A ventrolateral medulla-midline thalamic circuit for hypoglycemic feeding

Marked deficits in glucose availability, or glucoprivation, elicit organism-wide counter-regulatory responses whose purpose is to restore glucose homeostasis. However, while catecholamine neurons of the ventrolateral medulla (VLMCA) are thought to orchestrate these responses, the circuit and cellular mechanisms underlying specific counter-regulatory responses are largely unknown. Here, we combined anatomical, imaging, optogenetic and behavioral approaches to interrogate the circuit mechanisms by which VLMCA neurons orchestrate glucoprivation-induced food seeking behavior. Using these approaches, we found that VLMCA neurons form functional connections with nucleus accumbens (NAc)-projecting neurons of the posterior portion of the paraventricular nucleus of the thalamus (pPVT). Importantly, optogenetic manipulations revealed that while activation of VLMCA projections to the pPVT was sufficient to elicit robust feeding behavior in well fed mice, inhibition of VLMCA-pPVT communication significantly impaired glucoprivation-induced feeding while leaving other major counterregulatory responses intact. Collectively our findings identify the VLMCA-pPVT-NAc pathway as a previously-neglected node selectively controlling glucoprivation-induced food seeking. Moreover, by identifying the ventrolateral medulla as a direct source of metabolic information to the midline thalamus, our results support a growing body of literature on the role of the PVT in homeostatic regulation.

Separate cortical and hippocampal cell populations target the rat nucleus reuniens and mammillary bodies

Nucleus reuniens receives dense projections from both the hippocampus and the frontal cortices. Reflecting these connections, this nucleus is thought to enable executive functions, including those involving spatial learning. The mammillary bodies, which also support spatial learning, again receive dense hippocampal inputs, as well as lighter projections from medial frontal areas. The present study, therefore, compared the sources of these inputs to nucleus reuniens and the mammillary bodies. Retrograde tracer injections in rats showed how these two diencephalic sites receive projections from separate cell populations, often from adjacent layers in the same cortical areas. In the subiculum, which projects strongly to both sites, the mammillary body inputs originate from a homogenous pyramidal cell population in more superficial levels, while the cells that target nucleus reuniens most often originate from cells positioned at a deeper level. In these deeper levels, a more morphologically diverse set of subiculum cells contributes to the thalamic projection, especially at septal levels. While both diencephalic sites also receive medial frontal inputs, those to nucleus reuniens are especially dense. The densest inputs to the mammillary bodies appear to arise from the dorsal peduncular cortex, where the cells are mostly separate from deeper neurons that project to nucleus reuniens. Again, in those other cortical regions that innervate both nucleus reuniens and the mammillary bodies, there was no evidence of collateral projections. The findings support the notion that these diencephalic nuclei represent components of distinct, but complementary, systems that support different aspects of cognition.

Nucleus reuniens of the thalamus contains head direction cells

Discrete populations of brain cells signal heading direction, rather like a compass. These 'head direction' cells are largely confined to a closely-connected network of sites. We describe, for the first time, a population of head direction cells in nucleus reuniens of the thalamus in the freely-moving rat. This novel subcortical head direction signal potentially modulates the hippocampal CA fields directly and, thus, informs spatial processing and memory.

NFκB signaling is essential for the lipopolysaccharide-induced increase of type 2 deiodinase in tanycytes

The enzyme type 2 deiodinase (D2) is a major determinant of T₃ production in the central nervous system. It is highly expressed in tanycytes, a specialized cell type lining the wall of the third ventricle. During acute inflammation, the expression of D2 in tanycytes is up-regulated by a mechanism that is poorly understood at present, but we hypothesized that cJun N-terminal kinase 1 (JNK1) and v-rel avian reticuloendotheliosis viral oncogene homolog A (RelA) (the 65 kD subunit of NFκB) inflammatory signal transduction pathways are involved. In a mouse model for acute inflammation, we studied the effects of lipopolysaccharide (LPS) on mRNA expression of D2, JNK1, and RelA in the periventricular area (PE) and the arcuate nucleus-median eminence of the hypothalamus. We next investigated LPS-induced D2 expression in primary tanycyte cell cultures. In the PE, the expression of D2 was increased by LPS. In the arcuate nucleus, but not in the PE, we found increased RelA mRNA expression. Likewise, LPS increased D2 and RelA mRNA expression in primary tanycyte cell cultures, whereas JNK1 mRNA expression did not change. Phosphorylation of RelA and JNK1 was increased in tanycyte cell cultures 15-60 minutes after LPS stimulation, confirming activation of these pathways. Finally, inhibition of RelA with the chemical inhibitors sulfasalazine and 4-Methyl-N¹-(3-phenylpropyl)benzene-1,2-diamine (JSH-23) in tanycyte cell cultures prevented the LPS-induced D2 increase. We conclude that NFκB signaling is essential for the up-regulation of D2 in tanycytes during inflammation.

Congenital hydrocephalus and abnormal subcommissural organ development in Sox3 transgenic mice

Congenital hydrocephalus (CH) is a life-threatening medical condition in which excessive accumulation of CSF leads to ventricular expansion and increased intracranial pressure. Stenosis (blockage) of the Sylvian aqueduct (Aq; the narrow passageway that connects the third and fourth ventricles) is a common form of CH in humans, although the genetic basis of this condition is unknown. Mouse models of CH indicate that Aq stenosis is associated with abnormal development of the subcommmissural organ (SCO) a small secretory organ located at the dorsal midline of the caudal diencephalon. Glycoproteins secreted by the SCO generate Reissner's fibre (RF), a thread-like structure that descends into the Aq and is thought to maintain its patency. However, despite the importance of SCO function in CSF homeostasis, the genetic program that controls SCO development is poorly understood. Here, we show that the X-linked transcription factor SOX3 is expressed in the murine SCO throughout its development and in the mature organ. Importantly, overexpression of Sox3 in the dorsal diencephalic midline of transgenic mice induces CH via a dose-dependent mechanism. Histological, gene expression and cellular proliferation studies indicate that Sox3 overexpression disrupts the development of the SCO primordium through inhibition of diencephalic roof plate identity without inducing programmed cell death. This study provides further evidence that SCO function is essential for the prevention of hydrocephalus and indicates that overexpression of Sox3 in the dorsal midline alters progenitor cell differentiation in a dose-dependent manner.

Circadian transcriptional factor DBP regulates expression of Kiss1 in the anteroventral periventricular nucleus

The expression of Kiss1 in the anteroventral periventricular nucleus (AVPV) and its product, metastin/kisspeptin, show a circadian pattern with a peak in the evening, which shows a strong phase relationship with the time of the gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) surge in rodents. Here we report that a circadian transcriptional factor, albumin D-site binding protein (Dbp), was able to trigger mKiss1 transcription via the D-box, and this effect was combined with those of estrogen receptor α (ERα) and its ligand, estrogen. A histological study demonstrated that some cells in the AVPV co-expressed Dbp with ERα in adult female rats. Expression of ERα was not rhythmic in the AVPV, however, mRNA of Dbp in the AVPV accumulated with a robust diurnal rhythm in proestrus, but not on the first day of diestrus. Thus, these results suggest that Dbp and estrogen regulate the expression of Kiss1 in the AVPV, thereby mediating the GnRH/LH surge.

Electrical and morphological characteristics of anteroventral periventricular nucleus kisspeptin and other neurons in the female mouse

Neurons in the rodent anteroventral periventricular nucleus (AVPV) play a key role in integrating circadian and gonadal steroid hormone information in the control of fertility. In particular, estradiol-sensitive kisspeptin neurons located in the AVPV, and adjacent structures [together termed the rostral periventricular area of the third ventricle (RP3V)], are critical for puberty onset and the preovulatory LH surge. The present study aimed to establish the morphological and electrical firing characteristics of RP3V neurons, including kisspeptin neurons, in the adult female mouse. Cell-attached electrical recordings, followed by juxtacellular dye filling, of 129 RP3V neurons in the acute brain slice preparation revealed these cells to exhibit multipolar (53%), bipolar (43%), or unipolar (4%) dendritic morphologies along with silent (16%), irregular (41%), bursting (25%), or tonic (34%) firing patterns. Postrecording immunocytochemistry identified 17 of 100 filled RP3V cells as being kisspeptin neurons, all of which exhibited complex multipolar dendritic trees and significantly (P < 0.05) higher bursting or high tonic firing rates compared with nonkisspeptin neurons. The firing pattern of RP3V neurons fluctuated across the estrous cycle with a significant (P < 0.05) switch from irregular to tonic firing patterns found on proestrus. A similar nonsignificant trend was found for kisspeptin neurons. All RP3V neurons responded to gamma-aminobutyric acid and glutamate, about 10% to RFamide-related peptide-3, about 5% to vasopressin, 0% to vasoactive intestinal peptide, and 0% to kisspeptin. These studies provide a morphological and electrical description of AVPV/RP3V neurons and demonstrate their cycle-dependent firing patterns along with an unexpected lack of acute response to the circadian neuropeptides.

[Quantitative characteristic of primary structural modules in relay nuclei of thalamic sensory systems in man]

The module organization of neurons was studied in ventral posterior medial (VPM) and ventral posterior lateral (VPL) relay nuclei of thalamic sensory systems in adult man. Material, obtained from individuals aged 48-70 years, was fixed in 4% paraformaldehyde, sectioned at 40 microm and stained using Kluver-Barrer's method. The following parameters were determined: the numbers of neurons forming group and chain modules, profile field areas (PFA) of cell bodies of neurons forming modules, total number of satellite gliocytes and identified gliocytes (oligodendrocytes and astrocytes) in the module. Neuronal PFA was measured using digitizer on exact drawings of the cells made with the drawing device (at magnification of 1025). The data obtained were fed into the computer and processed using the program of non-parametric data analysis. Neurons, forming group and chain modules, were of medium size (201 to 350 microm2) in both nuclei. Most of group and chain modules in human VPM and VPL thalamic nuclei consisted of 3-4 cells. In VPM nucleus, a single group module includes 8.4 satellite gliocytes, and a chain module - 8.6 gliocytes. In VPL nucleus these parameters are equal to 7.7 and 8.2, respectively. Oligodendrocyte number in the modules in VPM and VPL thalamic nuclei is 3 times greater than that of the astrocytes.

Distribution of trigeminothalamic and spinothalamic lamina I terminations in the cat

The distribution in the thalamus of terminal projections from lamina I neurons of the trigeminal, cervical, and lumbosacral dorsal horn was investigated with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in the cat. Iontophoretic injections were guided by single- and multi-unit physiological recordings. The injections in particular cases were essentially restricted to lamina I, whereas in others they spread across laminae I-III or laminae I-V. The trigemino- and spinothalamic (TSTT) terminations were identified immunohistochemically. In all cases, regardless of the level of the injections, terminal fibers were consistently distributed in three main locations: the submedial nucleus; the ventral aspect of the basal ventral medial nucleus and ventral posterior nuclei; and, the dorsomedial aspect of the ventral posterior medial nucleus. The terminal fields in the submedial nucleus and the ventral aspect of the ventral posterior group were topographically organized. Terminations along the ventral aspect of the ventral posterior group extended posterolaterally into the caudal part of the posterior nucleus and anteromedially into the ventromedial part of the ventral lateral nucleus. In several cases with trigeminal lamina I injections, a terminal labeling patch was observed within the core of the ventral posterior medial nucleus. In cases with spinal lamina I injections, terminations were also consistently found in the lateral habenula, the parafascicular nucleus, and the nucleus reuniens. Isolated terminal fibers were occasionally seen in the zona incerta, the dorsomedial hypothalamus, and other locations. These anatomical observations extend prior studies of TSTT projections and identify lamina I projection targets that are important for nociceptive, thermoreceptive, and homeostatic processing in the cat. The findings are consistent with evidence from physiological (single-unit and antidromic mapping) and behavioral studies. The novel identification of spinal lamina I input to the lateral habenula could be significant for homeostatic behaviors.

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.

Anatomical analysis of afferent projections to 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. Using retrograde tracing techniques, we examined, compared, and contrasted afferent projections to the four divisions of the mPFC in the rat: the medial (frontal) agranular (AGm), anterior cingulate (AC), prelimbic (PL), and infralimbic (IL) cortices. Each division of the mPFC receives a unique set of afferent projections. There is a shift dorsoventrally along the mPFC from predominantly sensorimotor input to the dorsal mPFC (AGm and dorsal AC) to primarily 'limbic' input to the ventral mPFC (PL and IL). The AGm and dorsal AC receive afferent projections from widespread areas of the cortex (and associated thalamic nuclei) representing all sensory modalities. This information is presumably integrated at, and utilized by, the dorsal mPFC in goal directed actions. In contrast with the dorsal mPFC, the ventral mPFC receives significantly less cortical input overall and afferents from limbic as opposed to sensorimotor regions of cortex. The main sources of afferent projections to PL/IL are from the orbitomedial prefrontal, agranular insular, perirhinal and entorhinal cortices, the hippocampus, the claustrum, the medial basal forebrain, the basal nuclei of amygdala, the midline thalamus and monoaminergic nuclei of the brainstem. With a few exceptions, there are few projections from the hypothalamus to the dorsal or ventral mPFC. Accordingly, subcortical limbic information mainly reaches the mPFC via the midline thalamus and basal nuclei of amygdala. As discussed herein, based on patterns of afferent (as well as efferent) projections, PL is positioned to serve a direct role in cognitive functions homologous to dorsolateral PFC of primates, whereas IL appears to represent a visceromotor center homologous to the orbitomedial PFC of primates.

Orexin-induced modulation of state-dependent intrinsic properties in thalamic paraventricular nucleus neurons attenuates action potential patterning and frequency

The thalamic paraventricular nucleus (PVT) receives a dense innervation from orexin-synthesizing lateral hypothalamic neurons. Since PVT neurons display state-dependent tonic or low threshold spike-driven burst firing patterns, we examined how the response to exogenously applied orexins might modulate these features. Data were obtained with whole-cell patch clamp recording techniques in rat brain slices prepared during the subjective lights-on period. PVT neurons displayed a mean resting membrane potential of -61+/-6 mV and input conductance of 1.3+/-0.1 nS (n=60). The majority (90/107) of cells tested responded to orexin A and/or orexin B peptides (100-1000 nM), each inducing similar slowly rising and prolonged membrane depolarizations. We next evaluated associated changes in firing patterns and action potential frequency. Of 17 spontaneously silent neurons, 5 were induced into tonic firing and 4 into burst firing modes. Of nine spontaneously bursting neurons, three displayed an increase in burst frequency and in the number of action potentials within a burst. By contrast, another six cells were induced into tonic firing mode, with a marked decrease in instantaneous firing frequency and a shift in their excitatory postsynaptic potential-evoked responses from burst firing patterns to single action potentials. Under voltage clamp, orexins induced inward current (-21.8+/-2.4 pA at -60 mV) in 20/22 cells. In 13 cells, current-voltage (I-V) plots revealed a decrease in net conductance and reversal at -110+/-9 mV, while 3 cells displayed an increase in net conductance that reversed at -26+/-8 mV. These observations imply suppression of potassium and/or induction of nonselective cationic conductances in orexin-induced depolarization in PVT neurons, permitting these peptides to modulate intrinsic state-dependent properties. In vivo, such changes in firing patterns and frequency of action potential discharges could influence neurotransmission through PVT and activity-dependent synaptic plasticity at target sites of these neurons.

Differential activation of anterior and midline thalamic nuclei following retrieval of aversively motivated learning tasks

Two thalamic nuclear groups, the anterior thalamic nuclei (ATN) and midline and intralaminar thalamic complex (MITC) have connections to the prefrontal cortex, amygdala, hippocampus and accumbens that are important for learning and memory. However, the anatomical proximity between the ATN and MITC makes it difficult to reveal their roles in memory retrieval of aversive conditioned behavior. To address the issue, we explored the activation of the ATN and MITC, as represented by the expression of the immediate early gene c-fos, following either the retrieval of a conditioned taste aversion (CTA) induced by taste-LiCl pairing (visceral aversion) or of inhibitory avoidance (IA) induced by context-foot shock pairing (somatic aversion) in rats. The anterodorsal (AD) nucleus in the ATN was activated by foot shock and the recall of IA, but not by i.p. injection of LiCl or the recall of CTA. No significant elevation was observed in the other ATN following these treatments. Among nuclei of the MITC, the paraventricular thalamic nucleus (PVT) was activated by the delivery of shock or LiCl and by the recall of both CTA and IA, while the mediodorsal thalamus (MD) and central medial and intermediate thalamus (CM/IMD) were not. The innately aversive taste of quinine did not elevate c-fos expression in either the ATN or MITC. These results suggest that the PVT in the MITC is involved in the processing and retrieval of both taste-malaise and context-shock association tasks, while the AD in the ATN is involved in those of context-shock association only. The difference of the activity between the ATN and MITC demonstrates their functional and anatomical heterogeneity in neural substrates for aversive learning tasks.

Functional and anatomical connection between the paraventricular nucleus of the thalamus and dopamine fibers of the nucleus accumbens

The shell of the nucleus accumbens (NacSh) receives a dense innervation from dopamine (DA) neurons in the ventral tegmental area (VTA) and from glutamate neurons in the paraventricular nucleus of the thalamus (PVT). The present study examined in urethane-anesthetized rats the effects of electrical stimulation of the PVT on DA levels in the NacSh as measured with amperometry and chronoamperometry. Stimulation of the PVT (40 Hz, 1.0 ms, 400 microA, 5 seconds) resulted in a brief increase in electrochemical currents detected in the NacSh. Inhibition of DA neurons in the VTA using lidocaine (4%, 500 nL) or intravenous apomorphine (0.15 mg/kg) decreased the resting voltammetric signal but had no effect on PVT-evoked responses. Blocking of ionotropic glutamate receptors in the NacSh with local administration of kynurenic acid attenuated the PVT-evoked responses. Anterograde tracing with biotinylated dextran amine demonstrated that PVT targets regions of very dense tyrosine hydroxylase fiber staining in the NacSh. Consistent with the projection pattern of the PVT to the NacSh, stimulation of the PVT evoked the largest oxidation current changes in the NacSh, whereas small or no changes were elicited in other areas of the striatum. This study suggests that glutamate release from PVT terminals can act on ionotropic glutamate receptors in the NacSh to induce DA efflux. Modulation of DA levels in the NacSh by the PVT may be linked to arousal-induced increases in DA tone and could be involved in the facilitation of specific behavioral patterns associated with arousal or stressful situations.

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.

Heterogeneity in low voltage-activated Ca2+channel-evoked Ca2+responses within neurons of the thalamic paraventricular nucleus

Low voltage-activated Ca2+ channels (LVA or T-type Ca2+ channels) are crucial to burst firing and oscillations in thalamocortical relay cells and are exhibited by neurons in the paraventricular nucleus of thalamus (PVT), a dorsal midline nucleus deemed important in the neural representation of motivational behaviours. We used a functional approach (whole-cell patch-clamp electrophysiology combined with confocal laser scanning microscopy) to analyse the spatial distribution of LVA Ca2+ channel-evoked Ca2+ transients in PVT neurons. We observed that the magnitude of LVA Ca2+ channel-evoked Ca2+ transients was significantly greater in proximal dendrites (located up to 20 microm from the soma) than in the soma. In addition, the magnitudes of these Ca2+ transients varied significantly not only among different dendrites of the same cell but also within individual dendrites. These findings suggest that LVA Ca2+ channels are expressed (i) predominantly on the proximal dendrites and (ii) heterogeneously within individual dendrites of PVT neurons. The spatial characteristics of dendritic LVA Ca2+ channels in PVT neurons suggest that these channels may regulate burst firing by modulating dendritic afferent inputs.

Expression of a functional hyperpolarization-activated current (Ih) in the mouse nucleus reticularis thalami

The GABAergic neurons of the nucleus reticularis thalami (nRT) express the type 2 hyperpolarization-activated cAMP-sensitive (HCN2) subunit mRNA, but surprisingly, they were reported to lack the hyperpolarization-activated (Ih) current carried by this subunit. Using the voltage-clamp recordings in the thalamocortical slice preparation of the newborn and juvenile mice (P6-P23), we demonstrate that, in the presence of 1 mM barium (Ba2+), the nRT neurons express a slow hyperpolarization-activated inward current, suggesting that the Ih is present but masked in control conditions by K+ leak currents. We investigate the identity of the hyperpolarization-activated current in the nRT by studying its physiological and pharmacological profile in presence of Ba2+. We show that it has voltage- and time-dependent properties typical of the Ih, that it is blocked by cesium and ZD7288, two blockers of the Ih, and that it is carried both by the K+ and Na+ ions. We could also alter the gating characteristics of the hyperpolarization-activated current in the nRT by adding a nonhydrolysable analogue of cAMP to the pipette solution. Finally, using the current-clamp recording, we showed that blocking the hyperpolarization-activated current induced an hyperpolarization correlated with an increase of the R(in) of the nRT neurons. In conclusion, our results demonstrate that the nRT neurons express the Ih with slow kinetics similar to those described for the homomeric HCN2 channels, and we show that the Ih of the nRT contributes to the excitability of the nRT neurons in normal conditions.

Calcium-binding proteins in GABAergic calyciform synapses of the reticular nucleus

Large calyciform synapses in the rat reticular thalamic nucleus are characterized by the presence of gamma-aminobutyric acid. Presynaptic terminals are also loaded with calcium-binding proteins such as parvalbumin, calbindin, calretinin and calcineurin. The number of calyciform terminals containing gamma-aminobutyric acid and parvalbumin is 2005 in young adult rats; calbindin is present in 1,500, calretinin in 850 and calcineurin in 560 calyciform terminals. Developmental studies revealed that gamma-aminobutyric acid and calcium-binding proteins are virtually absent from calyciform terminals at birth but their occurrence increased considerably during postnatal life, suggesting increasing regulation of presynaptic calcium signaling during postnatal life. It is concluded that synaptic activity of large calyciform gamma-aminobutyric acid-containing synapses of the reticular thalamic nucleus is mediated, regulated or accompanied by calcium ions.

Changes in neuropeptide FF and NPY immunohistochemical patterns in rat brain under heroin treatment

Immunohistochemical distribution patterns of neuropeptide FF (NPFF) and neuropeptide tyrosine (NPY) were studied in the brain of rats submitted to two different protocols of heroin treatment. In drug-naive rats, acutely injected heroin significantly depleted NPFF-immunoreactive material within the neurons of the nucleus of solitary tract (NTS), significantly decreased the density of NPFF-immunoreactive nerve fibers within the median eminence, pituitary stalk, and neurohypophysis, and markedly increased NPY-immunoreactive neurons and nerve fibers in the thalamic paraventricular nucleus and bed nucleus of stria terminalis. In drug-sensitized rats, heroin significantly increased the number and immunostaining intensity of the NPFF-immunoreactive neurons within the NTS and induced minor changes in the NPFF-immunoreactive nerve fiber network of the median eminence, pituitary stalk, and neurohypophysis and a relatively minor increase in NPY neurons in the thalamic paraventricular nucleus and bed nucleus of stria terminalis. These heroin-induced changes suggest that NPFF is involved in regulating the effects of the heroin injection and in the mechanisms underlying behavioral sensitization. They also add further support to the key role of NPY in any conditions tending to change the animal homeostasis.

A daily palatable meal without food deprivation entrains the suprachiasmatic nucleus of rats

Food is considered a potent Zeitgeber for peripheral oscillators but not for the suprachiasmatic nucleus (SCN), which is entrained principally by the light-dark cycle. However, when food attains relevant properties in quantity and quality, it can be a potent Zeitgeber even for the SCN. Here we evaluated the entrainment influence of a daily palatable meal, without regular food deprivation, on the circadian rhythm of locomotor activity and the c-Fos and PER-1 protein expression in the SCN. Rats fed ad libitum, in constant darkness, received a palatable meal for 6 weeks starting in the middle of the subjective day. Locomotor activity showed entrainment when the offset of activity coincided with the palatable meal-time. In the SCN, the peak expression of c-Fos was observed at palatable meal-time and PER-1 showed a peak during the onset of subjective night, as predicted according to the behavioural entrained pattern. In addition, c-Fos and PER-1 expression in the paraventricular thalamic nucleus (PVT) showed increased expression at palatable meal-time, while the intergeniculate leaflet did not, suggesting that the PVT may be involved as an input pathway of palatable food-entrainment to the SCN. These results demonstrate that daily access to a palatable meal can entrain the SCN; several stimuli can be implicated in this process, including motivation and arousal.

Suprachiasmatic nucleus communicates with anterior thalamic paraventricular nucleus neurons via rapid glutamatergic and gabaergic neurotransmission: State-dependent response patterns observed in vitro

The hypothalamic suprachiasmatic nucleus uniquely projects to the midline thalamic paraventricular nucleus. To characterize this projection, patch clamp techniques applied in acute rat brain slice preparations examined responses of anterior thalamic paraventricular nucleus neurons to focal suprachiasmatic nucleus stimulation. Whole cell recordings from slices obtained during daytime (n=40) revealed neurons with a mean membrane potential of -66+/-1.2 mV, input conductance of 1.5+/-0.1 nS and state-dependent tonic or burst firing patterns. Electrical stimulation (one or four pulses) in suprachiasmatic nucleus elicited monosynaptic excitatory postsynaptic potentials (mean latency of 12.6+/-0.6 ms; n=12), featuring both AMPA and N-methyl-D-aspartate-glutamate receptor-mediated components, and monosynaptic bicuculline-sensitive inhibitory postsynaptic potentials (mean latency of 16.6+/-0.6 ms; n=7) reversing polarity at -72+/-2.6 mV, close to the chloride equilibrium potential. Glutamate microstimulation of suprachiasmatic nucleus also elicited transient increases in spontaneous excitatory or inhibitory postsynaptic currents in anterior thalamic paraventricular neurons. Recordings from rats under reverse light/dark conditions (n=22) yielded essentially similar responses to electrical stimulation. At depolarized membrane potentials, suprachiasmatic nucleus-evoked excitatory postsynaptic potentials triggered single action potentials, while evoked inhibitory postsynaptic potentials elicited a silent period in ongoing tonic firing. By contrast, after manual adjustment of membrane potentials to hyperpolarized levels, neuronal response to the same "excitatory" stimulus was a low threshold spike and superimposed burst firing, while responses to "inhibitory" stimuli paradoxically elicited excitatory rebound low threshold spikes and burst firing. These data support the existence of glutamatergic and GABAergic efferents from the suprachiasmatic nucleus to its target neurons. Additionally, in thalamic paraventricular nucleus neurons, responses to activation of their suprachiasmatic afferents may vary in accordance with their membrane potential-dependent intrinsic properties, a characteristic typical of thalamocortical neurons.

The paraventricular nucleus of the thalamus as an interface between the orexin and CART peptides and the shell of the nucleus accumbens

The paraventricular nucleus of the thalamus (PVT) receives afferents from the brainstem and has been thought to relay arousal related information to specific limbic forebrain areas, including the nucleus accumbens. More recent anatomical observations suggest that the PVT also receives afferents from various hypothalamic nuclei. The present anatomical experiments investigated the innervation of the PVT by fibers immunoreactive for orexin and cocaine and amphetamine related transcript (CART), two feeding-related peptides highly concentrated in the hypothalamus. Emphasis was placed on identifying the relationship between these neuropeptides and PVT neurons projecting to the shell of the nucleus accumbens (NacSh). Infusion of a retrograde tracer into the NacSh labeled numerous cells of the midline and intralaminar thalamus, most of which were restricted to the PVT. The retrograde tracer, orexin fibers, and CART fibers were immunopositive throughout the entire PVT whereas no overlap between signals was evident within adjacent thalamic regions. High-magnification light and confocal microscopy showed that both orexin and CART fibers made frequent contact with retrogradely labeled neurons throughout the anteroposterior PVT. Furthermore, single PVT cells retrogradely labeled from the NacSh were apposed by both orexin and CART fibers. The present experiments provide the first evidence suggesting a role for the PVT as a relay of hypothalamic activity to the nucleus accumbens. The PVT may function to link visceral arousal signals with limbic regions involved in behavioral responses.

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.

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.

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.

Afferent projections to nucleus reuniens of the thalamus

The nucleus reuniens (RE) is the largest of the midline nuclei of the thalamus and the major source of thalamic afferents to the hippocampus and parahippocampal structures. Nucleus reuniens has recently been shown to exert powerful excitatory actions on CA1 of the hippocampus. Few reports on any species have examined afferent projections to nucleus reuniens. By using the retrograde anatomical tracer Fluorogold, we examined patterns of afferent projections to RE in the rat. We showed that RE receives a diverse and widely distributed set of afferents projections. The main sources of input to nucleus reuniens were from the orbitomedial, insular, ectorhinal, perirhinal, and retrosplenial cortices; CA1/subiculum of hippocampus; claustrum, tania tecta, lateral septum, substantia innominata, and medial and lateral preoptic nuclei of the basal forebrain; medial nucleus of amygdala; paraventricular and lateral geniculate nuclei of the thalamus; zona incerta; anterior, ventromedial, lateral, posterior, supramammillary, and dorsal premammillary nuclei of the hypothalamus; and ventral tegmental area, periaqueductal gray, medial and posterior pretectal nuclei, superior colliculus, precommissural/commissural nuclei, nucleus of the posterior commissure, parabrachial nucleus, laterodorsal and pedunculopontine tegmental nuclei, nucleus incertus, and dorsal and median raphe nuclei of the brainstem. The present findings of widespread projections to RE, mainly from limbic/limbic-associated structures, suggest that nucleus reuniens represents a critical relay in the transfer of limbic information (emotional/cognitive) from RE to its major targets, namely, to the hippocampus and orbitomedial prefrontal cortex. RE appears to be a major link in the two-way exchange of information between the hippocampus and the medial prefrontal cortex.

Passive movements of the head do not abolish anticipatory firing properties of head direction cells

Neurons in the anterior dorsal thalamic nucleus (ADN) of the rat selectively discharge in relation to the animal's head direction (HD) in the horizontal plane. Temporal analyses of cell firing properties reveal that their discharge is optimally correlated with the animal's future directional heading by approximately 24 ms. Among the hypotheses proposed to explain this property is that ADN HD cells are informed of future head movement via motor efference copy signals. One prediction of this hypothesis is that when the rat's head is moved passively, the anticipatory time interval (ATI) will be attenuated because the motor efference signal reflects only the active contribution to the movement. The present study tested this hypothesis by loosely restraining the animal and passively rotating it through the cell's preferred direction. Contrary to our prediction, we found that ATI values did not decrease during passive movement but in fact increased significantly. HD cells in the postsubiculum did not show the same effect, suggesting independence between the two sites with respect to anticipatory firing. We conclude that it is unlikely that a motor efference copy signal alone is responsible for generating anticipatory firing in ADN HD cells.

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.

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.

Cells in midline thalamus, central amygdala, and nucleus accumbens responding specifically to antipsychotic drugs

RATIONALE

Determining brain regions in which neuroleptic drugs of different types produce similar effects, especially where these effects are not shared with drugs lacking antipsychotic efficacy, provides evidence as to how and where the clinical effects of neuroleptic drugs are mediated.

OBJECTIVE

For this study, the pattern of expression of the protein Fos, a marker of cellular activation, was compared after administration of the typical neuroleptic haloperidol, the antipsychotic drug clozapine, and the atypical neuroleptic olanzapine, as well as the sedative drug diphenhydramine and the anxiolytic lorazepam.

METHODS

Animals (Sprague-Dawley rats, three per cohort) received intraperitoneal injections of haloperidol (1 mg/kg), clozapine (20 mg/kg), olanzapine (5 mg/kg), diphenhydramine hydrochloride (1 mg/kg), lorazepam (5 mg/kg) or vehicle (2% lactic acid, 1 ml/kg). Two hours after drug administration, animals were killed. Patterns of activated cells were observed by immunohistochemistry for Fos-like antibodies in regions previously suggested as responding to all antipsychotic drugs, including nucleus accumbens, central amygdala, and central medial thalamus. Cells staining for Fos were counted by semi-automated methods. RESULTS. A very similar pattern and number of Fos positive cells in nucleus accumbens, central amygdala, and central medial thalamus followed administration of each antipsychotic drug. The numbers of apparently activated cells were much greater following antipsychotic drug administration than after vehicle, with differences between each drug and vehicle being highly statistically significant in each region. Lorazepam produced apparent activation of cells of the central amygdala similar in degree and location but not identical in distribution to that of antipsychotic drugs. Diphenhydramine produced no apparent activation of cells in any of the sites tested.

CONCLUSION

Typical and atypical antipsychotic drugs shared a distinctive pattern of robust activation of cells in nucleus accumbens, central medial thalamus, and central amygdala. Antipsychotic drug-induced activation of amygdala was shared by lorazepam, but activation of thalamus and nucleus accumbens was much greater following antipsychotic drugs than following lorazepam. The pattern of activated cells may be relevant to the therapeutic actions of antipsychotic drugs.

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.

Neurosecretory and non-neurosecretory parvocellular neurones of the hypothalamic paraventricular nucleus express distinct electrophysiological properties

Parvocellular neurones of the hypothalamic paraventricular nucleus (PVN) comprise neurosecretory and non-neurosecretory subpopulations. We labelled neurosecretory neurones with intravenous injection of the retrograde tracer, fluoro-gold, and recorded from fluoro-gold-positive and negative PVN parvocellular neurones in hypothalamic slices. Non-neurosecretory parvocellular neurones generated a low-threshold spike (LTS) and robust T-type Ca2+ current, whereas neurosecretory neurones showed no LTS and a small T-current. LTS neurones were located in non-neurosecretory regions of the PVN, and non-LTS neurones were located in neurosecretory regions of the PVN. These findings indicate that neurosecretory and non-neurosecretory subtypes of parvocellular PVN neurones express distinct membrane electrical properties.

Changes in the arginine-vasopressin immunoreactive systems in male mice lacking a functional aromatase gene

In male rodents, the arginine-vasopressin-immunoreactive (AVP-ir) neurones of the bed nucleus of the stria terminalis (BNST) and medial amygdala are controlled by plasma testosterone levels (decreased after castration and restored by exogenous testosterone). AVP transcription in these nuclei is increased in adulthood by a synergistic action of the androgenic and oestrogenic metabolites of testosterone and, accordingly, androgen and oestrogen receptors are present in both BNST and medial amygdala. We used knockout mice lacking a functional aromatase enzyme (ArKO) to investigate the effects of a chronic depletion of oestrogens on the sexually dimorphic AVP system. Wild-type (WT) and ArKO male mice were perfused 48 h after an i.c.v. colchicine injection and brain sections were then processed for AVP immunocytochemistry. A prominent decrease (but not a complete suppression) of AVP-ir structures was observed in the BNST and medial amygdala of ArKO mice by comparison with the WT. Similarly, AVP-ir fibres were reduced in the lateral septum of ArKO mice and but not in the medial preoptic area, a region where the AVP system is not sexually dimorphic in rats. No change was detected in the supraoptic and suprachiasmatic nuclei. However, a decrease in AVP-ir cell numbers was however, detected in one subregion of the paraventricular nucleus. These data support the hypothesis that the steroid-sensitive sexually dimorphic AVP system of the mouse forebrain is mainly under the control of aromatized metabolites of testosterone.

Cellular architecture of the nucleus reuniens thalami and its putative aspartatergic/glutamatergic projection to the hippocampus and medial septum in the rat

Little is known about the neurochemical features of the nucleus reuniens thalami (RE). In the present study, immunocytochemical experiments were performed to characterize the expression pattern of certain neurochemical markers, e.g. the calcium-binding proteins calbindin and calretinin and several neuropeptides. Colocalization studies revealed that half of the calbindin-positive cells express calretinin, and numerous calretinin-immunoreactive neurons contain calbindin. In contrast, immunolabelling for neuropeptides did not reveal cell bodies in the RE. The RE establishes widespread connections with several limbic structures. To correlate these projection patterns with the neurochemical characteristics of RE neurons, the retrograde tracer [3H]D-aspartate, which is selectively taken up by high affinity uptake sites that use glutamate as neurotransmitter, and the nonselective retrograde tracer wheatgerm agglutinin-conjugated colloidal gold was injected into the stratum lacunosum moleculare of the hippocampal CA1 subfield and into the medial septum. The results provide direct anatomical demonstration of aspartatergic/glutamatergic projection from the RE to the hippocampus and to the medial septum. Nearly all of the projecting neurons proved to be calbindin-immunopositive and many of them expressed calretinin. Both retrograde labelling techniques revealed that neurons projecting to the hippocampus were located in clusters in the dorsolateral part of the RE, whereas neurons projecting to the medial septum were mainly distributed in the ventromedial portion of the nucleus, indicating that different cell populations project to these limbic areas. These results suggest that neurons in the RE are heterogeneous and contribute to the excitatory innervation of the septo-hippocampal system.

Brainstem projections to midline and intralaminar thalamic nuclei of the rat

The projections from the brainstem to the midline and intralaminar thalamic nuclei were examined in the rat. Stereotaxic injections of the retrograde tracer cholera toxin beta -subunit (CTb) were made in each of the intralaminar nuclei of the dorsal thalamus: the lateral parafascicular, medial parafascicular, central lateral, paracentral, oval paracentral, and central medial nuclei; in the midline thalamic nuclei-the paraventricular, intermediodorsal, mediodorsal, paratenial, rhomboid, reuniens, and submedius nuclei; and, in the anteroventral, parvicellular part of the ventral posterior, and caudal ventral medial nuclei. The retrograde cell body labeling pattern within the brainstem nuclei was then analyzed. Nearly every thalamic site received a projection from the deep mesencephalic reticular, pedunculopontine tegmental, dorsal raphe, median raphe, laterodorsal tegmental, and locus coeruleus nuclei. Most intralaminar thalamic sites were also innervated by unique combinations of medullary and pontine reticular formation nuclei such as the subnucleus reticularis dorsalis, gigantocellular, dorsal paragigantocellular, lateral, parvicellular, caudal pontine, ventral pontine, and oral pontine reticular nuclei; the dorsomedial tegmental, subpeduncular tegmental, and ventral tegmental areas; and, the central tegmental field. In addition, most intralaminar injections resulted in retrograde cell body labeling in the substantia nigra, nucleus Darkschewitsch, interstitial nucleus of Cajal, and cuneiform nucleus. Details concerning the pathways from the spinal trigeminal, nucleus tractus solitarius, raphe magnus, raphe pallidus, and the rostral and caudal linear raphe nuclei to subsets of midline and intralaminar thalamic sites are discussed in the text. The discussion focuses on brainstem-thalamic pathways that are likely involved in arousal, somatosensory, and visceral functions.

Analysis of projections from the medial prefrontal cortex to the thalamus in the rat, with emphasis on nucleus reuniens

The medial prefrontal cortex (mPFC) is involved in high-order cognitive processes, including, but not limited to, decision making, goal directed behavior, and working memory. Although previous reports have included descriptions of mPFC projections to the thalamus in overall examinations of mPFC projections throughout the brain, no previous study has comprehensively examined mPFC projections to the thalamus. The present report compares and contrasts projections from the four divisions of the mPFC, i.e., the infralimbic, prelimbic, anterior cingulate and medial agranular cortices, to the thalamus in the rat by using the anterograde anatomic tracer Phaseolus vulgaris-leucoagglutinin. We showed that (1) the infralimbic, prelimbic, anterior cingulate cortices distribute heavily and selectively to midline/medial structures of the thalamus, including the paratenial, paraventricular, interanteromedial, anteromedial, intermediodorsal, mediodorsal, reuniens, and the central medial nuclei; (2) the medial agranular cortex distributes strongly to the rostral intralaminar nuclei (central lateral, paracentral, central medial nuclei) as well as to the ventromedial and ventrolateral nuclei of thalamus; and (3) all four divisions of the mPFC project densely to the nucleus reuniens (RE) of the thalamus. The nucleus reuniens is the major source of thalamic afferents to the hippocampal formation. There are essentially no direct projections from the mPFC to the hippocampus. The present demonstration of pronounced mPFC projections to RE suggests that the nucleus reuniens is a critical relay in the transfer of information from the medial prefrontal cortex to the hippocampus. Our further demonstration of strong mPFC projections to several additional thalamic nuclei, particularly to the mediodorsal nucleus, suggests that these thalamic nuclei, like RE, represent important output stations (or gateways) for the actions of mPFC on diverse subcortical and cortical structures of the brain.

Activation of the central nervous system in obese Zucker rats during food deprivation

This study was carried out to investigate the pattern of neuronal activations that occur in the obese fa/fa Zucker rat during food deprivation. The functional activation of neurons was estimated in lean and obese Zucker rats either fed ad libitum or food-deprived for 3, 6, 12, and 24 hours by assessing the expression of the immediate early gene c-fos. To identify the neurons instigating the activation of the hypothalamic-pituitary-adrenal axis in food-deprived obese rats, the retrograde tracer cholera toxin B subunit was injected in the parvocellular division of the paraventricular hypothalamic nucleus of obese rats and colocalized with c-fos mRNA during food deprivation. The expression of c-fos was barely detectable in food-deprived lean rats as well as in lean and obese animals fed ad libitum. However, 3 hours of food deprivation were sufficient to significantly induce c-fos in the paraventricular thalamic nucleus of obese rats. In addition, 6 and 12 hours of food deprivation resulted in the activation of regions that are similarly stimulated in "neurogenic" stresses. These regions include the parvocellular division of the paraventricular hypothalamic nucleus, the lateral septum, the basolateral amygdala, and some areas of the cortex. The highest number of neurons projecting to the parvocellular division of the paraventricular hypothalamic nucleus and revealing c-fos mRNA was, however, located in the paraventricular thalamic nucleus. In summary, the present results demonstrate in the obese fa/fa Zucker rats, that food deprivation leads to brain activations, which are in large part, similar to those induced by a "neurogenic" stress and that the paraventricular thalamic nucleus is involved in this response. These changes could contribute to the development of hyperphagia and obesity.

Fluctuation of extracellular hypocretin-1 (orexin A) levels in the rat in relation to the light-dark cycle and sleep-wake activities

Hypocretins/orexins are neuropeptides implicated in sleep regulation and the sleep disorder narcolepsy. In order to examine how hypocretin activity fluctuates across 24 h with respect to the sleep-wake cycle, we measured changes in extracellular hypocretin-1 levels in the lateral hypothalamus and medial thalamus of freely moving rats with simultaneous sleep recordings. Hypocretin levels exhibited a robust diurnal fluctuation; levels slowly increased during the dark period (active phase), and decreased during the light period (rest phase). Levels were not correlated with the amount of wake or sleep in each period. Although an acute 4-h light-shift did not alter hypocretin levels, 6-h sleep deprivation significantly increased hypocretin release during the forced-wake period. Hypocretin activity is, thus, likely to build up during wakefulness and decline with the occurrence of sleep. These findings, together with the fact that a difficulty in maintaining wakefulness during the daytime is one of the primary symptoms of hypocretin-deficient narcolepsy, suggest that hypocretin activity may be critical in opposing sleep propensity during periods of prolonged wakefulness.

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.

Superior colliculus projections to midline and intralaminar thalamic nuclei of the rat

The superior colliculus (SC) projections to the midline and intralaminar thalamic nuclei were examined in the rat. The retrograde tracer cholera toxin beta (CTb) was injected into one of the midline thalamic nuclei-paraventricular, intermediodorsal, rhomboid, reuniens, submedius, mediodorsal, paratenial, anteroventral, caudal ventromedial, or parvicellular part of the ventral posteriomedial nucleus-or into one of the intralaminar thalamic nuclei-medial parafascicular, lateral parafascicular, central medial, paracentral, oval paracentral, or central lateral nucleus. After 10-14 days, the brains from these animals were processed histochemically, and the retrogradely labeled neurons in the SC were mapped. The lateral sector of the intermediate gray and white layers of the SC send axonal projections to the medial and lateral parafascicular, central lateral, paracentral, central medial, rhomboid, reuniens, and submedius nuclei. The medial sector of the intermediate and deep SC layers project to the parafascicular and central lateral thalamic nuclei. The paraventricular thalamic nucleus is innervated almost exclusively by the medial sectors of the deep SC layers. The superficial gray and optic layers of the SC do not project to any of these thalamic areas. The discussion focuses on the role these SC-thalamic inputs may have on forebrain circuits controlling orienting and defense (i.e., fight-or-flight) reactions.

Parabrachial nucleus projections to midline and intralaminar thalamic nuclei of the rat

The projections from the parabrachial nucleus to the midline and intralaminar thalamic nuclei were examined in the rat. Stereotaxic injections of the retrograde tracer cholera toxin-beta (CTb) were made in each of the intralaminar nuclei of the dorsal thalamus (the lateral parafascicular, medial parafascicular, oval paracentral, central lateral, paracentral, and central medial nuclei), as well as the midline thalamic nuclei (the paraventricular, intermediodorsal, mediodorsal, paratenial, rhomboid, reuniens, parvicellular part of the ventral posterior, and caudal ventral medial nuclei). The retrograde cell body labeling pattern within the parabrachial subnuclei was then analyzed. The paracentral thalamic nucleus received an input only from the internal lateral parabrachial subnucleus. However, this subnucleus also projected to all the other intralaminar thalamic nuclei, except for the central lateral thalamic nucleus, which received no parabrachial afferent inputs. The external lateral parabrachial subnucleus projected to the lateral parafascicular, reuniens, central medial, parvicellular part of the ventral posterior, and caudal ventromedial thalamic nuclei. Following CTb injections in the paraventricular thalamic nucleus, retrogradely labeled cells were found in the central lateral, dorsal lateral, and external lateral parabrachial subnuclei. The medial and ventral lateral parabrachial subnuclei projected to the oval paracentral, parafascicular, and rhomboid thalamic nuclei. Finally, the waist area of the parabrachial nucleus was densely labeled after CTb injections in the parvicellular part of the ventral posterior thalamic nucleus. Nociceptive, visceral, and gustatory signals may reach specific cortical and other forebrain sites via this parabrachial-thalamic pathway.

Feeding reduces activity of growth hormone-releasing hormone and somatostatin neurons

Secretion of growth hormone (GH) is synchronized among castrate male cattle (steers) around feeding when access to feed is restricted to a 2-hr period each day. Typically, concentrations of GH increase before and decrease after feeding. Our objectives were to determine whether i) concentrations of GH decrease in blood after start of feeding; ii) activity of immunoreactive growth hormone-releasing hormone (GHRH-ir) neurons decreases in the arcuate nucleus (ARC) after feeding; iii) activity of immunoreactive somatostatin (SS-ir) neurons in the periventricular nucleus (PeVN) and ARC increase after feeding; and iv) GHRH stimulates release of GH to a similar magnitude at 0900 and at 1300 hr, in steers fed between 1000 and 1200 hr. Blood samples were collected at 20-min intervals from 0700 to 1300 hr. Groups of steers were euthanized at 0700, 0900, 1100, and 1300 hr (n = 5 per group). Dual-label immunohistochemistry was performed on free-floating sections of hypothalami using antibodies directed against Fos and Fos-related antigens (Fos/FRA) as a marker of neuronal activity in immunoreactive GHRH and SS neurons. Concentrations of GH were high before and decreased after feeding. The percentage of SS-ir neurons containing Fos/FRA-ir in the PeVN was 50% lower (P<0.01) at 1100 hr and 36% lower (P<0.05) at 1300 hr than at 0900 hr. There was no change in percentage of SS-ir neurons containing Fos/FRA-ir in the ARC. The percentage of GHRH-ir neurons containing Fos/FRA-ir in the ARC was 66% lower (P<0.05) at 1100 hr and 65% lower (P<0.05) at 1300 hr than at 0700 hr. In contrast, the number of GHRH-ir neurons increased from 0700 to 1300 hr. GHRH-induced release of GH was suppressed at 1300 hr compared with 0900 hr. In conclusion, reduced basal and GHRH-induced secretion of GH after feeding was associated with decreased activity of GHRH neurons in the ARC and decreased activity of SS neurons in the PeVN.