Hemodynamic, behavioral and biochemical disturbances induced by an experimental cranio-cervical injury (whiplash) in rats.

Two days after an experimental whiplash performed on anesthetized Long-Evans female rats, without any direct blow to the head, we observed: (1) a hypotension (in supine position) (P less than 0.01), (2) a disturbance of the postural regulation of cerebral blood flow (P less than 0.01), (3) a disturbance of learning behavior characterized by decreased acquisition and retention (conditioned avoidance response and labyrinth tests), (4) an increase of the dopamine level (whole brain, cerebellum, thalamus + hypothalamus, corpus striatum and rest), (5) a decrease of the noradrenaline level in whole brain (P less than 0.05) and in the medulla oblongata but an increase in thalamus plus hypothalamus, hippocampus and corpus striatum, (6) an increased reactivity of the peripheral alpha and beta receptors, determined by analyzing the hemodynamic consequences of i.v. injection of norepinephrine or isoproterenol, (7) there was no modification of the brain content of water or of serotonin and (8) finally, the injured rats displayed a remarkably aggressive behavior, though this was not quantified. These results are in agreement with the hypothesis that a change in brain amines metabolism could explain the different functional effects of whiplash. We therefore believe that the postconcussion syndrome is not subjective and that the neck injury is primary in the determination of the syndrome.