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PubMed1985

An investigation of the dorsal root reflex using an in vitro preparation of the hamster spinal cord.

A detailed description is given of an hemisected spinal cord preparation from adult golden hamsters and this preparation has been used to investigate the physiology of the dorsal root reflex. In addition to antidromic reflex discharges which could be recorded from lumbar dorsal roots following stimulation of adjacent dorsal roots or the dorsal columns, spontaneous firing was also recorded from the dorsal roots. This activity reached a peak at 27 degrees C and was abolished at temperatures above 35 degrees C. Both the evoked and the spontaneous dorsal root activity were demonstrated to be travelling antidromically along the dorsal roots out of the cord, and replacement of the calcium in the bathing medium by manganese showed them to be of synaptic origin. Stimulation of a lumbar dorsal root was found to evoke a reflex in up to 4 adjacent spinal segments in both rostral and caudal directions, and a period of depressed activity was demonstrated following both evoked and spontaneous discharges. A time-locked relationship was found between the dorsal root reflex and the slow dorsal horn potential recorded from within the spinal cord.

Animals↗
PubMed1986

Interactions between dopamine and amino acid-induced excitation and inhibition in the striatum.

Iontophoretic techniques were used to examine the effect of dopamine on glutamate-induced excitation and gamma-aminobutyric acid (GABA)-induced inhibition of single striatal neurons in rat brain. When dopamine was applied at concentrations that produced little or no inhibition of spontaneous firing rate, both glutamate-induced excitation and GABA-induced inhibition were enhanced. In contrast, when dopamine was applied at doses that significantly decreased spontaneous firing, glutamate-induced excitation was greatly reduced, though GABA-mediated inhibition remained enhanced. Thus, dopamine acts to modulate the efficacy of other neurotransmitters impinging on striatal neurons, but has a qualitatively different effect on the excitatory activity of striatal cells depending on its concentration.

Animals↗
PubMed1987

Physiological studies of brainstem reticular connectivity. I. Responses of mPRF neurons to stimulation of bulbar reticular formation.

The connectivity between medial pontine reticular formation (mPRF) and bulbar reticular formation (BRF) was studied by intracellular recordings of mPRF neuronal responses to microstimulation of BRF in unanesthetized, undrugged cats. There was a very high percentage (75-90%) of monosynaptic latency postsynaptic potentials (PSPs) in mPRF neurons in response to microstimulation of 3 BRF areas: the magnocellular tegmental field (FTM), the bulbar gigantocellular tegmental field (BFTG), and bulbar lateral tegmental field (BFTL). The type of initial orthodromic response produced in mPRF neurons by BRF stimulation was predominantly (75-95%) a monosynaptic excitatory PSP (EPSP) which was characterized by a rapid rise time, a nearly constant latency, and often led to spike potential generation. In contrast, the percentage of initial monosynaptic inhibitory PSPs (IPSPs) was much lower for FTM (12.3%), for BFTG (12.5%) and was zero for BFTL. While microstimulation techniques alone cannot differentiate between excitation of fibers of passage and neuronal somata, the very high percentage of initial EPSPs in our data and the anatomical evidence for dense BRF to mPRF neuronal projections as compared with less dense projections from fibers passing through BRF to mPRF suggest that excitatory BRF-mPRF connections are predominant. The high degree of connectivity between BRF and mPRF may furnish an important substrate for functional interaction. Comparison of the mPRF neuronal population that was not antidromically activated by FTM microstimulation vs the mPRF neuronal population that was antidromically activated from FTM and also studied for orthodromic responsiveness showed no statistically significant differences between these populations on the parameters of percentage of monosynaptic input, monosynaptic initial EPSPs, monosynaptic initial IPSPs and presence of a PSP with a latency of less than 5 ms. For BRF connectivity this suggests an identity of mPRF input and output neurons with respect to synaptic response properties.

Animals↗
PubMed1987

Do antidromic latency jumps indicate axonal branching in nigrostriatal and hypothalamo-neurohypophysial neurons?

Neurons in many brain regions exhibit discontinuous decreases in antidromic latency with small increases in stimulating current. We used an electrophysiological test requiring a single stimulating electrode to determine whether these 'latency jumps' are due to shifts in the site of spike initiation to the same or different axon branches. Latency jumps in response to stimulation of the striatal terminal fields of substantia nigra, pars compacta neurons represent spike initiation on different branches while those seen in paraventricular neurons with pituitary stalk stimulation usually reflect a change in site on a single branch.

Animals↗
PubMed1989

Effect of noxious tail pinch on the discharge rate of mesocortical and mesolimbic dopamine neurons: selective activation of the mesocortical system.

The effects of noxious tail pinch on the activity of mesocortical and mesolimbic dopamine (DA) neurons located in the ventromedial mesencephalic tegmentum were analyzed in ketamine-anesthetized rats. The great majority of mesocortical DA neurons responded to tail pinch, either by an excitation (65%), or by an inhibition (25%). In contrast, most DA neurons projecting either to the nucleus accumbens or the septum remained unaffected. These results demonstrate that noxious tail pinch selectively influences the firing rate of mesocortical DA neurons.

Action Potentials↗
PubMed1990

Stimulation of the subcallosal fornix excites neurones in the cat preoptic region which project to the medial basal hypothalamus and in the medial forebrain bundle.

The projection of neurones in the cat preoptic region driven by stimulation of the subcallosal fornix was systematically explored. We found 19% projected to the medial basal hypothalamus (MBH) and 10% projected in the medial forebrain bundle (MFB). Neurones projecting to the MBH were driven more often by stimulation of the lateral aspect of the fornix than the medial aspect (P = 0.006) and these neurones were thought to lie in the medial division of the preoptic nucleus (MPNm) since they were found significantly more often in the medial 0.6 mm of the preoptic region than more laterally (P = 0.028). A reverse projection from the preoptic region in the fornix is also suggested based on the finding of 24 antidromically activated neurones in the preoptic region following stimulation of the fornix.

Animals↗
PubMed1995

An electrophysiological demonstration of axonal projections of single ventral inspiratory neurons to the phrenic nucleus of the cat.

Axonal branching patterns of single inspiratory (I) neurons of the nucleus retroambigualis (NRA) were studied electrophysiologically in cat phrenic nucleus (C4-C6). Experiments were performed on Nembutal anesthetized, artificially ventilated cats, and extracellular spikes of I neurons were recorded. The cervical spinal gray matter was microstimulated from dorsal to ventral sites at 100 microns intervals with an intensity of 150-250 microA using a glass insulated tungsten microelectrode. The stimulations were made at 1 mm intervals rostrocaudally along the spinal cord, and effective stimulating sites of antidromic activation in axonal collaterals were systematically mapped. I neurons examined (n = 8) descending contralaterally distributed multiple collaterals in the phrenic nucleus. These collaterals were found throughout the rostrocaudal phrenic nucleus. An I neuron (n = 1) descending ipsilaterally also distributed collaterals in the ipsilateral phrenic nucleus. Axonal collaterals in the contralateral phrenic nucleus occupied 44.2% of the total length of the cervical spinal cord examined. To determine the detailed trajectory of collaterals in the cervical gray matter, microstimulation was performed in and around the collateral arborizations at the maximum intensity of 50 microA. The descending stem axons could be localized in the lateral funiculus in four I neurons and in the ventral funiculus in one I neuron. I neurons distributed axonal collaterals within the phrenic nucleus. Some part of the collaterals ran to the medial region of the gray matter, re-crossed the midline under the central canal and reached the phrenic nucleus ipsilateral to the I neuron. Re-crossed collaterals arborized in the phrenic nucleus, but did not extend to the gray matter more lateral than the phrenic nucleus. Rostrocaudal extension of the re-crossed collaterals was found to be narrow.

Animals↗
PubMed1996

Multisolutional clustering and quantization algorithm (MCQ).

We have developed a novel clustering and quantization algorithm that allows the user to create multiple one-to-one correspondences between the actual data and its transformed (clustered and quantized) values, based on the user's hypothesis regarding the nature of the classification task. The types of problems for which the algorithm can be beneficial are discussed. We report experiments employing simulated and real data that suggest the proposed algorithm may be useful in neural network analysis of various phenomena in medicine and biology.

Algorithms↗
PubMed1979

Topography and intracranial sources of somatosensory evoked potentials in the monkey. I. Early components.

Averaged somatosensory evoked potentials (SEP) were recorded in the monkey from arrays of surface electrodes overlying the brain, cervical cord and peripheral nerve; from epidural electrodes over the cerebral convexity; and from movable intracerebral electrodes. The initial cortically generated responses peak at mean latencies of 10 and 12 msec following stimulation of the median nerve at the wrist. Preceding these potentials 5 small positive wavelets were identified in scalp and epidural recordings. The sources of the latter three of these waves have been identified, based in part on the observation of amplitude maxima in depth recordings within cerebrum and brain stem. P7.2 is primarily generated within the thalamocortical radiations, whereas P5.3 and P6.2 reflect bursts of highly synchronized action potentials travelling along the medial lemniscus. Recordings of multiple unit activity within these tracts confirmed the source identifications made on the basis of potential distribution. Continuing activity within the more caudal portions of the somatosensory pathways produces potentials that sum with those generated more rostrally. This circumstance precludes the identification of the intracranial source of a surface recorded potential by demonstrating a concurrent wave form at a single location within the brain. It is necessary to examine the intracranial potential distribution and trace the potential from the surface to its maximum in order to identify its source with confidence. P3.1 and P3.8 were identified only as farfield potentials in intracranial recordings from the pons and more rostral regions. They were ascribed to activity of primary somatosensory neurons ascending in the dorsal columns on the basis of their timing, surface distribution and amplitude vs. interstimulus interval functions. The early SEP components recorded in the monkey closely resembled in configuration and topography those recorded from human subjects, although the latter were longer in latency, reflecting differences in length of the somatosensory pathways in the two species.

Action Potentials↗
PubMed1979

Short latency somatosensory potentials in humans.

A sequence of high frequency potentials was averaged from the scalp of 10 normal human subjects during the first 25 msec following median nerve stimulation. There was a large positive component with a peak latency between 18.9 and 22.3 msec localized to the somatosensory area contralateral to stimulation. This was preceded by an early positive potential arising peripherally (peak latency 7.7-9.7) and at least 3 negative to positive deflections which appear to originate in multiple subcortical structures. When corrected for arm length, intersubject variability was less than 5% for all components. With further clarification, this method should allow one to study neural conduction along the entire somatosensory pathway.

Adolescent↗
PubMed1979

Relation between extracellular potassium concentration and neuronal activities in cat thalamus (VPL) during projection of cortical epileptiform discharge.

Neuronal and potassium activities (ak) were measured in the nucleus ventro-posterolateralis thalami (VPL) during propagated epileptiform activity from the somatosensory cortex of cats. Seizures were induced by repetitive electrical stimulation of the cortical surface or by topical application of penicillin. The recruitment of VPL into a seizure resulted in large increases of ak to levels of up to 11.6 mmoles/l, accompanied by increased in neuronal discharge rate to 300/sec. Sometimes the rise in ak preceded active participation of a given thalamo-cortical relay (TCR) neuron in the seizure. After reaching a peak level, ak and neuronal discharge rate slowly declined during an ictal episode. After cessation of seizures all TCR neurons were inhibited, while ak fell to subnormal levels. The duration of these postictal depressions increased with the amplitude of preceding increases and subsequent undershoots in ak and could last up to 120 sec. During decay and undershoot in ak, relay capability of TCR neurons was reduced. Also the probability that action potentials elicited in intracortical endings of TCR cells would antidromically invade their cell bodies was decreased. The duration of these periods varied with the amplitude of undershoot in ak. Seizure threshold was increased during undershoots. These observations are consistent with a long-lasting postictal hyperpolarization of neuronal membranes. The hyperpolarization may be caused by the action of an electrogenic pump, which is probably involved in termination of seizure discharge.

Animals↗
PubMed1982

Interactions between cutaneous and muscle afferent projections to cerebral cortex in man.

In order to demonstrate interactions between cutaneous and muscle afferent volleys in the ascending somatosensory pathways, different nerves of the lower limb were stimulated together in a conditioning-test paradigm, the changes in the earliest component of the cerebral potential evoked by the test stimulus being taken to indicate such an interaction. It was first confirmed that the cerebral potential evoked by stimulation of the posterior tibial nerve at the ankle is derived from muscle afferents in the mixed nerve and has shorter latencies than the cerebral potential evoked by purely cutaneous volleys in the sural nerve (see Burke et al. 1981). Complete suppression of the cerebral potential evoked by stimulation of muscle or cutaneous afferents was produced by conditioning volleys in a different nerve or in a different fascicle of the same nerve. The major factors determining the degree of suppression were found to be the relative sizes of the conditioning and test volleys and their timing, rather than whether the volleys were of cutaneous or muscular origin. It is concluded that the transmission of cutaneous or muscle afferent volleys to cortex can be profoundly altered in normal subjects by conditioning activity. The possibility that normal background afferent activity can similarly modify afferent transmission has implications for diagnostic studies, particularly when they are performed under non-standard conditions, such as in the operating theatre or intensive care unit. It is also concluded that, although a subject may perceive cutaneous paraesthesiae when the posterior tibial nerve is stimulated at the ankle, there may be no cutaneous component to the evoked cerebral potential.

Adult↗