Postnatal development of GABAergic signalling in the rat lateral geniculate nucleus: presynaptic dendritic mechanisms.

Diverse forms of GABAergic inhibition are found in the mature brain. To understand how this diversity develops, we studied the changes in morphology of inhibitory interneurons and changes in interneuron-mediated synaptic transmission in the rat dorsal lateral geniculate nucleus (dLGN). We found a steady expansion of the dendritic tree of interneurons over the first three postnatal weeks. During this period, the area around a thalamocortical cell from which GABA(A) inhibition could be elicited also expanded. Dendritic branching and burst firing in interneurons evolved more slowly. The distal dendrites of interneurons began to branch extensively after the third week, and at the same time burst firing appeared. The appearance of burst firing and an elaborated dendritic tree were accompanied by a pronounced GABA(B) inhibition of thalamocortical cells. Thus, GABA inhibition of thalamocortical cells developed from one type of GABA(A) inhibition (spatially restricted) in the young animal into two distinct types of GABA(A) inhibition (short- and long-range) and GABA(B) inhibition in the adult animal. The close temporal relationships between the development of the diverse forms of inhibition and the postnatal changes in morphology of local GABAergic interneurons in the dLGN suggest that postnatal dendritic maturation is an important presynaptic factor for the developmental time course of the various types of feedforward inhibition in thalamus.