Effects of neonatal axoplasmic transport attenuation on the response properties of vibrissae-sensitive neurons in the trigeminal principal sensory nucleus of the rat

We have previously shown that attenuation of axoplasmic transport by application of vinblastine to the developing infraorbital nerve (ION) results in a loss of central vibrissae-related patterns that is not accompanied by changes in the receptive field sizes for the V primary afferents innervating the whisker follicles. The present study examines the relationship between the loss of central vibrissae-related patterns and alterations in the response properties of neurons in the V principal sensory nucleus (PrV) of adult rats that sustained application of vinblastine to the ION at birth. Absence of histochemically demonstrable vibrissae-related patterns in PrV resulted in only modest changes in the receptive fields and response properties of vibrissae-sensitive neurons in this nucleus that projected to the contralateral thalamus. Response latencies to electrical activation of the V ganglion were similar in treated and untreated animals. The mean receptive field size was significantly increased from 1.3 &#45 0.7 vibrissae in controls to 1.7 &#45 0.9 vibrissae in vinblastine-treated animals, and the percentage of cells yielding a tonic response to vibrissae deflection was markedly reduced (p < 0.01 for both measures). Phasically responding cells recorded in vinblastine-treated animals showed a significant reduction in the mean number of spikes per stimulus following deflection of the vibrissae in either the preferred or non-preferred direction relative to cells recorded in normal animals (p < 0.05). The present results indicate that disruption of the normal vibrissae-related aggregates of neurons in PrV by application of vinblastine to the ION has limited effects on the functional representation of the vibrissae in this nucleus.     

The contribution of the principal and spinal trigeminal nuclei to the receptive field properties of thalamic VPM neurons in the rat

Primary sensory information from neurons innervating whisker follicles on one side of a rat's face is relayed primarily through two subnuclei of the brainstem trigeminal complex to the contralateral thalamus. The present experiments were undertaken to separate the contribution of the principal trigeminal nucleus (PrV) from that of the spinal trigeminal nucleus (SpV) to whisker evoked responses in the ventral posterior medial (VPM) nucleus in the adult rat thalamus. Extracellular single-unit responses of VPM neurons to controlled stimulation of the contralateral whiskers under urethane anesthesia were quantified in terms of receptive field size, modal latency, response probability and response magnitude. The SpV contribution to VPM cell responses was isolated by making kainic acid lesions of the PrV. The PrV contribution was ascertained by cutting the trigeminothalamic axons arising from SpV just before they cross the midline. After destruction of the PrV, the SpV pathway alone produced large receptive fields (mean: 9.04 whiskers) and long latency (mean: 11.07 ms) responses from VPM neurons. In contrast, PrV input alone (SpV disconnected) generated small receptive fields (mean: 1.06 whiskers) and shorter latency (mean: 6.74 ms) responses. With both pathways intact the average receptive field size was 2.4 whiskers and peak (modal) response latency was 7.33 ms. The responses with both pathways intact were significantly different from either pathway operating in isolation. Response probability and magnitude followed the same trend. We conclude that normal responses of individual VPM neurons represent the integration of input activity transmitted through both PrV and SpV pathways.     

Cell structure and response properties in the trigeminal subnucleus oralis

Extra- and intracellular recording, electrical stimulation, receptive field mapping, and horseradish peroxidase injection techniques were used to study the structure of functionally identified neurons in trigeminal (V) brainstem subnucleus oralis of the rat. Of 15 heavily labeled cells located within oralis, 4 were local-circuit neurons with receptive fields restricted to either an incisor, guard hairs, one vibrissa, or deep facial tissue (nociceptors). Their morphologies were highly varied, with expansive and spiny dendritic trees and recurrent and intersubnuclear axon collaterals. Oralis local-circuit neurons therefore most closely resembled non-vibrissa-sensitive local-circuit cells in adjacent subnucleus interpolaris. Six other stained cells projected to contralateral thalamus, and two others projected to ipsilateral cerebellum. They typically had intramodality convergent receptive fields (i.e., spanning more than one receptor organ, such as multiple vibrissae or teeth) with widespread dendritic trees, and were therefore indistinguishable from similarly projecting cells in interpolaris. Two other cells projected to the ipsilateral spinal cord, as well as other V brainstem subnuclei. One of these responded to high-threshold mechanical stimulation of teeth; the other was discharged by deflection of one mystacial vibrissa. Their dendrites were very widespread and ended in spiny and bulbous appendages. Local axon collaterals were also extensive. The remaining oralis cell had two axons, one projecting to the thalamus, the other to the spinal cord. Its receptive field expressed convergence from multiple receptor organs, including vibrissae, guard hairs, and skin. Its somadendritic morphology was similar to that of oralis cells projecting only to thalamus. We conclude that, with some exceptions, the extensive dendritic trees, axon branching, convergence, and functional diversity of oralis cells approximate those described previously for functionally equivalent neurons in interpolaris (Jacquin et al., 1989a,b). Such anatomical and physiological properties are rarely seen, however, in nucleus principalis (Jacquin et al., 1988a). The structure and function of three atypical principalis cells with structural and functional characteristics typical of oralis cells are also described. It is argued that such cells are rostrally displaced oralis cells.     

Organization,development, and effects of infraorbital nerve transection on galanin binding sites in the trigeminal brainstem complex

Previous experiments from this laboratory have indicated that transection of the infraorbital nerve (ION, the trigeminal \[V] branch that supplies the mystacial vibrissae follicles) at birth and in adulthood has markedly different effects on galanin immunoreactivity in the V brainstem complex. Adult nerve transection increases galanin immunoreactivity in the superficial layers of V subnucleus caudalis (SpC) only, while neonatal nerve transection results in increased galanin expression in vibrissae-related primary afferents throughout the V brainstem complex. The present study describes the distribution of binding sites for this peptide in the mature and developing V ganglion and brainstem complex and determines the effects of neonatal and adult ION damage and the associated changes in galanin levels upon their distribution and density. Galanin binding sites are densely distributed in all V brainstem subnuclei and are particularly dense in V subnucleus interpolaris and the superficial layers of SpC. They are present at birth (P-0) and their distribution is similar to that in adult animals. Transection of the ION in adulthood and examination of brainstem 7 days later indicated marked reductions in the density of galanin binding sites in the V brainstem complex. With the exception of the superficial laminae of SpC, the same reduction in density remained apparent in rats that survived 45 days after nerve cuts. Transection of the ION on P-0 resulted in no change in the density of galanin binding sites in the brainstem after either 7 or 60 days survival. These results indicate that densely distributed galanin binding sites are present in the V brainstem complex of both neonatal and adult rats, that they are located in regions not innervated by galanin-positive axons, and that their density is not significantly influenced by large lesion-induced changes in the primary afferent content of their natural ligand.     

Whisker-related circuitry in the trigeminal nucleus principalis: Ultrastructure

Trigeminal (V) nucleus principalis (PrV) is the requisite brainstem nucleus in the whisker-to-barrel cortex model system that is widely used to reveal mechanisms of map formation and information processing. Yet, little is known of the actual PrV circuitry. In the ventral “barrelette” portion of the adult mouse PrV, relationships between V primary afferent terminals, thalamic-projecting PrV neurons, and gamma-aminobutyric acid (GABA)-ergic terminals were analyzed in the electron microscope. Primary afferents, thalamic-projecting cells, and GABAergic terminals were labeled, respectively, by Neurobiotin injections in the V ganglion, horseradish peroxidase injections in the thalamus, and postembedding immunogold histochemistry. Primary afferent terminals (Neurobiotin- and glutamate-immunoreactive) display asymmetric and multiple synapses predominantly upon the distal dendrites and spines of PrV cells that project to the thalamus. Primary afferents also synapse upon GABAergic terminals. GABAergic terminals display symmetric synapses onto primary afferent terminals, the somata and dendrites (distal, mostly) of thalamic-projecting neurons, and GABAergic dendrites. Thus, primary afferent inputs through the PrV are subject to pre- and postsynaptic GABAergic influences. As such, circuitry exists in PrV “barrelettes” for primary afferents to directly activate thalamic-projecting and inhibitory local circuit cells. The latter are synaptically associated with themselves, the primary afferents, and with the thalamic-projecting neurons. Thus, whisker-related primary afferent inputs through PrV projection neurons are pre- and postsynaptically modulated by local circuits.     

Effects of alterations of the vibrissae-related organization of thalamocortical axons upon the organization and outgrowth of intracortical connections in the barrelfield of the rat

Previous studies have shown that intracortical projections in layer IV of the vibrissae representation of primary somatosensory cortex (S-I) are arrayed in a pattern complementary to that of thalamocortical axons (TCAs). Elevation of cortical serotonin (5-HT) in rats during the first postnatal week results in a transient disruption of the vibrissae-related pattern of TCAs and layer IV neurons in S-I. The present study examines the influence of elevated cortical 5-HT levels and the attendant loss of vibrissae-related TCA clusters on the organization of S-I intracortical connections. Cortical 5-HT was elevated in neonatal rats via chronic injections of clorgyline from birth until P-6. Animals were euthanized on P-6 or allowed to survive an additional 4 days without further clorgyline treatment. Distributions of TCAs and intracortical axons were assessed via application of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Di-I) and 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide (Di-A) to the thalamic radiations and directly into the cortical barrelfield, respectively. Chronic administration of clorgyline resulted in a loss of the vibrissae-related organization of TCAs in layer IV of S-I. There was also a loss of the complementary pattern of intracortical projections in layer IV of this region. Discontinuation of clorgyline treatment resulted in a return of the vibrissae-related pattern of TCAs as well as the complementary pattern of intracortical projections. These results are consistent with the conclusion that the normal organization of intracortical projections in this region of S-I depends on the presence of the orderly array of TCAs.     

Effect of chronic morphine exposure on response properties of rat barrel cortex neurons.

Chronic exposure to morphine can impair performance in tasks which need sensory processing. Using single unit recordings we investigate the effect of chronic morphine exposure on the firing properties of neurons in layers IV and V of the whisker-related area of rat primary somatosensory cortex. In urethane-anesthetized animals, neuronal activity was recorded in response to principal and adjacent whisker deflections either stimulated independently or in a conditioning test paradigm. A condition test ratio (CTR) was calculated for assessing the inhibitory receptive field. In layer IV, chronic morphine treatment did not change the spontaneous discharge activity. On responses to principal and adjacent whisker deflections did not show any significant changes following chronic morphine exposure. The magnitude Off responses to adjacent whisker deflection decreased while its response latency increased. In addition, there was a significant increase in the latency of Off responses to principal whisker deflection. CTR did not change significantly following morphine exposure. Layer V neurons, on the other hand, did not show any significant changes in their spontaneous activity or their evoked responses following morphine exposure. Our results suggest that chronic morphine exposure has a subtle modulatory effect on response properties of neurons in barrel cortex.     

Responses of primary somatosensory cortical neurons to paired stimulation of the infraorbital nerve and vibrissae in cats

Extra- and intracellular responses of 128 neurons to paired stimulation of the infraorbital nerve and vibrissae, recorded in the projection zone of the vibrissae in cortical area SI, were studied in adult cats immobilized with tubocurarine. Conditioning stimulation completely suppressed the ability of different neurons to respond for periods of between 10 and 120 msec. The duration of the period of total suppression of test responses was shown to depend on the location of the stimulated vibrissa in the peripheral receptive field of the neurons studied. Excitatory and inhibitory responses of maximal intensity arose in the neurons to stimulation of receptive field centers. The functional role of the decrease in intensity of excitatory responses during stimulation of vibrissae located at different distances from centers of the receptive fields of cortical neurons is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 117–124, April, 1981.     

Afferent inhibition and functional properties of neurons in the vibrissae projection area of the cat somatosensory cortex]

The aim of this study was to investigate the role of inhibitory processes in S-1 cortex of cats. The inhibition was evoked by "natural" afferent stimulation of the fascial vibrissae. For this purpose, two neighboring vibrissae were sequentially stimulated by mechanical deflection; single unit activity was recorded simultaneously from the cortex. Results showed that conditioning by afferent stimulation significantly influenced the directional sensitivity of cortical neurons. These data and analysis of spatial pattern of stimulated vibrissa indicate that detector neurons could be quickly modified during sensory processing.     

Effects of alterations of the vibrissae-related organization of thalamocortical axons upon the organization and outgrowth of intracortical connections in the barrelfield of the rat

Previous studies have shown that intracortical projections in layer IV of the vibrissae representation of primary somatosensory cortex (S-I) are arrayed in a pattern complementary to that of thalamocortical axons (TCAs). Elevation of cortical serotonin (5-HT) in rats during the first postnatal week results in a transient disruption of the vibrissae-related pattern of TCAs and layer IV neurons in S-I. The present study examines the influence of elevated cortical 5-HT levels and the attendant loss of vibrissae-related TCA clusters on the organization of S-I intracortical connections. Cortical 5-HT was elevated in neonatal rats via chronic injections of clorgyline from birth until P-6. Animals were euthanized on P-6 or allowed to survive an additional 4 days without further clorgyline treatment. Distributions of TCAs and intracortical axons were assessed via application of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Di-I) and 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide (Di-A) to the thalamic radiations and directly into the cortical barrelfield, respectively. Chronic administration of clorgyline resulted in a loss of the vibrissae-related organization of TCAs in layer IV of S-I. There was also a loss of the complementary pattern of intracortical projections in layer IV of this region. Discontinuation of clorgyline treatment resulted in a return of the vibrissae-related pattern of TCAs as well as the complementary pattern of intracortical projections. These results are consistent with the conclusion that the normal organization of intracortical projections in this region of S-I depends on the presence of the orderly array of TCAs.     

Neonatal transection alters the percentage of substance-P-positive trigeminal ganglion cells that contribute axons to the regenerate infraorbital nerve

Neonatal transection results in a marked reduction of the number of trigeminal (V) ganglion cells that contribute axons to the regenerate infraorbital nerve (ION; Jacquin and Rhoades, 1985; Chiaia et al., 1987). Such lesions also produce a profound deafferentation of the V brain stem complex that appears to spare the innervation of layers I and II of subnucleus caudalis (SpC) by substance-P-positive (SP-positive) primary afferents (Jacquin and Rhoades, 1985; Rhoades et al., 1988). In the present study, we combined retrograde tracing with immunocytochemistry to determine whether neonatal transection of the ION alters the percentage of SP-positive V ganglion cells that contribute axons to this V branch upon regeneration. In V ganglia ipsilateral to the intact ION (n = 8), 11.6% +/- 3.2% of the cells labeled after application of true blue (TB) to the ION were also SP-positive. In ganglia ipsilateral to the neonatally damaged nerve (n = 8), 18.6% +/- 4.7% of the cells labeled after application of TB to the regenerate ION were also SP-positive (p less than 0.001). We also compared the SP content of intact ganglia (n = 10) with that of ganglia ipsilateral to the damaged nerve (n = 10) by means of radioimmunoassay. The normal V ganglia contained (mean +/- SD) 3496 +/- 774 pg SP/mg protein. The value for the ganglia ipsilateral to the damaged nerve was 5533 +/- 1746 pg SP/mg protein (p less than 0.01). There was no significant difference between SP levels on the control and partially deafferented sides of the brain stem in neonatally nerve-damaged adult rats. In one additional experiment, we injected TB into both vibrissa pads of seven rats on the day of birth prior to transection of the ION. After an 8-hr delay, the nerve on one side was then cut and allowed to regenerate, and both V ganglia were then processed for immunocytochemistry. On the nerve-damage side, 25.8% of the TB-labeled cells were SP-positive. The value for the intact side was 12.0% (p less than 0.000001). This result demonstrated that the lesion-induced change in the percentage of SP-positive ION cells was not the result of either late-growing axons from SP-positive ganglion cells that may have been missed by our nerve cuts or collateral sprouting into the regenerate ION by undamaged SP-positive ganglion cells.     

The facilitatory influence of anterior cingulate cortex on ON-OFF response of tactile neuron in thalamic ventrobasal nucleus

The structures of limbic system have been found to modulate the auditory, visual and pain afferent signals in the related nuclei of thalamus. One of those structures is anterior cingulate cortex (ACC) that influences nocuous response of the pain-sensitive neurons in the ventropos-tero-lateral nucleus of thalamus. Thus, we inferred that ACC would also modulate tactile information at the thalamic level. To test this assumption, single units were recorded extracellularly from thalamic ventrobasal nucleus (VB). Tactile ON-OFF response and the relationship between different patterns of the responses and the parameters of tactile stimulation were examined. Furthermore, the influence of ACC on the tactile ON-OFF response was studied. ACC stimulation was found to produce a facilitatory effect on the OFF-response of ON-OFF neurons. It lowered the threshold of the off-response of that neuron, and therefore changed the response pattern or enhanced the firing rate of the OFF-response of the neuron. The study on rec     

The facilitatory influence of anterior cingulate cortex on ON-OFF response of tactile neuron in thalamic ventrobasal nucleus

The structures of limbic system have been found to modulate the auditory, visual and pain afferent signals in the related nuclei of thalamus. One of those structures is anterior cingulate cortex (ACC) that influences nocuous response of the pain-sensitive neurons in the ventropostero-lateral nucleus of thalamus. Thus, we inferred that ACC would also modulate tactile information at the thalamic level. To test this assumption, single units were recorded extracellularly from thalamic ventrobasal nucleus (VB). Tactile ON-OFF response and the relationship between different patterns of the responses and the parameters of tactile stimulation were examined. Furthermore, the influence of ACC on the tactile ON-OFF response was studied. ACC stimulation was found to produce a facilitatory effect on the OFF-response of ON-OFF neurons. It lowered the threshold of the off-response of that neuron, and therefore changed the response pattern or enhanced the firing rate of the OFF-response of the neuron. The study on receptive fields of ON-OFF neurons showed that the excitation of the ACC could change an ON-response on the verge of a receptive field into an ON-OFF response. The above results suggest that the ACC modulation sharpens the response of a VB neuron to a moving stimulus within its receptive field, indicating that the limbic system can modulate tactile ascending sensory information.     

Predictive Feedback Can Account for Biphasic Responses in the Lateral Geniculate Nucleus

Biphasic neural response properties, where the optimal stimulus for driving a neural response changes from one stimulus pattern to the opposite stimulus pattern over short periods of time, have been described in several visual areas, including lateral geniculate nucleus (LGN), primary visual cortex (V1), and middle temporal area (MT). We describe a hierarchical model of predictive coding and simulations that capture these temporal variations in neuronal response properties. We focus on the LGN-V1 circuit and find that after training on natural images the model exhibits the brain's LGN-V1 connectivity structure, in which the structure of V1 receptive fields is linked to the spatial alignment and properties of center-surround cells in the LGN. In addition, the spatio-temporal response profile of LGN model neurons is biphasic in structure, resembling the biphasic response structure of neurons in cat LGN. Moreover, the model displays a specific pattern of influence of feedback, where LGN receptive fields that are aligned over a simple cell receptive field zone of the same polarity decrease their responses while neurons of opposite polarity increase their responses with feedback. This phase-reversed pattern of influence was recently observed in neurophysiology. These results corroborate the idea that predictive feedback is a general coding strategy in the brain.     

Changes in neuronal activities in the two ventral posterior medial thalamic nuclei in an experimental model of trigeminal pain in the rat by constriction of one infraorbital nerve

The present study analyzes the activity of 120 neurons recorded in the two ventro-postero-medial (VPM) nuclei of the thalamus in a rat model of trigeminal neuropathic pain. Twenty-eight rats were tested 2 weeks after a chronic constriction injury (CCI) of the infraorbital nerve (IoN). These animals exhibited violent pain-related reactions to extremely weak mechanical stimuli applied to the lesioned and, to a lesser extent, unlesioned IoN territories. The activities of neurons recorded in the VPMc (n = 80) and VPMi (n = 40), contralateral and ipsilateral to the injured nerve, respectively, were compared with those of 62 neurons recorded in the VPM of ten normal rats (VPMn). The neuronal background activity was higher in the VPM of CCI-IoN rats than in normal rats (about 4 vs 1 spike/s). The proportion of neurons which were driven by mechanical stimulations applied contralaterally to their recording site, was comparable in the three VPM (63-70%), but the effective stimulus modality differed significantly between the normal and the lesioned rats. In particular, the number of neurons driven by vibrissa or guard hair movements dramatically decreased in the VPM of CCI-IoN rats, mainly in the VPMc (67% of neurons with a receptive field (RF) in the VPMn vs 12% in the VPMc). Inversely, a consistent number of neurons in both the VPMc and VPMi were driven by other stimulus modalities applied to the IoN territory (moderate pressure for VPMc neurons, pinch or pinprick for both VPMc and VPMi neurons). The responses so induced were especially intense and included afterdischarges. In contrast to the VPMn neurons, the RFs of both the VPMc and VPMi neurons included two vibrissae at least, and were occasionally discontinuous and multimodal, including both vibrissae and cutaneous areas for VPMc units. The bilateral changes in VPM responsiveness and in behavior suggest the involvement of central processing of sensory information, which are set off by the CCI-IoN. The putative mechanisms and functional implication of the changes in the VPM neuronal activities are discussed.     

Role of c-Jun in cellular sensitivity to the microtubule inhibitor vinblastine

The role of c-Jun in the apoptotic response of cells to the microtubule inhibitor vinblastine was investigated using fibroblasts lacking or overexpressing c-Jun. c-Jun null cells were found to be more sensitive than wild-type cells at low (1-3 nM) concentrations of vinblastine, but showed essentially identical apoptotic responses as wild-type cells at a higher concentration of 10nM. In contrast, c-Jun overexpressing cells were highly vinblastine-resistant, with an IC50 of 12-fold greater than wild-type cells. The fate of cells exposed to lethal concentrations of vinblastine was examined by propidium iodide staining and flow cytometry. All cell types appeared to undergo mitotic arrest prior to apoptosis. Apoptosis of wild-type cells was associated with significant DNA re-replication. In contrast, DNA re-replication was much less prominent in vinblastine-treated c-Jun null cells and absent during apoptosis of c-Jun overexpressing cells. These results suggest that c-Jun plays a key role in the cellular sensitivity to vinblastine. In addition, c-Jun appears to regulate the pathway to cell death following mitotic arrest.     

Responses of neurons in the vibrissae projection area of the cat somatosensory cortex to afferent activation

Responses of 375 primary somatosensory cortical neurons located in the projection area of the vibrissae to electrical stimulation of the infraorbital nerve and also to adequate stimulation of the vibrissae were investigated in unanesthetized cats immobilized with tubocurarine. Stimulation of the nerve and vibrissae most frequently evoked synaptic responses in the neurons, in the form of a short EPSP followed by an IPSP or, less frequently, as a primary IPSP; during extracellular recordings corresponding changes were observed in spike activity. In response to stimulation of the vibrissae, initial inhibition was found more often than to stimulation of the nerve (in 45 and 16% of neurons respectively). The difference between the minimal values of latent periods of IPSP and EPSP evoked by stimulation of the infraorbital nerve was 0.8 msec in different neurons, and the difference between the mean values 1.4 msec. Directional sensitivity of the cortical neurons was demonstrated (to a change in the direction of deflection of the vibrissae). Neurons located close together could differ in the character of their directional sensitivity during stimulation of the same vibrissae. It is concluded that short-latency inhibition arising in the primary projection area of the cat somatosensory cortex is predominantly afferent and not recurrent. The probable mechanisms of directional sensitivity of the neurons studied are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSSR, Kiev. Translated from Neirofiziologia, Vol. 11, No. 6, pp. 550–559, November, 1979.     

Response properties of visual neurons in the turtle nucleus isthmi

The optic tectum holds a central position in the tectofugal pathway of non-mammalian species and is reciprocally connected with the nucleus isthmi. Here, we recorded from individual nucleus isthmi pars parvocellularis (Ipc) neurons in the turtle eye-attached whole-brain preparation in response to a range of computer-generated visual stimuli. Ipc neurons responded to a variety of moving or flashing stimuli as long as those stimuli were small. When mapped with a moving spot, the excitatory receptive field was of circular Gaussian shape with an average half-width of less than 3°. We found no evidence for directional sensitivity. For moving spots of varying sizes, the measured Ipc response-size profile was reproduced by the linear Difference-of-Gaussian model, which is consistent with the superposition of a narrow excitatory center and an inhibitory surround. Intracellular Ipc recordings revealed a strong inhibitory connection from the nucleus isthmi pars magnocellularis (Imc), which has the anatomical feature to provide a broad inhibitory projection. The recorded Ipc response properties, together with the modulatory role of the Ipc in tectal visual processing, suggest that the columns of Ipc axon terminals in turtle optic tectum bias tectal visual responses to small dark changing features in visual scenes.     

Correlations of neuronal spike discharges of VL neurons during spontaneous firing and during the activity evoked by peripheral stimulation

The temporal relations between simultaneously recorded neurons of the nucleus ventralis lateralis (VL) of cat thalamus were studied. The interaction and the functional connections between individual VL neurons are described. This was achieved with an application of cross correlation techniques. The response patterns of different individual neurons to somatic sensory and photic stimuli were also analyzed. For the purpose of classifying neurons as thalamocortical relay cells (T-C) and non relay cells (N-C) which do not project to the motor sensory cortex antidromic cortical stimulation was used. This stimulation was also used as conditioning one when proceeded peripheral stimuli. To analyze the nonspecific specific interactions upon single neurons conditioning photic stimuli were applied. The results show that T-C neurons are antidromically excited from a wide cortical areas and that the functional interaction between T-C neurons is mediated by a shared input from common sources. It is further postulated that N-C cells interposed between relay neurons subserve the functions of gating units modifying the neuronal network of lateral ventral nucleus of the thalamus.     

Scanning electron microscopic study of the effect of vinblastine on podocytes of rat kidney.

Loss of cytoplasmic microtubules was induced in rat renal podocytes by intravenous administration of the microtubule poison, vinblastine sulfate. Scanning electron microscopy was used to study the shape exhibited by podocytes 2, 8, or 12 h after initiation of vinblastine treatment. The podocytes of all vinblastine-treated rats possessed focal enlargements of cellular processes. At 8 and 12 h the focal enlargements were more abundant and often larger than those seen at 2 h. In addition, at the longer exposure times many cellular processes were smaller in diameter than comparable processes of control animals. There was no evidence that a loss of pedicel organization occurred with any of the three treatment times studied. The results suggest that in the absence of microtubules a redistribution of cytoplasm occurred within podocyte processes, resulting in the accumulation of cytoplasmic material at certain sites and a concomitant narrowing of the diameter of processes in other regions. Thus, intact microtubules appear to be essential for normal podocyte shape.