Somatostatin messenger RNA-containing neurons in Alzheimer's disease: an in situ hybridization study in hippocampus, parahippocampal cortex and frontal cortex

Anti-diabetic and neuroprotective effects of pancreatic islet transplantation into the central nervous system

During the last decades, the central nervous system (CNS) was intensively tested as a site for islet transplantation in different animal models of diabetes. Immunoprivilege properties of intracranial and intrathecal sites were found to delay and reduce rejection of transplanted allo-islets and xeno-islets, especially in the form of dispersed single cells. Insulin released from islets grafted in CNS was shown to cross the blood-brain barrier and to act as a regulator of peripheral glucose metabolism. In diabetic animals, sufficient nutrition and oxygen supply to islets grafted in the CNS provide adequate insulin response to increase glucose level resulting in rapid normoglycemia. In addition to insulin, pancreatic islets produce and secrete several other hormones, as well as neurotrophic and angiogenic factors with potential neuroprotective properties. Recent experimental studies and clinical trials provide a strong support for delivery of islet-derived macromolecules to CNS as a promising strategy to treat various brain disorders. This review article focuses mainly on analysis of current status of intracranial and intrathecal islet transplantations for treatment of experimental diabetes and discusses the possible neuroprotective properties of grafted islets into CNS as a novel therapeutic approach to brain disorders with cognitive dysfunctions characterized by impaired brain insulin signalling. Copyright © 2015 John Wiley & Sons, Ltd.

α-Melanocyte stimulating hormone prevents GABAergic neuronal loss and improves cognitive function in Alzheimer's disease

In Alzheimer's disease (AD), appropriate excitatory-inhibitory balance required for memory formation is impaired. Our objective was to elucidate deficits in the inhibitory GABAergic system in the TgCRND8 mouse model of AD to establish a link between GABAergic dysfunction and cognitive function. We sought to determine whether the neuroprotective peptide α-melanocyte stimulating hormone (α-MSH) attenuates GABAergic loss and thus improves cognition. TgCRND8 mice with established β-amyloid peptide pathology and nontransgenic littermates were treated with either α-MSH or vehicle via daily intraperitoneal injections for 28 d. TgCRND8 mice exhibited spatial memory deficits and altered anxiety that were rescued after α-MSH treatment. The expression of GABAergic marker glutamic acid decarboxylase 67 (GAD67) and the number of GABAergic GAD67+ interneurons expressing neuropeptide Y and somatostatin are reduced in the hippocampus in vehicle-treated TgCRND8 mice. In the septohippocampal pathway, GABAergic deficits are observed before cholinergic deficits, suggesting that GABAergic loss may underlie behavior deficits in vehicle-treated TgCRND8 mice. α-MSH preserves GAD67 expression and prevents loss of the somatostatin-expressing subtype of GABAergic GAD67+ inhibitory interneurons. Without decreasing β-amyloid peptide load in the brain, α-MSH improves spatial memory in TgCRND8 mice and prevents alterations in anxiety. α-MSH modulated the excitatory-inhibitory balance in the brain by restoring GABAergic inhibition and, as a result, improved cognition in TgCRND8 mice.

Neurochemical phenotype of cytoglobin-expressing neurons in the rat hippocampus

Cytoglobin (Cygb), a novel oxygen-binding protein, is expressed in the majority of tissues and has been proposed to function in nitric oxide (NO) metabolism in the vasculature and to have cytoprotective properties. However, the overall functions of Cygb remain elusive. Cygb is also expressed in a subpopulation of brain neurons. Recently, it has been shown that stress upregulates Cygb expression in the brain and the majority of neuronal nitric oxide synthase (nNOS)-positive neurons, an enzyme that produces NO, co-express Cygb. However, there are more neurons expressing Cygb than nNOS, thus a large number of Cygb neurons remain uncharacterized by the neurochemical content. The aim of the present study was to provide an additional and more detailed neurochemical phenotype of Cygb-expressing neurons in the rat hippocampus. The rat hippocampus was chosen due to the abundance of Cygb, as well as this limbic structure being an important target in a number of neurodegenerative diseases. Using triple immunohistochemistry, it was demonstrated that nearly all the parvalbumin- and heme oxygenase 1-positive neurons co-express Cygb and to a large extent, these neuron populations are distinct from the population of Cygb neurons co-expressing nNOS. Furthermore, it was shown that the majority of neurons expressing somastostatin and vasoactive intestinal peptide also co-express Cygb and nNOS. Detailed information regarding the neurochemical phenotype of Cygb neurons in the hippocampus can be a valuable tool in determining the function of Cygb in the brain.

Age-associated changes in hippocampal-dependent cognition in Diversity Outbred mice

Episodic memory impairment due to aging has been linked to hippocampal dysfunction. Evidence exists for alterations in specific circuits within the hippocampal system that are closely coupled to individual differences in the presence and severity of such memory loss. Here, we used the newly developed Diversity Outbred (DO) mouse that was designed to model the genetic diversity in human populations. Young and aged DO mice were tested in a hippocampal-dependent water maze task. Young mice showed higher proficiency and more robust memory compared to the overall performance of aged mice. A substantial number of the older mice, however, performed on par with the normative performance of the younger mice. Stereological quantification of somatostatin-immunoreactive neurons in the dentate hilus showed that high-performing young and unimpaired aged mice had similar numbers of somatostatin-positive interneurons, while aged mice that were impaired in the spatial task had significantly fewer such neurons. These data in the DO model tie loss of hilar inhibitory network integrity to age-related memory impairment, paralleling data in other rodent models.

Methylation analysis of SST and SSTR4 promoters in the neocortex of Alzheimer's disease patients

Several observations have pointed to a major pathogenic role of somatostatin depletion with respect to amyloid accumulation, which is often thought to be the crucial event in a cascade leading to Alzheimer's disease (AD). As methylation of CpG islands plays an important role in gene silencing, we studied the methylation status of the CpG islands in the promoters of somatostatin (SST) and in that of its receptor subtype in the cerebral cortex, SSTR4, in tissue samples from the middle temporal (Brodmann area 22) and superior frontal gyrus (Brodmann area 9) of 5 severely affected AD patients aged 72-94 years (Braak stages V-C or VI-C) and 5 non-demented controls aged 50-92 years. Bisulfite sequencing of DNA from cortical gray and infracortical white matter showed that the DNA methylation status at the promoters of SST and SSTR4 did not significantly differ between AD and control samples in any of the regions analyzed. We confirmed these results using deep bisulfite sequencing of PCR products from the SST promoter amplified from DNA from the cortical gray of the superior frontal gyrus of all AD patients and non-demented controls. We observed a trend toward increased DNA methylation with increasing age. In conclusion, deregulated somatostatin signaling in the AD cortices studied cannot be explained by hypermethylation of the SST or SSTR4 promoter CpG islands.

Reduced brain somatostatin in mood disorders: a common pathophysiological substrate and drug target?

Our knowledge of the pathophysiology of affect dysregulation has progressively increased, but the pharmacological treatments remain inadequate. Here, we summarize the current literature on deficits in somatostatin, an inhibitory modulatory neuropeptide, in major depression and other neurological disorders that also include mood disturbances. We focus on direct evidence in the human postmortem brain, and review rodent genetic and pharmacological studies probing the role of the somatostatin system in relation to mood. We also briefly go over pharmacological developments targeting the somatostatin system in peripheral organs and discuss the challenges of targeting the brain somatostatin system. Finally, the fact that somatostatin deficits are frequently observed across neurological disorders suggests a selective cellular vulnerability of somatostatin-expressing neurons. Potential cell intrinsic factors mediating those changes are discussed, including nitric oxide induced oxidative stress, mitochondrial dysfunction, high inflammatory response, high demand for neurotrophic environment, and overall aging processes. Together, based on the co-localization of somatostatin with gamma-aminobutyric acid (GABA), its presence in dendritic-targeting GABA neuron subtypes, and its temporal-specific function, we discuss the possibility that deficits in somatostatin play a central role in cortical local inhibitory circuit deficits leading to abnormal corticolimbic network activity and clinical mood symptoms across neurological disorders.

New insights into brain BDNF function in normal aging and Alzheimer disease

The decline observed during aging involves multiple factors that influence several systems. It is the case for learning and memory processes which are severely reduced with aging. It is admitted that these cognitive effects result from impaired neuronal plasticity, which is altered in normal aging but mainly in Alzheimer disease. Neurotrophins and their receptors, notably BDNF, are expressed in brain areas exhibiting a high degree of plasticity (i.e. the hippocampus, cerebral cortex) and are considered as genuine molecular mediators of functional and morphological synaptic plasticity. Modification of BDNF and/or the expression of its receptors (TrkB.FL, TrkB.T1 and TrkB.T2) have been described during normal aging and Alzheimer disease. Interestingly, recent findings show that some physiologic or pathologic age-associated changes in the central nervous system could be offset by administration of exogenous BDNF and/or by stimulating its receptor expression. These molecules may thus represent a physiological reserve which could determine physiological or pathological aging. These data suggest that boosting the expression or activity of these endogenous protective systems may be a promising therapeutic alternative to enhance healthy aging.

Protective effect of BDNF against beta-amyloid induced neurotoxicity in vitro and in vivo in rats

We examined the potential protective effect of BDNF against beta-amyloid-induced neurotoxicity in vitro and in vivo in rats. In neuronal cultures, BDNF had specific and dose-response protective effects on neuronal toxicity induced by Abeta(1-42) and Abeta(25-35). It completely reversed the toxic action induced by Abeta(1-42) and partially that induced by Abeta(25-35). These effects involved TrkB receptor activation since they were inhibited by K252a. Catalytic BDNF receptors (TrkB.FL) were localized in vitro in cortical neurons (mRNA and protein). In in vivo experiments, Abeta(25-35) was administered into the indusium griseum or the third ventricle and several parameters were measured 7 days later to evaluate potential Abeta(25-35)/BDNF interactions, i.e. local measurement of BDNF release, number of hippocampal hilar cells expressing SRIH mRNA and assessment of the corpus callosum damage (morphological examination, pyknotic nuclei counting and axon labeling with anti-MBP antibody). We conclude that BDNF possesses neuroprotective properties against toxic effects of Abeta peptides.

Twenty-first century brain banking. Processing brains for research: the Columbia University methods

Carefully categorized postmortem human brains are crucial for research. The lack of generally accepted methods for processing human postmortem brains for research persists. Thus, brain banking is essential; however, it cannot be achieved at the cost of the teaching mission of the academic institution by routing brains away from residency programs, particularly when the autopsy rate is steadily decreasing. A consensus must be reached whereby a brain can be utilizable for diagnosis, research, and teaching. The best diagnostic categorization possible must be secured and the yield of samples for basic investigation maximized. This report focuses on integrated, novel methods currently applied at the New York Brain Bank, Columbia University, New York, which are designed to reach accurate neuropathological diagnosis, optimize the yield of samples, and process fresh-frozen samples suitable for a wide range of modern investigations. The brains donated for research are processed as soon as possible after death. The prosector must have a good command of the neuroanatomy, neuropathology, and the protocol. One half of each brain is immersed in formalin for performing the thorough neuropathologic evaluation, which is combined with the teaching task. The contralateral half is extensively dissected at the fresh state. The anatomical origin of each sample is recorded using the map of Brodmann for the cortical samples. The samples are frozen at -160 degrees C, barcode labeled, and ready for immediate disbursement once categorized diagnostically. A rigorous organization of freezer space, coupled to an electronic tracking system with its attached software, fosters efficient access for retrieval within minutes of any specific frozen samples in storage. This report describes how this achievement is feasible with emphasis on the actual processing of brains donated for research.

Implications of age and diet on canine cerebral cortex transcription

Mechanisms contributing to age-related cognitive decline are poorly defined. Thus, we used canine microarrays to compare gene expression profiles of brain tissue from geriatric and young adult dogs. Cerebral cortex samples were collected from six geriatric (12-year old) and six young adult (1-year old) female beagles after being fed one of two diets (animal protein-based versus plant-protein based) for 12 months. RNA samples were hybridized to Affymetrix GeneChip Canine Genome Arrays. Statistical analyses indicated that the age had the greatest impact on gene expression, with 963 transcripts differentially expressed in geriatric dogs. Although not as robust as age, diet affected mRNA abundance of 140 transcripts. As demonstrated in aged rodents and humans, geriatric dogs had increased expression of genes associated with inflammation, stress response, and calcium homeostasis and decreased expression of genes associated with neuropeptide signaling and synaptic transmission. In addition to its existing strengths, availability of gene sequence information and commercial microarrays make the canine a powerful model for studying the effects of aging on cognitive function.

Alterations in GABA-related transcriptome in the dorsolateral prefrontal cortex of subjects with schizophrenia

In subjects with schizophrenia, impairments in working memory are associated with dysfunction of the dorsolateral prefrontal cortex (DLPFC). This dysfunction appears to be due, at least in part, to abnormalities in gamma-aminobutyric acid (GABA)-mediated inhibitory circuitry. To test the hypothesis that altered GABA-mediated circuitry in the DLPFC of subjects with schizophrenia reflects expression changes of genes that encode selective presynaptic and postsynaptic components of GABA neurotransmission, we conducted a systematic expression analysis of GABA-related transcripts in the DLPFC of 14 pairs of schizophrenia and age-, sex- and post-mortem interval-matched control subjects using a customized DNA microarray with enhanced sensitivity and specificity. Subjects with schizophrenia exhibited expression deficits in GABA-related transcripts encoding (1) presynaptic regulators of GABA neurotransmission (67 kDa isoform of glutamic acid decarboxylase (GAD(67)) and GABA transporter 1), (2) neuropeptides (somatostatin (SST), neuropeptide Y (NPY) and cholecystokinin (CCK)) and (3) GABA(A) receptor subunits (alpha1, alpha4, beta3, gamma2 and delta). Real-time qPCR and/or in situ hybridization confirmed the deficits for six representative transcripts tested in the same pairs and in an extended cohort, respectively. In contrast, GAD(67), SST and alpha1 subunit mRNA levels, as assessed by in situ hybridization, were not altered in the DLPFC of monkeys chronically exposed to antipsychotic medications. These findings suggest that schizophrenia is associated with alterations in inhibitory inputs from SST/NPY-containing and CCK-containing subpopulations of GABA neurons and in the signaling via certain GABA(A) receptors that mediate synaptic (phasic) or extrasynaptic (tonic) inhibition. In concert with previous findings, these data suggest that working memory dysfunction in schizophrenia is mediated by altered GABA neurotransmission in certain DLPFC microcircuits.

Anatomical localization and regulation of somatostatin gene expression in the basal ganglia and its clinical implications

The distribution of somatostatin in both the human and rat brain suggests that it is involved in numerous functions, including endocrine regulation, cognition and memory, autonomic regulation and motor activity. We have examined the regulation of somatostatin mRNA in the striatum, a brain region involved in motor and cognitive behaviour. Somatostatin and its mRNA are expressed in this region in interneurons which are resistant to ischaemia, excitotoxicity and Huntington's disease, possibly because they express high levels of superoxide dismutase. Striatal somatostatin mRNA is increased by stimulation of NMDA (N-methyl-D-aspartate) receptors. Ischaemia-induced cortical lesions also increase somatostatin gene expression in the striatum. In contrast, the levels of striatal somatostatin mRNA decrease after treatment with haloperidol, an antipsychotic agent that produces extrapyramidal symptoms, but not clozapine, which does not. Further evidence for a role for striatal somatostatin in extrapyramidal symptoms includes the observation that somatostatin mRNA levels decrease in the striatum after lesions are made in the dopaminergic pathway, a feature of Parkinson's disease. The largest change in somatostatin gene expression after dopaminergic lesions is the increase in somatostatin mRNA level sin neurons of the internal pallidum and lateral hypothalamus projecting to the lateral habenula. The results suggest that changes in brain somatostatin gene expression occur in pathological conditions and may be related to their symptoms.

Involvement of somatostatin receptor subtypes in membrane ion channel modification by somatostatin in pituitary somatotropes

1. Growth hormone (GH) secretion from pituitary somatotropes is mainly regulated by two hypothalamic hormones, GH-releasing hormone (GHRH) and somatotrophin releasing inhibitory factor (SRIF). 2. Somatotrophin releasing inhibitory factor inhibits GH secretion via activation of specific membrane receptors, somatostatin receptors (SSTRs) and signalling transduction systems in somatotropes. 3. Five subtypes of SSTRs, namely SSTR1, 2, 3, 4 and 5, have been identified, with the SSTR2 subtype divided into SSTR2A and SSTR2B. All SSTRs are G-protein-coupled receptors. 4. Voltage-gated Ca(2+) and K(+) channels on the somatotrope membrane play an important role in regulating GH secretion and SRIF modifies both channels to reduce intracellular free Ca(2+) concentration and GH secretion. 5. Using specific SSTR subtype-specific agonists, it has been found that reduction in Ca(2+) currents by SRIF is mediated by SSTR2 and an increase in K(+) currents is mediated by both SSTR2 and SSTR4 in rat somatotropes.

17β-Estradiol protects depletion of rat temporal cortex somatostatinergic system by β-amyloid

Estradiol prevents amyloid-beta peptide (Abeta)-induced cell death through estrogen receptors (ERs) and modulates somatostatin (SRIF) responsiveness in the rat brain. As intracerebroventricular (ICV) Abeta25-35 administration reduces SRIFergic tone in the temporal cortex of ovariectomized (Ovx) rats, we asked whether 17beta-estradiol (E2) treatment can restore the Abeta25-35 induced changes in SRIF content, SRIF receptor density and adenylyl cyclase (AC) activity, as well as if these effects are mediated by ERs. E2 treatment did not change Abeta25-35 levels in the temporal cortex, but partially restored the SRIFergic parameters affected by Abeta insult and decreased cell death, which was correlated with Akt activation. The ER antagonist ICI 182,780 prevented the protective effect of E2 on sst2 levels, but did not modify SRIF levels. Furthermore, ICI 182,780 treatment further decreased sst2 protein and mRNA levels when administered alone to Abeta25-35-treated rats, suggesting that it may block the effects of endogenous estrogens. These findings indicate that E2 protects the temporal cortical SRIFergic system from Abeta-induced depletion independently of Abeta accumulation.

β-Amyloid increases somatostatin expression in cultured cortical neurons

In beta-amyloid (Abeta)-induced neurotoxicity, activation of the NMDA receptor, increased Ca2+ and oxidative stress are intimately associated with neuronal cell death as normally seen in NMDA-induced neurotoxicity. We have recently shown selective sparing of somatostatin (SST)-positive neurons and increased SST expression in NMDA agonist-induced neurotoxicity. Accordingly, the present study was undertaken to determine the effect of Abeta25-35-induced neurotoxicity on the expression of SST in cultured cortical neurons. Cultured cortical cells were exposed to Abeta25-35 and processed to determine the cellular content and release of SST into medium by radioimmunoassay and SST mRNA by RT-PCR. Abeta25-35 induces neuronal cell death in a concentration- and time-dependent fashion, increases SST mRNA synthesis and induces an augmentation in the cellular content of SST. No significant changes were seen on SST release at any concentration of Abeta25-35 after 24 h of treatment. However, Abeta25-35 induces a significant increase of SST release into medium only after 12 h in comparison with other time points. Most significantly, SST-positive neurons are selectively spared in the presence of a lower concentration of Abeta25-35, whereas, in the presence of higher concentrations of Abeta25-35 for extended time periods, SST-positive neurons decrease gradually. Furthermore, Abeta25-35 induces apoptosis at lower concentrations (5 and 10 micromol/L) and necrosis at higher concentrations (20 and 40 micromol/L). Consistent with the increased accumulation of SST, these data suggest that Abeta25-35 impairs cell membrane permeability. Selective sparing of SST-positive neurons at lower concentrations of Abeta25-35 at early time points directly correlates with the pathophysiology of Alzheimer's disease.

Somatostatin in the dentate gyrus

The neuropeptide somatostatin (SST) is expressed in a discrete population of interneurons in the dentate gyrus. These interneurons have their soma in the hilus and project to the outer molecular layer onto dendrites of dentate granule cells, adjacent to perforant path input. SST-containing interneurons are very sensitive to excitotoxicty, and thus are vulnerable to a variety of neurological diseases and insults, including epilepsy, Alzheimer's disease, traumatic brain injury, and ischemia. The SST gene contains a prototypical cyclic AMP response element (CRE) site. Such a regulatory site confers activity-dependence to the gene, such that it is turned on when neuronal activity is high. Thus SST expression is increased by pathological conditions such as seizures and by natural stimulation such as environmental enrichment. SST may play an important role in cognition by modulating the response of neurons to synaptic input. In the dentate, SST and the related peptide cortistatin (CST) reduce the likelihood of generating long-term potentiation, a cellular process involved in learning and memory. Thus these neuropeptides would increase the threshold of input required for acquisition of new memories, increasing "signal to noise" to filter out irrelevant environmental cues. The major mechanism through which SST inhibits LTP is likely through inhibition of voltage-gated Ca(2+) channels on dentate granule cell dendrites. Transgenic overexpression of CST in the dentate leads to profound deficits in spatial learning and memory, validating its role in cognitive processing. A reduction of synaptic potentiation by SST and CST in dentate may also contribute to the well-characterized antiepileptic properties of these neuropeptides. Thus SST and CST are important neuromodulators in the dentate gyrus, and disruption of this signaling system may have major impact on hippocampal function.

Effects of single and continuous administration of amyloid beta-peptide (25-35) on adenylyl cyclase activity and the somatostatinergic system in the rat frontal and parietal cortex

It is unknown whether the amyloid beta-peptide (Abeta), a principal component found in extracellular neuritic plaques in the brain of patients with Alzheimer's disease (AD), is capable of altering adenylyl cyclase (AC) activity and the somatostatin (SRIF) receptor-effector system in the cerebral cortex of the patients. Therefore, the objective of this study was to investigate the effect of the beta fragment, beta (25-35), on AC activity and the somatostatinergic system in the rat frontoparietal cortex. A single dose of beta (25-35) (10microg) injected intracerebroventricularly significantly decreased the density of SRIF receptors (27.4%) and increased their affinity (32.2%) in the frontoparietal cortex. The inhibitory effect of SRIF on basal and forskolin (FK)-stimulated AC activity was significantly lower in the beta (25-35)-treated rats when compared with controls. beta (25-35) did not modify Gialpha1, Gialpha2 nor Gialpha3 levels in membranes from the frontoparietal cortex. Continuous infusion of the peptide induced a decrease in the SRIF receptor density in this brain area to a similar extent as that observed 14 days after the single administration of the peptide. Likewise, this treatment decreased the SRIF receptor density in the frontal cortex (15.3%) and parietal cortex (27.2%). This effect was accompanied by a decrease in the SRIF-mediated inhibition of FK-stimulated AC activity (from 41.6% to 25.6%) in the frontal cortex as well by a decrease in basal AC activity (from 36.9% to 31.6%) and FK-stimulated AC activity (from 35.6% to 27.1%) in the parietal cortex. Continuous infusion of Abeta (25-35) had no effect on Gialpha1, Gialpha2 or Gialpha3 levels in membranes from frontal and parietal cortex. However, this treatment caused a decrease in SRIF-like immunoreactivity content in the parietal (38.9%) and frontal (20.4%) cortex. These results suggest that Abeta might be involved in the alterations of somatostatinergic system reported in AD.

Protective effects of insulin-like growth factor-I on the somatostatinergic system in the temporal cortex of beta-amyloid-treated rats

Insulin-like growth factor-I (IGF-I) has protective effects against beta-amyloid (Abeta)-induced neuronal cell death. Because alterations of the somatostatinergic system have been described in Alzheimer's disease, we investigated the effects of the Abeta peptide and the possible protective role of IGF-I on the somatostatinergic system of the rat temporal cortex and on cell death and phosphorylated (p)-Akt levels in this area. Abeta25-35 was administered intracerebroventricularly to male rats via an osmotic minipump over 14 days (300 pmol/day). Another group received a subcutaneous IGF-I infusion (50 microg/kg/day), concomitant with Abeta25-35 administration, whereas a third group received IGF-I alone. Abeta25-35 significantly decreased the somatostatin (SRIF)-like immunoreactive content and the SRIF receptor density, as a result of a decrease in the levels of the SRIF receptor subtype 2. The inhibitory effect of SRIF on adenylyl cyclase activity was significantly lower after Abeta25-35 infusion, whereas the levels of the inhibitory G protein subunit Gialpha1, Gialpha2 or Gialpha3 were unaltered. Cell death was increased and p-Akt levels decreased in Abeta25-35-treated animals. IGF-I administration increased immunoreactive IGF-I levels in the temporal cortex and restored all parameters affected by Abeta25-35 to baseline values. These findings suggest that IGF-I prevents the deleterious effect of Abeta25-35 on the somatostatinergic system.

Changes in the levels of neuropeptides and their metabolizing enzymes in the brain regions of nucleus basalis magnocellularis-lesioned rats

The regulation mechanism of the interrelation between neuropeptides and their metabolizing enzymes in in vivo tissues is still not clear. In the present report, we attempted to measure the levels of neuropeptides and their enzymes in the frontal cortex, hippocampus, and striatum of the rat that had been bilaterally lesioned by the infusion of ibotenic acid or amyloid beta-peptide 25 - 35 (Abeta25 - 35) into the nucleus basalis magnocellularis. In the drug-treated rats, at two weeks after the infusion, the decrease of somatostatin-like immunoreactivity (SS-LI) and the increase of cholecystokinin-8S-LI were found in some brain regions relative to vehicle-treated rats. The immunoreactivities of endopeptidase 24.15 and puromycin-sensitive aminopeptidase and the leucine aminopeptidase- and aminopeptidase B-like enzyme activities did not change in the three brain regions, suggesting that the levels of those peptide-degrading enzymes do not correlate with the changes of the neuropeptide levels. The decrease of subtilisin-like proprotein convertase (SPC)-like enzyme activity was found in the hippocampus of the Abeta25 - 35-treated rats. The SS mRNA level decreased in the hippocampus in parallel with decreases in the SS-LI level and SPC-like enzyme activity. The present data indicate that some of the neuropeptide-processing enzymes may contribute to the control of neuropeptide levels.

Cellular biology of somatostatin receptors

Somatostatin, and the recently discovered neuropeptide cortistatin, exert their physiological actions via a family of six G protein-coupled receptors (sst1, sst2A, sst2B, sst3, sst4, sst5). Following the cloning of somatostatin receptors significant advances have been made in our understanding of their molecular, pharmacological and signaling properties although much progress remains to be done to define their physiological role in vivo. In this review, the present knowledge regarding neuroanatomical localization, signal transduction pathways, desensitization and internalization properties of somatostatin receptors is summarized. Evidence that somatostatin receptors can form homo- and heterodimers and can physically interact with members of the SSTRIP/Shank/ProSAP1/CortBP1 family is also discussed.

Alterations in bcl-2 and caspase gene family protein expression in human temporal lobe epilepsy

OBJECTIVE

To address the role of cell death regulatory genes of the bcl-2 and caspase families in the neuropathology of human epilepsy using tissue extracted from patients undergoing temporal lobectomy for intractable seizures.

METHODS

Using Western blotting and immunohistochemistry, the authors investigated the expression of bcl-2, bcl-xL, bax, caspase-1,and caspase-3 in temporal cortex samples from patients who had undergone temporal lobectomy surgery for intractable epilepsy (n = 19). Nonepileptic postmortem tissue from a brain bank served as control (n = 6).

RESULTS

Western blot analysis demonstrated significant increases in levels of bcl-2 and bcl-xL protein in seizure brain compared to control. Cleavage of caspase-1 was evidenced by a reduction in levels of the 45 kDa proenzyme form and an increase in levels of the p10 fragment. Levels of the 32 kDa proenzyme form of caspase-3 were elevated in seizure patients, as were levels of the 12 kDa cleaved fragment. Bcl-2, bax, and caspase-3 immunoreactivity was increased predominantly in cells with the morphologic appearance of neurons, whereas bcl-xL immunoreactivity was increased in cells with the appearance of glia. DNA fragmentation was detected in some but not all sections from epileptic brain samples.

CONCLUSIONS

Cell death regulatory genes of the bcl-2 and caspase families may play a role in ongoing neuropathologic processes in human epilepsy, and offer novel targets as an adjunct to anticonvulsant therapy.

Early histological maturation in the hippocampus of the guinea pig

The vesicular zinc-rich synaptic systems of the principal neurons of the hippocampus are well developed in newborn guinea pigs, a precocial species. In addition, alvear and fimbrial myelinated fibers as well as significant inhibitory interneurons (i.e. somatostatin, parvalbumin and opioid immunoreactive hippocampal interneurons) are also well developed. On the contrary, neither vesicular zinc synapses nor myelinated fibers nor the above mentioned immunoreactive interneurons are detectable in newborn specimens of other related altricial species such as rats or rabbits. These data suggest that early maturation of a highly integrative center related to cognitive map building such as the hippocampus is characteristic of precocial species.

Immunohistochemical estimation of rat brain somatostatin on avoidance learning impairment induced by thiamine deficiency

In rats, on the 25th day after the start of a thiamine-deficient (TD) diet, impairment of avoidance learning was significantly induced in proportion to the decrease somatostatin (SST) fluorescence intensity in the cortex, amygdala, thalamus, hypothalamus, and hippocampus, including the CA1, CA2, and dentate gyrus (DG). Only a single injection of thiamine HCl (0.5 mg/rat, subcutaneous) on the 14th day after the start of a TD diet improved the amnesia to the level of the pair-fed control and prevented the decrease in the SST level. Whereas these reversal effects of thiamine treatment were not found when the treatment was given on the 21st day after the start of a TD diet. These results indicate that, after a certain degree of thiamine deficiency, TD-induced behavioral effects might be reversible, but some neuronal fibers might be irreversibly damaged, probably due to the reduction of thiamine-dependent enzymes in brain mitochondria. The results also suggest the possibility that SST in the brain may be closely related to the avoidance learning impairment induced by TD.

Aberrant presenilin-1 expression downregulates LDL receptor-related protein (LRP): is LRP central to Alzheimer's disease pathogenesis?

Low density lipoprotein receptor-related protein (LRP) polymorphisms have recently been associated with an increased susceptibility of Alzheimer's disease (AD). Furthermore, LRP has been linked to molecules that confer susceptibility to AD (apolipoprotein E, alpha-2-macroglobulin, amyloid precursor protein), previously with the exception of the presenilins. Here we report that aberrant presenilin-1 expression in vivo and in vitro downregulates LRP. Specifically, transgenic mice overexpressing the M146L or L286V presenilin-1 mutation show decreased levels of LRP expression in neuronal populations where presenilin-1 and LRP are closely colocalized or coexpressed. Moreover, cell lines transfected with presenilin-1 also expressed decreased levels of LRP. These findings suggest that LRP may be central to AD pathogenesis since all proteins genetically associated with AD can now be linked via a single pathway to LRP.

A novel role for receptor-associated protein in somatostatin modulation: implications for Alzheimer's disease

Receptor-associated protein appears to play an important role in low-density lipoprotein receptor-related protein trafficking. Since ligands for the low-density lipoprotein receptor-related protein have been implicated in Alzheimer's disease and normal functioning of this protein is indispensable for central nervous system development, deficient receptor-associated protein expression may result in central nervous system alterations. In this study, receptor-associated protein knockout mice were behaviorally tested and nervous system integrity was assessed via in situ hybridization and immunocytochemical/laser confocal microscopy methods. Receptor-associated protein knockout mice were found to be cognitively impaired in the Morris water maze compared to controls. In wild-type mice, the receptor-associated protein was found to be highly co-expressed with somatostatin in hippocampal and neocortical inhibitory neurons. Receptor-associated protein knockout mice, however, showed a significant decrease in number of somatostatin-expressing neurons of the CA1 region and somatostatin expression within these neurons. The decreased number of somatostatin neurons significantly correlated with cognitive impairment observed in the receptor-associated protein knockout mice. These results suggest a novel role for receptor-associated protein in modulating the functioning of somatostatin-producing neurons. Furthermore, this has implications for Alzheimer's disease pathogenesis, in which altered regulation of both somatostatin and the known low-density lipoprotein receptor-related protein ligands are a consistent finding.

Loss of somatostatin-like immunoreactivity in the frontal cortex of Alzheimer patients carrying the apolipoprotein epsilon 4 allele

We measured somatostatin-like immunoreactivity, using a radioimmunoassay which does not cross react with cortistatin-like immunoreactivity, in postmortem frontal cortex (Brodmann area 9) from 32 patients, of different apolipoprotein E genotypes, and presenting with different degrees of cognitive impairment. Eleven subjects and eight patients presented with no (controls) or limited memory impairments (Borderline), respectively. Six patients with clinical criteria for possible Alzheimer's disease also presented with clinical or brain imaging of cerebrovascular disease (mixed dementia) and seven patients were classified as Alzheimer's disease (AD). In the 6 months preceeding their deaths, all subjects had been evaluated by Folstein's Mini Mental State examination (MMS). Sixty nine percent of patients with MMS >20 did not carry the epsilon 4 allele while 66% of patients with MMS <10 did. Somatostatin concentrations (ng/mg wet weight) were significantly lower in the patients carrying the epsilon 4 allele (E2/3: 0.71 +/- 0.05, n = 19 vs. E4: 0.42 +/- 0.06, n = 13; mean +/- SEM, P < 0.001). These results, which are reminiscent of those obtained on cholinergic markers, suggest that apolipoprotein E4 is involved in the somatostatinergic dysfunction early after the onset in AD.

Altered hippocampal kainate-receptor mRNA levels in temporal lobe epilepsy patients

This study determined whether hippocampal kainate (KA) receptor mRNA levels were increased or decreased in temporal lobe epilepsy patients compared with nonseizure autopsies. Hippocampal sclerosis (HS; n = 17), nonsclerosis (non-HS; n = 11), and autopsy hippocampi (n = 9) were studied for KA1-2 and GluR5-7 mRNA levels using semiquantitative in situ hybridization techniques, along with neuron densities. Compared with autopsy hippocampi, HS and non-HS cases showed decreased GluR5 and GluR6 hybridization densities per CA2 and/or CA3 pyramid. Furthermore, HS patients demonstrated increased KA2 and GluR5 hybridization densities per granule cell compared with autopsy hippocampi. These findings indicate that chronic temporal lobe seizures were associated with differential changes in hippocampal KA1-2 and GluR5-7 hybridization densities that vary by subfield and pathology group. In temporal lobe epilepsy patients, these results support the hypothesis that pyramidal cell GluR5 and GluR6 mRNA levels are decreased as a consequence of seizures, and in HS patients granule cell KA2 and GluR5 mRNA levels are increased in association with aberrant fascia dentata mossy fiber sprouting and/or hippocampal neuronal loss.

Selective increase in somatostatin mRNA expression in human basal ganglia in Parkinson's disease

Levels of the neurotransmitter somatostatin (SS) have previously been shown to be reduced in the cortex and hippocampus of demented parkinsonian patients and patients with Alzheimer's disease. In situ hybridisation histochemistry (ISHH) was performed with an 35S tail-labelled oligonucleotide DNA probe to human SS mRNA, to examine its expression within the striatum, medial medullary lamina (MML) and reticular thalamic nucleus in Parkinson's disease (PD) and in matched controls. A chronic unilaterally MPTP-lesioned L-DOPA-naive primate model was also examined for comparison of SS mRNA expression with that in human L-DOPA treated PD subjects. Quantitation of SS mRNA expression on emulsion dipped sections revealed a significant increase (82%) in the MML of the globus pallidus in PD (56.5 microm2 of silver grain/cell, n = 9 cases) compared to controls (26.3 microm2/cell, n = 13 cases, p < 0.01, Student's t-test), paralleling the increase previously observed by this group for NOS mRNA. SS mRNA expression was higher in the dorsolateral than ventromedial putamen in controls (p < 0.001; DL: 24.89 +/- SEM 1.35; VM: 17.96 +/- SEM 2.63; n = 14) but this gradient was lost in PD cases (p > 0.05; DL: 22.68 +/- 1.94; VM: 22.17 +/- 2.94; n = 10). These findings suggest specific modification of basal ganglia SS-ergic pathways in PD.

Molecular forms of somatostatin-like immunoreactivity in the cerebrospinal fluid of patients with senile dementia of the Alzheimer type

In the cerebrospinal fluid (CSF) of 53 patients with senile dementia of the Alzheimer type (SDAT) and 12 elderly controls, we measured somatostatin (SLI) and its molecular forms: high-molecular weight form (HMV-SST), somatostatin-14 (SST-14), somatostatin-25/28 (SST-28/25), and des-ala-somatostatin (des-ala-SST) using high pressure liquid chromatography (HPLC) and a radioimmunoassay. In SDAT, SLI was significantly decreased (p < 0.05) and correlated with dementia scores (r = -0.65, p < 0.05). HPLC separation showed a marked heterogeneity of SLI in the CSF with a preponderance of SST-14 and SST-25/28. The significant loss of SST-14 (p < 0.05) in SDAT was found to be correlated with dementia scores (r = 0.65). Moreover, qualitative and quantitative changes in the molecular pattern of SLI in SDAT indicated dysregulated synthesis and/or processing of somatostatin relating to the severity of dementia. The long-term administration of neuroleptics in severe cases of SDAT caused a significant increase of SLI (p < 0.05) and influenced the ratio of HMV-SST/SST-14 and SST25/28/SST-14.

Somatostatin and brain-derived neurotrophic factor mRNA expression in the primate brain: decreased levels of mRNAs during aging

The expression of the genes for somatostatin (SRIF) and brain-derived neurotrophic factor (BDNF) was investigated in the central nervous system (CNS) of the macaque monkey (Macaca fuscata fuscata). Using Northern blot analysis, one SRIF mRNA transcript, 0.65 kb, and two BDNF mRNA transcripts, 1.6 and 4.0 kb in length, were detected in the monkey brain tissues. During the aging process (2 years, 10 years, and > 30 years), the ratio of SRIF mRNA/glyceraldehyde-3 phosphate dehydrogenase (G3PDH) mRNA significantly decreased (60-70%) in the hippocampus and in several cerebral subdivisions such as frontal cortex, temporal cortex, motor cortex, somatosensory cortex and visual cortex. BDNF mRNA was expressed in the various cerebral subdivisions and in the hippocampus. During the aging process, the gene expression of BDNF declined (20-50% for the 4.0 kb transcript, and 40-70% for the 1.6 kb transcript) in the various cerebral subdivisions. In the hippocampus, the level of the 1.6 kb mRNA at > 30 years old declined to 60% of the level at 2 years old, while the 4.0 kb mRNA did not change significantly during the aging process. Recent studies have shown that BDNF enhances the expression of SRIF mRNA in the rodent cerebral cortex (Nawa, H. et al., J. Neurochem., 60 (1993) 772-775; Nawa, H. et al., J. Neurosci., 14 (1994) 3751-3765). These studies and our present results suggest that the decrease in gene expression for a neurotrophic molecule, such as BDNF, might cause the levels of SRIF mRNA to decline in the primate brain during the aging process.

Immunohistochemical localization of the somatostatin SST2(A) receptor in the rat brain and spinal cord

The neuropeptide somatostatin is widely distributed in the CNS and is believed to play a role as a neurotransmitter or a neuromodulator. Somatostatin mediates its actions by the binding of the peptide to high affinity membrane receptors. The genes for five somatostatin receptor types have been cloned recently and Northern blotting and in situ hybridization studies have shown that the transcripts of all five types are expressed in the CNS. Here we report the cellular distribution of somatostatin sst2(a) receptor protein in the adult rat CNS, using a polyclonal anti-peptide antibody directed against a portion of the C-terminal domain of the receptor. The specificity of the affinity-purified antibody was demonstrated by Western blotting and immunolabelling of cells transfected with a hemagglutinin epitope-tagged version of the sst2(a) receptor. Immunohistochemistry showed a distinct distribution of the receptor protein in the rat brain. Cells and processes were labelled in a number of areas, including the basolateral amygdala, the locus coeruleus, the endopiriform nucleus, the deep layers of the cerebral cortex, the subiculum, the claustrum, the habenula, the interpenduncular nucleus, the hippocampus and the central grey. In the spinal cord, the substantia gelatinosa showed strongly-labelled cell bodies and their processes. This study provides an improved understanding of the distribution of the sst2(a) receptor in rat brain.

Granule cell mRNA levels for BDNF, NGF, and NT-3 correlate with neuron losses or supragranular mossy fiber sprouting in the chronically damaged and epileptic human hippocampus

This study determined in temporal lobe epilepsy patients if there were correlations among hippocampal granule cell expression of neurotrophin mRNAs, aberrant supragranular mossy fiber sprouting, and neuron losses. Consecutive surgically resected hippocampi (n = 9) and comparison tissue from autopsies (n = 3) were studied for: 1. Granule cell mRNA levels using in situ hybridization for brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), and neurotrophin-3 (NT-3); 2. neo-Timm supragranular mossy fiber sprouting; and 3. Ammon's horn neuron densities. Clinically, patients were classified into those with hippocampal sclerosis (HS; n = 7) and non-HS cases (i.e., mass lesions and autopsies; n = 5). Results showed that compared to non-HS cases, HS patients showed increased granule cell mRNA levels for BDNF, NGF, and NT-3 (p = 0.035, p = 0.04, p = 0.045 respectively; one-tail directional test). Moreover, granule cell BDNF mRNA levels correlated inversely with Ammon's horn neuron densities (p = 0.02) and correlated positively with greater supragranular mossy fiber sprouting (p = 0.02). NGF mRNA levels correlated inversely with Ammon's horn neuron densities (p = 0.02), and NT-3 mRNA levels correlated inversely with age at surgery (p = 0.04) and correlated positively with greater mossy fiber sprouting (p = 0.026). These results indicate in the chronically damaged human hippocampus that granule cells express neurotrophin mRNAs, and mRNA levels correlate with either hippocampal neuron losses or aberrant supragranular mossy fiber sprouting. These data support the hypothesis that in the epileptic human hippocampus, there may be pathophysiologic associations among mossy fiber synaptic plasticity, hippocampal neuron damage, and granule cell mRNA neurotrophin levels.

Neuronal nitric oxide synthase (nNOS) mRNA expression and NADPH-diaphorase staining in the frontal cortex, visual cortex and hippocampus of control and Alzheimer's disease brains

Neuronal nitric oxide synthase (nNOS) mRNA levels and NADPH diaphorase (NADPH-d) staining were compared in the frontal cortex, visual cortex and hippocampus (dentate gyrus and CA subfields of Ammon's horn) of five Alzheimer's disease (AD) and six control brains. The cellular abundance of nNOS mRNA was quantified by in-situ hybridisation using 35S-labelled antisense oligonucleotides complementary to the human nNOS sequence. Although the mean level of nNOS expression was decreased in all three regions in AD cases as compared to controls, it did not reach significance. Neurones positively labelled for nNOS mRNA and neurones positive for NADPH-d histochemistry displayed similar distribution in control and AD cases. In AD brains the density of neurones having detectable levels of nNOS mRNA was significantly decreased in the white matter underlying the frontal cortex (P < 0.05) but not in the frontal cortex gray matter; no change was observed in the gray or white matter of the visual cortex in AD. The number of cells expressing detectable levels of nNOS mRNA in the hippocampus was also significantly decreased (P < 0.05) in AD. The density of NADPH-d-positive cells was not significantly decreased in the gray or white matter of the frontal or visual cortices in AD compared to controls; however, the number of NADPH-d-positive cells was significantly decreased in the hippocampus (P < 0.01). These data indicate that although the cellular abundance of nNOS mRNA is not significantly decreased in these three regions in AD, there is a significant decrease in the number of cells expressing detectable levels of nNOS mRNA in the white matter underlying the frontal cortex and in the dentate gyrus and CA subfields of the hippocampus in AD. Furthermore, there was also a significant decrease in the number of NADPH-d-positive cells in the dentate gyrus and CA subfields of the hippocampus in AD as compared to controls. These results suggest specific populations of nNOS/NADPH-d cells in the white matter underlying the frontal cortex and in the hippocampus are vulnerable in AD. The implications of these findings are discussed.

Somatostatin-like immunoreactivity, its molecular forms and monoaminergic metabolites in aged and demented patients with Parkinson's disease--effect of L-Dopa

There is some evidence that Parkinson's disease (PD) seems to be a heterogenous and generalized brain disorder reflecting a degeneration of multiple neuronal networks, including somatostatinergic neurons. Somatostatin-like immunoreactivity (SLI) and its molecular forms, high molecular weight form (HMV-SST), somatostatin-14 (SST-14), somatostatin-25/28 (SST-25/28) and Des-ala-somatostatin (Des-ala-SST), as well as homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were estimated using HPLC and radioimmunoassay in the cerebrospinal fluid (CSF) of 35 aged parkinsonian patients with different stages of intellectual deterioration. The influence of L-dopa-treatment on these neurochemical parameters was evaluated. Without a correlation with dementia scores (p = 0.11), SLI was significantly reduced in PD in comparison to the control group (p < 0.05). The reduction was related to the progression of the disease. Correlations between SLI, HVA and 5-HIAA indicate a heterogenous brain disorder in PD with alterations of several transmitter systems and functions. Complex qualitative and quantitative changes in the molecular pattern of SLI are compatible with a dysregulated synthesis and/or posttranslational processing. L-dopa-treatment was associated with a significant increase of HVA (p < 0.05) and HMV-SST (p < 0.05) and a slight, but insignificant increase of SLI (p = 0.11).

Distribution of substance P-immunoreactive neurons and fibers in the monkey hippocampal formation

Substance P containing neurons was visualized by immunocytochemistry in the monkey hippocampus, subicular complex, and entorhinal cortex. Immunoreactive neurons were found solely in the hilar region of the dentate gyrus, and in strata oriens and pyramidale of Ammon's horn. In the subicular complex, immunoreactive neurons were located in those layers which were close to the alveus, whereas in the entorhinal cortex most of the substance P-positive neurons appeared in the second and third layers above the lamina dissecans. The majority of substance P-containing neurons were large multipolar cells, but small bipolar and multipolar cells also occurred in Ammon's horn, subiculum and entorhinal cortex. Dendrites of immunoreactive cells were smooth and displayed a few small, faintly stained spines which were hard to identify in the light microscopic preparations, but were visible with electron microscopy. Substance P-positive dendrites were exclusively found in the hilar region and never observed in the upper two-thirds of the molecular layer of the dentate gyrus. Moreover, immunoreactive dendrites rarely penetrated the stratum lacunosum-moleculare of Ammon's horn. In the electron microscopic preparations, somal and dendritic features of substance P-positive neurons were similar to those observed for GABAergic local circuit neurons. Axons of the substance P-immunoreactive local circuit neurons were thin and richly arborized in the upper two-thirds of the molecular layer of the dentate gyrus, in the stratum lacunosum-moleculare of Ammon's horn as well as in the subpial layers of the subicular complex and entorhinal cortex. Their terminals formed exclusively symmetric synapses with dendrites and spines. However, substance P-immunoreactive boutons were not found to make symmetric, axosomatic synapses on the granule cells of the dentate gyrus and very few were present on the pyramidal neurons of Ammon's horn, subicular complex, and entorhinal cortex. Hippocampal neurons, which were immunoreactive for substance P, also contained the neuropeptide somatostatin. However, not all of the somatostatin-containing neurons were substance P-immunoreactive. Thus, substance P-positive neurons are a subpopulation of somatostatin immunoreactive, GABAergic neurons. In conclusion, substance P-immunoreactive neurons are ideally suited for feed-back dendritic inhibition which may control the effectiveness of the main excitatory cortical input to the granule cells of the dentate gyrus and pyramidal neurons of the Ammon's horn.

Correlations between water maze performance and cortical somatostatin mRNA and high-affinity binding sites during ageing in rats

Somatostatin levels and high-affinity (somatostatin-1) binding sites are decreased in post-mortem cortical samples of Alzheimer's disease patients but the relationships between such modifications and the cognitive deficits remain to be established. We investigated these relationships in the ageing rat. Three age groups (3-4, 14-15 and 26-27 months) were tested in a modified version of the Morris water maze. Somatostatin mRNA levels were quantified by in situ hybridization and somatostatin binding sites by radioautography using the selective agonist octreotide (SMS 201995) as a competing drug to evaluate high-affinity (somatostatin-1) and low-affinity (somatostatin-2) binding sites. The number of somatostatin mRNA-containing cells was not modified with age or memory performance in cortical, hippocampal and hypothalamic regions, but somatostatin mRNA densities were significantly decreased with age and with memory performance in the frontal and parietal cortex. In the frontal cortex somatostatin mRNA densities were already decreased in 14- to 15-month-old rats, whereas the decrease was observed only in 26- to 27-month-old rats in the parietal cortex. A decrease in somatostatin-1 binding was observed with memory performance, independently of age, in the basolateral amygdala only, while somatostatin-2 binding sites were not affected. In the frontal and parietal cortex, a significant correlation occurred between the latency to find the invisible platform in the water maze and somatostatin mRNA (r = -0.54 and 0.59 respectively, P < 0.02). These results indicate that ageing rats with memory impairments display some of the features of the somatostatinergic deficits observed in Alzheimer's disease.

Entorhinal cortex modules of the human brain

Much is known about modular organization in the cerebral cortex, but this knowledge is skewed markedly toward primary sensory areas, and in fact, it has been difficult to demonstrate elsewhere. In this report, we test the hypothesis that a unique form of modules exists in the entorhinal area of the human cortex (Brodmann's area 28). We examined this issue using classic cyto- and myeloarchitectonic stains, immunolabeling for various neurochemicals, and histochemistry for certain enzymes. The findings reveal that the entorhinal cortex in the human is formed by a mosaic of cellular aggregates whose most conspicuous elements are the cell islands of layer II and myelinated fibers around the cell islands, the disposition of glutamic acid decarboxylase-positive neurons and processes, cytochrome oxidase staining, and the pattern of cholinergic afferent fibers. The neuropathology of Alzheimer's disease cases highlights the modules, but inversely so, by destroying their features. The findings are of interest because 1) anatomically defined modules are shown to be present in areas other than the sensory and motor cortices, 2) the modules are morphological entities likely to reflect functions of the entorhinal cortex, and 3) the destruction of entorhinal cortex modules may account disproportionately for the severity of memory impairments in Alzheimer's disease.

Cellular localisation and co-expression of somatostatin receptor messenger RNAs in the human brain

Genes for five high affinity somatostatin receptors, named sst1-5, have been cloned recently. In this study we describe the tissue distribution and cellular localisation of mRNA encoding sst1, sst3 and sst4 receptors in the human cerebellum, frontal cortex (Brodmann's area 11) and hippocampus. RT-PCR and in situ hybridisation studies indicated a distinct, but partially overlapping pattern of expression of the receptor mRNAs. In situ hybridisation studies using co-expression techniques with probes for sst1, sst3 and sst4 receptor mRNA on paraffin sections revealed the presence of neurones expressing more than one somatostatin receptor mRNA type in both the hippocampus and pyramidal cells of layer V of the frontal cortex.