Patterns of overlap and segregation between insular cortical, intermediodorsal thalamic and basal amygdaloid afferents in the nucleus accumbens of the rat

A selective role for right insula--basal ganglia circuits in appetitive stimulus processing

Hemispheric lateralization of hedonic evaluation ('liking') and incentive motivation ('wanting') in neural networks connecting the basal ganglia and insula (BG-I) in humans was examined. Participants with brain damage restricted to the BG-I of the right (n = 5) or left (n = 5) hemisphere, and 26 healthy participants matched on age, sex and intelligence quotient were tested on positively and negatively valenced pictures drawn from varied stimulus categories (Vijayaraghavan et al., 2008). Liking was assessed with explicit ratings of pleasantness using a nine-point Likert scale. Wanting was quantified as the amount of work (via repeated keypresses) that participants expended to increase (approach) or decrease (withdraw) viewing time. Right-lesion patients showed abnormally low viewing times and liking ratings for positive images. For a subset of positive images depicting sexual content, right-lesion patients exhibited active withdrawal, while the other two groups approached such stimuli. These results suggest that the right basal ganglia-insula complex plays a greater role than the left in supporting hedonic evaluation and motivational approach to positively valenced stimuli. The finding that active avoidance of stimuli that were not 'liked' was spared in both right- and left-sided lesion subjects suggests that unilateral damage to insula/basal ganglia circuits may not be sufficient to affect general incentive motivation independent of preference.

GABAergic transmission in the rat ventral pallidum mediates a saccharin palatability shift in conditioned taste aversion

We previously found that the blockade of gamma-aminobutyric acid (GABA)(A) receptors in the ventral pallidum (VP) alters the taste palatability of a conditioned stimulus (CS) from aversive to ingestive after the establishment of conditioned taste aversion (CTA). Because these results suggest that GABAergic transmission in the VP mediates decreased palatability of the taste in CTA, the present study aimed to examine the effects of taste stimulation on the extracellular release of GABA in the VP using in vivo microdialysis. Initially, rats received a paired presentation of 5 mm saccharin or 0.3 mm quinine solution with an intraperitoneal injection of 0.15 m lithium chloride (S-CTA and Q-CTA groups) or saline (S-control and Q-control groups). After conditioning, microdialysis was carried out before, during and after the presentation of the CS via an intra-oral cannula. We measured the latency of the first aversive orofacial responses to the CS as behavioral indices. In the S-CTA group, which rapidly rejected the CS (within 100 s), the GABA efflux was significantly increased (147%) and was maintained for 2 h. On the other hand, the S-control group expressed no aversive responses and showed no significant alterations in GABA efflux. Although the Q-CTA group immediately expressed aversive responses to the CS (within 30 s), GABA release was not changed by presentation of the CS, which was similar in the Q-control group. These findings suggest that the palatability shift from ingestive to aversive in conditioned aversion to saccharin, but not quinine, is mediated by the change in GABAergic transmission in the VP.

Paraventricular thalamus mediates context-induced reinstatement (renewal) of extinguished reward seeking

Paraventricular thalamus (PvTh) is uniquely placed to contribute to reinstatement of drug and reward seeking. It projects extensively to regions implicated in reinstatement including accumbens shell (AcbSh), prefrontal cortex (PFC) and basolateral amygdala (BLA), and receives afferents from other regions important for reinstatement such as lateral hypothalamus. We used complementary neuroanatomical and functional approaches to study the role of PvTh in context-induced reinstatement (renewal) of extinguished reward-seeking. Rats were trained to respond for a reward in context A, extinguished in context B and tested in context A or B. We applied the neuronal tracer cholera toxin B subunit (CTb) to AcbSh and examined retrograde-labelled neurons, c-Fos immunoreactivity (IR) and dual c-Fos/CTb labelled neurons in PvTh and other AcbSh afferents. In PvTh there was c-Fos IR in CTb-positive neurons associated with renewal showing activation of a PvTh-AcbSh pathway during renewal. In PFC there was little c-Fos IR in CTb-positive or negative neurons associated with renewal. In BLA, two distinct patterns of activation and retrograde labelling were observed. In rostral BLA there was significant c-Fos IR in CTb-negative neurons associated with renewal. In caudal BLA there was significant c-Fos IR in CTb-positive neurons associated with being tested in either the extinction (ABB) or training (ABA) context. We then studied the functional role of PvTh in renewal. Excitotoxic lesions of PvTh prevented renewal. These lesions had no effect on the acquisition of reward seeking. These results show that PvTh mediates context-induced reinstatement and that this renewal is associated with recruitment of a PvTh-AcbSh pathway.

Role of dopamine D1 receptors in the prefrontal dorsal agranular insular cortex in mediating cocaine self-administration in rats

RATIONALE

Orbital/insular areas of the prefrontal cortex (PFC) are implicated in cocaine addiction. However, the role of dopamine D1 receptors in mediating cocaine self-administration in these sub-regions remains unknown.

OBJECTIVES

To define the role of the dorsal agranular insular (AId) sub-region of the PFC, we investigated the effects of D1 receptor manipulation on self-administration behavior maintained by cocaine and cocaine-related stimuli.

MATERIALS AND METHODS

Rats were trained to lever press for cocaine (1 mg/kg) under a fixed-interval 5-min (fixed-ratio 5:S) second-order schedule of reinforcement in the presence of conditioned light cues and contextual sound cues. Intra-AId infusions of vehicle, the D1-like receptor agonist SKF 81297 (0.1, 0.2, 0.4 microg/side) or the D1-like receptor antagonist SCH 23390 (1.0, 2.0, 4.0 microg/side), were administered prior to 1-h self-administration test sessions. Food-maintained responding under a second-order schedule was examined in separate rats to determine if pretreatment with D1 ligands produced general impairments in responding.

RESULTS

Infusion of SKF 81297 (0.2 and 0.4 microg/side) reduced active lever responses during the first 30 min of 1-h test sessions, but did not influence cocaine intake. Infusion of 4.0 microg/side SCH 23390 reduced active lever responses and cocaine intake throughout the 1-h test sessions. Additionally, this dose of SCH 23390 disrupted food-maintained responding and intake.

CONCLUSIONS

D1 receptor agonists and antagonists in the AId have diverse consequences and time courses of action. D1 receptor stimulation in the AId may reduce the motivating influence of cocaine-related stimuli on responding whereas D1 receptor blockade in this PFC sub-region produces global disruptions in behavior.

Three-dimensional organization of dendrites and local axon collaterals of shell and core medium-sized spiny projection neurons of the rat nucleus accumbens

Medium-sized spiny projection neurons (MSN) in the head of the primate caudate nucleus are thought to have preferred dendritic orientations that tend to parallel the orientations of the striosomes. Moreover, recurrent axon collaterals of MSN in the rat dorsal striatum have been categorized into two types, i.e., restricted and widespread. The nucleus accumbens (Acb) has a highly complex compartmental organization, and the spatial organization of dendritic and axonal arbors of MSN has not yet been systematically studied. In this study, using single-cell juxtacellular labeling with neurobiotin as well as anterograde neuroanatomical tracing with biotinylated dextran amine, we investigated the three-dimensional (3D) organization of dendrites and axons of MSN of the rat Acb in relation to subregional (shell-core) and compartmental (patch-matrix) boundaries. Our results show that dendritic arbors of MSN in both the Acb shell and core subregions are preferentially oriented, i.e., they are flattened in at least one of the 3D-planes. The preferred orientations are influenced by shell-core and patch-matrix boundaries, suggesting parallel and independent processing of information. Dendritic orientations of MSN of the Acb core are more heterogeneous than those of the shell and the dorsal striatum, suggesting a more complex distribution of striatal inputs within the core. Although dendrites respect the shell-core and patch-matrix boundaries, recurrent axon collaterals may cross these boundaries. Finally, different degrees of overlap between dendritic and axonal arborizations of individual MSN were identified, suggesting various possibilities of lateral inhibitory interactions within and between, functionally distinct territories of the Acb.

The orbital cortex in rats topographically projects to central parts of the caudate-putamen complex

Disturbances of the orbitofrontal-striatal pathways in humans have been associated with several psychopathologies including obsessive-compulsive disorder and drug addiction. In nonhuman primates, different subareas of the orbitofrontal cortex project topographically to central and ventromedial parts of the striatum. Relatively little is known about the anatomical organization of the rat orbital cortex while there is a growing interest in this cortical area from a functional and behavioral point of view. The aim of the present neuroanatomical tracing study was to determine in rats the striatal target area of the projections of the orbital cortex as well as the topographical organization within these projections. To this end, anterograde tracers were injected in the different cytoarchitectonically distinct subareas of the orbital cortex. The results show that the individual orbital areas, i.e. medial orbital area, ventral orbital area, ventrolateral orbital area and lateral orbital area, project to central parts of the caudate-putamen, exhibiting a mediolateral and, to a lesser degree, rostrocaudal topographical arrangement. Orbital projections avoid the most dorsal, as well as rostral and caudal parts of the caudate-putamen. Terminal fields from cytoarchitectonically different areas show a considerable overlap. Superficial cortical layers project preferentially to the striatal matrix, deep layers to the patch compartment. The projections from the ventrolateral orbital area are strongest and occupy the most extensive striatal area. In addition to projections to the caudate-putamen, the ventrolateral, lateral and dorsolateral orbital areas have a scarce projection to the most lateral part of the nucleus accumbens shell in the ventral striatum. In contrast to nonhuman primates, the remainder of the rat nucleus accumbens is virtually free of orbital projections.

Dysregulation of gene induction in corticostriatal circuits after repeated methylphenidate treatment in adolescent rats: differential effects on zif 268 and homer 1a

Psychostimulants and other dopamine agonists produce molecular changes in neurons of cortico-basal ganglia-cortical circuits, and such neuronal changes are implicated in behavioural disorders. Methylphenidate, a psychostimulant that causes dopamine overflow (among other effects), alters gene regulation in neurons of the striatum. The present study compared the effects of acute and repeated methylphenidate treatment on cortical and striatal gene regulation in adolescent rats. Changes in the expression of the immediate-early genes zif 268 and homer 1a were mapped in 23 striatal sectors and 22 cortical areas that provide input to these striatal sectors, in order to determine whether specific corticostriatal circuits were affected by these treatments. Acute administration of methylphenidate (5 mg/kg, i.p.) produced modest zif 268 induction in cortical areas. These cortical zif 268 responses were correlated in magnitude with zif 268 induction in functionally related striatal sectors. In contrast, after repeated methylphenidate treatment (10 mg/kg, 7 days), cortical and striatal gene induction were dissociated. In these animals, the methylphenidate challenge (5 mg/kg) produced significantly greater gene induction (zif 268 and homer 1a) in the cortex. This enhanced response was widespread but regionally selective, as it occurred predominantly in premotor, motor and somatosensory cortical areas. At the same time, striatal gene induction was partly suppressed (zif 268) or unchanged (homer 1a). Thus, repeated methylphenidate treatment disrupted the normally coordinated gene activation patterns in cortical and striatal nodes of corticostriatal circuits. This drug-induced dissociation in cortical and striatal functioning was associated with enhanced levels of behavioural stereotypies, suggesting disrupted motor switching function.

Effects of intra-accumbens NMDA and AMPA receptor antagonists on short-term spatial learning in the Morris water maze task

Glutamatergic transmission within the nucleus accumbens (Nac) is considered to subserve the transfer of different types of information from the cortical and limbic regions. In particular, it has been suggested that glutamatergic afferences from the hippocampus and the prefrontal cortex provide the main source of contextual information to the Nac. Accordingly, several authors have demonstrated that the blockade of glutamate receptors within the Nac impairs various spatial tasks. However, the exact role of the different classes of glutamate receptors within the Nac in short-term spatial memory is still not clear. In this study we investigated the involvement of two major classes of glutamate receptors, NMDA and AMPA receptors, within the Nac in the acquisition of spatial information, using the Morris water maze task. Focal injections of the NMDA antagonist, AP-5 (0.1 and 0.15 microg/side), and the AMPA antagonist, DNQX (0.005, 0.01 microg/side), were performed before a massed training phase, and mice were tested for retention immediately after. NMDA and AMPA receptor blockade induced no effect during training. On the contrary, injection of the two glutamatergic antagonists impaired spatial localization during the probe test. These data demonstrate an involvement of the Nac in short-term spatial learning. Moreover, they prove that within this structure the short-term processing of spatial information needs the activation of both NMDA and AMPA receptors.

Forebrain structures specifically activated by conditioned taste aversion

This study investigates which forebrain structures show Fos protein expression during conditioned taste aversion (CTA) acquisition and whether Fos expression depends on the aversion strength. A novel taste paired with an intraperitoneal injection of a low dose of the malaise-inducing agent lithium chloride (LiCl) induced a weak CTA, whereas associating this novel taste with a high dose of LiCl induced a strong CTA. Increasing the strength of the gastric malaise alone enhanced Fos expression in central, basal, and lateral amygdala nuclei and decreased Fos expression in the nucleus accumbens core. Taste-malaise association induced specific Fos activation in the insular cortex (with both the low and the high doses of LiCl) and the nucleus accumbens shell (with the high LiCl dose only). No significant variation of Fos expression was measured in the perirhinal cortex. Several forebrain areas may be sites of taste-malaise convergence during CTA acquisition depending on the strength of the aversion.

Taste Memory Formation: Role of Nucleus Accumbens

When a novel taste has been associated with postingestive malaise, animals recognize this taste as aversive. This associative learning is known as conditioned taste aversion. However, when an animal consumes a novel taste and no aversive consequences follow, it becomes recognized as a safe signal, leading to an increase in its consumption in subsequent presentations. In this review, we will discuss the results related to the taste memory formation focusing particularly on the nucleus accumbens (NAcc). The NAcc keeps projections with amygdala, insular cortex, parabrachial nucleus, and nucleus of the solitary tract areas important for taste memory formation. We will review the evidence relating to how the NAcc could be involved in taste memory formation, due to its role in the taste memory trace formation and its role in the association of the conditioned stimulus-unconditioned stimulus, and finally the retrieval of taste memory. In this context, we will review the participation of the cholinergic, dopaminergic, and glutamatergic systems in the NAcc during taste memory formation.

Thalamo-striatal projections in the hedgehog tenrec

Unlike the basal ganglia input from the midline and intralaminar nuclei, the origin and prominence of striatal projections arising in the lateral thalamus varies considerably among mammals being most restricted in the opossum and monkey, most extensive in the rat. To get further insight into the evolution of thalamo-striatal pathways the Madagascar lesser hedgehog tenrec (Afrotheria) was investigated using anterograde and retrograde flow techniques. An extensive medial thalamic region (including presumed equivalents to the paraventricular, parataenial and dorsomedial nuclei as well as the reuniens complex), the rostral (central) and caudal (parafascicular) intralaminar nuclei were shown to give rise to striatal projections. Additional projections originated in the ventral anterolateral nuclear group and regions within and around the medial geniculate complex. Similar to the rat there was also substantial projections from the lateral posterior-pulvinar complex and the ventral posterior nucleus. The fibers terminated extensively across the striatum in a mainly homogeneous fashion. Isolated patches of low-density terminations were found in the caudoputamen. This inhomogeneous labeling pattern appeared similar to one described in the cat with the unlabeled islands showing features of striosomes. The medial and intralaminar nuclei also projected heavily upon the olfactory tubercle. Differential innervation patterns were noted in the polymorphous layer, the deep and the superficial molecular layer.

NMDA and muscarinic receptors of the nucleus accumbens have differential effects on taste memory formation

Animals recognize a taste cue as aversive when it has been associated with post-ingestive malaise; this associative learning is known as conditioned taste aversion (CTA). When an animal consumes a new taste and no negative consequences follow, it becomes recognized as a safe signal, leading to an increase in its consumption in subsequent presentations (attenuation of neophobia, AN). It has been shown that the nucleus accumbens (NAcc) has an important role in taste learning. To elucidate the involvement of N-methyl-D-aspartate (NMDA) and muscarinic receptors in the NAcc during safe and aversive taste memory formation, we administrated bilateral infusions of DL-2-amino-5-phosphonopentanoic acid (APV) or scopolamine in the NAcc shell or core respectively. Our results showed that pre-training injections of APV in the NAcc core and shell disrupted aversive but not safe taste memory formation, whereas pre-training injections of scopolamine in the NAcc shell, but not core, disrupted both CTA and AN. These results suggest that muscarinic receptors seem to be necessary for processing taste stimuli for either safe or aversive taste memory, whereas NMDA receptors are only involved in the aversive taste memory trace formation.

Brain activation during craving for alcohol measured by positron emission tomography

OBJECTIVE

Craving for alcohol is probably involved in acquisition and maintenance of alcohol dependence to a substantial degree. However, the brain substrates and mechanisms that underlie alcohol craving await more detailed elucidation.

METHOD

Positron emission tomography was used to map regional cerebral blood flow (CBF) in 21 detoxified patients with alcohol dependence during exposure to alcoholic and non-alcoholic beverages.

RESULTS

During the alcohol condition compared with the control condition, significantly increased CBF was found in the ventral putamen. Additionally, activated areas included insula, dorsolateral prefrontal cortex and cerebellum. Cerebral blood flow increase in these regions was related to self-reports of craving assessed in the alcoholic patients.

CONCLUSIONS

In this investigation, cue-induced alcohol craving was associated with activation of brain regions particularly involved in brain reward mechanisms, memory and attentional processes. These results are consistent with studies on craving for other addictive substances and may offer strategies for more elaborate studies on the neurobiology of addiction.

Brain activation during craving for alcohol measured by positron emission tomography

OBJECTIVE

Craving for alcohol is probably involved in acquisition and maintenance of alcohol dependence to a substantial degree. However, the brain substrates and mechanisms that underlie alcohol craving await more detailed elucidation.

METHOD

Positron emission tomography was used to map regional cerebral blood flow (CBF) in 21 detoxified patients with alcohol dependence during exposure to alcoholic and non-alcoholic beverages.

RESULTS

During the alcohol condition compared with the control condition, significantly increased CBF was found in the ventral putamen. Additionally, activated areas included insula, dorsolateral prefrontal cortex and cerebellum. Cerebral blood flow increase in these regions was related to self-reports of craving assessed in the alcoholic patients.

CONCLUSIONS

In this investigation, cue-induced alcohol craving was associated with activation of brain regions particularly involved in brain reward mechanisms, memory and attentional processes. These results are consistent with studies on craving for other addictive substances and may offer strategies for more elaborate studies on the neurobiology of addiction.

Nucleus accumbens nitric oxide immunoreactive interneurons receive nitric oxide and ventral subicular afferents in rats

The nitric oxide generating neurons of the nucleus accumbens exert a powerful influence over striatal function, in addition, these nitrergic inputs are in a position to regulate the dopaminergic and glutamatergic inputs on striatal projection neurons. It was the aim of this study to establish the source of the glutamatergic drive to nitric oxide synthase interneurons of the nucleus accumbens. The nucleus accumbens nitric oxide-generating neurons receive asymmetrical, excitatory, presumably glutamatergic inputs. Possible sources of these inputs could be the limbic and cortical regions known to project to this area. To identify sources of the excitatory inputs to the nitric oxide synthase-containing interneurons of the nucleus accumbens in the rat we first examined the ultrastructural morphology of asymmetrical synaptic specializations contacting nitric oxide synthase-immunohistochemically labeled interneurons in the nucleus accumbens. Neurons were selected from different regions of the nucleus accumbens, drawn using camera lucida, processed for electron microscopic analysis, and the boutons contacting nitric oxide synthase-labeled dendrites were photographed and correlated to the drawings. Using vesicle size as the criterion the source was predicted to be either the prefrontal cortex or the ventral subiculum of the hippocampus. To examine this prediction, a further study used anterograde tracing from both the prefrontal cortex and the ventral subiculum, and nitric oxide synthase immunohistochemistry with correlated light and electron microscopy. Based on appositions by anterogradely labeled fibers, selected nitric oxide synthase-labeled neurons within the nucleus accumbens, were examined with electron microscopic analysis. With this technique we confirmed the prediction that subicular afferent boutons make synaptic contact with nitric oxide synthase interneurons, and demonstrated anatomically that nitric oxide synthase boutons make synaptic contact with the dendritic arbors of nitric oxide synthase interneurons. We suggest that the subicular input may excite the nitric oxide synthase neurons synaptically, while the nitric oxide synthase-nitric oxide synthase interactions underlie a nitric oxide signaling network which propagates hippocampal information, and expands the hippocampus's influence on 'gating' information flow across the nucleus accumbens.

Basolateral amygdala glutamatergic activation enhances taste aversion through NMDA receptor activation in the insular cortex

In conditioned taste aversion (CTA), a subject learns to associate a novel taste with visceral malaise. Brainstem, limbic and neocortical structures have been implicated in CTA memory formation. Nevertheless, the role of interactions between forebrain structures during these processes is still unknown. The present experiment was aimed at investigating the possible interaction between the basolateral nucleus of the amygdala (BLA) and the insular cortex (IC) during CTA memory formation. Injection of a low dose of lithium chloride (30 mg/kg, i.p.) 30 min after novel taste consumption (saccharin 0.1%) induces a weak CTA. Unilateral BLA injection of glutamate (2 microg in 0.5 microL) just before low lithium induces a stronger CTA. Unilateral injection of an N-methyl-d-aspartate (NMDA) receptor antagonist (AP5, 5 microg in 0.5 microL) in IC has no effect. However, AP5 treatment in IC at the same time or 1 h after the ipsilateral BLA injection reverses the glutamate-induced CTA enhancement. Injection of AP5 in IC 3 h after BLA injection does not interfere with the glutamate effect. Moreover, the CTA-enhancing effect of glutamate was also blocked by contralateral IC injection of AP5 at the same time. These results provide strong evidence that NMDA receptor activation in the IC is essential to enable CTA enhancement induced by glutamate infusion in the BLA during a limited time period that extends to 1 but not to 3 hours. These findings indicate that BLA-IC interactions regulate the strength of CTA. The bilateral nature of these amygdalo-cortical interactions is discussed.

Topography of methylphenidate (ritalin)-induced gene regulation in the striatum: differential effects on c-fos, substance P and opioid peptides

Dopamine action alters gene regulation in striatal neurons. Methylphenidate increases extracellular levels of dopamine. We investigated the effects of acute methylphenidate treatment on gene expression in the striatum of adult rats. Molecular changes were mapped in 23 striatal sectors mostly defined by their predominant cortical inputs in order to determine the functional domains affected. Acute administration of 5 and 10 mg/kg (i.p.) of methylphenidate produced robust increases in the expression of the transcription factor c-fos and the neuropeptide substance P. Borderline effects were found with 2 mg/kg, but not with 0.5 mg/kg. For 5 mg/kg, c-fos mRNA levels peaked at 40 min and returned to baseline by 3 h after injection, while substance P mRNA levels peaked at 40-60 min and were back near control levels by 24 h. These molecular changes occurred in most sectors of the caudate-putamen, but were maximal in dorsal sectors that receive sensorimotor and medial agranular cortical inputs, on middle to caudal levels. In rostral and ventral striatal sectors, changes in c-fos and substance P expression were weaker or absent. No effects were seen in the nucleus accumbens, with the exception of c-fos induction in the lateral part of the shell. In contrast to c-fos and substance P, acute methylphenidate treatment had minimal effects on the opioid peptides dynorphin and enkephalin. These results demonstrate that acute methylphenidate alters the expression of c-fos and substance P preferentially in the sensorimotor striatum. These molecular changes are similar, but not identical, to those produced by other psychostimulants.

Quantification of morphological differences in boutons from different afferent populations to the nucleus accumbens

The nucleus accumbens (Acb) receives convergent glutamatergic inputs from the prefrontal cortex (PFC), central thalamus, basolateral amygdala and the ventral subiculum of the hippocampus. The principal neurons of the nucleus accumbens are modulated by specific sets of convergent afferent inputs, the local circuit neurons also receive a substantial number of glutamatergic inputs, but the full complement of these has yet to be established. The aim of these studies was to define characteristics of the different glutamatergic afferent inputs to the nucleus accumbens that would aid their identification. To enable the characterisation of the glutamatergic inputs to nucleus accumbens neurons we first labelled the four main glutamatergic sources of afferent input to the accumbens with the anterograde tracer biotinylated dextran amine (BDA). Using an unbiased systematic sampling method, the morphological characteristics of their synaptic boutons were measured and assessed at the electron microscopic level. From the criteria assessed, a comparison of the four afferent sources was made, characteristics such as bouton size and vesicle density had significantly different population means, however, the only characteristic that allowed discrimination between the four major glutamatergic afferent to the nucleus accumbens was that of vesicle size. The vesicles in boutons from amygdala were larger than the subiculum which, in turn, were larger than the prefrontal cortex, the thalamus were the smallest in size. The methods used also allow a comparison of the relative frequency of different sized postsynaptic structures targeted, the prefrontal cortex almost exclusively targeted spines whereas the thalamus and the subiculum, in addition to spines, targeted proximal and distal dendrites.

Differential brain activity in alcoholics and social drinkers to alcohol cues: relationship to craving

Using fMRI, our group previously found that after a sip of alcohol and exposure to alcohol beverage pictures, alcoholics compared to social drinkers had increased differential brain activity in the prefrontal cortex and anterior thalamus. This study extends this earlier work with several improvements including imaging the entire brain (rather than the anterior half previously) and recording craving, while the subjects viewed images within the scanner. In a Philips 1.5 T MRI scanner, 10 nontreatment-seeking alcoholics and 10 age-matched healthy social drinkers were given a sip of alcohol before viewing a 12 min randomized presentation of pictures of alcoholic beverages, nonalcoholic beverages, and two different visual control tasks. During picture presentation, changes in regional brain activity were measured in 15 transverse T2(*)-weighted blood oxygen level dependent slices. Subjects rated their urge to drink after each picture sequence. After a sip of alcohol, while viewing alcohol cues compared to viewing other beverage cues, the alcoholics, but not social drinkers, reported higher craving ratings and had increased activity in the prefrontal cortex and anterior limbic regions. Brain activity in the left nucleus accumbens, anterior cingulate, and left orbitofrontal cortex significantly correlated with subjective craving ratings in alcohol subjects but not in control subjects. This study suggests, as did our earlier study, that alcoholics and not social drinkers, when exposed to alcohol cues, have increased brain activity in areas that reportedly subserve craving for other addictive substances.

Complementary distribution of vesicular glutamate transporters 1 and 2 in the nucleus accumbens of rat: Relationship to calretinin-containing extrinsic innervation and calbindin-immunoreactive neurons

The caudomedial shell of the rat nucleus accumbens exhibits inhomogeneous distribution patterns of the vesicular glutamate transporters 1 (VGLUT1) and 2 (VGLUT2). This paper focuses on the question of whether patterns of VGLUT1 and VGLUT2 correspond to cytoarchitectonically and cytochemically defined subterritories of the caudomedial shell region. VGLUT2 was shown to be coexpressed with calretinin in the dense axonal plexus known to emanate from the paraventricular thalamic nucleus. In regions termed corridors, which are spared by this paraventricular thalamic innervation, axonal terminals were found to be clustered and VGLUT1-immunoreactive. It is assumed that these fibers originate in the prelimbic cortex and/or in the parvicellular basal amygdaloid nucleus known to project to accumbal shell components. Our findings confirm the existence of two well-separated neuronal circuits in the caudomedial shell that are dominated by two different excitatory input systems originating from either thalamic, cortical, or cortex-like amygdaloid sources. The large lateral corridors-which resemble the accumbal core not only in respect to their VGLUT1 immunolabeling but also concerning their content of calbindin-positive cells-may represent a component of the anatomically weakly defined accumbal shore region.

Basolateral amygdala efferents to the ventral subiculum preferentially innervate pyramidal cell dendritic spines

The basolateral amygdala and the ventral subiculum of the hippocampal formation are two of the major limbic-related regions within the brain, both of which project heavily to the nucleus accumbens. The nucleus accumbens is regarded as the limbic-motor interface, in view of these limbic afferent and its somatomotor and autonomic efferent connections. These afferent inputs have been suggested to converge monosynaptically on cells within the accumbens and are hypothesised to play a role in functions such as affective motivational behaviour. Convergence between inputs from the basolateral amygdala and the hippocampus at the level of the accumbens can be demonstrated with electrophysiological recording methods, but these do not conclusively preclude polysynaptic mechanisms. In fact there is a robust reciprocal projection between the basolateral amygdala and the hippocampus, synaptic details of which have not been fully investigated. We examined the synaptic input from the basolateral amygdala to the projection neurons of the subiculum, the spiny pyramidal neurons. We labelled the afferents from basolateral amygdala with a small injection of biotinylated dextran amine, and revealed the anterogradely labeled fibers within the subiculum. The labeled basolateral amygdala fibers were studied with electron microscopy to identify their postsynaptic target structures. With this technique we have demonstrated anatomically that the basolateral amygdala preferentially innervates spiny subiculum neurons, presumed pyramidal projection neurons, although some dendrites and possibly local circuit neurons may be targeted.

Individual nucleus accumbens-projection neurons receive both basolateral amygdala and ventral subicular afferents in rats

The nucleus accumbens is regarded as the limbic-motor interface, in view of its limbic afferent and somatomotor and autonomic efferent connections. Within the accumbens, there appear to be specific areas in which limbic afferent fibres, derived from the hippocampus and the amygdala, overlap. These afferent inputs have been suggested to converge monosynaptically on cells within the accumbens and are hypothesized to play a role in paradigms such as conditioned place preference. Convergence between inputs from basolateral amygdala and hippocampus can be demonstrated with electrophysiological recording methods, but these do not conclusively preclude polysynaptic mechanisms. We examined the synaptic input to the projection neurons of the accumbens, the medium-sized densely spiny neurons. We labelled the projection neurons with a small injection of biotinylated dextran amine into the accumbens, and the afferents from the basolateral amygdala and ventral subiculum of the hippocampus with injections of biotinylated dextran amine and Phaseolus vulgaris-leucoagglutinin respectively, and revealed the anterogradely labelled fibres with different chromogens. The labelled accumbens-projection neurons were studied with correlated light and electron microscopy for identified monosynaptic inputs. With this technique we have demonstrated anatomically that monosynaptic convergence between the ventral subicular region of the hippocampus and the basolateral region of the amygdala occurs at the level of the proximal as well as distal dendrites. Finally, we suggest that these anatomical arrangements may represent the framework for the integrative role that has been assigned to the accumbens.

Pleasures of the brain

How does the brain cause positive affective reactions to sensory pleasure? An answer to pleasure causation requires knowing not only which brain systems are activated by pleasant stimuli, but also which systems actually cause their positive affective properties. This paper focuses on brain causation of behavioral positive affective reactions to pleasant sensations, such as sweet tastes. Its goal is to understand how brain systems generate 'liking,' the core process that underlies sensory pleasure and causes positive affective reactions. Evidence suggests activity in a subcortical network involving portions of the nucleus accumbens shell, ventral pallidum, and brainstem causes 'liking' and positive affective reactions to sweet tastes. Lesions of ventral pallidum also impair normal sensory pleasure. Recent findings regarding this subcortical network's causation of core 'liking' reactions help clarify how the essence of a pleasure gloss gets added to mere sensation. The same subcortical 'liking' network, via connection to brain systems involved in explicit cognitive representations, may also in turn cause conscious experiences of sensory pleasure.

Nucleus accumbens mu-opioids regulate intake of a high-fat diet via activation of a distributed brain network

Endogenous opioid peptides within the nucleus accumbens, a forebrain site critical for the regulation of reward-related behavior, are believed to play an important role in the control of appetite. In particular, this system is thought to mediate the hedonic aspects of food intake, governing the positive emotional response to highly palatable food such as fat and sugar. Previous work has shown that intra-accumbens administration of the mu-opioid agonist D-Ala2,Nme-Phe4,Glyol5-enkephalin (DAMGO) markedly increases food intake and preferentially enhances the intake of palatable foods such as fat, sucrose, and salt. Using information from recently performed c-fos mapping experiments, we sought to explore the involvement of structures efferent to the nucleus accumbens in this feeding response. Free-feeding rats with dual sets of bilateral cannulas aimed at the nucleus accumbens and one of several output structures were infused with DAMGO (0, 0.25 microg/0.5 microl) in the accumbens, and fat intake was measured over a 2 hr period. Concurrent temporary inactivation with the GABA(A) agonist muscimol (5-20 ng/0.25 microl) of the dorsomedial hypothalamic nucleus, lateral hypothalamus, ventral tegmental area, or the intermediate region of the nucleus of the solitary tract blocked the robust increase in fat intake induced by intra-accumbens DAMGO at doses of muscimol that did not affect general motor activity. Muscimol alone also inhibited and augmented baseline fat intake in the lateral and dorsomedial hypothalamic nuclei, respectively. These results suggest that intake of energy-dense palatable food is controlled by activity in a neural network linking ventral striatal opioids with diencephalic and brainstem structures.

Topography of cocaine-induced gene regulation in the rat striatum: relationship to cortical inputs and role of behavioural context

Psychostimulants alter gene expression in projection neurons of the striatum, and such neuroplasticity is implicated in drug addiction and dependence. Evidence indicates that excitatory inputs from the cortex and thalamus are critical for these molecular changes. In the present study, we determined the topography of cocaine-induced changes in gene expression in the rat striatum and investigated whether these molecular alterations are associated with particular cortical inputs. Acute induction of c-fos (by 25 mg/kg of cocaine), and the c-fos response and dynorphin expression after repeated cocaine treatment (25 mg/kg, 4 days) were assessed as examples for short-term and longer-term molecular changes, respectively. In addition, we examined whether these molecular effects were influenced by the behaviour performed during cocaine action (running-wheel training vs. open field). Our results demonstrate that the overall topography of cocaine-induced gene regulation in the striatum is remarkably stable. Both acute and longer-term molecular changes were maximal in caudal dorsal striatal sectors that receive convergent inputs from the medial agranular and the sensorimotor cortex. In contrast, relatively minor or no effects were found in rostral and ventral striatal sectors. However, running-wheel training under the influence of cocaine enhanced the c-fos response to a subsequent cocaine challenge selectively in parts of the caudal sensorimotor striatum. These results indicate that cocaine produces molecular adaptations preferentially in cortico-basal ganglia circuits through the sensorimotor striatum, and that some of these neuronal changes are influenced by the behaviour performed during drug exposure.

Projections from the amygdaloid complex to the claustrum and the endopiriform nucleus: a Phaseolus vulgaris leucoagglutinin study in the rat

The claustrum and the endopiriform nucleus contribute to the spread of epileptiform activity from the amygdala to other brain areas. Data of the distribution of pathways underlying the information flow between these regions are, however, incomplete and controversial. To investigate the projections from the amygdala to the claustrum and the endopiriform nucleus, we injected the anterograde tracer Phaseolus vulgaris leucoagglutinin into various divisions of the amygdaloid complex, including the lateral, basal, accessory basal, central, anterior cortical and posterior cortical nuclei, the periamygdaloid cortex, and the amygdalohippocampal area in the rat. Analysis of immunohistochemically processed sections reveal that the heaviest projections to the claustrum originate in the magnocellular division of the basal nucleus. The projection is moderate in density and mainly terminates in the dorsal aspect of the anterior part of the claustrum. Light projections from the parvicellular and intermediate divisions of the basal nucleus terminate in the same region, whereas light projections from the accessory basal nucleus and the lateral division of the amygdalohippocampal area innervate the caudal part of the claustrum. The most substantial projections from the amygdala to the endopiriform nucleus originate in the lateral division of the amygdalohippocampal area. These projections terminate in the central and caudal parts of the endopiriform nucleus. Lighter projections originate in the anterior and posterior cortical nuclei, the periamygdaloid cortex, the medial division of the amygdalohippocampal area, and the accessory basal nucleus. These data provide an anatomic basis for recent functional studies demonstrating that the claustrum and the endopiriform nucleus are strategically located to synchronize and spread epileptiform activity from the amygdala to the other brain regions. These topographically organized pathways also provide a route by means of which the claustrum and the endopiriform nucleus have access to inputs from the amygdaloid networks that process emotionally significant information.

Effects of cue exposure on brain glucose utilization 8 days after repeated cocaine administration

Relapse to cocaine use may involve exposure to cocaine-associated environmental cues. The present experiment tested the hypothesis that basal local cerebral metabolic rate for glucose (LCMR(glu)), as measured by the 2-deoxy-D-[l-(14)C]glucose (2-DG) autoradiography, would change in the presence of cocaine conditioned cues at 8 days after the last of seven daily cocaine injections (30 mg/kg). This dose regimen results in sensitization to the locomotor effects of cocaine. Cocaine was administered to two groups of rats while saline was administered to a third. In the conditioned group, the rats were placed into the 2-DG experimental chamber immediately after cocaine injection. Rats in the non-conditioned group were placed into their home cage after cocaine administration. A control group received only saline. The 2-DG experiment was conducted in non-drugged animals 8 days after treatment completion. The interaction between treatment status and brain region was significant. Mean basal LCMR(glu) was significantly lower in 12 brain regions in the conditioned group as compared to the control group, but was significantly lower in only four areas in the non-conditioned group. Regions in which there were significant changes in the conditioned group included the basolateral amygdala, subiculum, medial thalamus, lateral habenula and the substantia nigra pars compacta. LCMR(glu) was significantly reduced in the ventrolateral orbital cortex and rostral nucleus accumbens in both experimental groups. These findings indicate that repeated cocaine administration can cause protracted decreases in basal LCMR(glu), decreases that are more widespread in the brain during exposure to cocaine-associated cues.

The intralaminar and midline nuclei of the thalamus. Anatomical and functional evidence for participation in processes of arousal and awareness

The thalamic midline and intralaminar nuclei, long thought to be a non-specific arousing system in the brain, have been shown to be involved in separate and specific brain functions, such as specific cognitive, sensory and motor functions. Fundamental to the participation of the midline and intralaminar nuclei in such diverse functions seems to be a role in awareness. It is unknown whether the midline and intralaminar nuclei, together often referred to as the 'non-specific' nuclei of the thalamus, act together or whether each nucleus is involved idiosyncratically in separate circuits underlying cortical processes. Detailed knowledge of the connectivity of each of these nuclei is needed to judge the nature of their contribution to cortical functioning. The present account provides an overview of the results of neuroanatomical tracing studies on the connections of the individual intralaminar and midline thalamic nuclei in the rat, that have been performed over the past decade in our laboratory. The results are discussed together with those reported by other laboratories, and with those obtained in other species. On the basis of the patterns of the afferent and efferent projections, we conclude that the midline and intralaminar thalamic nuclei can be clustered into four groups. Each of the groups can be shown to have its own set of target and input structures, both cortically and subcortically. These anatomical relationships, in combination with functional studies in animals and in humans, lead us to propose that the midline and intralaminar nuclei as a whole play a role in awareness, with each of the groups subserving a role in a different aspect of awareness. The following groups can be discerned: (1) a dorsal group, consisting of the paraventricular, parataenial and intermediodorsal nuclei, involved in viscero-limbic functions; (2) a lateral group, comprising the central lateral and paracentral nuclei and the anterior part of the central medial nucleus, involved in cognitive functions; (3) a ventral group, made up of the reuniens and rhomboid nucleus and the posterior part of the central medial nucleus, involved in multimodal sensory processing; (4) a posterior group, consisting of the centre médian and parafascicular nuclei, involved in limbic motor functions.

Amygdaloid projections to ventromedial striatal subterritories in the primate

The ventral striatum is the part of the striatum associated with reward and goal-directed behaviors, which are mediated in part by inputs from the amygdala. The ventral striatum is divided into 'shell' and 'core' subterritories which have different connectional, histochemical and pharmacological properties. Behavioral studies also indicate that subterritories of the ventral striatum are differentially involved in specific goal-directed behaviors. The amygdala is a heterogeneous structure which has multiple nuclei involved in processing emotional information. While the existence of an amygdalostriatal pathway has long been established, the relationship between amygdaloid afferents and specific subterritories of the ventral striatum is not known. In this study we operationally defined the ventromedial striatum as the region receiving cortical inputs primarily from the orbital and medial prefrontal cortex. We placed retrograde tracer injections into subregions of the ventromedial striatum of macaques monkeys to determine the relative contribution of specific amygdaloid inputs to each region. Calbindin-D28k immunostaining was used to further define the shell subterritory of the ventromedial striatum. Based on these definitions, the amygdala innervates the entire ventromedial striatum, and has few to no inputs to the central striatum. The basal and accessory basal nuclei are the major source of input to the ventromedial striatum, innervating both the shell and ventromedial striatum outside the shell. However, a restricted portion of the dorsomedial shell receives few basal nucleus inputs. Afferent inputs from the basal nucleus subdivisions are arranged such that the parvicellular subdivision projects mainly to the ventral shell and core, and the magnocellular subdivision targets the ventral shell and ventromedial putamen. In contrast, the intermediate subdivision of the basal nucleus projects broadly across the ventromedial striatum avoiding only the dorsomedial shell. The shell has a specific set of connections derived from the medial part of the central nucleus and periamygdaloid cortex. Within the shell, the dorsomedial region is distinguished by additional inputs from the medial nucleus. The ventromedial caudate nucleus forms a unique transition zone with the shell, based on inputs from the periamygdaloid cortex. Together, these results indicate that subterritories of the ventromedial striatum are differentially modulated by amygdaloid nuclei which play roles in processing olfactory, visual/gustatory, multimodal sensory, and 'drive'-related stimuli.

Hippocampal and prefrontal cortical inputs monosynaptically converge with individual projection neurons of the nucleus accumbens

Afferents to the nucleus accumbens from different sources innervate specific areas of the central "core" and peripheral "shell" and are related to each other, at the light microscopical level, in an intricate overlapping and nonoverlapping way. This lack of homogeneity suggests that this region consists of circuits involving emsembles of neurons modulated by specific sets of convergent afferent inputs and abnormal regulation of such ensembles has been implicated in mental disorders. Early extracellular studies suggested that individual Acb neurons might respond to activation of afferents from more than one excitatory input: More recent studies of hippocampal and amygdalar or prefrontal cortical afferents suggest that hippocampal afferents gate the input from the prefrontal cortex or amygdala. Electrophysiological evidence for convergence of excitatory afferents in the Acb is strong and suggests that these pathways are monosynaptic. Nevertheless, this convergence has proved difficult to demonstrate anatomically as a result of the spatial distribution of the afferent inputs on the dendritic tree of the target neurons. To establish whether individual accumbens neurons receive monosynaptic input from pairs of afferents, one projection was labelled anterogradely with Phaseolus vulgaris leucoagglutinin and the second with biotinylated dextran amine (BDA) with Vector slate grey and 3,3'-diaminobenzidine tetrahydrochloride as the chromagens. Accumbens neurons possibly postsynaptic to these afferents, labelled by an in vivo focal injection of BDA, were examined using correlated light and electron microscopy to establish the proximal-distal distribution of labelled afferent synaptic inputs on their dendritic arbours. Individual cells were shown to receive monosynaptic afferent input from both ventral subiculum and prefrontal cortex, providing an anatomical framework for the hippocampal gating of other limbic inputs to the accumbens.

Dissociable effects of lidocaine inactivation of the rostral and caudal basolateral amygdala on the maintenance and reinstatement of cocaine-seeking behavior in rats

Cocaine addiction is a chronically relapsing brain disease, but its neural basis is not yet well understood. Clinical reports underscore the possible importance of associative processes for regulating at least some aspects of cocaine addiction. The present study reports the effects of reversible lidocaine-induced inactivation of rostral basolateral amygdala (rBLA) and caudal basolateral amygdala (cBLA) regions on the maintenance and reinstatement of drug-seeking behavior in rats trained to self-administer 1 mg/kg cocaine under a second order schedule of drug delivery. Both regions of the basolateral amygdala were investigated because they have dissociable effects on cognitive task performance. Results demonstrated that after self-administration training and a period of extinction and abstinence, lidocaine inactivation of the rBLA and cBLA attenuated the reinstatement of drug-seeking behavior induced by cocaine-associated cues examined in conjunction with a single priming injection of cocaine. In contrast, lidocaine inactivation of only the rBLA blocked reinstatement of drug-seeking behavior induced by cocaine-associated cues examined alone. Additional differences were shown during cocaine maintenance testing where inactivation of only the cBLA attenuated drug-seeking behavior. Drug intake was not altered. Thus, the rBLA and cBLA appear to selectively and dissociably regulate drug-seeking behavior under conditions of cocaine abstinence (cue-induced reinstatement) and repeated cocaine use (maintenance), respectively. These findings suggest that the basolateral amygdala may be more functionally heterogeneous than commonly thought for regulating drug-seeking behavior. The basis for this dissociation might be related to neuroanatomical connections of the rBLA and cBLA with segregated, but parallel, corticostriatalpallidothalamic circuits.

Neonatal development of projections from the basolateral amygdala to prefrontal, striatal, and thalamic structures in the rat

Recently, an animal model for neurodevelopmental disorders has been developed. In this model, the effects of an early neonatal (postnatal day 7 [Pd 7]) basolateral amygdala lesion are compared with the effects of a lesion later in life (Pd 21). The reported data indicate that amygdala damage at a specific point early in life results in enduring behavioral disturbances that become more manifest after puberty, for example, only an early lesion resulted in a disruption of the prepulse inhibition, which is also observed in people suffering from schizophrenia. Accordingly, it was postulated that the early damage may affect the neuroanatomic and neurochemical organization and functioning of other brain structures. This was studied by use of the anterograde tracers biotinylated dextran amine and Phaseolus vulgaris-leucoagglutinin. At neonatal days 7, 9, 11, 13, and 26, amygdaloid fibers were in particular present in the mediodorsal thalamus (MDT), nucleus accumbens (Acb), and prefrontal cortex (PFC). The development of the topography of the amygdaloid innervation, however, differed markedly for the MDT and Acb compared with the PFC. For the MDT and Acb, no major changes in innervation were observed between Pd 7 and Pd 26, whereas the innervation of the PFC reorganized from a neonatal diffuse (Pd 7 and 9) to a restricted pattern (Pd 11, 13, and 26). In addition, the innervation changed to an adult-like bilaminar pattern. These data provide information on the circuitry that may be involved in the aberrant neurodevelopment of neonatally amygdala-lesioned rats, which have been proposed as an animal model for neurodevelopmental psychopathological disorders.

In vivo characterization of basal amino acid levels in subregions of the rat nucleus accumbens: effect of a dopamine D(3)/D(2) agonist

Recent evidence demonstrates that two subdivisions of the nucleus accumbens, the dorsolateral core and the ventromedial shell can be distinguished by morphological, immunohistochemical and chemoarchitectural differences. In the present study, we measured basal levels of amino acids in microdialysates from both the shell and core subterritories of the nucleus accumbens in freely moving rats using HPLC with fluorescence detection. The effect of the dopamine D(3)/D(2) receptor agonist quinelorane (30 microg/kg s.c.) was then investigated in both subregions. With the exception of glutamate, histidine, and serine, which showed similar levels in both subterritories, alanine, arginine, aspartate, gamma-aminobutyric acid, glutamine, and tyrosine were significantly higher in the shell compared with the core. In contrast, taurine levels were significantly lower in the shell than in the core. A particularly striking difference across subregions of the nucleus accumbens was observed for basal GABA levels with a shell/core ratio of 18.5. Among all the amino acids investigated in the present study, quinelorane selectively decreased dialysate GABA levels in the core subregion of the nucleus accumbens. The results of the present study point to specific profiles of both shell and core in terms of: (1) basal chemical neuroanatomical markers for amino acids; and (2) GABAergic response to the DA D(3)/D(2) agonist quinelorane.

Pharmacology and behavioral pharmacology of the mesocortical dopamine system

The prefrontal cortex (PFC) has long been known to be involved in the mediation of complex behavioral responses. Considerable research efforts are directed towards refining the knowledge about the function of this brain area and the role it plays in cognitive performance and behavioral output. In the first part, this review provides, from a pharmacological perspective, an overview of anatomical, electrophysiological and neurochemical aspects of the function of the PFC, with an emphasis on the mesocortical dopamine system. Anatomy of the mesocortical system, basic physiological and pharmacological properties of neurotransmission within the PFC, and interactions between dopamine and glutamate as well as other transmitters within the mesocorticolimbic circuit are included. The coverage of these data is largely restricted to what is relevant for the second part of the review which focuses on behavioral studies that have examined the role of the PFC in a variety of phenomena, behaviors and paradigms. These include reward and addiction, locomotor activity and sensitization, learning, cognition, and schizophrenia. Although the focus of this review is on the mesocortical dopamine system, given the intricate interactions of dopamine with other transmitter systems within the PFC and the importance of the PFC as a source of glutamate in subcortical areas, these aspects are also covered in some detail where appropriate. Naturally, a topic as complex as this cannot be covered comprehensively in its entirety. Therefore this review is largely limited to data derived from studies using rats, and it is also specifically restricted to data concerning the medial PFC (mPFC). Since in several fields of research the findings concerning the function or role of the mPFC are relatively inconsistent, the question is addressed whether these inconsistencies might, at least in part, be related to the anatomical and functional heterogeneity of this brain area.

Autoregulation of dopamine synthesis in subregions of the rat nucleus accumbens

The discovery of a core-shell dichotomy within the nucleus accumbens has opened new lines of investigation into the neuronal basis of psychiatric disorders and drug dependence. In the present study, the autoregulation of dopamine synthesis in subdivisions of the rat nucleus accumbens was examined. We measured the accumulation of L-3,4-dihydroxyphenylalanine (DOPA) after the inhibition of aromatic L-amino acid decarboxylase with 3-hydroxylbenzylhydrazine (NSD-1015, 100 mg kg(-1)) as an in vivo index of dopamine synthesis. The effect of the dopamine D(1)/D(2) receptor agonist apomorphine (0, 20, 100, 500 microgram kg(-1)) and the dopamine D(2)/D(3) receptor agonist quinpirole (0, 20, 100, 500 microgram kg(-1)) on dopamine synthesis was determined in the dorsolateral core, ventromedial shell, and rostral pole of the nucleus accumbens. DOPA accumulation was also measured in the frontal cortex, olfactory tubercle, and caudate nucleus of the same rats for comparative purposes. The results show that the three sectors of the nucleus accumbens had similar basal levels of DOPA. Both apomorphine and quinpirole produced a decrease in the dopamine synthesis rate in all brain regions examined. In general, the dopamine D(2)/D(3) receptor agonist quinpirole produced a significantly greater decrease in DOPA accumulation than the dopamine D(1)/D(2) receptor agonist apomorphine. Within the nucleus accumbens, we found no core-shell differences in the agonist-induced suppression of dopamine synthesis, but the rostral pole was less sensitive to the highest dose of both dopamine agonists. These results suggest that differences in dopamine function between the core and shell might not involve region-specific differences in the receptor-mediated autoregulation of dopamine neurotransmission. Moreover, the blunted effect of dopamine agonists in the rostral pole illustrates that this region of the accumbens is functionally distinct, possibly due to a lower dopamine receptor reserve when compared to the core and shell.

The effects of acute antipsychotic drug administration on the neurotensin system of the developing rat brain

The effects of antipsychotic drugs on the neurotensin (NT) system have been well characterized in adult male animals. There is considerable evidence that the NT system undergoes distinct age-related changes during development of the rat brain. This observation in conjunction with antipsychotic pharmacotherapy in children and breast feeding women led us to characterize the effects of antipsychotic drug administration in neonatal rats. The effects of a single subcutaneous injection of haloperidol (2.0 mg/kg) on the developing NT system were determined between postnatal days 10 and 21. Haloperidol significantly increased NT/neuromedin N (NT/NN) mRNA expression and NT concentrations in the caudate/putamen as early as postnatal day 10. Haloperidol did not increase NT/NN mRNA expression in the nucleus accumbens until postnatal day 15 and did not increase NT concentrations in this brain region until postnatal day 21. These results demonstrate that there is a critical time point in development before which the NT system does not respond to antipsychotic drug administration in the same manner as the mature rat.

Enhanced intake of high-fat food following striatal mu-opioid stimulation: microinjection mapping and fos expression

Our previous studies have shown that stimulation of mu-opioid receptors within the nucleus accumbens preferentially enhances intake of palatable food containing sucrose and fat; thus, opioids in this brain area may mediate the rewarding characteristics of food by modulating taste and macronutrient preference. The present study was designed to further explore the nature of the involvement of striatal opioids in feeding behavior, such as the location of sensitive subregions of the ventral striatum and the brain neural circuits involved in opioid-mediated hyperphagia. In Experiment 1, we conducted a microinfusion mapping study of feeding behavior by microinfusion of the mu receptor agonist, D-Ala(2),NMe-Phe(4), Glyol(5)-enkephalin (0, 0.025 and 0.25 microg/0.5 microl per side; equivalent to 0, 0.04 and 0.40 nmol/0.5 microl per side), into several striatal subregions. In Experiment 2, detection of the expression of the immediate early gene, c-fos, was used to examine brain areas activated following intra-striatal microinfusion of D-Ala(2), NMe-Phe(4),Glyol(5)-enkephalin. The microinjection mapping study demonstrated a broad anatomical gradient within the striatum, with sensitivity highest in relatively more lateral and ventral regions of the striatum (ventrolateral striatum, lateral shell and core). The Fos mapping study demonstrated that circuitry including hypothalamic areas, the ventral tegmental area, the substantia nigra and the nucleus of the solitary tract was recruited by stimulation of mu receptors within the nucleus accumbens. A similar pattern was observed following stimulation of mu receptors in the dorsal striatum; however, the extent of activation was much smaller in magnitude. These results suggest that the role of mu receptors within the striatum in palatable feeding primarily involves ventral and lateral regions. Moreover, the pattern of activation in hypothalamic, midbrain and gustatory-visceral relay areas suggests that striatal mu receptors may participate in integrating motivational, metabolic and autonomic aspects of ingestive behavior.

Specific amygdaloid nuclei are involved in suppression or propagation of epileptiform activity during transition stage between oral automatisms and generalized clonic seizures

Kindling is a model of the neural plasticity that occurs following stimulation to the brain, which can result in epileptogenesis. The amygdala (Am), one of the most sensitive structures from which to induce electrical kindling, is comprised of distinct nuclei that possess differences in threshold for seizure initiation, unique cellular and molecular morphology, and specific neuroanatomical connections within the amygdala and, to other cortical and subcortical brain structures. The aim of this study was to map the spread of epileptiform activity throughout the ipsilateral and contralateral hemispheres during the transition stage between oral automatisms and generalized clonic seizures, by measuring changes in mRNA expression for c-fos, NGFI-A, and BDNF. The stimulating electrode was implanted in either the basolateral (BL) or the lateral (CeL) or medial (CeM) subdivisions of the central nucleus of the amygdala. The rats were kindled once daily using afterdischarge-threshold electrical stimulation until the first forelimb clonic seizure was induced. They were sacrificed 30 min later, and their brains were prepared for in situ hybridization to measure mRNA expression of c-fos, NGFI-A and BDNF. The results demonstrate that: (1) the threshold to elicit an afterdischarge from the BL was lower than that of either the medial (CeM) or lateral (CeL) subdivisions of the Ce, which did not differ from each other; (2) the patterns of mRNA expression for c-fos, NGFI-A and BDNF were highly similar to each other when the stimulation site was the BL or the CeL, and included mainly limbic cortical and subcortical areas ipsilateral to the electrode; (3) c-fos was the only probe to be expressed in the contralateral hemisphere following the first motor seizure, and the pattern of its expression reflected a subset of structures recruited in the ipsilateral hemisphere including the claustrum, insular and perirhinal cortices; (4) unexpectedly, stimulation of the CeM elicited seizures and afterdischarges of shorter duration than those evoked by stimulation of the BL or CeL, and failed to increase mRNA expression for any of the probes in the hippocampus or in the contralateral hemisphere. A neuroanatomical model of Am-induced seizure propagation is proposed suggesting that the Claust-Ins-PRh play a pivotal role during the transition between oral automatisms and generalized clonic convulsions.

Electrical stimulation of the insular cortex induces flavor-preferences in rats

The present study examined the role of the Insular cortex (IC) in flavor-guided behavior. For that purpose, a flavored stimulus was paired with delayed electrical stimulation of this region. In addition, a standard operant task explored the involvement of the IC in a prefrontal self-stimulation reward-circuit. The results showed strong preferences for the flavored stimulus previously paired to the Insular stimulation, in a discriminative free choice test. However, the operant task revealed a failure to induce IC self-stimulation, suggesting that flavor preferences elicited by electrical stimulation of the IC are not due to activation of the prefrontal-stimulation reward circuit. These results are discussed in terms of the Insular Cortex as critical in processing visceral stimulus, hedonic valence and/or food-reward incentive learning.

Specificity of amygdalostriatal interactions in the involvement of mesencephalic dopaminergic neurons in affective perception

We have recently shown that dopaminergic responses to an attractive or an aversive stimulus were respectively increased and decreased in the core part of the nucleus accumbens and the ventromedial dorsal striatum. By contrast, increases in dopaminergic responses were obtained in the shell part of the nucleus accumbens with stimuli of both affective values. In addition, the involvement of the basolateral amygdala in affective processes has been reported by several authors. Anatomo-functional relationships between the basolateral amygdala and striatal structures have also been described. Thus, in the present work we studied the regulation by the basolateral amygdala of affective dopaminergic responses in the two parts of the nucleus accumbens (core and shell) and the ventromedial dorsal striatum. More precisely, variations in extracellular levels of dopamine induced by an attractive or an aversive olfactory stimulus were studied using in vivo voltammetry in freely moving rats. Changes in dopamine levels in the three left striatal regions were measured after functional blockade of the ipsilateral basolateral amygdala with tetrodotoxin. Changes in place attraction or aversion toward the stimulus were studied in parallel to dopamine variations. The results obtained suggest a specific regulation of affective dopaminergic responses in the two parts of the nucleus accumbens by the basolateral amygdala and a lack of influence of the basolateral amygdala on the ventromedial dorsal striatum. The results suggest that attraction or aversion toward a stimulus are correlated with dopamine variations in the core of the nucleus accumbens and that the basolateral amygdala controls affective behavioural responses. These data may provide new insights into the pathophysiology of schizophrenic psychoses.

An integrative neuroanatomical perspective on some subcortical substrates of adaptive responding with emphasis on the nucleus accumbens

Neuroanatomical substrates associated in the literature with adaptive responding are discussed, with a focus on the nucleus accumbens. While it is emphasized that the accumbens exhibits multiple levels of complex organization, a fairly complete list of brief descriptions of recent studies devoted specifically to the accumbens shell and core subterritories is presented in tabular format. The distinct patterns of connectivity of the accumbens core and shell and structures related to them by connections are described. Multiple inputs, outputs and abundant reciprocity of connections within the ventral parts of the basal ganglia are emphasized and the implications for "through-put" of impulses is considered. It is noted, at least on neuroanatomical grounds, that there is ample reason to expect feed forward processing from shell and structures with which it is associated to core and structures with which it is associated. Furthermore, the potential for additional feed forward processing involving several forebrain functional anatomical systems, inlcuding the ventral striatopallidum, extended amygdala and magnocellular basal forebrain complex is considered. It is intended that from the considerations recorded here a conceptual framework will begin to emerge that is amenable to further experimental substantiation as regards how multiple basal forebrain systems and the cortices to which they are related by connections work together to fashion a unitary object--the adaptive response.

Functional specificity of ventral striatal compartments in appetitive behaviors

The nucleus accumbens and its associated circuitry subserve behaviors linked to natural or biological rewards, such as feeding, drinking, sex, exploration, and appetitive learning. We have investigated the functional role of neurotransmitter and intracellular transduction mechanisms in behaviors subserved by the core and shell subsystems within the accumbens. Local infusion of the selective NMDA antagonist, AP-5, into the accumbens core, but not the shell, completely blocked acquisition of a bar-press response for food in hungry rats. This effect was apparent only when infused during the early stages of learning. We have also recently shown that infusion of certain protein kinase inhibitors into the core also impairs learning in the same paradigm. These results suggest that plasticity-related mechanisms within the accumbens core, involving glutamate-linked intracellular second messengers, are important for response-reinforcement learning. In contrast to the core, which primarily connects to somatic motor output systems, the shell is more intimately linked to viscero-endocrine effector systems. We have shown that both AMPA and GABA receptors within the medial shell (but not the core) are critically involved in controlling the brain's feeding pathways, via activation of the lateral hypothalamus (LH). This effect is blocked by local inhibition of the LH in double-cannulae experiments and also strongly and selectively activates Fos expression in the LH. These results provide a newly emerging picture of the differentiated functions of this forebrain region and suggest an integrated role in the elaboration of adaptive motor actions.

Functional-anatomical implications of the nucleus accumbens core and shell subterritories

The nucleus accumbens, a major part of the ventral striatum, comprises numerous subterritories and compartments, of which the core and shell appear to be dominant. Shell exhibits greater chemical neuroanatomical diversity than core and is rather directly connected to it by a robust, feed-forward, striatopallido-thalamocortico-striatal pathway. Shell and extended amygdala share afferents, but the two are distinguished by their outputs, strongly toward cortex for shell and descendent toward brain stem effector sites for extended amygdala. Shell responds independently to stimulation by excitatory amino acids and dopamine, which are more mutually permissive in the core. Accordingly, the shell responds to a broad variety of physiological and pharmacological stimuli, including psychomotor and opioid drugs. Whereas locomotion and oro-facial movements are elicitable from the shell, lesions and blockade of EAA transmission in the core reduce locomotion. It is hypothesized that core-shell has a feed-forward functional organization.

Convergence and segregation of ventral striatal inputs and outputs

The ventral striatum, which prominently includes the nucleus accumbens (Acb), is a heterogeneous area. Within the Acb of rats, a peripherally located shell and a centrally situated core can be recognized that have different connectional, neurochemical, and functional identities. Although the Acb core resembles in many respects the dorsally adjacent caudate-putamen complex in its striatal character, the Acb shell has, in addition to striatal features, a more diverse array of neurochemical characteristics, and afferent and efferent connections. Inputs and outputs of the Acb, in particular of the shell, are inhomogeneously distributed, resulting in a mosaical arrangement of concentrations of afferent fibers and terminals and clusters of output neurons. To determine the precise relationships between the distributional patterns of various afferents (e.g., from the prefrontal cortex, the basal amygdaloid complex, the hippocampal formation, and the midline/intralaminar thalamic nuclei) and efferents to the ventral pallidum and mesencephalon, neuroanatomical anterograde and retrograde tracing experiments were carried out. The results of the double anterograde, double retrograde, and anterograde/retrograde tracing experiments indicate that various parts of the shell (dorsomedial, ventromedial, ventral, and lateral) and the core (medial and lateral) have different input-output characteristics. Furthermore, within these Acb regions, various populations of neurons can be identified, arranged in a cluster-like fashion, onto which specific sets of afferents converge and that project to particular output stations, distinct from the input-output relationships of neighboring, cluster-like neuronal populations. These results support the idea that the nucleus accumbens may consist of a collection of neuronal ensembles with different input-output relationships and, presumably, different functional characteristics.

NMDA receptor blockade attenuates the haloperidol induction of Fos protein in the dorsal but not the ventral striatum

Neuroleptic blockade of dopamine receptors is known to produce an increase in the expression of Fos. This increase may be related to elevations in glutamate transmission which in turn activates N-methyl-D-aspartate (NMDA) receptors. In the present study, we examine the role of these receptors in the haloperidol-induced augmentation of Fos in the caudate-putamen and nucleus accumbens of Wistar rats. Animals were divided into four groups for each experiment and each was injected either with saline; a noncompetitive NMDA antagonist, dizocilpine maleate (MK801, 5 mg/kg); haloperidol (0.5 mg/kg); or MK801 followed by an injection of haloperidol. Fos-immunoreactive cells appear in large numbers in all parts of the striatum 3 h after the administration of haloperidol. Pretreatment with MK801 attenuates the haloperidol-induced increase in Fos in the caudate-putamen. However, antagonism of the NMDA receptor does not significantly reduce the density of Fos-immunoreactive cells in any territory of nucleus accumbens, i.e., shell, core, or rostral pole. These data suggest that haloperidol acts in an NMDA-dependent manner in the caudate-putamen, but independently in parts of nucleus accumbens traditionally considered to be targets of antipsychotic drugs.