Cfl Hinrichsen

Modulation of the synaptic drive to respiratory premotor and motor neurons.

The characteristics of GABAergic inhibitory modulation of respiratory bulbospinal neuronal activity and short-term potentiation (STP) of phrenic motoneuronal activity were studied. Extracellular unit recording and picoejection techniques in anesthetized dogs showed that both the spontaneous rhythmic and reflexly induced discharge patterns of inspiratory (I) and expiratory (E) premotor neurons were proportionately amplified by the localized application of picomole amounts of bicuculline (Bic), a competitive GABAA antagonist. Intracellular recording and paired-pulse stimulation techniques in anesthetized rats demonstrated an STP of phrenic motor output that appears to be mediated by NMDA receptors and is associated with facilitation of EPSPs and prolonged depolarization of individual phrenic motoneurons. We speculate that both GABAergic gain modulation of premotor neuronal activity and NMDA-mediated STP of phrenic activity may be neural substrates which are involved with the optimization of respiratory and non-respiratory behaviors, via adaptive and/or differential control of breathing.

Epithelial morphology during closure of the secondary palate in the rat

Abstract This study was undertaken to elucidate the methods by which epithelium at the tip of a palatal shelf recognizes its opposite number, adheres and then breaks down. Electron micrographs indicate that within the epithelium there is evidence of secretion, mitosis, cellular autophagy and apoptosis beginning before the palatal shelves approximate. Cells of the deeper epithelial layers come to the surface, are thrown into microvillous projections and possess a surface filamentous coat; these cells make the first contact. The mesenchyme does not appear to react with epithelium before or during approximation and breakdown, and there is no breakdown of the basal lamina.

Substance P in the hypoglossal nucleus of the rat

The distribution of substance P (SP)-containing synaptic terminals in the hypoglossal nucleus (XII) of adult rats was examined by retrograde peroxidase labelling and immunocytochemistry. From the location of peroxidase injections into the tongue and of labelled neurones in the ventral lamina of XII, motor neurones that supply intrinsic vertical, longitudinal and transverse fibres as well as the extrinsic muscle genioglossus appear to have been labelled. SP-containing terminals were found making contact, and sometimes dual synapses, with unlabelled neuronal dendrites but not with retrogradely labelled somata or dendrites. These findings suggest that SP terminals may contact dendrites of interneurones or of neurones supplying other extrinsic muscles located in the anterior part of the tongue. Dual SP-containing synapses between XII motor neurones may be the means by which tongue muscle fibres are recruited and their function synchronized.

Fetuin in neurons of the retina and cerebellum during fetal and postnatal development of the rat.

Although long known to be a liver‐derived fetal plasma glycoprotein, fetuin has morerecently been shown to be present in sub‐populations of neurons in the developing nervous systemof a number of mammalian species. We have extended these observations to examine the fetuinimmunoreactivity (IR) in developing rat retina and cerebellum. Fetuin–IR was first seen in theretina on embryonic day (E)19 in a sub‐population of cells in the retinal ganglion cell layer and asmall proportion of cells in the neuroblastic layer. The proportion of cells in the ganglion layerexhibiting fetuin‐IR increased until postnatal day (P)10 when all cells in this layer were stronglyimmunoreactive. From P14 onwards fetuin–IR was absent or very weak and restricted to a smallproportion of ganglion cells. In the developing cerebellum, the outer and inner granule cell layers,the deep nuclei and cells in the sub‐cortical white matter exhibited fetuin–IR from E19 to P10.There was little fetuin–IR in the cerebellum at ages P14 and older, and Purkinje cells did notexhibit fetuin–IR at any time. The results show that fetuin appears in many neurons in the retinaand cerebellum that are differentiating during the period from E19 to P10. The concentration offetuin in cerebrospinal fluid is at its highest in this same period which suggests that somesub‐populations of neurons could obtain fetuin from extracellular fluid during this period ;however, the lack of fetuin–IR in other neuronal populations suggests that fetuin uptake is not ageneral property of developing neurons.

Fine structure of muscle spindles in the masseter muscle of the rat

Abstract Because of the unique central organization of primary sensory neurons subserving jaw muscle spindles, a study of the fine structure of the spindles was undertaken to compare them with known features of spindles of somatic origin. Particular interest was directed toward fibre ultrastructure because of possible functional implications and toward sensory endings as neurons are known to outnumber the spindles they supply. Intrafusal fibres classified as nuclear bag and nuclear chain in light micrographs did not show significant ultrastructural differences with respect to sarcomere length, size and distribution of mitochondria and presence of glycogen. Nuclear chain fibres possessed a higher concentration of dilated cisternae of sarcoplasmic reticulum. There was no evidence of cross innervation or indication of more than two morphologically distinct sensory endings.