The diaphragm, which previously has been shown to contain relatively few proprioceptors and to lack autogenetic facilitation, was found to be under reflex control from intercostal afferents. Electrical stimulation of the intercostal nerves of the lowest thoracic segments elicited a polysynaptic reflex excitation of phrenic motoneurones followed by a depression of ‘spontaneous’ phrenic motor activity. No phrenic responses were elicited from the upper thoracic segments. Increased phrenic activity was also elicited by mechanical stimulation of the trunk wall; the receptive area of these effects was similarly limited to the region of the insertion of the diphragm. Alike reflex effects were obtained from both the internal and the external intercostal nerves. In the internal nerve both group Ib and II afferents were found to contribute to the reflex whereas in the external nerve it was mainly the secondary muscle spindle endings which gave rise to the response. In contrast to the intercostal‐to‐intercostal reflexes cutaneous afferents proved to be without effect in the intercostal‐to‐phrenic reflex.
Background: Rats distinguish objects differing in surface texture by actively moving their vibrissae. In this paper we characterized some aspects of texture sensing in anesthetized rats during active touch. We analyzed the multifiber discharge from a deep vibrissal nerve when the vibrissa sweeps materials (wood, metal, acrylic, sandpaper) having different textures. We polished these surfaces with sandpaper (P1000) to obtain close degrees of roughness and we induced vibrissal movement with two-branch facial nerve stimulation. We also consider the change in pressure against the vibrissa as a way to improve the tactile information acquisition. The signals were compared with a reference signal (control) -vibrissa sweeping the air -and were analyzed with the Root Mean Square (RMS) and the Power Spectrum Density (PSD).
The intercostal‐to‐phrenic reflex connections, previously studied only in spinal preparations, have now been further analyzed in decerebrate cats and rabbits. The early excitatory part of the response was of the same nature as the corresponcling response component in spinal preparations. The subsequent inhibitory phase was due both to post‐firing depression, as in the spinal state, and to active inhibition. The responses in decerebrate animals showed marked respiratory variations with almost complete abolishment of the excitatory component in the end‐expiratory phase. In the decerebrate preparation the responses from the different portions of the diaphragm showed qualitative differences which disappeared after spinalization. Further signs of differentiated intercostal‐to‐phrenic relations were obtained by stimulating different intercostal nerves. Stimulation of the anterior lobe of cerebellum exerted pronounced effects both on the respiratory phrenic activity–inhibition, sometimes followed by post‐tetanic facilitation–and on the intercostal‐to‐phrenic reflex–removing the inhibition in the end‐expiratory phase. Some of the features of the synaptic organization of the phrenic nucleus are discussed.
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