A hypothalamic-thalamostriatal circuit that controls approach-avoidance conflict in rats.

Survival depends on a balance between seeking rewards and avoiding potential threats, but the neural circuits that regulate this motivational conflict remain largely unknown. Using an approach-food vs. avoid-predator threat conflict test in rats, we identified a subpopulation of neurons in the anterior portion of the paraventricular thalamic nucleus (aPVT) which express corticotrophin-releasing factor (CRF) and are preferentially recruited during conflict. Inactivation of aPVTCRF neurons during conflict biases animal's response toward food, whereas activation of these cells recapitulates the food-seeking suppression observed during conflict. aPVTCRF neurons project densely to the nucleus accumbens (NAc), and activity in this pathway reduces food seeking and increases avoidance. In addition, we identified the ventromedial hypothalamus (VMH) as a critical input to aPVTCRF neurons, and demonstrated that VMH-aPVT neurons mediate defensive behaviors exclusively during conflict. Together, our findings describe a hypothalamic-thalamostriatal circuit that suppresses reward-seeking behavior under the competing demands of avoiding threats.

A midline thalamic circuit determines reactions to visual threat.

How our internal state is merged with our visual perception of an impending threat to drive an adaptive behavioural response is not known. Mice respond to visual threats by either freezing or seeking shelter. Here we show that nuclei of the ventral midline thalamus (vMT), the xiphoid nucleus (Xi) and nucleus reuniens (Re), represent crucial hubs in the network controlling behavioural responses to visual threats. The Xi projects to the basolateral amygdala to promote saliency-reducing responses to threats, such as freezing, whereas the Re projects to the medial prefrontal cortex (Re→mPFC) to promote saliency-enhancing, even confrontational responses to threats, such as tail rattling. Activation of the Re→mPFC pathway also increases autonomic arousal in a manner that is rewarding. The vMT is therefore important for biasing how internal states are translated into opposing categories of behavioural responses to perceived threats. These findings may have implications for understanding disorders of arousal and adaptive decision-making, such as phobias, post-traumatic stress and addictions.

A prefrontal-thalamo-hippocampal circuit for goal-directed spatial navigation.

Spatial navigation requires information about the relationship between current and future positions. The activity of hippocampal neurons appears to reflect such a relationship, representing not only instantaneous position but also the path towards a goal location. However, how the hippocampus obtains information about goal direction is poorly understood. Here we report a prefrontal-thalamic neural circuit that is required for hippocampal representation of routes or trajectories through the environment. Trajectory-dependent firing was observed in medial prefrontal cortex, the nucleus reuniens of the thalamus, and the CA1 region of the hippocampus in rats. Lesioning or optogenetic silencing of the nucleus reuniens substantially reduced trajectory-dependent CA1 firing. Trajectory-dependent activity was almost absent in CA3, which does not receive nucleus reuniens input. The data suggest that projections from medial prefrontal cortex, via the nucleus reuniens, are crucial for representation of the future path during goal-directed behaviour and point to the thalamus as a key node in networks for long-range communication between cortical regions involved in navigation.

Hypothalamic, feeding/arousal-related peptidergic projections to the paraventricular thalamic nucleus in the rat.

Based on the importance of paraventricular thalamic nucleus (PVT) as a relay station of energy balance, arousal, and food reward, we aimed in the present study to determine projection patterns of neuropeptide Y (NPY), cocaine- and amphetamine-regulated transcript (CART), melanin-concentrating hormone (MCH), and orexin (ORX)-ergic fibers to the PVT. First, the distribution of peptidergic axon terminals within the PVT was examined. NPY and CART terminals were confined within the boundary of the thalamic nucleus, exhibiting almost identical distribution. MCH terminals were rarely observed. In contrast, ORX terminals were as extensive as NPY/CART terminals, but spread into the peri-PVT region. Second, neuronal origin of feeding/arousal-related peptides projecting to the PVT was investigated. NPY neurons were observed in the medial subdivision of the arcuate nucleus (Arc), whereas CART cells were in the lateral Arc as well as other hypothalamic regions including the paraventricular hypothalamic nucleus, lateral hypothalamus (LH), dorsal hypothalamic area, and zona incerta. Both NPY- and CART-fiber projections to the PVT were bilateral; ipsilateral proportion was 54.0% ± 3.6% (n = 6) for NPY and 57.1% ± 2.5% (n = 6) for CART. The total number of CART neurons projecting to the PVT exceeded that of NPY cells; the ratio of labeled CART neurons to NPY cells was 2.4 ± 0.2 (n = 6). In contrast, ORX-ergic fiber projection to the PVT exhibited a slight ipsilateral dominance (62.7% ± 1.6%, n = 6), with majority of labeled cells located in the LH medial to the fornix (72.2% ± 2.3%, n = 6). Third, based on heavy projection from the PVT to the nucleus accumbens shell (NAcSh), the convergence of NPY and CART terminals on a single PVT neuron was identified; the proportion of labeled PVT neurons that received converging NPY/CART terminals compared with the total PVT neurons projecting to the NAcSh was 2.7% ± 0.6% (n = 3). Finally, PVT cells receiving NPY, CART, or ORX terminals provided divergent axon collaterals to NAcSh and medial prefrontal cortex. The present observations provided the anatomical evidence that the PVT might play an essential role in the integration of antagonistically-acting, feeding/arousal-related peptidergic inputs on their way to the cortical reward circuit.

Effect of reversible inactivation of the reuniens nucleus on spatial learning and memory in rats using Morris water maze task.

The involvement of thalamic midline nuclei (MLN) in early stage of Alzheimer's disease and in diencephalic amnesia has drawn attention to the connectivity between the nucleus reuniens (RE) and structures of medial temporal lobe. RE is major source of thalamic afferents to the hippocampus and has been shown to exert powerful excitatory action on CA1 of hippocampus, which is supposed to be involved in learning and memory processes. However, the role of the RE on spatial memory is a controversial issue. The present study was designed to evaluate the role of the RE in acquisition, consolidation and retrieval of spatial reference memory (RM) and working memory (WM). We assessed the effect of reversible inactivation of RE with tetracaine (0.5 microl, 2%) on different stages of memory. Rats were trained on RM and WM versions of the Morris water maze (MWM) task. RE was inactivated before or immediately after training or before the probe trial of retrieval tests. The data showed that reversible inactivation of the RE significantly impaired both RM and WM versions of MWM. Therefore, it seems that nucleus reuniens of thalamus plays a role in spatial RM and WM version of the MWM task in rats.

Activation of orexin/hypocretin projections to basal forebrain and paraventricular thalamus by acute nicotine.

Orexin/hypocretin neurons of the lateral hypothalamus/perifornical area project to a diverse array of brain regions and are responsive to a variety of psychostimulant drugs. It has been shown that orexin neurons are activated by systemic nicotine administration suggesting a possible orexinergic contribution to the effects of this drug on arousal and cognitive function. The basal forebrain and paraventricular nucleus of the dorsal thalamus (PVT) both receive orexin inputs and have been implicated in arousal, attention and psychostimulant drug responses. However, it is unknown whether orexin inputs to these areas are activated by psychostimulant drugs such as nicotine. Here, we infused the retrograde tract tracer cholera toxin B subunit (CTb) into either the basal forebrain or PVT of adult male rats. Seven to 10 days later, animals received an acute systemic administration of (-) nicotine hydrogen tartrate or vehicle and were euthanized 2h later. Triple-label immunohistochemistry/immunofluorescence was used to detect Fos expression in retrogradely-labeled orexin neurons. Nicotine increased Fos expression in orexin neurons projecting to both basal forebrain and PVT. The relative activation in lateral and medial banks of retrogradely-labeled orexin neurons was similar following basal forebrain CTb deposits, but was more pronounced in the medial bank following PVT deposits of CTb. Our findings suggest that orexin inputs to the basal forebrain and PVT may contribute to nicotine effects on arousal and cognition and provide further support for the existence of functional heterogeneity across the medial-lateral distribution of orexin neurons.

Expression of vesicular glutamate transporters 1 and 2 in the cells of origin of the rat thalamostriatal pathway.

The present study is focused on the analysis of the vesicular glutamate transporters 1 and 2 (VGLUT1 and VGLUT2) used by thalamic neurons giving rise to the thalamostriatal system. Instead of studying the distribution of VGLUT proteins at the level of thalamostriatal terminals, this report is focused on identifying the expression of the VGLUT mRNAs within the parent cell bodies of thalamic neurons innervating the striatum. For this purpose, we have combined dual in situ hybridization to detect both VGLUT1 and VGLUT2 mRNAs together with retrograde tracing with cholera toxin. Our results show that VGLUT2 is the only vesicular glutamate transporter expressed in thalamostriatal-projecting neurons located in the midline and intralaminar nuclei, whereas all neurons from the ventral thalamic nuclei innervating the striatum express both VGLUTs, at least at the mRNA level. Indeed, the mRNAs encoding for VGLUT1 and VGLUT2 displayed a sharp complementary subcellular distribution within neurons from the ventral thalamic nuclei giving rise to thalamostriatal projections. The differential distribution of VGLUT mRNAs lead us to conclude that the thalamostriatal pathway is a dual system, composed by a preponderant projection arising from the midline and intralaminar nuclei using VGLUT2 as the glutamate transporter, together with another important source of striatal afferents arising from neurons in the ventral thalamic relay nuclei containing both kinds of vesicular glutamate transporters.

AVPV neurons containing estrogen receptor-beta in adult male rats are influenced by soy isoflavones.

BACKGROUND: Isoflavones, the most abundant phytoestrogens in soy foods, are structurally similar to 17beta-estradiol. It is known that 17beta-estradiol induces apoptosis in anteroventral periventricular nucleus (AVPV) in rat brain. Also, there is evidence that consumption of soy isoflavones reduces the volume of AVPV in male rats. Therefore, in this study, we examined the influence of dietary soy isoflavones on apoptosis in AVPV of 150 day-old male rats fed either a soy isoflavone-free diet (Phyto-free) or a soy isoflavone-rich diet (Phyto-600). RESULTS: The occurrence of apoptosis in AVPV was examined by TUNEL staining. The incidence of apoptosis was about 10 times higher in the Phyto-600 group (33.1 +/- 1.7%) than in the Phyto-free group (3.6 +/- 1.0%). Furthermore, these apoptotic cells were identified as neurons by dual immunofluorescent staining of GFAP and NeuN as markers of astrocytes and neurons, respectively. Then the dopaminergic neurons in AVPV were detected by immunohistochemistry staining of tyrosine hydroxylase (TH). No significant difference in the number of TH neurons was observed between the diet treatment groups. When estrogen receptor (ER) alpha and beta were examined by immunohistochemistry, we observed a 22% reduction of ERbeta-positive cell numbers in AVPV with consumption of soy isoflavones, whereas no significant change in ERalpha-positive cell numbers was detected. Furthermore, almost all the apoptotic cells were ERbeta-immunoreactive (ir), but not ERalpha-ir. Last, subcutaneous injections of equol (a major isoflavone metabolite) that accounts for approximately 70-90% of the total circulating plasma isoflavone levels did not alter the volume of AVPV in adult male rats. CONCLUSION: In summary, these findings provide direct evidence that consumption of soy isoflavones, but not the exposure to equol, influences the loss of ERbeta-containing neurons in male AVPV.

Orexin (hypocretin) innervation of the paraventricular nucleus of the thalamus.

The paraventricular nucleus of the thalamus (PVT) is a midline thalamic nucleus with projections to limbic forebrain areas such as the nucleus accumbens and amygdala. The orexin (hypocretin) peptides are synthesized in hypothalamic neurons that project throughout the CNS. The present experiments were done to describe the extent of orexin fiber innervation of the PVT in comparison to other midline and intralaminar thalamic nuclei and to establish the location and proportion of orexin neurons innervating the PVT. All aspects of the anteroposterior PVT were found to be densely innervated by orexin fibers with numerous enlargements that also stained for synaptophysin, a marker for synaptic vesicle protein associated with pre-synaptic sites. Small discrete injections of cholera toxin B into the PVT of rats resulted in the retrograde labeling of a relatively small number of orexin neurons in the medial and lateral hypothalamus. The results also showed a lack of topographical organization among orexin neurons projecting to the PVT. Previous studies indicate that orexin neurons and neurons in the PVT appear to be most active during periods of arousal. Therefore, orexin neurons and their projections to the PVT may be part of a limbic forebrain arousal system.

Cyto- and chemoarchitecture of the dorsal thalamus of the monotreme Tachyglossus aculeatus, the short beaked echidna.

We have examined the cyto- and chemoarchitecture of the dorsal thalamus of the short beaked echidna (Tachyglossus aculeatus), using Nissl and myelin staining, immunoreactivity for parvalbumin, calbindin, calretinin and non-phosphorylated neurofilament protein (SMI-32 antibody), and histochemistry for acetylcholinesterase and NADPH diaphorase. Immunohistochemical methods revealed many nuclear boundaries, which were difficult to discern with Nissl staining. Parvalbumin immunoreactive somata were concentrated in the ventral posterior, reticular, posterior, lateral and medial geniculate nuclei, while parvalbumin immunoreactivity of the neuropil was present throughout all but the midline nuclei. Large numbers of calbindin immunoreactive somata were also found within the midline thalamic nuclei, and thalamic sensory relay nuclei. Immunoreactivity for calretinin was found in many small somata within the lateral geniculate "a" nucleus, with other labelled somata found in the lateral geniculate "b" nucleus, ventral posterior medial and ventral posterior lateral nuclei. Immunoreactivity with the SMI-32 antibody was largely confined to somata and neuropil within the thalamocortical relay nuclei (ventral posterior medial and lateral nuclei, lateral and medial geniculate nuclei and the posterior thalamic nucleus). In broad terms there were many similarities between the thalamus of this monotreme and that of eutheria (e.g. disposition of somatosensory thalamus, complementarity of parvalbumin and calbindin immunoreactive structures), but there were some unique features of the thalamus of the echidna. These include the relatively small size of the thalamic reticular nucleus and the preponderance of calbindin immunoreactive neurons over parvalbumin immunoreactive neurons in the ventral posterior nucleus.

Hypothalamic STAT proteins: regulation of somatostatin neurones by growth hormone via STAT5b.

Signal transducers and activators of transcription (STATs) are a family of transcription factors linked to class I cytokine receptors. In the present study, we investigated whether their distribution in the hypothalamus reflects the feedback regulation by growth hormone and what role they might play in the functioning of target neurones. We demonstrate that each of the seven known STATs has a distinct distribution in the hypothalamus. Notably, the STAT5 proteins, that are important in growth hormone (GH) and prolactin signalling in peripheral tissues, were expressed in somatostatin neurones of the periventricular nucleus and dopamine neurones of the arcuate nucleus. Because somatostatin neurones are regulated by feedback from circulating GH, we investigated the importance of STAT5 in these neurones. We demonstrate that STAT5b protein expression, similar to somatostatin mRNA, is sexually dimorphic in the periventricular nucleus of rats and mice. Furthermore, chronic infusion of male dwarf rats with GH increased the expression of STAT5b, while a single injection of GH into similar rats induced the phosphorylation of STAT5 proteins. The cellular abundance of somatostatin mRNA in STAT5b-deficient mice was significantly reduced in the periventricular nucleus, effectively reducing the sexually dimorphic expression. These results are consistent with the hypothesis that STAT5 proteins are involved in the feedback regulation of somatostatin neurones by GH, and that these neurones may respond to patterned GH secretion to reinforce sexual dimorphism in the GH axis.

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.

Thalamic field potentials in chronic central pain treated by periventricular gray stimulation -- a series of eight cases.

Chronic deep brain stimulation (DBS) of the periventricular gray (PVG) has been used for the treatment of chronic central pain for decades. In recent years motor cortex stimulation (MCS) has largely supplanted DBS in the surgical management of intractable neuropathic pain of central origin. However, MCS provides satisfactory pain relief in about 50-75% of cases, a range comparable to that reported for DBS (none of the reports are in placebo-controlled studies and hence the further need for caution in evaluating and comparing these results). Our experience also suggests that there is still a role for DBS in the control of central pain. Here we present a series of eight consecutive cases of intractable chronic pain of central origin treated with PVG DBS with an average follow-up of 9 months. In each case, two electrodes were implanted in the PVG and the ventroposterolateral thalamic nucleus, respectively, under guidance of corneal topography/magnetic resonance imaging image fusion. The PVG was stimulated in the frequency range of 2-100 Hz in alert patients while pain was assessed using the McGill-Melzack visual analogue scale. In addition, local field potentials (FPs) were recorded from the sensory thalamus during PVG stimulation. Maximum pain relief was obtained with 5-35 Hz stimulation while 50-100 Hz made the pain worse. This suggests that pain suppression was frequency dependent. Interestingly, we detected low frequency thalamic FPs at 0.2-0.4 Hz closely associated with the pain. During 5-35 Hz PVG stimulation the amplitude of this potential was significantly reduced and this was associated with marked pain relief. At the higher frequencies (50-100 Hz), however, there was no reduction in the FPs and no pain suppression. We have found an interesting and consistent correlation between thalamic electrical activity and chronic pain. This low frequency potential may provide an objective index for quantifying chronic pain, and may hold further clues to the mechanism of action of PVG stimulation. It may be possible to use the presence of these slow FPs and the effect of trial PVG DBS on both the clinical status and the FPs to predict the probable success of future pain control in individual patients.

Protein kinase C gamma-like immunoreactivity of trigeminothalamic neurons in the medullary dorsal horn of the rat.

We examined protein kinase C gamma-like immunoreactivity (PKCgamma-LI) of trigeminothalamic neurons in the rat medullary dorsal horn (MDH) after injecting a retrograde tracer, Fluoro-Gold (FG), into the thalamus. Over 90% of FG-labeled neurons in the marginal layer (lamina I) and a few FG-labeled neurons in the superficial part of the magnocellular layer (lamina III) showed PKCgamma-LI. No PKCgamma-neurons in the substantia gelatinosa (lamina II) were labeled with FG. PKCgamma-mediated regulation of trigeminothalamic neurons may contribute to the changes in MDH activity during persistent pain.

Thalamic distribution of zinc-rich terminal fields and neurons of origin in the rat.

Several cortico-cortical and limbic-related circuits are enriched in zinc, which is considered as an important modulator of glutamatergic transmission. While heavy metals have been detected in the thalamus, the specific presence of zinc has not been examined in this region. We have used two highly sensitive variations of the Timm method to study the zinc-rich innervation in the rat thalamus, which was compared to the distribution of acetylcholinesterase activity. The origin of some of these zinc-rich projections was also investigated by means of retrograde transport after intracerebral infusions of sodium selenium (Na2SeO3). The overall zinc staining in the thalamus was much lower than in the neocortex, striatum or basal forebrain; however, densely stained terminal fields were observed in the dorsal tip of the reticular thalamic nucleus, the anterodorsal and lateral dorsal thalamic nuclei and the zona incerta. In addition, moderately stained zinc-rich terminal fields were found in the rostral intralaminar nuclei, nucleus reuniens and lateral habenula. Intracerebral infusions of Na2SeO3 in the lateral dorsal nucleus resulted in retrogradely labeled neurons that were located in the postsubiculum, and also in the pre- and parasubiculum. These results are the first to establish the existence of a zinc-rich subicular-thalamic projection. Similar infusions in either the intralaminar nuclei or the zona incerta resulted in labeling of neurons in several brainstem structures related to the reticular formation. Our results provide morphological evidence for zinc modulation of glutamatergic inputs to highly selective thalamic nuclei, arising differentially from either cortical limbic areas or from brainstem ascending activation systems.