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At least 199 records · Page 11Linked to original sources
PubMed1976

Effects of brain gangliosides on functional recovery in experimental regeneration and reinnervation.

The effect of brain cortex gangliosides has been tested in two different experimental models of peripheral sympathetic regeneration and reinnervation: a) the preganglionic trunks of the cervical sympathetic nerve were joined in an end-to-end anastomosis after severing the preganglionic trunk, caudally to the superior cervical ganglion; this reinnervation is mainly of cholinergic type. b) the postganglionic trunks of the superior cervical ganglion were joined in an end-to-end anastomosis after severing the postganglionic trunk; this reinnervation is mainly of adrenergic type. Functional recovery following the regeneration and reinnervation has been evaluated by measuring tha contraction of the nictitating membrane, evoked by electrical stimulation of the sympathetic trunk caudally to the point of anastomosis. Some of the operated animals were daily treated with 50mg/kg i.p. of brain cortex gangliosides during the entire post-operative period. Forty-five, sixty days after the operation we observed in the treated animals of both experimental sets a relevant increase in the functional recovery (between 30 and 100%) compared to the operated but untreated controls. In the case of postganglionic anastomosis the physio-pharmacological studies were substantiated by the histochemical fluorescence observations of the distributions of catecholamines in the smooth muscle of the nictitating membranes. These results strongly suggest that the treatment with gangliosides greatly influences the regeneration and reinnervation process of both cholinergic and adrenergic nerve fibers.

Animals↗
PubMed1992

Universality in neural networks: the importance of the 'mean firing rate'.

We present a general analysis of highly connected recurrent neural networks which are able to learn and retrieve a finite number of static patterns. The arguments are based on spike trains and their interval distribution and require no specific model of a neuron. In particular, they apply to formal two-state neurons as well as to more refined models like the integrate-and-fire neuron or the Hodgkin-Huxley equations. We show that the mean firing rate defined as the inverse of the mean interval length is the only relevant parameter (apart from the synaptic weights) that determines the existence of retrieval solutions with a large overlap with one of the learnt patterns. The statistics of the spiking noise (Gaussian, Poisson or other) and hence the shape of the interval distribution does not matter. Thus our unifying approach explains why, and when, all the different associative networks which treat static patterns yield basically the same results, i.e., belong to the same universality class.

Mathematics↗
PubMed1991

Reorganisation of descending motor pathways in patients after hemispherectomy and severe hemispheric lesions demonstrated by magnetic brain stimulation.

Numerous clinical studies on patients after hemispherectomy (HS) have provided clear evidence that two distinct groups can be recognized on the basis of the quality of their motor functions after operation. One of these consists of cases where HS was performed after normal brain maturation, the other of patients where the removed hemisphere was damaged early in life. The postoperative motor function has been found to be much better in the latter group. In the present paper it is demonstrated that in contrast to normal subjects ipsilateral compound muscle action potentials (CMAPs) induced by magnetic stimulation of the one intact motor cortex are present in patients after HS. The amplitudes of ipsilateral CMAPs in the muscles roughly correlate with their individual residual motor capacities and show a proximo-distal gradient. In patients with early brain damage prior to HS, CMAPs had short latencies and large amplitudes, whereas in patients with later acquired brain damage prior to HS, CMAPs had long latencies and small amplitudes. It is suggested that reinforcement of the ipsilateral corticospinal pathway may be responsible for residual motor functions in patients with early brain damage, whereas in patients with later acquired brain damage cortico-reticulospinal pathways may play a dominant role in ipsilateral motor control.

Action Potentials↗
PubMed1976

Spinal branching of corticospinal axons in the cat.

Branching patterns of single corticospinal (CS) neurons were studied in the cat by activating these neurons antidromically from various regions of the spinal cord. 1. One hundred and ninety-three neurons were activated antidromically by microstimulation in the gray substance of the cervical cord and the majority of them were found in the forelimb area of the pericruciate cortex. 2. Branches to the lower levels of the spinal cord were found for 30% of the neurons projecting to the cervical gray matter. 3. The remaining 70% sent axons only to the cervical gray matter and some of them sent multiple branches to several segments in the cervical cord. 4. Only a few CS neurons located outside of the forelimb area could be activated from the cervical cord, but all of them also sent branches to the lower levels of the spinal cord. Neurons projecting to both the cervical cord and the lower levels were intermingled in the cortex with those projecting only to the cervical cord. 5. CS neurons activated from a given area of the cervical cord were often clustered together in a small area of the cortex, although some of these CS neurons sent their other branches to other parts of the spinal cord and neurons projecting to other parts were also intermingled among them. 6. The functional significance of multiple axonal branching of CS neurons is discussed in relation to cortical motor functions.

Animals↗
PubMed1976

The effect of morphine on the activity evoked in ventrolateral tract axons of the cat spinal cord.

The effect of morphine on the activity in ventrolateral tract axons was studied in intercollicularly decerebrate cats with and without spinal section. Activity was elicited by electrical stimulation of Adelta- and C-fibres in the sural nerves. In spinal animals, morphine injected intravenously in a dose as low as 0.5 mg/kg reduced the post-stimulus discharge of impulses recorded in ventrolateral tract axons below the site of transection. The depression was not only abolished but reversed by levallorphan and naloxone. Pretreatment with reserpine did not diminish the effect of morphine. The effect of morphine was considerably weaker in decerebrate cats. Reversible block of the spinal cord produced by cold revealed that morphine reduced inhibition from the brain stem controlling the impulse transmission to ventrolateral tract axons. It is concluded that a spinal effect contributes to the analgesic action of morphine.

Afferent Pathways↗
PubMed1976

Excitatory nature of dopamine in the nigro-caudate pathway.

Inputs from the substantia nigra (SN) to the caudate nucleus (Cd) and the effects of electrophoretic dopamine on Cd neurones were studied in cats anaesthetized with pentobarbitone with intracellular techniques. Single shock electrical stimulation of the SN or the medial forebrain bundle (MFB) induced monosynaptic EPSPs in Cd neurones. Dopamine depolarized Cd neurones and chlorpromazine suppressed the SN or MFB induced EPSPs. Appropriate controls indicate that the drug effects were not artifactual. Some recorded neurones were identified by procion yellow dye injection as the medium-size intrinsic Cd neurones.

Animals↗