Distribution of cholecystokinin-like immunoreactivity in the nervous system. Co-existence with classical neurotransmitters and other neuropeptides

Levels of CCK immunoreactivity and dopamine in the nucleus accumbens after 6-hydroxydopamine lesions of the ventral tegmental area and the nucleus accumbens

The effects of 6-hydroxydopamine (6-OHDA) injected into either the ventral tegmental area (VTA) or the nucleus accumbens on dopamine and its metabolite DOPAC and CCK-immunoreactivity in the nucleus accumbens were studied. Measurements were made 1, 3 and 6 weeks after the lesion in both the anterior and posterior part of the nucleus accumbens. 6-OHDA applied in the VTA reduced the level of DA and DOPAC, but did not affect the CCK content in the nucleus accumbens. 6-OHDA lesions in the anterior part of the nucleus accumbens produced depletion of DA and DOPAC from one week after the injection, and decreased the CCK content 6 weeks after the injection. The results suggest that in the nucleus accumbens DA and CCK are localized, at least for the major part, in different nerve terminals.

Does cholecystokinin colocalize with dopamine in the human substantia nigra?

In situ hybridization was used to examine the distribution of neurons containing cholecystokinin (CCK) mRNA in human, monkey and rat brain. In rat and monkey brain CCK mRNA was visualized in the substantia nigra pars compacta and in the ventral tegmental area. The dopaminergic cell bodies in the human substantia nigra did not however show detectable amounts of CCK mRNA. Low levels of CCK mRNA were observed in the nucleus paranigralis, the human equivalent of the rodent ventral tegmental area. High levels of CCK mRNA were seen in other regions of the same brains including the cortex and the hippocampus. Thus, the adult human substantia nigra dopaminergic cells, in contrast to primate and rodent substantia nigra, do not express CCK. These results question the hypothesis of an involvement of CCK in the regulation of dopaminergic neurons and help to explain the absence of decreased CCK levels in the caudate and putamen of Parkinson's disease victims.

Cholecystokinin: Corelease with dopamine from nigrostriatal neurons in the cat

Halothane-anaesthetized cats were implanted with push-pull cannulae to demonstrate the in vivo release of cholecystokinin-like immunoreactivity (CCK-LI) in the substantia nigra and the ipsilateral caudate nucleus. The spontaneous and the calcium-dependent potassium-evoked release of CCK-LI were observed in both structures. In addition, the local application of tetrodotoxin (10-6 M) reduced the spontaneous release of the peptide. 6-OHDA lesions made in the substantia nigra pars compacta led to a complete destruction of nigrostriatal dopaminergic neurons. CCK-LI levels were not affected in the caudate nucleus but were reduced substantially in the substantia nigra. The activation of dopaminergic cells induced by the nigral application of alpha-methyl-para-tyrosine (10-4 M) stimulated the release of CCK-LI and dopamine in the ipsilateral caudate nucleus, whilst opposite effects were seen in the substantia nigra. Similar results were obtained when dopaminergic transmission was blocked in the caudate nucleus suggesting that the evoked release of CCK-LI by the alpha-methyl-para-tyrosine treatment originates from dopaminergic nerve terminals and not from other CCK-LI containing fibres in response to released dopamine. Dopamine (10-7 M) as well as the D1 agonist SKF 38393 (10-5 M) stimulated CCK-LI release when applied into the caudate nucleus while the D2 agonist, LY 171555 (10-6 M) slightly reduced peptide release. The local application of cholecystokinin-8 sulfate (CCK-8S) (10-8 M, for 30 min) into the substantia nigra pars compacta increased the firing rate of dopaminergic cells and stimulated the release of newly synthesized 3H-dopamine from dendrites and nerve terminals. These results suggest, but do not definitively prove, that, in the cat, CCK-LI and dopamine are coreleased from nigrostriatal mixed dopaminergic/CCK-LI neurons and that CCK-LI released from dendrites is, like dopamine, involved in the regulation of the activity of these cells.

The colocalization of cholecystokinin and tyrosine hydroxylase mRNAs in mesencephalic dopaminergic neurons in the rat brain examined by in situ hybridization

The colocalization of cholecystokinin and tyrosine hydroxylase mRNAs was studied with a cellular resolution in the mesencephalic dopaminergic neurons of the rat brain by in situ hybridization using synthetic oligonucleotides. An extensive colocalization of cholecystokinin-expressing cells, greater than that seen previously by immunohistochemistry, was found in the ventral tegmental area and in the substantia nigra pars compacta. We observed in these regions that cholecystokinin and tyrosine hydroxylase mRNAs coexisted in the same neurons but not all dopamine cells expressed cholecystokinin mRNA. 6-Hydroxydopamine-induced destruction of mesostriatal dopaminergic neurons resulted in a complete loss of cholecystokinin and tyrosine hydroxylase mRNA expression throughout the substantia nigra pars compacta, indicating that all cholecystokinin expressing cells are 6-hydroxydopamine-sensitive. While increased enkephalin mRNA expression in the striatum ipsilateral to the lesion was detected, no change of cholecystokinin mRNA expression was observed in any forebrain on the lesioned side, suggesting that cholecystokinin expression in the forebrain is not under dopaminergic control. These results show the usefulness of the in situ hybridization approach for the precise localization of cells in rat brain which express mRNAs for cholecystokinin and tyrosine hydroxylase and for the study of the effects of neurotoxic lesions on these cells.

Regional localization of the mRNA coding for the neuropeptide cholecystokinin in the rat brain studied by in situ hybridization

The regional localization of mRNA coding for the neuropeptide cholecystokinin (CCK) has been studied in the rat brain by in situ hybridization using a 32P-labelled synthetic 32 mer oligonucleotide. Autoradiograms were quantified using computer-assisted microdensitometry. High levels of hybridization were observed in the neocortex, claustrum, endopiriform nucleus, cingular cortex, amygdala, olfactory bulb, hippocampus, ventral tegmental area, geniculate nucleus, several thalamic nuclei and substantia nigra compacta. Very weak signal was detected in the striatum, the cerebellum and the brainstem. The topographic distribution of CCK neurons observed overlaps in part with that previously described by immunohistochemical techniques. However, some discrepancies were also found, particularly in the thalamus. These results show that in situ hybridization with oligonucleotide probes together with a semiquantitative method described can be used to map the expression of the CCK mRNA in rat brain sections as well as its modification after pharmacological or physiological manipulations.

Effects of sulphated cholecystokinin octapeptide (CCK-8) on the dorsal motor nucleus of the vagus

Sulphated cholecystokinin octapeptide (CCK-8) was applied by superfusion (2.1 x 10(-7) to 4.2 x 10(-6) M) to neurons of the dorsal motor nucleus of the vagus (DMV) in slice preparations of the rat medulla oblongata. Intracellular recordings show 23 of 54 (43%) neurons to be depolarized and the depolarization to be associated with an increase in membrane input resistance; 6 of 54 (11%) neurons were hyperpolarized and the hyperpolarization was associated with a decrease in membrane input resistance. Both effects were dose-dependent, reversible and persisted after blockade of synaptic transmission by Ca2+ free/high Mg2+ solution. On the other hand, nonsulphated CCK-8, a nonactive analogue of CCK-8, had no effect. These data show that vagal neurons in the DMV have receptors for CCK-8 and that CCK-8 may modulate vagal output mainly by increasing neuronal excitability.

Autoradiographic demonstration of the antagonism of anthramycin and diazepam against cholecystokinin in the mouse brain using the [14C]-2-deoxyglucose method

Effects of diazepam (DZP), a synthetic benzodiazepine drug, and anthramycin (ATM), a benzodiazepine antitumor antibiotic produced by a certain species of streptomyces, on the uptake of 2-deoxy-D-[14C]-glucose (2-DG) in mouse brain neurons with or without cholecystokinin were examined. 2-DG uptake in neurons was evaluated by using an autoradiographic technique. The sulfated octapeptide CCK (CCK8) was injected intracisternally; DZP and ATM, intraperitoneally; and 2-DG, intravenously to mice. Autoradiograms prepared from the slices of the brain were converted to false color images. CCK8 (1 microgram/mouse) markedly stimulated the 2-DG uptake in neurons in the various regions of the brain, but the stimulative effects of CCK8 was almost completely suppressed after an intraperitoneal administration of 1.0 mg/kg of DZP or 0.5 mg/kg of ATM. Since it has been previously shown that these doses of DZP and ATM almost completely reversed the antinociception produced by 1 microgram/mouse of CCK8, the present results on the 2-DG uptake in the mouse brain are considered to further support the antagonism between CCK8 and DZP or ATM in the central nervous system.

Electrophysiological effects of cholecystokinin octapeptide on identified rat nigrostriatal dopaminergic neurons

Cholecystokinin octapeptide (CCK-8) exists in a subpopulation of midbrain dopaminergic (DA) neurons and has been shown to affect the activity of unidentified DA cells. This study describes the effects of the sulfated (CCK-8S) and unsulfated (CCK-8US) peptides (8 micrograms/kg, i.v.) on the ability of apomorphine to inhibit the firing rate of nigrostriatal DA cells identified by antidromic activation from the caudate nucleus of anesthetized rats. CCK-8S excited 9/25 DA cells while CCK-8US was without effect on firing rate (n = 9). CCK-8S pretreatment resulted in complex changes in the sensitivity of nigrostriatal DA cells to apomorphine which were related to whether an initial excitatory response was elicited by CCK-8S. CCK-8US did not alter apomorphine sensitivity. These results suggest that CCK-8S can exert modulatory effects on DA cells independent of a direct excitatory action. The effect of acute CCK-8 injection on the number of spontaneously active DA cells in stereotaxically defined regions of the substantia nigra and ventral tegmental area was also determined. CCK-8S doubled the number of active cells in these areas; CCK-8US did not alter the population activities.

Clonidine regularizes substantia nigra dopamine cell firing

The effects of clonidine on the activity of single substantia nigra dopamine neurons were studied in the chloral hydrate anesthetized rat. Although clonidine did not affect the firing rate of the cells, it regularized the firing pattern and decreased burst firing at 2-8 micrograms kg-1 i.v. These effects were antagonized by the alpha 2-antagonist yohimbine. Yohimbine (1.0 mg kg-1) deregularized the firing pattern and increased the firing rate as well as the burst firing. The regularization produced by clonidine is discussed in terms of synaptic efficacy. The results might explain the therapeutic effects of clonidine in certain neuropsychiatric disorders.

neuropeptides in long ascending spinal tract cells in the rat: evidence for parallel processing of ascending information

A study has been made of the involvement of spinal peptidergic neurons in ascending tracts at lumbar-sacral levels in rats, by combining the retrograde transport of a protein-gold complex with immunocytochemistry. Ten neuropeptides have been considered for their presence in the cells of origin of the following six ascending tracts, including some involved in pain transmission: the spinosolitary tract, the medial and lateral spinoreticular tracts, the spinomesencephalic tract, the spinothalamic tract and the postsynaptic dorsal column tract. Although there was overlap in the distribution of several of the types of peptidergic cells and some ascending tract cells only a very small percentage of long ascending tract cells were found to contain neuropeptides. Most (90%) of those peptidergic ascending tract cells, however, were clearly congregated in two distinct spinal regions: the lateral spinal nucleus and the region surrounding the central canal (including lamina X). Ascending tract cells in both of these regions contained a wide variety of neuropeptides. Immunoreactivities for a total of seven different peptides were seen. The lateral spinal nucleus had the highest percentage of neuropeptide containing ascending tract cells; cells of all the four populations of peptidergic neurons lying in this region were involved in supraspinal projections; they stained for vasoactive intestinal polypeptide, bombesin, substance P or dynorphin and their axons projected in the spinomesencephalic, spinoreticular and spinosolitary tracts. The region surrounding the central canal contained bombesin-, enkephalin-, cholecystokinin- and somatostatin-immunoreactive ascending tract cells; these cells were found at the origin of the spinothalamic, spinomesencephalic, spinoreticular and spinosolitary tracts. In this region only the cells staining for substance P were not involved in supraspinal projections. The peptidergic ascending tract cells in other spinal regions were few; they were found in either lamina I or lateral part of lamina V. Ascending tract lamina I cells reacted for dynorphin or vasoactive intestinal polypeptide and their axons projected in the spinosolitary and spinomesencephalic tracts. Ascending tract lamina V cells reacted for somatostatin and were found at the origin of the medial component of the spinoreticular tract. It is proposed that peptidergic ascending tract cells form minor but distinct subgroups within each ascending tract. Each of the ascending tracts are divisible into peptide- and nonpeptide-containing groups of cells which convey information in a parallel fashion.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholecystokinin facilitates ejaculation in male rats: blockade with proglumide and apomorphine

Systemic administration of the active, sulfated form of cholecystokinin-octapeptide (CCK-8S), at a dose known to inhibit dopamine (DA) release, significantly reduced the latency to ejaculate and number of intromissions preceding ejaculation in sexually active male rats. This effect was identical to that reported for low doses of the DA receptor agonist apomorphine, which bind preferentially to presynaptic DA autoreceptors. The facilitatory effect of CCK-8S on ejaculation was blocked by the putative CCK receptor antagonist proglumide and by a presynaptic dose of apomorphine. Blockade of the effect of CCK-8S with a presynaptic dose of apomorphine is consistent with CCK induction of depolarization block in DA neurons. These data suggest that CCK-8S and apomorphine may reduce the ejaculation threshold in sexually active male rats by inhibition of DA release via two different mechanisms of action.

Regional distribution of cholecystokinin receptors in primate cerebral cortex determined by in vitro receptor autoradiography

Cholecystokinin (CCK) is a putative peptide neurotransmitter present in high concentration in the cerebral cortex. By using techniques of in vitro receptor autoradiography, CCK binding sites in primate cortex were labeled with 125I-Bolton-Hunter-labeled CCK-33 (the 33-amino-acid C-terminal peptide) and 3H-CCK-8 (the C-terminal octapeptide). Biochemical studies performed on homogenized and slide-mounted tissue sections showed that the two ligands labeled a high-affinity, apparently single, saturable site. Autoradiography revealed that binding sites labeled by both ligands were anatomically indistinguishable and were distributed in two basic patterns. A faint and diffuse label characterized portions of medial prefrontal cortex, premotor and motor cortices, the superior parietal lobule, and the temporal pole. In other cortical areas the pattern of binding was layer-specific; i.e., binding sites were concentrated within particular cortical layers and were superimposed upon the background of diffuse label. Layer-specific label was found in the prefrontal cortex, anterior and posterior cingulate gyrus, somatosensory cortex, inferior parietal lobule, retrosplenial cortex, insula, temporal lobe cortices, and in the primary visual and adjacent visual association cortices. The areal and laminar localization of layer-specific CCK binding sites consistently coincided with the cortical projections of thalamic nuclei. In prefrontal cortex, CCK binding sites were present in layers III and IV, precisely paralleling the terminal fields of thalamocortical projections from the mediodorsal and medial pulvinar nucleus of the thalamus. In somatosensory cortex, the pattern of CCK binding in layer IV coincided with thalamic inputs arising from the ventrobasal complex, while in the posterior cingulate gyrus, insular cortex, and retrosplenial cortex, layer IV and lower III binding mirrored the laminar distribution of cortical afferents of the medial pulvinar. CCK binding in layers IVa, IVc alpha, IVc beta, and VI of primary visual cortex corresponded to the terminal field disposition of lateral geniculate neurons, whereas in adjacent visual association cortex, binding in layers III, IV, and VI faithfully followed the cortical distribution of projections from the inferior and lateral divisions of the pulvinar nucleus of the thalamus. We interpret the diffusely labeled binding sites in primate cortex as being associated with the intrinsic system of CCK-containing interneurons that are distributed throughout all layers and areas of the cortex. The stratified binding sites, however, appear to be associated with specific extrinsic peptidergic projections.(ABSTRACT TRUNCATED AT 400 WORDS)

Coexistence of peptides with classical neurotransmitters

In the present article the fact is emphasized that neuropeptides often are located in the same neurons as classical transmitters such as acetylcholine, 5-hydroxy-tryptamine, catecholamines, gamma-aminobutyric acid (GABA) etc. This raises the possibility that neurons produce, store and release more than one messenger molecule. The exact functional role of such coexisting peptides is often difficult to evaluate, especially in the central nervous system. In the periphery some studies indicate apparently meaningful interactions of different types with the classical transmitter, but other types of actions including trophic effects have been observed. More recently it has been shown that some neurons contain more than one classical transmitter, e.g. 5-HT plus GABA, further underlining the view that transfer of information across synapses may be more complex than perhaps hitherto assumed.

A quantitative correlation of substance P-, calcitonin gene-related peptide- and cholecystokinin-like immunoreactivity with retrogradely labeled trigeminal ganglion cells innervating the eye

To evaluate the intraganglionic organization of ocular sensory neurons in the guinea pig, we studied the retrograde axonal transport from the eye to the trigeminal ganglion of cholera toxin B subunit and then applied immunohistochemistry for substance P, calcitonin gene-related peptide and cholecystokinin. Retrogradely labeled cells were observed only in the anteromedial portion of the ipsilateral ganglion. We observed no somatotopical organization to trigeminal neurons containing any of these three peptides, either for cells projecting to the eye or for the ganglion as a whole. The relative proportion of neurons immunoreactive for each of these three peptides was similar among the population of neurons retrogradely labeled with cholera toxin B and among the population of neurons without direct projections to the eye.

Cholecystokinin-like immunoreactivity occurs in ocular sensory neurons and partially co-localizes with substance P

Based on immunohistochemical analysis of the trigeminal, superior cervical, ciliary and sphenopalatine ganglia and of the eye after sensory denervation and sympathectomy, cholecystokinin (CCK)-like immunoreactive nerves in the guinea pig eye derive from the trigeminal ganglion. Substance P (SP) also occurs in some ocular sensory neurons, suggesting the possible co-localization in this system of CCK- and SP-immunoreactivities. A double-labeling immunofluorescence technique stained 3 types of trigeminal cells and ocular nerve fibers: some immunoreactive for both peptides, some immunoreactive only for CCK and some immunoreactive only for SP.

Does cholecystokinin-like immunoreactivity in rat primary sensory neurons represent calcitonin gene-related peptide?

Using immunohistochemistry, calcitonin gene-related peptide (CGRP)- and cholecystokinin (CCK)-like immunoreactivity (LI) were found in many of the same spinal and trigeminal ganglion cells and motoneurons in the spinal cord and hypoglossal nucleus, as well as in fibers with an overlapping distribution in the spinal cord (dorsal horn, bundle ventral to the central canal) and in the spinal trigeminal nucleus. CCK-LI in all these structures disappeared after preadsorption of CCK antisera with CGRP at 10(-4) M and almost completely at 10(-5) M. CCK peptide in concentrations up to 10(-4) M, on the other hand, did not influence CGRP staining. The present findings raise the possibility that some CCK-LI in primary sensory neurons in rat may represent CGRP or a similar peptide.