Daniel M. Dorsa

The opiomelanotropinergic neuronal and endocrine systems.

Abstract Opiomelanotropinergic cells in the intermediate lobe of the pituitary and in neurons in the brain secrete at least 7 peptides related to melanocyte stimulating hormone (MSH) and β-endorphin (BE). This paper reviews the anatomy, physiology and biochemistry of opiomelanotropinergic neurons and discusses the implications of multi-neurotransmitter and multi-hormone neurons and cells.

Insulin and insulin-like growth factors in the CNS

Abstract Insulin has long been recognized as a major endocrine regulator of the uptake, cellular transport, and intermediary metabolism of small nutrient molecules such as amino acids, fatty acids, and glucose 1 . Adipose tissue and skeletal muscle are the classical major target of insulin action; the CNS, in contrast, has traditionally been considered to be largely insulin-insensitive. However, clues that insulin may have physiological functions in the CNS began to emerge in the 1960s, and an impressive body of literature has since accumulated about insulin in the CNS. Although insulin now regularly appears in litanies cataloging CNS peptides, its status as a CNS regulatory peptide remains obscure and elusive. The situation has become more clouded with the recent discovery that insulin-like growth-factors (IGFs) and their receptors are also present in the CNS. Since IGFs and insulin share similar primary amino acid structure, receptor binding, and biological activity 2 , any discussion about insulin as a CNS regulatory peptide must also consider the IGFs. In the present article, we summarize the status of insulin and IGFs as regulatory peptides in the CNS. Our choice of literature has been selective, with a focus on recent reports, controversial issues, and unsolved problems. Readers are referred to previous reviews for much of the earlier literature 1–5 .

Estrogen protects primary cortical neurons from glutamate toxicity

The gonadal steroid estrogen has been shown to affect neuronal growth, differentiation and survival. We examined the ability of estrogen to protect primary cortical neurons from toxicity induced by the excitatory neurotransmitter glutamate. In these experiments, a 24-h pretreatment with 15 and 50 nM 17 beta-estradiol significantly reduced cellular lactate dehydrogenase (LDH) release from primary cortical neurons, indicating that neurons treated with 17 beta-estradiol were protected from a toxic glutamate exposure. Pretreatment with related steroids such as progesterone, dihydrotestosterone, dexamethasone or cholesterol did not significantly decrease LDH release. The anti-estrogen tamoxifen blocked the protective effects of 17 beta-estradiol suggesting that a classical steroid hormone receptor may be involved in the mechanism subserving estrogen neuroprotection during glutamate toxicity.

Distribution of mRNA for the calmodulin-sensitive adenylate cyclase in rat brain: Expression in areas associated with learning and memory

The Drosophila learning mutant, rutabaga, is deficient in the calmodulin-sensitive adenylate cyclase, and studies of associative learning in Aplysia have implicated this enzyme in neuroplasticity. Therefore, the distribution of mRNA encoding the calmodulin-sensitive adenylate cyclase in rat brain was examined by in situ hybridization. mRNA for this enzyme is expressed in specific areas of brain that have been implicated in learning and memory, including the neocortex, the hippocampus, and the olfactory system. The presence of mRNA for this enzyme in the pyramidal and granule cells of the hippocampal formation provides evidence that it is found in neurons. These data are consistent with the proposal that the calmodulin-sensitive adenylate cyclase plays an important role in learning and memory.

Estrogen Receptor (ER)α and ERβ Exhibit Unique Pharmacologic Properties When Coupled to Activation of the Mitogen-Activated Protein Kinase Pathway1

The rapid, nongenomic effects of estrogen are increasingly recognized as playing an important role in several aspects of estrogen action. Rapid activation of the mitogen-activated protein kinase (MAPK) signaling pathway by estrogen is among the more recently identified of these effects. To explore the role of estrogen receptors (ERs) in mediating these effects, we have transfected ER-negative Rat-2 fibroblasts with complementary DNA clones encoding either human ERalpha or rat ERbeta and examined their ability to couple to activation of MAPK in response to 17beta-estradiol (17beta-E(2)) and other ligands. For both receptors, addition of E(2) resulted in a rapid phosphorylation of MAPK. Activation of MAPK in ERalpha-transfected cells was partially and completely blocked by the antiestrogens tamoxifen and ICI 182,780, respectively. In ERbeta-transfected cells, MAPK activation was less sensitive to inhibition by tamoxifen and ICI 182,780. We have also observed that, in this model system, a membrane-impermeable estrogen (BSA-E(2)) and 17alpha-E(2) were both able to activate MAPK in a manner similar to E(2) alone. Here also, ICI 182,780 blocked the ability of BSA-E(2) to activate MAPK through ERalpha, but failed to block ERbeta-mediated effects. BSA-E(2) treatment, however, failed to activate nuclear estrogen-response-element-mediated gene transcription. These data show that these nuclear ERs are necessary for estrogens effects at the membrane. This model system will be useful in identifying molecular interactions involved in the rapid effects mediated by the ERs.

Prenatal Stress Generates Deficits in Rat Social Behavior: Reversal by Oxytocin

Neurodevelopmental changes induced by environmental stress exposure play a significant but poorly defined role in the etiology of schizophrenia. Exposure of pregnant female rats to a series of unpredictable stresses during the final week of pregnancy generates behavioral deficits and molecular changes in the offspring similar to those observed in schizophrenic individuals. We used this rat prenatal stress preparation to investigate social withdrawal behaviors that may have relevance to the negative symptoms of schizophrenia. The cumulative time adult male offspring of stress-exposed pregnant female rats actively interacted with a weight-matched, same-sex peer was decreased approximately 76% relative to non-stress exposed control rats. Prenatal stress exposure also diminished the quality of the social interaction behavior indicative of reduced social drive. Analysis of the oxytocinergic system in the prenatally stressed male rats revealed significantly less oxytocin mRNA in the paraventricular nucleus and increased oxytocin receptor binding in the central amygdala. Moreover, oxytocin, but not vasopressin, administration into the central amygdala reversed the social incompetence of the prenatally stressed rats without increasing behavior in non-stressed control animals. In addition, cross-fostering pups from prenatally stressed mothers to non-stressed mothers failed to improve the social deficit of the prenatally stressed male offspring. Two behavioral assays designed to measure anxiety did not differentiate the prenatally stressed rats from non-stressed controls. These data indicate that prenatal stress may be an etiologically appropriate animal model for some aspects of schizophrenic social withdrawal. Furthermore, unpredictable prenatal stress exposure selectively degrades social interaction behaviors without increasing anxiety measures.

Colocalization of serotonin receptor subtypes 5‐HT2A, 5‐HT2C, and 5‐HT6 with neuropeptides in rat striatum

There are two primary output pathways from the striatum: a projection to the globus pallidus, and a projection to the substantia nigra. Certain striatally expressed neuropeptides are differentially distributed between these two pathways. Specifically, enkephalin is expressed in striatopallidal neurons, whereas substance P and dynorphin are expressed in striatonigral neurons. Several serotonin receptors are also prominently expressed in the striatum, but little is known about how they fit into the molecular neuroanatomy described above.

Localization of binding sites for insulin-like growth factor-I (IGF-I) in the rat brain by quantitative autoradiography

In vitro quantitative autoradiography was used to localize IGF-I binding sites in rat brain. Slide-mounted sections of frozen rat brain were incubated in 0.01 nM 125I[Thr59]IGF-I, alone or mixed with 10 nM unlabeled [Thr59]IGF-I or insulin, for 22 h at 4 degrees C and apposed to LKB Ultrofilm. Measurement of labeled [Thr59]IGF-I binding by computer digital image analysis of the autoradiographic images indicated that high affinity IGF-I binding sites are widely distributed at discrete anatomical regions of the brain microarchitecture. The highest concentration of specific binding sites was in the choroid plexus of the lateral and third ventricles. Unlabeled porcine insulin was less potent than unlabeled IGF-I in competing for binding sites on brain slices. Regions of the olfactory, visual, and auditory, as well as visceral and somatic sensory systems were labeled, in particular the glomerular layer of the olfactory bulb, the anterior olfactory nucleus, accessory olfactory bulb, primary olfactory cortex, lateral-dorsal geniculate, superior colliculus, medial geniculate, and the spinal trigeminal nucleus. High concentrations of IGF-I-specific binding sites were present throughout the thalamus and the hippocampus, (dentate gyrus, Ca1, Ca2, Ca3). The hypothalamus had moderate binding in the paraventricular, supraoptic, and suprachiasmatic nucleus. Highest binding in the hypothalamus was in the median eminence. The arcuate nucleus showed very low specific binding, approaching the levels found in optic chiasm and white matter regions. Layers II and VI of the cerebral cortex also had moderate IGF-I binding. The results suggest that the development and functions of brain sensory and neuroendocrine pathways may be regulated by IGF-I.

Modulation of Bcl-2 expression : a potential component of estrogen protection in NT2 neurons

EUROPROTECTIVE effects of estrogen have been demonstrated against a variety of cytotoxic insults. We present data here addressing a possible mechanism of estrogen neuroprotection in the human teratocarcinoma cell line NT2 terminally differentiated to a neuronal phenotype. Cell death induced by H2O2 or glutamate results in a dose-dependent cell death of NT2 neurons, while 24 h of estrogen pretreatment significantly enhances neuronal viability. Bcl-2 expression has been shown to reduce oxidative stress and prevent cell death. In NT2 neurons, Bcl-2 levels are dramatically elevated upon differentiation and are further enhanced with estrogen treatment. These results suggest that neuroprotective effects of estrogen may be related to increases in Bcl-2 expression.

Social Interaction Deficits Caused by Chronic Phencyclidine Administration are Reversed by Oxytocin

Chronic administration of phencyclidine (PCP) has been advanced as a valid animal model of the social deficit symptoms of schizophrenia. In these studies, the cumulative time that male rats treated once a day for 14 days with PCP actively engaged in social behavior was decreased approximately 75% relative to saline-treated control animals. In addition, these socially impaired rats had an increase in the relative amount of noncontact interactions compared with saline-injected peers. Social behaviors were preferentially affected by PCP treatment because in two anxiety-related behavioral assays, the open field and light/dark emergence tests, there was a failure to differentiate between the PCP-treated rats and saline-injected control rats. Considering the general importance of the neuropeptides oxytocin and vasopressin in male social behaviors, studies of molecular markers related to these neuropeptides were performed. Hypothalamic oxytocin mRNA expression was significantly decreased while oxytocin receptor binding was increased in the central nucleus of the amygdala following chronic PCP treatment. Given the significance of central nucleus of the amygdala in social behavior, oxytocin was infused into the central nucleus of experimental and control male rats, and their postinfusion social interaction and open field behaviors were analyzed. A bilateral infusion of 1 μg of oxytocin into the central amygdala selectively restored the normal quantity and quality of social behavior in chronic PCP-treated male rats without altering open field behaviors. These findings suggest that deficits in the central oxytocinergic system may underlie the social impairment exhibited in this animal model of schizophrenia.