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J C Nussbaumer

Publications and source records attributed to J C Nussbaumer.

7 recordsLinked to original sources
PubMed1989

Pharmacological properties of a C-fibre response evoked by saphenous nerve stimulation in an isolated spinal cord-nerve preparation of the newborn rat.

1. An isolated spinal cord-peripheral nerve preparation of the newborn rat was developed. In this preparation it is possible to record spinal reflexes from a lumbar ventral root in response to stimulation of the ipsilateral saphenous or obturator nerve. 2. Single shock, weak intensity stimulation of the saphenous nerve induced a fast conducted compound action potential in the L3 dorsal root and a fast depolarizing response in the ipsilateral L3 ventral root. As a stronger stimulus was applied to the saphenous nerve, a slowly conducted compound action potential appeared in the dorsal root and a slow depolarizing ventral root potential (v.r.p.) in the L3 ventral root. 3. Single shock stimulation of the obturator nerve induced a rapidly conducted compound action potential in the L3 dorsal root and monosynaptic and polysynaptic reflexes, with a fast time course, in the ipsilateral L3 ventral root. 4. The slow v.r.p. evoked by saphenous nerve stimulation was depressed by the tachykinin antagonist, [D-Arg1, D-Trp7,9, Leu11] substance P (spantide), 4-16 microM. The response recovered its original shape and size 30-60 min after the removal of this antagonist. 5. The saphenous nerve-evoked slow v.r.p. was depressed by [Met5] enkephalin (0.1-1 microM), dynorphin (1-13)(0.2 microM) and morphine (1-2 microM), and these effects were reversed by naloxone (1 microM). 6. Two endogenous peptides, galanin (1-2 microM) and somatostatin (1-2.5 microM), inhibited the slow v.r.p. evoked by saphenous nerve stimulation, whereas another endogenous peptide, calcitonin gene-related peptide (0.1-0.5 microM), potentiated the slow v.r.p. The slow v.r.p. was also inhibited by gamma-aminobutyric acid (GABA, 20 microM) and muscimol (0.2 microM), and their effects were antagonized by bicuculline (1 microM). 7. The present results suggest that substance P and neurokinin A are involved in the saphenous nerve-evoked C-fibre response in the spinal cord of the newborn rat.

Animals↗
PubMed1987

A stain for ischaemic or excessively stimulated neurons.

Loyez' myelin stain sometimes impregnates the perikarya and processes of neurons. This is rare in normal adult mice, but can be provoked by various means including electrical stimulation and mild ischaemia shortly before fixation. Passing a direct current or a train of pulses across the dura of the cerebral cortex produces a patch at the site of stimulation in which the neurons, but not the glia, are Loyez-impregnated; pulse-trains evoke such impregnation even at remote sites, presumably through orthodromic and/or antidromic activation. The strength and duration of stimulation necessary to provoke impregnation are below the threshold for causing an overt lesion. Local ischaemia produced by irreversibly occluding a small subarachnoid artery for as little as 7 min evokes a small patch of impregnated neurons in the superficial layers adjacent to the occluded artery. After slightly longer-lasting (e.g. 17 min) ischaemia, the impregnated zone spans most of the cortical depth. Mild global ischaemia produced by irreversibly occluding one or both common carotid arteries 30 min before fixation causes large numbers of neurons to be impregnated in many parts of the brain. That interventions as different as electrical stimulation and arterial occlusion both lead to neuronal impregnation may most plausibly be explained by the fact that they both cause cells to be depolarized. The method will be useful for visualizing overstimulated or ischaemic neurons, and may be applicable to the tracing of neural pathways.

Animals↗
PubMed1985

Expansion of receptive fields in the mouse cortical barrelfield after administration of capsaicin to neonates or local application on the infraorbital nerve in adults.

A possible role fore peripheral unmyelinated fibres on the establishment and maintenance of stable receptive fields mediated by myelinated afferents has been studied in the mouse cortical barrelfield. The barrels are cytoarchitectonic units consituting a visible and particularly precise somatotopic map of the facial vibrissae. Barrelfields were mapped electrophysiologically in adults using two experimental setups: (i) after destruction of unmyelinated peripheral fibres by systemic administration of capsaicin neonatally; and (ii) after inactivation of these fibres by local application of capsaicin to the nerve subserving the vibrissae in the adult. The latter procedure is known not to destroy fibres. Control animals received the vehicle used to dissolve capsaicin. The effectiveness of capsaicin on the peripheral fibres was assessed histochemically on their terminals in the substantia gelatinosa. Both methods of application of capsaicin resulted in a large expansion of cortical receptive fields: units within a particular barrel were driven by a statistically significant, larger number of vibrissae than in controls. No morphological alterations of the barrels were found in cortical tangential sections. We concluded that capsaicin treatment 'defocusses' the normal physiological precision without destroying the general plan of representation and without alteration of the barrel pattern.

Age Factors↗
PubMed1985

An electrophysiological and anatomical study of projections to the mouse cortical barrelfield and its surroundings.

This study establishes a cortical map of the somatosensory periphery of the mouse head, with emphasis on the whisker pad. Data in the literature on the projection of the common hair follicles are confusing, notably the question whether or not this projection is separated from or overlaps with that of the facial vibrissae, the barrelfield. Microelectrode recordings in the barrelfield and its immediate surroundings upon natural stimulation of the periphery were followed by microlesions and histological reconstruction. Results show that the barrelfield consists of two parts: an anterior part where vibrissal follicles and the skin bearing them are represented, and a posterior part receiving only vibrissa inputs. The skin between these latter vibrissae is represented outside the barrelfield. We conclude that the partially dissociated cortical representation of skin and vibrissae may allow large vibrissae to be used in tasks requiring greater acuity than the shorter ones provide. This hypothesis is supported by the observation that, owing to special muscles, large vibrissae are more mobile than short ones. We also propose that the segregation of inputs from vibrissae and common fur is related to the number of nerve fibers serving one follicle, and we indicate an experimental model to test this possibility.

Animals↗