Amygdaloid projections to prefrontal and motor cortex.

Direct projections from the amygdala to the entire frontal cortex were demonstrated in the cat using the retrograde transport of horseradish peroxidase. Injections throughout the prefrontal cortex labeled neurons in the ipsilateral basal magnocellular amygdaloid nucleus; injections in the premotor and motor cortices labeled neurons in the same nucleus plus a few cells in the anterior amygdaloid area.

GABAergic structures in the ventral part of the oral pontine reticular nucleus: An ultrastructural immunogold analysis.

GABA mediates inhibitory effects in neurons of the ventral part of the oral pontine reticular nucleus (vRPO). Evidence increasingly suggests that GABA plays an important role in the modulation of rapid eye movement (REM) sleep generation in the cat vRPO. Here, we investigate the anatomical substrate of this modulation using GABA immunocytochemistry. Immunoperoxidase labeling revealed a few small GABA-immunoreactive cell bodies scattered throughout the vRPO. The numerical densities of all vRPO synapses and the GABA-immunoreactive synapses were estimated, at the electron microscopical level, by using a combination of the physical disector and the post-embedding immunogold techniques. We estimated that 30% of all vRPO synaptic terminals were immunoreactive to GABA. Our findings support the hypothesis that vRPO neuron activity is significantly controlled by inhibitory GABAergic terminals that directly target somata and the different parts of the dendritic tree, including distal regions. GABAergic input could inhibit vRPO REM sleep-inducing neurons during other states of the sleep-wakefulness cycle such as wakefulness or non-REM sleep.

Topographical organization of the thalamic afferent connections to the motor cortex in the cat.

The topographical distribution of the cortical afferent connections to the different subdivisions of the motor cortex (MC) was studied in adult cats. The retrograde axonal transport of horseradish peroxidase technique was used. Small single injections of the enzyme were made in the entire MC, including the hidden regions in the depth of the sulcus cruciatus. The areal location and density of the subsequent thalamic neuronal labeling were evaluated in each case. Comparison of the results obtained in the various cases shows that the following: (1) The ventral anterior-ventral lateral complex is the principal thalamic source of afferents to the MC. (2) The ventral medial, dorsal medial, the different components of the posterior thalamic group (lateral, medial, and ventral posteroinferior and suprageniculate nuclei), and the intralaminar, lateral anterior, lateral intermediate, lateral medial, and anteromedial thalamic nuclei are also thalamic sites in which neural projections to the MC arise. (3) The thalamocortical projections to the MC are sequentially organized. The connections arising from the lateral part of the thalamus end in the region of area 4 that is situated medially in the superior lip of the sulcus cruciatus and in the posterior sigmoid gyrus. The projections originating in the most medial thalamic regions terminate in that region of area 6a beta which is located in the medial part of the inferior lip of the cruciate sulcus, and in the anterior sigmoid gyrus. Moreover, the ventral thalamic areas send connections to the most anteriorly located zones of the MC, while the most dorsal thalamic ones project to the most posteriorly located parts of the MC. (4) This shift in the thalamocortical connections is not restrained by cytoarchitectonic boundaries, either in the thalamus or in the cortex. (5) The populations of thalamocortical cells which project to neighboring MC subdivisions exhibit consistent overlapping among themselves. (6) These findings suggest, moreover, that the basal ganglia and the cerebellar projections to the MC through the thalamus are arranged in a number of parallel pathways, which may occasionally overlap.

Topographical organization of the afferent connections of the principal ventromedial thalamic nucleus in the cat.

The afferent connections to the principal division of the ventromedial thalamic nucleus (VMP) were studied in the cat by means of the HRP retrograde transport technique. The large (40 nl) and small (20 nl) injections of this enzyme were delivered into the VMP using different stereotaxic approaches. The main afferents to VMP emanated bilaterally from the prefrontal, premotor, and rostral agranular insular cortices. Another important group of afferents to the VMP were those originating in the rostral third of the reticular thalamic nucleus, the entopeduncular nucleus, the substantia nigra pars reticulata, and the deep cerebellar nuclei. From the cerebellar nuclei, the contralateral lateral nucleus and the caudal third of both (ipsi and contralateral) medial cerebellar nuclei were the origin of afferents to the VMP. Other cortical areas projecting (in a lower density) to the VMP were the motor cortex, the cortex along the anterior ectosylvian sulcus, the granular insular cortex, the posterior agranular insular area, the prelimbic area, and the cortex along the posterior rhinal sulcus (SRP). Among other subcortical prosencephalic structures projecting to the VMP are the dorsal claustrum, substantia innominata, hypothalamic formations, and the zona incerta. Projections originated from the brainstem in the lateral part of the intermediate and deep layers of the superior colliculus, the central gray matter, the locus coeruleus, and the reticular formation. The nucleus tegmenti pedunculopontinus pars compacta, parabrachial nuclei, the vestibular complex, and the spinal trigeminal nucleus were also origins of projections to the VMP. We conclude by emphasizing the important bilateral cortical modulation of the different functions attributed to the VMP: recruiting-response mediation, reticular-activating system participation, and extrapyramidal motor integration. In light of the connections just described, the VMP may be considered as a point for impulses coming from complex association cortical areas and limbic formations to converge with those emanating from cortical and subcortical motor structures.

Topographical organization of the cortical afferent connections of the prefrontal cortex in the cat.

The topographical distribution of the cortical afferent connections of the prefrontal cortex (PFC) in adult cats was studied by using the retrograde axonal transport of horseradish peroxidase technique. Small single injections of the enzyme were made in different locations of the PFC, and the areal location and density of the subsequent neuronal labeling in neocortex and allocortex were evaluated in each case. The comparison of the results obtained in the various cases revealed that four prefrontal sectors (rostral, dorsolateral, ventral, and dorsomedial) can be distinguished, each exhibiting a particular pattern of cortical afferents. All PFC sectors receive projections from the ipsilateral insular (agranular and granular subdivisions) and limbic (infralimbic, prelimbic, anterior limbic, cingular, and retrosplenial areas) cortices. These cortices provide the most abundant cortical projections to the PFC, and their various subdivisions have different preferential targets within the PFC. The premotor cortex and the following neocortical sensory association areas project differentially upon the various ipsilateral PFC sectors: the portion of the somatosensory area SIV in the upper bank of the anterior ectosylvian sulcus, the visual area in the lower bank of the same sulcus, the auditory area AII, the temporal area, the perirhinal cortex, the posterior suprasylvian area, area 20, the posterior ectosylvian area, the suprasylvian fringe, the lateral suprasylvian area (anterolateral and posterolateral subdivisions), area 5, and area 7. The olfactory peduncle, the prepiriform cortex, the cortico-amygdaloid transition area, the entorhinal cortex, the subiculum (ventral, posteroventral, and posterodorsal sectors), the caudomedial band of the hippocampal formation and the postsubiculum are the allocortical sources of afferents to the PFC. The dorsolateral PFC sector is the target of the largest insular, limbic, and neocortical sensory association projections. The dorsomedial and rostral sectors receive notably less abundant cortical afferents than the dorsolateral sector. Those to the dorsomedial sector arise from the same areas that project to the dorsolateral sector and are more abundant to the dorsal part, where the medial frontal eye field cortex is located. The rostral sector receives projections principally from all other PFC sectors, and from the limbic and insular cortices. The projections from the allocortex reach preferentially the ventral PFC sector. Intraprefrontal connections are most abundant within each PFC sector. Commissural interprefrontal connections are largest from the site homotopic to the HRP injection.(ABSTRACT TRUNCATED AT 400 WORDS)

Topographic organization of the brainstem afferents to the mediodorsal thalamic nucleus.

The afferent projections from the brainstem to the mediodorsal thalamic nucleus (MD) were studied in the cat, by means of retrograde transport of horseradish peroxidase. A topographical arrangement of these projections is described. The medial part of MD is the area of the nucleus which receives fewer afferents from the brainstem. After injections in this part, labeled neurons were observed mainly in the interpeduncular nucleus, the ventral tegmental area and the substantia nigra. After injections of HRP in the intermediate part of the MD, labeled cells were seen mainly in the interpeduncular nucleus, substantia nigra, dorsal and centralis superior raphe nuclei, dorsal tegmental nucleus, and coeruleus complex. Less conspicuous was the number of labeled cells in the central gray and the dorsolateral portion of the tegmentum of the mesencephalon and pons. After injections in the lateral part of MD, labeled neurons were observed mainly in the deep layers of the superior colliculus, central gray, the oral paramedian pontine reticular tegmentum, and the interpeduncular nucleus. Labeled cells were also observed in the substantia nigra, locus coeruleus, dorsal tegmental nucleus, cuneiform area, and the mesencephalic reticular formation. These findings show the MD as a thalamic link of three different groups of brain-stem structures projecting to different cortical areas with different functional significance.

Prosencephalic afferents to the mediodorsal thalamic nucleus.

The afferent projections from the prosencephalon to the mediodorsal thalamic nucleus (MD) were studied in the cat by use of the method of retrograde transport of horseradish peroxidase (HRP). Cortical and subcortical prosencephalic structures project bilaterally to the MD. The cortical afferents originate mainly in the ipsilateral prefrontal cortex. The premotor, prelimbic, anterior limbic, and insular agranular cortical areas are also origins of consistent projections to the MD. The motor cortex, insular granular area, and some other cortical association areas may be the source of cortical connections to the MD. The subcortical projections originate principally in the ipsilateral rostral part of the reticular thalamic nucleus and the rostral lateral hypothalamic area. Other parts of the hypothalamus, the most caudal parts of the thalamic reticular nucleus, the basal prosencephalic structures, the zona incerta, the claustrum, and the entopeduncular and subthalamic nuclei are also sources of projections to the MD. Distinct, but somewhat overlapping areas of the prosencephalon project to the three vertical subdivisions of MD (medial, intermediate, and lateral). The medial band of the MD receives a small number of prosencephalic projections; these arise mainly in the caudal and ventral parts of the prefrontal cortex. Cortical projections also arise in the infralimbic area, while subcortical projections originate in the medial part of the rostral reticular thalamic nucleus and lateral hypothalamic area. The intermediate band of the MD receives the largest number of fibers from the prosencephalon. These arise principally in the intermediate and dorsal part of the lateral and medial surface of the prefrontal cortex, the premotor cortex, and the prelimbic and agranular insular areas. Projections also originate in basal prosencephalic formations (preoptic area, Broca's diagonal band, substantia innominata, and olfactory tubercle), rostral reticular thalamic nucleus, and lateral hypothalamic area. A large number of prosencephalic structures also project to the lateral band of the MD. These are mainly the most dorsal and caudal parts of the lateral and medial surface of the prefrontal cortex, the premotor and motor cortices, and the prelimbic, anterior limbic, and insular areas. Projections arise also in the lateral rostral and caudal parts of the reticular thalamic nucleus, the zona incerta, the lateral and dorsal hypothalamic area, the claustrum, and the entopeduncular nucleus. These and previous results demonstrate a gradation in the afferent connections to the three subdivisions of the MD.(ABSTRACT TRUNCATED AT 400 WORDS)

Insular cortex and neighboring fields in the cat: a redefinition based on cortical microarchitecture and connections with the thalamus.

The insular areas of the cerebral cortex in carnivores remain vaguely defined and fragmentarily characterized. We have examined the cortical microarchitecture and thalamic connections of the insular region in cats, as a part of a broader study aimed to clarify their subdivisions, functional affiliations, and eventual similarities with other mammals. We report that cortical areas, which resemble the insular fields of other mammals, are located in the cat's orbital gyrus and anterior rhinal sulcus. Our data suggest four such areas: (a) a "ventral agranular insular area" in the lower bank of the anterior rhinal sulcus, architectonically transitional between iso- and allocortex and sparsely connected to the thalamus, mainly with midline nuclei; (b) a "dorsal agranular insular area" in the upper bank of the anterior rhinal sulcus, linked to the mediodorsal, ventromedial, parafascicular and midline nuclei; (c) a "dysgranular insular area" in the anteroventral half of the orbital gyrus, characterized by its connections with gustatory and viscerosensory portions of the ventroposterior complex and with the ventrolateral nucleus; and (d) a "granular insular area", dorsocaudal in the orbital gyrus, which is chiefly bound to spinothalamic-recipient thalamic nuclei such as the posterior medial and the ventroposterior inferior. Three further fields are situated caudally to the insular areas. The anterior sylvian gyrus and dorsal lip of the pseudosylvian sulcus, which we designate "anterior sylvian area", is connected to the ventromedial, suprageniculate, and lateralis medialis nuclei. The fundus and ventral bank of the pseudosylvian sulcus, or "parainsular area", is associated with caudal portions of the medial geniculate complex. The rostral part of the ventral bank of the anterior ectosylvian sulcus, referred to as "ventral anterior ectosylvian area", is heavily interconnected with the lateral posterior-pulvinar complex and the ventromedial nucleus. Present results reveal that these areas interact with a wide array of sensory, motor, and limbic thalamic nuclei. In addition, these data provide a consistent basis for comparisons with cortical fields in other mammals.

Ultrastructural synaptic organization of axon terminals in the ventral part of the cat oral pontine reticular nucleus.

In an attempt to contribute to the current knowledge of the brainstem reticular formation synaptic organization, the ultrastructure and distribution of synaptic terminal profiles on neurons in the ventral part of the oral pontine reticular nucleus (vRPO), the rapid eye movement (REM) sleep-induction site, were studied quantitatively. Terminals with asymmetric contacts and rounded vesicles were classified according to vesicle density as type I or II (high or low density, respectively). The area, apposed perimeter length, and mitochondrial area of type I terminals, on average, were significantly smaller than those of type II terminals. Type III and IV terminals had symmetric contacts and oval and/or flattened vesicles; type III terminals formed synapses between them and on initial axons. Type V and VI terminals showed characteristics intermediate to those of asymmetric and symmetric synapses. Interestingly, some terminal features were related to both terminal area and postsynaptic dendritic diameter. The percentages of different synapses sampled on somata were as follows: asymmetric synapses (usually formed by type II terminals; mean +/- S.D.), 26.4% +/- 3%; symmetric synapses, 46.7% +/- 5.2%; and intermediate synapses, 26.9% +/- 6.1%. The percentages of different synapses sampled on dendrites were asymmetric synapses, 62.1% +/- 9%; symmetric synapses, 25.6% +/- 8.1%; and intermediate synapses, 12.3% +/- 1.7%. Comparison between large- and small-diameter dendrites revealed that the percentages of symmetric synapses and type II terminals decreased, whereas the percentages of type I terminals increased as postsynaptic dendritic diameters became smaller. Synaptic density was approximately four times lower on somata than on dendrites. The vRPO synaptic organization reflects some patterns that are similar to those found in other regions of the central nervous system as well as specific synaptic patterns that are probably related to its functions: the generation and maintenance of REM sleep and the control of eye movement or limb muscle tone.

Serotonergic connections to the ventral oral pontine reticular nucleus: implication in paradoxical sleep modulation.

Cholinergic microstimulation of the ventral part of the oral pontine reticular nucleus (vRPO) in cats generates and maintains paradoxical sleep. The implication of rostral raphe nuclei in modulating the sleep-wakefulness cycle has been based on their serotonergic projections to the pontine structures responsible for the induction of paradoxical sleep. However, serotonergic neurons have also been described in brainstem structures other than the raphe nuclei. The aim of the present work is to trace the origin of the serotonergic afferents to the vRPO and to the locus coeruleus alpha and perilocus coeruleu alpha nuclei, closely related with different paradoxical sleep events. Anterograde and retrograde horseradish peroxidase conjugated with wheat germ agglutinin tracer injections in these nuclei in cats were combined with serotonin antiserum immunohistochemistry. Our results demonstrate that reciprocal connections linking the rostral raphe nuclei to those oral pontine nuclei are scarce. The percentage of double-labeled neurons after injections in the vRPO averaged 18% in rostral raphe nuclei, while a level of 82% was estimated in mesopontine tegmentum structures other than the raphe nuclei. These results showed that the main source of serotonin to the vRPO, implicated in generation and maintenance of paradoxical sleep, arises from these mesopontine tegmentum structures. This indicates that the serotonin modulation of paradoxical sleep could be the result of activation in non-raphe mesopontine tegmentum structures. The existence of a complicated network in the vRPO, which maintains a balance between different neurotransmitters responsible for the generation and alternance of paradoxical sleep episodes, is discussed.

Topographical organization of the projections from the reticular thalamic nucleus to the intralaminar and medial thalamic nuclei in the cat.

The topography of the projections from the reticular nucleus of the thalamus (RT) to the intralaminar and medial thalamic nuclei were studied in the cat by the method of retrograde transport of horseradish peroxidase (HRP). Single small injections of the enzyme were made in the different intralaminar nuclei--mediodorsal, ventromedial, midline, and habenular--and in anterior group nuclei. The location and density of the neuronal labeling in the different parts of the RT were studied in each case. Our results show that 1) after injections located in all the nuclei here studied, a consistent number of labeled neurons were found in the RT, except for the injections in the lateral habenula and the anterior thalamic nuclear complex, both of which did not label neurons in the RT. 2) Among the other thalamic nuclei here studied, the most medially situated receive less numerous RT projections than those most laterally located. 3) Injections in all the nuclei studied gave rise to a cellular labeling in the anterior sectors of the RT, except for the anterior nuclear group and the lateral habenula. The projections from the rostral pole of the RT were topographically mediolaterally organized. 4) The anterodorsal part of the pregeniculate sector of the RT projects upon the large-celled part of the lateral central nucleus and to a lesser extent upon the paracentral, centromedian, and ventromedial nuclei, the anterior part of the lateral central nucleus, and the lateral band of the mediodorsal nucleus. The posterodorsal part of the RT pregeniculate sector only projects to the large-celled part of the lateral central nucleus. The dorsal portion of the posteroventral part of the RT pregeniculate sector also projects upon the large-celled part of the lateral central nucleus; its ventral portion projects to the ventromedial nucleus, the posterior part of the paracentral nucleus, the lateral band of the mediodorsal nucleus, and the centromedian nucleus. 5) The infrageniculate sector of the RT projects to the posterior part of the ventromedial nucleus. A weaker projection to the large-celled part of the lateral central nucleus, the centromedian nucleus, and the lateral band of the mediodorsal nucleus was also observed. 6) The ventral lateral geniculate nucleus projects upon the large-celled part of the lateral central nucleus, the lateral band of the mediodorsal nucleus, and the ventromedial nucleus. All these findings suggest an important modulatory action of the RT on the activity of the thalamic nuclei considered here.

Innervation from the claustrum of the frontal association and motor areas: axonal transport studies in the cat.

The anatomical organization of the projections from the claustrum to the motor and prefrontal cortical areas of the cat's brain was investigated. Both retrograde (single horseradish peroxidase or double fluorochrome deposits in the cortex) and anterograde (peroxidase-labeled wheat germ agglutinin deposits in the claustrum) tracing techniques were used. Within the claustrum, the neurons projecting to each sector of the frontal cortex were found to be distributed according to specific patterns of segregation and overlap. Spatial segregation was particularly marked between the cell populations projecting to the various sectors of area 4. The cells projecting to the subareas of area 6 and prefrontal cortex displayed a less marked but definite segregation. The neuronal populations projecting to some sectors of areas 4, 5, and the primary somatosensory cortex known to contain homotopical representations of the body map were found intermingled in the same small claustral portions. The few double-labeled neurons found after closely adjacent fluorochrome injections indicates that, in spite of their profuse intracortical branching, claustral axons spread little within the boundaries of a single architectonic area. Anterograde transport experiments showed that claustral fibers end primarily in layers IIIb/IV, VI, and I, whereas layer V is spared. This pattern is homogeneous throughout the frontal cortex. The possible role of the claustrum as a subcortical site for organized interactions amongst wide arrays of functionally related zones of the cerebral cortex is thereby suggested.

Age-related changes of serotonin and its metabolites content in the visual system of the rat.

Measurements have been taken of the serotonin and its metabolites (tryptophan, 5-hydroxytryptophan, 5-hydroxy-3-indolacetic acid and 5-hydroxytryptophol) in each structure of the geniculate and extrageniculate visual system of rats aged between 3 and 30 months. The concentration of tryptophan was the highest of all compounds studied. Its increase during ageing is statistically significant in the lateral geniculate and posterior thalamus. 5-HTP concentration was very low and in some cases not detectable. 5-HT concentrations and its principal metabolite, 5-HIAA, showed a different profile in each brain structure. The lateral geniculate and visual cortex showed statistically significant changes, but with opposite results. In the lateral geniculate the 5-HT and 5-HIAA concentrations were increased during the ageing period. However, in the visual cortex the 5-HT and 5-HIAA concentrations decreased in the same period. These age-related changes were not seen in the superior colliculus and posterior thalamus as in the 5-HT levels as in the 5-HIAA. 5-hydroxytryptophol was always found in low concentration. These results suggest age-related changes in the geniculate visual system.

A morphologic analysis of neurons and neuropil in the dorsal lateral geniculate nucleus of aged rats.

Light and electron microscopy were used to investigate the morphology of neuropil and neuronal cell bodies of the dorsal lateral geniculate nucleus (LGNd) of aged rats. Light microscopic examination reveals that, despite the optic tract showing signs of degeneration, the LGNd is scarcely affected. Thus, a slight but significant reduction in the diameters of both soma and nuclei is observed in aged neurons of the LGNd. Ultrastructural analysis demonstrates a few degenerating profiles of the neuropil. Neurons resembling relay cells exhibit typical features of aged neurons. Cells showing a very infolded nucleus, most of the ER cisternae connected with the nuclear envelope, abundant free polyribosomes and subsurface cisterns associated with mitochondria are similar to interneurons of adult rats. Therefore, aging and partial loss of visual input appear to induce small changes in the morphology of most of LGNd neurons.

An electron microscopic study of astroglia and oligodendroglia in the lateral geniculate nucleus of aged rats.

The ultrastructural features of glial cells in the lateral geniculate nucleus of aged rats have been studied. Abundant filaments as well as heterogeneous dense bodies are observed in the majority of astrocytes. They frequently surround both axons and nerve terminals showing signs of degeneration. In addition, some degenerating myelinated axons are seen in phase suggestive of engulfment by astrocyte processes. Oligodendrocytes display broad processes containing an organelle-rich cytoplasm and a continuity between their plasma membrane and the outer myelin lamellae which partially ensheath the adjacent axons. Multivesicular bodies and pleomorphic dense inclusions, composed of amorphous material as well as laminated structures, are also present in oligodendrocytes. The significance of these morphological features is discussed in relation to process of normal ageing.

Connections to the lateral posterior-pulvinar thalamic complex from the reticular and ventral lateral geniculate thalamic nuclei: a topographical study in the cat.

The projections from the reticular thalamic nucleus and the ventral lateral geniculate nucleus to the lateral posterior-pulvinar thalamic complex were studied in the adult cat using the retrograde transport of horseradish peroxidase. Small, stereotaxically guided injections of the enzyme were placed in the various nuclei of this complex, including the pulvinar, lateralis intermedius oralis, lateralis intermedius caudalis, lateralis posterior lateralis, lateralis posterior medialis and lateralis medialis nuclei. The distribution of labeled neurons indicates that these nuclei receive topographically organized projections from the reticular and ventral lateral geniculate nuclei. The pulvinar nucleus receives only very scarce projections from the reticular thalamic nucleus originating in its posterodorsal and posteroventral sectors. The reticular projection to the nucleus lateralis intermedius oralis is even sparser. The nuclei lateralis intermedius caudalis, lateralis posterior lateralis and lateralis posterior medialis receive substantial projections from the suprageniculate sector of the reticular thalamic nucleus. The nucleus lateralis medialis receives an abundant projection from the three sectors (suprageniculate, pregeniculate and infrageniculate) of the reticular thalamic nucleus. Except for the lateralis intermedius caudalis, all nuclei of the lateral posterior-pulvinar complex receive consistent projections from the ventral lateral geniculate nucleus, the nucleus lateralis medialis receiving the densest one. Our findings suggest that visual, auditory, somatosensory, motor and limbic impulses from thalamic nuclei and from primary sensory and association cortical areas modulate the activity of the nucleus lateralis medialis via the reticular thalamic nucleus. The remaining nuclei of the lateral posterior-pulvinar complex are mainly modulated by sectors of the reticular thalamic nucleus that receive afferent connections from visual structures. The intrathalamic projections arising from the ventral lateral geniculate nucleus may be the way through which visuomotor inputs reach the different components of the lateral posterior-pulvinar thalamic complex.

Sleep patterns after carbachol delivery in the ventral oral pontine tegmentum of the cat.

This study examines dose-related effects on sleep produced by low-volume and low-dose carbachol microinjections in the ventral part of the cat nucleus reticularis pontis oralis. Carbachol microinjections (0.04, 0.08, 0.8 or 4 microg; volume 20 nl) in this location triggered paradoxical sleep with a very short dose-unrelated latency. The four carbachol doses effectively generated all the polygraphic and behavioral signs of paradoxical sleep when microinjected at any level within the ventral part of the nucleus reticularis pontis oralis (AP 0.5 to -3.5, L 0.5-3.5, V 3.5-5.0, on the Reinoso-Suárez atlas [Topographischer Hirnatlas der Katze (1961); Merck, Darmstadt]). The dose-related increase of total paradoxical sleep time was due to the increase in both the duration and number of paradoxical sleep episodes. This paradoxical sleep increase was associated with a dose-related decrease in the amount of time spent in both slow wave sleep and drowsiness, but not with any decrease in total wakefulness. The lengthening of the latency to slow wave sleep onset was dose related. These results show that the ventral oral pontine tegmentum is a very sensitive site for the induction and maintenance of paradoxical sleep.

Topographical organization of the brainstem afferents to the lateral posterior-pulvinar thalamic complex in the cat.

Following stereotaxic injections of horseradish peroxidase in the dorsal thalamus of the cat which were restricted to the lateralis posterior-pulvinar complex, labelled neurons were found in the superficial layers of the superior colliculus and in the brainstem. The retrogradely-filled cells of the brainstem were situated principally in the nucleus tegmenti pedunculopontinus, the locus coeruleus complex, the parabrachial nuclei and the dorsal tegmental nucleus of Gudden; in each case, labelled cells were more numerous on the ipsilateral side. In addition, some scattered neurons were observed in the central grey matter, the mesencephalic reticular formation, the central superior and dorsal raphe nuclei, the cuneiform nucleus reticularis gigantocellularis, the nucleus praepositus hypoglossi and the oculomotor nuclei. The differential organization of these projections were observed. It is concluded that the rostrointermediate subdivision of the lateralis posterior-pulvinar complex receives most of its connections from the nucleus tegmenti pedunculopontinus, from the deep layers of the superior colliculus and from the other brainstem nuclei, while the caudal subdivision (extrageniculate visual subdivision) receives its main projection from the superficial layers of the superior colliculus. The findings may have functional implications for the role of the complex in oculomotor control.

Amygdaloid projections to the motor, premotor and prefrontal areas of the cat's cerebral cortex: a topographical study using retrograde transport of horseradish peroxidase.

The topographic organization of the projections from the amygdaloid complex to the frontal (motor, premotor and prefrontal) cortex has been investigated in the cat by means of the horseradish peroxidase retrograde transport technique. While most of these projections arise from the magnocellular component of the basal nucleus, some arise also from other nuclei, such as the parvocellular basal nucleus, the corticoamygdaloid transition area and the cortical nucleus. The projections from the latter nuclei are directed to the central portions of the prefrontal cortex, both laterally and medially. No clear-cut topographic segregation appeared to exist in the distribution within the magnocellular basal nucleus of the cells of origin of projections to the motor, premotor and prefrontal cortex. The gross topographic arrangement of the amygdalocortical projections seems to reciprocate, to some extent at least, the organization of corticoamygdaloid projections from high-order sensory and polymodal association areas.

Segregation and heterogeneity of thalamic cell populations projecting to superficial layers of posterior parietal cortex: a retrograde tracer study in cat and monkey.

The thalamic neurons projecting to the superficial layers of areas 5 and 7 in the cat, and area 5 in the monkey, were investigated by using superficial deposits of either horseradish peroxidase or Fast Blue in one hemisphere. In the contralateral hemisphere injections of the same tracer involving the full cortical depth were made in homotopical locations, and the distribution and soma size of retrogradely labeled thalamocortical neurons in each side of the thalamus were compared. It was found that, in the cat, labeled neurons in the lateral posterior pulvinar complex, and in paralaminar regions of the ventrolateral complex, were fewer in number and smaller in size in cases of superficial deposits than in cases of deep injection. In more lateral portions of the ventrolateral complex, however, there were no size differences. In the monkey, similar differences in number and size appeared in the caudal division of the ventrolateral complex and in the lateral posterior and pulvinar nuclei, whereas no such differences were found for neurons labeled in the oral and medial divisions of the ventrolateral complex, and in the ventral posteroinferior nucleus. In all cases the intralaminar and midline nuclei exhibited retrogradely labeled neurons only when deep layers were injected. These and previous findings point to the existence of a widely distributed layer I-projecting system of neurons which, in most nuclei, are interspersed among neurons projecting mainly to middle or deep layers. In some nuclei, however, as is the case with the ventromedial nucleus proper, layer I-projecting system neurons would make up the whole nucleus. The cell groups located in a paralaminar position, which would be but a part of this system, could provide through their projections to layer I in the posterior parietal and frontal cortical regions a final path for recruiting responses and spontaneous spindling activities.