Prodynorphin peptide immunocytochemistry in rhesus monkey brain

The Foundational Science of Endogenous Opioids and Their Receptors

The function of endogenous opioids spans from initiating behaviors that are critical for survival, to responding to rapidly changing environmental conditions. A network of interconnected systems throughout the body characterizes the endogenous opioid system (EOS). EOS receptors for beta-endorphin, enkephalin, dynorphin, and endomorphin underpin the diverse functions of the EOS across biological systems. This chapter presents a succinct yet comprehensive summary of the structure of the EOS, EOS receptors, and their relationship to other biological systems.

Mouse models of surgical and neuropathic pain produce distinct functional alterations to prodynorphin expressing neurons in the prelimbic cortex

The medial prefrontal cortex (mPFC) consists of a heterogeneous population of neurons that respond to painful stimuli, and our understanding of how different pain models alter these specific mPFC cell types remains incomplete. A distinct subpopulation of mPFC neurons express prodynorphin (Pdyn⁺), the endogenous peptide agonist for kappa opioid receptors (KORs). Here, we used whole cell patch clamp for studying excitability changes to Pdyn expressing neurons in the prelimbic region of the mPFC (PL^Pdyn+ neurons) in mouse models of surgical and neuropathic pain. Our recordings revealed that PL^Pdyn+ neurons consist of both pyramidal and inhibitory cell types. We find that the plantar incision model (PIM) of surgical pain increases intrinsic excitability only in pyramidal PL^Pdyn+ neurons one day after incision. Following recovery from incision, excitability of pyramidal PL^Pdyn+ neurons did not differ between male PIM and sham mice, but was decreased in PIM female mice. Moreover, the excitability of inhibitory PL^Pdyn+ neurons was increased in male PIM mice, but was with no difference between female sham and PIM mice. In the spared nerve injury model (SNI), pyramidal PL^Pdyn+ neurons were hyperexcitable at both 3 days and 14 days after SNI. However, inhibitory PL^Pdyn+ neurons were hypoexcitable at 3 days but hyperexcitable at 14 days after SNI. Our findings suggest different subtypes of PL^Pdyn+ neurons manifest distinct alterations in the development of different pain modalities and are regulated by surgical pain in a sex-specific manner. Our study provides information on a specific neuronal population that is affected by surgical and neuropathic pain.

Neuropeptide System Regulation of Prefrontal Cortex Circuitry: Implications for Neuropsychiatric Disorders

Neuropeptides, a diverse class of signaling molecules in the nervous system, modulate various biological effects including membrane excitability, synaptic transmission and synaptogenesis, gene expression, and glial cell architecture and function. To date, most of what is known about neuropeptide action is limited to subcortical brain structures and tissue outside of the central nervous system. Thus, there is a knowledge gap in our understanding of neuropeptide function within cortical circuits. In this review, we provide a comprehensive overview of various families of neuropeptides and their cognate receptors that are expressed in the prefrontal cortex (PFC). Specifically, we highlight dynorphin, enkephalin, corticotropin-releasing factor, cholecystokinin, somatostatin, neuropeptide Y, and vasoactive intestinal peptide. Further, we review the implication of neuropeptide signaling in prefrontal cortical circuit function and use as potential therapeutic targets. Together, this review summarizes established knowledge and highlights unknowns of neuropeptide modulation of neural function underlying various biological effects while offering insights for future research. An increased emphasis in this area of study is necessary to elucidate basic principles of the diverse signaling molecules used in cortical circuits beyond fast excitatory and inhibitory transmitters as well as consider components of neuropeptide action in the PFC as a potential therapeutic target for neurological disorders. Therefore, this review not only sheds light on the importance of cortical neuropeptide studies, but also provides a comprehensive overview of neuropeptide action in the PFC to serve as a roadmap for future studies in this field.

Dynorphin/Kappa-Opioid Receptor System Modulation of Cortical Circuitry

Cortical circuits control a plethora of behaviors, from sensation to cognition. The cortex is enriched with neuropeptides and receptors that play a role in information processing, including opioid peptides and their cognate receptors. The dynorphin (DYN)/kappa-opioid receptor (KOR) system has been implicated in the processing of sensory and motivationally-charged emotional information and is highly expressed in cortical circuits. This is important as dysregulation of DYN/KOR signaling in limbic and cortical circuits has been implicated in promoting negative affect and cognitive deficits in various neuropsychiatric disorders. However, research investigating the role of this system in controlling cortical circuits and computations therein is limited. Here, we review the (1) basic anatomy of cortical circuits, (2) anatomical architecture of the cortical DYN/KOR system, (3) functional regulation of cortical synaptic transmission and microcircuit function by the DYN/KOR system, (4) regulation of behavior by the cortical DYN/KOR system, (5) implications for the DYN/KOR system for human health and disease, and (6) future directions and unanswered questions for the field. Further work elucidating the role of the DYN/KOR system in controlling cortical information processing and associated behaviors will be of importance to increasing our understanding of principles underlying neuropeptide modulation of cortical circuits, mechanisms underlying sensation and perception, motivated and emotional behavior, and cognition. Increased emphasis in this area of study will also aid in the identification of novel ways to target the DYN/KOR system to treat neuropsychiatric disorders.

Synaptic Plasticity in the Nucleus Accumbens: Lessons Learned from Experience

Synaptic plasticity contributes to behavioral adaptations. As a key node in the reward pathway, the nucleus accumbens (NAc) is important for determining motivation-to-action outcomes. Across animal models of motivation including addiction, depression, anxiety, and hedonic feeding, selective recruitment of neuromodulatory signals and plasticity mechanisms have been a focus of physiologists and behaviorists alike. Experience-dependent plasticity mechanisms within the NAc vary depending on the distinct afferents and cell-types over time. A greater understanding of molecular mechanisms determining how these changes in synaptic strength track with behavioral adaptations will provide insight into the process of learning and memory along with identifying maladaptations underlying pathological behavior. Here, we summarize recent findings detailing how changes in NAc synaptic strength and mechanisms of plasticity manifest in various models of motivational disorders.

Distribution and regulation of gonadotropin-releasing hormone, kisspeptin, RF-amide related peptide-3, and dynorphin in the bovine hypothalamus

Recent work has led to the hypothesis that kisspeptin/neurokinin B/dynorphin (KNDy) neurons in the arcuate nucleus (ARC) play a key role in gonadotropin-releasing hormone (GnRH) pulse generation and gonadal steroid feedback, with kisspeptin driving GnRH release and neurokinin B and dynorphin acting as pulse start and stop signals, respectively. A separate cell group, expressing RFamide-related peptide-3 (RFRP-3) has been shown to be a primary inhibitor of GnRH release. Very little is known regarding these cell groups in the bovine. In this study, we examined the relative immunoreactivity of kisspeptin, dynorphin, and RFRP-3 and their possible connectivity to GnRH neurons in the hypothalami of periestrus and diestrus bovine. While GnRH and RFRP-3 immunoreactivity were unchanged, kisspeptin and dynorphin immunoreactivity levels varied in relation to plasma progesterone concentrations and estrous status. Animals with higher plasma progesterone concentrations in diestrus had lower kisspeptin and increased dynorphin immunoreactivity in the ARC. The percentage of GnRH cells with kisspeptin or RFRP-3 fibers in close apposition did not differ between estrous stages. However, the proportions of GnRH cells with kisspeptin or RFRP-3 contacts (∼49.8% and ∼31.3%, respectively) suggest direct communication between kisspeptin and RFRP-3 cells to GnRH cells in the bovine. The data produced in this work support roles for kisspeptin and dynorphin, within the KNDy neural network, in controlling GnRH release over the ovarian cycle and conveying progesterone-negative feedback onto GnRH neurons in the bovine.

Intimate associations between the endogenous opiate systems and the growth hormone-releasing hormone system in the human hypothalamus

Although it is a general consensus that opioids modulate growth, the mechanism of this phenomenon is largely unknown. Since endogenous opiates use the same receptor family as morphine, these peptides may be one of the key regulators of growth in humans by impacting growth hormone (GH) secretion, either directly, or indirectly, via growth hormone-releasing hormone (GHRH) release. However, the exact mechanism of this regulation has not been elucidated yet. In the present study we identified close juxtapositions between the enkephalinergic/endorphinergic/dynorphinergic axonal varicosities and GHRH-immunoreactive (IR) perikarya in the human hypothalamus. Due to the long post mortem period electron microscopy could not be utilized to detect the presence of synapses between the enkephalinergic/endorphinergic/dynorphinergic and GHRH neurons. Therefore, we used light microscopic double-label immunocytochemistry to identify putative juxtapositions between these systems. Our findings revealed that the majority of the GHRH-IR perikarya formed intimate associations with enkephalinergic axonal varicosities in the infundibular nucleus/median eminence, while endorphinergic-GHRH juxtapositions were much less frequent. In contrast, no significant dynorphinergic-GHRH associations were detected. The density of the abutting enkephalinergic fibers on the surface of the GHRH perikarya suggests that these juxtapositions may be functional synapses and may represent the morphological substrate of the impact of enkephalin on growth. The small number of GHRH neurons innervated by the endorphin and dynorphin systems indicates significant differences between the regulatory roles of endogenous opiates on growth in humans.

The dynorphin/κ-opioid receptor system and its role in psychiatric disorders

The dynorphin/κ-opioid receptor system has been implicated in the pathogenesis and pathophysiology of several psychiatric disorders. In the present review, we present evidence indicating a key role for this system in modulating neurotransmission in brain circuits that subserve mood, motivation, and cognitive function. We overview the pharmacology, signaling, post-translational, post-transcriptional, transcriptional, epigenetic and cis regulation of the dynorphin/κ-opioid receptor system, and critically review functional neuroanatomical, neurochemical, and pharmacological evidence, suggesting that alterations in this system may contribute to affective disorders, drug addiction, and schizophrenia. We also overview the dynorphin/κ-opioid receptor system in the genetics of psychiatric disorders and discuss implications of the reviewed material for therapeutics development.

Opioids and anxiety

The opioid system plays a crucial role in the neural modulation of anxiety. The involvement of opioid ligands and receptors in physiological and dysfunctional forms of anxiety is supported by findings from a wide range of preclinical and clinical studies, including clinical trials, experimental research, and neuroimaging, genetic, and epidemiological data. In this review we provide a summary of studies from a variety of research disciplines to elucidate the role of the opioid system in the neurobiology of anxiety. First, we report data from preclinical studies using animal models to examine the modulatory role of central opioid system on defensive responses conducive to fear and anxiety. Second, we summarize the human literature providing evidence that clinical and experimental human studies are consistent with preclinical models. The implication of these data is that activation of the opioid system leads to anxiolytic responses both in healthy subjects and in patients suffering from anxiety disorders. The role of opioids in suppressing anxiety may serve as an adaptive mechanism, collocated in the general framework of opioid neurotransmission blunting acute negative and distressing affective responses.

Reward processing by the opioid system in the brain

The opioid system consists of three receptors, mu, delta, and kappa, which are activated by endogenous opioid peptides processed from three protein precursors, proopiomelanocortin, proenkephalin, and prodynorphin. Opioid receptors are recruited in response to natural rewarding stimuli and drugs of abuse, and both endogenous opioids and their receptors are modified as addiction develops. Mechanisms whereby aberrant activation and modifications of the opioid system contribute to drug craving and relapse remain to be clarified. This review summarizes our present knowledge on brain sites where the endogenous opioid system controls hedonic responses and is modified in response to drugs of abuse in the rodent brain. We review 1) the latest data on the anatomy of the opioid system, 2) the consequences of local intracerebral pharmacological manipulation of the opioid system on reinforced behaviors, 3) the consequences of gene knockout on reinforced behaviors and drug dependence, and 4) the consequences of chronic exposure to drugs of abuse on expression levels of opioid system genes. Future studies will establish key molecular actors of the system and neural sites where opioid peptides and receptors contribute to the onset of addictive disorders. Combined with data from human and nonhuman primate (not reviewed here), research in this extremely active field has implications both for our understanding of the biology of addiction and for therapeutic interventions to treat the disorder.

Dysregulation of dynorphins in Alzheimer disease

The opioid peptides dynorphins may be involved in pathogenesis of Alzheimer disease (AD) by inducing neurodegeneration or cognitive impairment. To test this hypothesis, the dynorphin system was analyzed in postmortem samples from AD and control subjects, and subjects with Parkinson or cerebro-vascular diseases for comparison. Dynorphin A, dynorphin B and related neuropeptide nociceptin were determined in the Brodmann area 7 by radioimmunoassay. The precursor protein prodynorphin, processing convertase PC2 and the neuroendocrine pro7B2 and 7B2 proteins required for PC2 maturation were analyzed by Western blot. AD subjects displayed robustly elevated levels of dynorphin A and no differences in dynorphin B and nociceptin compared to controls. Subjects with Parkinson or cerebro-vascular diseases did not differ from controls with respect to any of the three peptides. PC2 levels were also increased, whereas, those of prodynorphin and pro7B2/7B2 were not changed in AD. Dynorphin A levels correlated with the neuritic plaque density. These results along with the known non-opioid ability of dynorphin A to induce neurodegeneration suggest a role for this neuropeptide in AD neuropathology.

Distribution of preprodynorphin mRNA and dynorphin-a immunoreactivity in the sheep preoptic area and hypothalamus

Endogenous opioid peptides (EOP) are important modulators in a variety of neuroendocrine systems, including those mediating reproduction, energy balance, lactation, and stress. Recent work in the ewe has implicated the EOP, dynorphin (DYN), in the inhibitory effects of progesterone on pulsatile gonadotropin releasing hormone secretion. Although DYN is involved in a number of hypothalamic functions in the sheep, little is known regarding the localization of preprodynorphin (PPD) expression and its major product DYN A (1-17). In this study, we determined the distribution of PPD mRNA and DYN A-containing cell bodies in the brains of ovary-intact, luteal ewes. To detect PPD mRNA, an ovine PPD mRNA was subcloned by reverse transcription-polymerase chain reaction from sheep hypothalamus and used to create a (35)S-labeled riboprobe for in situ hybridization. Neurons that expressed PPD mRNA and DYN A immunoreactivity were widely distributed in the ovine preoptic area and hypothalamus. PPD mRNA-expressing cells were seen in the supraoptic nucleus, paraventricular nucleus, preoptic area, anterior hypothalamus area, bed nucleus of the stria terminalis, ventromedial nucleus (VMN), dorsomedial nucleus of the hypothalamus, and the arcuate nucleus. All of these regions also contained DYN A-positive cell bodies except for the VMN, raising the possibility that PPD is preferentially processed into other peptide products in the VMN. In summary, based on the expression of both mRNA and peptide, DYN cells are located in a number of key hypothalamic regions involved in the neuroendocrine control of homeostasis in sheep.

Relations between brain network activation and analgesic effect induced by low vs. high frequency electrical acupoint stimulation in different subjects: a functional magnetic resonance imaging study

Two- or 100-Hz electrical acupoint stimulation (EAS) can induce analgesia via distinct central mechanisms. It has long been known that the extent of EAS analgesia showed tremendous difference among subjects. Functional MRI (fMRI) studies were performed to allocate the possible mechanisms underlying the frequency specificity as well as individual variability of EAS analgesia. In either frequencies, the averaged fMRI activation levels of bilateral secondary somatosensory area and insula, contralateral anterior cingulate cortex and thalamus were positively correlated with the EAS-induced analgesic effect across the subjects. In 2-Hz EAS group, positive correlations were observed in contralateral primary motor area, supplementary motor area, and ipsilateral superior temporal gyrus, while negative correlations were found in bilateral hippocampus. In 100-Hz EAS group, positive correlations were observed in contralateral inferior parietal lobule, ipsilateral anterior cingulate cortex, nucleus accumbens, and pons, while negative correlation was detected in contralateral amygdala. These results suggest that functional activities of certain brain areas might be correlated with the effect of EAS-induced analgesia, in a frequency-dependent dynamic. EAS-induced analgesia with low and high frequencies seems to be mediated by different, though overlapped, brain networks. The differential activations/de-activations in brain networks across subjects may provide a neurobiological explanation for the mechanisms of the induction and the individual variability of analgesic effect induced by EAS, or that of manual acupuncture as well.

Prodynorphin and kappa opioid receptor mRNA expression in the cingulate and prefrontal cortices of subjects diagnosed with schizophrenia or affective disorders

The present study examined the prodynorphin and kappa opioid receptor mRNA expression levels in the anterior cingulate and dorsolateral prefrontal cortices of subjects diagnosed with schizophrenia, bipolar disorder, or major depression as compared with normal controls without a psychiatric diagnosis. Multivariate analyses failed to reveal any differences in the mRNA expression levels between the four diagnostic groups, though a group trend (non-significant) was evident for the expression of the kappa opioid receptor and prodynorphin mRNAs in the prefrontal cortex. The mRNA expression levels were not associated with lifetime history of antipsychotic treatment or with suicide as a cause of death. The results, however, suggested an influence of certain drugs of abuse on the prodynorphin cortical mRNA expression. Prodynorphin mRNA expression levels were found to be elevated in individuals with a history of marihuana or stimulant use, but not alcohol. Overall, our data do not provide strong evidence for impaired prodynorphin or kappa opioid receptor mRNA levels in the dorsolateral prefrontal or cingulate cortices of schizophrenic, bipolar disorder, or major depressed subjects.

The distribution of dynorphinergic terminals in striatal target regions in comparison to the distribution of substance P-containing and enkephalinergic terminals in monkeys and humans

Single- and double-label immunohistochemical techniques using several different highly specific antisera against dynorphin peptides were used to examine the distribution of dynorphinergic terminals in globus pallidus and substantia nigra in rhesus monkeys and humans in comparison to substance P-containing and enkephalinergic terminals in these same regions. Similar results were observed in monkey and human tissue. Dynorphinergic fibers were very abundant in the medial half of the internal pallidal segment, but scarce in the external pallidal segment and the lateral half of the internal pallidal segment. In substantia nigra, dynorphinergic fibers were present in both the pars compacta and reticulata. Labeling of adjacent sections for enkephalin or substance P showed that the dynorphinergic terminals overlapped those for substance P in the medial half of the internal pallidal segment, but showed only slight overlap with enkephalinergic terminals in the external pallidal segment. The substance P-containing fibers were moderately abundant along the borders of the external pallidal segment, and enkephalinergic fibers were moderately abundant in parts of the internal pallidal segment. Dynorphinergic and substance P-containing terminals overlapped extensively in the nigra, and both extensively overlapped enkephalinergic fibers in medial nigra. Immunofluorescence double-labeling studies revealed that dynorphin co-localized extensively with substance P in individual fibers and terminals in the medial half of the internal pallidal segment and in substantia nigra. Thus, as has been found in non-primates, dynorphin within the striatum and its projection systems appears to be extensively localized to substance P-containing striatopallidal and striatonigral projection neurons. Nonetheless, our results also raise the possibility that a population of substance P-containing neurons that projects to the internal pallidal segment and does not contain dynorphin is present in primate striatum. Our results also suggest the possible existence of populations of striatopallidal and striatonigral projection neurons in which substance P and enkephalin or dynorphin and enkephalin, or all three, are co-localized. Thus, striatal projection neurons in primates may not consist of merely two types, one containing substance P and dynorphin and the other enkephalin.

Differential messenger RNA expression of prodynorphin and proenkephalin in the human brain

The opiate system is involved in a wide variety of neural functions including pain perception, neuroendocrine regulation, memory, drug reward, and tolerance. Such functions imply that endogenous opioid peptides should have anatomical interactions with limbic brain structures believed to be involved in the experience and expression of emotion. Using in situ hybridization histochemistry, the messenger RNA expression of the opioid precursors, prodynorphin and proenkephalin, was studied in whole hemisphere human brain tissue. Different components of the limbic system were found to be characterized by a high gene expression of either prodynorphin or proenkephalin messenger RNA. Brain regions traditionally included within the limbic system (e.g. amygdala, hippocampus, entorhinal cortex and cingulate cortex) as well as limbic-associated regions including the ventromedial prefrontal cortex and patch compartment of the neostriatum showed high prodynorphin messenger RNA expression. In contrast, high levels of proenkephalin messenger RNA were more widely expressed in the hypothalamus, periaqueductal gray, various mesencephalic nuclei, bed nucleus of the stria terminalis, and ventral pallidum; brain regions associated with endocrine-reticular-motor continuum of the limbic system. The marked anatomical dissociation between the expression of these two opioid peptide genes, seen clearly in whole hemisphere sections, indicates that distinct functions must be subserved by the prodynorphin and proenkephalin systems in the human brain.

Proenkephalin gene regulation in the neuroendocrine hypothalamus: a model of gene regulation in the CNS

During the past decade, a great deal of progress has been made in studying the mechanisms by which transcription of neuropeptides is regulated by second messengers and neural activity. Such investigations, which have depended to a great extent on the use of transformed cell lines, are far from complete. Yet a major challenge for the coming decade is to understand the regulation of neuropeptide genes by physiologically and pharmacologically relevant stimuli in appropriate cell types in vivo. The proenkephalin gene, a member of the opioid gene family, has served as a model to study regulated transcription, not only in cell lines, but also in central (e.g., hypothalamic) and peripheral (e.g., adrenal) neuroendocrine tissues. Here we review regulation of proenkephalin gene expression in the hypothalamus. Several approaches, including in situ hybridization, use of transgenic mice, and the adaptation of electrophoretic mobility shift assays to complex tissues, have played critical roles in recent advances. A summary of possible future developments in this field of research is also presented.

Opioid precursor gene expression in the human hypothalamus

Using in situ hybridization histochemistry, we studied the distribution of neurons that express preproopiomelanocortin (pre-POMC), preprodynorphin (pre-PDYN), and preproenkephalin (pre-PENK) gene transcripts within the human hypothalamus and surrounding structures. Of the three opioid systems, pre-POMC neurons have the most restricted distribution. Pre-POMC cells are most numerous in the infundibular nucleus and retrochiasmatic area of the mediobasal hypothalamus; a few labeled cells are present within the boundaries of the ventromedial nucleus and infundibular stalk. Pre-POMC message was not found in the limited samples of structures adjacent to the hypothalamus. In contrast to neurons that express pre-POMC, neurons expressing pre-PDYN and pre-PENK are more widely represented throughout the hypothalamus and extrahypothalamic structures. However, pre-PDYN and pre-PENK cells differ from one another in distribution. Pre-PDYN message is especially abundant in neurons of the tuberal and mammillary regions, with a distinct population of labeled cells in the premammillary nucleus and dorsal posterior hypothalamus. Pre-PDYN gene expression also is found in neurons of the dorsomedial nucleus, ventromedial nucleus, caudal magnocellular portion of the paraventricular nucleus, dorsolateral supraoptic nucleus, tuberomammillary nucleus, caudal lateral hypothalamus, and retrochiasmatic area. In structures immediately adjacent to the hypothalamus, pre-PDYN neurons were observed in the caudate nucleus, putamen, cortical nucleus of the amygdala, and bed nucleus of the stria terminalis. Pre-PENK neurons occur in varying numbers in all hypothalamic nuclei except the mammillary bodies. The chiasmatic region is particularly rich in pre-PENK neurons, with the highest packing density in the intermediate nucleus [the intermediate nucleus (Braak and Braak [1987] Anat. Embryol. 176:315-330) has also been termed the sexually dimorphic nucleus of the preoptic area (SDA-POA; Swaab and Fliers [1985] Science 228:1112-1115) or the interstitial nucleus of the anterior hypothalamus 1 (Allen et al. [1989] J. Neurosci. 9:497-506)], dorsal suprachiasmatic nucleus, medial preoptic area, and rostral lateral hypothalamic area. Pre-PENK neurons are numerous in the infundibular nucleus, ventromedial nucleus, dorsomedial nucleus, caudal parvicellular portion of the paraventricular nucleus, tuberomammillary nucleus, lateral hypothalamus, and retrochiasmatic area. Only a few lightly labeled cells were found in the periphery of the supraoptic nucleus and lateral tuberal nucleus. In areas adjacent to the hypothalamus, cells that contain pre-PENK message occur in the nucleus basalis of Meynert, central nucleus of amygdala, bed nucleus of the stria terminalis, caudate nucleus, and putamen.(ABSTRACT TRUNCATED AT 400 WORDS)

Prodynorphin-derived peptide expression in primate cortex and striatum

The distributions of four prodynorphin-derived peptides, dynorphin A (1-17), dynorphin A (1-8), dynorphin B, and alpha-neo-endorphin were determined in 10 cortical regions and the striatum of the old world monkey (Macaca nemestrina). alpha-neo-endorphin was the most abundant peptide in both cortex and striatum. The concentrations of all four peptides were significantly greater in the striatum compared to the cortex. In general, concentrations of each peptide tended to be higher in allocortex than in neocortex. Possible inter- and intradomain processing differences, as estimated by ratios of these peptides, did not vary within cortex, but the intradomain peptide ratio, dyn A (1-17)/dyn A (1-8), was significantly greater in cortex than in striatum. These results indicate that prodynorphin is, in some ways, uniquely processed in the primate. Particularly unusual is the relatively low abundance of prodynorphin-derived products in the cortex, in the face of moderately high levels of kappa opiate receptor expression.

Expression of prodynorphin-derived peptides and mRNA in guinea-pig cortex

The distributions and extent of processing of four prodynorphin-derived peptides (dynorphin A (1-17), dynorphin A (1-8), dynorphin B, and alpha-neoendorphin) were determined in ten regions of the cortex as well as in the striatum of the guinea-pig. There were significant differences between concentrations of these peptides in most cortical regions, with alpha-neoendorphin being several times more abundant than the other peptides, and dynorphin A (1-17) being present in the least amount. There were significant between-region differences in concentration for each peptide, although most regions had concentrations similar to those seen in the striatum. Concentrations of each peptide tended to be higher in piriform, entorhinal, motor, and auditory cortex than in other cortical regions. The extent of processing of prodynorphin varied across cortical regions as well, primarily due to the extent of processing to alpha-neoendorphin. Prodynorphin mRNA levels were not significantly different between cortical regions or from the amount observed in the striatum. Although specific regional variation exists, it appears that in general prodynorphin is expressed and processed in a similar manner in the cortex as in the striatum.

Attenuation of the inhibitory effect of dynorphin on dopamine release in the rat nucleus accumbens by repeated treatment with methamphetamine

Dynorphin (1-100 nM) dose dependently inhibited both spontaneous and electrically evoked endogenous dopamine (DA) release from slices of the nucleus accumbens of untreated rats. When this inhibitory effect was compared, it was significantly reduced in rats pretreated (for 9 days) with methamphetamine (6 mg/kg per day i.p.) relative to rats treated with saline. These findings indicate that dynorphin inhibits DA release from the nucleus accumbens, and that treatment with methamphetamine reduces the modulatory action of dynorphin on DA release. It is possible that repeated administration of methamphetamine leads to attenuation of the inhibition of DA release from the nucleus accumbens via presynaptic dynorphin-sensitive receptors.

Striatonigral projection neurons: a retrograde labeling study of the percentages that contain substance P or enkephalin in pigeons

Two largely separate populations of neuropeptide-containing striatonigral projection neurons have been distinguished in pigeons, one population whose neurons contain substance P (SP) and dynorphin (DYN) and a second population whose neurons contain enkephalin (ENK) (Reiner, '86a; Anderson and Reiner, '90a). In the present study, we investigated the abundance of these two types of neurons relative to all striatonigral projection neurons by combining retrograde labeling by the fluorescent dye fluorogold with immunofluorescence labeling for SP and ENK. Pigeons received large intranigral injections of fluorogold to retrogradely label the striatonigral projection neurons, and several days later they were treated with colchicine (32 hours before transcardial perfusion). Adjacent series of sections through the basal ganglia were labeled for SP and ENK using immunofluorescence techniques. The tissue was examined using fluorescence microscopy and the percentages of retrogradely labeled neurons containing either SP or ENK were quantified. We found that 85-95% of the fluorogold-labeled striatonigral neurons were SP+, whereas only 1-4% were ENK+. Thus the majority of striatonigral projection neurons in pigeons appear to contain SP, whereas a small percentage contain ENK. Only a small percentage of striatonigral neurons did not contain either. Since striatal projection neurons also contain GABA (Reiner, '86b), the present results suggest that a high percentage of striatonigral projection neurons coexpress SP, DYN and GABA, whereas a small fraction coexpress ENK and GABA. The available data are consistent with the conclusion that this is true in reptilian and mammalian species as well.

The patterns of neurotransmitter and neuropeptide co-occurrence among striatal projection neurons: conclusions based on recent findings

The neurotransmitter organization of striatal projection neurons appears to be less complex than once thought. Only 4 major evolutionarily conserved populations appear to be present. The neurons of two of these populations contain SP, DYN and GABA, with one of these two populations consisting of striatonigral projection neurons and the other of striatopallidal projection neurons. The two additional major populations of striatal projection neurons consist of striatopallidal and striato-nigral neurons that both contain both ENK and GABA. Although these conclusions greatly simplify the understanding of the organization of striatal projection neurons by suggesting that only a few major populations are present, these conclusions complicate understanding of neurotransmission between these neurons and their target areas by suggesting that each neuron utilizes multiple neuroactive substances to influence target neurons. Further studies will therefore be required to explore the mechanisms of neurotransmission by which striatal neurons communicate with their target areas.

Extensive co-occurrence of substance P and dynorphin in striatal projection neurons: an evolutionarily conserved feature of basal ganglia organization

A number of different neuroactive substances have been found in striatal projection neurons and in fibers and terminals in their target areas, including substance P (SP), enkephalin (ENK), and dynorphin (DYN). In a preliminary report on birds and reptiles, we have suggested that SP and DYN are to a large extent found in the same striatal projection neurons and that ENK is found in a separate population of striatal projection neurons. In the present study, we have examined this issue in more detail in pigeons and turtles. Further, we have also explored this issue in rats to determine whether this is a phylogenetically conserved feature of basal ganglia organization. Simultaneous immunofluorescence double-labeling procedures were employed to explore the colocalization of SP and DYN, SP and ENK, and ENK and DYN in striatal neurons and in striatal, nigral, and pallidal fibers in pigeons, turtles, and rats. To guard against possible cross-reactivity of DYN and ENK antisera with each others' antigens, separate double-label studies were carried out with several different antisera that were specific for DYN peptides (e.g., dynorphin A 1-17, dynorphin B, leumorphin) or ENK peptides (leucine-enkephalin, metenkephalin-arg6-gly7-leu8, methionine-enkephalin-arg6-phe7). The results showed that SP and DYN co-occur extensively in specific populations of striatal projection neurons, whereas ENK typically is present in different populations of striatal projection neurons. In pigeons, 95-99% of all striatal neurons containing DYN were found to contain SP and vice versa. In contrast, only 1-3% of the SP+ striatal neurons and no DYN neurons contained ENK. Similarly, in turtles, greater than 75% of the SP+ neurons were DYN+ and vice versa, whereas ENK was observed in fewer than 5% of the SP+ neurons and 2% of the DYN+ neurons. Finally, in rats, more than 70% of the SP+ neurons contained DYN and vice versa, but ENK was found in only 5% of the SP+ neurons and in none of the DYN+ perikarya. Fiber double-labeling in the striatum and its target areas (the pallidum and substantia nigra) was also consonant with these observations in pigeons, turtles, and rats. These results, in conjunction with studies in cats by M.-J. Besson, A.M. Graybiel, and B. Quinn (1986; Soc Neurosci. Abs. 12:876) strongly indicate that the co-occurrence of SP and DYN in large numbers of striatonigral and striatopallidal projection neurons in a phylogenetically widespread, and therefore evolutionarily conserved, feature of basal ganglia organization.(ABSTRACT TRUNCATED AT 400 WORDS)

Measurement and chromatographic characterization of prodynorphin-derived peptides in the guinea-pig ileum

Guinea-pig ileum was dissected and the mucosa, submucosa and external musculature extracted with aqueous acetic acid for measurement of four prodynorphin-derived peptides, namely dynorphin A 1-8, dynorphin A 1-17, dynorphin B, and alpha-neoendorphin. The peptide-like immunoreactive material extracted from the external musculature was characterized by multi-dimensional chromatographic analysis and compared to synthetic porcine standards. The chromatographic methods utilized were: reversed-phase high performance liquid chromatography (RP-HPLC), using two different eluants; cation exchange high performance liquid chromatography (CE-HPLC) and gel filtration chromatography. The dynorphin A 1-8-like immunoreactive material was homogeneous and coeluted with the standard in all chromatographic modes. The dynorphin A 1-17-like and dynorphin B-like immunoreactive material was heterogeneous but showed a peak that coeluted with synthetic standard in all chromatographic modes. The alpha-neoendorphin-like immunoreactive material also appeared to be heterogeneous with the major component on CE-HPLC coeluting with the synthetic peptide standard while the major component on RP-HPLC eluted differently. It was concluded that the guinea-pig ileum contains immunoreactivity for peptides derived from all coding regions of the prodynorphin gene and that these peptides may be present in multiple immunoreactive forms.

Immunocytochemical demonstration of dynorphin(PH-8P)-like immunoreactive elements in the human hypothalamus

PH-8P (dynorphin[1-8])-like immunoreactive neuronal perikarya, processes, and terminals located within the human hypothalamus were investigated by the avidin-biotin peroxidase complex (ABC) immunocytochemical procedure. Immunopositive neurons were distributed throughout the hypothalamus. The distributional pattern was found to be similar to that in other mammalian species by the use of antisera against dynorphin. A large number of immunoreactive neuronal perikarya were detected in the supraoptic nucleus (SON) and the magnocellular portion of the paraventricular nucleus (PVN). Their processes appeared to project to the posterior pituitary via the internal layer of the median eminence and their distribution seemed to be less dense than in other mammalian species. PH-8P and vasopressin were colocalized in the neuronal perikarya in the human SON unlike the colocalization of these peptides in the rat SON and PVN. There were a few immunoreactive terminals in the external layer of the median eminence; their immunoreactive substances may be released into the portal veins to act on anterior pituitary cells. In addition, PH-8P-like immunoreactive neurons in the human hypothalamus may project to the extrahypothalamic area.

Nerve fibers surrounding intracranial and extracranial vessels from human and other species contain dynorphin-like immunoreactivity

Dynorphin B(20-32) was visualized by immunohistochemistry in guinea-pig and rat perivascular nerve fibers and was measured by radioimmunoassay within the walls of feline, canine, bovine and human cephalic and systemic arteries and veins. Canine vessels contained the highest levels. When human blood vessels or trigeminal ganglia were subjected to reverse-phase high-performance liquid chromatography, dynorphin immunoreactivity exhibited a retention time identical to that of synthetic dynorphin B. No differences in dynorphin-like immunoreactivity were measurable between feline systemic arteries and veins, or between cephalic and systemic vessels. The highest amounts were present in leptomeninges devoid of large pial arteries. Relatively high levels were also measured in feline and human trigeminal ganglia and feline superior cervical and sphenopalatine ganglia, three sources of projecting perivascular axons. Levels did not diminish, however, in ipsilateral feline cephalic vessels following either unilateral trigeminal or superior cervical ganglionectomies. Hence, dynorphin-containing fibers may project from parasympathetic cell bodies or perhaps from intrinsic brain sources. Previously published reports indicate that the kappa agonist dynorphin does not modify vessel tone when added in vitro but does inhibit release of neurotransmitters from afferent and sympathetic axons via prejunctional receptors. These observations suggest a pharmacological role for dynorphin on sensory and autonomic functions of the vasculature.

Immunocytochemical localization of pro-opiomelanocortin-derived peptides in the adult rat spinal cord

A dispersed descending pro-opiomelanocortin (POMC) fiber system has been demonstrated by peroxidase-antiperoxidase (PAP) immunocytochemistry in the adult rat spinal cord. beta-endorphin, adrenocorticotrophic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH) and 16K immunoreactive fibers exist in the spinal cord from cervical down to sacral level. Descending fibers running parallel in the dorsolateral and lateral funiculus send collaterals ventromedially or medially to terminate in the gray matter surrounding the central canal, where nociceptive neurons have recently been located, in addition to those nociceptive cells in the dorsal horn. After spinal transection at lower thoracic level, POMC peptide immunoreactivities disappeared below the lesion. Moreover, no POMC cell bodies were found in the spinal cord. Therefore, the descending fibers are most likely of supraspinal origin.

Steady state levels of pro-dynorphin-related end products in the striatum and substantia nigra of the adult rhesus monkey

Analysis of an acid extract of the striatum of the rhesus monkey revealed that the molar ratio of dynorphin A(1-8)-sized material and dynorphin (A(1-17)-sized material is approximately 1:1. In addition, the molar ratios of the dynorphin A-related end products to both dynorphin B(1-13)-sized material and alpha-neo-endorphin-sized material were approximately 1:1. Fractionation of an acid extract of the substantia nigra by gel filtration and reverse phase HPLC revealed the following molar ratios for pro-dynorphin-related end products. The molar ratio of dynorphin A(1-8) to dynorphin A(1-17) is approximately 6:1. The molar ratios of dynorphin A-related end products to dynorphin B(1-13) and alpha-neo-endorphin were approximately 0.5 and 0.8, respectively. Comparisons between proteolytic processing patterns of pro-dynorphin in the striatum and the substantia nigra of the rhesus monkey are considered. In addition, comparisons between pro-dynorphin processing in the substantia nigra of the rhesus monkey and the substantia nigra of the rat are discussed.