Connexions between the dorsomedial division of the ventromedial hypothalamus and the dorsal periaqueductal grey matter are critical in the elaboration of hypothalamically mediated panic-like behaviour

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The electrical and chemical stimulation of the dorsal periaqueductal grey matter (dPAG) elicits panic-like explosive escape behaviour. Although neurons of the ventromedial hypothalamus (VMH) seem to organise oriented escape behaviour, when stimulated with excitatory amino acids at higher doses, non-oriented/explosive escape reactions can also be displayed. The aim of this work was to examine the importance of reciprocal projections between the VMH and the dPAG for the organisation of this panic-like behaviour. The chemical stimulation of the VMH with 9 nmol of N-methyl-D-aspartic acid (NMDA) elicited oriented and non-oriented escape behaviours. The pretreatment of the dPAG with a non-selective blocker of synaptic contacts, cobalt chloride (CoCl2), followed by stimulation of the dorsomedial part of the ventromedial hypothalamus (dmVMH) with 9 nmol of NMDA, abolished the non-oriented/explosive escape and freezing responses elicited by the stimulation of the dmVMH. Nonetheless, the rats still showed oriented escape to the burrow. On the other hand, when the blockade of the dmVMH with CoCl2 was followed by stimulation of the dPAG with 6 nmol of NMDA, no effect was observed either on the non-oriented/explosive escape or on the freezing behaviour organised by the dPAG. Furthermore, Fos protein-labelled neurons were observed in the dPAG after the stimulation of the dmVMH with 9 nmol of NMDA. Additionally, when the anterograde neurotracer biotinylated dextran amine (BDA) was deposited in the dmVMH subsequent stimulation of the dmVMH produced BDA-labelled neural fibres with terminal boutons surrounding Fos-labelled neurons in the dPAG, suggesting synaptic contacts between dmVMH and dPAG neurons for eliciting panic-like behavioural responses. The current data suggest that the dPAG is the key structure that organises non-oriented/explosive escape reactions associated with panic attack-like behaviours.

Graphical abstract

The chemical stimulation of the dorsomedial division of the ventromedial hypothalamic nucleus (dmVMH) with NMDA at 9 nmol elicits panic-like behavioural responses with increase of Fos protein in neuronal nuclei of the dorsal periaqueductal grey matter (dPAG). Fos-immunolabelled neurons in dPAG are surrounded by dmVMH-dPAG neuronal pathways terminal buttons. The inactivation of synaptic contacts in dPAG with CoCl2 abolishes the panic-like behaviour elicited by dmVMH neuronal activation with 9 nmol of NMDA.

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