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G Stampacchia

Publications and source records attributed to G Stampacchia.

46 records · Page 3Linked to original sources
PubMed1983

Responses of forelimb extensors to sinusoidal stimulation of macular labyrinth and neck receptors.

In precollicular decerebrate cats the multiunit EMG activity was recorded from forelimb extensors (triceps brachii) during isolated or combined sinusoidal stimulation of labyrinth and neck receptors at frequencies of 0.026--0.15 Hz. As expected from previous work, the first harmonic component of the EMG responses to roll tilt of the animal leading to selective stimulation of labyrinth receptors was characterized by an increased activity during side-down tilt and a decreased activity during side-up tilt (labyrinth responses); on the other hand just the opposite changes were elicited for the same directions of neck rotation (neck responses). For the peak amplitude of displacement of 10 degrees, the responses were always related to position and not to velocity of displacement. In some experiments in which the sensitivity of the neck responses was usually comparable to that of the labyrinth responses and the corresponding peaks were almost 180 degrees out of phase, a cancellation of the responses occurred during head rotation, leading to costimulation of labyrinth and neck receptors. In other experiments, however, in which the sensitivity of the neck responses was higher than that of the labyrinth responses, the forelimb extensors responded to head rotation in a fashion predictable from the vectorial summation of the responses obtained from separate macular and neck stimulation.

Animals↗
PubMed1983

Cholinergic mechanism controlling the response gain of forelimb extensor muscles to sinusoidal stimulation of macular labyrinth and neck receptors.

The multiunit EMG activity of the triceps brachii was recorded in precollicular decerebrate cats during roll tilt of the animal or neck rotation at the frequencies of 0.026-0.15 Hz and at the peak amplitude of 10 degrees, leading to selective stimulation of labyrinth or neck receptors. The first harmonic component of the EMG responses to labyrinth stimulation was characterized by an increased activity during side-down tilt of the animal and a decreased activity during side-up tilt; however, just the opposite changes were elicited for the same directions of neck rotation. The peak of the responses was closely related to the extreme animal or neck displacement, thus being attributed to stimulation of position-sensitive macular labyrinth and receptors. Moreover, the modulation as well as the gain of the EMG responses were small in amplitude. Intravenous injections of an anticholinesterase at a dose which in some instances slightly decreased the extensor tonus as well as the background activity of the triceps brachii (eserine sulphate, 0.05-0.075 mg/kg), greatly enhanced the response gain of this extensor muscle to animal tilt or neck rotation at the parameters reported above. This finding was also observed in the absence of any decrease in spontaneous EMG activity of the extensor muscle after injection of the anticholinesterase. In no instance did the phase angle of the response change following these injections. The increased gain of the EMG response of the forelimb extensor muscle to sinusoidal stimulation of labyrinth and neck receptors was first observed 5-10 min after the injection and reached the highest value in about one hour. This effect, was not only time-dependent, but also state-dependent. In fact, the increase in response gain described above either did not occur or was negligible during the sudden recovery of the extensor rigidity which occurred either spontaneously or after somatosensory stimulations. The effects elicited by eserine sulphate were reversed within seconds by a 0.1-0.5 mg/kg dose of atropine sulphate, an anticholinergic drug. It is postulated that for the same labyrinthine or neck signal giving rise to excitatory vestibulospinal volleys acting on extensor motoneurons, the amplitude of the EMG modulation of limb extensor muscles depends on the activity of a cholinergic system.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMedDate not supplied

Labyrinthine influences on locus coeruleus neurons.

The locus coeruleus (LC) complex, located in the dorsolateral pontine tegmentum, is composed principally of noradrenergic neurons, which project to broad regions of the CNS, including the spinal cord. Experiments were performed in precollicular decerebrate cats to ascertain whether units histologically identified within the LC complex, and having the physiological characteristics of noradrenergic neurons, would respond to sinusoidal stimulation of labyrinth receptors. Among 141 LC complex neurons, 16 of which could be activated antidromically by stimulation of the spinal cord at T12-L1, 80 (i.e. 56.7%) responded to roll tilt of the animal at 0.15 Hz, +/- 10 degrees. The responses were particularly related to the extreme animal displacements, thus being attributed to stimulation of macular utricular receptors. The proportion of responsive units, and also the average gain of the responses, were higher in the LCd and the subcoerular (subLC) area than in the LCa. Moreover in the same structures the majority of units showed a beta-pattern of response (excitation during side-up tilt), which contrasted with the predominant alpha-pattern (excitation during side-down tilt) displayed by the previously recorded vestibulospinal neurons projecting to the same segments of the spinal cord. The role that the noradrenergic coeruleospinal neurons exert in the dynamic control of posture during the vestibulospinal reflexes is discussed.

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PubMedDate not supplied

The role of the locus coeruleus in the gain regulation of vestibulospinal reflexes.

In precollicular decerebrate cats, activation of limb extensors during side-down roll tilt of the animal depends on both an increased discharge of excitatory vestibulospinal neurons and a reduced discharge of inhibitory medullary reticulospinal (mRS) neurons. These inhibitory neurons are tonically excited by a cholinergic pontine reticular formation (pRF) system, which is in turn inhibited by norepinephrine (NE)-containing locus coeruleus (LC) neurons. Functional inactivation of LC neurons, produced by local injection of clonidine, which acts on the somatodendritic alpha 2-adrenoceptors by enhancing recurrent and/or lateral inhibition of the NE neurons, enhanced the response gain of the triceps brachii to animal tilt. We postulate that inactivation of LC neurons releases the cholinergic pRF system and the related mRS system from the suppressive influence exerted by the noradrenergic terminals. The increased discharge of these neuronal systems in the animal at rest would lead to a greater disinhibition which affects the limb extensor motoneurons during side-down tilt, thus increasing the response gain of the corresponding muscle to the same amount of labyrinth stimulation.

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