GABAERGIC PROJECTIONS FROM THE THALAMIC RETICULAR NUCLEUS TO THE ANTEROVENTRAL AND ANTERODORSAL THALAMIC NUCLEI OF THE RAT

We have studied GABAergic projections from the thalamic reticular nucl eus to the anterior thalamic nuclei of the rat by combining retrograde labelling with horseradish peroxidase and GABA-immunohistochemistry. Small iontophoretic injections of the tracer into subnuclei of the ant erior thalamic nuclear complex resulted in retrograde labelling of cel ls in the rostrodorsal pole of the ipsilateral thalamic reticular nucl eus. All of these cells were also GABA-positive. The projections were topographically organized. Neurons located in the most dorsal part of the rostral reticular nucleus projected to the dorsal half of both the posterior subdivision and the medial subdivision of the anteroventral thalamic nucleus, and to the rostral portion of the anterodorsal thal amic nucleus. Immediately ventral to this group of neurons, but still within the dorsal portion of the reticular nucleus, a second group of neurons, extending from the dorsolateral to the dorsomedial edge of th e nucleus, projected to the ventral parts of the posterior and medial subdivisions of the anteroventral nucleus. Following injection of trac er into the dorsal part of the rostral anteroventral nucleus, retrogra de labelled GABA-containing cell bodies were also found in the ipsilat eral anterodorsal nucleus.