Beta-adrenergic-receptor localization by light microscopic autoradiography

Brain systems in cocaine abstinence-induced anxiety-like behavior in rodents: A review

Cocaine use disorder (CUD) is a significant public health issue that generates substantial personal, familial, and economic burdens. Still, there are no FDA-approved pharmacotherapies for CUD. Cocaine-dependent individuals report anxiety during withdrawal, and alleviation of anxiety and other negative affective states may be critical for maintaining drug abstinence. However, the neurobiological mechanisms underlying abstinence-related anxiety in humans or anxiety-like behavior in rodents are not fully understood. This review summarizes investigations regarding anxiety-like behavior in mice and rats undergoing cocaine abstinence, as assessed using four of the most common anxiety-related assays: the elevated plus (or its derivative, the elevated zero) maze, open field test, light-dark transition test, and defensive burying task. We first summarize available evidence that cocaine abstinence generates anxiety-like behavior that persists throughout protracted abstinence. Then, we examine investigations concerning neuropeptide, neurotransmitter, and neuromodulator systems in cocaine abstinence-induced anxiety-like behavior. Throughout, we discuss how differences in sex, rodent strain, cocaine dose and dosing strategy and abstinence duration interact to generate anxiety-like behavior.

Receptor visualization and the atomic bomb. A historical account of the development of the chemical neuroanatomy of receptors for neurotransmitters and drugs during the Cold War

This is a historical account of how receptors for neurotransmitters and drugs got to be seen at the regional, cellular, and subcellular levels in brain, in the years going from the end of the World War II until the collapse of the Soviet Union, the Cold War (1945-1991). The realization in the US of the problem of mental health care, as a consequence of the results of medical evaluation for military service during the war, let the US Government to act creating among other things the National Institute for Mental Health (NIMH). Coincident with that, new drug treatments for these disorders were introduced. War science also created an important number of tools and instruments, such as the radioisotopes, that played a significant role in the development of our story. The scientific context was marked by the development of Biochemistry, Molecular Biology and the introduction in the early 80's of the DNA recombinant technologies. The concepts of chemical neurotransmission in the brain and of receptors for drugs and transmitters, although proposed before the war, where not generally accepted. Neurotransmitters were identified and the mechanisms of biosynthesis, storage, release and termination of action by mechanisms such as reuptake, elucidated. Furthermore, the synapse was seen with the electron microscope and more important for our account, neurons and their processes visualized in the brain first by fluorescence histochemistry, then using radioisotopes and autoradiography, and later by immunohistochemistry (IHC), originating the Chemical Neuroanatomy. The concept of chemical neurotransmission evolved from the amines, expanded to excitatory and inhibitory amino acids, then to neuropeptides and finally to gases and other "atypical" neurotransmitters. In addition, coexpression of more than one transmitter in a neuron, changed the initial ideas of neurotransmission. The concept of receptors for these and other messengers underwent a significant evolution from an abstract chemical concept to their physical reality as gene products. Important steps were the introduction in the 70's of radioligand binding techniques and the cloning of receptor genes in the 80's. Receptors were first visualized using radioligands and autoradiography, and analyzed with the newly developed computer-assisted image analysis systems. Using Positron Emission Tomography transmitters and receptors were visualized in living human brain. The cloning of receptor genes allowed the use of in situ hybridization histochemistry and immunohistochemistry to visualize with the light and electron microscopes the receptor mRNAs and proteins. The results showed the wide heterogeneity of receptors and the diversity of mode of signal transmission, synaptic and extra-synaptic, again radically modifying the early views of neurotransmission. During the entire period the interplay between basic science and Psychopharmacology and Psychiatry generated different transmitter or receptor-based theories of brain drug action. These concepts and technologies also changed the way new drugs were discovered and developed. At the end of the period, a number of declines in these theories, the use of certain tools and the ability to generate new diagnostics and treatments, the end of an era and the beginning of a new one in the research of how the brain functions.

Sexual dimorphisms in swimming behavior, cerebral metabolic activity and adrenoceptors in adult zebrafish (Danio rerio)

Sexually dimorphic behaviors and brain sex differences, not only restricted to reproduction, are considered to be evolutionary preserved. Specifically, anxiety related behavioral repertoire is suggested to exhibit sex-specific characteristics in rodents and primates. The present study investigated whether behavioral responses to novelty, have sex-specific characteristics in the neurogenetic model organism zebrafish (Danio rerio), lacking chromosomal sex determination. For this, aspects of anxiety-like behavior (including reduced exploration, increased freezing behavior and erratic movement) of male and female adult zebrafish were tested in a novel tank paradigm and after habituation. Male and female zebrafish showed significant differences in their swimming activity in response to novelty, with females showing less anxiety spending more time in the upper tank level. When fish have habituated, regional cerebral glucose uptake, an index of neuronal activity, and brain adrenoceptors' (ARs) expression (α2-ARs and β-ARs) were determined using in vivo 2-[(14)C]-deoxyglucose methodology and in vitro neurotransmitter receptors quantitative autoradiography, respectively. Intriguingly, females exhibited higher glucose utilization than males in hypothalamic brain areas. Adrenoceptor's expression pattern was dimorphic in zebrafish telencephalic, preoptic, hypothalamic nuclei, central gray, and cerebellum, similarly to birds and mammals. Specifically, the lateral zone of dorsal telencephalon (Dl), an area related to spatial cognition, homologous to the mammalian hippocampus, showed higher α2-AR densities in females. In contrast, male cerebellum included higher densities of β-ARs in comparison to female. Taken together, our data demonstrate a well-defined sex discriminant cerebral metabolic activity and ARs' pattern in zebrafish, possibly contributing to male-female differences in the swimming behavior.

Specificity and impact of adrenergic projections to the midbrain dopamine system

Dopamine (DA) is a neuromodulator that regulates different brain circuits involved in cognitive functions, motor coordination, and emotions. Dysregulation of DA is associated with many neurological and psychiatric disorders such as Parkinson's disease and substance abuse. Several lines of research have shown that the midbrain DA system is regulated by the central adrenergic system. This review focuses on adrenergic interactions with midbrain DA neurons. It discusses the current neuroanatomy including source of adrenergic innervation, type of synapses, and adrenoceptors expression. It also discusses adrenergic regulation of DA cell activity and neurotransmitter release. Finally, it reviews several neurological and psychiatric disorders where changes in adrenergic system are associated with dysregulation of the midbrain DA system. This article is part of a Special Issue entitled SI: Noradrenergic System.

Pre- and postsynaptic modulations of hypoglossal motoneurons by α-adrenoceptor activation in wild-type and Mecp2(-/Y) mice

Hypoglossal motoneurons (HNs) control tongue movement and play a role in maintenance of upper airway patency. Defects in these neurons may contribute to the development of sleep apnea and other cranial motor disorders including Rett syndrome (RTT). HNs are modulated by norepinephrine (NE) through α-adrenoceptors. Although postsynaptic mechanisms are known to play a role in this effect, how NE modulates the synaptic transmissions of HNs remains poorly understood. More importantly, the NE system is defective in RTT, while how the defect affects HNs is unknown. Believing that information of NE modulation of HNs may help the understanding of RTT and the design of new therapeutical interventions to motor defects in the disease, we performed these studies in which glycinergic inhibitory postsynaptic currents and intrinsic membrane properties were examined in wild-type and Mecp2(-/Y) mice, a mouse of model of RTT. We found that activation of α1-adrenoceptor facilitated glycinergic synaptic transmission and excited HNs. These effects were mediated by both pre- and postsynaptic mechanisms. The latter effect involved an inhibition of barium-sensitive G protein-dependent K(+) currents. The pre- and postsynaptic modulations of the HNs by α1-adrenoceptors were not only retained in Mecp2-null mice but also markedly enhanced, which appears to be a compensatory mechanism for the deficiencies in NE and GABAergic synaptic transmission. The existence of the endogenous compensatory mechanism is an encouraging finding, as it may allow therapeutical modalities to alleviate motoneuronal defects in RTT.

Ultrastructural characterization of noradrenergic axons and Beta-adrenergic receptors in the lateral nucleus of the amygdala

Norepinephrine (NE) is thought to play a key role in fear and anxiety, but its role in amygdala-dependent Pavlovian fear conditioning, a major model for understanding the neural basis of fear, is poorly understood. The lateral nucleus of the amygdala (LA) is a critical brain region for fear learning and regulating the effects of stress on memory. To understand better the cellular mechanisms of NE and its adrenergic receptors in the LA, we used antibodies directed against dopamine beta-hydroxylase (DβH), the synthetic enzyme for NE, or against two different isoforms of the beta-adrenergic receptors (βARs), one that predominately recognizes neurons (βAR 248) and the other astrocytes (βAR 404), to characterize the microenvironments of DβH and βAR. By electron microscopy, most DβH terminals did not make synapses, but when they did, they formed both asymmetric and symmetric synapses. By light microscopy, βARs were present in both neurons and astrocytes. Confocal microscopy revealed that both excitatory and inhibitory neurons express βAR248. By electron microscopy, βAR 248 was present in neuronal cell bodies, dendritic shafts and spines, and some axon terminals and astrocytes. When in dendrites and spines, βAR 248 was frequently concentrated along plasma membranes and at post-synaptic densities of asymmetric (excitatory) synapses. βAR 404 was expressed predominately in astrocytic cell bodies and processes. These astrocytic processes were frequently interposed between unlabeled terminals or ensheathed asymmetric synapses. Our findings provide a morphological basis for understanding ways in which NE may modulate transmission by acting via synaptic or non-synaptic mechanisms in the LA.

Regional distribution and cellular localization of beta2-adrenoceptors in the adult zebrafish brain (Danio rerio)

The beta(2)-adrenergic receptors (ARs) are G-protein-coupled receptors that mediate the physiological responses to adrenaline and noradrenaline. The present study aimed to determine the regional distribution of beta(2)-ARs in the adult zebrafish (Danio rerio) brain by means of in vitro autoradiographic and immunohistochemical methods. The immunohistochemical localization of beta(2)-ARs, in agreement with the quantitative beta-adrenoceptor autoradiography, showed a wide distribution of beta(2)-ARs in the adult zebrafish brain. The cerebellum and the dorsal zone of periventricular hypothalamus exhibited the highest density of [(3)H]CGP-12177 binding sites and beta(2)-AR immunoreactivity. Neuronal cells strongly stained for beta(2)-ARs were found in the periventricular ventral telencephalic area, magnocellular and parvocellular superficial pretectal nuclei (PSm, PSp), occulomotor nucleus (NIII), locus coeruleus (LC), medial octavolateral nucleus (MON), magnocellular octaval nucleus (MaON) reticular formation (SRF, IMRF, IRF), and ganglionic cell layer of cerebellum. Interestingly, in most cases (NIII, LC, MON, MaON, SRF, IMRF, ganglionic cerebellar layer) beta(2)-ARs were colocalized with alpha(2A)-ARs in the same neuron, suggesting their interaction for mediating the physiological functions of nor/adrenaline. Moderate to low labeling of beta(2)-ARs was found in neurons in dorsal telencephalic area, optic tectum (TeO), torus semicircularis (TS), and periventricular gray zone of optic tectum (PGZ). In addition to neuronal, glial expression of beta(2)-ARs was found in astrocytic fibers located in the central gray and dorsal rhombencephalic midline, in close relation to the ventricle. The autoradiographic and immunohistochemical distribution pattern of beta(2)-ARs in the adult zebrafish brain further support the conserved profile of adrenergic/noradrenergic system through vertebrate brain evolution.

Neuronal and glial localization of alpha(2A)-adrenoceptors in the adult zebrafish (Danio rerio) brain

The alpha(2A)-adrenoceptor (AR) subtype, a G protein-coupled receptor located both pre- and postsynaptically, mediates adrenaline/noradrenaline functions. The present study aimed to determine the alpha(2A)-AR distribution in the adult zebrafish (Danio rerio) brain by means of immunocytochemistry. Detailed mapping showed labeling of alpha(2A)-ARs, in neuropil, neuronal somata and fibers, glial processes, and blood vessels. A high density of alpha(2A)-AR immunoreactivity was found in the ventral telencephalic area, preoptic, pretectal, hypothalamic areas, torus semicircularis, oculomotor nucleus (NIII), locus coreruleus (LC), medial raphe, medial octavolateralis nucleus (MON), magnocellular octaval nucleus (MaON), reticular formation (SRF, IMRF, IRF), rhombencephalic nerves and roots (DV, V, VII, VIII, X), and cerebellar Purkinje cell layer. Moderate levels of alpha(2A)-ARs were observed in the medial and central zone nuclei of dorsal telencephalic area, in the periventricular gray zone of optic tectum, in the dorsomedial part of optic tectum layers, and in the molecular and granular layers of all cerebellum subdivisions. Glial processes were found to express alpha(2A)-ARs in rhombencephalon, intermingled with neuronal fibers. Medium-sized neurons were labeled in telencephalic, diencephalic, and mesencephlic areas, whereas densely labeled large neurons were found in rhombencephalon, locus coeruleus, reticular formation, oculomotor area, medial octavolateralis and magnocellular octaval nuclei, and Purkinje cell somata. The functional role of alpha(2A)-ARs on neurons and glial processes is not known at present; however, their strong relation to the ventricular system, somatosensory nuclei, and nerves supports a possible regulatory role of alpha(2A)-ARs in autonomic functions, nerve output, and sensory integration in adult zebrafish brain.

Role of alpha and beta adrenoceptors in locus coeruleus stimulation-induced reduction in rapid eye movement sleep in freely moving rats

Based on the results of independent studies the involvement of norepinephrine in REM sleep regulation was known. Isolated studies showed that the effect could be mediated through either one or more subtypes of adrenoceptors. Earlier we have reported that REM-OFF neurons continue firing during REM sleep deprivation and mild but continuous stimulation of locus coeruleus (LC) or picrotoxin injection into the LC, that did not allow the REM-OFF neurons in the LC to stop firing, reduced REM sleep. However, the mechanism of action and type of adrenoreceptors involved in REM sleep regulation were unknown. The possible mechanism of action has been investigated in this study. It was proposed that if LC stimulation-induced decrease in REM sleep was due to norepinephrine, adrenergic antagonist must prevent the effect. Therefore, in this study, the effects of alpha1, alpha2 and beta-antagonists, viz. prazosin, yohimbine and propranolol, respectively, and alpha2 agonist, clonidine, on LC stimulation-induced reduction in REM sleep were investigated. The results showed that stimulation of LC inhibited REM sleep by reducing the frequency of generation of REM sleep, although the duration per episode remained unaffected. This decrease in the frequency of REM sleep was blocked by beta-antagonist propranolol while the duration of REM sleep per episode was blocked by alpha1-antagonist, prazosin. Also, a critical level of norepinephrine in the system was required for the generation of REM sleep, however, a higher level may be inhibitory. Based on the results of this study and our earlier studies, an interaction between neurons, containing different neurotransmitters and their subtypes of receptors for LC-mediated regulation of REM sleep has been proposed.

Comparative anatomy of α2 and β adrenoceptors in the adult and developing brain of the marine teleost the red porgy (Pagrus pagrus, Sparidae): [3H]clonidine and [3H]dihydroalprenolol quantitative autoradiography and receptor subtypes immunohistochemistry

The present study aimed to determine the anatomic distribution and developmental profile of alpha(2) and beta adrenoceptors (AR) in marine teleost brain. Alpha 2 and beta adrenoceptors were studied at different developmental stages by using [(3)H]clonidine and [(3)H]dihydroalprenolol, respectively, by means of in vitro quantitative autoradiography. Furthermore, immunohistochemical localization of the receptor subtypes was performed to determine their cellular distribution. Saturation studies determined a high-affinity component of [(3)H]clonidine and [(3)H]dihydroalprenolol binding sites. High levels of both receptors were found in preglomerular complex, ventral hypothalamus, and lateral torus. Dorsal hypothalamus and isthmus included high levels of alpha(2) AR, whereas pretectum and molecular and proliferative zone of cerebellum were specifically characterized by high densities of beta AR. From the first year of life, adult levels of both AR were found in most medial telencephalic, hypothalamic, and posterior tegmental areas. Decreases in both receptors densities with age were prominent in ventral and posterior telencephalic, pretectal, ventral thalamic, hypothalamic, and tegmental brain regions. Immunohistochemical data were well correlated with autoradiography and demonstrated the presence of alpha(2A), alpha(2C), beta(1), and beta(2) AR subtype-like immunoreactivity. Both the neuronal (perikaryal or dendritic) and the glial localization of receptors was revealed. The localization and age-dependent alterations in alpha(2) and beta AR were parallel to plasticity mechanisms, such as cell proliferation in periventricular thalamus, hypothalamus, and cerebellum. In addition, the biochemical characteristics, distribution pattern, and neuronal or glial specificity of the receptors in teleost brain support a similar profile of noradrenergic transmission in vertebrate brain evolution.

Spontaneous and auditory-evoked activity of medial agranular cortex as a function of arousal state in the freely moving rat: interaction with locus coeruleus activity

To characterize the electrophysiological properties of neurons in the medial agranular frontal cortex (Fr2) with respect to arousal level and locus coeruleus (LC) activity, we recorded spontaneous and auditory-evoked single unit activity in these areas simultaneously during different states of arousal in the rat. In the low-arousal state, as determined by EEG, 14/56 Fr2 neurons showed a tonic increase in spontaneous firing rate and 9/56 presented a clear inhibitory response to tone (onset latency 37 ms, duration 200 ms). The inhibitory response was not clear during the high-arousal state. Cross-correlation analysis of pairs of Fr2 and LC units, excluding activity during the actual tone, also showed a negative correlation from 120 ms before, to 170 ms after, Fr2 discharge in 5/63 pairs, only during low arousal. Significantly, 4/5 of the Fr2 neurons having this negative correlation with LC were included in that population which showed a tonic increase in spontaneous firing rate and inhibited to tone during low arousal. LC neurons, on the other hand, all showed excitation to tone stimulation (peak latency 30 ms), and response amplitude was not affected by changes in arousal level. The negative correlation in spontaneous activity, as well as their differential responses to tone, suggests an interaction between a select population of Fr2 neurons and the LC during the low-arousal state. Future studies with lesion or pharmacological manipulations would be necessary to confirm the presence of this interaction.

Synaptic control of motoneuronal excitability

Movement, the fundamental component of behavior and the principal extrinsic action of the brain, is produced when skeletal muscles contract and relax in response to patterns of action potentials generated by motoneurons. The processes that determine the firing behavior of motoneurons are therefore important in understanding the transformation of neural activity to motor behavior. Here, we review recent studies on the control of motoneuronal excitability, focusing on synaptic and cellular properties. We first present a background description of motoneurons: their development, anatomical organization, and membrane properties, both passive and active. We then describe the general anatomical organization of synaptic input to motoneurons, followed by a description of the major transmitter systems that affect motoneuronal excitability, including ligands, receptor distribution, pre- and postsynaptic actions, signal transduction, and functional role. Glutamate is the main excitatory, and GABA and glycine are the main inhibitory transmitters acting through ionotropic receptors. These amino acids signal the principal motor commands from peripheral, spinal, and supraspinal structures. Amines, such as serotonin and norepinephrine, and neuropeptides, as well as the glutamate and GABA acting at metabotropic receptors, modulate motoneuronal excitability through pre- and postsynaptic actions. Acting principally via second messenger systems, their actions converge on common effectors, e.g., leak K(+) current, cationic inward current, hyperpolarization-activated inward current, Ca(2+) channels, or presynaptic release processes. Together, these numerous inputs mediate and modify incoming motor commands, ultimately generating the coordinated firing patterns that underlie muscle contractions during motor behavior.

Regional brain distribution of noradrenaline uptake sites, and of alpha1-alpha2- and beta-adrenergic receptors in PCD mutant mice: a quantitative autoradiographic study

The mouse "Purkinje cell degeneration" (pcd) is characterized by a primary loss of Purkinje cells, as well as by retrograde and secondary partial degeneration of cerebellar granule cells and inferior olivary neurons; this neurological mutant can be considered as an animal model of human degenerative ataxia. To determine the consequences of this cerebellar pathology on the noradrenergic system, noradrenaline transporters as well as alpha1-, alpha2- and beta-adrenergic receptors were evaluated by quantitative ligand binding autoradiography in adult control and pcd mice using, respectively, [3H]nisoxetine, [3H]prazosin, [3H]idazoxan and [3H]CGP12177. In cerebellar cortex and deep nuclei of pcd mutants, [3H]nisoxetine labelling of noradrenaline transporters was higher than in control mice. However, when binding densities were corrected by surface area, they remained unchanged in the cerebellar cortex but associated with 25% and 40% lower levels of labelling of alpha1 and beta receptors, as well as a very important increase (275%) of alpha2 receptors. In deep cerebellar nuclei, surface corrections did not reveal any changes either in transporter or in receptor densities. Higher densities of [3H]nisoxetine labelling were found in several regions related with the cerebellum, namely inferior olive, inferior colliculus, vestibular, reticular, pontine, raphe and red nuclei, as well as in primary motor and sensory cerebral cortex; they may reflect an increased noradrenergic innervation related to motor adjustments for the cerebellar dysfunction. Increased [3H]nisoxetine labelling was also measured in vegetative brainstem regions and in dorsal hypothalamus, implying altered autonomic functions and possible compensation in pcd mutants. Other changes found in extracerebellar regions affected by the mutation, such as thalamus and the olfactory system implicated both noradrenaline transporters and adrenergic receptors. In contrast to the important alterations of the noradrenergic system in cerebellar cortex, the lack of receptor changes in deep cerebellar nuclei suggests that local adaptations may be sufficient to minimize the consequence of the cerebellar atrophy on motor control. An intense labelling by [3H]idazoxan of the inner third of the molecular layer was a novel, albeit unexplained finding, and could represent a postsynaptic subset of alpha2-adrenergic receptors.

Noradrenaline excites non-cholinergic laterodorsal tegmental neurons via two distinct mechanisms

Cholinergic neurons of the laterodorsal tegmental nucleus have been hypothesized to play a critical role in the-generation and maintenance of rapid eye movement sleep. Less is known about the function of non-cholinergic laterodorsal tegmental nucleus neurons. As part of our ongoing studies of the brainstem circuitry controlling behavioral state, we have begun to investigate the functional properties of these neurons. In the course of these experiments, we have observed a novel response to the neurotransmitter noradrenaline. Whole-cell patch-clamp recordings of laterodorsal tegmental nucleus neurons were carried out in 21- to 35-day-old rat brain slices. A subpopulation of laterodorsal tegmental nucleus cells responded to a 30-s application of 50 microM noradrenaline with depolarization and a decrease in input resistance which lasted several minutes. Following return to resting membrane potential, these cells invariably exhibited barrages of excitatory postsynaptic potentials which lasted at least 12 min. These excitatory postsynaptic potentials were reversibly abolished by bath application of tetrodotoxin, as well as by the non-N-methyl-D-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione, but were insensitive to application of the N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonopentanoic acid. To examine whether these neurons were cholinergic, the recorded cells were labeled with biocytin and tested for co-localization with reduced nicotinamide adenine dinucleotide phosphate-diaphorase, a marker for laterodorsal tegmental nucleus cholinergic neurons. In every instance, neurons with these properties were non-cholinergic. However, they were always located in close proximity to reduced nicotinamide adenine dinucleotide phosphate-diaphorase-positive laterodorsal tegmental nucleus cells. The present data indicate that noradrenaline, in addition to directly inhibiting cholinergic cells of the laterodorsal tegmental nucleus, also results in the direct and indirect excitation of non-cholinergic cells of the laterodorsal tegmental nucleus. The indirect excitation is long lasting and mediated by glutamatergic mechanisms. Our working hypothesis is that these non-cholinergic cells are local circuit inhibitory interneurons and that prolonged excitation of these neurons by noradrenaline may serve as a mechanism for inhibition of cholinergic laterodorsal tegmental nucleus cells during wakefulness, when noradrenaline tone is high.

Pre- and post-hatching developmental changes in beta-adrenoceptor subtypes in chick brain

This study used [3H]CGP 12177 as a radioligand to determine the beta1 and beta2-adrenoceptor changes from the pre-hatching E17 stage, where the beta2 subtype is first detected, to the post-hatching P30 stage. While beta1-adrenoceptors were found to be present from E18 and were limited to cerebellum and hyperstriatum in all stages studied, beta2-adrenoceptors showed a wider distribution throughout the brain. In most of the structures analysed both beta1- and beta2-adrenoceptor binding values reached a maximum in the P2 stage, followed by a decrease over the following days. A second increase in both subtypes was detected again in the P15 and P30 stages. These results support the notion of a specific role for beta-adrenoceptors in neural plasticity in the first week after hatching and suggest that the beta2 subtype is the main adrenoceptor in chick brain throughout its development.

Adrenergic innervation of the monkey thalamus: an immunohistochemical study

The distribution and function of the neurotransmitter adrenaline in the primate brain are poorly understood. Biochemical studies have shown the presence of adrenaline or its biosynthetic enzyme, phenylethanolamine-N-methyltransferase, in the rat and human thalamus. However, the distribution of the adrenergic fibres in the thalamus has only been demonstrated in rats. We study the adrenergic innervation of the macaque monkey thalamus using immunohistochemistry against phenyletanolamine-N-methyltransferase. The distribution of phenyletanolamine-N-methyltransferase-immunoreactive fibres is markedly heterogeneous and principally restricted to those nuclei, or their portions, that are located in or close to the midline, with the highest density being found in the paraventricular, parafascicular and mediodorsal nuclei. The paraventricular nucleus is densely innervated by adrenergic axons throughout, while the densest innervation of the parafascicular nucleus is located in its medial part and the strongest mediodorsal nuclear immunolabelling is found in its most posterior and medial region. Moderate or low concentrations of phenyletanolamine-N-methyltransferase-immunopositive fibres are present in the paratenial nucleus, and all parts of the central nucleus, nucleus reuniens, central medial nucleus, centromedian nucleus, medial geniculate body and medial pulvinar nucleus, while only scattered immunoreactive axons are found in other thalamic nuclei. The morphology of the phenyletanolamine-N-methyltransferase-immunoreactive axons is quite diverse, as they have different diameters and most are endowed with diversely-shaped varicosities. These findings are the first morphological evidence for the presence of adrenergic innervation in the primate thalamus and reveal that this innervation is highly selective, heterogeneous and more widely distributed in primates than in rats. The thalamic nuclei innervated by adrenaline are connected to widespread limbic and associative cortical areas as well as to subcortical structures, in particular the neostriatum and amygdala. We hypothesize that thalamic adrenaline may be implicated in emotional, social and attentional mechanisms through its facilitation of co-ordinated action by these brain regions.

Beta-adrenoceptors in the tree shrew brain. I. Distribution and characterization of [125I]iodocyanopindolol binding sites

1. The number and distribution pattern of beta-adrenergic receptors in the brain have been reported to be species specific. The aim of the present study was to describe binding of the beta-adrenoceptor ligand [125I]iodocyanopindolol in the brain of the tree shrew (Tupaia belangeri), a species which provides an appropriate model for studies of psychosocial stress and its consequences on central nervous processes. 2. 125I-Iodocyanopindolol (125ICYP) labeling revealed a high degree of nonspecific binding, which was due mainly to interactions of this ligand with serotonin binding sites. For a quantitative evaluation of beta 1- and beta 2-adrenoceptors, serotonin binding sites had to be blocked by 100 microM 5HT. 3. Binding of the radioligand to beta 1- and beta 2-adrenoceptors was characterized using the beta 1-specific antagonist CGP20712A and the beta 2-specific antagonist ICI118.551. beta 1-adrenoceptor binding is present in the whole brain, revealing low receptor numbers in most brain regions (up to 1.5 to 2.7 fmol/mg). A slight enrichment was observed in cortical areas (lateral orbital cortex: 4.0 +/- 0.7 fmol/mg) and in the cerebellar molecular layer (8.7 +/- 1.0 fmol/mg). 4. Competition experiments demonstrated high- and low-affinity binding sites with considerable variations in Ki values for CGP20712A, showing that various affinity states of beta 1-adrenoceptors are present in the brain (Ki: 0.61 nM to 67.1 microM). In the hippocampus, only low-affinity beta 1-adrenoceptors were detected (Ki: 1.3 +/- 0.2 microM). Since it is known that 125ICYP labels not only membrane bound but also internalized beta-adrenoceptors, it can be assumed that the large population of the low-affinity sites represents internalized receptors which may be abundant due to a high sequestration rate. 5. High numbers of beta 2-adrenoceptors are present in only a few brain structures of tree shrews (external layer of the olfactory bulb, 15.8 +/- 2.0 fmol/mg; claustrum, 19.3 +/- 1.5 fmol/mg; anteroventral thalamic nucleus, 19.4 +/- 1.5 fmol/mg; cerebellar molecular layer, 55.0 +/- 4.3 fmol/mg). Also for this class of beta-adrenoceptors, high- and low-affinity binding sites for the beta 2-selective antagonist ICI118.551 were observed, indicating that 125ICYP labels membrane bound and internalized beta 2-adrenoceptors. Only in the cerebellar molecular layer was a high percentage of high-affinity beta 2-adrenoceptors detected (Ki for ICI118.551 was 1.8 +/- 0.3 nM for 90% of the receptors). 6. In conclusion, beta 1- and beta 2-adrenoceptor binding can be localized and quantified by in vitro receptor autoradiography in the brains of tree shrews when serotonergic binding sites are blocked. Modulatory effects of long-term psychosocial conflict on the central nervous beta-adrenoceptor system in male tree shrews are described in the following paper.

Dopamine depletion attenuates amphetamine-induced increases of cortical acetylcholine release

The extent to which the d-amphetamine (2.0 mg/kg)-induced increase in cortical acetylcholine release is mediated by dopamine and/or noradrenaline was assessed using in vivo microdialysis in freely moving rats. Unilateral 6-hydroxydopamine lesions of the mesotelencephalic dopaminergic system, which depleted forebrain dopamine by 99% on the lesioned side, significantly attenuated the effect of d-amphetamine on cortical acetylcholine release compared to a surgical control group (160% baseline vs. 270%), suggesting that dopamine at least in part mediates this effect of d-amphetamine. In contrast, bilateral 6-hydroxydopamine lesions of the dorsal noradrenergic bundle which depleted forebrain noradrenaline by at least 95% had no effect on d-amphetamine-stimulated cortical acetylcholine release. These results point to an important role for forebrain dopamine in the regulation of cortically projecting cholinergic neurons and fail to support the hypothesis that the ascending noradrenergic projections of the locus coeruleus are significantly involved.

Cellular localization of messenger RNA for beta-1 and beta-2 adrenergic receptors in rat brain: an in situ hybridization study

Selective, 35S-labeled, oligonucleotide probes were designed from sequences of the rat beta-1 and beta-2 adrenoceptor messenger RNAs for use in situ hybridization experiments on sections of unfixed rat brain and spinal cord. After hybridized sections were exposed to film or dipped in autoradiographic emulsion, specific and selective labeling patterns characteristic for each receptor messenger RNA and region of the central nervous system were observed. For example, labeling for beta-1 messenger RNA was found in the anterior olfactory nucleus, cerebral cortex, lateral intermediate septal nucleus, reticular thalamic nucleus, oculomotor complex, vestibular nuclei, deep cerebellar nuclei, trapezoid nucleus, abducens nucleus, ventrolateral pontine and medullary reticular formations, the intermediate gray matter of the spinal cord and in the pineal gland, while beta-2 messenger RNA labeling was strongest in the olfactory bulb, piriform cortex, hippocampal formation, thalamic intralaminar nuclei and cerebellar cortex. In some of these regions the beta-1 labeling seemed mainly confined to the cell nucleus. Whether or not this apparently nuclear labeling is specific, i.e. indicates synthesis of beta-1 receptor, remains to be established. However, all labeling patterns described disappeared when excess unlabeled probes were added to their respective radiolabeled probes or when sense probes were employed. Since the in situ method labels only cell bodies that produce the messenger RNA for these two beta receptor subtypes, a comparison between these maps and those of past autoradiographic studies mapping the location of central beta receptors using drugs as radioligands may produce further insights regarding the pre- and postsynaptic localization of these receptors in the various parts of the central nervous system circuitry.

The evidence for astrocytes as a target for central noradrenergic activity: expression of adrenergic receptors

Our recognition and understanding of adrenergic receptor expression by astrocytes and their cultured counterparts, astroglia, has occurred primarily over the past 2 decades. The advances in our knowledge have come about largely through the advent of new techniques with which to study neurotransmitter receptors, coupled with improvements in our ability to isolate, purify, and identify this central nervous system (CNS) cell type. The development of pharmacological tools such as second messenger assays, iodinated ligands, autoradiography, and intracellular electrophysiological recordings, paralleled that of cultured clonal cells lines of glial origin, purified astroglial primary cultures, isolations of astrocytes from adult tissues, and immunocytochemical staining for the astrocyte-specific glial fibrillary acidic protein (GFAP). As these techniques were combined and applied to the study of astrocyte pharmacology, our understanding of adrenergic receptor expression by these cells deepened. This review is an account of how these events have shaped our understanding of astrocytic adrenergic receptor expression.

Multiple heteroreceptors on limbic thalamic axons: M2 acetylcholine, serotonin1B, beta 2-adrenoceptors, mu-opioid, and neurotensin

Ligand binding to many transmitter receptors is much higher in layer Ia of rat posterior cingulate cortex than it is in other layers, and this is where most axons from the anterior thalamus terminate. The present study explores the possibility that a number of receptors may be expressed on axons from limbic thalamic nuclei that terminate in layer Ia. Unilateral thalamic lesions were placed in rats and, 2 weeks later, five ligand binding protocols, coverslip autoradiography, and single grain counting techniques were used to quantify binding in control and ablated hemispheres. Binding to the following receptor subtypes was analyzed: M2 acetylcholine, 3H-oxotremorine-M, or 3H-AF-DX 116 with 50 nM pirenzepine; serotonin1B, 125I-(-)-cyanopindolol with 30 microM isoproterenol; beta 2-adrenoceptors, 125I-(-)-cyanopindolol with 1 microM serotonin and 10 microM atenolol; mu-opioid, 3H-T[r-D-Ala-Gly-MePhe-Gly-ol; neurotensin, 3H-neurotensin. Thalamic lesions reduced binding in two laminar patterns. In one pattern, there was a major reduction in binding in most superficial layers with that in layer Ia ranging from 50 to 70% for binding to M2 muscarinic and serotonin1B receptors. Binding to beta 2-adrenoceptors was also reduced in most superficial layers but to a lesser extent. In the second pattern, reductions were limited to layer I with losses in layer Ia of 20-30% for mu-opioid and neurotensin receptors. In no instance was layer Ia binding completely abolished (i.e., postlesion peaks remained). Since the transmitters for each of the five receptors analyzed in this study are not synthesized by anterior or laterodorsal thalamic neurons, these receptors are heteroreceptors. The greatest postlesion reduction in M2 binding was for AF-DX 116 and so most M2 heteroreceptors are of the "cardiac" subtype. Finally, the diverse population of heteroreceptors on limbic thalamic axons provides for presynaptic modulation by a wide range of transmitter systems and suggests that thalamocortical transmission may not be a simple, unmodulated event.

Distribution of excitatory and inhibitory amino acid, sigma, monoamine, catecholamine, acetylcholine, opioid, neurotensin, substance P, adenosine and neuropeptide Y receptors in human motor and somatosensory cortex

Autoradiography was used to visualise N-methyl-D-aspartate, phencyclidine, strychnine-insensitive glycine, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid, kainic acid, benzodiazepine, gamma-aminobutyric acid type A, sigma, serotonergic, dopaminergic, alpha 2-adrenergic, beta-adrenergic, muscarinic cholinergic, nicotinic, opioid, neurotensin, substance P, adenosine A1 and neuropeptide Y receptors in the human primary motor (Brodmann's area 4) and somatosensory cortex (Brodmann's areas 3, 2 and 1). With the exception of serotonin type 2 receptors, all receptor types examined had a similar distribution in area 4 which showed little dependence on the underlying distribution of cell somata, often continuing unaltered through the somatosensory cortex despite marked cytoarchitectural changes. The highest densities occurred in the outer (most superficial) 30-40% of the cortical grey matter, followed by a band of relatively low binding and then moderate levels in the inner (deeper) region. In many instances, an additional band of dense binding could be discerned in the region of laminae IV/Va running unbroken through both gyri. The distribution of most receptor types in the somatosensory cortex also followed this pattern, except for opioid and kainic acid receptors which showed higher levels in the inner rather than the outer third of this region. At the edge of area 4, a change occurred such that a high density outer band appeared, giving these receptor types the same pattern in area 4 as the majority. Serotonin type 2 receptor levels were quite low in the outermost region of area 4, although the pattern was otherwise similar to that of the other receptors. Thus, with the exception of serotonin receptors, the similarity in many binding site distributions recently noted in area 4 of the rhesus monkey also tends to occur in the human area 4, to the extent that 2 ligands will reverse their usual cortical binding pattern to conform with the common area 4 pattern.

Noradrenergic facilitation of motor neurons: localization of adrenergic receptors in neurons and nonneuronal cells in the trigeminal motor nucleus

Both alpha- and beta-adrenergic receptors (ARs) are involved in the facilitation of the monosynaptic jaw-closing reflex in the trigeminal motor nucleus (MoV) caused by norepinephrine (NE). The amplitude of muscle spindle afferent-evoked EPSPs in masseter motor neurons is 65% greater when noradrenergic axons to the motor nucleus are concomitantly activated and seems to be due to a presynaptic mechanism (Vornov, J. J., and J. Sutin. 1986. J. Neurosci. 6: 30-37). To determine the subtypes of ARs located on motor neurons and other cells, the cytotoxic lectin Ricin communis was injected into the masseter nerve of the trigeminal motor root to eliminate motor neurons in the masseter subnucleus of MoV. Autoradiography following incubation of tissue sections in the alpha 1 ligand 125IBE 2254 (125I-HEAT) or the nonselective beta ligand [125I]iodocyanopindolol (125ICYP) showed a decrease in alpha 1-AR binding related to the motor neuron degeneration and an increase in beta-AR binding associated with the glial reaction. To determine the extent to which glial proliferation was responsible for the increase in beta-ARs, cytosine arabinofuranoside (AraC) was administered to inhibit mitosis. Following AraC treatment, the total number of glial cells in the ricin-treated MoV was similar to that in normal MoV. Both beta-AR density and GFAP immunoreactivity remain increased, but to a lesser degree than following the ricin treatment alone. AraC also partially prevented the increase of immunolabeled or histochemically visualized microglia and capillary endothelial cells. The coincidence of the increases in beta-AR binding and GFAP in a region devoid of neurons argues that reactive astrocytes and other nonneuronal cells express beta-ARs in vivo. To determine whether the increase in astroglial beta-ARs was due to an up-regulation resulting from transynaptic degeneration of NE terminals, NE content was measured in MoV tissue punches, and NE terminals were visualized by immunocytochemical labeling of dopamine-beta-hydroxylase. NE content and NE terminal density remained unchanged following ricin-induced motor neuron degeneration.

Effects of GABAergic and noradrenergic injections into the cerebellar flocculus on vestibulo-ocular reflexes in the rabbit

The role of the vesitibulo-cerebellum of the rabbit in the control of the vestibulo-ocular response (VOR) and optokinetic response (OKR) reflexes was investigated by bilateral microinjections, into the flocculus, of substances affecting GABAergic or noradrenergic neurotransmission. GABA, the main transmitter through which cerebellar interneurons inhibit Purkinje cells directly or indirectly, acts normally through GABAA receptors (mainly located in the granular layer) and GABAB receptors (predominantly located in the molecular layer). Despite this different distribution, floccular injections of the GABAA agonist muscimol and of the GABAB agonist baclofen had a similar effect, presumably by profound inhibition of Purkinje cells. This effect consisted of a reduction in the gain of the VOR (in darkness and in light) as well as of the OKR by at least 50%. This provides firm evidence that the net effect of normal Purkinje-cell activity in the flocculus is to enhance the VOR and OKR, rather than to inhibit these responses, as is sometimes supposed. Intrafloccular injections of the beta-noradrenergic agonist isoproterenol or the beta-noradrenergic antagonist sotalol did not affect the basic magnitude of the VOR and OKR. However, these substances markedly affected the adaptive processes, which cause the VOR and OKR to change its magnitude when this is no longer adequate in stabilizing the retinal image. By a suitable combination of vestibular and optokinetic stimuli, consistent upward changes in the gain of these reflexes could be reliably and reproducibly induced in uninjected animals. Floccular injections of sotalol impaired these adaptive changes markedly, whereas injections of isoproterenol enhanced the adaptation, particularly of the VOR measured in darkness. These findings strongly suggest that the effectuation of adaptive changes of vestibular, and possibly other, motor control systems is strongly facilitated by the noradrenergic innervation of the flocculus, which is normally provided by the locus coeruleus (LC), by way of the beta-receptor system, although the activity of this system does not directly affect the signal transmission supporting the basic reflexes as such.

Locus coeruleus and dorsal pontine reticular influences on the gain of vestibulospinal reflexes

Experimental anatomical and physiological studies have shown that noradrenergic locus coeruleus (LC) neurons, which are NE-sensitive due to inhibitory adrenoceptors, send inhibitory afferents to neurons of the peri-LC alpha and the adjacent dorsal pontine reticular formation (pRF); on the other hand these tegmental neurons, which are, in part at least, cholinergic as well as cholinoceptive, send excitatory afferents to the medullary inhibitory reticulospinal (RS) system. Experiments performed in precollicular decerebrate cats indicate that these pontine structures exert a regulatory influence on posture as well as on the gain of vestibulospinal (VS) reflexes. In particular, the increased discharge of dorsal pontine reticular neurons, and the related inhibitory RS neurons induced by microinjection of cholinergic agonists into the peri-LC alpha and the adjacent pRF of one side, decreased the postural activity, but greatly increased the response gain of the ipsilateral triceps brachii in response to stimulation of labyrinth receptors resulting from roll tilt of the animal (at 0.15 Hz, +/- 10 degrees). Similar results were also obtained when the discharge of these pontine and medullary reticular neurons was raised, either by local injection into the peri-LC alpha and the dorsal pRF of the beta-adrenergic antagonist propranolol, which blocked the inhibitory influence of the noradrenergic LC neurons on these structures, or by local injection into the LC complex of an alpha 2- or beta-adrenergic agonist (clonidine or isoproterenol) which led to functional inactivation of the noradrenergic neurons; in the latter case the effects were bilateral. Just the opposite results were obtained after microinjection into the LC of a cholinergic agonist, leading to activation of the corresponding neurons. Evidence was also presented indicating that the cholinergic excitatory afferents to the LC originated from the ipsilateral dorsal pRF. The effects described above were dose-dependent and site-specific, as shown by histological controls. Under given conditions, the decrease in postural activity induced either by direct activation of presumptive cholinergic and cholinoceptive pRF neurons or by inactivation of noradrenergic and NE-sensitive LC neurons was followed by transient episodes of postural atonia which lasted several minutes and affected the ipsilateral and sometimes also the contralateral limbs. In these instances, the EMG modulation of the corresponding triceps brachii to animal tilt was suppressed. These findings suggest two different ranges of operation for the noradrenergic and cholinergic structures located in the dorsolateral pontine tegmentum, leading either to a decrease or to an increase in gain of the VS reflexes. The cellular basis of these gain changes is discussed.(ABSTRACT TRUNCATED AT 400 WORDS)

Regional and laminar distributions of alpha 1-adrenoceptors and their subtypes in human and rat hippocampus

The distributions of the alpha 1-adrenoceptor and its subtypes (alpha 1A and alpha 1B) in human and rat hippocampus are analysed by quantitative receptor autoradiography. alpha 1-Adrenoceptors are labelled by [3H]prazosin. The alpha 1A subtype is visualized by [3H]prazosin after irreversible blockade of alpha 1B adrenoceptors with chloroethylclonidine or directly by [3H]5-methyl-urapidil. The alpha 1B subtype is investigated by [3H]prazosin binding in the presence of the alpha 1A antagonist 5-methyl-urapidil. Considerable differences in the regional and laminar patterns of alpha 1-adrenoceptors are found between rat and human hippocampi. The rat hippocampus is characterized by a low overall density and a rather homogeneous regional and laminar distribution. This is in contrast to the human pattern, which shows a much higher overall level of alpha 1 receptor density and a restriction of alpha 1 receptors to the CA3 region of Ammon's horn and the dentate gyrus. Moreover, alpha 1A and alpha 1B receptors of the human hippocampus are differentially distributed with the alpha 1A subtype concentrated in the hilus and lucidum layer of CA3, and the alpha 1B subtype concentrated in the molecular layer of the dentate gyrus. Additionally, the distribution of alpha 1 receptors is compared with the distribution of 5-hydroxytryptamine 1A receptors. The subtype specific pattern is correlated with the distribution of glutamatergic systems in the human (but not in the rat) hippocampus. alpha 1A Receptor localization coincides with the target area of the mossy fibre system, and alpha 1B receptors are preferentially localized in the target area of the hippocampal associational fibres and partly of the perforant pathway. This result points to possible interactions between noradrenaline- and glutamate-mediated neurotransmission differentiated by topographically segregated alpha 1-adrenoceptor subtypes.

Effects of local pontine injection of noradrenergic agents on desynchronized sleep of the cat

Brain noradrenergic (NA) systems have often been implicated in the regulation of desynchronized sleep (DS). The present experiments investigate the effects on DS of the microinjection, into the cat dorsal pontine tegmentum (DPT), of the alpha 2-agonist clonidine (CLON), the beta-agonist isoproterenol and the beta-antagonist propranolol. The DPT comprises most NA neurons belonging to the locus coeruleus (LC) complex, as well as other cell groups thought to be crucially involved in DS generation. Cats were implanted with standard electrodes (electroencephalogram, electrooculogram and electromyogram, PGO waves, hippocampal activity) and with guide tubes aimed at the DPT. Unilateral or bilateral injections (0.25 microliter) were performed by way of thin cannulae inserted through the guide tubes. Polygraphic activity was then recorded in daily sessions lasting 4 h and scored according to standard criteria. Bilateral injections of CLON into the DPT greatly reduced DS, while unilateral injections were much less effective. Since CLON is known to powerfully inhibit NA LC neurons, its effect was thus opposite to that expected on the basis of the reciprocal interaction model of DS generation, which postulates that NA neurons in the LC inhibit DS-executive cells located in the pontine reticular formation. Bilateral injections of the beta-agonist isoproterenol also reduced DS, while the beta-antagonist propranolol consistently enhanced it, the latter largely due to an increased number of DS episodes. These effects were dose-dependent and strictly site-specific, since injections in immediately neighboring structures were ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

Noradrenergic agents into the cerebellar anterior vermis modify the gain of vestibulospinal reflexes in the cat

The noradrenergic (NA) afferent projection to the cerebellar cortex, which originates mainly from the locus coeruleus (LC), may act on the target neurons by utilizing both alpha- and beta-adrenoceptors. Experiments performed in decerebrate cats have shown that unilateral injection into the vermal cortex of the cerebellar anterior lobe of 0.25 microliter of the alpha 1-adrenergic agonist metoxamine or the alpha 2-agonist clonidine (at 2-8 micrograms/microliters of saline) as well as of the non-selective beta-agonist isoproterenol (at 8-16 micrograms/microliters) decreased the postural activity in the ipsilateral forelimb, while the extensor tonus either remained unmodified or slightly increased on the contralateral side. The same agents also increased the gain of the vestibulospinal (VS) reflexes elicited by recording the multiunit EMG responses of the ipsilateral and the contralateral triceps brachii to roll tilt of the animal (at 0.15 Hz, +/- 10 degrees), leading to sinusoidal stimulation of labyrinth receptors. The crossed effects were more prominent for the alpha 2- than for the alpha 1- and beta-agonists. Only slight changes in the phase angle of the responses were observed. The effects described above appeared 5-10 min after the injection, reached the peak values after 15-30 min and disappeared within 2 h. The effective area was located within the third and/or the fourth folium of the culmen rostral to the fissura prima, 1.4-1.8 mm lateral to the midline. This area corresponded to zone B of the cerebellar cortex, which projects to the ipsilateral lateral vestibular nucleus (LVN), on which it exerts a prominent inhibitory influence. In fact, monopolar stimulation of this area with three negative pulses (at 300/sec) performed prior to the local injection inhibited the spontaneous EMG activity of the ipsilateral triceps brachii. The effects described above were dose-dependent; injection of an equal volume of saline was ineffective. All changes in posture and reflexes elicited by metoxamine or clonidine were impaired by previous injection into the same corticocerebellar area of the corresponding alpha 1- or alpha 2-adrenergic antagonist prazosin or yohimbine, respectively (0.25 microliters at 8-16 micrograms/microliters). However, cross-interactions between alpha 1- and alpha 2-adrenergic agonists and antagonists were also observed. In fact, injection of the alpha 2-adrenergic antagonist yohimbine prevented the occurrence of all the metoxamine effects, while administration of the alpha 1-adrenergic antagonist prazosin prevented the occurrence of the ipsilateral, but not of the contralateral effects induced by clonidine injection.(ABSTRACT TRUNCATED AT 400 WORDS)

Fetal ethanol exposure diminishes hippocampal beta-adrenergic receptor density while sparing muscarinic receptors during development

Because of ostensible effects of fetal exposure to ethanol on cardiac and memory functions, beta-adrenergic and muscarinic receptor binding were surveyed in hippocampus and heart in 8- and 17-day-old rat pups. Pregnant, multiparous rats were intubated with either 6 g/kg ethanol or isocaloric dextrose twice daily from gestational days 10-16. At birth, offspring were fostered to untreated mothers. Pups exposed to ethanol had diminished birth weights, although there was no difference in the amount of weight gain by ethanol and control dams during gestation, nor in litter size. Ethanol pups remained smaller than control pups, but this difference was significant only until 8 days of age. At 17 days of age, ethanol pups had fewer hippocampal beta-adrenergic receptors than age-matched controls; muscarinic receptors and CA1 cell densities were not disparate. Parallel studies suggested that approximately 50% of the hippocampal beta-adrenergic receptors in 8-day-olds were of the beta 1 and beta 2 subtypes, while by 17 days of age approximately 70% of the receptors were beta 1. There was an ontogenetic increment in both beta-adrenergic and muscarinic binding from 8 to 17 days of age in hippocampus. No differences between age or drug groups were found in the binding measures in heart tissue. The present findings indicate that fetal ethanol treatment affects developmental measures and beta-adrenergic receptors in the hippocampus in a quasi-selective manner, but not hippocampal CA1-cell density.

Neuromodulation: associative and nonlinear adaptation

Neuromodulation, the interaction between at least two chemical messengers in the nervous system, serves as a mechanism by which biochemical association can occur. A simple, yet compelling, hypothesis is that the criteria for expression of associative learning and memory are subserved by biochemical events which are also associative in nature. A neuromodulatory interaction that has been linked to memory function and which has been the subject of biochemical inquiry is the interaction between the catecholamine, norepinephrine (NE) and the neuropeptide, vasopressin (AVP). Studies described in this report show that vasopressin acts to potentiate norepinephrine (NE)-induced cyclic adenosine monophosphate (cAMP) accumulation in the hippocampus by a calcium-dependent mechanism. Results of these studies are considered in the context of the nonlinear properties of synergism and conditionality and in the context of the associative learning requirements of spatial and temporal coupling. Secondly, the calcium dependency of AVP-induced neuromodulation is considered in relation to the calcium dependency for induction of associative long-term potentiation. Lastly, the potential for changes in neuronal morphology in response to neuromodulatory events is considered. By using vasopressin potentiation of noradrenalin-induced cAMP formation as a model system, I have applied the theoretical framework of associative learning and memory to test the hypothesis that neuromodulation can serve as a biochemical analog of associative cognitive events.

Injections of beta-noradrenergic substances in the flocculus of rabbits affect adaptation of the VOR gain

Noradrenaline (NA) has been implicated as a neuromodulator in plasticity, presumably facilitating adaptive processes. Recent experiments by others have suggested a modulatory role of NA in adaptive changes in the vestibulo-ocular reflex (VOR). These experiments showed that general depletion of brain NA resulted in a decreased ability to produce adaptive changes in the VOR gain. In order to identify the specific brain region responsible for these effects, as well as the nature of the adrenoceptors involved, we injected beta-adrenergic substances bilaterally into the flocculus of rabbits. The flocculus is known to receive noradrenergic afferents and, moreover, ablation of the flocculus interferes strongly with the normal adaptive changes in the VOR gain. We injected the beta-agonist isoproterenol and the beta-antagonist sotalol, and compared the adaptive capacity of the rabbits after these injections to that in a situation without injection. The rabbit was oscillated in a direction opposite to the direction of motion of the platform on which the rabbit was mounted, a condition which normally results in an increase in the VOR gain, measured either in light or in darkness. Injection of the beta-agonist did not greatly affect the adaptation of the VOR measured in the light. In darkness, the increase in gain after the injection of isoproterenol was larger than in the non-injection experiments in 9 out of 10 rabbits. The beta-antagonist sotalol reduced the adaptation of the VOR gain significantly in the light, as well as in darkness. In a control condition without pressure for adaptation (only intermittent testing of the VOR gain over a period of 2.5 h), the gain of the VOR either remained unaffected or was only slightly affected by similar injections of beta-adrenergic agents in individual rabbits. For the group as a whole, these effects were insignificant. We conclude from these results that noradrenergic systems facilitate the adaptation of the VOR gain to retinal slip in rabbits, without affecting the VOR gain directly. At least part of this influence is exerted through beta-receptors located in the cerebellar flocculus.

Receptor modification in the brains of spontaneously hypertensive and Wistar-Kyoto rats: regionally specific and selective increase in cerebellar beta 2-adrenoceptors

Quantitative in vitro autoradiography was used to study beta-adrenergic and benzodiazepine receptor density in discrete regions from sagittal brain sections of 20 week old hypertensive (SHR) and normotensive (WKY) rats. The density of beta-adrenoceptors was increased by 68% in the granule cell layer of the cerebellum of the SHR without a change in receptor affinity; this increase was specific for receptors of the beta 2-subtype. On the other hand, benzodiazepine receptor density was unchanged in the cerebella of SHR. These results indicate that brain beta-adrenoceptors are differentially modulated by the hypertensive state which may be either a cause or a consequence of alterations in adrenergic nervous system activity found in the SHR.

Alzheimer's disease: changes in hippocampal N-methyl-D-aspartate, quisqualate, neurotensin, adenosine, benzodiazepine, serotonin and opioid receptors--an autoradiographic study

The following receptors were assessed post-mortem in the hippocampi (anterior region) of eight patients with Alzheimer's disease and nine age-matched controls, using autoradiography: N-methyl-D-aspartate (including glutamate, phencyclidine and glycine binding sites), quisqualate, kainic acid, adenosine A1, benzodiazepine, serotonin (1 and 2), muscarinic cholinergic, beta-adrenergic, neurotensin and opioid receptors. In CA1 there were significant parallel losses of binding to the three N-methyl-D-aspartate-linked sites (average reduction 46%) and also losses of quisqualate (38%) and serotonin2 (58%) receptor binding, with a 47% loss of binding to A1 sites. Binding to all of these receptors was also reduced in CA3 (except binding to A1 sites which was normal) but only the serotonin2 receptor binding loss reached significance (52%). A significant reduction in binding was also observed in the entorhinal area to the N-methyl-D-aspartate receptor-linked sites (average reduction = 39%), benzodiazepine (40%) and serotonin2 receptors (45%), and there was a loss of binding to neurotensin (57%) and opioid receptors (42%). Significant reductions in the dentate gyrus molecular layer were seen for serotonin2 receptors (44%), and binding to opioid (44%) and A1 receptors (46%). Levels of ligand binding to muscarinic cholinergic, serotonin1, beta-adrenergic and kainic acid receptors were not significantly different from control values in any of the four areas examined. These results provide support for observations of selective receptor changes in Alzheimer's disease involving a broad range of receptor types which encompass both excitatory amino acid and other receptors (notably serotonin2, A1, benzodiazepine, neurotensin and opioid receptors). The implications of the pattern of receptor changes for the suggestion that excitotoxicity plays a role in the disease are discussed, as is the possible contribution of the receptor changes to the symptomatology of Alzheimer's disease.

Modulation of desynchronized sleep through microinjection of beta-adrenergic agonists and antagonists in the dorsal pontine tegmentum of the cat

Brain noradrenergic systems have often been implicated in the regulation of desynchronized sleep (DS). In particular, the reciprocal interaction model of DS generation postulates that noradrenergic neurons in the locus coeruleus inhibit DS-executive cells located in the pontine reticular formation. Accordingly, since noradrenergic inhibition is generally mediated by beta-receptors, one should expect beta-agonists to decrease and beta-antagonists to increase DS. However, systemic injection experiments yielded just the opposite results. Assuming that local microinjection techniques were better suited to testing the model, beta-agonists and antagonists were directly infused into the dorsal pontine tegmentum (DPT), a region crucially implicated in the generation of DS. Cats were implanted with standard electrodes for polygraphic recordings and with guide tubes for chemical microinjections. It was observed that, when injected into the DPT, the beta-agonist isoproterenol almost suppressed DS, while the beta-antagonist propranolol consistently enhanced it, the latter largely due to an increased number of DS episodes. These effects were dose-dependent and strictly site-specific, since injections in immediately neighbouring structures were ineffective. These results: (a) confirm that cell groups located in the DPT play a key role in the generation of DS, and (b) indicate that they undergo a strong noradrenergic modulation, being inhibited by beta-receptor stimulation and disinhibited by beta-receptor blockade as predicted by the reciprocal interaction model.

Immunocytochemical localization of beta-adrenergic receptors in the rat brain

The localization of beta-adrenergic receptors (beta-AdR) in the rat brain was examined immunocytochemically with antibody against affinity-purified beta 2-receptors. This antibody was confirmed to cross-react with beta 1-AdR. beta-AdR were widely but unevenly distributed in the rat brain. In the forebrain and diencephalon, cells with beta-AdR were abundant in the cerebral cortex, hippocampus, and various hypothalamic nuclei other than the ventromedial hypothalamic nucleus and the suprachiasmatic nucleus. Few or no cells with beta-AdR were found in the thalamus except in the lateral and medial geniculate nucleus, habenular nucleus and paraventricular thalamic nucleus. The striatum, globus pallidus, and accumbens nucleus also contained few beta-AdR. In the lower brainstem, areas related to auditory function, such as the inferior colliculus, the nucleus of the lateral lemniscus and the cochlear nuclei, as well as areas related to cerebellar function, such as the reticulotegmental nucleus of the pons, the pontine nuclei, the lateral reticular nucleus and the inferior olive, were rich in beta-AdR. Considerable immunoreactivity was also found in the parabrachial nucleus and the nucleus of the solitary tract.

Multiple changes in noradrenergic mechanisms in the coeruleo-hippocampal pathway during aging. Structural and functional correlates in intraocular double grafts

Age-related changes of the coeruleo-hippocampal noradrenergic system were investigated using intraocular double transplants. Pieces of fetal hippocampus were grafted into the anterior chamber of the eye and placed into contact with previously inserted locus coeruleus grafts. Ages of both transplants and hosts were varied to enable studies of intrinsic versus extrinsic determinants of aging in an isolated neuronal circuit. Four different experimental groups, with the approximate age in months of grafts/hosts at the time of recording given in parentheses, were studied; young grafts in the eyes of young hosts (3/7), young grafts in the eyes of old hosts (3/23), mature transplants in adult host rats (8/12) and aged transplants in the eyes of aged rats (21/25). Extracellular recordings from the hippocampal part of the double grafts were performed. Superfusion with alpha-adrenergic antagonists and the alpha 2-agonist clonidine elicited significant increases in the discharge rate of the grafted hippocampal neurons in all groups except the aged transplants in the aged hosts (21/25), where a small excitation was elicited with clonidine and no effect at all was seen with alpha-adrenergic antagonists. The host age did not seem to be important since young transplants in the old hosts (3/23) showed a similar increase in discharge rate as transplants in the young and adult hosts. Tyrosine hydroxylase immunohistochemistry and high-performance liquid chromatography revealed that hippocampal transplants remaining in oculo for a minimum of 6-10 months became permanently hyperinnervated by noradrenergic fibers from the locus coeruleus grafts. The density of noradrenergic fibers was significantly lower in young transplants.(ABSTRACT TRUNCATED AT 250 WORDS)

Presence of catecholaminergic axon-terminals containing beta-adrenergic receptor in the periventricular zone of the rat hypothalamus

The present study, using a light microscopic double-immunofluorescence method, has revealed the presence of fibers containing both tyrosine hydroxylase- and beta-adrenergic receptor-like immunoreactivities in the rat hypothalamic periventricular zone. Subsequent immunoelectron microscopic analysis demonstrated that these belong to axon terminals. These findings suggest that presynaptic beta-adrenergic receptor is present in catecholaminergic terminals.

Age-related alterations in noradrenergic input to the hippocampal formation: structural and functional studies in intraocular transplants

Intrinsic versus extrinsic determinants of age-related alterations in hippocampal noradrenergic transmission were investigated using intraocular allografts in rats. Three groups of animals were examined: young hippocampal transplants in young hosts, old transplants in old hosts and young transplants in old hosts. Postsynaptic sensitivity to noradrenaline (NA) was measured by extracellular recordings of spontaneous activity and superfusion with known concentrations of catecholamines in the anterior chamber of the eye. Hill plots demonstrated that the dose-response relationships of NA-induced depressions were linear and parallel in the 3 groups. Aged hippocampal grafts displayed a highly significant subsensitivity to NA of one order of magnitude. The EC50 for this group was 203.1 microM as compared to 29.2 in young grafts. Young intraocular grafts in old hosts responded similarly to transplants in young hosts, with an EC50 of 32.4 microM for the depressant actions of NA. Collaterals of the host iris sympathetic ground plexus invaded the hippocampal grafts. The density of this noradrenergic innervation was estimated by immunohistochemistry for tyrosine hydroxylase. A slightly increased density and fluorescence intensity of the noradrenergic fibers were observed in the old transplants as compared to the young transplants in young and old hosts. This was correlated with a significantly (P less than 0.01) increased content of NA in old transplants, as measured with high performance liquid chromatography. The old transplants also contained a large number of autofluorescent lipofuchsin granules, which were absent in the young transplants, regardless of the recipient age. Taken together, these results suggest the existence of alterations in pre- as well as postsynaptic noradrenergic mechanisms in the aging hippocampus. These changes were dependent on transplant age rather than host age, thus suggesting an involvement of intrinsic rather than extrinsic determinants in this model system.

Expression of beta-adrenergic receptors by astrocytes isolated from adult rat cortex

Astrocytes are the most numerous cell type in the central nervous system. When cultured, these cells express a wide variety of receptors for neurotransmitters. Nonetheless, it has yet to be firmly established that adult astrocytes in situ express receptors for neurotransmitters. In this report the technique of combined receptor autoradiography and immunocytochemistry has been applied to isolated astrocytes from adult animals to examine beta-adrenergic receptor (beta-AR) expression by these cells. It is shown that fibrous and protoplasmic astrocytes isolated from adult rat cerebral cortices specifically bind the beta-AR ligand iodocyanopindolol and that this binding is inhibited by the beta-AR ligands propranolol and isoproterenol. These results indicate that at least two of the major morphological subtypes of adult astrocytes express beta-ARs.

Distribution of major neurotransmitter receptors in the motor and somatosensory cortex of the rhesus monkey

The in vitro quantitative autoradiographic technique was used to characterize the distributions of alpha 1, alpha 2, beta 1 and beta 2 adrenergic, D1 and D2 dopaminergic, 5-HT1 and 5-HT2 serotonergic, M1 and M2 cholinergic, GABAA and benzodiazepine receptors in the motor (Brodmann's area 4) and somatosensory (Brodmann's areas 3, 1 and 2) cortex of the adult rhesus monkey. All receptor subtypes studied were present throughout all layers of both areas. In the somatosensory cortex, each receptor had its own laminar distribution. Some subtypes of the same receptor (5-HT1 and 5-HT2; alpha 1 and alpha 2) had complementary distributions while others (beta 1 and beta 2; D1 and D2; M1 and M2) had largely overlapping distributions. In contrast, different receptors had remarkably coincidental distributions in the motor cortex. In this area, they all tended to concentrate in layers I, II and the upper part of layer III. However, such coextensive distribution of many types of neurotransmitter receptors is not observed in motor cortex of rats and humans and therefore may be a distinctive feature of motor cortex in the rhesus monkey. The findings described in this paper indicate that somatosensory and motor areas are distinct in their receptor architecture and that receptor autoradiography provides a useful complement to classical histological techniques in elucidating areal differences in the cortex.

Electrophysiological characterization of adrenoceptors in the rat dorsal hippocampus. I. Receptors mediating the effect of microiontophoretically applied norepinephrine

The rat hippocampus receives a dense noradrenergic innervation originating exclusively from the locus coeruleus. The present electrophysiological study was undertaken to characterize the adrenoceptor mediating the suppressant effect of microiontophoretically applied norepinephrine (NE) on CA1 and CA3 dorsal hippocampus pyramidal neurons of the rat. The rank order of potency of microiontophoretically applied agonists, in suppressing the firing rate of hippocampus pyramidal neurons was: oxymetazoline greater than NE greater than phenylephrine greater than isoproterenol greater than clonidine. In the hippocampus, oxymetazoline was more potent than NE, whereas it was ineffective in the lateral geniculate nucleus where the effect of NE is mediated by an alpha 1-adrenoceptor. Low currents of clonidine antagonized the effect of NE suggesting that clonidine may exert a partial agonistic effect. The rank order of potency of i.v. administered adrenergic antagonists in blocking the suppressant effect of microiontophoretically applied NE was: idazoxan much greater than prazosin much greater than propranolol. Idazoxan also blocked the effect of oxymetazoline, phenylephrine, and isoproterenol but did not modify the effect of microiontophoretically applied gamma-aminobutyric acid (GABA). In addition, idazoxan, applied by microiontophoresis, readily blocked the suppressant effect of NE without affecting that of GABA. These results suggest that the suppressant effect of microiontophoretically applied NE on rat dorsal hippocampus pyramidal neurons is primarily mediated by alpha 2-adrenoceptors.

Electrophysiological effects of norepinephrine on Purkinje neurons in intraocular cerebellar grafts: alpha- vs beta-specificity

The present study investigates the receptor specificity of the electrophysiological effects of norepinephrine (NE) on cerebellar Purkinje neurons. Intraocular cerebellar grafts were utilized to allow both superfusion and local administration of selective adrenergic agonists and antagonists. Fetal cerebellar anlagen (E13-15) were homologously transplanted to the anterior chamber of the eye of adult recipient rats and allowed to mature in the eye for at least 5 weeks. Spontaneous activity of Purkinje neurons was recorded extracellularly in the intraocular grafts. Superfusion of 5 microM NE caused elevations of the spontaneous firing rate. Superfusion of 30 microM NE caused depressions, which were occasionally preceded by an excitation. Iontophoretic application of NE to grafted Purkinje neurons primarily caused depressions of the spontaneous discharge rate. Thus, the NE-induced excitations previously reported from in vitro slices are not anomalies of the in vitro slice preparation, but can be observed with superfusion of NE in our in vivo preparation as well. In general, the excitations caused by low doses of superfused NE were blocked by timolol, a specific beta-adrenergic antagonist, while the depressions caused by 30 microM superfused NE or iontophoretically applied NE were blocked by the specific alpha-adrenergic antagonist phentolamine. Large doses of sotalol were found to block both excitatory and depressant responses while lower doses only antagonized the NE-induced excitations. Taken together, these results suggest that the inhibitory effects of NE on PUrkinje neuron firing rate in intraocular cerebellar grafts in vivo are mediated via an alpha-adrenergic receptor mechanism, while the excitations caused by NE may be beta-mediated.

A detailed mapping of histamine H1-receptors in guinea-pig central nervous system established by autoradiography with [125I]iodobolpyramine

[125I]Iodobolpyramine, a potent and selective histamine H1-receptor antagonist derived from mepyramine, was used to generate light microscopic autoradiograms on sections of guinea-pig brain and spinal cord. Histamine H1-receptors were labelled with high sensitivity over a low background as determined using mianserin or other H1-receptor antagonists as competing agents. An atlas of H1-receptors was established using five sagittal sections and 39 frontal sections, the latter serially prepared at 50 micron intervals. Labelled areas were identified by comparison with corresponding, classically stained sections and their density was rated according to an arbitrary scale. Autoradiographic grains were detected in a large variety of gray matter areas whereas they were generally absent from white matter areas. In the cerebral cortex, H1-receptors are present in all areas and layers with a higher density in lamina IV. In the hippocampal formation, H1-receptors display a laminated pattern of distribution and are the most abundant in the dentate gyrus (hilus and molecular layer) and in several areas of the subiculum and commissural complex. In the amygdaloid complex, the highest densities are found in the medial group of nuclei. In the basal forebrain, the striatum is moderately labelled whereas the nucleus accumbens, islands of Calleja and most septal nuclei are highly labelled. In the thalamus, H1-receptors are present in high density, particularly in the anterior, median and lateral groups of nuclei. In the hypothalamus the labelling is highly heterogeneous with high densities in, for example, medial preoptic area, dorsomedial, ventromedial and most posterior nuclei, including the tuberomammillary complex in which histaminergic perikarya and short axons are present.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased beta-adrenergic receptors in rat brain after chronic administration of the selective serotonin uptake inhibitor fluoxetine

Fluoxetine, a novel antidepressant compound that potently and selectively inhibits serotonin uptake, was chronically administered to laboratory rats. Using in vitro receptor autoradiographic techniques, we found that the binding of [3H]-dihydroalprenolol [( 3H]-DHA) decreased significantly in frontal cortex layers. Analysis of saturation experiments indicated that the reduction was due to a change in number but not affinity of [3H]-DHA binding sites. The data support the hypothesis that the mechanism of action of most antidepressant compounds involves a change in beta-adrenergic receptor function.