The effect of medial hypothalamus lesions on pain control

In the rat, discrete electrolytic lesions located in 6 different parts of the medial hypothalamus (MH) are shown to induce clearcut hyperalgesia. During a time limit of 14 days following the lesions, no other obvious deficits were noticed (in sensory and/or motor functions, affectivity towards conspecifics, food and water intake). Three nociceptive reactions (tail withdrawal, vocalization, vocalization after-discharge) were tested and their thresholds measured following electrical stimulation of the tail. The lesions aimed at the rostral part of the arcuate nucleus, as well as at ventromedial and dorsomedial nuclei, produced the most profound hyperalgesia. The possible involvement of the endorphinergic and enkephalinergic systems known to be located in the MH is discussed. The relation between the hyperalgesic effects of MH lesions and various structures (limbic areas, descending pain control system, pituitary) is also considered.

Periodic fluctuation in burst amplitude during 'fictive locomotion' in the cat

In decorticated unanaesthetized and paralysed cats, locomotor bursting may develop spontaneously on hind-limb motor nerves. In defined experimental conditions, the amplitude of successive rhythmic bursts may fluctuate periodically as if a 'secondary oscillation' was superimposed upon the basic locomotor rhythm. The possible meaning of such amplitude fluctuation is discussed in connection with present data about the generation of locomotion.

Central locomotor programming in the rabbit

In decorticate, unanaesthetized and curarized rabbit preparations, with both hindlimbs deafferented, locomotor-like discharges were recorded from nerves to flexors and extensors and their time patterns were compared. The bursts of rhythmic activities recorded from nerves to several flexor muscles acting at either joint were shown to be synchronous, with no differences in their time of onset. The same was true for the extensors. Nerves to bifunctional muscles (biceps posterior, semi-tendinosus and tenuissimus) acting on two consecutive joints (knee flexors, hip extensors) could display two consecutive bursts in each locomotor cycle, one being pure flexor and the other an extensor discharge. It is shown here that this functional bivalence is programmed centrally and can be modulated, i.e. the relative importance of the flexor and the extensor bursts can be changed in a predictable way through afferent (proprioceptive or cutaneous) influences, or through activation of the descending monoaminergic pathways. In extreme cases, complete functional reversal was observed in these bifunctional muscle nerves.

Coordinated rhythmic bursting in respiratory and locomotor muscle nerves in the spinal rabbit

In unanaesthetized, curarized spinal rabbits (C2 level) treated with Niamide and DOPA, rhythmic activities were recorded from the phrenic nerves; close coordination was observed between the phrenic bursts and the locomotor bursts which developed in hindlimb muscle nerves. The frequency of phrenic bursts was reduced after a second spinal transection at the Th12 level, while rhythms in the hindlimb remained unchanged. It thus appears that in the spinal preparation and under certain pharmacological conditions, phrenic bursts generated by the cervico-thoracic spinal cord can be driven by the lumbar generators of locomotion; spinal links thus exist between these hindlimb locomotion generators and spinal interneuronal networks involved in phrenic motoneuronal activation, may be via hindlimb forelimb driving.

Acetylcholinesterase from Wistar rat brain

Acetylcholinesterase (E.C.3.1.1.7) was partially purified from rat brains stored in toluene. Extraction was performed using buffers containing non-ionic tensoactive detergents. Some properties of the enzyme were affected by the use of different activity measurement methods, such as the short-time radiometric or the long-time colorimetric method. There were two zones of maximum activity in the range pH 7.5-8.0 and 8.0-8.6, respectively. There seems to be a histidine residue in the enzyme that participates in the catalytic process. Thermal denuration presented first order kinetics and different thermodynamic parameters were obtained on using different incubation periods. On using the short-time activity measurement method there was activation at high substrate concentration, but with the long time method there was a marked inhibition produced by excess of substrate. However, if the enzyme was extracted from fresh rat brain, toluene untreated, these differences dissapeared. Gel filtration and disc electrophoresis showed the presence of multiple and interconvertible forms of the enzyme.