Descending projections of infralimbic cortex that mediate stimulation-evoked changes in arterial pressure

The infralimbic cortex (IL) of the rat can modify autonomic nervous system activity, but the critical pathway(s) that mediate this influence are uncle ar. To define the potential pathways, the first series of experiments chara cterizes the descending projections of LL and the neighboring cortical area s using Phaseolus vulgaris leucoagglutinin (PHA-L). IL has prominent projec tions to the central nucleus of the amygdala (Ce), the mediodorsal nucleus of the thalamus (MD), the lateral hypothalamic area (LHA), the periaqueduct al gray (PAG), the parabrachial nucleus (Pb), and the nucleus of the solita ry tract (NTS). The density and selectivity of these projections suggest th at the LHA and the PAG mediate the ability of the IL to regulate cardiovasc ular function. The second series of experiments demonstrates that locally a nesthetizing neurons in either the LHA or PAG with lidocaine attenuates the hypotensive effects produced by electrical stimulation of the IL. Similarl y, microinjections of cobalt chloride (a neurotransmission blocker) into th e anterior portion of the LHA also decrease the arterial pressure responses to IL stimulation, suggesting that the ability of lidocaine to reversibly block the evoked response is due to inactivation of neurons in the LHA. The se data indicate that hypotension evoked by stimulation of IL is mediated, at least in part, by direct or indirect projections to the LHA and through the PAG. (C) 2000 Elsevier Science B.V. All rights reserved.