O. Pompeiano et al., NORADRENERGIC AGENTS IN THE CEREBELLAR VERMIS AFFECT ADAPTATION OF THE VESTIBULOSPINAL REFLEX GAIN, Brain research bulletin, 35(5-6), 1994, pp. 433-444
In precollicular decerebrate cats, the vestibulospinal reflex (VSR) wa
s intermittently recorded from the triceps brachii during sinusoidal r
oll tilt of the whole animal (at 0.15 Hz, +/-10 degrees), leading to s
elective stimulation of labyrinth receptors. This reflex, tested durin
g and after a 3-h period of sustained animal tilt at the same paramete
rs indicated above, showed an adaptive increase in gain in some experi
ments but not in others. In a second group of experiments, however, ro
tation of the head (at 0.15 Hz, +/-10 degrees) was associated with a s
ynchronous body rotation (at 0.15 Hz, +/-12.5 degrees) which led to an
additional neck input, due to 2.5 degrees of out-phase body-to-head d
isplacement. In these experiments, the VSR, tested every 10-15 min, co
nsistently showed an adaptive increase in gain during and after a 3-h
period of sustained vestibular and neck stimulation. Microinjection in
to the cerebellar anterior vermis of beta-adrenergic agents (0.25 mu l
at 8 mu g/mu l saline) produced slight and short-lasting changes in t
he basic amplitude of the VSR, due to the neuromodulatory influence of
these agents on the Purkinje cells activity. In addition, the beta-ad
renergic agonist isoproterenol brought to the light an adaptive proces
s in those experiments in which no adaptation occurred during a sustai
ned roll tilt of the whole animal. On the other hand, the beta-adrener
gic antagonists propranolol or sotalol either suppressed the increase
in gain of the VSR which occurred in other experiments during sustaine
d animal rotation, or prevented the occurrence of an adaptive increase
in gain during a continuous out-phase head and body rotation. We conc
lude that the adaptive changes in gain of the VSR are facilitated by t
he noradrenergic system acting within the cerebellar cortex through be
ta-adrenoceptors.