Mapping of the functional interconnections between thalamic reticular neurons using photostimulation.
The thalamic reticular nucleus is strategically located in the axonal pathways between thalamus and cortex, and reticular cells exert strong, topographic inhibition on thalamic relay cells. Although evidence exists that reticular neurons are interconnected through conventional and electrical synapses, the spatial extent and relative strength of these synapses are unclear. To address these issues, we used uncaging of glutamate by laser-scanning photostimulation to provide precisely localized and consistent activation of reticular cell bodies and dendrites in an in vitro slice preparation from the rat as a means to study reticulo-reticular connections. Among the 47 recorded reticular neurons, 29 (62%) received GABAergic axodendritic input from an area immediately surrounding each of the recorded cell bodies, and 8 (17%) responded with depolarizing spikelets, suggesting inputs through electrical synapses. We also found that TTX completely blocked all evoked IPSCs, implying that any dendrodendritic synapses between reticular cells either are relatively weak, have no nearby glutamatergic receptors, or are dependent on back-propagation of action potentials. Finally, we showed that the GABAergic connections between reticular cells are weaker than those from reticular cells to relay cells. Our results suggest that the GABAergic axodendritic synapse is the dominant form of reticulo-reticular connectivity, and because they are much weaker than the reticulo-relay cell synapses, their functional purpose may be to regulate the spatial extent of the reticular inhibition on relay cells.
Lam
Ying-Wan
YW
Department of Neurobiology, Pharmacology and Physiology, Univ. of Chicago, 947 E. 58th St., MC 0926, 316 Abbott, Chicago, IL 60637, USA.
Nelson
Christopher S
CS
Sherman
S Murray
SM
D000818:Animals; D001369:Axons / Q000502:physiology; D001931:Brain Mapping; D003627:Data Interpretation, Statistical; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D017629:Gap Junctions / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism; D066298:In Vitro Techniques; D007395:Interneurons / Q000502:physiology*; D007834:Lasers; D009434:Neural Pathways / Q000502:physiology; D010775:Photic Stimulation; D011724:Pyridazines / Q000494:pharmacology; D051381:Rats; D012154:Reticular Formation / Q000166:cytology / Q000502:physiology*; D013569:Synapses / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D013787:Thalamic Nuclei / Q000166:cytology / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D011724:Pyridazines; D018698:Glutamic Acid; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; C049853:gabazine