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Horseradish peroxidase was injected into the medial and lateral columns of the facial nucleus of the rat. Following medial injections, cells were labelled by retrograde transport in the ipsilateral spinal trigeminal nucleus (caudalis) both medial vestibular nuclei, contralateral midbrain reticular formation and nucleus of the lateral lemniscus. The periaqueductal grey, interstitial nucleus and nucleus of Darkschewitch were also labelled ipsilaterally. Injections into the lateral column of the facial nucleus labelled the spinal trigeminal nucleus (oralis) and parabrachial nuclei ipsilaterally and the Darkschewitch and red nuclei contralaterally.

The representation of facial muscle groups in the facial nucleus of rat was examined by retrograde transport of HRP. Motoneurons supplying muscle groups are arranged in longitudinal columns. Those supplying nasolabial muscles are located in the lateral and ventral intermediate segments, posterior auricular muscles in a medial column, platysma in a n intermediate column; the lower lip and ocular muscles are in the ventral and dorsal segments respectively of the intermediate column. The posterior belly of the digastric muscle is supplied by motoneurons extending from the dorsal aspect of the facial nucleus to the caudal pole of the trigeminal motor nucleus.Several techniques have been employed to determine the central organization of the facial nucleus in a variety of species. These include chromatolysis (Marinesco, 1899; Van Gehuchten, 1898;Yagita, 1910;Papez, 1927;Vraa-Jensen, 1942), the Gudden method (Courville, 1966) loss of cholinesterase in the nucleus (Dom et al., 19731, and application of peroxidase to nerve stumps (Provis, 1977). All of these methods require section of peripheral nerves, although more than one peripheral facial nerve branch has been shown to supply some muscles (Provis, 1977). In addition, recent studies have cut adjacent nerves to avoid their uptake of protein tracer (Kume et al., 19781, or prepared only some facial nerve branches to avoid current spread from stimulation Martin and Lodge, 1977). These methods may have imposed an artificial organization on the nucleus. Similarly, the placement of lesions in parts of the facial nucleus with subsequent examination of individual muscles for evidence of degenerating motor end plates (Szentagothai, 1948) imposes restrictions upon the information that has been obtained. It is therefore not surprising that 3-6 anatomical subdivisions of the nucleus described from coronal Nissl-stained sections (Marinesco, 1899; Van Gehuchten, 1898;Yagita, 1910;Papez, 1927;Hogg, 1928;Nishi, 1965; Courville, 1966) have been related to peripheral branches of the facial nerve rather than to individual muscles or muscle groups.This study was undertaken to map the representation of muscle groups in the facial nucleus of the rat by retrograde transport of horseradish peroxidase (HRP) after its injection into individual facial muscle groups. It was a n essential prerequisite to tracing of central connections of the facia1 nucleus because afferents have been shown to terminate preferentially within the facial nucleus from the red nucleus (Courville, 1966;Martin and Dom, 1970;Mizuno and Nakamura, 1971;Yu et al., 1972;Edwards, 1972), the trigeminal nerve Stewart and King, 1963; Erzulumulu and Killackey, 19791, the hypoglossal nerve (Tanaka et al., 19711, and from respiratory centers (Sherrey and Megirian, 1977). Conflicting maps of the representation of muscles within the facial nucleus render the significance of these inputs unclear. MATERIALS AND METHODSThirty 250-g female hooded rats (Wistar strain) were given injections of 1-5 p1 of a 50% solution of HRP ...

Respiratory afferent stimulation can elicit increases in respiratory motor output that outlast the period of stimulation by seconds to minutes [short-term potentiation (STP)]. This study examined the potential contribution of spinal mechanisms to STP in anesthetized, vagotomized, paralyzed rats. After C(1) spinal cord transection, stimulus trains (100 Hz, 5-60 s) of the C(1)-C(2) lateral funiculus elicited STP of phrenic nerve activity that peaked several seconds poststimulation. Intracellular recording revealed that individual phrenic motoneurons exhibited one of three different responses to stimulation: 1) depolarization that peaked several seconds poststimulation, 2) depolarization during stimulation and then exponential repolarization after stimulation, and 3) bistable behavior in which motoneurons depolarized to a new, relatively stable level that was maintained after stimulus termination. During the STP, excitatory postsynaptic potentials elicited by single-stimulus pulses were larger and longer. In conclusion, repetitive activation of the descending inputs to phrenic motoneurons causes a short-lasting depolarization of phrenic motoneurons, and augmentation of excitatory postsynaptic potentials, consistent with a contribution to STP.

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Membrane capacity was measured as a function of fibre diameter in mammalian skeletal muscle fibres under normal conditions and under conditions designed to reduce the membrane chloride conductance, i.e. in solutions in which chloride ions were replaced by sulphate or methylsulphate ions, or in normal Krebs solutions containing 2,4-dichlorophenoxyacetic acid (2.5 mM). The experiments were done on rat sternomastoid, extensor digitorum longus and soleus muscle fibres. The average membrane capacity of fibres in each muscle was greater than normal when chloride conductance was reduced and the slope of the relationship between membrane capacity and fibre diameter increased. The results were consistent with the hypothesis that the space constant of the transverse tubule system in mammalian fibres is normally short because the transverse tubule membrane has a high chloride conductance. The experimental results imply that the space constant of the transverse tubule system was less than 40 microns for fibres in normal Krebs solution and greater than 100 microns for fibres with low membrane chloride conductance. The space constant was calculated using measured geometrical parameters of the transverse tubule, and measured membrane conductance, and the values were close to 20 microns for fibres in normal Krebs solution and between 50 and 120 microns for fibres with low chloride conductance.