Neural inputs of the hypothalamic “aggression area” in the rat

A part of the mediobasal hypothalamus (known as hypothalamic attack area) plays a central role in the control of aggressive behavior as its electrical stimulation reliably and rapidly elicits biting attacks in cats and rodents. The efferent connections of this brain region were described in rats, but afferent pathways were not investigated so far. We injected the retrograde tracer cholera toxin B subunit into the mediobasal hypothalamus of male Wistar rats and studied the distribution of labeled cells by immunohistochemical method. The retrograde labeling outlined three continuous, distinct afferent cell populations: (i) a telencephalic midline “plate” containing the orbitofrontal – medial prefrontal – septal regions which ends in the bed nucleus of stria terminalis; (ii) a temporal column including the medial amygdala, amigdalohippocampal area and subiculum; (iii) a diffuse column along the medial hypothalamus which ends in the posterior hypothalamic nucleus. Sparse labeling was present in brainstem nuclei, except for the lateral parabrachial nucleus that provides a significant input. The projections of the medial prefrontal cortex to the hypothalamic attack area indicate a direct, earlier undescribed pathway with marked importance in the control of aggressive behavior. Similarly, we identified several brain regions which send very significant projections to the hypothalamic attack area but their importance in the control of aggressive behavior are nearly unknown. The comparison of the present and earlier findings shows that efferent and afferent connections overlap in many regions to a significant extent, suggesting that reverberating circuits are important in the control of aggressive behavior.