Blockade of micro-opioid receptors in the medial thalamus inhibits acquisition, but not expression, of morphine-induced conditioned place preference

The medial thalamus contains abundant mu-opioid receptors and is activated by acute morphine administration. However, the role of the medial thalamus in the rewarding effects of morphine is unclear. The present study examined whether mu-opioid receptors of the medial thalamus influenced the acquisition and expression of morphine-induced conditioned place preference (CPP) in rats. An unbiased apparatus and biased subject assignment were used. Administration of morphine in increasing doses (2 mg/kg, 4 mg/kg, 6 mg/kg, 10 mg/kg, s.c.) was paired with an initially non-preferred chamber and saline administration was paired with an initially preferred chamber. Conditioning trials were conducted twice daily for 4 days. Microinjection of the irreversible mu-opioid receptor antagonist, beta-funaltrexamine (5 microg/rat), into the medial thalamus 23 h prior to each morphine conditioning completely blocked the acquisition of CPP. However, microinjection of beta-funaltrexamine into the medial thalamus after morphine conditioning trials, but 23 h prior to a test session, had no effect on the expression of CPP. It is concluded that mu-opioid receptors in the rat medial thalamus are involved in the acquisition, but not expression, of morphine-induced CPP.

Fos and glutamate AMPA receptor subunit coexpression associated with cue-elicited cocaine-seeking behavior in abstinent rats

Cocaine-associated cues acquire incentive motivational effects that manifest as craving in humans and cocaine-seeking behavior in rats. We have reported an increase in neuronal activation in rats, measured by Fos protein expression, in various limbic and cortical regions following exposure to cocaine-associated cues. This study examined whether the conditioned neuronal activation involves glutamate AMPA receptors by measuring coexpression of Fos and AMPA glutamate receptor subunits (GluR1, GluR2/3, or GluR4). Rats trained to self-administer cocaine subsequently underwent 22 days of abstinence, during which they were exposed daily to either the self-administration environment with presentations of the light/tone cues previously paired with cocaine infusions (Extinction group) or an alternate environment (No Extinction group). All rats were then tested for cocaine-seeking behavior (i.e. responses without cocaine reinforcement) and Fos and AMPA glutamate receptor subunits were measured postmortem using immunocytochemistry. The No Extinction group exhibited increases in cocaine-seeking behavior and Fos expression in limbic and cortical regions relative to the Extinction group. A large number of Fos immunoreactive cells coexpressed GluR1, GluR2/3, and GluR4, suggesting that an action of glutamate at AMPA receptors may in part drive cue-elicited Fos expression. Importantly, there was an increase in the percentage of cells colabeled with Fos and GluR1 in the anterior cingulate and nucleus accumbens shell and cells colabeled with Fos and GluR4 in the infralimbic cortex, suggesting that within these regions, a greater, and perhaps even different, population of AMPA receptor subunit-expressing neurons is activated in rats engaged in cocaine-seeking behavior.

Morphine actions in the rat forebrain: role of protein kinase C

Acute administration of morphine induces expression of the immediate-early gene (IEG) c-Fos in dorsomedial striatum, portions of cerebral cortex, and in several midline-intralaminar thalamic nuclei, partly via a trans-synaptic mechanism that involves activation of glutamate receptors. Because activation of protein kinase C (PKC) may occur following the activation of glutamate receptors, we determined whether pharmacological inhibition of PKC would attenuate morphine-induced c-Fos expression, and whether acute administration of morphine would induce translocation of PKC. The selective PKC antagonist NPC 15437 given 30 min prior to morphine significantly decreased morphine-induced c-Fos expression in striatum and cingulate cortex, but not in centrolateral thalamus. In another experiment, rats were given an acute dose of morphine, and immunocytochemical analysis was performed for the betaI and betaII isoforms of PKC. Morphine induced a rapid and transient translocation of PKC betaII, but not betaI, from perinuclear spots to plasma membrane in numerous cortical and striatal neurons. Prior administration of naloxone blocked this response. Ultrastructural studies confirmed translocation from Golgi apparatus to plasma membrane 15 min after morphine injection. Double immunocytochemistry at the light microscopic level demonstrated co-localization of translocated PKC betaII and c-Fos in some cortical neurons 90 min after morphine injection. These results support a role for PKC, especially PKC betaII, in the rapid effects of morphine on the brain.

Morphine induction of c-fos expression in the rat forebrain through glutamatergic mechanisms: role of non-n-methyl-D-aspartate receptors

Acute injection of morphine induces expression of the immediate-early genes c-Fos and JunB in several forebrain regions of the rat, in part through an N-methyl-D-aspartate (NMDA) receptor-dependent mechanism. Because membrane depolarization through (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors is believed to be necessary for full activation of NMDA receptors, we determined the role of AMPA receptors in morphine-induced c-Fos expression. Rats were given the AMPA receptor antagonist GYKI-52466 (12.9 mg/kg, i.p.) 15 min before morphine (10 mg/kg, s.c.), or the AMPA receptor enhancer CX516 (30 mg/kg, i.p.) 5 min after morphine. The c-Fos response was attenuated by the antagonist and augmented by the enhancer. Using double immunocytochemistry, we found that morphine induced c-Fos in neurons containing the GluR2/3, but not the GluR1 and rarely the GluR4, subunits of the AMPA receptor. Double immunocytochemistry for mu opioid receptor and c-Fos showed that c-Fos expression was mainly absent in the patch compartment of the striatum, which is enriched in mu opioid receptors. The glutamatergic synapse often contains metabotropic receptors as well as ionotropic receptors. Type I metabotropic glutamate receptors are coupled to activation of protein kinase C, which has also been shown to mediate the immediate-early gene response to morphine. To determine if activation of metabotropic glutamate receptors is involved in rapid effects of morphine on the brain, rats were given the type I metabotropic glutamate receptor antagonist (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA; 0.2 mg/kg, i.p.) or vehicle 30 min before morphine treatment. Pretreatment with AIDA completely blocked morphine-induced c-Fos expression in the caudate-putamen.Taken together, these results demonstrate involvement of both AMPA and type I metabotropic glutamate receptors in the acute effects of morphine on the forebrain, supporting an important role for glutamatergic neurotransmission mediated by non-NMDA glutamate receptors in morphine's actions.

Modulation of glutamate receptor expression by gonadal steroid hormones in the rat striatum

The non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist dizocilpine (MK-801) attenuates morphine-induced immediate-early gene expression in the rat striatum in a sexually dimorphic manner that depends in part on gonadal steroids. To determine if this effect was dependent on modulation of glutamate receptor gene expression, we studied the effect of gonadal hormones on levels of the NR1 subunit of NMDA receptor and the GluR2 subunit of the AMPA-subtype of glutamate receptor in the rat striatum, using autoradiographic immunocytochemistry. We found that ovariectomy decreased GluR2 immunoreactivity in the striatum, but no changes were seen in levels of NR1 following gonadectomy in either sex. Thus, the effects of gonadal steroids on NMDA receptor-mediated responses are not due to regulation of NR1 expression.

Immunolocalization of PICK1 in the ascending auditory pathways of the adult rat

Protein that interacts with C-kinase alpha (PICK1) is a PDZ domain protein that interacts with many binding partners in the central nervous system (CNS), including activated protein kinase Calpha and subunits of the AMPA subtype of glutamate receptor. Almost nothing is known about the anatomic distribution of PICK1 in the intact adult CNS. By using PICK1 antisera and peroxidase immunocytochemistry, we report on the distribution of PICK1 in the ascending pathways of the central auditory system of the adult rat. PICK1-immunoreactivity (ir) was observed in many component nuclei of the central auditory system, including the dorsal cochlear nucleus, anteroventral cochlear nucleus, posteroventral cochlear nucleus, some divisions of the superior olivary complex, inferior colliculus, medial geniculate body, and primary auditory cortex. The general staining pattern for PICK1-immunoreactivity was somatodendritic with scattered puncta in neuropil and somatodendritic regions. The distribution of PICK1 partially overlaps with PKCalpha and glutamate receptor subunits such as GluR2. These data suggest that PICK1 may function in the regulation of PKCalpha and GluR2 localization in components of the rat auditory system, which may be a fundamental mechanism of synaptic transmission and/or plasticity. J. Comp. Neurol.

Sexually dimorphic effects of morphine and MK-801: sex steroid-dependent and -independent mechanisms

Rats show gender differences in responses to morphine and the N-methyl-D-aspartate receptor antagonist dizocilpine (MK-801); the role of sex steroids in mediating these differences is unclear. We tested the overall hypothesis that circulating gonadal steroids determine the gender differences in morphine- and MK-801-induced behavior and c-Fos expression. Morphine caused a greater expression of c-Fos in the striatum of intact males than of that females, which was independent of sex steroids. MK-801 completely inhibited morphine-induced c-Fos in intact females but only caused partial inhibition in intact males; castrated males showed complete inhibition, which was reversed by testosterone, but gonadal steroids had no effect on this response in females. In thalamus, there was a large sex difference in the response to MK-801 that was independent of gonadal steroids. Behavioral responses to morphine were greater in males, but responses to MK-801 were greater in females; both were sex steroid independent. These findings show significant sex differences in response to morphine and MK-801 that are mediated by sex steroid-dependent and -independent mechanisms, which may be important in treatment outcomes of drug addiction.

Involvement of nitric oxide in morphine-induced c-Fos expression in the rat striatum

Induction of expression of immediate-early gene c-Fos in the striatum is a common effect of many drugs of abuse, including morphine. Previous studies have shown that the morphine-mediated c-Fos response is attenuated by antagonists of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. Other evidence suggests that the NDMA receptor may be coupled to the enzyme neuronal nitric oxide synthase (nNOS). NMDA receptor-mediated increases in intracellular calcium can activate nNOS, which catalyzes the formation of the signaling molecule nitric oxide. Because activation of NMDA receptors mediates morphine-induced c-Fos expression, we tested the hypothesis that activation of nNOS is involved in this cascade. Male rats were injected with the nNOS-selective inhibitor 7-nitroindazole (7-NI) or vehicle 30 min prior to injection of morphine sulfate or vehicle. Two hours later they were perfused with fixative and the brains removed for immunocytochemical analysis for c-Fos. Morphine induced c-Fos expression in the striatum, cerebral cortex, and midline/intralaminar nuclei of thalamus. Expression in the striatum, but not thalamus or cortex, was significantly blocked by 7-NI. Double-label immunocytochemistry revealed no co-localization of c-Fos and nNOS in any brain region. These results support a role for nNOS in the neural circuits activated by morphine.

Deafferentation-induced changes in protein kinase C expression in the rat cochlear nucleus

Isoforms of the signal transducing molecule, protein kinase C (PKC), may play a role in neural plasticity following sensory deafferentation. To explore the role of PKC in central auditory plasticity, we studied the effect of auditory deafferentation on the expression of PKC betaI, betaII, gamma, and delta in the rat dorsal (DCN) and ventral cochlear nucleus (VCN), using immunocytochemistry. Male rats were treated with kanamycin and furosemide to induce hair cell loss. At various intervals post-treatment, brains were perfusion-fixed and processed for immunocytochemistry. Following deafferentation, we observed a gradual increase in PKC betaI immunoreactivity (ir) in the deepest layers of the DCN, possibly representing synapses of primary afferents or parallel fibers on unlabeled neurons. Correlated with this, we observed an increase in the number of neurons in the deep DCN that showed PKC delta ir. In controls, we observed PKC gamma ir in small ovoid cells concentrated in the middle layer of the DCN. From days 4 through 14 after deafferentation, we found an increase in the intensity of staining of these cells, with a return toward control levels by day 28. Finally, Purkinje-like cells (PLC) in the VCN, which express only PKC delta in control rats, began to express PKC gamma after deafferentation, correlated with increased expression of calbindin D28k in PLC. Thus PKC isoforms are differentially regulated in the CN following deafferentation, supporting a role for PKC in auditory plasticity.

Immunocytochemical detection of two nuclear proteins within the same neuron using light microscopy

We developed a method of double immunocytochemistry (ICC) that can be used with conventional light microscopy for localizing two different nuclear proteins. The procedure involves two sequential rounds of ICC that both employ the avidin and biotin conjugated enzyme (ABC) amplification method, separated by an Avidin D and biotin blocking step to reduce non-specific avidin-biotin reactions. Round one of ICC employs the use of avidin and biotin conjugated alkaline phosphatase (ABC-AP) and the Vector Red (VR) substrate, which produces a red colorimetric reaction product. The second round of ICC makes use of avidin and biotin conjugated peroxidase (ABC-HRP) and the Vector(R) SG substrate, which produces a gray colorimetric reaction product. Neuronal nuclei that are double-labeled for both proteins appear red with a gray core. This protocol allows the simultaneous detection of two proteins within the same subcellular compartment of a single neuron, without the need for epifluorescence or scanning confocal laser microscopy.

Androgenic-anabolic steroids blunt morphine-induced c-fos expression in the rat striatum: possible role of beta-endorphin

Self-administration of large doses of androgenic-anabolic steroids (AAS) in a significant portion of the population suggests that these agents are drugs of abuse. However, acute administration of AAS did not induce striatal immediate-early genes (IEG) expression in male rats, indicating that AAS do not share a common mechanism of action with other drugs of abuse. Surveys have indicated that people who abuse AAS are more likely to self-administer other drugs of abuse than do people who do not take AAS. In the present study, chronic administration of AAS blunted the striatal c-fos response to morphine, indicating that AAS can alter the molecular responses to at least one drug of abuse. Chronic administration of AAS also increased the content of beta-endorphin in the midline thalamus, suggesting a possible mechanism by which AAS may modulate the response to morphine through regulation of thalamo-striatal neurons.

Sexual dimorphism in the response to N-methyl-D-aspartate receptor antagonists and morphine on behavior and c-Fos induction in the rat brain

It has been suggested that there are sex differences in the neural response to drugs of abuse. Previous studies have shown that, upon administration of morphine, the immediate early gene c-Fos is induced in the striatum, nucleus accumbens and cortex of the rat brain. This induction of c-Fos is reduced by administration of the N-methyl-D-aspartate receptor antagonist dizocilpine maleate. However, in studies using immunocytochemistry, we found that the pattern of this expression differed markedly between the sexes. In male rats treated with morphine (10 mg/kg, s.c.) and killed 2 h later, there was an induction of c-Fos in the dorsomedial caudate-putamen, the nucleus accumbens and in the intralaminar nuclei of the thalamus. Administration of dizocilpine maleate (0.2 mg/kg, i.p.; 30 min before morphine) partially blocked the response in the caudate-putamen, but not in the thalamus. In females, morphine induced c-Fos in the caudate-putamen, but with more inter-animal variability than in males. In the midline intralaminar thalamic nuclei, female rats showed less induction than males. In male rats, dizocilpine maleate alone caused negligible induction of c-Fos, whereas in female rats, it caused a large induction in the rhomboid, reuniens and central medial nuclei of the thalamus, and in the cortex. Whereas dizocilpine maleate partially blocked the morphine-induced c-Fos expression in the caudate-putamen of males, it completely blocked this response in females. With dizocilpine maleate alone, there was little or no effect on behavior in male rats, whereas in female rats, it caused head bobbing, thrashing, hyperactivity and uncoordinated movements. These behavioral sex differences were not seen on treatment of rats with the competitive N-methyl-D-aspartate receptor antagonist 2R,4R,5S-2-amino-4,5-(1,2-cyclohexyl)-7-phosphoheptanoic acid (NPC-17742; 10 mg/kg, i.p.) and this drug did not induce c-Fos expression in either sex. In the caudate-putamen, morphine-induced c-Fos expression was significantly reduced by NPC-17742 (30 min before morphine) in males and completely blocked in females. These results suggest that the responses to both morphine and N-methyl-D-aspartate receptor antagonists differ between the sexes and emphasize that glutamate is involved in morphine-induced immediate early gene expression in the brain. These studies thus have important implications for gender differences in drug addiction.

Role of the dorsal raphe nucleus in morphine-induced immediate early gene expression in the rat striatum

Serotonin (5-HT) is thought to be involved in morphine action in the brain. To determine if the periaqueductal gray (PAG) and the dorsal raphe nucleus (DRN) are involved in morphine-induced c-Fos and JunB expression in the caudate-putamen (CPu), the mu receptor antagonist, beta-funaltrexamine (beta-FNA), was unilaterally infused into the PAG adjacent to DRN prior to morphine. Behaviorally, beta-FNA prevented morphine-induced loss of righting and Straub tail. In the CPu of beta-FNA treated rats, morphine-induced c-Fos and JunB were attenuated compared to vehicle-infused rats. These results suggest that morphine acts within the PAG-DRN to exert rapid behavioral effects and to induce c-Fos and JunB in the striatum.

Infusion of beta-FNA into the thalamus attenuates morphine-induced c-Fos induction in the rat caudate putamen

The medial thalamus contains mu opioid receptors and sends a glutamatergic projection to the caudate putamen (CPu) in rat. Morphine-induced c-Fos expression in the CPu has been shown to be blocked by pretreatment with antagonists to N-methyl-D-aspartate receptors, indicating the involvement of glutamate in this morphine-induced response. The importance of the glutamatergic projections from the thalamus was assessed by infusing the mu opioid receptor antagonist, beta-funaltrexamine (beta-FNA), prior to systemic morphine injection. Infusion of beta-FNA near specific medial thalamic nuclei attenuated morphine-induced c-Fos expression in the CPu.

Chronic administration of morphine alters immediate-early gene expression in the forebrain of post-dependent rats

Previous studies from this laboratory have demonstrated that acute, systemic administration of morphine results in an induction of the immediate-early gene (IEG) proteins, c-Fos and Jun-B, in the dorsomedial portion of the rat caudate-putamen (CPu). These studies have also shown that morphine can induce c-Fos in the central medial nucleus of the thalamus (CM). To determine whether this response is altered in post-dependent rats, twice-daily injections of an ascending dose of morphine were administered for 5 days, followed by a withdrawal period of 7 or 14 days. A challenge injection of morphine (10 mg/kg) was administered on the last day of withdrawal. As compared to an acute dose of morphine in a naive animal, the induction of c-Fos was increased in the dorsolateral CPu following challenge injection at 7 days, but not at 14 days. Induction of c-Fos in the CM following the challenge injection was blunted following 7 day, but not at 14 days, of withdrawal. An increase in the IEG protein, Jun-B, was also seen following 7 but not 14 days of withdrawal in both the dorsomedial and dorsolateral CPu. These findings demonstrate that a chronic treatment of morphine can result in altered patterns of IEG expression upon challenge with acute morphine, in a time-dependent manner, within the rat CPu and CM.

Tests used to assess the cognitive abilities of aged rats: their relation to each other and to hippocampal morphology and neurotrophin expression

BACKGROUND

Aged rodents have proven to be a useful tool in studying age-related cognitive decline, particularly with regard to hippocampal function. A number of maze tests have been developed to evaluate hippocampal function in aged rodents, including the eight-arm radial maze, Barnes circular platform maze and Morris water maze. To some extent, these mazes have been used interchangeably to evaluate aged animals. Few researchers, however, have examined how performance of individual, aged animals compares in these three mazes.

OBJECTIVE

The purpose of this study was to compare the performances in the three mazes and to examine how such performances are related to each other, to hippocampal morphology and to neurotrophin gene expression.

METHODS

We screened groups of young and old Fisher 344 x Brown Norway rats for general health and physical abilities, tested the animals in the three mazes and examined correlations among performances in the mazes and in screening tests. Hippocampal neuron density and expression of hippocampal neurotrophin mRNAs were also examined and compared with behavior in the three mazes.

RESULTS

Aged animals were found to be impaired in all three mazes and to have lower hippocampal neuron densities compared with young animals, with poor learning behavior significantly correlating with reduced hippocampal neuron density. Differences were observed between performance in the different mazes, but in general the Morris water maze and Barnes circular platform maze were found to give similar results.

The 5-HT3 receptor antagonist, MDL 72222, dose-dependently potentiates morphine-induced immediate-early gene expression in the rat caudate putamen

Previous studies from this laboratory have demonstrated that acute administration of morphine induces the immediate-early genes (IEGs) c-Fos and JunB in the rat caudate putamen (CPu). In the present study, we tested the hypothesis that the serotonin-3 receptor (5-HT3R) is involved in morphine-induced IEG expression, using the selective antagonist to the 5-HT3R, MDL 72222. Rats were divided into three pretreatment groups: MDL 72222, 1 mg/kg or 10 mg/kg; or vehicle (DMSO). Thirty minutes following the pretreatment, the rats were administered either morphine (10 mg/kg) or vehicle. Morphine significantly induced c-Fos expression in the dorsomedial CPu, as we have reported previously. Whereas MDL 72222 alone did not induce c-Fos, it potentiated the morphine-induced c-Fos expression. Morphine also induced JunB expression in the same region of the dorsomedial CPu. At 1 mg/kg, MDL 72222 both induced JunB expression and potentiated the response induced by morphine. At 10 mg/kg, MDL 72222 had no effect on basal JunB levels, but augmented the response to morphine. These findings demonstrate that the 5-HT3R antagonist, MDL 72222, can positively modulate morphine-induced IEG expression in the rat CPu in a dose dependent manner, in contrast to the reported suppressive effect observed when this antagonist is administered prior to amphetamine.

Drugs of abuse and immediate-early genes in the forebrain

A diverse array of chemical agents have been self administered by humans to alter the psychological state. Such drugs of abuse include both stimulants and depressants of the central nervous system. However, some commonalties must underlie the neurobiological actions of these drugs, since the desire to take the drugs often crosses from one drug to another. Studies have emphasized a role of the ventral striatum, especially the nucleus accumbens, in the actions of all drugs of abuse, although more recent studies have implicated larger regions of the forebrain. Induction of immediate-early genes has been studied extensively as a marker for activation of neurons in the central nervous system. In this review, we survey the literature reporting activation of immediate-early gene expression in the forebrain, in response to administration of drugs of abuse. All drugs of abuse activate immediate-early gene expression in the striatum, although each drug induces a particular neuroanatomical signature of activation. Most drugs of abuse activate immediate-early gene expression in several additional forebrain regions, including portions of the extended amygdala, cerebral cortex, lateral septum, and midline/intralaminar thalamic nuclei, although regional variations are found depending on the particular drug administered. Common neuropharmacological mechanisms responsible for activation of immediate-early gene expression in the forebrain involve dopaminergic and glutamatergic systems. Speculations on the biological significance and clinical relevance of immediate-early gene expression in response to drugs of abuse are presented.

A two focal plane method for digital quantification of nuclear immunoreactivity in large brain areas using NIH-image software

In principle, digital acquisition of cell-count data from serially-sectioned immunocytochemical material is a straightforward enterprise. First, a serial brain section is magnified by use of a microscope interfaced to a computer. Then, using appropriate hardware and software, a digital image is captured, and cellular profiles of interest are segmented from background objects according to mean grayscale intensity and pixel area. Ideally, the cells of interest would be uniformly distinguishable from other objects or areas of the image, with respect to grayscale intensity and size. However, due to non-uniformity in background staining of neuropil, immunocytochemical material often departs markedly from this ideal situation. As a consequence, determining grayscale intensity and cell size cutoff values which separate cells of interest from background becomes laborious and arbitrary. This problem can be diminished by increasing the magnification of the digitized image, which increases the figure-ground resolution of the image. However, high-magnification images make tissue navigation difficult and require that multiple images be captured. This paper describes a two focal plane procedure for obtaining cell counts from nuclear-stained immunocytochemistry material. This procedure allows the capturing and cell counting of relatively low-magnification images with high digital figure-ground resolution.

Aging in the hippocampus: interrelated actions of neurotrophins and glucocorticoids

Over the past two decades, evidence has been accumulating that diffusible molecules, such as growth factors and steroids hormones, play an important part in neural senescence, particularly in the hippocampus. There is also evidence that these molecules do not act as independent signals, but show interrelated regulation and cooperative control over the aging process. Here, we review some of the changes that occur in the hippocampus with age, and the influence of two classes of signaling substances: glucocorticoids and neurotrophins. We also examine the interactions between these substances and how this could influence the aging process.

Tumor necrosis factor-alpha: a neuromodulator in the CNS

In the central nervous system (CNS), the cytokine tumor necrosis factor-alpha (TNF alpha) is produced by both neurons and glial cells, participates in developmental modeling, and is involved in many pathophysiological conditions. There are activity-dependent expressions of TNF alpha as well as low levels of secretion in the resting state. In contrast to the conventional view of a cytotoxic effect of TNF alpha, accumulating evidence suggests a beneficial effect when TNF alpha is applied at optimal doses and at specific periods of time. The bimodal effect is related to subtypes of receptors, activation of different signal transduction pathways, and the presence of other molecules that alter the intracellular response elements such as immediate-early genes. TNF alpha may be an important neuromodulator in development of the CNS, diseases of demyelination and degeneration, and in the process of regeneration. It could induce growth-promoting cytokines and neurotrophins, or it could increase the production of antiproliferative cytokines, nitric oxide, and free radicals, thereby contributing to apoptosis.

Protein kinase C in central vestibular, cerebellar, and precerebellar pathways of the rat

The protein kinase C family of enzymes is composed of at least ten different isoforms that display a variety of distinct biochemical specificities. Many of these isoforms are highly expressed in brain, and some show regional specificity in their distribution, suggesting that they may serve specific functions. By using immunocytochemistry to localize the betaI, betaII, gamma, or delta isoforms of protein kinase C in the central vestibular system of the adult rat, we found the vestibular ganglion and its peripheral and central processes of the eighth nerve to be heavily labeled with protein kinase C betaI immunoreactivity. Labeled axons and terminals were also found in all four vestibular nuclei. Some neurons of the vestibular ganglion were weakly stained with the antibody to protein kinase C betaII, as were scattered axons in the eighth nerve, and scattered axons and terminals were found in all four vestibular nuclei among weakly labeled neurons. A few axons in the vestibular portion of the eighth nerve were labeled with protein kinase C gamma immunoreactivity, and neurons of the spinal, lateral, and superior vestibular nuclei were heavily decorated with synapses, presumably derived from Purkinje neurons, which were also strongly immunoreactive. Neurons of the medial vestibular nucleus were not as heavily innervated. With the antibody to protein kinase C delta, we found scattered, weakly immunoreactive neurons in the vestibular portion of the eighth nerve. Myelinated fiber bundles of the spinal vestibular nucleus contained moderate numbers of labeled axons, and the other vestibular nuclei were well innervated by protein kinase C delta axons and terminals. Most of these probably derive from Purkinje cells, which were labeled in longitudinal bands interspersed with bands of labeled basket cells. These data suggest that particular protein kinase C isoforms play specific roles in vestibular and cerebellar function.

Protein kinase C in central auditory pathways of the rat

Protein kinase C is an important intracellular signaling molecule. Many of its ten isoforms are highly expressed in brain, and protein kinase C has been implicated in the regulation of the activity of receptors of several major neurotransmitters, including glutamate, acetylcholine, glycine, and gamma-aminobutyric acid. These neurotransmitters and their receptors are present in central auditory pathways, suggesting their role in auditory signal processing. Although they may be important modulators of the function of these neurotransmitter receptors, the distribution of protein kinase C isoforms in central auditory systems has not been well characterized. By using immunocytochemistry with specific antibodies, we studied the distribution of immunoreactivity of four isoforms of protein kinase C, betaI, betaII, gamma, and gamma, in central auditory systems of rat brain. Each of these protein kinase C isoforms was found to have a unique distribution in the auditory brainstem and cortex, supporting a role for these isoforms of protein kinase C in different aspects of auditory sensory processing.

The accumbens: beyond the core-shell dichotomy

This article highlights recent discoveries related to the accumbens and closely associated structures, with special reference to their importance in neuropsychiatry. The development of "striatal patches" in the accumbens is reviewed in a series of pictures. Neuronal ensembles are discussed as potentially important functional-anatomical units. Attention is also drawn to recent discoveries related to the neuronal circuits that the primate accumbens establishes with the mesencephalic dopamine system. On the basis of histological and neurochemical differences, the accumbens has been divided into core and shell compartments. In the context of this article, the shell, which is an especially diversified part of the accumbens, is the subject of special attention because of its close relation to the extended amygdala and distinctive response to antipsychotic and psychoactive drugs.

Substantia innominata: a notion which impedes clinical-anatomical correlations in neuropsychiatric disorders

Comparative neuroanatomical investigations in primates and non-primates have helped disentangle the anatomy of the basal forebrain region known as the substantia innominata. The most striking aspect of this region is its subdivision into two major parts. This reflects the fundamental organizational scheme for this portion of the forebrain. According to this scheme, two major subcortical telencephalic structures, i.e. the striatopallidal complex and extended amygdala, form large diagonally oriented bands. The rostroventral extension of the pallidum accounts for a large part of the rostral subcommissural substantia innominata, while the sublenticular substantia innominata is primarily occupied by elements of the extended amygdala. Also dispersed across this region is the basal nucleus of Meynert, which is part of a more or less continuous collection of cholinergic and non-cholinergic corticopetal and thalamopetal cells, which stretches from the septum diagonal band rostrally to the caudal globus pallidus. The basal nucleus of Meynert is especially prominent in the primate, where it is sometimes inappropriately applied as a synonym for the substantia innominata, thereby tacitly ignoring the remaining components. In most mammals, the extended amygdala presents itself as a ring of neurons encircling the internal capsule and basal ganglia. The extended amygdala may be further subdivided, i.e. into the central extended amygdala (related to the central amygdaloid nucleus) and the medial extended amygdala (related to the medial amygdaloid nucleus), which generally form separate corridors both in the sublenticular region and along the supracapsular course of the stria terminalis. The extended amygdala is directly continuous with the caudomedial shell of the accumbens, and to some extent appears to merge with it. Together the accumbens shell and extended amygdala form an extensive forebrain continuum, which establishes specific neuronal circuits with the medial prefrontal-orbitofrontal cortex and medial temporal lobe. This continuum is particularly characterized by a prominent system of long intrinsic association fibers, and a variety of highly differentiated downstream projections to the hypothalamus and brainstem. The various components of the extended amygdala, together with the shell of the accumbens, are ideally structured to generate endocrine, autonomic and somatomotor aspects of emotional and motivational states. Behavioral observations support this proposition and demonstrate the relevance of these structures to a variety of functions, ranging from the various elements of the reproductive cycle to drug-seeking behavior. The neurochemical and connectional features common to the accumbens shell and the extended amygdala are especially relevant to understanding the etiology and treatment of neuropsychiatric disorders. This is discussed in general terms, and also in specific relation to the neurodevelopmental theory of schizophrenia and to the neurosurgical treatment of neuropsychiatric disorders.

Effects of melatonin on estrogen receptor expression in the forebrain of outbred (Lak.LVG) golden hamsters

Studies have shown that the pineal gland via its hormone, melatonin, induces the involution of male and female reproductive systems in seasonally reproducing animals. Melatonin has direct inhibitory effects on both hypothalamic and pituitary functions, which are also exquisitely sensitive to the feedback effects of estradiol. Since melatonin can modulate estrogen receptor (ER) expression in other tissues, immunocytochemical and ribonuclease protection analyses were used to examine the effects of 12 weeks of daily late afternoon injections of melatonin on ER protein and mRNA levels in the hypothalamus of Lak.LVG golden hamsters. Significant decreases in ER-immunoreactivity were noted in the medial preoptic area (MPOA) and bed nucleus of the stria terminalis (BNST) in response to melatonin, while other hypothalamic areas which express ER, e.g. the anterior hypothalamus, showed less dramatic changes. Hypothalamic ER mRNA was decreased in response to melatonin in both intact and ovariectomized animals by 25%. In intact, cycling female hamsters, there was a significant reduction in uterine weight after melatonin treatment. These results suggest that melatonin exerts its anti-reproductive effects in hamsters by modulating ER levels in neurons of the MPOA and BNST, thereby influencing steroid feedback mechanisms.

Chronic morphine decreases calbindin D28k immunoreactivity in a subset of cerebellar Purkinje neurons of rat brain

Calbindin D28k is an intracellular calcium binding protein that is expressed in the cell bodies, nuclei, dendrites, and axons of nearly all Purkinje neurons of the rat cerebellum. Acute morphine administration has been reported to decrease the level of calbindin mRNA in extracts of whole rat cerebellum [75]. Using immunocytochemistry, we studied the effects of chronic morphine administration and morphine abstinence on levels of calbindin in cerebellar Purkinje neurons. Treatment of male rats for 5 days with either morphine injections (10 mg/kg s.c., twice daily) or subcutaneously implanted morphine pellets (75 mg/pellet, once daily) markedly decreased levels of calbindin immunoreactivity in long stretches of Purkinje cell bodies in various folia of cerebellum. After 7 days of abstinence from morphine, the number of calbindin-positive neurons was still significantly decreased, and at 14 days of abstinence, the number of labeled neurons continued to be below that in control rat brain. The effects of morphine in cerebellum were not antagonized by co-administration of the N-methyl-D-aspartate receptor antagonist, MK-801 (0.2 mg/kg, twice daily for 5 days). MK-801 alone also decreased the number of calbindin-positive cells, but in a different pattern from that of morphine. Our findings of decreased calbindin immunoreactivity in Purkinje neurons following chronic morphine administration and abstinence suggest that persistent alterations in intracellular calcium buffering may be associated with opiate tolerance and dependence in cerebellum.

Alterations in immediate-early gene proteins in the rat forebrain induced by acute morphine injection

Injection of morphine (10 mg/kg) induced a complex immediate-early gene response in the rat forebrain, as detected with immunocytochemistry. The c-Fos protein was induced consistently in the dorsomedial caudate-putamen, the nucleus accumbens, and in midline and intralaminar nuclei of the thalamus. In some rats induction was also seen in the parietal and insular cortex and in lateral regions of the caudate-putamen. Induction was detectable, although weak, at 30 min, was maximal at 2 h, and was undetectable 3 h after injection. JunB was induced in the same regions of the caudate-putamen as found for c-Fos, but was not induced in the nucleus accumbens or thalamus. In the caudate-putamen, JunB induction was still present 3 h after injection. A considerably smaller induction of c-Jun was noted in the dorsomedial caudate-putamen and in deep neocortex. Expression of JunD was inhibited in intralaminar and midline thalamic nuclei. Increases in numbers of cells immunoreactive for a Jun-related antigen (Jra) were found in the caudate-putamen and nucleus accumbens. These results indicate a complex immediate-early gene response to acute morphine, suggesting that morphine activates or inhibits specific neurons and circuits in the forebrain.

Charting of Jun family member proteins in the rat forebrain and midbrain: immunocytochemical evidence for a new Jun-related antigen

Immunocytochemistry was used to localize members of the Jun family of immediate-early genes in the forebrain and midbrain of non-stimulated male rats. Antibodies against specific peptide sequences of c-Jun (Ab-1 and Ab-2 from Oncogene Science) and against expressed proteins of JunB and JunD (both from Dr. R. Bravo) revealed widespread and unique distributions for each of these antigens. Charts were made of the distribution of each antigen, and extensive comparisons were made of previous results obtained using in situ hybridization to localize mRNAs for c-jun, junB and junD. Our results indicate a generally favorable comparison between immunoreactivity and distribution of mRNAs for JunB and JunD, but in the case of c-Jun, immunoreactivity and mRNA were comparable only with the Ab-1 antibody. Indeed, the immunocytochemical distribution of the antigen recognized by the c-Jun Ab-2 antibody was distinctly different from that of the other Jun proteins or mRNAs in the rat brain. This antibody (Ab-2) recognized a nuclear protein found extensively in the caudate-putamen, nucleus accumbens, layer II of the olfactory tubercle, the central nucleus of the amygdala, and the lateral division of the bed nucleus of the stria terminalis. Scattered labeled nuclei were found in a few other forebrain structures. Within the caudate-putamen, immunoreactivity was restricted to the matrix compartment, as determined by immunostaining of adjacent sections with the matrix-marker calbindin D28k. Western blots of caudate-putamen demonstrated that this antibody recognized a protein doublet of molecular masses approximately 37 and 34 kDa, distinct from the molecular masses of c-Jun, JunB and JunD. This unique neuroanatomical distribution and molecular mass suggests that this antibody recognizes a previously undescribed Jun-related antigen.

Cholinergic regulation of tachykinin- and enkephalin-gene expression in the rat striatum

Ninety-five percent of the neurons in the corpus striatum of the rat are medium spiny projection neurons, which contain tachykinins such as substance P, neurokinin A, and neurokinin B and the opiate peptides, enkephalin and dynorphin. The remaining 5% consist of interneurons, of which a small but significant proportion are cholinergic. The influence of these cholinergic interneurons on the neuropeptidergic projection systems in the striatum is poorly understood at this time. The present study explores the relationship between cholinergic receptor activation or muscarinic blockade on striatal neuropeptide gene expression. Adult male Sprague-Dawley rats were treated chronically either with a cholinergic agonist (physostigmine: 0.5 mg/kg/3 x day), a muscarinic antagonist (scopolamine HCl: 0.4 mg/kg/3 x day), or vehicle (PBS: 0.1 ml/100 g) administered for 6 days (s.c.). In situ hybridization was performed with probes directed against mRNAs for beta-preprotachykinin (a transcript containing substance P, neurokinin A, and other tachykinins), neurokinin B and preproenkephalin. Physostigmine administration resulted in a 12% decrease in the dorsolateral caudate-putamen and a 27% increase in the core of the nucleus accumbens in substance P/neurokinin A mRNA; and a 29% increase in the caudate-putamen and an 11% increase in the core of the nucleus accumbens in preproenkephalin mRNA levels. Scopolamine treatment resulted in a 28% and 48% decrease, respectively, in the caudate-putamen and in the shell of the nucleus accumbens in substance P/neurokinin A mRNA levels. Neurokinin B mRNA levels were increased by 50% in the shell of the accumbens after scopolamine. Preproenkephalin mRNA levels increased by 24% in the caudate-putamen and decreased by 20% in the core of the nucleus accumbens. From these results we tentatively conclude that cholinoceptive neuropeptidergic neurons are segregated along dorsoventral and mediolateral axes in the striatum, thus giving rise to non-homogenous responses upon cholinergic receptor activation or muscarinic blockade.

Interleukin-3 or erythropoietin induced nuclear localization of protein kinase C beta isoforms in hematopoietic target cells

Protein kinase C (PKC) has been implicated in the signal transduction pathways for the biological effect of both interleukin-3 (IL-3) and erythropoietin (EPO) in hematopoietic target cells. The goal of this study was to identify specific classical isoforms of PKC and their localization in hematopoietic cells in response to the growth factors, IL-3 or EPO. In addition to murine fetal liver cells as a source of normal erythroid progenitor cells, we have utilized the B6SUt.EP cell line, a non-transformed hematopoietic cell line that requires IL-3 for proliferation, but for which EPO can substitute as a growth factor. With polyclonal antibodies prepared against peptide sequences specific for the alpha, beta I, beta II and gamma isoforms of PKC, we have identified beta I and beta II as the predominant nuclear isoforms in target cells that proliferate in response to IL-3 or EPO.

Androgenic-anabolic steroids modify beta-endorphin immunoreactivity in the rat brain

Immunocytochemical localization of beta-endorphin in the brains of intact and castrated male rats was conducted after the administration of high levels of androgenic-anabolic steroids (AAS; 14 daily injections of sesame oil or a cocktail of 2 mg/kg testosterone cypionate, 2 mg/kg nandrolone decanoate, and 1 mg/kg boldenone undecylenate) at doses commonly self-administered by athletes who are considered 'heavy abusers'. In normal intact oil-treated males, cytoplasmic immunoreactivity was prevalent throughout the arcuate nucleus while intense fiber tract immunoreactivity was most prevalent in the bed nucleus of the stria terminalis and the paraventricular hypothalamic nucleus. Administration of AAS significantly decreased the number of neurons exhibiting cytoplasmic immunoreactivity only in the rostral region of the arcuate nucleus. AAS treatment had no effect on beta-endorphin immunoreactivity in the middle or caudal aspects of the arcuate nucleus.

The development of enkephalin and substance P neurons in the basal ganglia: insights into neostriatal compartments and the extended amygdala

To study the comparative development of the two major neuropeptide genes of the striatum, we used immunocytochemistry to detect immunoreactivity (ir) for substance P and synenkephalin (the N terminus of proenkephalin), and in situ hybridization to detect proenkephalin mRNA. Earliest detection of substance P-ir was in the anlage of the bed nucleus of the stria terminalis (BST, at E15) and in the rostral-lateral caudate-putamen (CPu), at E16. Substance P in the BST was immediately subjacent to the medial ganglionic eminence, while immunoreactivity in the CPu was associated with the lateral ganglionic eminence. Earliest detection of synenkephalin-ir or proenkephalin mRNA was in the caudal-lateral CPu and the adjacent central nucleus of the amygdala (Ce), at E16. Over the next several days, expression of each neuropeptide spread toward the region of first expression of the other neuropeptide. The first overlap of expression of the two neuropeptides was at E18, at the level of the septum. Despite correspondence of substance P-ir and proenkephalin mRNA in patches at P0, very little co-expression of the two neuropeptides was evident in individual neurons. We propose a model in which the CPu develops primarily from the lateral ganglionic eminence, and the extended amygdala develops primarily from the medial ganglionic eminence. Within each structure, two poles of neuropeptide gene expression are established initially: substance P-ir in the rostral CPu and in the rostral-medial pole of the extended amygdala (represented by the BST), and synenkephalin/proenkephalin in the caudal CPu and in the caudal-lateral pole of the extended amygdala (represented by the Ce). A stream of substance P-ir cells connects the two poles of the extended amygdala, in the sublenticular substantia innominata.

Genesis and migration patterns of neurons forming the patch and matrix compartments of the rat striatum

The mammalian striatum is divided into two compartments, the patch (or striosome) and the matrix, which differ on the basis of several cytochemical markers, connection patterns, and time of neurogenesis. In the rat, the patch compartment consists of clusters of neurons isolated by matrix neurons; included in the patch compartment is a rim of neurons subjacent to the corpus callosum and external capsule, called the subcallosal streak. To study the genesis and migration patterns of striatal neurons forming these compartments, we injected pregnant rats with 5-bromo-2'-deoxyuridine (BrdU, which is incorporated into DNA during S-phase mitosis) on embryonic (E) day 14, to label patch neurons, or on E19, to label matrix neurons. Embryos were sacrificed at intervals after injection, for detection of BrdU by immunocytochemistry. Cells labeled at E14 were distributed fairly uniformly in the differentiated portion of the caudate-putamen through E19. However, by the day of birth (P0), E14-labeled cells were clustered into patches and the subcallosal streak. Using double immunocytochemistry for BrdU and for the patch marker substance P, we demonstrated a caudal-rostral gradient in the birth dates of neurons in the patch compartment; E14-labeled cells occupied substance P-labeled patches at the level of the posterior limb of the anterior commissure, but patches further rostral were nearly devoid of E14-labeled cells. The distance between the lateral ventricle and the nearest E14-labeled cells was greater on E19 than on E16 or on P0, suggesting secondary movement of early-born neurons during the process of cluster formation. Neurons labeled at E19 formed the matrix surrounding clusters of unlabeled cells, except in the nucleus accumbens (ventral striatum), where E19-labeled cells formed clusters. The data suggest that the uniformly-distributed population of early-born neurons is disrupted by the invasion of later-born (matrix) neurons, forcing the early-born neurons into clusters which are displaced toward the ventricular surface to form the patch compartment. Early-born neurons adjacent to the external capsule are not displaced, forming the subcallosal streak.

Androgen receptor immunoreactivity in somatostatin neurons of the periventricular nucleus but not in the bed nucleus of the stria terminalis in male rats

Somatostatin (SS) is a neuropeptide responsible for the inhibition of growth hormone (GH) release from the anterior pituitary. The existence of sexual dimorphism in the pattern of GH secretion in several mammalian species strongly suggests a role of sex steroids in the regulation of GH release. It has been recently demonstrated that SS mRNA levels are decreased by gonadectomy in male rats while administration of testosterone reversed the postgonadectomy decrease in hypothalamic SS mRNA levels. The mechanism(s) by which androgens regulate somatostatin neurons are unknown at this time. Both direct and indirect pathways have been suggested. In this study, double-labeling immunocytochemistry was used to address the question of whether SS neurons have androgen receptors in adult male rats. About 70-75% of SS-immunoreactive (-ir) neurons in the periventricular hypothalamic nucleus possess androgen receptors and this co-localization persists throughout the rostrocaudal extent of this nucleus. In the bed nucleus of the stria terminalis, no SS-ir neurons were shown to have androgen receptors. These results suggest that androgens may directly exert their effect upon SS neurons in the periventricular nucleus.

Semiquantitative analysis of in-situ hybridization results using IMAGE software: a rapid method for counting reduced silver grains over mRNA-positive cells

The advent of microcomputers has brought about a revolution in the computing power available to the average user. Image analysis is a very resource-intensive process, making great demands on computing power, memory, and display capabilities of most computers. Thus, in the past, dedicated, single-use hardware and software had to be custom made for environments requiring image analysis. We present here an easy-to-use image analysis protocol available to most users with a Macintosh II series computer and access to IMAGE (a public domain image analysis program). The protocol allows for semi-quantitation of silver grains over cells used in the interpretation of in-situ hybridization results. We show that the method provides a quick and reliable means of counting grains over mRNA-positive cells in an automated fashion. We also provide evidence that the method can be used to detect differences between experimental treatments.

Ontogeny of the distribution of tachykinins in rat cerebral cortex: immunocytochemistry and in situ hybridization histochemistry

Tachykinins in the mammalian brain are derived from two genes: preprotachykinin A, encoding substance P and neurokinin A, and preprotachykinin B, encoding neurokinin B. Using immunocytochemistry and in situ hybridization histochemistry, we have investigated the ontogeny and distribution of substance P and neurokinin B in various cortical areas of rat cerebrum at different prenatal and postnatal ages. Preprotachykinin A mRNA-positive and -immunoreactive cells were first detected at birth and were abundant in layer VIb and the adjacent white matter in the cingulate and frontal cortices. By postnatal day 5, the numbers of substance P-expressing cells were diminished dramatically in those layers. However, their number gradually increased and spread out laterally to cover parietal and temporal cortices from P5 to P15 in layer V. At these stages, cells were also observed in layer II, although fewer in number. The number of substance P mRNA-positive neurons and substance P-immunoreactive cells decreased gradually from P10 and P15 onward, respectively. On the other hand, expression of neurokinin B, as detected by in situ hybridization histochemistry or immunocytochemistry, was not evident until P10. Neurons expressing this tachykinin were concentrated in layer II, and to a lesser extent in layers V and VI. This pattern of distribution was retained through P45. The present data show a marked difference between these two tachykinins in onset and trends of development, suggesting functional independence of these two tachykinins in the cerebral cortex.

Chronic morphine increases calbindin D28k in rat striatum: possible NMDA receptor involvement

The neuronal intracellular calcium-binding protein calbindin D28k is a neurochemical marker in the striatum, normally expressed in the matrix compartment and absent from the mu-opiate receptor-enriched striosomal (patch) compartment. Because chronic treatment with morphine has been reported to increase calcium levels in synaptosomes of rat striatum, we studied effects of morphine on calbindin immunoreactivity (ir) in rat brain, using immunocytochemistry. Treatment with morphine for 5 days increased calbindin-ir in the striatal matrix, and induced intense calbindin-ir in the patch compartment. Increased calbindin-ir in patches persisted through day 14 post-morphine. Co-administration of the NMDA receptor antagonist MK-801 blocked the morphine-induced increase in calbindin-ir in patches. We suggest that chronic morphine treatment may increase calcium and calbindin levels via increased glutamatergic transmission in striatum. These findings are consistent with reports that MK-801 inhibits tolerance to morphine, and provide a possible mechanism and anatomical substrate for this inhibition.

Absence of androgen receptors in LHRH immunoreactive neurons

Androgen has a negative feedback effect upon reproductive functions. Studies have suggested that this effect is mediated partially at the hypothalamic level. However, it is not clear whether the action is direct or indirect on LHRH neurons. In the present study, double immunocytochemistry was used to localize LHRH and androgen receptors. Out of 5892 LHRH immunoreactive neurons, no double-labelled neurons were observed. We conclude that the feedback effect of androgen on the central nervous system is mediated by indirect pathway(s).

Up-regulation of androgen receptor immunoreactivity in the rat brain by androgenic-anabolic steroids

To characterize central nervous system changes that occur with anabolic steroid abuse in humans, immunocytochemical localization of androgen receptors in the brains of 10 intact and 10 castrated male rats was conducted after the administration of high levels of androgenic-anabolic steroids (AAS; 14 daily injections of sesame oil or a cocktail of 2 mg/kg testosterone cypionate, 2 mg/kg nandrolone decanoate, and 1 mg/kg boldenone undecylenate). In normal intact oil-treated males, nuclear androgen receptor immunoreactivity was present in many 'classical' and 'non-classical' androgen target sites in the brain. Administration of AAS increased the intensity of immunoreactivity in most classical androgen target sites and increased both the intensity of immunoreactivity and number of immunoreactive cells in most non-classical androgen target sites. These results may suggest that androgen receptors in the brain are up-regulated by AAS. The simultaneous androgen receptor up-regulation in these regions by AAS may account for the complex anabolic steroid abuse syndrome. Consistently, androgen receptor immunoreactivity in most brain regions was reduced or absent after castration, suggesting that endogenous androgen levels are necessary for normal androgen receptor immunoreactivity. These results identify the distribution of one central nervous system mechanism modified by AAS.

Protein kinase C-delta in rat brain: association with sensory neuronal hierarchies

Originally characterized as the calcium- and phospholipid-dependent protein kinases, the protein kinases C include at least eight separate isoforms, some of which are calcium-independent and all of which are highly enriched in brain. Of the calcium-independent isoforms, the delta subspecies of protein kinase C has the most restricted complement of lipid activators and substrate specificity, suggesting that it may have a unique role in cell signalling pathways. Using immunocytochemistry, we report that the distribution of protein kinase C-delta immunoreactivity in rat brain is also restricted, being present in all sensory systems. Moreover, it is found in alternating hierarchies of sensory pathways: in all sensory systems except auditory, it is found in first- and third-order neurons, while in the auditory system, it is found in second- and fourth-order neurons. Thalamocortical systems are intensely immunoreactive, including barrel fields of the rat parietal cortex. Outside of sensory systems, protein kinase C-delta is present in cerebellum within longitudinal stripes in Purkinje neurons, and in the caudate-putamen, it appears to be associated with the striosome (patch) compartment. In contrast to all other protein kinase C isoforms, protein kinase C-delta is absent from hippocampus. These findings suggest that protein kinase C-delta may have a unique role in signal transduction in the central nervous system (CNS), especially in sensory systems.

Ontogeny of the proenkephalin system in the rat corpus striatum: its relationship to dopaminergic innervation and transient compartmental expression

The earliest detection of the proenkephalin gene was on embryonic day 16 in neuronal cell bodies in the ventrolateral portion of the caudal neostriatum. This expression was identified by both immunocytochemistry for synenkephalin, the nonopioid N-terminus of proenkephalin (1-70), and preproenkephalin in situ hybridization with a complementary DNA probe. Two developmental gradients of preproenkephalin expression and synenkephalin immunoreactivity were observed: (i) a ventrolateral to dorsomedial and caudal to rostral gradient in the rostral caudate-putamen; and (ii) a ventromedial to dorsolateral and rostral to caudal gradient in the caudal caudate-putamen. Ventrolateral to dorsomedial and caudal to rostral developmental gradients of synenkephalin fiber immunoreactivity were also identified in the globus pallidus. Methionine enkephalin immunoreactivity was not consistently detectable until postnatal day 10 and 15 in the rostral and caudal globus pallidus, respectively. A transient patchy distribution of increased preproenkephalin expression from embryonic day 20 through postnatal day 5 occurred. These patches and a subcallosal streak were found to overlap partially with areas of increased tyrosine hydroxylase immunoreactivity by adjacent section analyses. The earliest detection of tyrosine hydroxylase immunoreactivity was found to coincide with that of proenkephalin on embryonic day 16, but in differing regions of the corpus striatum. Tyrosine hydroxylase immunoreactivity in the rostral caudate-putamen preceded, while in the caudal caudate-putamen it followed first expression of the proenkephalin gene. Early proenkephalin expression, by both synenkephalin immunocytochemistry and preproenkephalin in situ hybridization, was also detected in the central nucleus of the amygdala on embryonic day 16 immediately ventral to the area of expression in the caudate-putamen. Preproenkephalin expression in the olfactory tubercle and nucleus accumbens first appeared on embryonic day 20 and expression proceeded in a lateral to dorsomedial gradient continuous with the ventral part of the rostral caudal-putamen. Relatively late detection of methionine enkephalin immunoreactivity in comparison to synenkephalin possibly indicates a developmental delay in the complete enzymatic processing of the proenkephalin precursor. Differing gradients in the ontogeny of preproenkephalin expression in the rostral vs the caudal caudate-putamen suggest possible anatomical and developmental differences of these two regions. Also, transient compartmentalization of preproenkephalin expression and differences in dopaminergic innervation as detected by tyrosine hydroxylase immunoreactivity were further support for the existence of two subsets of proenkephalinergic neurons in the caudate-putamen. Contemporaneous development of preproenkephalin expression and synenkephalin immunoreactivity in the central nucleus of the amygdala with the ventral part of the caudal caudate-putamen also suggested developmental homology.(ABSTRACT TRUNCATED AT 400 WORDS)