RETROGRADE TRANSPORT OF NERVE GROWTH-FACTOR FROM HIPPOCAMPUS AND AMYGDALA TO TRKA MESSENGER-RNA EXPRESSING NEURONS IN PARAVENTRICULAR AND REUNIENS NUCLEI OF THE THALAMUS

We previously reported the presence of trkA messenger RNA expressing n on-cholinergic neurons in the paraventricular anterior and reuniens nu clei, which are located in the thalamic midline.(30) In the present st udy, retrograde labeling with iodinated (I-125) nerve growth factor wa s used to identify the innervation target of these cells. Neurons in t he paraventricular anterior and reuniens nuclei were labeled following injection of iodinated nerve growth factor into amygdala and hippocam pus, but not into nucleus accumbens and entorhinal cortex, the two oth er main areas receiving strong innervation from the thalamic midline.( 14,24,28) Target ablation of hippocampus or amygdala failed to downreg ulate trkA messenger RNA expression in the two thalamic nuclei, thus s uggesting a role for nerve growth factor different from a critical sur vival factor. The thalamic paraventricular anterior and reuniens nucle i are part of the reticular formation which plays a role in general co rtical activation, behavioral arousal and control of awareness. Retrog rade transport of nerve growth factor by trkA messenger RNA expressing neurons in these nuclei suggests a physiological role of this trophic factor in the function of these cells.