Further mapping out of central noradrenaline neuron systems: projections of the "subcoeruleus" area

Understanding electrical and chemical transmission in the brain

The histochemical Falck-Hillarp method for the localization of dopamine (DA), noradrenaline (NA) and serotonin in the central nervous system (CNS) of rodents was introduced in the 1960s. It supported the existence of chemical neurotransmission in the CNS. The monoamine neurons in the lower brain stem formed monosynaptic ascending systems to the telencephalon and diencephalon and monoamine descending systems to the entire spinal cord. The monoamines were early on suggested to operate via synaptic chemical transmission in the CNS. This chemical transmission reduced the impact of electrical transmission. In 1969 and the 1970s indications were obtained that important modes of chemical monoamine communication in the CNS also took place through the extra-synaptic fluid, the extracellular fluid, and long-distance communication in the cerebrospinal fluid involving diffusion and flow of transmitters like DA, NA and serotonin. In 1986, this type of transmission was named volume transmission (VT) by Agnati and Fuxe and their colleagues, also characterized by transmitter varicosity and receptor mismatches. The short and long-distance VT pathways were characterized by volume fraction, tortuosity and clearance. Electrical transmission also exists in the mammalian CNS, but chemical transmission is in dominance. One electrical mode is represented by electrical synapses formed by gap junctions which represent low resistant passages between nerve cells. It allows for a more rapid passage of action potentials between nerve cells compared to chemical transmission. The second mode is based on the ability of synaptic currents to generate electrical fields to modulate chemical transmission. One aim is to understand how chemical transmission can be integrated with electrical transmission and how putative (aquaporin water channel, dopamine D2R and adenosine A2AR) complexes in astrocytes can significancy participate in the clearance of waste products from the glymphatic system. VT may also help accomplish the operation of the acupuncture meridians essential for Chinese medicine in view of the indicated existence of extracellular VT pathways.

Evidence for a dynorphin-mediated inner ear immune/inflammatory response and glutamate-induced neural excitotoxicity: an updated analysis

Acoustic overstimulation (AOS) is defined as the stressful overexposure to high-intensity sounds. AOS is a precipitating factor that leads to a glutamate (GLU)-induced Type I auditory neural excitotoxicity and an activation of an immune/inflammatory/oxidative stress response within the inner ear, often resulting in cochlear hearing loss. The dendrites of the Type I auditory neural neurons that innervate the inner hair cells (IHCs), and respond to the IHC release of the excitatory neurotransmitter GLU, are themselves directly innervated by the dynorphin (DYN)-bearing axon terminals of the descending brain stem lateral olivocochlear (LOC) system. DYNs are known to increase GLU availability, potentiate GLU excitotoxicity, and induce superoxide production. DYNs also increase the production of proinflammatory cytokines by modulating immune/inflammatory signal transduction pathways. Evidence is provided supporting the possibility that the GLU-mediated Type I auditory neural dendritic swelling, inflammation, excitotoxicity, and cochlear hearing loss that follow AOS may be part of a brain stem-activated, DYN-mediated cascade of inflammatory events subsequent to a LOC release of DYNs into the cochlea. In support of a DYN-mediated cascade of events are established investigations linking DYNs to the immune/inflammatory/excitotoxic response in other neural systems.

The Neurotoxin DSP-4 Induces Hyperalgesia in Rats that is Accompanied by Spinal Oxidative Stress and Cytokine Production

Central neuropathic pain (CNP) a significant problem for many people, is not well-understood and difficult to manage. Dysfunction of the central noradrenergic system originating in the locus coeruleus (LC) may be a causative factor in the development of CNP. The LC is the major noradrenergic nucleus of the brain and plays a significant role in central modulation of nociceptive neurotransmission. Here, we examined CNS pathophysiological changes induced by intraperitoneal administration of the neurotoxin DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride). Administration of DSP-4 decreased levels of norepinephrine in spinal tissue and cerebrospinal fluid (CSF) and led to the development of thermal and mechanical hyperalgesia over 21 days, that was reversible with morphine. Hyperalgesia was accompanied by significant increases in noradrenochrome (oxidized norepinephrine) and expression of 4-hydroxynonenal in CSF and spinal cord tissue respectively at day 21, indicative of oxidative stress. In addition, spinal levels of pro-inflammatory cytokines (interleukins 6 and 17A, tumor necrosis factor-α), as well as the anti-inflammatory cytokine interleukin10 were also significantly elevated at day 21, indicating that an inflammatory response occurred. The inflammatory effect of DSP-4 presented in this study that includes oxidative stress may be particularly useful in elucidating mechanisms of CNP in inflammatory disease states.

Changes in the Cholinergic, Catecholaminergic, Orexinergic and Serotonergic Structures Forming Part of the Sleep Systems of Adult Mice Exposed to Intrauterine Alcohol

We examined the effect of chronic prenatal alcohol exposure on certain neuronal systems involved with the sleep-wake cycle of C57BL/6J mice exposed to prenatal alcohol once they had reached 56 days post-natal. Pregnant mice were exposed to alcohol, through oral gavage, on gestational days 7–16, with recorded blood alcohol concentration (BAC)s averaging 1.84 mg/ml (chronic alcohol group, CA). Two control groups, an oral gavage sucrose control group (chronic alcohol control group, CAc) and a non-treated control group (NTc), were also examined. At 56 days post-natal, the pups from each group were sacrificed and the whole brain sectioned in a coronal plane and immunolabeled for cholineacetyltransferase (ChAT), tyrosine hydroxylase (TH), serotonin (5HT) and orexin-A (OxA) which labels cholinergic, catecholaminergic, serotonergic and orexinergic structures respectively. The overall nuclear organization and neuronal morphology were identical in all three groups studied, and resemble that previously reported for laboratory rodents. Quantification of the estimated numbers of ChAT immunopositive (+) neurons of the pons, the TH+ neurons of the pons and the OxA+ neurons of the hypothalamus showed no statistically significant difference between the three experimental groups. The stereologically estimated areas and volumes of OxA+ neurons in the CA group were statistically significantly larger than the groups not exposed to prenatal alcohol, but the ChAT+ neurons in the CA group were statistically significantly smaller. The density of orexinergic boutons in the anterior cingulate cortex was lower in the CA group than the other groups. No statistically significant difference was found in the area and volume of TH+ neurons between the three experimental groups. These differences are discussed in relation to the sleep disorders recorded in children with fetal alcohol spectrum disorder (FASD).

Distribution of catecholaminergic presympathetic-premotor neurons in the rat lower brainstem

We previously characterized the organization of presympathetic-premotor neurons (PSPMNs), which send descending poly-synaptic projections with collaterals to skeletal muscle and the adrenal gland. Such neurons may play a role in shaping integrated adaptive responses, and many of them were found within well-characterized regions of noradrenergic cell populations suggesting that some of the PSPMNs are catecholaminergic. To address this issue, we used retrograde trans-synaptic tract-tracing with attenuated pseudorabies virus (PRV) recombinants combined with multi-label immunofluorescence to identify PSPMNs expressing tyrosine hydroxylase (TH). Our findings indicate that TH-immunoreactive (ir) PSPMNs are present throughout the brainstem within multiple cell populations, including the A1, C1, C2, C3, A5 and A7 cell groups along with the locus coeruleus (LC) and the nucleus subcoeruleus (SubC). The largest numbers of TH-ir PSPMNs were located within the LC and SubC. Within SubC and the A7 cell group, about 70% of TH-ir neurons were PSPMNs, which was a significantly greater fraction of neurons than in the other brain regions we examined. These findings indicate that TH-ir neurons near the pontomesencephalic junction that are distributed across the LC, SubC, and the A7 may play a prominent role in somatomotor-sympathetic integration, and that the major functional role of the A7 and SubC noradrenergic cell groups maybe in the coordination of concomitant activation of somatomotor and sympathetic outflows. These neurons may participate in mediating homeostatic adaptations that require simultaneous activation of sympathetic and somatomotor nerves in the periphery.

Organization of cholinergic, catecholaminergic, serotonergic and orexinergic nuclei in three strepsirrhine primates: Galago demidoff, Perodicticus potto and Lemur catta

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Cholinergic, catecholaminergic, serotonergic and orexinergic systems in the brains of strepsirrhine primates are described.

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All species show a similar global pattern of nuclear organization of these systems.

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For these systems there appears to be a primate-typical organization.

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Certain variations indicate a phylogenetic relationship between primates and megachiropterans.

The nuclear organization of the cholinergic, catecholaminergic, serotonergic and orexinergic systems in the brains of three species of strepsirrhine primates is presented. We aimed to investigate the nuclear complement of these neural systems in comparison to those of simian primates, megachiropterans and other mammalian species. The brains were coronally sectioned and immunohistochemically stained with antibodies against choline acetyltransferase, tyrosine hydroxylase, serotonin and orexin-A. The nuclei identified were identical among the strepsirrhine species investigated and identical to previous reports in simian primates. Moreover, a general similarity to other mammals was found, but specific differences in the nuclear complement highlighted potential phylogenetic interrelationships. The central feature of interest was the structure of the locus coeruleus complex in the primates, where a central compactly packed core (A6c) of tyrosine hydroxylase immunopositive neurons was surrounded by a shell of less densely packed (A6d) tyrosine hydroxylase immunopositive neurons. This combination of compact and diffuse divisions of the locus coeruleus complex is only found in primates and megachiropterans of all the mammalian species studied to date. This neural character, along with variances in a range of other neural characters, supports the phylogenetic grouping of primates with megachiropterans as a sister group.

Etude Histopathologique et Neurochimique Suite a des Lesions Unilaterales du Locus Coeruleus Chez le Rat et de la Region Postlocus Chez le Chat (Part 2)

Unilateral lesions involving the area immediately caudal to the locus coeruleus in the cat are associated with slight decreases of noradrenaline (NA) in both sides of the spinal cord without any important change of serotonin (5-HT) concentration in the spinal cord and of N A and 5-HT concentrations in the cerebral cortex of both sides. In other cats with similar lesions involving the same area bilaterally (postlocus lesions) NA is markedly decreased and 5-H T slightly decreased in the hypothalamus and spinal cord but the concentrations of NA and 5-HT of the cerebral cortex, striât urn and thalamus are not conspicuously modified by such postlocus lesions.

Unilateral lesions in the area of the loci coeruleus and subcoeruleus in the rat are associated with a marked decrease of noradrenaline (NA) in the ipsilateral cerebral cortex without any important change of NA in the contralateral cortex and in the spinal cord of both sides. Under such conditions the concentrations of serotonin (5-HT) are not significantly modified in the cerebral cortex and spinal cord of both sides. NA and 5-HT concentrations of the cerebral cortex of both sides are unmodified by unilateral lesions of the cerebellar nuclei in the rat. In the latter group of animals slight increases of NA and 5-HT in the spinal cord are significant in comparison to the values obtained in the control animals but not from one side of the spinal cord to the other.

These results further support the suggestion that the noradrenergic coeruleo-cortical pathway originating in the loci coeruleus and subcoeruleus ascends on the same side and ends in the ipsilateral cerebral cortex. In the light of the results of this investigation and of those reported in a companion paper (Marchand et ai, 1979) NA fibers reaching the hypothalamus and spinal cord most likely arise from neurons located caudally in respect to the locus coeruleus. Moreover NA fibers ending in the hypothalamus do not ascend in the dorsolateral part of the isthmic area and, therefore, have a different course than the N A fibers reaching the cerebral cortex and thalamus.

Volume Transmission in Central Dopamine and Noradrenaline Neurons and Its Astroglial Targets

Already in the 1960s the architecture and pharmacology of the brainstem dopamine (DA) and noradrenaline (NA) neurons with formation of vast numbers of DA and NA terminal plexa of the central nervous system (CNS) indicated that they may not only communicate via synaptic transmission. In the 1980s the theory of volume transmission (VT) was introduced as a major communication together with synaptic transmission in the CNS. VT is an extracellular and cerebrospinal fluid transmission of chemical signals like transmitters, modulators etc. moving along energy gradients making diffusion and flow of VT signals possible. VT interacts with synaptic transmission mainly through direct receptor-receptor interactions in synaptic and extrasynaptic heteroreceptor complexes and their signaling cascades. The DA and NA neurons are specialized for extrasynaptic VT at the soma-dendrtitic and terminal level. The catecholamines released target multiple DA and adrenergic subtypes on nerve cells, astroglia and microglia which are the major cell components of the trophic units building up the neural-glial networks of the CNS. DA and NA VT can modulate not only the strength of synaptic transmission but also the VT signaling of the astroglia and microglia of high relevance for neuron-glia interactions. The catecholamine VT targeting astroglia can modulate the fundamental functions of astroglia observed in neuroenergetics, in the Glymphatic system, in the central renin-angiotensin system and in the production of long-distance calcium waves. Also the astrocytic and microglial DA and adrenergic receptor subtypes mediating DA and NA VT can be significant drug targets in neurological and psychiatric disease.

Cellular and axonal diversity in molecular layer heterotopia of the rat cerebellar vermis

Molecular layer heterotopia of the cerebellar primary fissure are a characteristic of many rat strains and are hypothesized to result from defect of granule cells exiting the external granule cell layer during cerebellar development. However, the cellular and axonal constituents of these malformations remain poorly understood. In the present report, we use histochemistry and immunocytochemistry to identify neuronal, glial, and axonal classes in molecular layer heterotopia. In particular, we identify parvalbumin-expressing molecular layer interneurons in heterotopia as well as three glial cell types including Bergmann glia, Olig2-expressing oligodendrocytes, and Iba1-expressing microglia. In addition, we document the presence of myelinated, serotonergic, catecholaminergic, and cholinergic axons in heterotopia indicating possible spinal and brainstem afferent projections to heterotopic cells. These findings are relevant toward understanding the mechanisms of normal and abnormal cerebellar development.

The effects of locus coeruleus and norepinephrine in methamphetamine toxicity

The activity of locus coeruleus (LC) neurons has been extensively investigated in a variety of behavioural states. In fact this norepinephrine (NE)-containing nucleus modulates many physiological and pathological conditions including the sleep-waking cycle, movement disorders, mood alterations, convulsive seizures, and the effects of drugs such as psychostimulants and opioids. This review focuses on the modulation exerted by central NE pathways on the behavioural and neurotoxic effects produced by the psychostimulant methamphetamine, essentially the modulation of the activity of mesencephalic dopamine (DA) neurons. In fact, although NE in itself mediates some behavioural effects induced by methamphetamine, NE modulation of DA release is pivotal for methamphetamine-induced behavioural states and neurotoxicity. These interactions are discussed on the basis of the state of the art of the functional neuroanatomy of central NE- and DA systems. Emphasis is given to those brain sites possessing a remarkable overlapping of both neurotransmitters.

Nuclear organization of cholinergic, putative catecholaminergic, serotonergic and orexinergic systems in the brain of the African pygmy mouse (Mus minutoides): organizational complexity is preserved in small brains

This study investigated the nuclear organization of four immunohistochemically identifiable neural systems (cholinergic, catecholaminergic, serotonergic and orexinergic) within the brain of the African pygmy mouse (Mus minutoides). The African pygmy mice studied had a brain mass of around 275 mg, making these the smallest rodent brains to date in which these neural systems have been investigated. In contrast to the assumption that in this small brain there would be fewer subdivisions of these neural systems, we found that all nuclei generally observed for these systems in other rodent brains were also present in the brain of the African pygmy mouse. As with other rodents previously studied in the subfamily Murinae, we observed the presence of cortical cholinergic neurons and a compactly organized locus coeruleus. These two features of these systems have not been observed in the non-Murinae rodents studied to date. Thus, the African pygmy mouse displays what might be considered a typical Murinae brain organization, and despite its small size, the brain does not appear to be any less complexly organized than other rodent brains, even those that are over 100 times larger such as the Cape porcupine brain. The results are consistent with the notion that changes in brain size do not affect the evolution of nuclear organization of complex neural systems. Thus, species belonging to the same order generally have the same number and complement of the subdivisions, or nuclei, of specific neural systems despite differences in brain size, phenotype or time since evolutionary divergence.

On the role of volume transmission and receptor-receptor interactions in social behaviour: focus on central catecholamine and oxytocin neurons

This article is focused on understanding the mechanisms for the interactions between the central catecholamine (CA) and oxytocin (OXY) neurons and their relevance for brain function especially social behaviour in the field of pair bonding. Such a topic is analysed under two perspectives namely the intercellular communication modes between CA and OXT neurons and the molecular integrative mechanisms at the plasma membrane level between their respective decoding systems. As a matter of fact, recent observations strongly indicate a major role of volume transmission and receptor-receptor interactions in the CA/OXT neuron interplay in the brain control of social behaviour and pair bonding. This article is part of a Special Issue entitled: Brain Integration.

Organization of cholinergic, putative catecholaminergic and serotonergic nuclei in the diencephalon, midbrain and pons of sub-adult male giraffes

The current study describes the nuclear organization and neuronal morphology of the cholinergic, putative catecholaminergic and serotonergic systems within the diencephalon, midbrain and pons of the giraffe using immunohistochemistry for choline acetyltransferase, tyrosine hydroxylase and serotonin. The giraffe has a unique phenotype (the long neck), a large brain (over 500 g) and is a non-domesticated animal, while previous studies examining the brains of other Artiodactyls have all been undertaken on domesticated animals. The aim of the present study was to investigate possible differences in the nuclear organization and neuronal morphology of the above-mentioned systems compared to that seen in other Artiodactyls and mammals. The nuclear organization of all three systems within the giraffe brain was similar to that of other Artiodactyls. Some features of interest were noted for the giraffe and in comparison to other mammals studied. The cholinergic neuronal somata of the laterodorsal tegmental nucleus were slightly larger than those of the pedunculopontine tegmental nucleus, a feature not described in other mammals. The putative catecholaminergic system of the giraffe appeared to lack an A15 dorsal nucleus, which is commonly seen in other mammals but absent in the Artiodactyls, had a large and expanded substantia nigra pars reticulata (A9 ventral), a small diffuse portion of the locus coerueleus (A6d), an expansive subcoeruleus (A7sc and A7d), and lacked the A4 nucleus of the locus coeruleus complex. The nuclear organization of the serotonergic system of the giraffe was identical to that seen in all other eutherian mammals studied to date. These observations in the giraffe demonstrate that despite significant changes in life history, phenotype, brain size and time of divergence, species within the same order show the same nuclear organization of the systems investigated.

Fos expression in pontomedullary catecholaminergic cells following rapid eye movement sleep-like episodes elicited by pontine carbachol in urethane-anesthetized rats

Pontine noradrenergic neurons of the locus coeruleus (LC) and sub-coeruleus (SubC) region cease firing during rapid eye movement sleep (REMS). This plays a permissive role in the generation of REMS and may contribute to state-dependent modulation of transmission in the CNS. Whether all pontomedullary catecholaminergic neurons, including those in the A1/C1, A2/C2 and A7 groups, have REMS-related suppression of activity has not been tested. We used Fos protein expression as an indirect marker of the level of neuronal activity and linear regression analysis to determine whether pontomedullary cells identified by tyrosine hydroxylase (TH) immunohistochemistry have reduced Fos expression following REMS-like state induced by pontine microinjections of a cholinergic agonist, carbachol in urethane-anesthetized rats. The percentage of Fos-positive TH cells was negatively correlated with the cumulative duration of REMS-like episodes induced during 140 min prior to brain harvesting in the A7 and rostral A5 groups bilaterally (P < 0.01 for both), and in SubC neurons on the side opposite to carbachol injection (P < 0.05). Dorsal medullary A2/C2 neurons did not exhibit such correlation, but their Fos expression (and that in A7, rostral A5 and SubC neurons) was positively correlated with the duration of the interval between the last REMS-like episode and the time of perfusion (P < 0.05). In contrast, neither of these correlations was significant for A1 /C1 or caudal A5 neurons. These findings suggest that, similar to the prototypic LC neurons, neurons of the A7, rostral A5 and A2/C2 groups have reduced or abolished activity during REMS, whereas A1 /IC1 and caudal A5 neurons do not have this feature. The reduced activity of A2/C2, A5 and A7 neurons during REMS, and the associated decrements in norepinephrine release, may cause state-dependent modulation of.transmission in brain somato- and viscerosensory, somatomotor, and cardiorespiratory pathways.

Distribution and morphology of putative catecholaminergic and serotonergic neurons in the brain of the greater canerat, Thryonomys swinderianus

The distribution, morphology and nuclear subdivisions of the putative catecholaminergic and serotonergic systems within the brain of the greater canerat (sometimes spelt cane rat) were identified following immunohistochemistry for tyrosine hydroxylase and serotonin. The aim of the present study was to investigate possible differences in the complement of nuclear subdivisions of these systems when comparing those of the greater canerat with reports of these systems in other rodents. The greater canerat was chosen for investigation as it is a large rodent (around 2.7kg body mass) and has an average brain mass of 13.75g, more than five times larger than that of the laboratory rat. The greater canerats used in the present study were caught from the wild, which is again another contrast to the laboratory rat. While these differences, especially that of size, may lead to the prediction of significant differences in the nuclear complement of these systems, we found that all nuclei identified in both systems in the laboratory rat and other rodents in several earlier studies had direct homologs in the brain of the greater canerat. Moreover, there were no additional nuclei in the brain of the greater canerat that are not found in the laboratory rat or other rodents. It is noted that the locus coeruleus of the laboratory rat differs in appearance to that reported for several other rodent species. The greater canerat is phylogenetically distant from the laboratory rat, but still a member of the order Rodentia. Thus, changes in the nuclear organization of these systems appears to demonstrate a form of constraint related to the phylogenetic level of the order.

Distribution and morphology of catecholaminergic and serotonergic neurons in the brain of the highveld gerbil, Tatera brantsii

The distribution, morphology and nuclear subdivisions of the putative catecholaminergic and serotonergic systems within the brain of the highveld gerbil were identified following immunohistochemistry for tyrosine hydroxylase and serotonin. The aim of the present study was to investigate possible differences in the complement of nuclear subdivisions of these systems when comparing those of the highveld gerbil with those of the laboratory rat. The highveld gerbil was chosen as it is relatively closely related to the laboratory rat, but the Gerbillinae and Murinae lineages diverged over 20 million years ago. Moreover, even though brain sizes are similar, the life history and phenotypes between these two species are substantially different. The gerbils used in the present study were caught from the wild, which is again another contrast to the laboratory rat. While these differences may lead to the prediction of significant differences in the nuclear complement of these systems, we found that all nuclei identified in both systems in the laboratory rat in several earlier studies had direct homologs in the brain of the highveld gerbil. Moreover, there were no additional nuclei in the brain of the highveld gerbil that are not found in the laboratory rat. The only discernable difference between the two species was a greater density and number of catecholaminergic neurons in the olfactory bulb of the highveld gerbil. Thus, the evolution of nuclear parcellation in these systems appears to demonstrate a form of phylogenetic constraint related to the order Rodentia.

From the Golgi–Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: Wiring and volume transmission

After Golgi-Cajal mapped neural circuits, the discovery and mapping of the central monoamine neurons opened up for a new understanding of interneuronal communication by indicating that another form of communication exists. For instance, it was found that dopamine may be released as a prolactin inhibitory factor from the median eminence, indicating an alternative mode of dopamine communication in the brain. Subsequently, the analysis of the locus coeruleus noradrenaline neurons demonstrated a novel type of lower brainstem neuron that monosynaptically and globally innervated the entire CNS. Furthermore, the ascending raphe serotonin neuron systems were found to globally innervate the forebrain with few synapses, and where deficits in serotonergic function appeared to play a major role in depression. We propose that serotonin reuptake inhibitors may produce antidepressant effects through increasing serotonergic neurotrophism in serotonin nerve cells and their targets by transactivation of receptor tyrosine kinases (RTK), involving direct or indirect receptor/RTK interactions. Early chemical neuroanatomical work on the monoamine neurons, involving primitive nervous systems and analysis of peptide neurons, indicated the existence of alternative modes of communication apart from synaptic transmission. In 1986, Agnati and Fuxe introduced the theory of two main types of intercellular communication in the brain: wiring and volume transmission (WT and VT). Synchronization of phasic activity in the monoamine cell clusters through electrotonic coupling and synaptic transmission (WT) enables optimal VT of monoamines in the target regions. Experimental work suggests an integration of WT and VT signals via receptor-receptor interactions, and a new theory of receptor-connexin interactions in electrical and mixed synapses is introduced. Consequently, a new model of brain function must be built, in which communication includes both WT and VT and receptor-receptor interactions in the integration of signals. This will lead to the unified execution of information handling and trophism for optimal brain function and survival.

The role of the locus coeruleus in the development of Parkinson's disease

In Parkinson's disease, together with the classic loss of dopamine neurons of the substantia nigra pars compacta, neuropathological studies and biochemical findings documented the occurrence of a concomitant significant cell death in the locus coeruleus. This review analyzes the latest data obtained from experimental parkinsonism indicating that, the loss of norepinephrine in Parkinson's disease might worsen the dopamine nigrostriatal damage. Within this latter context, basic research provided a new provocative hypothesis on the significance of locus coeruleus in conditioning the natural history of Parkinson's disease. In particular, the loss of a trophic influence of these neurons might be crucial in increasing the sensitivity of nigrostriatal dopamine axons to various neurotoxic insults. In line with this, recently, it has been shown that locus coeruleus activity plays a pivotal role in the expression of various immediate early genes and in inducing the phosphorilation of cyclic adenosine monophosphate response element-binding proteins, suggesting a role of the nucleus in sustaining a protective effect.

Involvement of the noradrenergic system in modulating the blink reflex in humans

Several researches have shown that the spinal reflex transmission in animals, as well as humans, was inhibited by alpha(2)-agonists, due to a disfacilitation of tonic noradrenergic control on motoneuronal output. To understand better the mechanisms regulating certain aspects of motor activity, here we reinvestigated the possible role of noradrenergic systems in modulating reflex activity of the brainstem in humans. To this aim, blink reflex responses (R1 and R2) evoked by electrical stimulation of the supraorbital nerve were electromyographically recorded in healthy volunteers. Both R1 and R2 areas were measured at 10-min intervals before and after i.v. injection of alpha(2)-agonist clonidine (0.5 microg/kg). The substance induced consistent depression of R1, which reached its maximum 40 min after drug administration (-43% of the control values). Ipsilateral R2 area resulted little affected by clonidine (-15% at 50 min), whereas no effects were observed in contralateral R2. Blood pressure values were never altered by drug injections. These results, taken together with previous observations, support the hypothesis that alpha(2)-agonist substances may cause a transient inactivation of noradrenergic neurons, thus releasing neurons involved in the circuitry of the blink reflex from a facilitatory drive. Since clonidine differentially modulated blink reflex responses, it is likely to assume that such a disfacilitation concerns mostly pontine units mediating the R1. However, the complexity of clonidine's effects at multiple pre- and postsynaptic sites does not allow us to exclude that other systems are involved in the alpha(2)-mediated control of facial motoneurons.

Hormonal integration of neurochemical and sensory signals governing female reproductive behavior

This review focuses on findings from our laboratory regarding mechanisms by which the ovarian steroid hormones, estradiol (E2) and progesterone (P), act in the hypothalamus (HYP) to regulate the expression of lordosis, an important component of female reproductive behavior in rats and many other species. The first section summarizes recent work suggesting that cGMP, perhaps via P-receptor activation, may be an intracellular mediator of the facilitatory actions of a variety of hormones and neurotransmitters on lordosis behavior in E2-primed rats. In the second section, we focus on E2 and P regulation of norepinephrine (NE) neurotransmission in the HYP. We review evidence that ovarian hormones act both peripherally and centrally to determine whether NE is released in the HYP in response to copulatory stimuli. We also suggest that the steroid milieu determines the cellular responses of hypothalamic neurons to released NE, favoring the activation of pathways implicated in the facilitation of both lordosis behavior and the preovulatory gonadotropin surge. It is likely that E2 and P have similar actions on other neurotransmitter and neuromodulator systems, thereby maximizing the probability that females are sexually receptive during the periovulatory period.

Cerebellar and spinal projections of the coeruleus complex in the duck: a fluorescent retrograde double-labeling study

The double fluorescent retrograde tracing technique was used to identify, within the coeruleus complex (Co complex) of the duck, the nerve cells projecting to the cerebellar cortex and to the spinal cord. This technique was also used to investigate the possibility that the cerebellar and spinal projections of the Co complex are collaterals of the same axons. In the same animal, nuclear Diamidino yellow dihydrochloride (DY) fluorescent tracer was placed into the cerebellar cortex of folia V-VII, and cytoplasmic fluorescent Fast blue (FB) dye was injected into C3-C4 spinal cord segments. FB labeled multipolar somata and DY fluorescent nuclei were intermingled within the dorsal caudal region of the locus coeruleus (LCo) and within the dorsal division of the nucleus subcoeruleus (dSCo). Moreover, in the LCo, a low proportion of double-labeled neurons (about 3-4% of labelings) was evidenced among single-labeled neurons. In the ventral division of the nucleus subcoeruleus (vSCo), occasional DY labeled nuclei were found, whereas FB-labeled cells were frequently present. The present findings reveal the location of the coeruleocerebellar and coeruleospinal projecting neurons within the Co complex of the duck. They are intermingled in the caudal portion of the LCo and along the rostrocaudal extent of the subjacent dSco. The LCo and the dSCo are the major source of the projections to the folia V-VII, whereas the vSCo contributes very slightly to the innervation of the cerebellar injected areas. Moreover, the double-labeling study demonstrates that in the duck a low percentage of neurons within the ventrolateral portion of the caudal region of the LCo projects both to the cerebellar cortex of folia V-VII and to C3-C4 spinal cord segments via collaterals. Therefore, these neurons simultaneously influence the cerebellar cortex and spinal cord. The possibility that the projections studied are noradrenergic and that they play a role in feeding is discussed.

Peripheral administration of cholecystokinin activates c-fos expression in the locus coeruleus/subcoeruleus nucleus, dorsal vagal complex and paraventricular nucleus via capsaicin-sensitive vagal afferents and CCK-A receptors in the rat

Intraperitoneal (i.p.) administration of sulfated CCK octapeptide (CCK-8S) has been shown to induce changes in neuronal activity in the nucleus of the solitary tract (NTS) and area postrema (AP), sensory parts of the dorsal vagal complex (DVC), and in the paraventricular nucleus of the hypothalamus (PVN), as determined by activation of c-fos expression. Whether peripheral CCK influences neuronal activity in the locus coeruleus (LC)/subcoeruleus nucleus (SC) was investigated in awake rats at intraperitoneal (i.p.) injection of CCK-8S by c-Fos immunohistochemistry. CCK-8S i.p. (25, 50, and 100 micrograms/kg, respectively) dose-dependently increased the average number of c-Fos-LI-positive cells/section in the LC/SC by the factor 5.9, 8.2, and 11.7, respectively. Pretreatment with the CCK-A receptor antagonist MK-329 (devazepide; 1 mg/kg and 2 mg/kg i.p.) reduced the CCK-induced increase in c-fos expression in the LC/SC by 54% and 75%, respectively; the CCK-B receptor antagonist L-365,260 had no effect. Perivagal capsaicin pretreatment diminished the CCK-induced increase in the number of c-Fos-LI-positive cells in the LC/SC by 65%. In comparison, the CCK-A antagonist devazepide (1 mg/kg and 2 mg/kg i.p.) reduced the increase in c-fos expression by 76% and 88% in the PVN, 69% and 88% in the NTS, 86% and 83%, respectively, in the AP. Capsaicin diminished the CCK-induced increase in c-Fos-LI-positive cells in the PVN by 64%, in the NTS by 60%, but in the AP only by 25%. Immunostaining against the nuclear antigen c-Fos and the cytoplasmatic antigen tyrosine hydroxylase (TH) showed that 40% of all c-Fos-LI-positive cells in the LC/SC were TH-LI positive at 25 micrograms CCK/kg. The data indicate that CCK-8S i.p. induces modulation of neuronal activity in the LC/SC, DVC and PVN predominantly by peripheral action of CCK-A receptors and capsaicin-sensitive vagal afferents. These findings suggest that the LC/SC is involved in CNS-mediated regulatory influences of peripheral CCK.

Cellular quantification of tyrosine hydroxylase in the rat brain by immunoautoradiography

We developed a rapid and sensitive radioimmunohistochemical method for the quantification of tyrosine hydroxylase (TH) at both the anatomical and cellular level. Coronal tissue sections from fresh-frozen rat brains were incubated in the presence of a TH monoclonal antibody. The reaction was revealed with a 35S-labeled secondary antibody. TH content was quantified in catecholaminergic brain areas by measuring optical density on autoradiographic films or silver grain density on autoradiographic emulsion-coated sections. Regional TH concentrations determined in the locus ceruleus (LC), substantia nigra pars compacta (SNC), and ventral tegmental area (VTA) were significantly increased by 45% after reserpine treatment in the LC but unchanged in the SNC and VTA. Microscopic examination of TH radioimmunolabeling showed a heavy accumulation of silver grains over catecholaminergic cell bodies. In the LC, grain density per cell was heterogeneous and higher in the ventral than in the dorsal part of the structure. After reserpine treatment, TH levels were significantly increased (57%) in the neurons of the LC but not in those of the SNC or VTA. The data support the validity of this radioimmunohistochemical method as a tool for quantifying TH protein at the cellular level and they confirm that TH protein content is differentially regulated in noradrenergic and dopaminergic neurons in response to reserpine.

Neuronal projections to the medial preoptic area of the sheep, with special reference to monoaminergic afferents: immunohistochemical and retrograde tract tracing studies

The preoptic area contains most of the luteinizing hormone releasing hormone immunoreactive neurons and numerous monoaminergic afferents whose cell origins are unknown in sheep. Using tract tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the medial preoptic area in sheep. Among the retrogradely labeled neurons, immunohistochemistry for tyrosine hydroxylase, dopamine-beta-hydroxylase, phenylethanolamine N-methyltransferase, and serotonin was used to characterize catecholamine and serotonin fluorogold labeled neurons. Most of the afferents came from the ipsilateral side to the injection site. It was observed that the medial preoptic area received major inputs from the diagonal band of Broca, the lateral septum, the thalamic paraventricular nucleus, the lateral hypothalamus, the area dorsolateral to the third ventricle, the perimamillary area, the amygdala, and the ventral part of the hippocampus. Other numerous, scattered, retrogradely labeled neurons were observed in the ventral part of the preoptic area, the vascular organ of the lamina terminalis, the ventromedial part of the hypothalamus, the periventricular area, the area lateral to the interpeduncular nucleus, and the dorsal vagal complex. Noradrenergic afferents came from the complex of the locus coeruleus (A6/A7 groups) and from the ventro-lateral medulla (group A1). However, dopaminergic and adrenergic neuronal groups retrogradely labeled with fluorogold were not observed. Serotoninergic fluorogold labeled neurons belonged to the medial raphe nucleus (B8, B5) and to the serotoninergic group situated lateral to the interpeduncular nucleus (S4). In the light of these anatomical data we hypothesize that these afferents have a role in the regulation of several functions of the preoptic area, particularly those related to reproduction. Accordingly these afferents could be involved in the control of luteinizing hormone releasing hormone (LHRH) pulsatility or of preovulatory LHRH surge.

Presynaptic inhibitory effect of TNF-alpha on the release of noradrenaline in isolated median eminence

The effect of tumor necrosis factor-alpha (TNF-alpha) on the stimulation-evoked release of noradrenaline (NA) from isolated rat median eminence (ME) was investigated, using a low-volume perfusion system. Median eminence, loaded with [3H]noradrenaline, was superfused with Krebs solution and stimulated electrically (2 Hz, 120 shocks). The effect of TNF-alpha was studied on the S2/S1 ratio. It was found that stimulation-evoked release of NA from noradrenergic axon terminals in the isolated rat ME was inhibited by TNF-alpha and this effect was concentration-dependent. In contrast, TNF-alpha had no effect on the release of [3H]NA from the spleen. Since NA released in the ME might be involved in the modulation of corticotropin-releasing factor (CRF) production, it is suggested that TNF-alpha, through presynaptic modulation of NA release from noradrenergic nerve terminals in the ME, might regulate CRF and other neurohormone release in this hypothalamic structure.

Ventral pontine catecholaminergic pathway mediates the vasopressin response to splanchnic osmostimulation in conscious rats

This study examines the role of catecholamines, cell bodies and fibers of passage within the subcoeruleus area (subLC) in the arginine vasopressin (AVP) response to splanchnic osmotic stimulation and hemorrhage. Bilateral chemical lesions were induced into the subLC, approximately 1 mm ventral to the locus coeruleus (LC), using 6-hydroxydopamine (6-OHDA) and ibotenic acid to selectively destroy catecholaminergic components and cell bodies, respectively. Vehicle and 5,7-dihydroxytryptamine (5,7-DHT) injections into the subLC area, 6-OHDA injections into the LC, as well as systemic desipramine pretreatment, were performed as controls for the possible non-specific effects of the lesions. Seven and 8 days later, plasma AVP level, plasma osmolality, mean arterial pressure and heart rate were measured following either gastric infusion of hypertonic (598 mOsm/kg; 2 ml/4 min) or isotonic (290 mOsm/kg) saline or a mild hemorrhage (2.5 ml/300 g) in conscious rats with indwelling tail artery catheters and naso-gastric tubes. 6-OHDA injections into subLC reduced the AVP response to the osmotic stimulation by 62.3% (P less than 0.01), as compared to vehicle-injected controls. These same rats demonstrated a normal AVP response to hemorrhage implying a specificity of the disrupted pathway. All controls confirmed that the effects of the 6-OHDA were due to specific action on noradrenergic components within the subLC area. Ibotenic acid lesions in the subLC did not significantly decrease the AVP response, demonstrating that mainly fibers and not cell bodies in this region are part of the pathway. 6-OHDA injections just anterior to the LC, where the dorsal noradrenergic bundle (DNAB) forms, reduced the AVP secretion due to hemorrhage by 77.0% (P less than 0.05), but had minor effects on the response to osmotic stimulation. These results indicate that catecholaminergic fibers travelling primarily within the subLC, in the ventral noradrenergic bundle (VNAB), carry splanchnic osmotic input to the hypothalamus, whereas the DNAB may mediate the AVP response to hemorrhage.

3-Methoxy-4-hydroxyphenylethyleneglycol concentrations in discrete hypothalamic nuclei reflect the activity of noradrenergic neurons

An analytical technique is described which permits the quantitation of picogram concentrations of 3-methoxy-4-hydroxyphenylethylene-glycol (MHPG) in acid hydrolyzed extracts of microdissected regions of the rat brain, and this procedure is used to determine if alterations in the activity of noradrenergic neurons are reflected by changes in the concentrations of MHPG in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the rat hypothalamus. MHPG was not detected in non-hydrolyzed samples of either the PVN or SON, but following acid hydrolysis (heating of samples at 94 degrees C for 5 min in 0.16 M perchloric acid) MHPG was detected in both of these regions. These results indicate that MHPG exists primarily as a conjugate in the PVN and SON. Neurotoxin-induced lesions of the ventral noradrenergic bundle decreased norepinephrine (NE) and MHPG concentrations in the PVN and SON, demonstrating that tissue levels of MHPG in these brain regions are dependent upon the presence of noradrenergic neurons. Electrical stimulation of the locus coeruleus increased MHPG concentrations in the PVN, but not in the SON, whereas electrical stimulation of the medial forebrain bundle increased MHPG concentrations in both of these regions. The alpha 2-adrenergic receptor antagonist idazoxan increased, while the alpha 2-adrenergic receptor agonist clonidine decreased MHPG concentrations in both the PVN and SON, but neither idazoxan nor clonidine altered NE concentrations in these regions. Immobilization of rats in the supine position increased MHPG concentrations in the PVN and SON, and this was accompanied by a decrease in NE concentrations in the SON.(ABSTRACT TRUNCATED AT 250 WORDS)

Noradrenergic innervation to the VMN or MPN is not necessary for lordosis

The purpose of the present study was to determine the importance of noradrenergic neurons terminating in the ventromedial nucleus (VMN) and medial preoptic nucleus (MPN) of the hypothalamus for lordosis behavior in ovariectomized, estrogen/progesterone-treated female rats. Seven days following bilateral injections of the noradrenergic neurotoxin 5-amino-2,4-dihydroxy-alpha-methylphenylethylamine (5-ADMP) into the ventral noradrenergic bundle (VNAB), norepinephrine (NE) concentrations (ng/mg protein) were reduced to 30-35% of control in the VMN and MPN. 5-ADMP-induced lesions of the VNAB also reduced lordosis quotients in these animals, and this effect was reversed by intracerebral ventricular administration of the alpha 1-adrenergic receptor agonist phenylephrine. These results indicate that neurotoxin-induced disruption of noradrenergic neurons in the VNAB is associated with a deficit in sexual receptivity in female rats. To determine if the reduction in sexual receptivity following 5-ADMP-induced lesions of the VNAB resulted from loss of noradrenergic neuronal projections specifically to the VMN or MPN, lordosis quotients were determined in ovariectomized, estrogen/progesterone-treated rats in which noradrenergic terminals in these hypothalamic nuclei were selectively lesioned. Injection of 5-ADMP directly into either the VMN or MPN reduced NE concentrations to 17% of control in these hypothalamic nuclei, but failed to alter lordosis. Furthermore, injection of phenylephrine into either the VMN or MPN of VNAB-lesioned rats failed to reinstate lordosis to the levels comparable to sham-lesioned controls. Taken together, these results indicate that noradrenergic neurons terminating in either the VMN or MPN are not essential for gonadal steroid induction of sexual receptivity in ovariectomized female rats.

Central neural pathway mediating splanchnic osmosensation

To determine the central neural pathway which carries splanchnic osmosensory information to vasopressin (AVP) neurons in the hypothalamus, bilateral electrolytic lesions were placed in the ascending catecholaminergic fiber bundle, the locus coeruleus (LC), the locus subcoeruleus (subLC), the lateral parabrachial nucleus (LPB), the caudal periaqueductal gray (PAG) and the median preoptic nucleus (MPO). Six and seven days later, plasma AVP levels, plasma osmolality, mean arterial pressure and heart rate were measured following gastric infusion of hypertonic (598 mosm/kg; 2 ml/4 min) or isotonic (290 mosm/kg) saline in conscious rats with indwelling tail artery catheters and nasogastric tubes. The most effective pontine lesions, which were located in the ventral locus subcoeruleus (vsubLC) approximately 1.0 mm below the LC, decreased the AVP response to hypertonic gastric infusion by 59.7% (P less than 0.05) as compared to sham-lesioned controls. In addition, unilateral vsubLC lesions dramatically reduced the catecholamine innervation of the ipsilateral paraventricular nucleus (PVN), as qualitatively determined with dopamine beta-hydroxylase immunocytochemistry, suggesting that a pathway ascending with catecholaminergic fibers was disrupted. Lesions of the MPO were also very effective, decreasing the AVP response to hypertonic saline infusion by 60.3% (P less than 0.05), suggesting that the MPO is an integral relay center in this pathway. On the other hand, LC, LPB and PAG lesions were ineffective. Systemic plasma osmolality or cardiovascular factors did not mediate the AVP response. These results demonstrate, for the first time, that splanchnic osmotic information is transmitted to the hypothalamus via pathways within the ascending catecholaminergic fiber bundles, the MPO is a relay center where peripheral and central osmotic information may be integrated, and the LC, LPB, and PAG are not part of the splanchnic osmotic pathway.

The effect of medial forebrain bundle lesion on thyrotropin secretion in the rat

The medial forebrain bundle (MFB) was partially lesioned with 6-hydroxydopamine (6-OHDA) in order to investigate the effect of deficient central noradrenergic regulation on thyrotropin (TSH) secretion in the rat. 6-OHDA injection into the MFB significantly reduced the noradrenaline (NA), dopamine (DA) and serotonin (5-HT) content of the whole hypothalamus. NA and 5-HT concentrations were also significantly decreased in the paraventricular nucleus (PVN). The MFB lesion did not affect the clonidine (250 micrograms/kg, i.p.) induced stimulation of TSH release or the isoproterenol (1 mg/kg i.p.) induced decrease in TSH levels. Thyrotropin releasing hormone (TRH, 5 micrograms/kg i.v.) caused a similar significant stimulation of TSH secretion in lesioned and non-lesioned rats. The present results do not support the hypothesis that the blunted TSH response to TRH observed in depressed patients results from a deficiency in noradrenergic neurotransmission.

Descending noradrenergic influences on pain

Multiple separate and distinct supraspinally organized descending inhibitory systems have been identified which are capable of powerfully modulating spinal nociceptive transmission. Until recently, brainstem sites known to be involved in the centrifugal modulation of spinal nociceptive transmission were few in number, being limited to midline structures in the midbrain and medulla (e.g., periaqueductal gray and nucleus raphe magnus). However, with continued investigation, that number has increased and brainstem sites previously thought to be primarily involved in cardiovascular function and autonomic regulation (e.g., nucleus tractus solitarius; locus coeruleus/subcoeruleus (LC/SC); A5 cell group; lateral reticular nucleus) also have been demonstrated to play a role in the modulation of spinal nociceptive transmission. Spinal monoamines (norepinephrine (NE) and serotonin) have been shown to mediate stimulation-produced descending inhibition of nociceptive transmission from these brainstem sites. The majority of NE-containing fibers and terminations in the spinal cord arise from supraspinal sources; thus, the LC/SC, the parabrachial nuclei, the Kölliker-Fuse nucleus and the A5 cell group have all been suggested as possible sources of the spinal noradrenergic (NA) innervation involved in the centrifugal modulation of spinal nociceptive transmission. Several lines of evidence suggest that the LC/SC plays a significant role in a functionally important descending inhibitory NA system. Focal electrical stimulation in the LC produces an antinociception and increases significantly the spinal content of NA metabolites. The inhibition of the nociceptive tail-flick withdrawal reflex produced by electrical stimulation in the LC/SC has been demonstrated to be mediated by postsynaptic alpha 2-adrenoceptors in the lumbar spinal cord. Similarly, electrical or chemical stimulation given in the LC/SC inhibits noxious-evoked dorsal horn neuronal activity. Thus, results reported in electrophysiological experiments confirm those reported in functional studies and the NA coeruleospinal system appears to play a significant role in spinal nociceptive processing.

Topographically organized projections from the nucleus subceruleus to the hypoglossal nucleus in the rat: a light and electron microscopic study with complementary axonal transport techniques

Projections from the nucleus subceruleus (nSC) to the hypoglossal nucleus (XII) were investigated with complementary retrograde and anterograde axonal transport techniques at the light and electron microscopic level in the rat. Injections of WGA-HRP into XII resulted in labeling of neurons in and around the nSC. Labeled nSC neurons were few in number (less than 4 per 40-60 microns sections) and variable in size and shape. Most labeled nSC neurons were medium-sized (mean = 16.89 microns), fusiform, triangular, or oval, with 3-4 dendrites typically oriented dorsomedially and ventrolaterally. These neurons were found throughout the rostrocaudal extent of the nSC but were most numerous medial, dorsomedial, and ventromedial to the motor trigeminal nucleus. Others were observed rostral to the motor trigeminal nucleus and ventral to the parabrachial nuclear complex. Confirmation of retrograde results was obtained following injections of tritiated amino acids or WGA-HRP into the nSC. This resulted in labeling throughout the rostrocaudal extent of XII mainly ipsilaterally. Labeled fibers descended the brainstem in the dorsolateral and, to a lesser extent, in the ventromedial component of Probst's tract. Fibers entered XII mainly rostrally along the lateral border of the nucleus. All regions of XII were recipients of nSC afferents, but the caudoventromedial quadrant contained the greatest density of terminal labeling. Electron microscopic evaluation confirmed that nSC afferents synapsed on motoneurons in XII. Axon terminals containing WGA-HRP reaction product were found contacting dendrites and somata, but primarily the former (81.3% versus 10.6%). Axodendritic terminals synapsed mainly on medium-to-small sized dendrites (less than 3 microns in diameter). The majority of labeled axodendritic terminals (90.1%) contained small, round, and clear synaptic vesicles (S-type: 20-50 nm) and were associated with an asymmetric (60.6%), symmetric (11.4%), or no (18%) postsynaptic specialization. By contrast, most axosomatic terminals contained flattened vesicles (F-type) and formed a symmetric or no postsynaptic specialization (75%). Large dense core vesicles (55-90 nm) were observed within a small proportion of all labeled axon terminals (1.3%). The results from this study demonstrate that the nSC projects to XII, preferentially targets a specific subgrouping of protrusor motoneurons, and synapses on both somata and dendrites, although mainly on the latter. The implications of these data are discussed relative to tongue control.

Projections to the pontine nuclei from choline acetyltransferase-like immunoreactive neurons in the brainstem of the cat

By use of retrograde transport of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) in combination with monoclonal antibodies against choline acetyltransferase (ChAT), we show that putative cholinergic inputs to the feline pontine nuclei originate from cells in the dorsolateral pontine tegmentum. These cells form a loosely arranged continuum that nevertheless may be subdivided into two groups on the basis of differences in cell morphology. One group consists of double-labeled cells in the periventricular gray substance medial to, and partly merging with, the nucleus locus coeruleus. The other group consists of double-labeled cells surrounding the brachium conjunctivum. In two cats with tracer injections in the pontine nuclei, 81% and 84%, respectively, of the retrogradely labeled cells in the dorsolateral pontine tegmentum are ChAT-like immunoreactive (ChAT-LI). In the same experiments, many ChAT-LI cells, but no retrogradely labeled cells, are seen in the basal telencephalon. The pontine nuclei contain a plexus of thin ChAT-LI fibers with varicosities resembling en passant as well as terminal boutons. These ChAT-LI fibers appear to branch extensively and cover all parts of the pontine nuclei. Following injections of rhodamine-B-isothiocyanate (RITC) in the thalamus and Fluoro-Gold in the pontine nuclei and surrounding regions in the same animal, all retrogradely labeled cells in the dorsolateral pontine tegmentum are labeled with both tracers, whereas most cells in the paramedian pontine reticular formation are labeled either with RITC or Fluoro-Gold. Thus it appears that all cells in the dorsolateral pontine tegmentum that project to the pontine nuclei also project to the thalamus. In analogy with findings by others in the dorsal lateral geniculate nucleus, we suggest that the putative cholinergic projections to the pontine nuclei may serve to modulate transmission of cerebellar afferent information in accordance with the behavioral state of the animal.

The human locus coeruleus complex: an immunohistochemical and three dimensional reconstruction study

The CA (catecholamine/catecholaminergic) cell populations of the locus coeruleus (LC) and subcoeruleus (SubC) were studied using serial sections of the human brainstem immunostained with an antibody against tyrosine hydroxylase. The tyrosine hydroxylase-immunoreactive (TH-IR) neurons were plotted in a computer reconstruction system and their number and soma size determined. Serial section computer analysis was then used to create a three dimensional reconstruction of the LC complex. The number of cells containing neuromelanin pigment was also determined and compared with the number of TH-IR cells. In our sample there were 53,900 TH-IR cells in the LC and a further 6260 cells in the SubC. These numbers were very similar to our estimates of the number of cells containing neuromelanin pigment and we concluded that virtually all of these cells were also tyrosine hydroxylase positive. The average soma size of the TH-IR cells of the LC was 37 microns and in the SubC 34 microns. In addition to these quantitative observations the morphology of the TH-IR and the Nissl stained cells is described in some detail. We also compared the groups of immunoreactive cells in the human pons with the noradrenergic groups A5-A7 described in the rat. Although in the human these groups are contiguous, A5 is not part of the LC complex. However we did find that the A7 group is equivalent to the rostroventral part of SubC while the remainder of SubC is formed by ventral A6.

Branching projections from subcoeruleus area neurons to medial preoptic area and cervical spinal cord revealed by double retrograde neuronal labeling

In this study we utilized a double retrograde axonal tracing technique to investigate the possible existence of collateralized axonal projections of subcoeruleus area neurons to both 'medial preoptic area (MPA) and cervical (C1-C3) spinal cord'. Following microinjections of fluorescent tracers (Fast blue (FB) and Diamidino yellow (DY) within MPA and C1-C3, substantial numbers of FB and DY single-labeled neurons as well as FB-DY double-labeled branched neurons have been found within subcoeruleus area.

Subcortical projections to the pontine nuclei in the cat

In a systematic attempt to trace all projections from the brainstem and diencephalon to the pontine nuclei of the cat, implantations and injections of horseradish peroxidase-wheat germ agglutinin (HRP-WGA) or Fluoro-Gold were placed in the pontine nuclei of 21 cats. In most of the cases there was no evidence of spread of tracer outside the pontine nuclei. Retrogradely labeled cells in the brainstem and diencephalon were carefully mapped and counted. The number labeled cells in the brainstem and diencephalon ranged from 24 in cases with very small implantations to 3,490 in cases with large injections in the pontine nuclei (counts from every fifth section). The labeled cells are located bilaterally with an ipsilateral preponderance. After large injections, 25-38% of the labeled cells were located in the brainstem reticular formation, 10-16% in the pretectal nuclei, 10-15% in the hypothalamus, 7-9% in the zona incerta, 3-9% in the fields of Forel, 4-5% in the nucleus locus coeruleus, 3-5% in the ventral lateral geniculate body, 2-4% in the superior colliculus, 3% in the periaqueductal gray, and 14-15% in other parts of the brainstem. Judging from cases with small tracer deposits entirely confined to the pontine nuclei, there appear to be two types of subcortical inputs: Projections from the reticular formation, the nucleus locus coeruleus, the periaqueductal gray, and the raphe nuclei are widespread, presumably reaching all parts of the pontine nuclei, while projections from a diversity of other sources are localized, reaching limited parts of the pontine nuclei only or predominantly.

Branching axons from subcoeruleus area project to the nucleus raphe pontis and hypothalamic zona incerta, as studied with the double fluorescent retrograde tracing technique

In this study we utilized a double retrograde axonal tracing technique to investigate the possible existence of collateralized axonal projections of subcoeruleus area neurons to both raphe pontis nucleus and hypothalamic zona incerta. Following microinjections of fluorescent tracers (Fast blue (FB) and Diamidino yellow (DY] within raphe pontis and zone incerta, substantial numbers of double-labeled branched neurons have been found within the subcoeruleus area.

Catecholamine neurons in the brainstem of the reptile Caiman crocodilus

Immunohistochemical methods were used to map the distribution of neurons exhibiting tyrosine hydroxylase-like immunoreactivity (TH) in the brainstem of the reptile Caiman crocodilus. The results reveal that many catecholamine systems previously described in mammalian and avian species are present in the brainstem of the caiman. Within the medulla, many immunoreactive neurons surround the central canal. This neuronal field extends rostrally to the level of the dorsal motor nucleus of the vagus. Many TH neurons overlap the region of the solitary nucleus, and an extensive system of fibers derived from these neurons extends ventrally and laterally into the region immediately bordering the descending nucleus of the trigeminal nerve. Some TH neurons are also present in the ventrolateral tegmentum of the medulla at this level. A large number of TH cells are present in the pons and midbrain. These include the locus coeruleus, nucleus subcoeruleus ventralis, nucleus subcoeruleus dorsalis, substantia nigra (Brauth et al., '83), and area ventralis of Tsai. The subcoeruleus nuclei are considerably larger in the caiman than in other reptilian species including turtles and lizards and closely resemble the subcoeruleus nuclei of birds in terms of position and anterior-posterior extent. Within the diencephalon, numerous small, intensely staining, TH-immunoreactive and CSF-contacting neurons were observed within the preoptic recess and in close proximity to the ventricular wall at rostral hypothalamic and preoptic levels. Many intensely stained, immunoreactive cell bodies were observed in the medial hypothalamus similar in position to the A13 cell group of mammals. In the subthalamus, TH neurons completely surround the ventral peduncle of the forebrain bundle (which contains fibers of the ansa lenticularis) and extend into the ventromedial and ventrolateral thalamic areas. A rich plexus of TH-positive axons and terminals invests the external layer of the median eminence.

Noradrenergic projections to brainstem nuclei: evidence for differential projections from noradrenergic subgroups

Retrograde transport of the fluorescent tracer True Blue was used in combination with immunohistochemical staining of dopamine-beta-hydroxylase (a marker protein for noradrenergic neurons) to determine the origin of noradrenergic projections to three cranial nerve nuclei: 1) the motor nucleus of the trigeminal nerve, 2) the motor nucleus of the facial nerve, and 3) the spinal trigeminal nucleus pars interpolaris. Noradrenergic cells in the rat brainstem were divided into subgroups and their numbers were determined in serial sections stained with an antiserum to rat dopamine-beta-hydroxylase. Following tracer injections into the three brainstem nuclei, retrogradely labeled noradrenergic neurons were counted and the percentage of True Blue-labeled noradrenergic cells in each subgroup was calculated. Injections of tracer into the three cranial nerve nuclei resulted in distinctly different labeling patterns of noradrenergic cells. Of the total number of norepinephrine neurons projecting to the motor nucleus of the trigeminal nerve, 68% were observed within the A7 cell group; 75% of those innervating the motor nucleus of the facial nerve were found in the A5 cell group, and 65% of those projecting to the spinal trigeminal nucleus pars interpolaris were present in the locus ceruleus and subceruleus. These findings indicate that norepinephrine cells in the rat brainstem do not constitute a homogeneous population of cells but that several discrete systems can be identified that differ not only in topography but also in the terminal distribution of their axons. This combined retrograde transport-immunohistochemical study reveals a much higher degree of topographic order in the projections of norepinephrine neurons than has previously been recognized. The observation of differential projections of noradrenergic subgroups argues against the notion of a global influence of these cells over functionally diverse areas of the brainstem.