Colocalization of muscarinic acetylcholine receptors and protein kinase C gamma in rat parietal cortex

Transplantation of neural progenitors enhances production of endogenous cells in the impaired brain

Grafting of neural progenitors has been shown to reverse a wide variety of neurobehavioral defects. While their role of replacing injured cells and restoring damaged circuitries has been shown, it is widely accepted that this cannot be the only mechanism, as therapy can occur even when an insufficient number of transplanted cells are found. We hypothesized that one major mechanism by which transplanted neural progenitors exert their therapeutic effect is by enhancing endogenous cells production. Consequently, in an allographic model of transplantation, prenatally heroin-exposed genetically heterogeneous (HS) mice were made defective in their hippocampal neurobehavioral function by exposing their mothers to heroin (10 mg kg(-1) heroin on gestation days 9-18). Hippocampal damage was confirmed by deficient performance in the Morris maze (P<0.009), and decreased production of endogenous cells in the dentate gyrus by 39% was observed. On postnatal day 35, they received an HS-derived neural progenitors transplant followed by repeated bromodeoxyuridine injections. The transplant returned endogenous cells production to normal levels (P<0.006) and reversed the behavioral defects (P<0.03), despite the fact that only 0.0334% of the transplanted neural progenitors survived and that they differentiated mainly to astrocytes. An immunological study demonstrated the presence of macrophages and T cells as a possible explanation for the paucity of the transplanted cells. This study suggests one mechanism for the therapeutic action of neural progenitors, the enhancement of the production of endogenous cells, pointing to future clinical applications in this direction by use of neural progenitors or by analogous cell-inducing techniques.

Reversal of heroin neurobehavioral teratogenicity by grafting of neural progenitors

A major objective in identifying the mechanisms underlying neurobehavioral teratogenicity in an animal model is the possibility of designing therapies that reverse or offset teratogen-induced neural damage. In our previous studies, we identified deficits in hippocampal muscarinic cholinergic receptor-induced translocation of protein kinase C (PKC) gamma as the likely central factor responsible for the adverse behavioral effects of pre-natal heroin exposure. Neural progenitors (NP) have the ability to recover behavioral deficits after focal hippocampal damage. Therefore, we explored whether behavioral and synaptic defects could be reversed in adulthood by neural progenitor grafting. Pregnant mice were injected daily with 10 mg/kg of heroin on gestational days 9-18. In adulthood, offspring showed deficits in the Morris maze, a behavior dependent on the integrity of septohippocampal cholinergic synaptic function, along with the loss of the PKCgamma and PKCbetaII responses to cholinergic stimulation. Mice that were exposed pre-natally to heroin and vehicle control mice were then grafted in adulthood with NP. Importantly, most grafted cells differentiated to astrocytes. NP reversed the behavioral deficits (p = 0.0043) and restored the normal response of hippocampal PKCgamma and PKCbetaII (p = 0.0337 and p = 0.0265 respectively) to cholinergic receptor stimulation. The effects were specific as the PKCalpha isoform, which is unrelated to the behavioral deficits, showed almost no changes. Neural progenitor grafting thus offers an animal model for reversing neurobehavioral deficits originating in septohippocampal cholinergic defects elicited by pre-natal exposure to insults.

Spatial memory in aged rats is related to PKCgamma-dependent G-protein coupling of the M1 receptor

In the present study, individual differences in spatial memory in aged Fischer 344 (F344) rats were associated with the extent of G-protein coupling of the M1 muscarinic receptor and the dendritic-to-somal ratio of hippocampal PKCgamma (d/sPKCgamma) immunogenicity. Following testing in the eight-arm radial maze task, 7 young and 13 aged rat brains were sectioned through the dorsal hippocampal formation (HF). G-protein coupling of the M1 receptor was assessed autoradiographically using competition binding studies in the presence and absence of a G-protein uncoupler to determine high (K(H)) and low (K(L)) affinity states for agonist in the HF, neocortex, and amygdala. In aged animals, a relationship between choice accuracy in the maze and K(H), a measure of M1 receptor-G-protein coupling was seen in the dentate gyrus, CA3, CA1, and neocortex. Furthermore, choice accuracy and d/sPKCgamma immunogenicity showed a significant relationship in CA1. Lastly, a correlation was seen in the CA1 of aged animals between K(H) and d/sPKCgamma. These relationships did not hold for the amygdala. Thus, individual differences in a naturally occurring age-dependent disruption of cholinergic-PKCgamma signal transduction is associated with spatial memory dysfunction.

Aging-related alterations in the distribution of Ca(2+)-dependent PKC isoforms in rabbit hippocampus

The immunocytochemical and subcellular localization of the Ca(2+)-dependent protein kinase C (cPKC) isoforms (PKCalpha, beta1, beta2, and gamma) was examined in rabbit hippocampus of young (3 months of age; n = 11) and aging (36 months of age; n = 14) subjects. Detailed immunocytochemical analyses revealed a significant increase in PKCbeta1, beta2, and gamma immunoreactivity in principal cell bodies and associated dendrites, and interneurons of the hilar region in the aging rabbits. The number of PKCalpha- and gamma-positive interneurons in the aging stratum oriens declined significantly. PKCalpha was least affected in principal cells, showing an increase in immunostaining in granule cells only. Weakly PKC-positive principal cells intermingled between densely stained ones were seen in parts of the hippocampus in most of the aging rabbits, showing that the degree of aging-related alterations in PKC-immunoreactivity varies between neurons. Changes in PKC expression in the molecular and subgranular layer of the aging dentate gyrus suggested a reorganization of PKC-positive afferents to this region. Western blot analysis revealed a significant loss of PKC in the pellet fraction for all isoforms, and a tendency for increased levels of cytosolic PKC. However, no significant changes were found in total PKC content for any PKC isoform. A concurrent dramatic loss of the PKC anchoring protein receptor for activated C kinase (RACK1) in the pellet fraction was shown by Western blotting. These findings suggest that the loss of RACK1 contributes to the dysregulation of the PKC system in the aging rabbit hippocampus. The enhanced PKC-immunoreactivity might relate to reduced protein-protein interactions of PKC with the anchoring protein RACK1 leading to increased access of the antibodies to the antigenic site. In conclusion, the results suggest that memory deficits in aging rabbits are (in part) caused by dysregulation of subcellular PKC localization in hippocampal neurons.

Nicotine therapy in adulthood reverses the synaptic and behavioral deficits elicited by prenatal exposure to phenobarbital

A major objective in identifying the mechanisms underlying neurobehavioral teratogenicity is the possibility of designing therapies that reverse or offset drug- or toxicant-induced neural damage. In our previous studies, we identified deficits in hippocampal muscarinic cholinergic receptor-induced membrane translocation of protein kinase C (PKC)gamma as the likely mechanism responsible for adverse behavioral effects of prenatal phenobarbital exposure. We therefore explored whether behavioral and synaptic defects could be reversed in adulthood by nicotine administration. Pregnant mice were given milled food containing phenobarbital to achieve a daily dose of 0.5-0.6 g/kg from gestational days 9-18. In adulthood, offspring showed deficits in the Morris maze, a behavior dependent on the integrity of septohippocampal cholinergic synaptic function, along with the loss of the PKCgamma response. Phenobarbital-exposed and control mice then received nicotine (10 mg/kg/day) for 14 days via osmotic minipumps. Nicotine reversed the behavioral deficits and restored the normal response of hippocampal PKCgamma to cholinergic receptor stimulation. The effects were regionally specific, as PKCgamma in the cerebellum was unaffected by either phenobarbital or nicotine; furthermore, in the hippocampus, PKC isoforms unrelated to the behavioral deficits showed no changes. Nicotine administration thus offers a potential therapy for reversing neurobehavioral deficits originating in septohippocampal cholinergic defects elicited by prenatal drug or toxicant exposures.

Prenatal heroin exposure alters cholinergic receptor stimulated activation of the PKCβII and PKCγ isoforms

Prenatal exposure of mice to heroin (SC injection of 10mg/kg to the dams on gestational days 9-18) resulted at adulthood in behavioral deficits related to septohippocampal cholinergic innervation accompanied with both presynaptic and postsynaptic cholinergic hyperactivity; including an increase membrane PKC activity, and a desensitization of PKC to cholinergic input which were highly correlated with the behavioral performance and were reversed by cholinergic grafting. Therefore, we studied the receptor induced activation of the behaviorally relevant PKCgamma and PKCbetaII isoforms and the less behaviorally relevant PKCalpha isoform. Time course studies revealed peak translocation after 40 min incubation with carbachol for PKCgamma (110% increase from basal, i.e. no carbachol level, P < 0.01), 30 min for phosphorylated PKCbetaII (130%, P < 0.05) and 5 min for non-phosphorylated PKCbetaII (64%, P < 0.05) with no peak for alpha. Prenatal heroin abolished the translocation of PKCgamma and PKCbetaII while PKCalpha remained unaffected. A decrease occurred in basal phosphorylated membrane (-45%, P < 0.01) and cytosol-associated (-29%, P < 0.01) PKCbetaII, in membrane-associated non-phosphorylated PKCbetaII (-32%, P < 0.01) and PKCgamma (-25%, P < 0.01) and in cytosolic PKCalpha (-27%, P < 0.01), while membrane-associated PKCalpha was slightly increased (11%, P < 0.05). The results suggest that prenatal heroin disrupts cholinergic receptor induced PKC translocation and activation with the underlying mechanism of neuroteratogenicity potentially lying in the PKCgamma and PKCbetaII, while PKCalpha remains unaffected.

Cholinergic plasticity in the hippocampus

Tests were made for use-dependent plasticity in the cholinergic projections to hippocampus. Transient infusion of the cholinergic agonist carbachol into hippocampal slices induced rhythmic activity that persisted for hours after washout. Comparable effects were obtained with physostigmine, a drug that blocks acetylcholine breakdown and thereby enhances cholinergic transmission. It thus seems that activation of cholinergic synapses induces lasting changes in hippocampal physiology. Two lines of evidence indicated that cholinergic synapses are also the sites at which the plasticity is expressed. First, the induction and expression of the rhythms were not blocked by the N-methyl-D-aspartate receptor antagonist D-2-amino-5-phosphonovaleric acid, indicating that a long-term potentiation effect between pyramidal cells was not involved. Second, a muscarinic antagonist (atropine) completely abolished stable rhythmic activity after agonist washout. This result indicates that endogenous cholinergic activity is responsible for the persistence of rhythmic oscillations. These experiments suggest that short periods of intense cholinergic activity induce lasting changes in cholinergic synapses and thus extend such forms of plasticity to beyond the glutamatergic system.

Effects of prenyl pyrophosphates on the binding of PKCgamma with RACK1

Receptors for activated C kinase (RACKs) are a group of PKC binding proteins that have been shown to mediate isoform-selective functions of PKC and to be crucial in the translocation and subsequent functioning of the PKC isoenzymes on activation. RACK1 cDNA from the shrimp Penaeus japonicus was isolated by homology cloning. The hepatopancreas cDNA from this shrimp was found to encode a 318-residue polypeptide whose predicted amino acid sequence shared 91% homology with human G(beta2)-like proteins. Expression of the cDNA of shrimp RACK1 in vitro yielded a 45-kDa polypeptide with positive reactivity toward the monoclonal antibodies against RACK1 of mammals. The shrimp RACK1 was biotinylated and used to compare the effects of geranylgeranyl pyrophosphate and farnesyl pyrophosphate on its binding with PKCgamma in anti-biotin-IgG precipitates. PKCgammas were isolated from shrimp eyes and mouse brains. Both enzyme preparations were able to inhibit taxol-induced tubulin polymerization. Interestingly, when either geranylgeranyl pyrophosphate or farnesyl pyrophosphate was reduced to the submicrogram level, the recruitment activity of RACK1 with purified PKCgamma was found to increase dramatically. The activation is especially significant for RACK1 and PKCgamma from different species. The observation implies that the deprivation of prenyl pyrophosphate might function as a signal for RACK1 to switch the binding from the conventional isoenzymes of PKC (cPKC) to the novel isoenzymes of PKC (nPKC). A hydrophobic binding pocket for geranylgeranyl pyrophosphate in RACK1 is further revealed via prenylation with protein geranylgeranyl transferase I of shrimp P. japonicus.

A prospective study of serum pseudocholinesterase levels in patients with chronic spinal pain: a preliminary study

STUDY DESIGN

One-dimensional polyacrylamide gel electrophoresis was used to study serum esterase enzymatic activity in three groups of patients and one group of normal volunteers.

OBJECTIVES

To determine whether there is a statistically significant correlation between variations of serum pseudocholinesterase and the perception of pain in patients with chronic spinal pain.

SUMMARY OF BACKGROUND DATA

Changes in levels of cholinesterase in the extracellular space of the brain and in the cerebral spinal fluid have been found to be associated in animal pain experimentation.

METHODS

Ninety-three surgical patients with chronic spinal pain, six surgical control subjects operated for conditions not associated with pain, 21 normal control volunteers, and nine disabled patients receiving monetary benefits were studied. The patients were analyzed for a period of time by rating the perception of their pain with a visual assessment score at the time venous blood was drawn. Serum samples were prepared, serum pseudocholinesterase was monitored, separated, and quantified according to Allen et al.5 Paired sample t tests were used to statistically evaluate the data.

RESULTS

A trend of correlation was noted between preoperative serum pseudocholinesterase levels and visual assessment score: serum pseudocholinesterase levels increased as visual assessment score increased. The mean preoperative serum pseudocholinesterase level of chronic spinal pain patients (1313; SE = 26), which was significantly higher than the mean levels of the normal control volunteers (941; SE = 24; P<0.001) and that of surgical control subjects (1018; SE = 63; P <0.01), decreased significantly with anesthesia (P<0.005). The mean preoperative serum pseudocholinesterase level of the surgical controls, however, remained unchanged with anesthesia. A correlation demonstrated between visual assessment score and serum pseudocholinesterase in chronic spinal pain patients was not observed in six of nine patients receiving disability payments for more than a year.

CONCLUSIONS

Measurements of quantitative alterations of serum pseudocholinesterase levels may be useful in the treatment of patients with chronic spinal pain.

Muscarinic acetylcholine receptors in the hippocampus, neocortex and amygdala: a review of immunocytochemical localization in relation to learning and memory

Immunocytochemical mapping studies employing the extensively used monoclonal anti-muscarinic acetylcholine receptor (mAChR) antibody M35 are reviewed. We focus on three neuronal muscarinic cholinoceptive substrates, which are target regions of the cholinergic basal forebrain system intimately involved in cognitive functions: the hippocampus; neocortex; and amygdala. The distribution and neurochemistry of mAChR-immunoreactive cells as well as behaviorally induced alterations in mAChR-immunoreactivity (ir) are described in detail. M35+ neurons are viewed as cells actively engaged in neuronal functions in which the cholinergic system is typically involved. Phosphorylation and subsequent internalization of muscarinic receptors determine the immunocytochemical outcome, and hence M35 as a tool to visualize muscarinic receptors is less suitable for detection of the entire pool of mAChRs in the central nervous system (CNS). Instead, M35 is sensitive to and capable of detecting alterations in the physiological condition of muscarinic receptors. Therefore, M35 is an excellent tool to localize alterations in cellular cholinoceptivity in the CNS. M35-ir is not only determined by acetylcholine (ACh), but by any substance that changes the phosphorylation/internalization state of the mAChR. An important consequence of this proposition is that other neurotransmitters than ACh (especially glutamate) can regulate M35-ir and the cholinoceptive state of a neuron, and hence the functional properties of a neuron. One of the primary objectives of this review is to provide a synthesis of our data and literature data on mAChR-ir. We propose a hypothesis for the role of muscarinic receptors in learning and memory in terms of modulation between learning and recall states of brain areas at the postsynaptic level as studied by way of immunocytochemistry employing the monoclonal antibody M35.

Distribution of muscarinic receptors on the endothelium of cortical vessels in the rat brain

Functional and pharmacological studies have suggested that there are muscarinic receptors (mAChRs) on the endothelial cells of major cerebral arteries, while recent immunological studies indicate that there are no mAChRs on the endothelium of brain capillaries. This difference may be because the distribution of mAChR on the endothelium varies with the type of vessel. This paper examines the distribution of mAChR on the vascular endothelium along intraparenchymal blood vessels in the rat brain by immunolabelling and laser confocal microscopy. Sections were immunostained by combinations of an anti-mAChR antibody (M35) with antibodies to endothelial (anti-GLUT1), or to smooth muscle markers (anti-actin). Antibody labellings were detected with fluorescent second antibodies. Most of the penetrating vessels bore mAChR immunolabelling which coincided over almost all the vessel surface with endothelial labelling. The mAChR immunolabelling was less widespread over the endothelium on the medium sized vessels (diameter < 50 microm) and only 50% of these vessels had mAChR staining on the endothelium. There was no mAChR immunostaining on the endothelium of the capillaries. In contrast with the basilar artery, there was no mAChR immunolabelling on the smooth muscle layer of the intracortical vessels. These data indicate that the intensity of mAChR immunolabelling decreases along the vascular tree from large conducting vessels to capillaries.

Learning-induced alterations in hippocampal PKC-immunoreactivity: a review and hypothesis of its functional significance

1. To localize protein kinase C (PKC) in the hippocampus, PKC activity measures, mRNA in situ hybridization, and [3H]phorbol ester binding techniques were used until in the 1980s antibodies became available for in situ immunocytochemistry. In the late 1980s, PKC-isoform-specific antibodies were first used to map hippocampal PKC at the cellular and subcellular level. The mammalian hippocampus contains all four Ca(2+)-dependent PKC isoforms, but the (sub)cellular localization is both isoform- and species-specific. 2. Hippocampally-dependent spatial and associative learning in rat, mice and rabbit induce an increase in PKC immunoreactivity (ir) in hippocampal principal cells studied 24 hours after the animals had learned the task. Among the four Ca(2+)-dependent PKC subtypes, this increase is selective for the gamma-isoform. The presence of the gamma-isoform in dendritic spines (the most likely site for synaptic plasticity and information storage), in contrast to PKC alpha, beta 1, and beta 2, may underlie the isoform-selectivity. 3. Compared to fully trained animals, subjects halfway training showed intermediate levels of increased PKC gamma-ir. Poor learners that were not able to learn the task showed considerably less enhanced PKC gamma-ir as compared to good learners. 4. Associative learning induced a decrease in astroglial PKC beta 2 and gamma-ir in those regions where a simultaneous increase in neuronal PKC gamma-ir was observed. This decrease most likely reflects PKC down-regulation, enabling the astrocytes to maintain their K+ buffering capacity necessary to support neuronal activity such as accompanying learning and memory. 5. Western blot analyses revealed that the increase in PKC gamma-ir was not due to an increase in total amount of PKC gamma, translocation, or the proteolytic generation of the fragment PKM. The increase in PKC gamma-ir must therefore reflect a learning-induced conformational change in the PKC gamma molecule that results in the exposure of the antigenic site(s). 6. Although a large number of hippocampal pyramidal cells display learning-induced enhancement of PKC gamma-ir at the 24 hours post-training time point, this does not indicate, however, that all synapses in these neurons are used, or that the maximal PKC signal transduction capacity per call has been reached. 7. The enhanced PKC gamma-ir may reflect a form of activated PKC, since PKC stimulation by phorbol esters (both in hippocampal slices and mildly aldehyde fixed sections) mimicked the increase in PKC gamma-ir similar as seen after learning. 8. The most likely transmitter systems which may have induced the altered PKC gamma-ir are acetylcholine and glutamate. Their contribution and interaction at the cellular level are depicted in a schematic circuit terminating on a CA1 pyramidal cell (Fig. 4). 9. Several functional roles for PKC gamma in learning and memory are discussed, and a hypothetical model is proposed based on an endogeneous PKC inhibitor protein that may explain altered antibody-binding to PKC gamma after learning (Fig. 6). 10. The immunocytochemical approach can contribute significantly to the ongoing attempts to decipher part of the cellular and biochemical mechanism of learning and memory. The development of ever more specific and better characterized antibodies reactive with different sites of proteins like PKC gamma will offer the necessary tools for further immunocytochemical research to help unravel complex brain functions.

Muscarinic acetylcholine receptor immunoreactivity in the amygdala--I. Cellular distribution correlated with fear-induced behavior

This study examined the distribution of muscarinic acetylcholine receptor-immunoreactive neurons in the amygdaloid complex of the rat, with emphasis on the central nucleus. The monoclonal antibody M35 raised against purified muscarinic acetylcholine receptor protein was used to visualize muscarinic acetylcholine receptor-immunoreactive cells. Muscarinic acetylcholine receptor immuno-reactivity was high in the central nucleus and low to moderate in all other regions of the amygdaloid complex. Within the central nucleus, the muscarinic acetylcholine receptor-immunoreactive neurons were found predominantly in the lateral subdivision. This region contained medium-sized neurons (largest diameter ranging from 10 to 15 microns), with a round or slightly ovoid cell shape. At the subcellular level, however, the labeled neurons revealed relatively few muscarinic acetylcholine receptor-immunoreactive postsynaptic densities. Immunofluorescent double-labeling demonstrated that nearly all of the muscarinic acetylcholine receptor-immunoreactive neurons (98.6%) in the central nucleus expressed abundant amounts of nicotinic acetylcholine receptors, further substantiating the cholinoceptive character of these cells. In addition, the vast majority of these muscarinic acetylcholine receptor-immunoreactive neurons (94.3%) were GABAergic neurons. The muscarinic acetylcholine receptor-immunoreactive neurons expressed moderate levels of protein kinase gamma, one of the likely intracellular mediators between muscarinic acetylcholine receptors and their elicited physiological response. The number and staining intensity of muscarinic acetylcholine receptor-immunoreactive neurons in the central nucleus varied dramatically among rats. This individual variation correlated positively with the rat's expression of conditioned immobility and correlated negatively with active shock avoidance performance. These results suggest that the GABAergic/cholinoceptive neuronal elements in the central nucleus are involved in the expression of fear-induced behaviors. This interpretation is further elaborated in a forthcoming paper.

Global and serial neurons form A hierarchically arranged interface proposed to underlie memory and cognition

It is hypothesized that the cholinergic and monoaminergic neurons of the brain from a global network. What is meant by a global network is that these neurons operate as a unified whole, generating widespread patterns of activity in concert with particular electroencephalographic states, moods and cognitive gestalts. Apart from cholinergic and monoaminergic global systems, most other mammalian neurons relay sensory information about the external and internal milieu to serially ordered loci. These "serial" neurons are neurochemically distinct from global neurons and commonly use small molecule amino acid neurotransmitters such as glutamate or aspartate. Viewing the circuitry of the mammalian brain within the global-serial dichotomy leads to a number of novel interpretations and predictions. Global systems seem to be capable of transforming incoming sensory data into cognitive-related activity patterns. A comparative examination of global and serial systems anatomy, development and physiology reveals how global systems might turn sensation into mentation. An important step in this process is the permanent encoding of memory. Global neurons are particularly plastic, as are the neurons receiving global inputs. Global afferents appear to be capable of reorganizing synapses on recipient serial cells, thus leading to enhanced responding to a signal, in a particular context and state of arousal.

Loss of cortical serotonin2A signal transduction in senescent rats: reversal following inhibition of protein kinase C

Using grease gap recordings, age-related changes in serotonin2A receptors were assessed in sensorimotor regions of the cortex by examining serotonin-induced facilitation of the N-methyl-D-aspartate depolarization in cortical wedges prepared from young adult (3-6 months) and senescent (22-34 months) Fisher 344 rats. Serotonin (10-100 microM) facilitated the N-methyl-D-aspartate depolarization in wedges from young adult rats in a concentration-dependent manner, whereas no facilitation was observed in wedges from senescent rats. Similar results were obtained when +/- 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, a mixed serotonin2A and serotonin2C receptor agonist, was substituted for serotonin. In contrast, agonists at alpha 1A-adrenoceptors, metabotropic glutamate receptors and muscarinic cholinoceptors facilitated the N-methyl-D-aspartate depolarization in wedges from both young adult and senescent rats. Chelerythrine and staurosporine, inhibitors of protein kinase C, but not concanavalin A, myo-inositol or calmodulin antagonists, restored the serotonin facilitation in wedges from senescent animals. In situ hybridization histochemistry revealed that serotonin2A receptor messenger RNA was present in layers II-VI of the cortex, with the highest density of silver grains located in layers III and V of both young adult and senescent rats. Detailed examination of layer V showed that silver grains were significantly higher than background only over pyramidal cells. We conclude that serotonin2A receptors are expressed by pyramidal cells in both young adult and senescent rats and that serotonin acts directly on these receptors to facilitate the N-methyl-D-aspartate depolarization. Moreover, in senescent rats, signal transduction at cortical serotonin2A receptors involved with facilitation of the N-methyl-D-aspartate response is compromised as a result of protein kinase C activation.

Differential distribution of protein kinase C (PKC alpha beta and PKC gamma) isoenzyme immunoreactivity in the chick brain

Protein kinase C (PKC) is involved in neural plasticity. The phosphorylation of the myristoylated alanine-rich protein kinase C substrate (MARCKS) in the left intermediate and medial hyperstriatum ventrale (IMHV) of the chick brain has been shown previously to correlate significantly with the strength of learning in filial imprinting. The distribution of PKC alpha, beta I, beta II and PKC gamma in the brain of 1-day-old dark-reared chicks was determined immunocytochemically, using the monoclonal antibodies MC5 and 36G9, raised against purified PKC alpha beta and PKC gamma, respectively. PKC gamma-stained cells were distributed widely in the telencephalon, including all hyperstriatal structures (including the IMHV), the hippocampus, neostriatum, ectostriatum and archistriatum. There were fewer stained cells in the septum and the least cellular staining was in the paleostriatum primitivum. Fluorescent double-labelling with neuron-specific enolase (NSE) and with the glial calcium-binding protein S100 suggested that PKC gamma immunoreactivity was present in neurones but not in glia. The distribution of PKC alpha beta-stained cells was more limited, with staining in the archistriatum, hippocampus and septum but not in the hyperstriatum. However, there was PKC alpha beta-staining of some fibres in the IMHV (but little elsewhere in the hyperstriatum ventrale), in the neostriatum, paleostriatal complex and the lobus parolfactorius. Double-labelling with NSE and S100 revealed PKC alpha beta/S100-positive glial cells present in the paleostriatal region only. There was some PKC alpha beta-staining of putative neurones in the hippocampus, septum and archistriatum. The differential distribution of PKC isoenzymes suggests that in the IMHV some axonal inputs contain PKC alpha beta whereas some postsynaptic cells contain the gamma form of PKC.

Alterations in the immunoreactivity for muscarinic acetylcholine receptors and colocalized PKC gamma in mouse hippocampus induced by spatial discrimination learning

This study describes changes in the immunoreactivity for muscarinic acetylcholine receptors (mAChRs) in the hippocampus of mice in relation to spatial discrimination behavior, employing the monoclonal antibody M35 raised against purified bovine mAChR protein. Performance in a hole board in which the animals learned the pattern of 4 baited holes out of 16 holes served as the measure of spatial discrimination learning and memory. Twenty-six adult male house mice were used, divided into four groups. Three groups served as various controls: group N (naive; blank controls); group H (habituated; animals were introduced to the hole board with all holes baited for 5 consecutive days), and group P (pseudo-trained; the animals were admitted to the hole board for 13 consecutive days with all holes baited). The T group (trained) was subjected to the hole board for 5 consecutive habituation days with all holes baited (similar to the H and P groups), followed by 8 successive training days with only four holes baited in a fixed pattern. During the 8 training days, the T group gradually acquired a pattern to visit the baited holes, whereas the P group continued visiting holes in a random fashion. The mice were killed 24 h after the last behavioral session. All principal cells in teh cornu ammonis (CA) and dentate gyrus (DG) of the habituated animals revealed increased levels of mAChR immunoreactivity (mAChR-ir) over the naive mice. A minor increase in mAChR-ir was found in the apical dendrites of the CA1 pyramidal cells. Pseudotraining resulted in a CA1-CA2 region with a low level of mAChR-ir, resembling naive animals, whereas the trained mice showed a further increase in mAChR-ir in the CA1-CA2 pyramidal cell bodies and apical dendrites. Optical density measures of the mAChR-ir in the CA1 region revealed a significant (P < 0.05) increase in the pyramidal cell bodies of the H and T group over the N and P group, and a significant (P < 0.05) increase in the apical dendrites of the T group over all other groups. In contrast to the CA1-CA2 region, both pseudotrained and trained mice revealed high mAChR staining in the CA3-CA4 region and the DG. These results indicate that prolonged exposure to the hole board is sufficient for an enhanced mAChR-ir in the CA3-CA4 and DG, whereas the increase in CA1-CA2 pyramidal cells is a training-specific feature related to spatial orientation. Nonpyramidal neurons within the CA1-CA2 region with enhanced mAChR-ir in the pyramidal cells, however, revealed a decreased level of mAChR-ir. The opposing effect of pyramidal and nonpyramidal cells suggests a shift in the excitability of the hippocampal microcircuitry. Previously we demonstrated an increase and redistribution of hippocampal protein kinase C gamma-immunoreactivity (PKC gamma-ir) induced by hole board learning in mice (Van der Zee et al., 1992, J Neurosci 12:4808-4815). Immunofluorescence double-labeling experiments conducted in the present study in naive and trained animals revealed that the principal cells and DG interneurons co-express mAChRs and PKC gamma, and that the immunoreactivity for both markers increased in relation to spatial orientation within these neurons. The mAChR-positive nonpyramidal cells of the CA1-CA2 region were devoid of PKC gamma and revealed an opposite training-induced effect. These results suggest that the postsynaptic changes in mAChR- and PKC gamma-ir reflect functional alterations of the hippocampal formation induced by spatial learning.

Reversed alterations of hippocampal parvalbumin and protein kinase C-gamma immunoreactivity after stroke in spontaneously hypertensive stroke-prone rats

BACKGROUND AND PURPOSE

Aging spontaneously hypertensive stroke-prone rats (SHR-SP) were previously shown to develop neocortical strokes. Because the hippocampal CA1 is selectively vulnerable to abnormal brain perfusion, the neuropathological effects of spontaneous strokes were investigated on specific neurochemical alterations in two major cell types of the hippocampal CA1 in SHR-SP.

METHODS

The immunoreactivity for the gamma-isoform of protein kinase C (in pyramidal cells) and parvalbumin (in interneurons) was determined in the hippocampal CA1 by applying monoclonal antibodies. Because chronic treatment with the calcium antagonist nimodipine prevents the development of strokes in SHR-SP, we compared SHR-SP (stroke) with age-matched nimodipine-treated rats (nonstroke).

RESULTS

After stroke in control animals, we observed a strikingly enhanced immunoreactivity for protein kinase C-gamma in CA1 pyramidal cells compared with nimodipine-treated rats, which can be interpreted as the result of an increased activation of these cells. The pathological increase of protein kinase C-gamma immunoreactivity was accompanied by a reduced parvalbuminergic innervation of these pyramidal cells in symptomatic SHR-SP.

CONCLUSIONS

Because parvalbumin is present in a subset of GABAergic inhibitory interneurons, these data suggest that increased activity of CA1 pyramidal cells after spontaneous stroke may partially be related to a decreased inhibitory input on these cells.