great proportion of the input synapses occur away from the soma (cell body) on dendrites. Liu analyzed the distribution and relative activities of E and I inputs on the dendritic trees of cultured hippocampal neurons. His results suggest that the functional E/I balance in the dendrites is regulated through a feedback mechanism to attain a constant compound synaptic potential (Vs) at the soma. In the cultured hippocampal neurons, larger dendrites (based on diameter) had more synaptic inputs and the functional E/I balance was also constant at a given time in culture. The majority of E inputs were canceled within the dendrite by I inputs before reaching the soma. Treatments that increased Vs changed the E/I balance such that I input was increased. Changes that decreased Vs also predominantly affected I inputs, but such that I inputs were decreased with only a small increase in E inputs. Thus, synaptic activity is dictated by the E/I balance, and this balance is adjusted through a feedback mechanism that alters the amount of I input to maintain a constant somatic activity.

G. Liu, Local structural balance and functional interaction of excitatory and inhibitory synapses in hippocampal dendrites. Nat. Neurosci. 7, 373-379 (2004). [Online Journal]