Microinjections of beta-noradrenergic substances in the cerebellar vermis of decerebrate cats modify the gain of the vestibulospinal reflexes.

Abstract

1. The noradrenergic (NA) afferent system, which originates mainly from the locus coeruleus and projects to the cerebellar cortex, may act on the corresponding neurons by utilizing not only alpha- but also beta-adrenoceptors. Since the vermal cortex of the cerebellar anterior lobe receives a labyrinth input and projects to the lateral vestibular nucleus (LVN), experiments were performed in precollicular decerebrate cats to find out whether the noradrenergic system intervenes in the control of posture as well as of the dynamic characteristics of vestibulospinal (VS) reflexes elicited by recording the multiunit EMG responses of the forelimb extensor triceps brachii of both sides to roll tilt of the animal at 0.15 Hz, +/- 10 degrees. In particular, we used the method of local microinjection into the vermal cortex of the cerebellar anterior lobe of the non-selective beta-adrenergic agonist ((+/-) -isoproterenol hydrochloride) or antagonist (dl-propranolol hydrochloride) to act on both beta 1- and beta 2-adrenoceptors. 2. Unilateral injection into the vermal cortex of the culmen of isoproterenol (0.25-0.50 microliters at the concentration of 8-16 micrograms/microliter of saline stained with pontamine 5%) decreased the extensor tonus in the ipsilateral forelimb, while the postural activity either remained unmodified or slightly increased in the contralateral fore-limb. The same injection significantly increased the gain (imp./sec/deg) of the first harmonic component of the EMG responses of the ipsilateral and to a lesser extent also of the contralateral triceps brachii to animal tilt. This effect was also associated with slight changes in the phase angle of the responses, which remained positional throughout the experiments. The effects described above occurred within 5-10 min after the injection and reached the highest values after 20-30 min; they were then followed for about 2 hours after the injection, before disappearing. 3. In contrast to these findings, injection in other experiments of 0.25-0.50 microliter of a solution of propranolol at the concentration of 16 micrograms/microliter of saline increased the extensor tonus in the ipsilateral limbs, while the decerebrate rigidity either remained unmodified or slightly decreased in the contralateral limbs. In addition, the amplitude of modulation and thus the response gain of the ipsilateral triceps brachii to the same parameters of animal tilt decreased. This effect was associated with slight changes in the phase angle of the responses. There was also a slight but insignificant decrease in gain of the responses recorded contralaterally to the side of the propranolol injection.(ABSTRACT TRUNCATED AT 400 WORDS)