Organization of the dorsocaudal neostriatal complex: A retrograde and anterograde tracing study in the domestic chick with special emphasis on pathways relevant to imprinting

In the forebrain of domestic chicks, a network of distinct regions is crucially involved in auditory and visual filial imprinting. Among these areas, a distinct part of the dorsocaudal neostriatal complex (dNC complex), termed neostriatum dorsocaudale (Ndc), was recently discovered by its enhanced metabolic activity during the presentation of auditory and visual imprinting stimuli. Since there is evidence that the dNC complex consists of several distinct functional subareas, we investigated the neural connections of different parts of the dNC complex by retro- and anterograde pathway tracing. Special emphasis was put on the connections of the dNC complex with other imprinting relevant regions in the rostral telencephalon, such as the mediorostral neostriatum/hyperstriatum ventrale (MNH) and the intermediate and medial part of the hyperstriatum ventrale (IMHV). By anterograde and multiple retrograde pathway tracing, we found that the dNC complex may at least be subdivided into three major constituents. The most medial part of the dNC complex, termed neostriatum dorsale (Nd), is characterized by strong reciprocal connections with the neostriatal part of the MNH and by its auditory related inputs, including those from the output layers L1 and L3 of field L, and the shell region of the thalamic n. ovoidalis. The Ndc, which occupies the central aspects of the dNC complex, is mainly characterized by reciprocal connections with the ectostriatal belt (Ep) and the adjacent neostriatum (N). Furthermore, Nd and Ndc receive strong thalamic input from the n. dorsolateralis posterior (DLP), both project to the IMHV, and both are reciprocally connected with the archistriatum intermedium (AI). The most lateral aspect of the dNC complex, termed Ndl, is characterized by afferents from the neostriatum frontale, pars trigeminalis (NFT), and by the lack of a thalamic input. Results indicate that the dNC complex comprises distinct subregions, which are characterized by their specific afferents from parasensory areas of different sensory modalities. These different subregions may be integral components of a general pattern of sensory processing in the avian telencephalon. The strong interconnections between Nd, Ndc, and MNH as well as IMHV may constitute essential parts of auditory and visual imprinting circuits. J. Comp. Neurol. 395:380–404, 1998. © 1998 Wiley-Liss, Inc.     

c-fos is induced in the hippocampus during consolidation of sexual imprinting in the zebra finch (Taeniopygia guttata)

c-fos was used to mark regions of enhanced neuronal activity during sexual imprinting, an early learning process by which information about the prospective sexual partner is acquired and consolidated. In the present study, we demonstrate that the hippocampus, already known for its specialized spatial memory capacities in navigating pigeons and in food-storing birds, depicts a selective differential c-fos induction in a situation shown to lead to sexual imprinting, that is, exposing previously isolated male birds to a female for 1 h. c-fos induction is lateralized, the left hippocampus showing more c-fos activity than the right. Our results would indicate a role for the hippocampus in the consolidation process of imprinting, probably in the transfer of information to the other telencephalic areas that show alterations in synaptic connectivity as a result of consolidation of sexual imprinting.     

Postnatal changes in the distribution and density of neuronal nuclei and doublecortin antigens in domestic chicks (Gallus domesticus)

To understand better the rate of neurogenesis and the distribution of new neurons in posthatch domestic chicks, we describe and compare the expression of the neuronal nuclei protein (NeuN, a.k.a. Fox-3) and doublecortin antigens in the whole brain of chicks 2 days, 8 days, and 14 weeks posthatch. In the forebrain ventricular and paraventricular zones, the density of bromodeoxyuridine-, NeuN-, and doublecortin-labeled cells was compared between chicks 24 hours and 7 days after an injection of bromodeoxyuridine (2 and 8 days posthatch, respectively). The distribution of NeuN-labeled neurons was similar to Nissl-stained tissue, with the exception of some areas where neurons did not express NeuN: cerebellar Purkinje cells and olfactory bulb mitral cells. The ventral tegmental area of 2-day-old chicks was also faintly labeled. The distribution of doublecortin was similar at all timepoints, with doublecortin-labeled profiles located throughout all forebrain areas as well as in the cerebellar granule cell layer. However, doublecortin labeling was not detectable in any midbrain or brainstem areas. Our data indicate that a significant number of new neurons is still formed in the telencephalon of posthatch domestic chicks, whereas subtelencephalic areas (except for the cerebellum) finish their neuronal expansion before hatching. Most newly formed cells in chicks leave the paraventricular zone after hatching, but a pool of neurons stays in the vicinity of the ventricular zone and matures in situ within 7 days. Proliferating cells often migrate laterally along forebrain laminae into still-developing brain areas.     

Olfactory learning is associated with increased spine density along apical dendrites of pyramidal neurons in the rat piriform cortex

We studied the effect of olfactory learning on the dendritic spine density of pyramidal neurons in the rat piriform (olfactory) cortex. Rats were trained to distinguish between two pairs of odours in an olfactory discrimination task. Three days after training completion, rats were killed and layer II pyramidal neurons identified by Golgi impregnation were examined with a light microscope. Counts of visible spines were performed along the secondary and tertiary branches of both the apical dendrites and the basal dendrites, which are the sites of intracortical synaptic inputs. An estimate of the true spine density was obtained using Feldman and Peters' method (1979, The Journal of Comparative Neurology, 188, 527--542). The estimated true spine density along apical dendrites was higher in neurons from trained rats than those in pseudotrained and naive rats by 15%. As length of spiny dendrites did not change significantly after learning, the learning-related increase in spine density in neurons from trained rats may indicate on an increased number of excitatory synapses interconnecting pyramidal neurons in the piriform cortex, following olfactory learning.     

Fear conditioning is associated with synaptogenesis in the lateral amygdala

Fear conditioning in the rat typically involves pairing a conditioned stimulus (tone) with an aversive unconditioned stimulus (foot shock) which elicits a freeze response. Although the circuitry that underlies this form of learning is well defined, potential synaptic changes associated with this form of learning have not been fully investigated. This experiment examined synaptic structural plasticity in the lateral amygdala which is critical for the acquisition of the conditioned fear response. Adult male rats were randomly allocated to either a paired, unpaired or tone only condition. One day after the initial fear conditioning session and 1 h after a probe trial confirmation of a conditioned fear response, the rats were perfused and the relevant tissue was embedded for electron microscopic analysis. Synaptic changes were quantified in the lateral amygdala using a stereological approach. The results showed a significant increase in the number of synapses in the conditioned animals compared to controls. This finding suggests that an increase in synaptic compliment in the amygdala may underlie the acquisition of the conditioned fear response.     

Role of the Dorso—Caudal Neostriatum in Filial Imprinting of the Domestic Chick: a Pharmacological and Autoradiographical Approach Focused on the Involvement of NMDA-Receptors

Newly hatched domestic chicks were either acoustically imprinted on 400 Hz tone pulses or visually imprinted on a rotating red light. Compared to naive control animals, both groups of imprinted chicks expressed significantly enhanced stimulus evoked 2-fluoro-2-deoxyglucose (2-FDG) uptake in circumscribed areas of the dorso-caudal neostriatum (Ndc). This enhanced excitability after imprinting seems not to be related to changes of NMDA-receptor densities as measured by quantitative receptor autoradiography. However, pharmacological blockade of NMDA-receptors in the dorso-caudal neostriatum leads to a marked suppression of stimulus-evoked 2-FDG uptake in the dorso-caudal neostriatum and also in the interconnected imprinting relevant forebrain area, medio-rostral neostriatum/hyperstriatum ventrale (MNH). Furthermore, chicks which received bilateral Ndc injections of the competitive NMDA antagonist DL-2-amino-5-phosphono valeric acid (APV) during the imprinting experiments showed a dose-dependent decrease of imprinting success compared to vehicle-injected controls. These results indicate that the dorso-caudal neostriatum may represent a polysensory associative brain region in which visual and acoustic features of imprinting objects may be integrated. The activation in this area evoked by the imprinting stimulus during and after imprinting is critically dependent on NMDA-receptor activation, which appears to be required for this learning process.     

Plasminogen activator is enriched in the synaptosomal plasma membranes

The intracellular localization of the serine protease plasminogen activator was analyzed in homogenates of bovine brain cortex using differential fractionation procedures. The distribution of the enzyme was clearly different from that of cytosol and mitochondrial markers, and was similar to that of plasma membrane proteins and of the muscarinic acetylcholine receptor, which is a specific marker for the synaptic membrane. The specific activity of plasminogen activator was increased in fractions enriched in intact synaptosomes. Most of the enzyme in intact synaptosomes was found to be firmly associated with the synaptosomal membrane, and could be solubilized by high concentrations of salt or by non-ionic detergent. Purified synaptic vesicles, however, did not contain large amounts of plasminogen activator. Bovine brain synaptosomes were shown to contain two species of the enzyme, having apparent molecular weights of 80,000 and 55,000. The presence of plasminogen activator in the synaptosomal membrane may indicate its possible involvement in the functioning of nerve terminals.     

The prefrontal ‘cortex’ in the pigeon. Biochemical evidence

Concentrations of dopamine and noradrenaline were determined in 6 regions of the telencephalon and in the cerebellum of the pigeon. Noradrenaline was rather evenly distributed. A significant variation was found of the dopamine-noradrenaline ratio (DA:NA), a measure which makes it possible to distinguish dopamine found in dopaminergic fibers from dopamine which is precursor of noradrenaline. The highest ratio was found in the anteroventromedial region (containing the presumed homologue of the mammalian neostriatum), and the next highest in the posteroventrolateral region (containing the archistriatum). Like in mammals, the lowest concentration of the non-precursor dopamine in the pigeon brain seems to be contained in the cerebellum. Among the regions which show physiological and anatomical similarities with the mammalian cerebral cortex, the DA:NA ratio was significantly higher in the posterodorsolateral, than in the posterodorsomedial and anterodorsomedial regions. The two dorsomedial regions contain the equivalents of the hippocampus and sensory cortical areas of mammals. The strong dopamine innervation of the posterodorsolateral region is comparable to that of the mammalian prefrontal cortex.     

The induction of behavioural sensitization is associated with cocaine-induced structural plasticity in the core (but not shell) of the nucleus accumbens

Repeated exposure to cocaine increases the density of dendritic spines on medium spiny neurons in the nucleus accumbens (Acb) and pyramidal cells in the medial prefrontal cortex (mPFC). To determine if this is associated with the development of psychomotor sensitization, rats were given daily i.p. injections of 15 mg/kg of cocaine (or saline) for 8 days, either in their home cage (which failed to induce significant psychomotor sensitization) or in a distinct and relatively novel test cage (which induced robust psychomotor sensitization). Their brains were obtained 2 weeks after the last injection and processed for Golgi-Cox staining. In the Acb core (AcbC) cocaine treatment increased spine density only in the group that developed psychomotor sensitization (i.e. in the Novel but not Home group), and there was a significant positive correlation between the degree of psychomotor sensitization and spine density. In the Acb shell (AcbS) cocaine increased spine density to the same extent in both groups; i.e. independent of psychomotor sensitization. In the mPFC cocaine increased spine density in both groups, but to a significantly greater extent in the Novel group. Furthermore, when rats were treated at Home with a higher dose of cocaine (30 mg/kg), cocaine now induced psychomotor sensitization in this context, and also increased spine density in the AcbC. Thus, the context in which cocaine is experienced influences its ability to reorganize patterns of synaptic connectivity in the Acb and mPFC, and the induction of psychomotor sensitization is associated with structural plasticity in the AcbC and mPFC, but not the AcbS.     

Small-scale pattern formation in a cortical area of the embryonic chicken telencephalon

The parahippocampal area is a cortical region of the avian dorsomedial telencephalon. In the chicken embryo, it contains discrete clusters of cadherin-7-positive cells, which are embedded in a cadherin-7-negative matrix. In the present work, the development and spatial distribution of these clusters is studied in whole-mount specimens. The clusters form a complex, coherent pattern of patches of variable size, spacing, and staining intensity. The pattern is especially prominent and regularly spaced in the rostral part of the caudolateral parahippocampal area. Here, it consists of stripes and connecting bridges with an average periodicity of approximately 0.3 mm. This pattern vaguely resembles some animal fur patterns and the ocular dominance domain of the mammalian visual cortex. The cadherin-7-positive patches also differ from their surrounding area by their cytoarchitecture and their increased acetylcholinesterase activity, suggesting that they represent functionally specialized subregions within the parahippocampal area. During development, the patchiness is first observed between 9 and 10 days of incubation and gradually becomes more prominent until 15 days of incubation. Our results indicate that the patchy organization of cortical gray matter on a small scale of periodicity (below 1 mm), which is well studied in the mammalian neocortex, is also found in the avian telencephalon.     

Distribution of mu, delta, and kappa opioid receptor binding sites in the brain of the one-day-old domestic chick (Gallus domesticus): an in vitro quantitative autoradiographic study

Three highly specific opioid ligands--[D-Ala2,Gly-ol]-enkephalin (DAGO) for mu (mu) receptor sites, [D-Pen2,D-Pen5]-enkephalin (DPDPE) for delta (delta) sites, and U-69593 for kappa (kappa) sites--were used to determine the regional distribution of the three major subtypes of opioid receptor binding sites in the brains of 1-day-old domestic chicks by the technique of quantitative receptor autoradiography. Whilst there was a degree of heterogeneity in the binding levels of each of the ligands, some notable similarities existed in the binding of the mu and kappa ligands in several forebrain regions, and in the optic tectum of the midbrain where mu and delta binding was very high. In the forebrain there was a high level of binding of mu and kappa ligands in the hyperstriatum, and for the mu ligand there was a very distinct lamination of binding sites in hyperstriatum accessorium, intercalatum supremum, dorsale and ventrale. Levels of binding of the mu and kappa ligands were also high in nucleus basalis, and (for mu only) in the neostriatum. The distribution of binding of the delta specific ligand in the forebrain showed marked differences to that of mu and kappa, being particularly low in the hyperstriatum and neostriatum. Very high levels of labelling of delta binding sites were, however, found in the nucleus rotundus. Binding of the three ligands was generally low or absent in the cerebellum and medulla, apart from a distinct labelling of the granule cell layer by the mu-ligand. A kinetic analysis was made of the binding of the three ligands to whole forebrain sections using scintillation counting methods.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lacking social support is associated with structural divergences in hippocampus–default network co-variation patterns

Elaborate social interaction is a pivotal asset of the human species. The complexity of people’s social lives may constitute the dominating factor in the vibrancy of many individuals’ environment. The neural substrates linked to social cognition thus appear especially susceptible when people endure periods of social isolation: here, we zoom in on the systematic inter-relationships between two such neural substrates, the allocortical hippocampus (HC) and the neocortical default network (DN). Previous human social neuroscience studies have focused on the DN, while HC subfields have been studied in most detail in rodents and monkeys. To bring into contact these two separate research streams, we directly quantified how DN subregions are coherently co-expressed with specific HC subfields in the context of social isolation. A two-pronged decomposition of structural brain scans from ∼40 000 UK Biobank participants linked lack of social support to mostly lateral subregions in the DN patterns. This lateral DN association co-occurred with HC patterns that implicated especially subiculum, presubiculum, CA2, CA3 and dentate gyrus. Overall, the subregion divergences within spatially overlapping signatures of HC–DN co-variation followed a clear segregation into the left and right brain hemispheres. Separable regimes of structural HC–DN co-variation also showed distinct associations with the genetic predisposition for lacking social support at the population level.     

Disturbance of perineuronal nets in the perilesional area after photothrombosis is not associated with neuronal death

Perineuronal nets (PNNs) are a condensed form of extracellular matrix that covers the surface of a subset of neurons. Their presence limits neuronal plasticity and may protect neurons against harmful agents. Here we analyzed the relationship between spatiotemporal changes in PNN expression and cell death markers after focal cortical photothrombotic stroke in rats. We registered a substantial decrease in PNN density using Wisteria floribunda agglutinin staining and CAT-315 and brevican immunoreactivity; the decrease occurred not only in the lesion core but also in the perilesional and remote cortex as well as in homotopic contralateral cortical regions. Fluoro Jade C and TUNEL staining in perilesional and remote areas, however, showed a low density of dying cells. Our results suggest that the PNN reduction was not a result of cellular death and could be considered an attempt to create conditions favorable for synaptic remodeling.     

Enhanced striatal and prefrontal activity is associated with individual differences in nonreinforced preference change for faces

Developing effective preference modification paradigms is crucial to improve the quality of life in a wide range of behaviors. The cue‐approach training (CAT) paradigm has been introduced as an effective tool to modify preferences lasting months, without external reinforcements, using the mere association of images with a cue and a speeded button response. In the current work for the first time, we used fMRI with faces as stimuli in the CAT paradigm, focusing on face‐selective brain regions. We found a behavioral change effect of CAT with faces immediately and 1‐month after training, however face‐selective regions were not indicative of behavioral change and thus preference change is less likely to rely on face processing brain regions. Nevertheless, we found that during training, fMRI activations in the ventral striatum were correlated with individual preference change. We also found a correlation between preference change and activations in the ventromedial prefrontal cortex during the binary choice phase. Functional connectivity among striatum, prefrontal regions, and high‐level visual regions was also related to individual preference change. Our work sheds new light on the involvement of neural mechanisms in the process of valuation. This could lead to development of novel real‐world interventions.     

Ipsilateral cortical connections of granular frontal cortex in the strepsirhine primate Galago, with comparative comments on anthropoid primates.

Modern studies of granular frontal cortex (GFC) in large-brained, anthropoid primates, such as Macaca, indicate that this region is comprised of many areal subdivisions. These areas vary in their architectonic appearance and each has a distinctive, diverse set of corticocortical connections. The great extent of the GFC region in anthropoids, and its high degree of areal parcellation, suggest that some GFC areas may be specializations of anthropoids, not found in other mammals. To investigate this possibility, we studied the corticocortical connections of GFC in the relatively small-brained, strepsirhine primate Galago, with a series of eight tracer injections in the frontal cortex, and an additional eight injections of parietal and temporal cortex. Tracers used were wheat-germ agglutinin conjugated to horseradish peroxidase and tritiated amino acids. Our results indicate that Galago GFC has strong, reciprocal connections with the parietal area-7 complex and with higher-order temporal areas; there are additional connections with extrastriate visual cortex, parahippocampal, and cingulate areas, and frontal cortex. Thus GFC has an extremely diverse array of cortical connections in Galago, as in Macaca. However, we also found that the pattern of parietofrontal connections is simpler in Galago than in Macaca. Specifically, parietal areas project to fewer discrete zones within the GFC of Galago, consistent with the view that these animals have fewer GFC areas than Macaca. In addition, Galago GFC possesses connections that specifically resemble those of Macaca arcuate cortex, but lacks connectional patterns that are characteristic of principalis cortex. These results are in accord with our previous architectonic studies, which indicated that Galago does not possess homologues of principalis areas. We conclude that the arcuate areas are common elements of primate GFC organization, while the areas located within and adjacent to the principal sulcus are anthropoid specializations.     

Labeling of poly(A) associated RNA in synaptosomes and the other subcellular fractions of rat cerebral cortex in basal conditions and during training

The labeling of total and poly(A) associated RNA from the subcellular fractions of cerebral cortex was studied after a 1-hour ³H-uridine pulse in control and trained rats. In the control animals, the fraction of newly synthesized brain cortex RNA which is found in synaptosomes is the minimal one. However, in synaptosomes the proportion of poly(A)⁺ RNA within newly synthesized RNA is maximal. Training of the rats does not influence total incorporation of label into RNA in the brain cortex and the distribution of newly synthesized RNA within the subcellular fractions. The proportions of poly(A)⁺ RNA within total labeled RNA in the various fractions are also unaffected.     

Abnormal corticomuscular coherence is associated with the small amplitude cortical myoclonus in Parkinson's disease.

Coherence is the degree of time-locked correlation between two signals as a function of frequency. The purpose of this study was to test the following hypotheses: (1) corticomuscular coherence is abnormally increased in those Parkinson's disease (PD) patients with small amplitude cortical myoclonus, and (2) corticomuscular coherence peaks around the time of the myoclonus electromyographic (EMG) discharge. We studied Parkinson's disease patients with and without myoclonus and controls. The data were digitally collected and processed off-line with EMG rectification, creation of 511-msec epochs, Fast-Fourier transform, and coherence analysis. In the 12 to 30 Hz frequency band, but not at 30 to 60 Hz or above, coherence peaks were observed in the PD subjects with myoclonus that were significantly greater than in the control subjects (P < 0.001) and in PD subjects without myoclonus (P < 0.001). The abnormal coherence values are evidence for abnormal rhythmic activity in cortical motor areas in those Parkinson's disease patients with myoclonus. In combination with previous findings on back-averaging, our results show that this myoclonus occurs when neuronal populations are driven to an extreme amount of synchronous activity with higher corticomuscular coherence values. These results have mechanistic implications for cortical dysfunction in Parkinson's disease and for cortical myoclonus in general.     

Resistance to ethanol sensitization is associated with a loss of synaptic plasticity in the hippocampus

Behavioral sensitization to repeated ethanol (EtOH) exposure induces an increase in locomotor activity in mice. However, not all animals express such sensitization. Although the literature indicated that the hippocampus may play a role in EtOH sensitization, it is not known whether behavioral sensitization to EtOH is associated with preferential changes in bidirectional synaptic plasticity, i.e., LTP and LTD, two markers of learning capabilities that have also been shown to be involved in addictive behavior. In the present study, we examined whether the vulnerability to develop and express behavioral sensitization to EtOH is associated with altered bidirectional synaptic plasticity in the CA1 area of the dorsal hippocampus. For this purpose, we analyzed both LTP and LTD in resistant and sensitized mice during the expression phase, i.e., 7 days after 10 days of repeated EtOH i.p. administration. We found that resistant mice showed a lack of LTD without changes in LTP. The lack of LTD was associated with an increase in GluN2A protein level and was not due to an altered level of neuronal activity, since no difference was observed between the number of c‐FOS positive neurons in sensitized and resistant mice. Given that both types of synaptic plasticity signals may have distinct roles in specific learning and behaviors, our results suggest that resistant mice could exhibit different phenotypes in terms of learning/memory and addictive behaviors compared to sensitized ones. Synapse 71:e21899, 2017 . © 2016 Wiley Periodicals, Inc.