Fisk, G.D., & Wyss, J.M. (2000). Descending projections of infralimbic cortex that mediate stimulation-evoked changes in arterial pressure. Brain Research, 859, 83-95.
The infralimbic cortex of the rat can modify autonomic nervous system activity, but the critical pathway(s) that mediate this influence are unclear. To define the potential pathways, the first series of experiments characterizes the descending projections of infralimbic cortex and the neighboring cortical areas using Phaseolus vulgaris leucoagglutinin. Infralimbic cortex has prominent projections to the central nucleus of the amygdala, the mediodorsal nucleus of the thalamus, the lateral hypothalamic area, the periaqueductal gray, the parabrachial nucleus, and the nucleus of the solitary tract. The density and selectivity of these projections suggests that the lateral hypothalamic area and the periaqueductal gray mediate the ability of the infralimbic cortex to regulate cardiovascular function. The second series of experiments demonstrates that locally anesthetizing neurons in either the lateral hypothalamic area or periaqueductal gray with lidocaine attenuates the hypotensive effects produced by electrical stimulation of the infralimbic cortex. Similarly, microinjections of cobalt chloride (a neurotransmission blocker) into the anterior portion of the lateral hypothalamic area also decrease the arterial pressure responses to infralimbic cortex stimulation, suggesting that the ability of lidocaine to reversibly block the evoked response is due to inactivation of neurons in the lateral hypothalamic area. These data indicate that hypotension evoked by stimulation of infralimbic cortex is mediated, at least in part, by direct or indirect projections to the lateral hypothalamic area and through the periaqueductal gray.