Spontaneous discharge and peripherally evoked orofacial responses of trigemino-thalamic tract neurons during wakefulness and sleep.

In the present study, ongoing and evoked activity of antidromically identified trigemino-thalamic tract (TGT) neurons was examined over the sleep-wake cycle in cats. There was no difference in the mean spike discharge rate of TGT neurons when quiet sleep (QS) and active sleep (AS) were compared with wakefulness (W). However, tooth pulp-evoked responses of TGT neurons were decreased during AS when compared to W. Conversely, the responses of TGT neurons to air puff activation of facial hair mechanoreceptors reciprocally increased during AS when compared to W. The present data demonstrate that ascending sensory information emanating from distinct orofacial areas is differentially modified during the behavioral state of AS. Specifically, the results obtained suggest that during AS, sensory information arising from hair mechanoreceptors is enhanced, whereas information arising from tooth pulp afferents is suppressed. These data may provide functional evidence for an AS-related gate control mechanism of sensory outflow to higher brain centers.

Dorsal spinocerebellar tract neurons in the chronic intact cat during wakefulness and sleep: analysis of spontaneous spike activity.

Relatively little is known about the transmission of ascending sensory information from lumbar levels across the behavioral states of sleep and wakefulness. The present study used extracellular recording methods in chronically instrumented intact behaving cats to monitor the activity of lumbar dorsal spinocerebellar tract (DSCT) neurons within Clarke's column during the states of wakefulness, quiet sleep, and active sleep. Clarke's column DSCT neurons were identified using antidromic identification and retrograde labeling techniques. The spontaneous spike rate and interspike interval data of DSCT neurons were quantified as a function of behavioral state. During wakefulness and quiet sleep, the spike rate of DSCT neurons was stable, and interspike interval histograms (ISIH) indicated a relatively high degree of regularity in DSCT neuronal spike train patterns. In contrast, during active sleep there was a marked reduction in the ongoing spike rate in a vast majority of cells tested. The magnitude of change in ISIHs and interspike interval data during active sleep depended in part on whether the reduction in cell firing was maintained or periodic throughout active sleep. Further suppression of spontaneous activity also was observed during intense rapid-eye-movement episodes of active sleep that were associated with clustered pontogeniculo-occipital wave and muscular twitches and jerks. After re-awakening, spontaneous spike activity of Clarke's column DSCT neurons resembled that recorded during previous episodes of wakefulness. These data provide evidence that ascending proprioceptive and exteroceptive sensory transmission through Clarke's column is diminished during the behavioral state of active sleep.

Morphology and distribution of neurons and glial cells expressing beta-adrenergic receptors in developing kitten visual cortex.

The morphology and distribution of cells expressing beta-adrenergic receptors has been studied in developing kitten visual cortex using a monoclonal antibody which recognizes both beta-1 and beta-2 adrenergic receptors. We found specific populations of neurons and glial cells which express beta-adrenergic receptor immunoreactivity in the kitten visual cortex. In adult animals, the receptors are most concentrated in the superficial and deep cortical layers (layers I, II, III and VI). About 50% of the stained neural cells in adult cat visual cortex are glial cells. Most of the immunoreactive neurons in layers III and V are pyramidal cells while those in layers II and IV are more likely to be nonpyramidal cells. In neonatal kittens, staining is weaker than that in adult cats and it appears to be concentrated in neurons of the deep cortical layers and in the subcortical plate and white matter. Only a few immunoreactive glial cells were found at this age. Receptor numbers increase after birth and by 24 days of age, the laminar distribution of beta-adrenergic receptors approaches that of adult animals. Immunoreactive glial cells in the white matter show a progressive increase in number throughout postnatal development.

Calcium calmodulin dependent kinase II in cat visual cortex and its development.

A monoclonal antibody against the alpha-subunit of calcium/calmodulin-dependent protein kinase II (CAM-K II) was used to visualize the kinase in developing kitten visual cortex. CAM-K II was first expressed in neurons of the deep cortical layers (V and VI) at postnatal day 1-4 and appeared in the remaining cortical layers within the first 2 weeks. The level of immunoreactivity declined in cells of layer V and upper layer VI at about 30-40 days of age. By postnatal day 90, the most densely labelled neurons were concentrated in cortical layers II, III, lower layer IV and in layer VI. This laminar pattern remained constant into adulthood. EM studies showed that the kinase was found in both pre- and postsynaptic locations. About twice as many immunopositive neurons were found in cortical layers II-IV and VI in young adult cats when geniculate input was removed by an unilateral thalamic lesion performed early in life. These results indicate that expression of CAM-K II is developmentally regulated in visual cortical neurons; the alteration of immunoreactivity after early LGN lesions suggests that the level of the kinase (or its alpha-subunit) is also regulated by cortical input.

Protein kinase C immunoreactivity in kitten visual cortex is developmentally regulated and input-dependent.

Immunocytochemistry with polyclonal antibodies directed against protein kinase C (PKC) was utilized to investigate the development of the kinase in kitten visual cortex neurons. The immunoreaction product was found at postsynaptic sites at all ages studied. However, PKC was localized in presynaptic terminals only during the first few weeks of postnatal life, during the period when the cortex is most susceptible to visual experience. The overall level of PKC immunoreactivity was high at early postnatal ages (up to 6 weeks) and declined afterwards till adulthood. This decline in reactivity was not equal across the cortex and was particularly marked in the middle cortical layers, especially layer IV. The reduction of PKC immunoreactivity in all cortical layers but layer IV was abolished by isolating a portion of cortex from its neuronal inputs early in life. Indirect evidence points to the lateral geniculate nucleus as the source of input that is required for input-dependent maturational changes in the kinase level. The results reported here suggest that the expression of PKC in kitten visual cortex in not only developmentally regulated but is also use-dependent.

Cellular and subcellular localization of protein kinase C in cat visual cortex.

Polyclonal antibodies against 3 protein kinase C (PKC) subtypes (I, II and III) were applied to localize the kinase in cat visual cortex. These antibodies exclusively stained neuronal cells. Both pyramidal and non-pyramidal cells exhibiting PKC-like immunoreactivity were concentrated in layers, II, III, V and VI with relatively few cells in layer IV. Electron microscopic examination did not reveal any presynaptic localization of the kinase. PKC immunoreactivity remained normal in a zone of cortex surgically isolated from the rest of the brain by an undercut procedure. These results suggest that PKC is heterogenously distributed in adult cat visual cortex; the kinase recognized by the polyclonal antibodies is localized postsynaptically in intracortical neurons of the superficial and deep cortical layers and the expression of the kinase is not regulated by extracortical input.

Functional organization of the cortical 17/18 border region in the cat.

The representation of the visual field in the 17/18 border region of the cat's visual cortex, and the layout of orientation and ocular dominance columns, were studied by making many closely spaced electrode penetrations into the superficial layers of the flattened dorsal region of the marginal gyrus and recording response properties at each location. The 17/18 border region was defined by measuring the change in the horizontal component of receptive field position within the gyrus: as the position of the recording electrode moved from medial to lateral, the receptive fields moved towards the vertical midline, indicating that the electrode was in area 17; as penetrations were made in increasingly lateral positions, the trend reversed, and receptive field positions moved away from the midline, indicating that the electrode was in area 18. The receptive fields of cells close to the border straddled, or lay within 2 degrees-3 degrees on either side of the vertical midline. In addition, patches of cortex were sometimes encountered in which cells had receptive field centers located up to 7 degrees in the ipsilateral visual field. Experiments in which maps were made in the left and right hemispheres of a single animal showed that these patches had a complementary distribution in the two hemispheres. Cells within the patches behaved as though driven by Y-cell inputs: they usually had large receptive fields and responded to rapidly-moving stimuli. They were broadly tuned for orientation and strongly dominated by the contralateral eye. Fourier spectral analysis of orientation selectivity maps showed that iso-orientation bands had an average spacing of 1.14 +/- 0.1 mm and tended to be elongated in a direction orthogonal to the 17/18 border. Individual bands crossed the border without obvious interruption, although singularities (points of discontinuity in the layout of orientations) were more frequently observed in the border region than in adjacent areas. Two dominant periodicities could be measured in the maps of ocular dominance, one at around 0.8 +/- 0.2 mm and a second at 2.0 +/- 0.3 mm. No constant direction of elongation was noted. These are close to the periods present within areas 17 and 18 respectively.

Phorbol 12,13-dibutyrate regulates muscarinic receptors in rat cerebral cortical slices by activating protein kinase C.

Stimulation of muscarinic acetylcholine receptors (mAChR) elicits phosphatidylinositol turnover, which yields inositol phosphates (InsP) and diacylglycerol (DG) the latter activating protein kinase C (PKC). Activating PKC with phorbol esters inhibits mAChR agonist-stimulated phosphoinositide hydrolysis and InsP production. A possible mechanism of this inhibition may be down-regulation of mAChR by PKC. In the present work, rat cortical slices were preincubated with phorbol 12,13-dibutyrate (PDBu) followed by binding assays for [3H]quinuclidinyl benzilate [( 3H]QNB), [N-methyl-3H]scopolamine [( 3H]NMS) or [3H]pirenzepine [( 3H]PZ). Our data demonstrate that activation of PKC by phorbol esters causes a rapid down-regulation of muscarinic cholinergic receptors. This down-regulation is also rapidly reversible. Receptors on the cell surface appear to be more sensitive to the effect of PKC than do internal ones. This down-regulation occurs by a decrease in the number of receptors, rather than by changes in receptor affinity. The results suggest that PKC may exert negative feedback on its own activation by down-regulating the receptors that normally elicit phosphatidylinositol turnover.