Thalamocortical synapses involving identified neurons in mouse primary somatosensory cortex: A terminal degeneration and golgi/EM study

Synapses involving thalamocortical afferents and hitherto unexamined neuron types of the posteromedial barrel subfield (PMBSF) of the mouse have been identified using a combined degeneration and Golgi/EM technique (Peters et al., '77). Degeneration of thalamocortical axon terminals was produced with electrolytic lesions of the nucleus ventralis posterior, pars lateralis thalami, and the nucleus posterior thalami. Four days after receiving lesions, the animals were perfused, and blocks of cortex containing the PMBSF were processed by the Golgi method. The blocks were tissue‐chopped at 125 μm and examined with the light microscope. Sections containing neurons of interest were gold‐toned and deimpregnated in preparation for electron microscopy (Fairén et al., '77). Portions of selected neurons contained in layers III‐V were serially thin‐sectioned and examined with an electron microscope to determine if they were involved in synapses with degenerating thalamocortical axon terminals. Results showed thalamocortical synapses on the apical dendrites of five different sized pyramidal cells whose somata occurred in layers V and VI, and on dendrites of one spiny bitufted neuron and one non‐spiny multipolar neuron with somata in layer V. A non‐spiny bitufted neuron of layer IV which was not impregnated also received thalamocortical synapses.