A search for brain stem cell groups integrating the defence reaction in the rat.

Abstract

SUMMARY1. The defence areas of the rat brain stem have been extensively explored using electrical and chemical stimulation in an attempt to locate the regions containing the perikarya of neurones which may initiate or integrate the visceral and behavioural components of the defence reaction.2. In rats anaesthetized with alphaxalone-alphadolone, a cannula electrode was used to compare the responses to electrical stimuli with those evoked by microinjection of the excitatory amino acid D,L-homocysteic acid (DLH), at the same site. A total of 128 sites throughout the brain stem was studied in 75 rats.3. The pattern of visceral and somatic changes characteristic of the defence reaction, viz. increases in arterial blood pressure and heart rate, vasodilatation in hind-limb muscles and vasoconstriction in the kidney, hyperpnoea and tachypnoea, exophthalmos, mydriasis, twitching of the vibrissae and retroflexion of the tail, was evoked by electrical stimulation within well-defined regions of the brain stem, from the anterior hypothalamus to the pons.4. Microinjection of DLH into the same regions could evoke the full defence reaction, as defined above, but only from the dorsomedial periaqueductal grey matter. Three other regions were defined from which almost all the autonomic components of the defence reaction were evoked, except that blood pressure fell. These were located: (a) immediately dorsal to the optic chiasma, (b) in the medial tuberal region of the hypothalamus and (c) in the lateral pontine tegmentum.5. In conscious rats with implanted guide cannulae, darting and flight responses were evoked by microinjections of DLH into the periaqueductal grey matter but not from the hypothalamus or tegmentum. Brisk locomotion followed injections of DLH into the region overlying the optic chiasma.6. It is concluded that the brain stem neurones involved in integrating the somatic and visceral components of the defence reaction are concentrated within the four regions defined above. Whereas neurones in the periaqueductal grey matter can initiate the fully integrated defence reaction, those concentrated in the three other areas cannot be shown to do so. Of these three cell groups, the suprachiasmatic neurones seem to be closer in function to the periaqueductal group than are the neurones in the tuberal hypothalamus and pontine tegmentum.

Rostral Elements of Sympatho-motor Circuitry: A Virally Mediated Transsynaptic Tracing Study

“…This response can be elicited in experimental animals by exposure to a rival or a predator and can be mimicked by electrical stimulation of the LH (Hilton, 1982) or chemical disinhibition of this region (Kayaba et al, 2003). The descending component of the defense reaction is thought to be mediated in part by neurons in the dorsomedial PAG (Hilton and Redfern, 1986). However, we found relatively few double-labeled neurons in this region, suggesting that this response may be mediated by a small number of cells.…”

“…Several studies have examined the role that different brain regions may play in mediating behaviors that require concomitant activation of sympathetic and somatomotor efferent systems. In these studies, one or several brain regions were stimulated either electrically (Abrahams et al, 1960;Yardley and Hilton, 1986) or chemically with injections of excitatory amino acids (Bandler, 1982;Hilton and Redfern, 1986), and then behavioral, somatomotor, and autonomic parameters were simultaneously measured. Electrical stimulation has the potential to activate cell bodies as well as fibers of passage, thus complicating interpretation of observed effects.…”

Prevention by NMDA receptor antagonists of the centrally‐evoked increases of cardiac inotropic responses in rabbits

“…The heart rate response was the most variable, bradycardia being probably due to the baroreflex activation. This excitatory haemodynamic reaction mimicked the one provoked by situations of stress or physical effort in conscious animals (Hilton & Redfern, 1986).…”

The Periaqueductal Gray: From Longitudinal columns to defensive behaviour

“…They also provided evidence that the descending pathway from the lateral hypothalamus was glutamatergic. This finding was contradicted by Hilton and Redfern as there was no sympathetic arousal as observed in the cardiovascular defensive response evoked by electrical or chemical stimulation of the hypothalamus (Hilton and Redfern, 1986). Furthermore, Hilton and associates demonstrated that sympathoexcitatory responses characteristic of the defence reaction were readily evoked by both electrical and chemical PAG stimulation (Hilton andRedfern, 1986, Yardley and.…”