Prefrontal system in the rat visualized by means of labeled deoxyglucose--further evidence for functional heterogeneity of the neostriatum.

An epileptic focus was formed in the anteromedial part of the prefrontal cortex in rats by means of intracortical injection of penicillin, and radioactively labeled deoxyglucose was immediately injected intravenously. Auto-radiograms revealed that, in addition to the injected cortical area, a number of formations increased their consumption of deoxyglucose. The labeled formations were the posterior medial and perirhinal cortical areas, the anteromedial part of the neostriatum, the anterior and intermediodorsal part of globus pallidus, the entopeduncular nucleus, the reticular portion of the substantia nigra, the claustrum, and the basolateral nucleus of amygdala. In addition, several thalamic nuclei were activated, including the entire parataenial, paraventricular, anteromedial, and axial nuclei, as well as distinct parts of the mediodorsal and lateral nuclei and, in the instances of spread of cortical activity to the dorsal surface, of the ventral nucleus. In some animals, activation of the ventral tegmental area of Tsai was also found. All these formations have previously been shown by neuro anatomical techniques to be directly connected with the anteromedial cortex of the neostriatum. Some of them were included in the "prefrontal system." The present findings, in agreement with earlier neurobehavioral studies, indicate that, in the rat, the anteromedial part of the neostriatum, but not other neostriatal regions, is functionally related to the anteromedial part of the prefrontal cortex. The present and earlier similar studies suggest that the mammalian forebrain contains a number of "systems," each of which consists of a neocortical area and a set of associated subcortical sites.

The monocular and binocular subfields of the rat's primary visual cortex: a quantitative morphological approach.

Primary visual cortex in the rat was studied by a variety of methods: transsynaptic transport of labelled amino acids, 2-deoxyglucose, and staining for perikarya, myelin, and acetylcholinesterase. The analysis was aided by a computer-controlled television image analyzer. The results obtained with different methods agree with one another in describing the position and extent of the entire primary visual cortex as well as its monocular (medial) and binocular (lateral) subareas.

Converging projections from the mediodorsal thalamic nucleus and mesencephalic dopaminergic neurons to the neocortex in three species.

Previous studies in the rat have shown that the neocortical dopaminergic afferents, originating in the mesencephalon, terminate in those areas of the frontal lobe which receive projections from the mediodorsal thalamic nucleus i.e., the prefrontal cortex. In order to clarify whether this overlap is accidental for the rat or a consistent feature of several species we have compared the projection areas of the ventral tegmental area and the mediodorsal thalamic nucleus in three species, rat, opossum and tree shrew, using HRP injections in combination with glyoxylic acid histofluorescence method. The results have shown, first, that the area innervated by the mediodorsal nucleus of the thalamus is localized in a different part of the frontal lobe in each species: dorsolateral in the opossum, anteromedial, polar and suprarhinal in the rat and frontopolar in the tree shrew. Secondly, this area alone in each species receives projections from the ventral tegmental area. Thirdly, this area alone receives a dense innervation in the deep cortical layers by fluorescent fibres probably containing dopamine. The neighbouring neocortical areas receive afferents neither from the mediodorsal nucleus of the thalamus nor from the ventral mesencephalic tegmentum; their catecholamine innervation is mainly confined to the superficial layers and appears to be of noradrenergic nature. Although the techniques used did not allow a precise determination of the borders of the two projection areas and, therefore, the exact degree of overlap, it appears that mesencephalic dopaminergic innervation is a characteristic feature of the prefrontal cortex in the mammalian brain.

Two levels of functional heterogeneity of the neostriatum.

Autoradiography following administration of 2-deoxy-[14C]glucose has shown that penicillin-induced epileptic foci in the cerebral cortex selectively coactivate associated neostriatal regions. The present material demonstrates that this coactivation may appear in patches in the rat neostriatum. Activity from a cortical area seems to spread first to islands of the associated neostriatal region and may either spread gradually to the surrounding 'matrix' or not involve the 'matrix' for tenths of minutes. The regionally restricted functional patchiness lends additional support to the notion that the neostriatum, like the neocortex, can be divided into regions which consist of modules.

The prefrontal "cortex" in the pigeon catecholamine histofluorescence.

The prefrontal cortex of mammals is densely innervated with dopaminergic fibers. We report a comparable, dense network of catecholamine (probably dopamine)-containing fluorescent fibers in the posterodorsolateral neostriatum of the pigeon. This region is clearly separable from paleostriatum augmentatum, lobus parolfactorius, posterior archistriatum, posteromedial corticoid and septum, all of which also show strong catecholamine fluorescence. Parallel biochemical, anatomical and neurobehavioral data support the suggestion that posterodorsolateral neostriatum in the pigeon may be comparable to the mammalian prefrontal cortex. Thus the telencephalic tissue represented as the prefrontal cortex in mammals and the posterodorsolateral neostriatum in the pigeon, may turn out to be a phylogenetically ancient neural device.

On the projections from the neostriatum to the cerebral cortex: the "displaced" neurons.

The entire dorsal and lateral cortex of one cerebral hemisphere of rats was infiltrated with different fluorescent tracers and the neostriatum was examined for labelled perikarya. In spite of the extensive infiltration of the cortex, such neurons were seen only sporadically in the ipsilateral neostriatum and almost only in the vicinity of the globus pallidus and the subcortical white matter. The size and shape of these neurons, and particularly their proximity to some cell groups which surround the neostriatum and project to the cerebral cortex, suggest that these neurons belong to the neighbouring structures such as the magnocellular nuclei of the basal forebrain, the claustrum and the VIb cortical layer.

Representation of a single vibrissa in the rat neostriatum: peaks of energy metabolism reveal a distributed functional module.

In unanaesthetized rats, mechanical stimulation of a single vibrissa increased glucose utilization in one cortical column of the somatosensory area and in several spots in the dorsolateral neostriatum, predominantly on the side contralateral to the stimulation. Two or three peaks of glucose utilization unique to the stimulated animals were seen in cross sections throughout a 1.8 mm anteroposterior extent in the dorsolateral striatum. These observations suggest that one cortical column is functionally related to several neostriatal regions. The distributed modularity may be an important characteristic of the basal ganglia system.

Distribution of seven major neurotransmitter receptors in the striate cortex of the New World monkey Callithrix jacchus.

The distribution of seven different binding sites for the transmitters L-glutamate (L-glutamate binding sites and N-methyl-D-aspartate receptor), GABA (GABAA receptor), noradrenaline (alpha 1 receptor), acetylcholine (muscarinic M1 and M2 receptors) and serotonin (5-hydroxytryptamine1 receptor) are analysed in the primary visual cortex (area 17) of the common marmoset, Callithrix jacchus, using quantitative autoradiography. All binding sites show a well-defined laminar pattern, which changes sharply at the cytoarchitectonic border to area 18. The quantitative data show that the distribution of different receptors is relatively invariant across the cortical layers. Almost all receptors show a maximum in supragranular layers, low densities in layers IVA/IVB and a second maximum in layer IVC. Statistical analysis of these similarities in laminar distribution patterns of different receptors (co-distribution) reveals, as in other brain regions and species, that L-glutamate binding sites are co-distributed with N-methyl-D-aspartate, GABAA, and muscarinic M1 and M2 receptors. This may reflect the structural basis of a possible interaction between these receptors and their respective transmitters on the level of single cortical layers. Further co-distributions are found between N-methyl-D-aspartate, GABAA and M1, as well as between alpha 1 and M1 and finally between M1 and M2 receptors. Since not all receptors are co-distributed, the similarities in laminar patterns reveal specific aspects of the neurochemical organization of the cortex when receptors of different transmitter systems are analysed in the same brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ablation of the presumed equivalent of the mammalian prefrontal cortex on pigeon homing.

Pigeons (Columba livia) with bilateral ablation of the postero-dorsolateral neostriatum and the overlying corticoid were compared with unoperated control subjects in homing from both familiar and unfamiliar sites. Before the operation all the pigeons were subjected to 8 training flights from a site destined to be the familiar one. Postoperatively, the groups did not differ in orientation from the familiar site. In their releases from unfamiliar sites, however, the operated birds oriented in the training flight direction, whereas the control subjects were oriented homeward. In all the releases the homing performance, including both the homing speed and the number of returned birds, was significantly higher in the control group. Thus, the ablated tissue plays a role in homing behavior possibly through mediation of spatial orientation, of olfactory navigation, or of both.

Memory of radial maze behavior in pigeons after ablations of the presumed equivalent of mammalian prefrontal cortex.

Pigeons were trained and postoperatively tested in an 8-arm radial maze in which 1 arm was always used for start, 3 were never baited, and 4 were always baited. Of 2 groups of pigeons, 1 (n = 6) received ablations of the postero-dorso-lateral neostriatum (PDLNS) as well as the corticoid, and the other (n = 8) was sham operated. After the surgery, in the PDLNS group the number of reference memory errors (entering the never-baited arms) was significantly increased, but the number of working memory errors (entering previously visited baited arms) was not. Two of 6 pigeons with PDLNS ablations did not show any impairment, 3 were impaired in the reference memory, and 1 was impaired in working memory. This outcome resembles behavioral effects obtained in rats with prefrontal lesions. In pigeons and rats, the lesion seems to "release" the normal "win-shift" tendency and/or impair the ability to choose correctly in simultaneous multiple-choice situations.

NOS neurones lie near branchings of cortical arteriolae.

We show that numerous neurones labelled for NADPH-diaphorase, which synthetize nitric oxide, lie near branching points of the arteriolae which descend through the cerebral cortex from its pial surface. This spatial relationship suggests the possibility of neural control of cortical blood flow by the NADPH-diaphorase neurones, possibly mediated by the rapid action of nitric oxide.

NADPH-diaphorase (NOS) is induced in pyramidal neurones of hippocampal slices.

We found NADPH-diaphorase (presumably identical with nitric oxide synthase) in pyramidal neurones of the hippocampus in slices that stayed in a chamber for 30 min or longer. In some instances parallel slices showed normal membrane properties when studied electrophysiologically. In freshly made slices the pyramidal neurones were not stained. Thus, after induction of the enzyme, the hippocampal pyramidal neurones can synthesize nitric oxide which may serve as a retrograde messenger in long-term potentiation. The enzyme may also play a role in cell loss seen in slices which stayed in a chamber for 9-22 h before fixation.

Anti-inflammatory drugs suppress injury-induced NADPH-d activity in CA1 pyramidal neurones.

Inducibility of NADPH-diaphorase (NADPH-d) or nitric oxide synthase (NOS) has been demonstrated in pyramidal neurones of the hippocampus, but the mechanisms of this induction are not known. The present study aimed to assess the role of anti-inflammatory drugs in injury-induced production of NADPH-d/NOS in CA1 pyramidal neurones. We found that either a steroid, dexamethasone or a non-steroid, indomethacin, prevents induction of these enzymes. We also found that NO is not necessary for the induction. None of the three drugs used had detectable effect on the neurones which contain constitutive NADPH-d/NOS.

Improved contrast in histochemical detection of cytochrome oxidase: metallic ions protocol.

The standard current technique for demonstration of cytochrome oxidase (CyOx) provides low-contrast diaminobenzidine (DAB) polymer. In order to enhance the contrast with divalent metalic ions, we have screened a number of buffers and found that Hepes, Mops and cacodylate neither precipitate these ions nor inactivate CyOx in a concentration of 0.1 M. Staining thus obtained shows a broad range of gradations between black and white. With fresh tissue the resulting image is superior to that obtained with the brown DAB product, even if a recommended blue filter or printing on very hard paper are used. The technique is as simple as the one which is currently standard. Fixed tissue, cut either in a cryostat or vibratome, can be stained well when floating but not when mounted on slides. The stained floating tissue can be used for electron microscopy, but has no advantage over the standard method.

Behavioural effects of ablation of the pigeon-equivalent of the mammalian prefrontal cortex.

Six pigeons were trained to perform delayed alternation and brightness discrimination. Three of them underwent ablation of the posterodorsolateral neostriatum (PDLNS) which is believed to correspond to the mammalian prefrontal cortex. In the other three pigeons hyperstriatal lesions were induced by local injections of ibotenic acid. Ablation of PDLNS impaired performance of delayed alternation much more than did the hyperstriatal lesion. In brightness discrimination, a mild impairment occurred only on the first postoperative session and only in the PDLNS group. We conclude that the ablation of PDLNS in pigeons and of the prefrontal cortex in mammals induce similar impairments. Thus, the prefrontal cortex appears not to be a privilege of mammals, but may appear in different architectonic variants in all "higher" vertebrates.

Retention and relearning of spatial delayed alternation in rats after ablation of the prefrontal or total non-prefrontal isocortex.

In the present study we addressed the question whether, within the isocortex, the prefrontal area of the rat is uniquely involved in mediation of delayed alternation. In one group of rats the dorsolateral isocortex, from the dorsomedial shoulder to the dorsal lip of the rhinal sulcus was removed bilaterally in a single surgical session. In these rats delayed alternation in a T-maze was significantly less impaired than in rats with one stage bilateral removal of the medial prefrontal cortex. The prefrontal cortex seems not to depend crucially on isocortical input for its medication of delayed alternation.

Behavioural effects of ablations of the presumed 'prefrontal cortex' or the corticoid in pigeons.

This study further explored functional similarities of mammalian prefrontal cortex and its presumed equivalent in pigeons. Our results show that the performance of delayed alternation of pigeons in an Y-maze is impaired following ablations of the prefrontal equivalent together with the corticoid but not of the corticoid alone. In the same maze, discrimination between vertical and horizontal stripes was unimpaired regardless of the lesion. Our results added the following new information. (1) Corticoid is not essentially involved in mediation of delayed responding. (2) Like monkeys, pigeons take much fewer trials to learn delayed alternation in a maze than in an operant chamber. (3) Lesions of the pigeon equivalent of the prefrontal cortex impair delayed responding also in the new apparatus. (4) These lesions do not impair visual pattern discrimination. Our results do not contradict the hypothesis that the postero-dorso-lateral neostriatum in pigeons is comparable to the prefrontal cortex in mammals.

Synaptic proteins in frontal and control brain regions of rats after exposure to spatial problems.

Synaptic proteins D1, D2, D3, synaptin and 14-3-2, as well as the glial protein glutamine synthetase, were measured by crossed immunoelectrophoresis in the anteromedial (prefrontal) cortex, occipital (visual) cortex and the anterior and posterior parts of the neostriatum of rats. The 3 experimental groups consisted of rats trained to criterion in a spatial delayed alternation, those run as yoked controls and, finally, rats kept in individual cages and not subjected to any training. Statistical analysis showed that two variables: behavioral procedures and brain regions, had a significant effect. Their interaction was also significant. Further analysis revealed that only in the prefrontal cortex of the yoked control animals was there a significant decrease of the synaptic membrane proteins D1, D2 and D3. Thus, particular behavioral treatment seems capable of affecting synapses in a specific 'association' cortical area. The change is more easily related to the amount of 'work' than to formation of 'memory trace' within the critical area.

Presumed 'prefrontal cortex' lesions in pigeons: effects on visual discrimination performance.

The posterodorsolateral neostriatum (PDLNS) in pigeons may be an equivalent of the prefrontal cortex (PFC) in mammals. Here we report that lesions of this brain region in pigeons have a detrimental effect on various learned visual discriminations. Pigeons with lesions of the overlying area corticoidea dorsolateralis (CDL) served as controls. Both the postoperative re-learning to criterion of a preoperatively learned simultaneous double visual mirror pattern discrimination and the learning of a simple successive go, no-go discrimination were impaired by the PDLNS lesions. The PDLNS and CDL groups did not differ significantly in the postoperative learning of a reversal of the simultaneous discrimination. The results are discussed in relation to the presumed equivalence between the avian PDNLS and the mammalian PFC.

Magnocellular nuclei of the basal forebrain project to neocortex, brain stem, and olfactory bulb. Review of some functional correlates.

Horseradish peroxidase was injected into the neocortex of squirrel monkeys, rats, tree shrews and one opossum, in the brain stem of one squirrel monkey and rats, and in the olfactory bulb, the corpus vitreum or the vascular system of rats. Following the cortical, brain stem and bulbar injections labeled cells were found (predominatly ipsilaterally) in the magnocellular nuclei of the basal forebrain: nucleus of the diagonal band, the magnocellular preoptic nucleus and nucleus basalis. These nuclei may, therefore, be classified together hodologically as well as cytologically and histochemically. The number of labeled cells was proportional to the size of the injected region. It is uncertain whether the same cells project to all target regions. Large labeled cells were found scattered among pallidal and entopeduncular neurons in rats with cortical or brain stem injections. These neurons may be the equivalent to the nucleus basalis in other species.