Cholecystokinin Modulates the Release of Dopamine from the Anterior and Posterior Nucleus Accumbens by Two Different Mechanisms

The effects of various cholecystokinin (CCK)-related peptides were investigated on 35 mM K(+)-stimulated endogenous dopamine release from slices of either anterior or posterior nucleus accumbens of the rat. CCK sulphated octapeptide (1-10 microM), but not pentagastrin or CCK unsulphated octapeptide, was found to cause a dose-dependent increase in the release from the posterior nucleus accumbens. This effect was blocked by low doses of the CCKA receptor antagonist L364,718 (10 nM) but not the CCKB receptor antagonist L365,260. In the anterior nucleus accumbens CCK sulphated octapeptide (1 microM) and CCK unsulphated octapeptide (0.1-1 microM) inhibited the dopamine release, and this effect was blocked by L365,260 (10-100 nM) but not by L364,718. These results suggest that CCK has a different effect on dopamine release from the anterior and posterior nucleus accumbens and that these effects are mediated by two different types of CCK receptor.     

Regional and cell-type-specific effects of DAMGO on striatal D1 and D2 dopamine receptor-expressing medium-sized spiny neurons

The striatum can be divided into the DLS (dorsolateral striatum) and the VMS (ventromedial striatum), which includes NAcC (nucleus accumbens core) and NAcS (nucleus accumbens shell). Here, we examined differences in electrophysiological properties of MSSNs (medium-sized spiny neurons) based on their location, expression of DA (dopamine) D1/D2 receptors and responses to the μ-opioid receptor agonist, DAMGO {[D-Ala²-MePhe⁴-Gly(ol)⁵]enkephalin}. The main differences in morphological and biophysical membrane properties occurred among striatal sub-regions. MSSNs in the DLS were larger, had higher membrane capacitances and lower Rin (input resistances) compared with cells in the VMS. RMPs (resting membrane potentials) were similar among regions except for D2 cells in the NAcC, which displayed a significantly more depolarized RMP. In contrast, differences in frequency of spontaneous excitatory synaptic inputs were more prominent between cell types, with D2 cells receiving significantly more excitatory inputs than D1 cells, particularly in the VMS. Inhibitory inputs were not different between D1 and D2 cells. However, MSSNs in the VMS received more inhibitory inputs than those in the DLS. Acute application of DAMGO reduced the frequency of spontaneous excitatory and inhibitory postsynaptic currents, but the effect was greater in the VMS, in particular in the NAcS, where excitatory currents from D2 cells and inhibitory currents from D1 cells were inhibited by the largest amount. DAMGO also increased cellular excitability in the VMS, as shown by reduced threshold for evoking APs (action potentials). Together the present findings help elucidate the regional and cell-type-specific substrate of opioid actions in the striatum and point to the VMS as a critical mediator of DAMGO effects.     

Involvement of Dopamine D1 and D2 Receptors in the Regulation of Proenkephalin mRNA Abundance in the Striatum and Accumbens of the Rat Brain

The effects of short-term treatment (6 h) with selective D1 or D2 agonists and antagonists on the mRNA for proenkephalin in the medial and anterior aspects of the caudate-putamen and the nucleus accumbens were assessed by in situ hybridization histochemistry. Proenkephalin mRNA abundance was significantly changed in the striatum and accumbens in response to D2 receptor manipulation. D2 blockade with haloperidol or raclopride increased, whereas D2 stimulation with LY-171555 (D2 agonist) decreased, striatal and accumbens proenkephalin mRNA abundance. Antagonism of D1 receptor activity with SCH-23390 significantly decreased proenkephalin mRNA abundance in all brain regions. Concurrent administration of the D1 agonist SKF-38393 prevented the SCH-23390 effect in all brain areas. The data demonstrate that acute treatment with dopaminergic D2 agonists and antagonists affects proenkephalin mRNA abundance in the striatum and accumbens via a D2 receptor mechanism, consistent with the concept that D2 receptor function inhibits the synthesis of the mRNA encoding the enkephalin peptides. Moreover, D1 receptor activity, directly or indirectly, exerts modulatory effects on proenkephalin mRNA abundance in the striatum and nucleus accumbens.     

A comparison of the locomotor effects induced by centrally injected TRH and TRH analogues

Thyrotrophin-releasing hormone (TRH) and its stable analogues CG3509 and RX77368 were injected directly into the nucleus accumbens, septum and striatum of the rat and locomotor activity was recorded. TRH (5-20 micrograms) caused a dose-dependent increase in locomotor activity when injected into the nucleus accumbens. TRH (20 micrograms) also increased locomotor activity after administration into the septum but not when put into the striatum. Both the TRH analogues (0.1 and 1.0 microgram) produced closely related increases in activity when injected into either the nucleus accumbens or septum but CG3509 was more potent with a longer lasting effect. Also, in contrast with TRH (20 micrograms), both TRH analogues stimulated locomotor activity when injected into the striatum at a dose of 1 microgram but the effect was less marked and delayed in onset compared to the nucleus accumbens and septum response. Dopamine (100 micrograms) injected into the accumbens or septum also produced significant increases in locomotor activity. The locomotor effects of the peptides are discussed in relation to a possible dopamine-mediated mechanism which contrasts with the actions of TRH and the analogues on barbiturate anaesthesia.     

gamma-Endorphin and N alpha-acetyl-gamma-endorphin interfere with distinct dopaminergic systems in the nucleus accumbens via opioid and non-opioid mechanisms

Low doses (10 ng) of the dopamine agonist apomorphine induced hypolocomotion when injected into the nucleus accumbens of rats. This behavioral response was antagonized by local treatment with either the opioid peptide gamma-endorphin (gamma E) or the non-opioid peptide N alpha-acetyl-gamma-endorphin (Ac gamma E) in a dose of 100 pg. High doses of apomorphine (10 micrograms) r amphetamine (2 micrograms) injected into the nucleus accumbens resulted in hyperlocomotion. This response was blocked by pretreatment with gamma E but not with Ac gamma E. This effect of gamma E could be prevented by local treatment with naloxone. Neither peptides interfered with the apomorphine-induced stereotyped sniffing when the substances were injected into the nucleus caudatus. It is concluded that gamma E and Ac gamma E differentially interact with distinct dopaminergic systems in the nucleus accumbens of the rat brain via an opioid and a non-opioid mechanism, suggesting that the peptide fragments originating from pro-opiomelanocortin may be specifically implicated in the control of dopaminergic activity in this brain area.     

D(1) dopamine receptor stimulation increases GluR1 phosphorylation in postnatal nucleus accumbens cultures

Postsynaptic interactions between dopamine and glutamate receptors in the nucleus accumbens are critical for acute responses to drugs of abuse and for neuroadaptations resulting from their chronic administration. We tested the hypothesis that D(1) dopamine receptor stimulation increases phosphorylation of the AMPA receptor subunit GluR1 at the protein kinase A phosphorylation site (Ser845). Nucleus accumbens cell cultures were prepared from postnatal day 1 rats. After 14 days in culture, GluR1 phosphorylation was measured by western blotting using phosphorylation site-specific antibodies. The D(1) receptor agonist SKF 81297 increased Ser845 phosphorylation in a concentration- dependent manner, with marked increases occurring within 5 min. This was prevented by the D(1) receptor antagonist SCH 23390 and the protein kinase A inhibitor H89, and reproduced by forskolin. The D(2) receptor agonist quinpirole attenuated the response to D(1) receptor stimulation. Neither D(1) nor D(2) receptor agonists altered GluR1 phosphorylation at Ser831, the site phosphorylated by protein kinase C and calcium/calmodulin-dependent protein kinase II. In other systems, phosphorylation of GluR1 at Ser845 is associated with enhancement of AMPA receptor currents. Thus, the present results suggest that AMPA receptor transmission in the nucleus accumbens may be augmented by concurrent D(1) receptor stimulation.     

RGS9 modulates dopamine signaling in the basal ganglia

Regulators of G protein signaling (RGS) modulate heterotrimeric G proteins in part by serving as GTPase-activating proteins for Galpha subunits. We examined a role for RGS9-2, an RGS subtype highly enriched in striatum, in modulating dopamine D2 receptor function. Viral-mediated overexpression of RGS9-2 in rat nucleus accumbens (ventral striatum) reduced locomotor responses to cocaine (an indirect dopamine agonist) and to D2 but not to D1 receptor agonists. Conversely, RGS9 knockout mice showed heightened locomotor and rewarding responses to cocaine and related psychostimulants. In vitro expression of RGS9-2 in Xenopus oocytes accelerated the off-kinetics of D2 receptor-induced GIRK currents, consistent with the in vivo data. Finally, chronic cocaine exposure increased RGS9-2 levels in nucleus accumbens. Together, these data demonstrate a functional interaction between RGS9-2 and D2 receptor signaling and the behavioral actions of psychostimulants and suggest that psychostimulant induction of RGS9-2 represents a compensatory adaptation that diminishes drug responsiveness.     

Role of dopamine-dependent negative feedback in the hippocampal--basal ganglia--thalamo---hippocampal loop in response decrement

The mechanism of response decrement in hippocampal and dopaminergic neurons on repeating stimuli based on the dopamine-dependent negative feedback in the hippocampal--basal ganglia--thalamo--hippocampal loop is suggested. Activation of hippocampal neurons caused by new stimulus facilitates occurrence of reaction of dopaminergic cells due to their disinhibition through striatopallidal cells of nucleus accumbens and ventral pallidum. However, increase in dopamine level and activation accumbens and ventral pallidum. However, increase in dopamine level and activation of D2 receptors on the striatopallidal cell, while promoting depression of hippocampal inputs, prevents disinhibition of dopaminergic cells, and their reactions start their decrement. The subsequent decrease in D1 receptor activation leads to reduction of efficiency of neuron excitation in the hippocampal CA1 fields, as well as in striatonigral cells of nucleus accumbens. This leads to a decrease of disinhibition through a direct pathway via the basal ganglia of thalamic nucleus reunions which activates neurons of the CA1 field. This effect causes decrement of reactions of the hippocampal neurons, a subsequent reduction of dopaminergic cell disinhibition, and further decrement of their responses.     

Sleep-deprivation regulates α-2 adrenergic responses of rat hypocretin/orexin neurons

We recently demonstrated, in rat brain slices, that the usual excitation by noradrenaline (NA) of hypocretin/orexin (hcrt/orx) neurons was changed to an inhibition following sleep deprivation (SD). Here we describe that in control condition (CC), i.e. following 2 hours of natural sleep in the morning, the α(2)-adrenergic receptor (α(2)-AR) agonist, clonidine, had no effect on hcrt/orx neurons, whereas following 2 hours of SD (SDC), it hyperpolarized the neurons by activating G-protein-gated inwardly rectifying potassium (GIRK) channels. Since concentrations of clonidine up to a thousand times (100 μM) higher than those effective in SDC (100 nM), were completely ineffective in CC, a change in the availability of G-proteins is unlikely to explain the difference between the two conditions. To test whether the absence of effect of clonidine in CC could be due to a down-regulation of GIRK channels, we applied baclofen, a GABA(B) agonist known to also activate GIRK channels, and found that it hyperpolarized hcrt/orx neurons in that condition. Moreover, baclofen occluded the response to clonidine in SDC, indicating that absence of effect of clonidine in CC could not be attributed to down-regulation of GIRK channels. We finally tested whether α(2)-ARs were still available at the membrane in CC and found that clonidine could reduce calcium currents, indicating that α(2)-ARs associated with calcium channels remain available in that condition. Taken together, these results suggest that a pool of α(2)-ARs associated with GIRK channels is normally down-regulated (or desensitized) in hcrt/orx neurons to only become available for their inhibition following sleep deprivation.     

Plasminogen activator inhibitor-2 (PAI-2) mRNA is localized in the accumbens nucleus of the mouse brain and is induced in specific brain sites after kainate excitation

Plasminogen activator inhibitor-2 (PAI-2) specifically inhibits plasminogen activators, extracellular fibrinolytic serine proteases that are also implicated in brain plasticity and toxicity. Primarily localized intracellularly, PAI-2 is thought to also counteract apoptosis mediated by a currently undefined intracellular protease. Here we localized PAI-2 mRNA through in situ hybridization in brain cryosections derived from normal adult mice or after kainate excitation. We found that in the normal brain PAI-2 mRNA was confined to an area within the accumbens nucleus shell. After kainate was injected (i.p.), PAI-2 mRNA was substantially and rapidly (within 2 h) induced in neuron-like cells primarily in layers II–III of the neocortex; the cingulate, piriform, entorhinal and perirhinal cortices; the olfactory bulb, nucleus and tubercle; in the accumbens nucleus, shell and core; throughout the caudate putamen and the amygdaloid complex; in the CA1 and CA3 areas of the hippocampus, and in the parasubiculum. These findings suggest that PAI-2 could play a role in the accumbens nucleus as well as in activity-related events associated with olfactory, striatal, and limbic structures.     

Activation of central orexin/hypocretin neurons by dietary amino acids

Hypothalamic orexin/hypocretin (orx/hcrt) neurons regulate energy balance, wakefulness, and reward; their loss produces narcolepsy and weight gain. Glucose can lower the activity of orx/hcrt cells, but whether other dietary macronutrients have similar effects is unclear. We show that orx/hcrt cells are stimulated by nutritionally relevant mixtures of amino acids (AAs), both in brain slice patch-clamp experiments, and in c-Fos expression assays following central or peripheral administration of AAs to mice in?vivo. Physiological mixtures of AAs electrically excited orx/hcrt cells through a dual mechanism involving inhibition of K(ATP) channels and activation of system-A amino acid transporters. Nonessential AAs were more potent in activating orx/hcrt cells than essential AAs. Moreover, the presence of physiological concentrations of AAs suppressed the glucose responses of orx/hcrt cells. These results suggest a new mechanism of hypothalamic integration of macronutrient signals and imply that orx/hcrt cells sense macronutrient balance, rather than net energy value, in extracellular fluid.     

Autoradiographic Visualization of the Receptor Subclasses for Vasoactive Intestinal Polypeptide (VIP) in Rat Brain

Vertongen, P., S. N. Schiffmann, P. Gourlet and P. Robberecht. Autoradiographic visualization of the receptor subclasses for Vasoactive Intestinal Polypeptide (VIP) in rat brain. Peptides 18(10) 1547–1554, 1997.—Vasoactive Intestinal Polypeptide (VIP) exerts its biological effects through interaction with two high affinity receptors named the VIP₁- and the VIP₂ receptors. Their messenger RNAs have been mapped in rat brain by in situ hybridization. A cyclic peptide (RO 25-1553) and a secretin analogue ([R¹⁶]chicken secretin) were identified as selective agonist peptides for the VIP₂- and VIP₁ receptors, respectively. The iodinated peptides retained the high affinity and selectivity of the unlabelled peptides and were used for the mapping of each receptor subclass in rat brain. VIP₁ receptors were present in the cerebral cortex, the piriform cortex, the claustrum, the caudate-putamen, the dentate gyrus, the lateral amygdaloïd nucleus, the anteroventral thalamic nucleus, the rhomboïd nucleus, the supraoptic nucleus and the choroïd plexus. VIP₂ receptors were present in the cerebral cortex, the claustrum, the caudate-putamen, the nucleus accumbens, the lateral septal nuclei, the bed nucleus of the stria terminalis, the basolateral amygdaloïd nucleus, the Ammon’s horn, the thalamic nuclei except some centromedial nuclei, the medial habenula, the suprachiasmatic nucleus, the periventricular nucleus, the mammilary nucleus, the superior colliculus and the choroïd plexus.     

The histaminergic system regulates wakefulness and orexin/hypocretin neuron development via histamine receptor H1 in zebrafish

The histaminergic and hypocretin/orexin (hcrt) neurotransmitter systems play crucial roles in alertness/wakefulness in rodents. We elucidated the role of histamine in wakefulness and the interaction of the histamine and hcrt systems in larval zebrafish. Translation inhibition of histidine decarboxylase (hdc) with morpholino oligonucleotides (MOs) led to a behaviorally measurable decline in light-associated activity, which was partially rescued by hdc mRNA injections and mimicked by histamine receptor H1 (Hrh1) antagonist pyrilamine treatment. Histamine-immunoreactive fibers targeted the dorsal telencephalon, an area that expresses histamine receptors hrh1 and hrh3 and contains predominantly glutamatergic neurons. Tract tracing with DiI revealed that projections from dorsal telencephalon innervate the hcrt and histaminergic neurons. Translation inhibition of hdc decreased the number of hcrt neurons in a Hrh1-dependent manner. The reduction was rescued by overexpression of hdc mRNA. hdc mRNA injection alone led to an up-regulation of hcrt neuron numbers. These results suggest that histamine is essential for the development of a functional and intact hcrt system and that histamine has a bidirectional effect on the development of the hcrt neurons. In summary, our findings provide evidence that these two systems are linked both functionally and developmentally, which may have important implications in sleep disorders and narcolepsy. development via histamine receptor H1 in zebrafish.     

Plasminogen

Plasminogen activator inhibitor-2 (PAI-2) specifically inhibits plasminogen activators, extracellular fibrinolytic serine proteases that are also implicated in brain plasticity and toxicity. Primarily localized intracellularly, PAI-2 is thought to also counteract apoptosis mediated by a currently undefined intracellular protease. Here we localized PAI-2 mRNA through in situ hybridization in brain cryosections derived from normal adult mice or after kainate excitation. We found that in the normal brain PAI-2 mRNA was confined to an area within the accumbens nucleus shell. After kainate was injected (i.p.), PAI-2 mRNA was substantially and rapidly (within 2 h) induced in neuron-like cells primarily in layers II-III of the neocortex; the cingulate, piriform, entorhinal and perirhinal cortices; the olfactory bulb, nucleus and tubercle; in the accumbens nucleus, shell and core; throughout the caudate putamen and the amygdaloid complex; in the CA1 and CA3 areas of the hippocampus, and in the parasubiculum. These findings suggest that PAI-2 could play a role in the accumbens nucleus as well as in activity-related events associated with olfactory, striatal, and limbic structures.     

Cerebrospinal Fluid Hypocretin-1 (Orexin-A) Level Fluctuates with Season and Correlates with Day Length

The hypocretin/orexin neuropeptides (hcrt) are key players in the control of sleep and wakefulness evidenced by the fact that lack of hcrt leads to the sleep disorder Narcolepsy Type 1. Sleep disturbances are common in mood disorders, and hcrt has been suggested to be poorly regulated in depressed subjects. To study seasonal variation in hcrt levels, we obtained data on hcrt-1 levels in the cerebrospinal fluid (CSF) from 227 human individuals evaluated for central hypersomnias at a Danish sleep center. The samples were taken over a 4 year timespan, and obtained in the morning hours, thus avoiding impact of the diurnal hcrt variation. Hcrt-1 concentration was determined in a standardized radioimmunoassay. Using biometric data and sleep parameters, a multivariate regression analysis was performed. We found that the average monthly CSF hcrt-1 levels varied significantly across the seasons following a sine wave with its peak in the summer (June—July). The amplitude was 19.9 pg hcrt/mL [12.8–26.9] corresponding to a 10.6% increase in midsummer compared to winter. Factors found to significantly predict the hcrt-1 values were day length, presence of snow, and proximity to the Christmas holiday season. The hcrt-1 values from January were much higher than predicted from the model, suggestive of additional factors influencing the CSF hcrt-1 levels such as social interaction. This study provides evidence that human CSF hcrt-1 levels vary with season, correlating with day length. This finding could have implications for the understanding of winter tiredness, fatigue, and seasonal affective disorder. This is the first time a seasonal variation of hcrt-1 levels has been shown, demonstrating that the hcrt system is, like other neurotransmitter systems, subjected to long term modulation.     

Effect of experimenter-delivered and self-administered cocaine on extracellular beta-endorphin levels in the nucleus accumbens

Beta-endorphin is an endogenous opioid peptide that has been hypothesized to be involved in the behavioral effects of drugs of abuse including psychostimulants. Using microdialysis, we studied the effect of cocaine on extracellular levels of beta-endorphin in the nucleus accumbens, a brain region involved in the reinforcing effects of psychostimulant drugs. Experimenter-delivered cocaine (2 mg/kg, i.v.) increased extracellular beta-endorphin immunoreactive levels in the nucleus accumbens, an effect attenuated by 6-hydroxy-dopamine lesions or systemic administration of the D1-like receptor antagonist, SCH-23390 (0.25 mg/kg, i.p.). The effect of cocaine on beta-endorphin release in the nucleus accumbens was mimicked by a local perfusion of dopamine (5 microm) and was blocked by coadministration of SCH-23390 (10 microm). Self-administered cocaine (1 mg/kg/infusion, i.v.) also increased extracellular beta-endorphin levels in the nucleus accumbens. In addition, using functional magnetic resonance imaging, we found that cocaine (1 mg/kg, i.v.) increases regional brain activity in the nucleus accumbens and arcuate nucleus. We demonstrate an increase in beta-endorphin release in the nucleus accumbens following experimenter-delivered and self-administered cocaine mediated by the local dopaminergic system. These findings suggest that activation of the beta-endorphin neurons within the arcuate nucleus-nucleus accumbens pathway may be important in the neurobiological mechanisms underlying the behavioral effects of cocaine.     

Neuronal systems immunologically related to the somatostatin system in the garden dormouse

Cells and fibers containing somatostain (SRIF) or SRIF-like peptides were detected immunocytochemically in the brain of the garden dormouse (Eliomys quercinus L.). The periventricular preoptic nucleus and the paraventricular nucleus encompass a component of the SRIF-immunoreactive hypothalamo-infundibular and hypothalamo-neurohypophyseal systems. The suprachiastmatic, ventromedial and arcuate nuclei contain a number of SRIF-positive cells and receive a rich SRIF innervation. The extrahypothalamic systems containing SRIF can be subdivided into the following groups: (1) Afferents, the cellular origin of which is not always clearly evident, i.e., fibers of the septum, the lateral preoptic area, the thalamus, the superior olivary nucleus, the mesencephalic gray matter, and the subfornical organ; (2) dispersed cells with short projections (neocortex, caudate nucleus, putamen); (3) scattered cells with short projections (nucleus accumbens) or innervating remote territories (nucleaus interpeduncularis); (4) vascular organ of the lamina terminalis, a neurohemal area comparable to the median eminence. These observations lead to a theory of a functional bipotentiality of the somatostatin molecule. Immunocytological results depend on the antisera employed, the type of fixation and the experimental conditions. Adrenalectomy is followed by an accumulation of immunoreactive material in all SRIF-containing systems of the brain. These results clearly indicate the SRIF participates in the function of the CRF-ACTH-adrenal axis. The endocrine disturbance induced by adrenalectomy appears to modify the activity of both the neurohormonal and neuromodulator components of the SRIF system.     

Alpha-MSH injected into the substantia nigra or intraventricularly alters behavior and the striatal dopaminergic activity

Rats were injected with 1 μg of alpha-melanocyte stimulating hormone (α-MSH) into the third ventricle and locally in the ventral tegmental area and in different regions of the substantia nigra. The modifications produced on grooming behavior and locomotion as well as on the dopamine content of the nucleus accumbens and the caudate putamen, were studied. Both intraventricular peptide administration and microinjections into the ventral tegmental area induced excessive grooming and a significant increase of the locomotor activity. The dopamine content of the nucleus accumbens and caudate putamen was markedly reduced. Injections of the peptide into the substantia nigra pars compacta failed to induce excessive grooming but did provoke a slight increase in locomotor activity and a smaller change in caudate dopamine content than that observed by injections in the ventral tegmental area or in the third ventricle. Dopamine levels in the nucleus accumbens were not changed. Finally, the injections of α-MSH into the lateral substantia nigra did not produce either biochemical or behavioral changes.The results suggests that α-MSH can modify, directly or indirectly, the striatal dopaminergic activity and that the behavioral alterations observed such as excessive grooming, could be mediated by the activation of the dopamine cells from the ventral tegmental area, that in turn may provoke a significative release of dopamine at the caudate putamen nucleus as well as in nucleus accumbens.     

Distribution of pro-opiomelanocortin and its peptide end products in the brain and hypophysis of the aquatic toad, Xenopus laevis

Using in situ hybridization with a pro-opiomelanocortin (POMC)-mRNA probe and immunocytochemistry with antisera to POMC and to various POMC-derived peptides, it is shown that melanotrope cells in the pars intermedia of the hypophysis of the South African aquatic toad Xenopus laevis contain POMC, α-melanophore-stimulating hormone (α-MSH), γ-MSH, acetylated and non-acetylated endorphins and adrenocorticotropic hormone (ACTH). With the exception of γ-MSH, these peptides are also found in the corticotrope cells in the rostral pars distalis. In the Xenopus brain, neuronal cell bodies in the ventral hypothalamic nucleus express POMC, α-MSH, γ-MSH, non-acetylated endorphins and ACTH, neurones in the anterior preoptic area reveal POMC, α-MSH, γ-MSH and non-acetylated endorphin, neurones in the suprachiasmatic nucleus contain α-MSH, non-acetylated endorphin and ACTH and neurones in the posterior tubercle show α-MSH, non-acetylated endorphin and ACTH immunoreactivities. In the locus coeruleus POMC and ACTH coexist, whereas α-MSH and non-acetylated endorphin occur together in the nucleus accumbens, the striatum and the nucleus of the paraventricular organ. Finally, α-MSH alone is present in the olfactory bulb, the medial septum, the medial and lateral parts of the amygdala, the ventromedial and posterior thalamic nuclei, the optic tectum and the anteroventral tegmental nucleus, and non-acetylated endorphin alone appears in the epiphysis. It is suggested that neurones that form POMC-derived peptides may play a direct or indirect role in the control of POMC-producing hypophyseal cells and/or in the physiological processes these endocrine cells regulate. This idea is supported by the fact that the suprachiasmatic nucleus and the locus coeruleus, both involved in melanotrope cell control, show POMC and POMC-peptide expression. A possible involvement in melanotrope and/or corticotrope control of the anterior preoptic and ventral hypothalamic nuclei, which both express POMC and various POMC-derived peptides, deserves future attention.