A hypothalamic-thalamostriatal circuit that controls approach-avoidance conflict in rats.

Survival depends on a balance between seeking rewards and avoiding potential threats, but the neural circuits that regulate this motivational conflict remain largely unknown. Using an approach-food vs. avoid-predator threat conflict test in rats, we identified a subpopulation of neurons in the anterior portion of the paraventricular thalamic nucleus (aPVT) which express corticotrophin-releasing factor (CRF) and are preferentially recruited during conflict. Inactivation of aPVTCRF neurons during conflict biases animal's response toward food, whereas activation of these cells recapitulates the food-seeking suppression observed during conflict. aPVTCRF neurons project densely to the nucleus accumbens (NAc), and activity in this pathway reduces food seeking and increases avoidance. In addition, we identified the ventromedial hypothalamus (VMH) as a critical input to aPVTCRF neurons, and demonstrated that VMH-aPVT neurons mediate defensive behaviors exclusively during conflict. Together, our findings describe a hypothalamic-thalamostriatal circuit that suppresses reward-seeking behavior under the competing demands of avoiding threats.

Identification of barosensitive neurons in the mediobasal forebrain using juxtacellular labeling.

Previous investigations suggest a possible role in cardiovascular regulation for neurons of the mediobasal forebrain. The present study was designed to determine the location and morphology of basal forebrain neurons that respond to acute changes in arterial blood pressure. Extracellular recordings of single units were done in alpha-chloralose- or urethan-anesthetized rats. The effect of cardiovascular pressor (phenylephrine, 1-2 microgram/kg iv) and depressor (sodium nitroprusside, 0.5-1 microgram/kg iv) events on the discharge rates of units was determined. Some of the neurons tested were subsequently filled with biocytin using the juxtacellular method. Brain sections were processed using the avidin-biotin complex reaction to reveal a Golgi-like appearance of the neuron. Of 32 neurons located in the horizontal limb of the diagonal band of Broca (hDB), 13 (41%) were found to be excited by depressor events. Barosensitive biocytin-labeled cells were located in all regions of the hDB and had small- to medium-sized cell bodies with sparse and simple dendritic morphology. Only 2 of 47 neurons tested in the region of the olfactory tubercle, islands of Calleja (IC), and ventral pallidum responded to changes in arterial blood pressure. The results of the present investigation suggest a role in the regulation of cardiovascular function for neurons of the hDB. The findings also suggest that most neurons in the olfactory tubercle, including the IC complex, do not respond to acute changes in arterial blood pressure.

Topographical organization in the nucleus accumbens of afferents from the basolateral amygdala and efferents to the lateral hypothalamus.

The basolateral region of the amygdala and the lateral hypothalamic area are involved in cardiovascular regulation. The aim of the present investigation was to determine if the terminal field of afferent projections from the basolateral nucleus of the amygdala to the nucleus accumbens overlap with the origin of the efferent projections from the nucleus accumbens to the lateral hypothalamic area. Neurons projecting from the nucleus accumbens to the lateral hypothalamic area were labeled by injecting the retrograde tracer Fluoro-Gold in the lateral hypothalamus of rats. In the same rats, fiber terminals from the amygdala to the nucleus accumbens were labeled by injecting the anterograde tracer Fluoro-Ruby in the basolateral region of the amygdala. Injections of Fluoro-Gold in the lateral hypothalamus labeled neurons in the posteromedial portion of the nucleus accumbens. Injections of Fluoro-Ruby in the basolateral amygdala labeled fibers and terminals in all parts of the nucleus accumbens with the highest density being found in the posteromedial part of the nucleus accumbens where Fluoro-Gold-labeled neurons were located. When regions of the posteromedial nucleus accumbens were examined under high-magnification, Fluoro-Ruby-labeled terminals appeared to make contact on Fluoro-Gold-labeled dendrites and cell bodies. This investigation demonstrates that there is a distinct overlap in the posteromedial region of the nucleus accumbens between the terminal field from neurons originating in the amygdala and neurons which project to the lateral hypothalamus. In addition, neurons in the basolateral amygdala appear to make synaptic contact with neurons in the nucleus accumbens that project to the lateral hypothalamic area.(ABSTRACT TRUNCATED AT 250 WORDS)