Cholecystokinin innervation of rat thalamus, including fibers to ventroposterolateral nucleus from dorsal column nuclei

Effect of intracerebroventricular administration of two molecular forms of sulfated CCK octapeptide on anxiety-like behavior in the zebrafish danio rerio

Cholecystokinin octapeptide with sulfate (CCK-8s) regulates feeding behavior and psychomotor activity. In rodents and goldfish, intracerebroventricular (ICV) injection of CCK-8s decreases food intake and also induces anxiety-like behavior. The zebrafish has several merits for investigating the psychophysiological roles of neuropeptides. However, little is known about the brain localization of CCK and the behavioral action of CCK-8s in this species. Here we investigated the brain localization of CCK-like immunoreactivity and found that it was distributed throughout the brain. As CCK-like immunoreactivity was particularly evident in the ventral habenular nucleus, the interpeduncular nucleus and superior raphe, we subsequently examined the effect of zebrafish (zf) CCK-8s on psychomotor control. Since the zebrafish possesses two molecular forms of zfCCK-8s (zfCCKA-8s and zfCCKB-8s), two synthetic peptides were administered intracerebroventricularly at 1, 5 and 10 pmol g^-1 body weight (BW). As the zebrafish shows a greater preference for the lower area of a tank than for to the upper area, we used this preference for assessment of anxiety-like behavior. ICV administration of zfCCKA-8 s or zfCCKB-8s at 10 pmol g^-1 BW significantly shortened the time spent in the upper area. The actions of these peptides mimicked that of the central-type benzodiazepine receptor inverse agonist FG-7142 (an anxiogenic agent) at 10 pmol g^-1 BW. The anxiogenic-like action of the two peptides was attenuated by treatment with the CCK receptor antagonist proglumide at 200 pmol g^-1 BW. These results indicate that zfCCKA-8s and zfCCKB-8s potently induce anxiety-like behavior via the CCK receptor-signaling pathway in the zebrafish brain.

Degeneration of cholecystokinin-immunoreactive afferents to the VPL thalamus in a mouse model of Niemann-Pick disease type C

Niemann-Pick disease type C (NP-C) is a progressive neurological disorder of lipid metabolism. The Balb/C npc1 mutant strain is a genetically authentic murine model of NPC, which reproduce the clinical and histologic features of human NP-C. In the present study, we show that cholecystokinin (CCK)-immunoreactive fibers in the thalamic VPL nuclei, which are densely distributed in controls, degenerate in NPC mice. This degeneration is associated with the appearance of CCK-immunoreactive axonal spheroids containing characteristic intracellular inclusions of NP-C. These observations provide supportive evidence of the occurrence of dying-back axonopathy of neurons in the dorsal column nuclei in this mouse model.

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.

A cholecystokinin-mediated pathway to the paraventricular thalamus is recruited in chronically stressed rats and regulates hypothalamic-pituitary-adrenal function

Chronic stress alters hypothalamic-pituitary-adrenal (HPA) responses to acute, novel stress. After acute restraint, the posterior division of the paraventricular thalamic nucleus (pPVTh) exhibits increased numbers of Fos-expressing neurons in chronically cold-stressed rats compared with stress-naive controls. Furthermore, lesions of the PVTh augment HPA activity in response to novel restraint only in previously stressed rats, suggesting that the PVTh is inhibitory to HPA activity but that inhibition occurs only in chronically stressed rats. In this study, we further examined pPVTh functions in chronically stressed rats. We identified afferent projections to the pPVTh using injection of the retrograde tracer fluorogold. Of the sites containing fluorogold-labeled cells, neurons in the lateral parabrachial, periaqueductal gray, and dorsal raphe containing fluorogold also expressed cholecystokinin (CCK) mRNA. We then examined whether these CCKergic inputs to the pPVTh were involved in HPA responses to acute, novel restraint after chronic stress. We injected the CCK-B receptor antagonist PD 135,158 into the PVTh before restraint in control and chronically cold-stressed rats. ACTH responses to restraint stress were augmented by PD 135,158 only in chronically stressed rats but not in controls. In addition, CCK-B receptor mRNA expression in the pPVTh was not altered by chronic cold stress. We conclude that previous chronic stress specifically facilitates the release of CCK into the pPVTh in response to acute, novel stress. The CCK is probably secreted from neurons in the lateral parabrachial, the periaqueductal gray, and/or the dorsal raphe nuclei. Acting via CCK-B receptors in pPVTh, CCK then constrains facilitated ACTH responses to novel stress in chronically stressed but not naive rats. These results demonstrate clearly that chronic stress recruits a new set of pathways that modulate HPA responsiveness to a novel stress.

Cholinergic modulation of neuronal responses to cholecystokinin in anesthetized rats

The aim of this study was to investigate whether the effects of the neuropeptide cholecystokinin on neuronal firing can be changed by acetylcholine in various structures of the brain. Single unit activity was extracellularly recorded in rats anesthetized with urethane. The neurons were located in several nuclei of the thalamus, the basal ganglia and the cerebral cortex. Neurons responding to the sulfated octapeptide of cholecystokinin (CCK-8S) were mainly activated by the drug [Wilcoxon test (Wt) p < 0.0001, n=113]. Thalamic neurons could also increase the number of burst discharges (Wt p < 0.005, n=39). Iontophoretically administered acetylcholine could reduce the activating effects of CCK-8S on firing and burst discharges. In its presence, even inhibitory effects of CCK-8S predominated (Wt p < 0.0001, n=113). The suppressive action seemed not to depend on the direction of the effect of acetylcholine itself and concerned neurons of all locations studied. Atropine could diminish or block the suppressive action of acetylcholine. In the presence of both drugs, CCK-8S mainly activated the neurons (Wt p < 0.005, n=43). Atropine itself did not significantly change the responses to CCK-8S (Wt p > 0.05). It can be concluded that cholecystokinin may reduce neuronal firing instead of increasing it during activation of the cholinergic system.

Thalamic-projecting preprocholecystokinin messenger RNA-expressing neurons in the dorsal column nuclei of the rat

This study aimed at investigating the expression of preprocholecystokinin messenger RNA among thalamic-projecting neurons in the dorsal column nuclei of the rat. Thalamic-projecting neurons were identified by injection of cholera toxin subunit b into the ventroposterolateral nucleus. Following immunohistochemical detection of retrogradely transported tracer substance, the expression of preprocholecystokinin messenger RNA in the projection neurons of the dorsal column nuclei was detected by in situ hybridization, using autoradiographic visualization of a 35S-labeled RNA probe complementary to preprocholecystokinin messenger RNA. Many preprocholecystokinin-expressing neurons were seen in the dorsal column nuclei. A large proportion of these neurons were also labeled with cholera toxin. The double-labeled neurons, as well as neurons single-labeled with preprocholecystokinin messenger RNA or cholera toxin, were preferentially found within the middle region of the dorsal column nuclei, located just caudal to the obex. These findings demonstrate that neurons in the dorsal column nuclei express preprocholecystokinin messenger RNA, and show that these neurons provide a peptidergic projection from the dorsal column nuclei to the ventroposterolateral nucleus of the thalamus. These observations suggest that cholecystokinin may be involved in the transmission of somatosensory (tactile) information from the dorsal column nuclei to the thalamus.

Peptidergic modulation of intrathalamic circuit activity in vitro: actions of cholecystokinin

Cholecystokinin (CCK)-mediated actions on intrathalamic rhythmic activities were examined in an in vitro rat thalamic slice preparation. Single electrical stimuli in the thalamic reticular nucleus (nRt) evoked rhythmic activity (1-15 sec duration) in nRt and the adjacent ventrobasal nucleus (VB). Low CCK concentrations (20-50 nM) suppressed rhythmic oscillations in 43% of experiments but prolonged such activities in the remaining slices. Higher CCK concentrations (100-400 nM) had a predominantly antioscillatory effect. Suppression of oscillations was associated with a relatively large membrane depolarization of nRt neurons that changed their firing mode from phasic (burst) to tonic (single-spike) output. This decreased burst discharge of nRt neurons during CCK application reduced inhibitory drive onto VB neurons from multiple peaked inhibitory postsynaptic currents (IPSCs) to single peaked inhibitory events. We hypothesize that suppression of inhibitory drive onto VB neurons decreases their probability of burst output, which, together with a reduction of nRt burst output, dampens the oscillatory activity. Low CCK concentrations, which produced little or no depolarization of nRt neurons, did not alter the firing mode of the nRt neurons. However, the probability of burst output from nRt neurons in response to subthreshold stimuli was increased in low CCK concentrations, presumably leading to an increase in the number of nRt neurons participating in the rhythmic activity. Our findings suggest that the neuropeptide CCK, by altering the firing characteristics of nRt neurons, has powerful modulatory effects on intrathalamic rhythms; the ultimate action was dependent on CCK concentration and resting state of these cells.

Expression of cholecystokinin mRNA in corticothalamic projecting neurons: a combined fluorescence in situ hybridization and retrograde tracing study in the ventrolateral thalamus of the rat

Cholecystokinin (CCK), a well-known neuroactive peptide, has been observed in the axon endings within the thalamic reticular nucleus and the adjacent ventrolateral nucleus of the thalamus. The origin of this CCK innervation remains undefined. In this study, a fluorescence in situ hybridization (FISH) technique was used in conjunction with latex microsphere retrograde tracing to investigate whether cortical neurons may provide a source of CCK afferents to the ventrolateral thalamic nucleus. Rhodamine latex beads were injected into the ventrolateral thalamic nucleus of adult male rats to retrogradely label corticothalamic cells. After 7 days, tissues were processed for FISH using a 24-base oligonucleotide probe complementary to the 3' coding region of rat preprocholecystokinin mRNA. It was found that CCK transcripts are expressed in about 80% of identified corticothalamic projecting neurons. We therefore conclude that the descending cortical projections to the ventrolateral thalamus may provide an important source of CCK innervation to this region of the brain.

Enrichment of glutamate immunoreactivity in lemniscal terminals in the ventropostero lateral thalamic nucleus of the rat: an immunogold and WGA-HRP study

BACKGROUND

The ventropostero lateral nucleus (VPL) is a thalamic somatosensory center receiving inputs from limbs and trunk; some of this input is via terminals of the dorsal column medial lemniscal pathway. These fibers convey non-noxious somesthesic information.

METHODS

In this study the neurochemical content of lemniscal afferents in VPL of rats was investigated at the electron microscopic level by combining anterograde transport of horseradish peroxidase conjugated to wheat germ agglutinin, injected in the dorsal dorsal column nuclei, with postembedding immunogold labeling for glutamate (Glu).

RESULTS

Anterograde labeling in VPL was detected only in myelinated axons and in large terminals containing round synaptic vesicles, interpreted as lemniscal afferents. Quantitative evaluation of gold particle density showed enrichment of Glu immunolabeling in the identified lemniscal terminals with respect to other neuronal profiles. Observation of serial sections immunoreacted for Glu demonstrated consistency of labeling, whereas in alternate sections immunoreacted for Glu and for the inhibitory amino acid GABA these two antigens were always present in distinct types of terminals.

CONCLUSIONS

These findings are in agreement with several lines of evidence, obtained with different experimental approaches, supporting the hypothesis that Glu plays a major role in conveying sensory stimuli to the thalamus from second order neurons in the dorsal column nuclei.

Neurotransmitters in subcortical somatosensory pathways

Investigations during recent years indicate that many different neuroactive substances are involved in the transmission and modulation of somesthetic information in the central nervous system. This review surveys recent developments within the field of somatosensory neurotransmission, emphasizing immunocytochemical findings. Increasing evidence indicates a widespread role for glutamate as a fast-acting excitatory neurotransmitter at different levels in somatosensory pathways. Several studies have substantiated a role for glutamate as a neurotransmitter in primary afferent neurons and in corticofugal projections, and also indicate a neurotransmitter role for glutamate in ascending somatosensory pathways. Other substances likely to be involved in somatosensory neurotransmission include the neuropeptides. Many different peptides have been detected in primary afferent neurons with unmyelinated or thinly myelinated axons, and are thus likely to be directly involved in primary afferent neurotransmission. Some neurons giving rise to ascending somatosensory pathways, primarily those with cell bodies in the dorsal horn, are also immunoreactive for peptides. Recent investigations have shown that the expression of neuropeptides, both in primary afferent and ascending tract neurons, may change as a result of various kinds of peripheral manipulation. The occurrence of neurotransmitters in intrinsic neurons and neurons providing modulating inputs to somatosensory relay nuclei (the dorsal horn, the lateral cervical nucleus, the dorsal column nuclei and the ventrobasal thalamus) is also reviewed. Neurotransmitters and modulators in such neurons include acetylcholine, monoamines, GABA, glycine, glutamate, and various neuropeptides.

Reversal of electroacupuncture tolerance by CCK-8 antiserum: an electrophysiological study on pain-related neurons in nucleus parafascicularis of the rat

Two varieties of neurons were found in nucleus parafascicularis (pf) of the rat: one responds to noxious stimuli with an increase in firing (pain-excited neuron, PEN), the other with a decrease in firing (pain-inhibited neuron, PIN). Electroacupuncture (EA) has been shown to suppress PEN and excite PIN, which can be taken as an electrophysiological index for EA analgesia. This effect of EA subsided after prolonged (6 h) EA stimulation, suggesting the development of tolerance to EA. Intracerebroventricular (icv) injection of CCK-8 antiserum aiming at neutralizing endogenously released CCK-8 resulted in a complete restoration of the EA effect. Normal rabbit serum was not effective. CCK-8 antiserum per se did not affect the firing pattern of the PEN or PIN in nontolerant rat. The results obtained from single neuron recording in anesthetized animals thus confirmed those obtained in intact animals using the tail flick as the end point, implying that an excess of endogenously released CCK-8 may constitute one of the mechanisms for the development of EA tolerance.

The relationship of calbindin-containing neurons with substance P, Leu-enkephalin and cholecystokinin fibres: an immunohistochemical study in the rat thalamus

In the rat thalamus, immunoreactivity for the calcium binding protein calbindin (Cb) is mostly confined to neuronal cell bodies, sometimes revealing proximal dendrites, of the midline, intralaminar and posterior regions. Substance P (SP)-, cholecystokinin (CCK)- and Leu-enkephalin (L-ENK)-immunoreactive (ir) elements in the thalamus are fibre-like structures, intermingled with punctate elements probably representing axonal arborizations and their synaptic boutons. These peptidergic fibres are unevenly distributed in several thalamic domains, including the areas that contain Cb-ir neurons. The relationship between Cb-ir cell bodies and these three different peptidergic systems of thalamic innervation was studied with immunohistochemistry. Single-labelling experiments on adjacent sections and double immunostaining on the same section were performed. A considerable overlap between Cb-ir perikarya and SP-ir fibres was found in most thalamic nuclei. In particular, in the intralaminar nuclei and posterior complex, SP-ir punctate elements were frequently observed in close proximity to Cb-ir cell bodies and dendrites. On the other hand, no consistent topographical correspondence between Cb-ir perikarya and CCK- or L-ENK-ir fibres was evident. Altogether, the present data suggest a selective anatomical and, possibly, functional relationship between SP and Cb in at least a subpopulation of rat thalamic neurons.

Topographic organization of subcortical projections to the anterior thalamic nuclei in the rat

Subcortical projections to the anterior thalamic nuclei were studied in the rat, with special reference to projections from the mammillary nuclei, by retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. The medial mammillary nucleus (MM) projects predominantly ipsilaterally to the entire anterior thalamic nuclei, whereas the lateral mammillary nucleus projects bilaterally to the anterodorsal nucleus (AD) of the anterior thalamic nuclei. A topographic relationship was recognized between the MM and the anterior thalamic nuclei. The dorsal region of the pars mediana of the MM projects to the interanteromedial nucleus (IAM), whereas the ventral region projects to the rostral part of the anteromedial nucleus (AM). The dorsal and the ventral regions of the pars medialis project to the dorsomedial part of the AM at its caudal and rostral levels, respectively. The dorsomedial region of the pars lateralis projects to the ventral AM. The ventrolateral region of the pars lateralis projects to the ventral part of the anteroventral nucleus (AV) in such a manner that rostral cells project rostrally and caudal cells project caudally. The pars basalis projects predominantly ipsilaterally to the dorsolateral AV and bilaterally to the AD. The rostrolateral region of the pars posterior projects to the lateral AV, whereas the medial and the caudal regions of the pars posterior project to the dorsomedial AV. The rostrodorsal part of the nucleus reticularis thalami was found to project to the anterior thalamic nuclei; cells located rostrally in this part project to the IAM and AM, whereas cells located caudodorsally project to the AV and AD. The laterodorsal tegmental nucleus projects predominantly ipsilaterally to the AV, especially to its dorsolateral part. The present study demonstrates that subdivisions of the subcortical structures are connected to the subnuclei of the anterior thalamic nuclei, with a clear-cut topography arranged in the dorsoventral and the rostrocaudal dimensions.

Sources of presumptive glutamatergic/aspartatergic afferents to the mediodorsal nucleus of the thalamus in the rat

The distribution of presumptive glutamatergic and/or aspartatergic neurons retrogradely labeled following injections of 3HD-aspartate into the mediodorsal nucleus of the thalamus (MD) in the rat was compared to the distribution of neurons labeled by comparable injections of the nonspecific retrograde tracer wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP). Cells retrogradely labeled by WGA-HRP were found in the prefrontal and agranular insular cortices; in forebrain structures such as the amygdaloid complex, the piriform cortex, the ventral pallidum and the reticular nucleus of the thalamus; and in several different parts of the brainstem, such as the superior colliculus, central grey, and substantia nigra, pars reticulata. Some, but not all, of these projections are presumably glutamatergic and/or aspartatergic. The projections to MD from the prefrontal and agranular insular cortices are well labeled with 3H-D-aspartate, as are projections from the anterior cortical amygdaloid nucleus. Projections from the superior colliculus to the lateral portion of MD also label with this tracer. However, other forebrain and brainstem projections to MD are not labeled with 3H-D-aspartate, and apparently do not use glutamate or aspartate as a neurotransmitter. These include the projections from the basal and accessory basal amygdaloid nuclei, as well as possibly GABAergic projections from the ventral pallidum and the substantia nigra, pars reticulata. A small fraction of the cells in the piriform cortex that project to MD label with 3H-D-aspartate, suggesting that this projection may be heterogeneous. In other experiments, presumptive GABAergic projections to MD were studied by using 3H-GABA as a retrograde tracer. Although in these cases the thalamic reticular nucleus is well labeled, the ventral pallidum and the substantia nigra, pars reticulata are only poorly labeled. Pallidal projections to the ventromedial thalamic nucleus (VM), which are likely to be GABAergic, were also studied with this technique. After injections of 3H-GABA into VM, only a few cells in the substantia nigra, pars reticulata, or entopeduncular nucleus were labeled. This result suggests 3H-GABA has limited usefulness as a transmitter-specific retrograde tracer.

The reticular thalamic nucleus (RTN) of the rat: cytoarchitectural, Golgi, immunocytochemical, and horseradish peroxidase study

Experiments have been performed on adult albino rats in order to study the cellular organization of the thalamic reticular nucleus. For this purpose four approaches have been used: Nissl stain, Golgi impregnation, retrograde transport of horseradish peroxidase after injection in different thalamic nuclei, and immunocytochemistry with antibodies against GABA and glutamic acid decarboxylase. In sections through the horizontal plane, three morphologically different neurons have been observed. Cells with round perikarya and with multipolar dendrites were found predominantly in the rostral pole of the nucleus. Neurons with large fusiform cell body and with dendrites arborizing mainly on the horizontal plane were detected through the whole extent of the nucleus. Small fusiform neurons were observed almost exclusively in the medial third of the dorso-ventral extent of the nucleus. The Golgi impregnation method demonstrated that dendrites of small fusiform neurons develop in the vertical plane perpendicular to the dendritic arborization of large fusiform neurons. In coronal sections neurons with round perikarya and with large fusiform cell bodies are detectable while small fusiform neurons are only rarely visible. These data have been confirmed by statistical form factor analysis. Moreover, by means of the horseradish peroxidase and the immunocytochemical study, it has been confirmed that all three groups of neurons project within the thalamus and that they are GABAergic. The data concerning the distribution within the nucleus of the three morphologically different neurons are discussed in relation to the topographic distribution of cortical sensory afferents and to the topographic maps within different sectors of the reticular nucleus.

Thalamic midline cell populations projecting to the nucleus accumbens, amygdala, and hippocampus in the rat

The organization of the thalamic midline efferents to the amygdaloid complex, hippocampal formation, and nucleus accumbens was investigated in the rat by means of multiple retrograde fluorescent tracing. The present findings indicate that these connections derive from separate cell populations of the thalamic midline, with a low degree of divergent collateralization upon more than one of the targets examined. The neural populations projecting to the amygdala, hippocampus, or accumbens are highly intermingled throughout the thalamic midline, but display some topographical prevalence. Midline thalamo-hippocampal cells are concentrated in the nucleus reuniens; thalamo-accumbens neurons prevail in the ventral portion of the paraventricular nucleus, and in the central medial nucleus. Thalamo-amygdaloid cells display a topographical prevalence in the rostral third of the thalamic midline and are concentrated in the dorsal part of the paraventricular nucleus and in the medial part of the nucleus reuniens. Both dorsally in the paraventricular nucleus and ventrally in the nucleus reuniens, thalamo-amygdaloid cells are located closer to the ependymal lining than the neurons projecting to the hippocampus or nucleus accumbens. Further, thalamo-amygdaloid cells, especially in the paraventricular nucleus, extend their dendritic processes in the vicinity of the ependymal lining, where they arborize profusely. These features indicate a close topographical relationship of neurons projecting to the amygdala with ependymal cells. The fairly discrete origin of midline outputs to the amygdala, hippocampus, and accumbens indicates that the flow of information is conveyed through separate channels from the thalamic midline to limbic and limbic-related targets. Together with the literature on the limbic afferents to the thalamus, these findings emphasize the relationships between the thalamus and the limbic system subserved by parallel input-output routes. However, because of the overlap of the projection cell populations, the thalamic midline may represent a locus of interaction among neurons connected with different parts of the limbic system. The functional implications of these findings are discussed in relation to the "nonspecific" thalamic system, as well as to the circuits involved in memory formation.

Postnatal changes in the density and distribution of neurotensin-like immunoreactive fibers in the mediodorsal nucleus of the thalamus in the rat

A previous report (Inagaki et al., Brain Res. 260:143-146, '83) suggested that the peptide neurotensin is contained in neurons of the piriform cortex that project to the mediodorsal thalamic nucleus (MD) in young rats. To confirm this, we have studied the distribution of neurotensin-like immunoreactive (NTIR) fibers in MD during development, using three antisera directed at different parts of the neurotensin molecule (Emson et al., J. Neurochem. 38:992-999, '82). In adult rats, NTIR fibers in MD are sparse. They are located mostly at the medial edge of MD and in the adjacent midline thalamic nuclei, with a few poorly stained NTIR fibers in the central part of MD. In contrast, during the first postnatal week, both the medial and central portions of MD stain heavily for neurotensin. The density of NTIR fibers in MD then progressively decreases until the density typical of adult rats is reached, at about 5 weeks. Changes in the distribution of NTIR fibers in MD also occur. In 7-day-old rats, the patches of NTIR fibers in the medial and central parts of MD are contiguous, but by 10 days a sparsely immunoreactive zone forms between them. With maturation, this zone enlarges as the density of neurotensin staining decreases, until the medial contingent of NTIR fibers reaches its adult position at the medial edge of MD. From a comparison of the distribution of NTIR cells with that of cells that can be retrogradely labeled from MD or the midline thalamus, the probable source of the NTIR fibers to the central part of MD is in the deep layer of the piriform cortex, while the NTIR fibers to the medial edge of MD and the midline nuclei may arise from the preoptic region and the medial amygdala. In neonatal rats, neurons are found in the piriform cortex, the preoptic region, and the medial amygdala, which can be double-labeled both for neurotensin and with a retrograde tracer injected into MD and the midline thalamus. Projections of the preoptic region to the thalamus have a distribution similar to that of the medial population of NTIR fibers, whereas the distribution of piriform cortical afferents in central MD matches the central patch of NTIR fibers.

Co-existence of vasoactive intestinal polypeptide (VIP)- and cholecystokinin (CCK)-like immunoreactivities in thalamocortical neuron in the ventrolateral nucleus of the rat

Cholecystokinin (CCK)- and/or vasoactive intestinal polypeptide (VIP)-like immunoreactivity (LI) was seen in many thalamocortical VL neurons which were retrogradely labeled with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injected into the frontal cortex of the rat. VIP- or CCK-LI was observed in 70-80% or 50-60% of thalamocortical VL neurons, respectively. Almost all of thalamocortical VL neurons with CCK-LI exhibited VIP-LI.

Neurons containing cholecystokinin mRNA in the mammillary region: ontogeny and adult distribution in the rat

1. The ontogeny and adult distribution of neurons containing cholecystokinin (CCK) mRNA in the premammillary and mammillary nuclei and supramammillary region of the rat brain were studied using hybridization histochemistry. 2. The earliest detection of CCK mRNA in the mammillary region was on E14, followed by a marked increase in transcript levels during the next 4 days, a time during which neurons in this region still divide. During the first 2 weeks of life, few changes in the levels of CCK transcripts were seen, and an adult-like pattern of expression was seen on the twenty-first day of life. 3. Low levels of transcripts were present in numerous neurons located in all divisions of the medial nucleus and in the posterior nucleus known to project ipsilaterally to the anteroventral and anteromedial thalamic nuclei. In contrast, none of the neurons in the lateral nucleus (projecting bilaterally to the anterodorsal thalamic nucleus) had detectable transcripts. 4. Many neurons in the supramammillary nucleus had low, moderate, or high levels of transcripts. Some nearby nuclei (such as the dorsal premammillary nucleus) had smaller numbers of neurons with low levels of CCK mRNA, whereas others (such as the ventral premammillary nucleus) had none.

Expression of cholecystokinin and enkephalin mRNA in discrete brain regions

The levels of preprocholecystokinin mRNA were measured in several regions of rat brain using RNA blot analysis. In both species, high levels of expression were observed in the thalamus, amygdala, neocortical areas and hippocampus. Intermediate levels were observed in the periaqueductal grey, hypothalamus, substantia nigra, ventral tegmental area, and olfactory bulbs; little or no mRNA was detected in the caudate nucleus, nucleus accumbens, olfactory tubercle, cerebellum or a liver control. In contrast, the caudate and olfactory tubercle expressed large amounts of preproenkephalin mRNA. Other regions, such as the periaqueductal grey and olfactory bulbs, expressed both transcripts while regions like the hippocampus contained prominent amounts of preprocholecystokinin mRNA and relatively little preproenkephalin mRNA.

The distribution of thalamic projection neurons containing cholecystokinin messenger RNA, using in situ hybridization histochemistry and retrograde labeling

The distribution of cholecystokinin (CCK) synthesizing neurons in the thalamus was studied using in situ hybridization histochemistry. The message coding for CCK is present at different levels of intensity in almost all neurons (95%) of the anterior, ventral, medial and lateral groups of nuclei, with the ventral nuclei having the highest grain density. Many neurons (90%) of the medial and dorsal lateral geniculate nuclei also contained high levels of CCK transcripts. Very few neurons were found to express CCK in the parafascicular and paraventricular nuclei (2% and 10%, respectively), whereas the other intralaminar and midline nuclei had intermediate levels of CCK transcripts (75% of the neurons). The ventral lateral geniculate nucleus and the reticular nucleus were completely devoid of signal. After injection of the fluorescent dye, Fluorogold, into several areas of the cortex and corpus striatum, almost all retrogradely labeled cells in the thalamus (except in the parafascicular nucleus) expressed the CCK gene.

Distributions of certain neuropeptides in the primate thalamus

The distributions of fibers and terminals immunoreactive for somatostatin (SRIF), neuropeptide Y (NPY), substance P (SP) and cholecystokinin octapeptide (CCK), were studied in the diencephalon of cynomolgus monkeys. Immunoreactivity for all 4 peptides is found in extrinsic afferent fibers innervating the dorsal thalamus, ventral thalamus and epithalamus. The distributions of such fibers are more extensive than previously described and include many relay nuclei in their zones of terminations. SP fibers are particularly concentrated in the ventral posteromedial nucleus. All peptides are especially concentrated in fibers in the intralaminar and reticular nuclei. Afferent fibers immunoreactive for each of the 4 peptides approach the thalamus by two pathways. An anterior route is formed by the classical periventricular system ascending from the hypothalamus to the epithalamus. A posterior pathway ascends in the lateral midbrain tegmentum and provides innervation to posterior, intralaminar, and many relay nuclei, plus the ventral thalamus. A basal forebrain pathway, containing SRIF and NPY immunoreactive fibers, enters the thalamus in association with the ansa lenticularis and SP fibers also ascend from the substantia nigra.