A novel birefrmgent a-BaB2O4 crystal with 40mm in diameter, 35mm in height has been grown successfully in our laboratory by Czochralski method. The proportion of B203 and BaO of starting material, crystal cracking and the transmission spectrum of a-BaB2O4 crystal have been briefly analyzed.

We compared the ultrastructure and synaptic targets of terminals of cortical or retinal origin in the rat dorsal lateral geniculate nucleus (LGN) and lateral posterior nucleus (LPN). Following injections of biotinylated dextran amine (BDA) into cortical area 17, two types of corticothalamic terminals were labeled by anterograde transport. Type I terminals, found throughout the LGN and LPN, were small, drumstick-shaped terminals that extended from thin axons. At the ultrastructural level in both the LGN and LPN, labeled type I corticothalamic terminals were observed to be small profiles that contained densely packed round vesicles (RS profiles) and contacted small-caliber dendrites. In tissue stained for gamma amino butyric acid (GABA) using postembedding immunocytochemical techniques, most dendrites postsynaptic to type I corticothalamic terminals did not contain GABA (97%). Type II corticothalamic terminals, found only in the LPN, were large terminals that sometimes formed clusters. At the ultrastructural level, type II terminals were large profiles that contained round vesicles (RL profiles) and contacted large-caliber dendrites, most of which did not contain GABA (98%). Retinogeniculate terminals, identified by their distinctive pale mitochondria, were similar to type II corticothalamic terminals except that 26% of their postsynaptic targets were vesicle-containing profiles that contained GABA (F2 profiles). Our results suggest that type I corticothalamic terminals are very similar across nuclei but that the postsynaptic targets of RL profiles vary. Comparison of the responses to retinal inputs in the LGN and to layer V cortical inputs in the LPN may provide a unique opportunity to determine the function of interneurons in the modulation of retinal signals and, in addition, may provide insight into the signals relayed by cortical layer V.

No abstract

A major inhibitory input to the dorsal thalamus arises from neurons in the thalamic reticular nucleus (TRN), which use gamma-aminobutyric acid (GABA) as a neurotransmitter. We examined the synaptic targets of TRN terminals in the visual thalamus, including the A lamina of the dorsal lateral geniculate nucleus (LGN), the medial interlaminar nucleus (MIN), the lateral posterior nucleus (LP), and the pulvinar nucleus (PUL). To identify TRN terminals, we injected biocytin into the visual sector of the TRN to label terminals by anterograde transport. We then used postembedding immunocytochemical staining for GABA to distinguish TRN terminals as biocytin-labeled GABA-positive terminals and to distinguish the postsynaptic targets of TRN terminals as GABA-negative thalamocortical cells or GABA-positive interneurons. We found that, in all nuclei, the TRN provides GABAergic input primarily to thalamocortical relay cells (93-100%). Most of this input seems targeted to peripheral dendrites outside of glomeruli. The TRN does not appear to be a significant source of GABAergic input to interneurons in the visual thalamus. We also examined the synaptic targets of the overall population of GABAergic axon terminals (F1 profiles) within these same regions of the visual thalamus and found that the TRN contacts cannot account for all F1 profiles. In addition to F1 contacts on the dendrites of thalamocortical cells, which presumably include TRN terminals, another population of F1 profiles, most likely interneuron axons, provides input to GABAergic interneuron dendrites. Our results suggest that the TRN terminals are ideally situated to modulate thalamocortical transmission by controlling the response mode of thalamocortical cells.