CHARACTERIZATION OF GABAERGIC NEURONS IN HIPPOCAMPAL CELL-CULTURES

The morphological characteristics of GABAergic neurons and the distrib ution of GABAergic synaptic terminals were examined in cultures of hip pocampal neurons from 4-35 days in vitro. Neurons expressing GABA immu noreactivity represented about 6% of the total number of cultured neur ons at all time points. Although the morphological characteristics of GABAergic cells suggested a heterogeneous population, GABAergic cells as a class were notably different from the non-GABAergic, presumably p yramidal cells. Most GABAergic cells had more fusiform or polygonal sh aped somata, non-spiny and less tapering dendrites and appeared more p hase-dense than nonGABAergic cells. Quantitative analysis revealed tha t GABAergic cells had fewer primary dendrites, more elongated dendriti c arbors, and longer dendritic segments than non-GABAergic neurons-cha racteristics that are similar to GABAergic cells in situ. Double immun ostaining revealed that GAD65-positive varicosities were also immunopo sitive for synapsin I, suggesting that GAD65-positive varicosities tha t contacted somata and dendrites represented presynaptic specializatio ns. Confocal microscopy revealed the proportion of the synaptic specia lizations on the cell soma that were GAD65-positive was greater than o n the dendrites, suggesting that somata and dendrites differ in their ability to induce the formation of presynaptic specializations by GABA ergic axons. These data indicate that the GABAergic cells that develop in culture exhibit distinctive morphological characteristics and part icipate in different synaptic interactions than nonGABA cells. Thus ma ny of the features that distinguish GABAergic neurons in culture are r eminiscent of the characteristics that distinguish GABAergic neurons i n situ.