Restricted cortical termination fields of the midline and intralaminar thalamic nuclei in the rat

Hypocretin and nicotine excite the same thalamocortical synapses in prefrontal cortex: correlation with improved attention in rat

Thalamic projections to prefrontal cortex are important for executive aspects of attention. Using two-photon imaging in prefrontal brain slices, we show that nicotine and the wakefulness neuropeptide hypocretin (orexin) excite the same identified synapses of the thalamocortical arousal pathway within the prefrontal cortex. Although it is known that attention can be improved when nicotine is infused directly into the midlayer of the prefrontal cortex in the rat, the effects of hypocretin on attention are not known. The overlap in thalamocortical synapses excited by hypocretin and nicotine and the lack of direct postsynaptic effects prompted us to compare their effects on a sustained and divided attention task in the rat. Similar to nicotine, infusions of hypocretin-2 peptide into the prefrontal cortex significantly improved accuracy under high attentional demand without effects on other performance measures. We show for the first time that hypocretin can improve attentional processes relevant to executive functions of the prefrontal cortex.

Forebrain projections of tuberoinfundibular peptide of 39 residues (TIP39)-containing subparafascicular neurons

Neurons containing tuberoinfundibular peptide of 39 residues (TIP39) constitute a rostro-caudally elongated group of cells in the posterior thalamus. These neurons are located in the rostral part of the subparafascicular nucleus and in the subparafascicular area, caudally. Projections of the caudally located TIP39 neurons have been previously identified by their disappearance following lesions. We have now mapped the projections of the rat rostral subparafascicular neurons using injections of the anterograde tracer biotinylated dextran amine and the retrograde tracer cholera toxin B subunit, and confirmed the projections from more caudal areas previously inferred from lesion studies. Neurons from both the rostral subparafascicular nucleus and the subparafascicular area project to the medial prefrontal, insular, ecto- and perirhinal cortex, nucleus of the diagonal band, septum, central and basomedial amygdaloid nuclei, fundus striati, basal forebrain, midline and intralaminar thalamic nuclei, hypothalamus, subthalamus and the periaqueductal gray. The subparafascicular area projects more densely to the amygdala and the hypothalamus. In contrast, only the rostral part of the subparafascicular nucleus projects significantly to the superficial layers of prefrontal, insular, ectorhinal and somatosensory cortical areas. Double labeling showed that anterogradely labeled fibers from the rostral part of the subparafascicular nucleus contain TIP39 in many forebrain areas, but do not in hypothalamic areas. Injections of the retrograde tracer cholera toxin B subunit into the lateral septum and the fundus striati confirmed that they were indeed target regions of both the rostral subparafascicular nucleus and the subparafascicular area. In contrast, TIP39 neurons did not project to the anterior hypothalamic nucleus. Our data provide an anatomical basis for the potential involvement of rostral subparafascicular neurons in limbic and autonomic regulation, with TIP39 cells being major subparafascicular output neurons projecting to forebrain regions.

Excitatory actions of the ventral midline thalamus (rhomboid/reuniens) on the medial prefrontal cortex in the rat

The medial prefrontal cortex (mPFC) has been associated with diverse functions including attentional processes, visceromotor activity, decision making, goal directed behavior, and working memory. The present report examined the effects of stimulation of the midline thalamus, concentrating on ventral nuclei of the midline thalamus, on evoked activity at the mPFC. The nucleus reuniens (RE) of the ventral midline thalamus is a major source of projections to the hippocampus and to the mPFC, and has been shown to exert pronounced excitatory effects on the hippocampus. No previous study has systematically examined the actions of the ventral midline thalamus on the mPFC. We showed that stimulation of the dorsal and ventral midline thalamus, but not of an intermediate region lying between them (null zone), produced short latency, large amplitude evoked potentials throughout the dorsoventral extent of the medial PFC. The largest effects were elicited with ventral midline stimulation (rhomboid/reuniens nuclei) at the ventral mPFC--the prelimbic (PL) and infralimbic (IL) cortices. Specifically, stimulation of RE produced evoked potentials (early negative component, N2) at the PL cortex at a mean latency of 22.6 msec and mean amplitude of 0.85 mV, indicative of monosynaptic effects. In addition, we showed that paired pulse stimulation of RH/RE produced strong facilitatory actions (paired pulse facilitation) at IL (83%) and PL (75%). These findings indicate that RE exerts strong direct excitatory effects on the mPFC, and coupled with the demonstration that RE produces similar actions on the hippocampus, indicates that RE is in a position to influence and possibly coordinate the activity of these two forebrain structures subserving memory.

Current source density analysis of laser heat-evoked intra-cortical field potentials in the primary somatosensory cortex of rats

The role of the primary somatosensory cortex in thermal pain perception has been established. However, the cortical circuitry that mediates the thermo-nociceptive information processing has not been elucidated. The aim of present study was to investigate the intracortical synaptic currents in primary somatosensory cortex evoked by short laser pulses and to determine their transmission pathway. Noxious CO2 laser pulse stimuli or innocuous electrical and mechanical stimuli were delivered to the hind paw of halothane-anesthetized rats. Multi-channel field potentials were recorded simultaneously in primary somatosensory cortex and laminar-specific transmembrane currents were analyzed using a current source density method. A distinct spatial-temporal pattern of intra-cortical sink source currents was evoked by laser pulse stimuli. The amplitude of the early component was graded by laser energy output and influenced by contralateral signals, whereas the late components were not intensity-dependent and exhibited bilateral excitation. Intra-cortical current flows revealed that synaptic activation occurred initially at layers IV and VI separately and then was relayed transynaptically to the more superficial and the deeper layers. Latency, amplitude and intracortical distributions of the activated intra-cortical currents evoked by noxious stimuli differed significantly from those evoked by innocuous stimuli. Conduction velocity data together with the results of tetrodotoxin, capsaicin and morphine treatments indicated that the early and late components were mediated separately by A-delta and C fibers. Our results suggest that large and small diameter thermal nociceptive afferents generated laminar-specific intracortical synaptic currents in primary somatosensory cortex and that these excitatory synaptic currents were conveyed separately by lateral and medial thalamic nuclei.

Afferent connections of the subparafascicular area in rat

The subparafascicular nucleus and the subparafascicular area are the major sites of synthesis of the recently discovered neuropeptide, tuberoinfundibular peptide of 39 residues (TIP39). Better knowledge of the neuronal inputs to the subparafascicular area and nucleus will facilitate investigation of the functions of TIP39. Thus, we have injected the retrograde tracer cholera toxin B subunit into the rostral, middle, and caudal parts of the rat subparafascicular nucleus. We report that the afferent projections to the subparafascicular nucleus and area include the medial prefrontal, insular, and ectorhinal cortex, the subiculum, the lateral septum, the anterior amygdaloid area, the medial amygdaloid nucleus, the caudal paralaminar area of the thalamus, the lateral preoptic area, the anterior, ventromedial, and posterior hypothalamic nuclei, the dorsal premamillary nucleus, the zona incerta and Forel's fields, the periaqueductal gray, the deep layers of the superior colliculus, cortical layers of the inferior colliculus, the cuneiform nucleus, the medial paralemniscal nucleus, and the parabrachial nuclei. Most of these regions project to all parts of the subparafascicular nucleus. However, the magnocellular subparafascicular neurons, which occupy the middle part of the subparafascicular nucleus, may not receive projections from the medial prefrontal and insular cortex, the medial amygdaloid nucleus, the lateral preoptic area, and the parabrachial nuclei. In addition, double labeling of cholera toxin B subunit and TIP39 revealed a remarkable similarity between input regions of the subparafascicular area and the brain TIP39 system. Neurons within regions that contain TIP39 cell bodies as well as regions that contain TIP39 fibers project to the subparafascicular area. Overall, the afferent connections of the subparafascicular nucleus and area suggest its involvement in central reproductive, visceral, nociceptive, and auditory regulation.

Long-term functional consequences of quinolinic acid striatal lesions and their alteration following an addition of a globus pallidus lesion assessed using pharmacological magnetic resonance imaging

The present study tested the hypothesis that lesion to the rat globus pallidus (GP) can "normalize" the functioning of the basal ganglia-thalamocortical circuits in striatal-lesioned rats by assessing the functional connectivity of these regions using functional magnetic resonance imaging (fMRI). Changes in brain activation following systemic administration of amphetamine were assessed in (1) rats sustaining a unilateral lesion to the striatum, (2) rats sustaining a combined striatal and pallidal lesion, and (3) control rats. Striatal-lesioned rats showed attenuated cortical activation following amphetamine administration and lower correlations between the responses to amphetamine in different brain regions compared to control rats. Although the addition of an excitotoxic GP lesion failed to prevent striatal lesion-induced attenuation of cortical activation by amphetamine, it was effective in "normalizing" the correlations between the responses to amphetamine in the different areas. These results suggest that, although the GP lesion is ineffective in correcting the global changes in activity caused by the striatal lesion, it may have the capacity to partially restore alterations in functional connectivity resulting from the striatal lesion. These results are further discussed in view of our previous demonstration that lesions to the GP can reverse several behavioral deficits produced by a striatal lesion.

Dissociable memory effects after medial thalamus lesions in the rat

Variable neuropathology in cases of diencephalic amnesia has led to uncertainty in identifying key thalamic nuclei and their potential role in learning and memory. Based on the principal neural connections of the medial thalamus, the current study tested the hypothesis that different aggregates of thalamic nuclei contribute to separate memory systems. Lesions of the anterior thalamic aggregate (AT), which comprises the anterodorsal, anteromedial and anteroventral nuclei produced substantial deficits in both working and reference spatial memory in a radial arm maze task in rats, supporting the view that the AT is an integral part of a hippocampal memory system. Lesions to the lateral thalamic aggregate (LT), which comprises the intralaminar nuclei (centrolateral, paracentral and rostral central medial nuclei) and lateral mediodorsal thalamic nuclei (lateral and paralamellar nuclei) produced a mild working memory impairment only, while lesions to the posteromedial thalamic aggregate (MT), which comprises the central and medial mediodorsal thalamic nuclei and the intermediodorsal nucleus had no effect on radial arm maze performance. In contrast, only MT lesions impaired learning associated with memory for reward value, consistent with the idea that the MT contributes to an amygdala memory system. Compared with chance discrimination, the control and AT groups, but not MT or LT groups, showed evidence for temporal order memory for two recently presented objects; all groups showed intact object recognition for novel vs. familiar objects. These new dissociations show that different medial thalamic aggregates participate in multiple memory systems and reinforce the idea that memory deficits in diencephalic amnesics may vary as a function of the relative involvement of different thalamic regions.

Intrinsic connections of the cingulate cortex in the rat suggest the existence of multiple functionally segregated networks

The cingulate cortex is a functionally and morphologically heterogeneous cortical area comprising a number of interconnected subregions. To date, the exact anatomy of intracingulate connections has not been studied in detail. In the present study we aimed to determine the topographical and laminar characteristics of intrinsic cingulate connections in the rat, using the anterograde tracers Phaseolus vulgaris-leucoagglutinin and biotinylated dextran amine. For assessment of these data we further refined and compared the existing cytoarchitectonic descriptions of the two major cingulate constituents, the anterior cingulate and retrosplenial cortices. The results of this study demonstrate that rostral areas, i.e. the infralimbic and prelimbic cortices and the rostral one third of the dorsal anterior cingulate cortex are primarily interconnected with each other and not with other cingulate areas. The caudal two thirds of the dorsal anterior cingulate cortex project to the caudal part of the ventral anterior cingulate cortex, whereas the entire ventral anterior cingulate cortex projects to only the mid-rostro-caudal part of the dorsal anterior cingulate cortex. Dense reciprocal connections exist between the remaining, i.e. the supracallosal parts of the anterior cingulate and retrosplenial cortices with a general rostro-caudal topography, in the sense that the rostral part of the anterior cingulate cortex and caudal part of the retrosplenial cortex are interconnected and the same holds true for the caudal part of the anterior cingulate cortex and rostral part of the retrosplenial cortex. This topographical pattern of intracingulate connections relates to the results of several functional studies, suggesting that specific cingulate functions depend on a number of interconnected cingulate subregions. Through their intricate associational connections, these subregions form functionally segregated networks.

Retinal projections to the midline and intralaminar thalamic nuclei in the common marmoset (Callithrix jacchus)

In this study, we report the identification of a hitherto not reported direct retinal projection to midline and intralaminar thalamic nuclei in the marmoset brain. After unilateral intravitreal injections of cholera toxin subunit B (CTb), anterogradely transported CTb-immunoreactive fibers and presumptive terminals were seen in the following thalamic midline nuclei: paraventricular, rhomboid, interanteromedial, and reuniens, and thalamic intralaminar nuclei: central medial, central lateral, central dorsal, and parafascicular. Studies employing sensitive tracers in other primate species are needed in order to verify the possible universality of these projections. Some of the possible functional correlates of the present data are briefly discussed. The present results may contribute to the elucidation of the anatomical substrate of the functionally demonstrated involvement of this midline/intralaminar thalamic nuclear complex in several domains that include arousal and awareness, besides specific cognitive, sensory, and motor functions.

Single-axon tracing and three-dimensional reconstruction of centre median-parafascicular thalamic neurons in primates

The axonal projections from the centre median (CM)/parafascicular (Pf) thalamic complex in squirrel monkeys were studied after microiontophoretic injections of biotinylated dextran amine under electrophysiological guidance. A total of 29 axons connected to their parent cell body were entirely reconstructed from serial sections with a camera lucida. Our investigation shows that the CM and Pf nuclei in primates comprise three types of projection neurons: (1) neurons that innervate densely and focally the striatum; (2) neurons that arborize diffusely in the cerebral cortex; and (3) neurons that innervate both striatum and cerebral cortex. Striatal innervation of CM origin consists of dense clusters of axon terminals exhibiting pedunculated varicosities and forming oblique bands in the dorsolateral sector of putamen (sensorimotor striatal territory). The same type of striatal innervation occurs in the head of caudate nucleus (associative striatal territory) in cases of Pf-labeled neurons. The CM neurons that target cerebral cortex arborize principally in motor and premotor areas, whereas Pf neurons innervate chiefly prefrontal areas. Cortical innervation from both nuclei is much more profuse in layers V and VI than in layer I. Our three-dimensional reconstruction studies show that dendritic and axonal arborizations of CM neurons extend essentially along the sagittal plane. These results revealed that, in contrast to rodents where virtually all Pf neurons project to both striatum and cortex, the primate CM/Pf complex harbors several types of highly patterned projection neurons. As such, this complex might be considered as an integral part of the widely distributed basal ganglia neuronal system.

Vglut2 afferents to the medial prefrontal and primary somatosensory cortices: a combined retrograde tracing in situ hybridization study [corrected]

Glutamate transmission is critical for controlling cortical activity, but the specific contribution of the different isoforms of vesicular glutamate transporters in subcortical pathways to the neocortex is largely unknown. To determine the distribution and neocortical projections of vesicular glutamate transporter2 (Vglut2)-containing neurons, we used in situ hybridization and injections of the retrograde tracer Fluoro-Gold into the medial prefrontal and primary somatosensory cortices. The thalamus contains the majority of Vglut2 cells projecting to the neocortex (approximately 90% for the medial prefrontal cortex and 96% for the primary somatosensory cortex) followed by the hypothalamus and basal forebrain, the claustrum, and the brainstem. There are significantly more Vglut2 neurons projecting to the medial prefrontal cortex than to the primary somatosensory cortex. The medial prefrontal cortex also receives a higher percentage of Vglut2 projection from the hypothalamus than the primary somatosensory cortex. About 50% of thalamic Vglut2 projection to the medial prefrontal cortex and as much as 80% of the thalamic projection to primary somatosensory cortex originate in various relay thalamic nuclei. The remainder arise from different midline and intralaminar nuclei traditionally thought to provide nonspecific or diffuse projection to the cortex. The extrathalamic Vglut2 corticopetal projections, together with the thalamic intralaminar-midline Vglut2 corticopetal projections, may participate in diffuse activation of the neocortex.

Degenerative neuronal changes in the rat thalamus induced by status epilepticus at different developmental stages

SE was induced in Wistar rats at post-natal (P) days 12, 15, 18, 21, and 25 to determine distribution and severity of thalamic damage in relation to time after SE. Six different intervals from 4 h up to 1 week were studied using Fluoro-Jade B (FJB) staining. Severity of damage was semi-quantified for every age-and-interval group. Distribution of neuronal damage within various thalamic nuclei was mapped by a computer-aided digitizing system. A consistent neuronal damage occurred in functionally heterogenous thalamic nuclei. Damage was found in all age groups although its extension and time course as well as the number of involved thalamic nuclei varied. Number of injured thalamic nuclei rapidly increased with age on SE-onset. In P12 group, degenerating neurons were consistently seen in the mediodorsal and lateral dorsal thalamic nuclei. Since P15, neurodegeneration was observed additionally in midline, ventral and caudal thalamic nuclei (visual and auditory thalamic nuclei), in the lateral posterior and in the reticular nucleus. In P21 and P25 animals, the majority of thalamic nuclei exhibited marked neuronal damage. Nuclei with a small number (anterior and intralaminar) or no FJB-positive neurons (the ventral nucleus of the lateral geniculate body) were exceptional. The pattern of thalamic damage is age-specific; its extent and severity increases with age.

Distribution of the NMDA receptor NR3A subunit in the adult pig-tail macaque brain

The NMDA subtype of glutamate receptors are heteromeric complexes comprised of multiple subunits encoded by at least seven different genes (NR1, NR2A-2D and NR3A-3B), and differential expression of these subunits alters the pharmacological and electrophysiological properties of NMDA receptors. NR3A is a recently identified unique modulatory subunit that decreases NMDA receptor current and calcium influx. In rodents, NR3A is developmentally expressed, displaying robust expression early in development that declines with age, reaching low levels in the adult brain. A distinct and highly selective pattern of expression is observed in the developing and mature rodent brain, suggesting that NR3A may play a very specific role in NMDA receptor-mediated processes. NR3A expression in other species, however, is unknown. Therefore, we examined the expression of NR3A mRNA and protein in the adult macaque brain. Our results indicate that NR3A mRNA is expressed throughout much of the adult primate brain, and at high levels in specific brain regions including the neocortex, substantia nigra par compacta and cerebellum, as well as select areas of the hippocampus, amygdala, thalamus and hypothalamus. Western blot analysis reflects that this protein is translated and expressed in multiple brain regions. In contrast to the rat mRNA, our results suggest that NR3A transcript is widely expressed in the adult primate brain. Particular enrichment in some brain areas may reflect brain-region or circuit-specific functions for this NMDA receptor subunit.

Contributions of the anterior cingulate cortex and amygdala to pain- and fear-conditioned place avoidance in rats

The pain experience includes a sensory-discriminative and an affective-emotional component. The sensory component of pain has been extensively studied, while data about the negative affective component of pain are quite limited. The anterior cingulate cortex (ACC), and amygdala are thought to be key neural substrates underlying emotional responses. Using formalin-induced conditioned place avoidance (F-CPA) and electric foot-shock conditioned place avoidance (S-CPA) models, the present study observed the effects of bilateral excitotoxic (quinolinic acid 200 nmol/microl) lesions of the ACC and amygdala on pain and fear induced negative emotion, as well as on sensory component of pain. In the place-conditioning paradigm, both intraplantar (i.pl.) injection of formalin and electric foot-shock produced conditioned place avoidance. Excitotoxin-induced lesion of either the ACC or amygdala significantly reduced the magnitude of F-CPA. However, the decrease in the magnitude of S-CPA occurred only in the amygdala, but not ACC lesioned animals. Neither ACC nor amygdala lesion significantly changed formalin-induced acute nociceptive behaviors. These results suggest that the amygdala is involved in both pain- and fear-related negative emotion, and the ACC might play a critical role in the expression of pain-related negative emotion.

Synaptic relationships between axon terminals from the mediodorsal thalamic nucleus and gamma-aminobutyric acidergic cortical cells in the prelimbic cortex of the rat

Although the reciprocal interconnections between the prefrontal cortex and the mediodorsal nucleus of the thalamus (MD) are well known, the involvement of inhibitory cortical interneurons in the neural circuit has not been fully defined. To address this issue, we conducted three combined neuroanatomical studies on the rat brain. First, the frequency and the spatial distribution of synapses made by reconstructed dendrites of nonpyramidal neurons were identified by impregnation of cortical cells with the Golgi method and identification of thalamocortical terminals by degeneration following thalamic lesions. Terminals from MD were found to make synaptic contacts with small dendritic shafts or spines of Golgi-impregnated nonpyramidal cells with very sparse dendritic spines. Second, a combined study that used anterograde transport of Phaseolus vulgaris leucoagglutinin (PHA-L) and postembedding gamma-aminobutyric acid (GABA) immunocytochemistry indicated that PHA-L-labeled terminals from MD made synaptic junctions with GABA-immunoreactive dendritic shafts and spines. Nonlabeled dendritic spines were found to receive both axonal inputs from MD with PHA-L labelings and from GABAergic cells. In addition, synapses were found between dendritic shafts and axon terminals that were both immunoreactive for GABA. Third, synaptic connections between corticothalamic neurons that project to MD and GABAergic terminals were investigated by using wheat germ agglutinin conjugated to horseradish peroxidase and postembedding GABA immunocytochemistry. GABAergic terminals in the prelimbic cortex made symmetrical synaptic contacts with retrogradely labeled corticothalamic neurons to MD. All of the synapses were found on cell somata and thick dendritic trunks. These results provide the first demonstration of synaptic contacts in the prelimbic cortex not only between thalamocortical terminals from MD and GABAergic interneurons but also between GABAergic terminals and corticothalamic neurons that project to MD. The anatomical findings indicate that GABAergic interneurons have a modulatory influence on excitatory reverberation between MD and the prefrontal cortex.

Derivation and analysis of basic computational operations of thalamocortical circuits

Shared anatomical and physiological features of primary, secondary, tertiary, polysensory, and associational neocortical areas are used to formulate a novel extended hypothesis of thalamocortical circuit operation. A simplified anatomically based model of topographically and nontopographically projecting ("core" and "matrix") thalamic nuclei, and their differential connections with superficial, middle, and deep neocortical laminae, is described. Synapses in the model are activated and potentiated according to physiologically based rules. Features incorporated into the models include differential time courses of excitatory versus inhibitory postsynaptic potentials, differential axonal arborization of pyramidal cells versus interneurons, and different laminar afferent and projection patterns. Observation of the model's responses to static and time-varying inputs indicates that topographic "core" circuits operate to organize stored memories into natural similarity-based hierarchies, whereas diffuse "matrix" circuits give rise to efficient storage of time-varying input into retrievable sequence chains. Examination of these operations shows their relationships with well-studied algorithms for related functions, including categorization via hierarchical clustering, and sequential storage via hash- or scatter-storage. Analysis demonstrates that the derived thalamocortical algorithms exhibit desirable efficiency, scaling, and space and time cost characteristics. Implications of the hypotheses for central issues of perceptual reaction times and memory capacity are discussed. It is conjectured that the derived functions are fundamental building blocks recurrent throughout the neocortex, which, through combination, gives rise to powerful perceptual, motor, and cognitive mechanisms.

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.

Center median-parafascicular complex and pain control. Review from a neurosurgical perspective

The center median-parafascicular (CM-Pf) complex, which constitutes the major portion of the intralaminar thalamus in man, has long been known to be involved in the processing of pain under normal and pathological conditions. Yet, these 'forgotten' nuclei with their rich connectivity to other thalamic nuclei, the basal ganglia and cortical areas have received only relatively little attention over the past two decades. With regard to the recent reinterest in functional stereotactic neurosurgery as a treatment option for chronic refractory pain, the CM-Pf complex has been reconsidered as a target. This review provides a systematic overview on the current knowledge about the anatomy and connectivity of the CM-Pf complex, neurophysiological studies, and on concepts of its role in pain processing under various conditions. We also review the previous experience with ablative surgery and deep brain stimulation of the CM-Pf complex. Studies in men and experimental animals indicate that the CM-Pf complex is part of a medial pain system, which appears to be involved primarily in affective and motivational dimensions of pain. Single-unit recordings from the CM-Pf complex have shown that the activity of CM-Pf cells is modified by painful stimuli. Under pathological conditions, bursting firing patterns and altered discharge rates were found. Thalamotomies targeting at the CM-Pf complex yielded beneficial results for chronic pain, but interpretation of the results is limited. With bifocal deep brain stimulation, short-term effects of CM-Pf stimulation were superior to those of somatosensory thalamic stimulation in neuropathic pain. There is evidence, that the CM-Pf complex might also be involved in the mediation of the beneficial effects of somatosensory thalamic stimulation and periventricular grey stimulation.

Thalamic innervation of striatal and subthalamic neurons projecting to the rat entopeduncular nucleus

The present study analyses the anatomical arrangement of the projections linking the Wistar rat parafascicular thalamic nucleus (PF) and basal ganglia structures, such as the striatum and the subthalamic nucleus (STN), by using neuroanatomical tract-tracing techniques. Both the thalamostriatal and the striato-entopeduncular projections were topographically organized, and several areas of overlap between identified circuits were noticed, sustaining the existence of up to three separated channels within the Nauta-Mehler loop. Thalamic afferents arising from dorsolateral PF territories are in register with striatofugal neurons located in dorsolateral striatal areas, which in turn project to dorsolateral regions of the entopeduncular nucleus (ENT). Medial ENT regions are innervated by striatal neurons located within medial striatal territories, these neurons being the target for thalamic afferents coming from medial PF areas. Finally, afferents from neurons located in ventrolateral PF areas approached striatal neurons in ventral and lateral striatal territories, which in turn project towards ventral and lateral ENT regions. Efferent STN neurons projecting to ENT were found to be the apparent postsynaptic target for thalamo-subthalamic axons. The thalamo-subthalamic projection was also topographically organized. Medial, central and lateral STN territories are innervated by thalamic neurons located within medial, ventrolateral and dorsolateral PF areas, respectively. Thus, each individual PF subregion projects in a segregated fashion to specific parts of the striato-entopeduncular and subthalamo-entopeduncular systems. These circuits enabled the caudal intralaminar nuclei to modulate basal ganglia output.

Naloxone-induced morphine withdrawal increases the number and degranulation of mast cells in the thalamus of the mouse

Naloxone-induced jumping in morphine-dependent mice is inhibited by cromolyn, a mast cell stabilizer, suggesting that this characteristic withdrawal behavior results from degranulation of mast cells. Because withdrawal is considered as a central phenomenon, degranulation of mast cells located within the CNS may influence aspects of opioid withdrawal. The present study evaluates histologically whether naloxone, injected into opioid dependent mice, induces degranulation of mast cells. Seventy-two hours after the s.c. implantation of a 75 mg morphine pellet, the number and degranulation of thalamic mast cells did not differ from those in placebo-implanted controls. However, two injections of 50 mg/kg of naloxone, 30 and 60 min before tissue collection, increased the number of degranulated mast cells compared to those in mice injected with saline. Analysis throughout the entire thalamus (90 40-micro sections) revealed increases in the total number of mast cells as well as the number that were degranulated, especially in sections 52-60, corresponding to Bregma -2.18 to 2.54. Here, mast cells were clustered in the IGL and VPL/VPM nuclei, and redistributed from the ventromedial to the dorsolateral aspects of the Po and PF nuclei during withdrawal. Degranulation was also greater throughout the LD, LP nuclei during withdrawal. These data reveal a novel neuroimmune reaction to opioid withdrawal in the CNS.

Stimulation of adenosine A2A receptors elicits zif/268 and NMDA epsilon2 subunit mRNA expression in cortex and striatum of the "weaver" mutant mouse, a genetic model of nigrostriatal dopamine deficiency

Interaction between basal ganglia and cerebral cortex is critical for normal goal-directed behavior. In the present study we have used the immediate early gene zif/268, as functional marker to investigate how the stimulation of adenosine A2A receptors, i.e. of the "indirect" striatal output pathway, affects striatal and cortical function in "weaver" mouse, a genetic model of dopamine deficiency. Furthermore, we have examined the effect of A2A receptor stimulation on glutamate receptor expression in the "weaver" brain. A single injection of CGS21680 (A2A receptor agonist), induced strong expression of zif/268 mRNA, detected by in situ hybridization, not only in striatum but also in the motor cortex of the "weaver" mutant. This cortical response seems to be elicited through the basal-ganglia-thalamo-cortical circuit, rather than through a direct cortical effect, since A2A receptors are not detectable in cortex according to our autoradiographic study. Co-administration of CGS21680 and quinpirole (D2 receptor agonist) attenuated the expression of zif/268 mRNA in dorsal striatum but not in motor cortex, indicating that the cortical response is dopamine-D2-receptor-independent. However, this co-administration induced an increase in zif/268 mRNA expression in somatosensory cortex, which could rely on disinhibition of the thalamo-cortical pathway. The motor cortical response could be of clinical interest, as it would further stimulate the "indirect" striatal pathway in a feed forward circuit, thus worsening the parkinsonian symptoms. Furthermore, the up-regulation of epsilon2 subunit mRNA of the NMDA receptor, induced by CGS21680 administration, seen in striatum and cortex of the "weaver" mouse, would lead to overactivity of these receptors worsening dyskinesias. These results suggest adenosine to play a significant role in regulating striatal and cortical neurochemistry in a dopamine-depleted mouse. Blockade of these receptors by specific A2A antagonists could ameliorate parkinsonian symptoms.

Rostral agranular insular cortex and pain areas of the central nervous system: a tract-tracing study in the rat

The rostral agranular insular cortex (RAIC) has recently been identified as a site where local changes in GABA and dopamine levels, or application of opioids, can alter nociceptive thresholds in awake animals. The connections of the cortex dorsal to the rhinal fissure that includes the RAIC have been examined previously, with emphasis on visceral and gustatory functions but not nociception. Here we examined the afferent and efferent connections of the RAIC with sites implicated in nociceptive processing. Sensory information from the thalamus reaches the RAIC via the submedius and central lateral nuclei and the parvicellular part of the ventral posterior nucleus. The RAIC has extensive reciprocal cortico-cortical connections with the orbital, infralimbic, and anterior cingulate cortices and with the contralateral RAIC. The amygdala, particularly the basal complex, and the nucleus accumbens are important targets of RAIC efferent fibers. Other connections include projections to lateral hypothalamus, dorsal raphe, periaqueductal gray matter, pericerulear region, rostroventral medulla, and parabrachial nuclei. The connectivity of the RAIC suggests it is involved in multiple aspects of pain behavior. Projections to the RAIC from medial thalamic nuclei are associated with motivational/affective components of pain. RAIC projections to mesolimbic/mesocortical ventral forebrain circuits are likely to participate in the sensorimotor integration of nociceptive processing, while its brainstem projections are most likely to contribute to descending pain inhibitory control.

Glutamatergic activation of anterior cingulate cortex produces an aversive teaching signal

Noxious stimuli have motivational power and can support associative learning, but the neural circuitry mediating such avoidance learning is poorly understood. The anterior cingulate cortex (ACC) is implicated in the affective response to noxious stimuli and the motivational properties of conditioned stimuli that predict noxious stimulation. Using conditioned place aversion (CPA) in rats, we found that excitatory amino acid microinjection into the ACC during conditioning produces avoidance learning in the absence of a peripheral noxious stimulus. Furthermore, microinjection of an excitatory amino acid antagonist into the ACC during conditioning blocked learning elicited by a noxious stimulus. ACC lesions made after conditioning did not impair expression of CPA. Thus, ACC neuronal activity is necessary and sufficient for noxious stimuli to produce an aversive teaching signal. Our results support the idea that a shared ACC pathway mediates both pain-induced negative affect and a nociceptor-driven aversive teaching signal.

Chemical anatomy of the human paraventricular thalamic nucleus

The paraventricular thalamic nucleus (Pa) lies in the most medial aspect of the thalamus and is considered one of the midline thalamic nuclei. In the present study, we carried out histochemical and immunohistochemical procedures in the Pa of normal individuals to visualize the pattern of distribution of acetylcholinesterase (AChE), calbindin D-28k (CB), parvalbumin (PV), calretinin (CR), limbic system-associated membrane protein (LAMP), substance P (SP), and enkephalin (ENK). Other cytoarchitectural and myeloarchitectural techniques, such as Nissl and Gallyas, were also employed to delineate the boundaries of the Pa. The main findings of this study are: 1) AChE staining in the Pa was heterogeneously distributed along its anteroposterior and mediolateral axes; 2) the Pa harbored numerous CB- and CR-immunoreactive (ir) cells and neuropil, but this nucleus was largely devoid of PV; 3) the Pa was highly enriched in LAMP and this protein appeared uniformly distributed through its whole extent; and, 4) the SP and ENK immunoreactivities in the Pa revealed numerous highly varicose fibers scattered throughout this nucleus, but no stained cells. This morphological study demonstrates that the Pa is a heterogeneous chemical structure in humans. The functional significance of these results is discussed in the light of similar data gathered in several mammalian species.

Stimulation of α1-adrenoceptors in the rat medial prefrontal cortex increases the local in vivo 5-hydroxytryptamine release: reversal by antipsychotic drugs

Pyramidal neurons of the medial prefrontal cortex (mPFC) project to midbrain serotonergic neurons and control their activity. The stimulation of prefrontal 5-HT2A and AMPA receptors increases pyramidal and serotonergic cell firing, and 5-hydroxytryptamine (5-HT) release in mPFC. As the mPFC contains abundant alpha1-adrenoceptors whose activation increases the excitability of pyramidal neurons, we examined the effects of their stimulation on local 5-HT release, using microdialysis. The application of the alpha1-adrenoceptor agonist cirazoline by reverse dialysis increased the prefrontal 5-HT release in a concentration-dependent manner, an effect antagonized by coperfusion of TTX, prazosin (alpha1-adrenoceptor antagonist), BAY x 3702 (5-HT1A agonist), NBQX (AMPA/KA antagonist) and 1S,3S-ACPD (mGluR II/III agonist), but not by MK-801 (NMDA antagonist). Cirazoline also enhanced the increase in 5-HT release induced by DOI (5-HT2A/2C agonist) and AMPA. In addition, M100907 (5-HT2A antagonist) but not SB-242084 (5-HT2C antagonist) reversed the cirazoline- and AMPA-induced 5-HT release. These results suggest that the stimulation of prefrontal alpha1-adrenoceptors activates pyramidal afferents to ascending serotonergic neurons. The effect of cirazoline was also reversed by coperfusion of classical (chlorpromazine, haloperidol) and atypical (clozapine, olanzapine) antipsychotics, which suggests that a functional antagonism of the alpha1-adrenoceptor-mediated activation of prefrontal neurons may partly underlie their therapeutic action.

Distribution of dopamine D2-like receptors in the human thalamus: autoradiographic and PET studies

The distribution of dopamine (DA) D(2)-like receptors in the human thalamus was studied using in vitro autoradiographic techniques and in vivo positron emission tomography in normal control subjects. [(125)I]Epidepride, which binds with high affinity to DA D(2) and D(3) receptors, was used in autoradiographic studies to determine the distribution and density of D(2)-like receptors, and the epidepride analogue [(18)F]fallypride positron was used for positron emission tomography studies to delineate D(2)-like receptors in vivo. Both approaches revealed a heterogeneous distribution of thalamic D(2/3) receptors, with relatively high densities in the intralaminar and midline thalamic nuclei, including the paraventricular, parataenial, paracentral, centrolateral, and centromedian/parafascicular nuclei. Moderate densities of D(2/3) sites were seen in the mediodorsal and anterior nuclei, while other thalamic nuclei expressed lower levels of D(2)-like receptors. Most thalamic nuclei that express high densities of D(2)-like receptors project to forebrain DA terminal fields, suggesting that both the thalamic neurons expressing D(2)-like receptors and the projection targets of these neurons are regulated by DA. Because the midline/intralaminar nuclei receive prominent projections from both the ascending reticular activating core and the hypothalamus, these thalamic nuclei may integrate activity conveying both interoceptive and exteroceptive information to telencephalic DA systems involved in reward and cognition.

Do rats have a prefrontal cortex?

The lack of a single anatomical or functional definition of 'prefrontal cortex' has led to different and, in some respects, controversial views on the existence of a prefrontal cortex in non-primate mammals, in particular in rats. Until the classic paper by Rose and Woolsey [Res. Publ. Assoc. Nerv. Ment. Dis. 27 (1948) 210], the general idea was that a prefrontal cortex is unique to primate species. Rose and Woolsey's 'prefrontal cortex' definition was based upon a single anatomical criterion, i.e. the cortical projection area of the mediodorsal thalamic nucleus. Single criteria, however, do not appear to be sufficient for defining the prefrontal cortex. Therefore, other anatomical and functional characteristics are currently used to identify the prefrontal cortex in different species. Yet, recently the debate about the nature of the prefrontal cortex in non-primate species has been resumed. In the present paper we will compare the structural and functional characteristics of the prefrontal cortex of nonhuman primates and rats. We will argue that rats have a functionally divided prefrontal cortex that includes not only features of the medial and orbital areas in primates, but also some features of the primate dorsolateral prefrontal cortex.

Differential projections of the infralimbic and prelimbic cortex in the rat

The medial prefrontal cortex has been associated with diverse functions including attentional processes, visceromotor activity, decision-making, goal-directed behavior, and working memory. The present report compares and contrasts projections from the infralimbic (IL) and prelimbic (PL) cortices in the rat by using the anterograde anatomical tracer, Phaseolus vulgaris-leucoagglutinin. With the exception of common projections to parts of the orbitomedial prefrontal cortex, olfactory forebrain, and midline thalamus, PL and IL distribute very differently throughout the brain. Main projection sites of IL are: 1) the lateral septum, bed nucleus of stria terminalis, medial and lateral preoptic nuclei, substantia innominata, and endopiriform nuclei of the basal forebrain; 2) the medial, basomedial, central, and cortical nuclei of amygdala; 3) the dorsomedial, lateral, perifornical, posterior, and supramammillary nuclei of hypothalamus; and 4) the parabrachial and solitary nuclei of the brainstem. By contrast, PL projects at best sparingly to each of these structures. Main projection sites of PL are: the agranular insular cortex, claustrum, nucleus accumbens, olfactory tubercle, the paraventricular, mediodorsal, and reuniens nuclei of thalamus, the capsular part of the central nucleus and the basolateral nucleus of amygdala, and the dorsal and median raphe nuclei of the brainstem. As discussed herein, the pattern of IL projections is consistent with a role for IL in the control of visceral/autonomic activity homologous to the orbitomedial prefrontal cortex of primates, whereas those of PL are consistent with a role for PL in limbic-cognitive functions homologous to the dorsolateral prefrontal cortex of primates.

Infusions of midazolam into the medial prefrontal cortex produce anxiolytic effects in the elevated plus-maze and shock-probe burying tests

Previous research has shown that lesions of the medial prefrontal cortex (MPFC) inhibit fear-related behavior in rats (Brain Res. 969 (2003) 183-194). However, at present little is known about the role of specific neurotransmitter receptor systems within the MPFC in the mediation of fear and anxiety. For example, extensive research has demonstrated the effectiveness of benzodiazepines in decreasing fear-related behavior. However, no research has yet been published regarding the effects of micro-infusions of benzodiazepines, or any other GABA-A receptor agonist, into the MPFC. In addition, previous work has suggested that there may be functional differences between the dorsal and ventral subregions of the MPFC in regard to fear and anxiety. Therefore, the present study examined the effects of dorsal and ventral MPFC infusions of the benzodiazepine midazolam in two well-validated animal models of anxiety, the elevated plus maze and the shock probe burying test. The results showed that bilateral (5 microg/side) infusions of midazolam into the MPFC produced anxiolytic effects in both behavioural tests, without affecting general activity or pain sensitivity. Furthermore, these anxiolytic effects were found in both the dorsal and ventral regions of the MPFC. The present findings indicate that the benzodiazepine receptors of the MPFC are capable of modulating fear-related behaviors.

Differential projections from the mediodorsal and centrolateral thalamic nuclei to the frontal cortex in rats

The aim of the present study was to investigate afferent projections from the medial thalamic nuclei (MT) to the frontal cortical areas using a single small iontophoretic injection of biotinylated dextran amine (BDA) and analysis of the anterogradely labeled fibers and varicosities. Projections from the mediodorsal (MD) nuclei were found primarily and extensively in the anterior cingulate cortex (ACC), whereas those from the centrolateral (CL) thalamic nucleus were found in the frontal motor cortex. The density of terminals in the ACC was high in layers II and III and sparse in layer I. The majority of projected fibers from the CL were found at a high density in layer V, with a moderate density in the superficial layers. The differential projection patterns were topographically organized in the medial prefrontal cortex and sensory motor cortex. These findings support the results of our previous electrophysiological studies suggesting that neurons in the medial thalamic nuclei relay nociceptive information to the limbic or sensory motor cortical areas. The present results agree with the current notion that the medial thalamo-frontal cortical network circuitry plays an important role in processing the emotional aspect of nociception.

Rat intralaminar thalamic nuclei projections to the globus pallidus: A biotinylated dextran amine anterograde tracing study

The topographical organization and ultrastructural features of the intralaminar thalamic nuclei (ITN) projections to the globus pallidus (GP) were studied using the biotinylated dextran amine (BDA) anterograde tracing method in the rat. To assess the functional association of BDA injection sites in the ITN, the known topographical organization of the ITN-neostriatal (Str) projections and calcium binding protein (CaBP) immunostaining patterns of the Str and GP were used. BDA injection in the lateral part of the lateral parafascicular nucleus and the caudal part of the central lateral nucleus labeled fibers and boutons mainly in the dorsolateral sensorimotor territory of the Str and the middle territories of the GP. BDA injection in the medial part of the lateral parafascicular nucleus and the central lateral nucleus labeled mainly the middle association territory of the Str and the border and the caudomedial territories of the GP. BDA injection in the medial parafascicular nucleus and the central medial nucleus labeled mainly the medial limbic territory of the Str. The medial parafascicular nucleus projected to the medial-most region of the GP, while the central medial nucleus projection to the GP was very sparse. Electron microscopic observations indicated that BDA-labeled boutons form asymmetric synapses mainly on 0.5-2.0 microm diameter dendritic shafts in the GP. The boutons were small but had a relatively long active zone. The present observations together with the known topographical organization of striatopallidal projections indicated that the ITN-GP projections were topographically organized in parallel to the ITN-Str projections. Thus, each part of the ITN projecting to the sensorimotor, the association, and the limbic territories of the Str also projects to the corresponding functional territories of the GP.

Axonal projections from the parasubthalamic nucleus

The parasubthalamic nucleus (PSTN) is a differentiation of the lateral hypothalamic area, characterized by a distinct population of neurons expressing beta-preprotachykinin (beta-PPT) mRNA. The axonal projections from the PSTN have been analyzed with the PHAL anterograde tract tracing method in rats. The results indicate that the cell group is distinguished by massive projections to parasympathetic preganglionic neurons in the brainstem (especially in the salivatory nuclei and dorsal motor nucleus of the vagus nerve) and to parts of the parabrachial nucleus and nucleus of the solitary tract that relay viscerosensory and gustatory information. In addition, the PSTN projects to cortical parts of the cerebral hemisphere (infralimbic, agranular insular, postpiriform transition and lateral entorhinal areas, and posterior basolateral amygdalar nucleus)-directly and also indirectly via thalamic feedback loops involving the paraventricular and mediodorsal nuclei-and to nuclear parts of the cerebral hemisphere (central amygdalar nucleus, striatal fundus, rhomboid nucleus of the bed nuclei of the stria terminalis, and substantia innominata). The PSTN is thus positioned to influence directly many cerebral hemisphere and hindbrain components of the central parasympathetic control network that is active, for example, during feeding behavior and cardiovascular regulation.

Hypocretin (orexin) induces calcium transients in single spines postsynaptic to identified thalamocortical boutons in prefrontal slice

In vivo, thalamocortical axons are susceptible to the generation of terminal spikes which antidromically promote bursting in the thalamus. Although neurotransmitters could elicit such ectopic action potentials at thalamocortical boutons, this hypothesis has never been confirmed. Prefrontal cortex is the cortical area most implicated in arousal and is innervated by thalamic neurons that are unusual since they burst rhythmically during waking. We show that a neurotransmitter critical for alertness, hypocretin (orexin), directly excites prefrontal thalamocortical synapses in acute slice. This TTX-sensitive activation of thalamic axons was demonstrated electrophysiologically and by two-photon sampling of calcium transients at single spines in apposition to thalamic boutons anterogradely labeled in vivo. Spines receiving these long-range projections constituted a unique population in terms of the presynaptic excitatory action of hypocretin. By this mechanism, the hypocretin projection to prefrontal cortex may play a larger role in prefrontal or "executive" aspects of alertness and attention than previously anticipated.

The medial prefrontal cortex in the rat: evidence for a dorso-ventral distinction based upon functional and anatomical characteristics

The prefrontal cortex in rats can be distinguished anatomically from other frontal cortical areas both in terms of cytoarchitectonic characteristics and neural connectivity, and it can be further subdivided into subterritories on the basis of such criteria. Functionally, the prefrontal cortex of rats has been implicated in working memory, attention, response initiation and management of autonomic control and emotion. In humans, dysfunction of prefrontal cortical areas with which the medial prefrontal cortex of the rat is most likely comparable is related to psychopathology including schizophrenia, sociopathy, obsessive-compulsive disorder, depression, and drug abuse. Recent literature points to the relevance of conducting a functional analysis of prefrontal subregions and supports the idea that the area of the medial prefrontal cortex in rats is characterized by its own functional heterogeneity, which may be related to neuroanatomical and neurochemical dissociations. The present review covers recent findings with the intent of correlating these distinct functional differences in the dorso-ventral axis of the rat medial prefrontal cortex with anatomical and neurochemical patterns.

Projections from the rhomboid nucleus of the bed nuclei of the stria terminalis: implications for cerebral hemisphere regulation of ingestive behaviors

The basic organization of an exceptionally complex pattern of axonal projections from one distinct cell group of the bed nuclei of the stria terminalis, the rhomboid nucleus (BSTrh), was analyzed with the PHAL anterograde tract-tracing method in rats. Brain areas that receive a strong to moderate input from the BSTrh fall into nine general categories: central autonomic control network (central amygdalar nucleus, descending hypothalamic paraventricular nucleus, parasubthalamic nucleus and dorsal lateral hypothalamic area, ventrolateral periaqueductal gray, lateral parabrachial nucleus and caudal nucleus of the solitary tract, dorsal motor nucleus of the vagus nerve, and salivatory nuclei), gustatory system (rostral nucleus of the solitary tract and medial parabrachial nucleus), neuroendocrine system (periventricular and paraventricular hypothalamic nuclei, hypothalamic visceromotor pattern generator network), orofaciopharyngeal motor control (rostral tip of the dorsal nucleus ambiguus, parvicellular reticular nucleus, retrorubral area, and lateral mesencephalic reticular nucleus), respiratory control (lateral nucleus of the solitary tract), locomotor or exploratory behavior control and reward prediction (nucleus accumbens, substantia innominata, and ventral tegmental area), ingestive behavior control (descending paraventricular nucleus and dorsal lateral hypothalamic area), thalamocortical feedback loops (medial-midline-intralaminar thalamus), and behavioral state control (dorsal raphé and locus coeruleus). Its pattern of axonal projections and its position in the basal telencephalon suggest that the BSTrh is part of a striatopallidal differentiation involved in modulating the expression of ingestive behaviors, although it may have other functions as well.

Single CNS neurons link both central motor and cardiosympathetic systems: a double-virus tracing study

Two anatomical experiments were performed to test the hypothesis that single CNS neurons link the central areas that regulate the somatomotor and sympathetic systems. First, the retrograde neuronal tracer cholera toxin beta-subunit was injected into the lateral parafascicular thalamic nucleus, a region that projects to both the motor cortex and striatum. Several days later, a second injection of the retrograde transneuronal tracer, pseudorabies virus (PRV), was made in the same rats in the stellate ganglion, which provides the main sympathetic supply to the heart. Using immunohistochemical methods, we demonstrate that the cholinergic neurons of the pedunculopontine tegmental nucleus (PPN) are connected to both systems. The second experiment used two isogenic strains of Bartha PRV as double transneuronal tracers. One virus contained the unique gene for green fluorescent protein (GFP) and the other had the unique gene for beta-galactosidase (beta-gal). GFP-PRV was injected in the stellate ganglion and beta-gal-PRV was injected into the primary motor cortex. Double-labeled neurons were found in the lateral hypothalamic area (50% contained orexin) and PPN (approximately 95% were cholinergic). Other double-labeled neurons were identified in the deep temporal lobe (viz., amygdalohippocampal zone and lateral entorhinal cortex), posterior hypothalamus, ventral tuberomammillary nucleus, locus coeruleus, laterodorsal tegmental nucleus, periaqueductal gray matter, dorsal raphe nucleus, and nucleus tractus solitarius. These results suggest these putative command neurons integrate the somatomotor and cardiosympathetic functions and may affect different behaviors (viz., arousal, sleep, and/or locomotion).

Regional differences in the circadian modulation of human sleep spindle characteristics

Electroencephalographic oscillations in the sleep spindle frequency range (11-16 Hz) are a key element of human nonrapid eye movement sleep. In the present study, sleep spindle characteristics along the anterior-posterior axis were analysed during and outside the circadian phase of melatonin secretion. Sleep electroencephalograms were recorded during naps distributed over the entire circadian cycle and analysed with two different methodological approaches, the classical fast Fourier transform in the frequency-domain and a new method for instantaneous spectral analysis, the fast time frequency transform that yields high-resolution parameters in the combined time-frequency-domain. During the phase of melatonin secretion, spindle density was generally increased and intraspindle frequency variation reduced. Furthermore, lower spindle frequencies were promoted: peak frequencies shifted towards the lower end of the spindle frequency range, and spindle amplitude was enhanced in the low-frequency range (11-14.25 Hz) and reduced in the high-frequency range (approximately 14.5-16 Hz). The circadian variation showed a clear dependence on brain topography such that it was maximal in the parietal and minimal in the frontal derivation. Our data provide evidence that the circadian pacemaker actively promotes low-frequency sleep spindles during the biological night with a parietal predominance.

Anatomical organization of the telencephalic connections of the parafascicular nucleus in adult and developing rats

The parafascicular nucleus (PFN) of the rat, homologous to the human centre médian, is an intralaminar nucleus of the thalamus, classically considered as part of the ascending activating system. We have previously demonstrated that it is also connected to several subcortical nuclei. To obtain a more detailed picture of the connectivity of the PFN, the organization and the topography of the reciprocal parafascicular-telencephalic relationships were studied in both adult and developing rats, using anterograde and retrograde neuronal tracers. In the adult rat, the ascending parafascicular projections were densest to the striatum, dense to the frontal and least dense to cingulate cortex, and were strictly ipsilateral. They displayed a loose topography, with the more medial parafascicular neurons projecting to the medial frontal and cingulate cortex and medial striatum, and the more lateral neurons projecting to the lateral frontal cortex and lateral striatum. All these connections were already present at embryonic day 19. Parafascicular neurons projecting to the telencephalon in adult rats were mostly of the multipolar type, with a few bipolar neurons. In neonatal rats they showed a bipolar morphology at birth; they became mostly multipolar later on, with an increasing complexity of the dendritic arbor up to postnatal day 10. Neurons in the frontal cortex retrogradely labelled from the PFN were more numerous perinatally, and decreased as early as postnatal day 5. The telencephalic connections of the PFN were found to be more discrete and restricted than previously thought, thus suggesting a more specific functional role for the nucleus than cortical recruitment.

Representations of motivational drives in mesial cortex, medial thalamus, hypothalamus and midbrain

We propose that neural representations of motivational drives, including sexual desire, hunger, thirst, fear, power-dominance, the motivational aspect of pain, the need for sleep, and nurturance, are represented in four areas in the brain. These are located in the medial hypothalamic/preoptic area, the periaqueductal gray matter (PAG) in the midbrain/pons, the midline and intralaminar thalamic nuclei, and in the anterior part of the mesial cortex, including the medial prefrontal and anterior cingulate areas. We attempt to determine the locations of each of these representations within the hypothalamus/preoptic area, periaqueductal gray and cortex, based on the available literature on activation of brain structures by stimuli that evoke these forms of motivation, on the effects of electrical and chemical stimulation and lesions of candidate structures, and on hodological data. We discuss the hierarchical organization of the representations for a given drive, outputs from these representations to premotor structures in the medulla, caudate-putamen, and cortex, and their contributions to involuntary, learned-sequential (operant) and voluntary behaviors.

Projections from the paraventricular nucleus of the thalamus to the rat prefrontal cortex and nucleus accumbens shell: ultrastructural characteristics and spatial relationships with dopamine afferents

The paraventricular nucleus of the thalamus (PVT) participates in the functional integration of limbic cortical and striatal circuitry. In the rat, the PVT projects to the deep layers of the medial prefrontal cortex (PFC) and to the shell of the nucleus accumbens (NAc). However, the synaptic organization of PVT afferents within these regions remains undescribed. Furthermore, although dopamine (DA) modulates excitatory glutamate transmission in both areas, possible anatomic substrates for specific DA modulation of PVT inputs have not yet been investigated. To address these issues, immunoperoxidase labeling for tyrosine hydroxylase (TH) in DA axons was combined with anterograde tract-tracing, either by biotinylated dextran amine (BDA) labeled with immunogold-silver or by degeneration after lesions of the PVT. In both regions, and with either tracing method, PVT terminals formed primarily asymmetric axospinous synapses; in the NAc, a proportion of PVT terminals also synapsed onto dendrites. PVT profiles in both regions were often seen in direct apposition to TH-immunoreactive axons; this association was more evident in the NAc where the DA innervation is denser. Within the PFC, PVT profiles and TH-labeled axons were occasionally apposed to the same dendrites, but synaptic specializations were not typically seen at these seeming points of convergence. Within the NAc, PVT profiles occasionally made synapses onto spines and distal dendrites that received convergent synapses from TH-immunoreactive varicosities. These findings represent the first demonstration of postsynaptic convergence between DA and thalamic afferents to a striatal region and are consistent with direct synaptic modulation of PVT transmission by DA in the NAc but not the PFC.

Excitotoxic lesions of the medial prefrontal cortex attenuate fear responses in the elevated-plus maze, social interaction and shock probe burying tests

Previous research investigating the effects of medial prefrontal cortex (MPFC) lesions on fear- and anxiety-related behavior has yielded an inconsistent body of findings. Behavioral studies have reported increases, decreases, and no effect on anxiety. In addition, many studies are complicated by the use of lesioning techniques that destroy fibers of passage, and the use of conditioned fear tests, which may introduce the confounding effects of learning and memory. Therefore, the present study examined the effects of ibotenic acid lesions of the MPFC (including prelimbic, infralimbic and anterior cingulate) on three wide-ranging and well-validated behavioral assays of anxiety: the elevated plus maze (EPM), social interaction (SI) and the shock-probe tests (SP). In the EPM test, lesioned rats showed a significantly higher percentage of open arm entries and open arm time than controls. In a version of the SI test sensitive to anxiolytic effects, lesioned rats were found to spend a significantly greater amount of time in active interaction with a conspecific; while another version of the SI test sensitive to anxiogenic effects did not show any differences between lesioned and non-lesioned controls. In the SP test, lesioned rats exhibited significantly lower rates of burying. In contrast, retention of shock probe avoidance was not affected. No effects of lesions on measures of locomotor activity or shock reactivity were found. The concordant anxiolytic-like effects found in the three behavioral assays strongly suggests a general reduction in fear responsiveness in MPFC lesioned rats.

The associative striatum: cortical and thalamic projections to the dorsocentral striatum in rats

Corticostriatal projections to the dorsocentral striatum (DCS) were investigated using retrograde fluorescent axonal tracing. The DCS is of interest because of its role in directed attention and recovery from multimodal hemispatial neglect following cortical lesions of medial agranular cortex (AGm), an association area that is its major source of cortical input. A key finding was that the multimodal posterior parietal cortex (PPC) also contributes substantial input to DCS. This is significant because PPC and AGm are linked by corticocortical connections and are both critical components of the circuitry involved in spatial processing and directed attention. Other cortical areas providing input to DCS include visual association areas, lateral agranular cortex and orbital cortex. These areas also have reciprocal connections with AGm and PPC. Less consistent labeling was seen in somatic sensorimotor areas FL, HL and Par 1. Thalamic afferents to DCS are prominent from the intralaminar, ventrolateral, mediodorsal, ventromedial, laterodorsal (LD) and lateral posterior (LP) nuclei. Collectively, these nuclei constitute the sources of thalamic input to cortical areas AGm and PPC. Nuclei LD and LP are only labeled with injections in dorsal DCS, the site of major input from PPC, and PPC receives its thalamic input from LD and LP. We conclude that DCS receives inputs from cortical and thalamic areas that are themselves linked by corticocortical and thalamocortical connections. These findings support the hypothesis that DCS is a key component of an associative network of cortical, striatal and thalamic regions involved in multimodal processing and directed attention.

Cardiac nociception in rats: neuronal pathways and the influence of dermal neurostimulation on conveyance to the central nervous system

Neurostimulation for refractory angina pectoris is often advocated for its clinical efficacy. However, the recruited pathways to induce electroanalgesia are partially unknown. Therefore, we sought to study the effect of neurostimulation on experimentally induced cardiac nociception, using capsaicin as nociception-induced substance. Four different groups of male Wistar rats were pericardially infused with either saline or capsaicin with or without neurostimulation. Group StimCap was infused with capsaicin, and group StimVeh was infused with saline. Both groups were treated with neurostimulation. Group ShamCap was only infused with capsaicin without stimulation, whereas group ShamVeh was only infused with saline. Neuronal activation differences were assessed with cytochemical staining, revealing the cellular expression of c-fos. Pain behavior was registered on video and was quantitatively analyzed. In the StimCap and ShamCap groups, all animals exerted typical pain behavior, whereas in the StimVeh group only moderate changes in behavior were observed. Group ShamVeh animals were unaffected by the procedure. The upper thoracic spinal cord showed high numbers of c-fos-positive cells, predominantly in laminae III and IV in both StimCap and StimVeh groups. Almost no c-fos expression was noticed in groups ShamCap and ShamVeh in these sections of the spinal cord. In groups StimCap and ShamCap a significantly higher number of c-fos-positive cells in comparison with groups StimVeh and ShamVeh were noticed in the periambigus region, the nucleus tractus solitarius, and the paraventricular hypothalamus. In the paraventricular thalamus, periaqueductal gray, and central amygdala, no significant differences were noticed among the first three groups, and the c-fos concentration in these three groups was significantly higher than in group ShamVeh. It is concluded that neurostimulation does not influence capsaicin-induced cardiac nociceptive pain pulses to the central nervous system. Furthermore, capsaicin-induced cardiac pain and neurostimulation may utilize two different pathways.

Synergistic action of 5-HT2A antagonists and selective serotonin reuptake inhibitors in neuropsychiatric disorders

Recently, the addition of drugs with prominent 5-HT(2) receptor antagonist properties (risperidone, olanzapine, mirtazapine, and mianserin) to selective serotonin reuptake inhibitors (SSRIs) has been shown to enhance therapeutic responses in patients with major depression and treatment-refractory obsessive-compulsive disorder (OCD). These 5-HT(2) antagonists may also be effective in ameliorating some symptoms associated with autism and other pervasive developmental disorders (PDDs). At the doses used, these drugs would be expected to saturate 5-HT(2A) receptors. These findings suggest that the simultaneous blockade of 5-HT(2A) receptors and activation of an unknown constellation of other 5-HT receptors indirectly as a result of 5-HT uptake inhibition might have greater therapeutic efficacy than either action alone. Animal studies have suggested that activation of 5-HT(1A) and 5-HT(2C) receptors may counteract the effects of activating 5-HT(2A) receptors. Additional 5-HT receptors, such as the 5-HT(1B/1D/5/7) receptors, may similarly counteract the effects of 5-HT(2A) receptor activation. These clinical and preclinical observations suggest that the combination of highly selective 5-HT(2A) antagonists and SSRIs, as well as strategies to combine high-potency 5-HT(2A) receptor and 5-HT transporter blockade in a single compound, offer the potential for therapeutic advances in a number of neuropsychiatric disorders.

Nigrothalamostriatal and nigrothalamocortical pathways via the ventrolateral parafascicular nucleus

The present tract-tracing study in the rat indicated that neurons in the ventrolateral part of the parafascicular thalamic nucleus (PF), where nigral fibers from the dorsolateral part of the substantia nigra pars reticulata (SNr) terminated, sent their axons to the ventrolateral part of the striatum as well as to the rostrolateral part of the lateral agranular cortex (AGl). We further demonstrated that symmetrical synaptic contacts were made between these nigral axons and striatum- or AGl-projecting PF neurons. Since the dorsolateral part of the SNr, ventrolateral part of the striatum and rostrolateral part of the AGl are responsible regions for orofacial behaviors, the nigrothalamostriatal and nigrothalamo-cortical pathways via the ventrolateral part of the PF may play a role in the control of orofacial motor function.

Suprachiasmatic nucleus projection to the medial prefrontal cortex: a viral transneuronal tracing study

The viral transneuronal labeling method was used to examine whether the suprachiasmatic nucleus (SCN) is linked by multisynaptic connections to the medial prefrontal cortex of the rat. In separate experiments, pseudorabies virus (PRV) was injected into one of the three different cytoarchitectonic regions that comprise the medial prefrontal cortex: infralimbic (Brodmann area 25), prelimbic (Brodmann area 32), and cingulate (Brodmann area 24) cortical areas. After 4-days survival, extensive SCN transneuronal labeling was found following infralimbic cortex (ILC) injections, but almost none occurred when the PRV injections were centered in the prelimbic or cingulate areas. In the ILC cases, transneuronal labeling was localized mainly in the dorsomedial SCN, although a moderate number of labeled neurons were found in the ventrolateral SCN. About 13% of the infected neurons were vasopressin immunoreactive and 4% were vasoactive intestinal polypeptide-positive. Another set of experiments was performed in which the paraventricular thalamic nucleus (PVT) was destroyed 2 weeks prior to making PRV injections into the ILC. Almost no SCN transneuronal labeling occurred in these animals, suggesting that the SCN projection to the ILC is dependent on a relay in the PVT. We propose that the SCN sends timing signals, via its relay in the PVT, to the ILC. This pathway may modulate higher-level brain functions, such as attention, mood, or working memory. Assuming that a homologous circuit exists in humans, we speculate that neurochemical changes affecting this pathway may account for some of the symptoms associated with clinical depression and attention-deficit/hyperactivity disorder.

Group II metabotropic glutamate receptor modulation of DOI-induced c-fos mRNA and excitatory responses in the cerebral cortex

Recent studies have demonstrated that the hallucinogen 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) enhances glutamatergic transmission in the prefrontal cortex. This increase can be suppressed by metabotropic glutamate2/3 (mGlu2/3) receptor activation. In addition to enhancing glutamatergic transmission, DOI increases cortical c-fos expression. We tested if a reduction in glutamate release produced by mGlu2/3 receptor activation attenuates DOI-induced c-fos expression in the cortex. Similar to previous studies, DOI produced a robust increase in c-fos mRNA throughout the cortex, including the prefrontal, frontoparietal, and somatosensory regions. Pretreatment with the mGlu2/3 agonist LY379268 attenuated the DOI-induced increase in the prefrontal cortex. This suppression was blocked by the mGlu2/3 antagonist LY341495. In contrast, the DOI-induced increase in c-fos mRNA in the frontoparietal and somatosensory cortex was unaffected by the mGlu2/3 agents. These findings suggest that Group II metabotropic glutamate receptor agonists are capable of modulating postsynaptic function preferentially in the limbic cortex under conditions of enhanced glutamate release.

A comparative reappraisal of projections from the superficial laminae of the dorsal horn in the rat: The forebrain

Projections to the forebrain from lamina I of spinal and trigeminal dorsal horn were labeled anterogradely with Phaseolus vulgaris-leucoagglutinin (PHA-L) and/or tetramethylrhodamine-dextran (RHO-D) injected microiontophoretically. Injections restricted to superficial laminae (I/II) of dorsal horn were used primarily. For comparison, injections were also made in deep cervical laminae. Spinal and trigeminal lamina I neurons project extensively to restricted portions of the ventral posterolateral and posteromedial (VPL/VPM), and the posterior group (Po) thalamic nuclei. Lamina I also projects to the triangular posterior (PoT) and the ventral posterior parvicellular (VPPC) thalamic nuclei but only very slightly to the extrathalamic forebrain. Furthermore, the lateral spinal (LS) nucleus, and to a lesser extent lamina I, project to the mediodorsal thalamic nucleus. In contrast to lamina I, deep spinal laminae project primarily to the central lateral thalamic nucleus (CL) and only weakly to the remaining thalamus, except for a medium projection to the PoT. Furthermore, the deep laminae project substantially to the globus pallidus and the substantia innominata and more weakly to the amygdala and the hypothalamus. Double-labeling experiments reveal that spinal and trigeminal lamina I project densely to distinct and restricted portions of VPL/VPM, Po, and VPPC thalamic nuclei, whereas projections to the PoT appeared to be convergent. In conclusion, these experiments indicate very different patterns of projection for lamina I versus deep laminae (III-X). Lamina I projects strongly onto relay thalamic nuclei and thus would have a primary role in sensory discriminative aspects of pain. The deep laminae project densely to the CL and more diffusely to other forebrain targets, suggesting roles in motor and alertness components of pain.

Synaptic organization of GABAergic projections from the substantia nigra pars reticulata and the reticular thalamic nucleus to the parafascicular thalamic nucleus in the rat

The ventrolateral part of the parafascicular thalamic nucleus (PF), which is considered to take part in the control mechanism of orofacial motor functions, receives projection fibers not only from the dorsolateral part of the substantia nigra pars reticulata (SNr) but also from the ventral part of the reticular thalamic nucleus (RT) [Tsumori et al., Brain Res. 858 (2000) 429]. In order to better understand the influence of these fibers upon the PF projection neurons, the morphology, synaptology and chemical nature of them were examined in the present study. After ipsilateral injections of Phaseolus vulgaris-leucoagglutinin (PHA-L) into the dorsolateral part of the SNr and biotinylated dextran amine (BDA) into the ventral part of the RT, overlapping distributions of PHA-L-labeled SNr fibers and BDA-labeled RT fibers were seen in the ventrolateral part of the PF. At the electron microscopic level, the SNr terminals made synapses predominantly with the medium to small dendrites and far less frequently with the somata and large dendrites, whereas approximately half of the RT terminals made synapses with the somata and large dendrites and the rest did with the medium to small dendrites of PF neurons. Some of single dendritic as well as single somatic profiles received convergent synaptic inputs from both sets of terminals. These terminals were packed with pleomorphic synaptic vesicles and formed symmetrical synapses. After combined injections of PHA-L into the dorsolateral part of the SNr, BDA into the ventral part of the RT and wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into the ventrolateral part of the striatum or into the rostroventral part of the lateral agranular cortex, WGA-HRP-labeled neurons were embedded in the plexus of PHA-L- and BDA-labeled axon terminals within the ventrolateral part of the PF, where the PHA-L- and/or BDA-labeled terminals were in synaptic contact with single somatic and dendritic profiles of the WGA-HRP-labeled neurons. Furthermore, the SNr and RT axon terminals were revealed to be immunoreactive for gamma-aminobutyric acid (GABA), by using the anterograde BDA tracing technique combined with immunohistochemistry for GABA. The present data suggest that GABAergic SNr and RT fibers may exert different inhibitory influences on the PF neurons for regulating the thalamic outflow from the PF to the cerebral cortex and/or striatum in the control of orofacial movements.