New view of the organization of the pulvinar nucleus in Tupaia as revealed by tectopulvinar and pulvinar-cortical projections

The projections of the superficial layers of the superior colliculus to the pulvinar nucleus in Tupaia were reexamined by injecting WGA-HRP into the tectum. The main result was finding two different patterns of terminations in the pulvinar nucleus: a zone remote from the lateral geniculate nucleus, which occupies the dorsomedial and caudal poles of the pulvinar nucleus, was almost entirely filled with terminals in every case irrespective of the location of the injection site; and a second division of the pulvinar nucleus, adjacent to the lateral geniculate nucleus, contained irregular patches--much more densely populated--and the distribution of patches varied from case to case. We call the first projection "diffuse" and the patchy projection "specific." Next we injected several divisions of the extrastriate visual cortex to find the cortical target of each pathway. The diffuse path terminates in the ventral temporal area (Tv). The specific path terminates in the dorsal temporal area (Td) and area 18. We speculated about the significance of the two pathways: the specific path may be responsible for the preservation of vision after removal of the striate cortex; the diffuse path may have an important place in the evolution of the visual areas of the temporal and occipital lobe. We argued that the target of the diffuse path is in a position to relate limbic and visual impulses and relay the product of such integration to the other visual areas, striate as well as extrastriate cortex.     

Only activated but not non-activated presynaptic α2-autoreceptors interfere with neighbouring presynaptic receptor mechanisms

Summary Experiments were carried out in rabbit cerebrocortical slices in order to find out whether the attenuation by presynaptic ₂-autoreceptors of effects mediated by presynaptic opioid - and adenosine A₁-receptors requires activation of the ₂-receptors. The slices were preincubated with ³H-noradrenaline and then superfused with medium containing desipramine 1 mol/l. They were stimulated electrically either with single pulses or with trains of 32 pulses at 1 Hz.The overflow of tritium elicited by a single pulse amounted to 0.21% of the tritium content of the tissue. It was Ca²⁺-dependent and tetrodotoxin-sensitive and not changed by rauwolscine 1 mol/l or yohimbine 0.3 mol/l. Ethylketocyclazocine (EK; 0.1–10 nmol/l) and R-(–)-N⁶-phenylisopropyladenosine (PIA; 1–1,000 nmol/1) potently inhibited the overflow evoked by a single pulse, and their effects were not changed by yohimbine. — The overflow of tritium elicited by trains of 32 pulses at 1 Hz amounted to 0.92% of the tritium content of the tissue and was increased approximately fourfold by yohimbine 0.3 mol/l. EK and PIA were less potent inhibitors than in the one pulse experiments. Yohimbine greatly enhanced the effects of EK and PIA. The enhancement was even more pronounced when the Ca²⁺ concentration in the medium was reduced in order to obtain a control tritium overflow similar to that evoked by 32 pulses in the absence of yohimbine.The results demonstrate that there is no ₂-adrenergic autoinhibition when noradrenaline release is elicited by a single pulse. Under these conditions, the non-activated presynaptic ₂-adrenoceptor does not interfere with presynaptic opioid - and adenosine A₁-receptor mechanisms. It is only when the autoreceptor is activated by released noradrenaline that it attenuates neighbouring presynaptic receptor mechanisms, and this attenuation is removed by ₂-adrenoceptor antagonists.Send offprint requests to N. Limberger at the above address     

Dose-response curves of homovanillic acid in pre-frontal cortex and caudate following antipsychotic drugs: relation to clinical potencies

Dose-response curves for the elevation of homovanillic acid (HVA) levels, determined by high performance liquid chromatography using electrochemical detection, in the pre-frontal cortex and caudate of rats after acute treatment with 12 antipsychotic drugs are presented. The order of potency in both brain regions was: haloperidol fluphenazine > loxapine > trifluoperazine > thiothixene > molindone > clopenthixol > chlorpromazine > metoclopramide > thioridazine > clozapine > sulpiride. This ranking is roughly correlated with that based on clinical potencies. The relative elevation of the content of HVA was weaker in the pre-frontal cortex than in the caudate for all drugs tested, except clozapine at a high dose.     

Local axonal trajectories in mouse barrel cortex

Summary Quantitative studies were made of the distribution of labeled intracortical axons after focal injections of horseradish peroxidase (HRP) into mouse barrel cortex, in vitro. The pattern of labeled fibers was compared to that of labeled cell bodies with respect to the barrel map in layer IV. We analyzed 4 cortices with injections in supragranular layers and centered above a single barrel row. Computer microscope/image analysis routines were used to collect the data and to perform various statistical analyses on them. The distributions of both labeled cells and fibers in layer IV and in the infragranular layers show strong connectional tendencies between barrels representing a whisker row. This result is consistent with single unit recordings from barrel cortex. Fiber labeling is more widespread than cell body labeling in layer IV. In addition, the fibers show a directional bias into the adjacent anterior barrel row (e.g., C D, D E). In earlier 2-deoxyglucose (2-DG) studies of behaving animals, the anterior barrel rows were more heavily labeled; inter-row projections are therefore predominantly from less active to more active barrel columns. These data show that labeled fiber distribution differs from the distribution pattern of labeled cell bodies. The findings indicate that integration of information between whisker rows within barrel cortex involves asymmetrical connections within layer IV and infragranular layers.     

Human slow-wave sleep and the cerebral cortex

SUMMARY  Recent hypotheses about the roles of human slow-wave sleep (hSWS—delta EEG activity) are appraised. The possible linkage between hSWS and the functions of the prefrontal cortex (PFC) are explored with respect to normal subjects and to disorders involving PFC deficits.     

Senile plaques,amyloid β-protein,and acetylcholinesterase fibres: laminar distributions in Alzheimer's disease striate cortex

Summary The laminar distributions of senile plaques and amyloid -protein (AP) within the striate cortex of patients with Alzheimer's disease (AD) were studied with enhanced Bielschowsky (roughly equivalent to the Campbell technique) and immunohistochemical methods. The laminar distribution of acetylcholinesterase (AChE) fibres within the striate cortex of both AD patients and control patients was studied with an enzyme histochemical method. Quantification of Bielschowsky-stained plaque numbers along intersect lines drawn parallel to laminar boundaries revealed a significant aggregation of plaques at the interface of layers IVc and V. Lines drawn through layer VI intersected significantly fewer plaques than lines through other laminae. Immunoperoxidase staining for AP revealed a similar distribution fo senile plaques, and additional, prominent, diffuse deposits of AP within layers I and IVc. AChE fibres were markedly depleted in the striate cortex of AD cases. In control cases, AChE fibres were, like AP immunoreactivity, concentrated within layers I and IVc. The results indicate that enhanced silver methods may not reveal the complete distribution of AP. The codistribution of AP-immunoreactive diffuse amyloid deposits and AChE fibres to the same cortical laminae is consistent with the possibility that these deposits may be formed from degenerating cholinergic elements. The formation of a line of senile plaques at the interface of two cortical laminae within the striate cortex, in an anatomically analogous situation to a similar line of plaques within the dentate gyrus, suggests that formation of well-defined plaques may be accelerated by the interaction of specific neuronal systems.Supported by a Fellowship from the British Columbia Health Care Research Foundation to TGB. This work is part of the PhD. dissertation of Dr. Beach (University of British Columbia, 1991)     

Cerebellar connections with the motor cortex and the arcuate premotor area: an analysis employing retrograde transneuronal transport of WGA-HRP

We have employed transneuronal transport to examine the anatomical relationships between the deep cerebellar nuclei and 2 cortical motor areas: the primary motor cortex and the arcuate premotor area (APA). In the same animals, we have also examined the patterns of labeling in the thalamus and the red nucleus to provide evidence for the potential routes of transneuronal transport to the cerebellum. When the appropriate technical procedures were employed, cortical injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) resulted in transneuronal labeling within portions of the contralateral deep cerebellar nuclei. Injections into the primary motor cortex labeled neurons in the dentate and in the 2 subdivisions of the interpositus. Injections into the APA labeled neurons in the dentate and in only the posterior subdivision of the interpositus. In most instances, dentate neurons were more intensely labeled following the cortical injections than interpositus neurons. The transneuronal labeling observed in the dentate nucleus was topographically organized. The dentate region that was labeled following injections into the "arm area" of the APA was caudal and ventral to the dentate region that was labeled following injections into the "arm area" of the primary motor cortex. This observation provides evidence for two "arm areas" in the dentate: one anatomically related to the APA, and the other related to the primary motor cortex. More than one route of transport may be responsible for the labeling of cerebellar neurons. We propose that the labeling observed in the dentate nucleus reflects the pattern of connections in the cerebellothalamocortical pathways that link the dentate with the cerebral cortex. Thus, our observations support the concept proposed by Schell and Strick (J. Neurosci. 4:539-560, '84)--that the cortical targets of the dentate nucleus include both the primary motor cortex and the APA.     

[3H]5-HT binding in post-mortem human cerebral cortex: methodological considerations

Summary The effects of different membrane preparations and assay conditions on [³H]5-HT binding to post-mortem human cortical tissue was studied. Optimal binding necessitated thorough removal of endogenous 5-HT and this was achieved either by hypotonic lysis or by preincubation of the membranes at 37C. Calcium chloride (4 mM) increased specific [³H]5-HT binding. The further addition of ascorbic acid (5.7 mM) or ascorbic acid and clorgyline (10 M) reduced specific [³H]5-HT binding.     

Inputs from the olfactory bulb and olfactory cortex to the entorhinal cortex in the cat

Summary The spatial organization and laminar distribution of projections from the olfactory bulb and the anterior (PPCa) and posterior (PPCp) divisions of the prepiriform cortex to the entorhinal cortex were studied with anterograde (³H-leucine) and retrograde (WGA-HRP) tracing techniques. After ³H-leucine injections into the olfactory bulb transported labeling was seen over the lateral entorhinal area, except its most medial part, and over the rostral part of the medial entorhinal area. The labeling covers exclusively layer Ia. The lateral and medial entorhinal areas are also reached by fibers from the prepiriform cortex. The projection to the medial entorhinal area has not been described previously. Following injections of ³H-leucine into the PPCa transported labeling is present over the entire expanse of the entorhinal cortex and is located over layer Ib with the greatest density in its superficial part. Injections of ³H-leucine into the PPCp give rise to transported labeling over much of the entorhinal cortex. No labeling was found over the most medial parts of the medial subdivision (VMEA) of the lateral entorhinal area and the medial entorhinal area. Labeling occupies layer Ib, especially its middle part, and layers II and III. Both PPCa and PPCp appear to project most heavily to the dorsal (DLEA) and ventral (VLEA) subdivisions of the lateral entorhinal area. From the retrograde experiments it can be inferred that cells of layers II and III of the PPCa project predominantly to the DLEA, whereas those of the PPCp project predominantly to the VLEA. The MEA receives its heaviest projection from layer II of both PPCa and PPCp. In control experiments with ³H-leucine injections into the endopiriform nucleus it was found that this nucleus projects to the entire expanse of the entorhinal cortex. The fibers distribute to all layers with the exception of layer Ia.Abbreviations AI agranular insular cortex - AL lateral nucleus of the amygdala - BL basolateral nucleus of the amygdala - BM basomedial nucleus of the amygdala - C claustrum - CoA cortical nucleus of the amygdala - DLEA dorsal division of the lateral entorhinal cortex - END endopiriform nucleus - H hippocampus - I granular insular cortex - lot lateral olfactory tractus - MCL mitral cell layer of the olfactory bulb - MEA medial entorhinal area - OB olfactory bulb - PPCa anterior part of the prepiriform nucleus - PPCp posterior part of the prepiriform nucleus - VLEA ventral division of the lateral entorhinal cortex - VMEA ventromedial division of the lateral entorhinal cortex - 35 area 35 of the perirhinal cortex - 36 area 36 of the perirhinal cortex     

Changes in the retino-fugal pathways following cortical and tectal lesions in neonatal and adult rats

Summary Several months after unilateral removal of the striate cortex or superior colliculus, or both, in infant and adult rats the retinal projections were studied autoradiographically. The retinal projection areas in adult-operated animals were not different from those of unoperated controls, but aberrant pathways were found in the infant group. Following removal of striate cortex there was a small aberrant pathway to the lateral posterior nucleus of the thalamus (LP) and possibly to the pretectum. After removal of the superior colliculus there was a conspicuous aberrant projection to LP, which was even more prominent after combined removal of striate cortex and superior colliculus. The results support the proposal that when the normal field of termination is damaged, either directly by a tectal lesion or indirectly by a cortical lesion, axons grow and innervate LP, which has been partly deafferented by the lesion and which consequently possesses vacant synaptic space. Although the different consequences of early and late lesions may indicate that only infantile damaged terminals can redistribute themselves an alternative is that in infants many axons have not yet reached their normal terminal sites at the time of operation and that only those axons have the ability to continue growing and to form an aberrant pathways. The role of the aberrant pathway in vision is unknown.