PubMed · 370907
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R E Baker. 1978. Synapse selectivity in somatic afferent systems.. https://doi.org/10.1016/s0079-6123(08)61017-1
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1. Cardiac vagal receptors are chemically and/or mechanically sensitive but it is unknown if this information is preserved centrally within the nucleus of the solitary tract (NTS). The present study had two aims: first, to investigate qualitatively whether both mechanically and chemically sensitive cardiac vagal encoding were preserved within the NTS, and second, to determine the patterns of convergence from other cardiorespiratory afferents to NTS neurones receiving cardiac vagal inputs. 2. The extracellular activity of single NTS neurones was investigated during stimulation of both chemically and mechanically sensitive cardiac vagal receptors in a working heart-brainstem preparation of mouse. Chemically sensitive cardiac receptors were stimulated using intra-left ventricular injections of either veratridine (1-3 microg kg-1), bradykinin (0.25-1 microg) or prostaglandin E2 (100-200 ng), whereas the left ventricle was distended to activate cardiac mechanoreceptors. 3. Forty-three NTS neurones were activated both synaptically by electrical stimulation of the ipsilateral vagus nerve (latency, 35 +/- 3 ms), and by intra-left ventricular injection of veratridine and also, in some cases, by bradykinin and/or PGE2. These NTS neurones were delineated into two populations based on their response to left ventricular distension and convergence properties. Left ventricular distension-insensitive neurones (n = 30) were excited by stimulation of carotid body chemoreceptors (81 %) but not arterial baroreceptors (3 %; i.e. n = 1 neurone), whereas distension-sensitive cells (n = 13) were activated mainly by baroreceptors (86 %) rather than peripheral chemoreceptors (14 %; i.e. n = 1 neurone). 4. The data reveal two distinct populations of NTS neurones receiving cardiac vagal inputs: (a) cells responsive to veratridine stimulation only, and (b) neurones activated by both veratridine and mechanical stimuli. The specific convergence pattern of baroreceptors and chemoreceptors to these cardioreceptive NTS neurones is discussed in relation to a common afferent modality integration within the NTS.
Central projections of nerves innervating the rabbit maxillary sinus were localized by using wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or choleragenoid-horseradish peroxidase (B-HRP). Tracer was placed into the left maxillary sinus; rabbits were killed 3 or 5 days later, and histochemical localization of transported WGA-HRP or B-HRP was performed. Labeled cell bodies (437-545/animal) were seen in the ipsilateral trigeminal ganglion. Very few labeled cell bodies (zero to three/animal) were observed in the contralateral ganglion. The area of cell bodies labeled by WGA-HRP appeared similar to the area of cell bodies labeled by B-HRP. Transganglionic projections from either tracer were localized to lamina II of the ipsilateral subnucleus caudalis. In addition, WGA-HRP labeling was occasionally observed in lamina I. No labeling was present in other areas of the brainstem. In contrast to the above results, other studies have demonstrated that B-HRP produces terminal-like labeling in deeper layers of the gray matter. We injected B-HRP into the infraorbital nerve and sciatic nerve, which are known to contain projections to deep layers of the gray matter. Labeling was observed in the deep layers of the medullary or spinal dorsal horn 5 days later, suggesting that nerves innervating the sinus only project to superficial laminae. These results suggest that neurons in superficial laminae of the subnucleus caudalis may be important for the reflex initiation of the increased glandular secretions in the maxillary sinus during sinusitis.
Postsynaptic potentials evoked in motoneurons innervating m. posterior biceps and semitendinosus (PBSt) and m. triceps surae (GS) by low threshold afferents from various tail muscles located at the level of the second-third caudal vertebrae were investigated in the non-anesthetized and spinalized cat. Afferent inputs from tail muscles on both sides predominantly evoked depolarizing potential in PBSt motoneurons and hyperpolarizing potential in GS motoneurons. The findings suggest that in general, tail muscle afferents facilitate flexor and inhibit extensor hindlimb motoneurons through polysynaptic pathways, so that the pelvic girdle is kept in a low position to maintain the stability of the body irrespective of different movements or posture of the tail.