Mapping neuronal inputs to REM sleep induction sites with carbachol-fluorescent microspheres

Ventral hippocampal projections to the medial prefrontal cortex regulate social memory

Inputs from the ventral hippocampus (vHIP) to the medial prefrontal cortex (mPFC) are implicated in several neuropsychiatric disorders. Here, we show that the vHIP-mPFC projection is hyperactive in the Mecp2 knockout mouse model of the autism spectrum disorder Rett syndrome, which has deficits in social memory. Long-term excitation of mPFC-projecting vHIP neurons in wild-type mice impaired social memory, whereas their long-term inhibition in Rett mice rescued social memory deficits. The extent of social memory improvement was negatively correlated with vHIP-evoked responses in mPFC slices, on a mouse-per-mouse basis. Acute manipulations of the vHIP-mPFC projection affected social memory in a region and behavior selective manner, suggesting that proper vHIP-mPFC signaling is necessary to recall social memories. In addition, we identified an altered pattern of vHIP innervation of mPFC neurons, and increased synaptic strength of vHIP inputs onto layer five pyramidal neurons as contributing factors of aberrant vHIP-mPFC signaling in Rett mice.

In Vivo Visualization of Active Polysynaptic Circuits With Longitudinal Manganese-Enhanced MRI (MEMRI)

Manganese-enhanced magnetic resonance imaging (MEMRI) is a powerful tool for in vivo non-invasive whole-brain mapping of neuronal activity. Mn²⁺ enters active neurons via voltage-gated calcium channels and increases local contrast in T₁-weighted images. Given the property of Mn²⁺ of axonal transport, this technique can also be used for tract tracing after local administration of the contrast agent. However, MEMRI is still not widely employed in basic research due to the lack of a complete description of the Mn²⁺ dynamics in the brain. Here, we sought to investigate how the activity state of neurons modulates interneuronal Mn²⁺ transport. To this end, we injected mice with low dose MnCl₂ 2. (i.p., 20 mg/kg; repeatedly for 8 days) followed by two MEMRI scans at an interval of 1 week without further MnCl₂ injections. We assessed changes in T₁ contrast intensity before (scan 1) and after (scan 2) partial sensory deprivation (unilateral whisker trimming), while keeping the animals in a sensory enriched environment. After correcting for the general decay in Mn²⁺ content, whole brain analysis revealed a single cluster with higher signal in scan 1 compared to scan 2: the left barrel cortex corresponding to the right untrimmed whiskers. In the inverse contrast (scan 2 > scan 1), a number of brain structures, including many efferents of the left barrel cortex were observed. These results suggest that continuous neuronal activity elicited by ongoing sensory stimulation accelerates Mn²⁺ transport from the uptake site to its projection terminals, while the blockage of sensory-input and the resulting decrease in neuronal activity attenuates Mn²⁺ transport. The description of this critical property of Mn²⁺ dynamics in the brain allows a better understanding of MEMRI functional mechanisms, which will lead to more carefully designed experiments and clearer interpretation of the results.

The anatomical, cellular and synaptic basis of motor atonia during rapid eye movement sleep

Rapid eye movement (REM) sleep is a recurring part of the sleep-wake cycle characterized by fast, desynchronized rhythms in the electroencephalogram (EEG), hippocampal theta activity, rapid eye movements, autonomic activation and loss of postural muscle tone (atonia). The brain circuitry governing REM sleep is located in the pontine and medullary brainstem and includes ascending and descending projections that regulate the EEG and motor components of REM sleep. The descending signal for postural muscle atonia during REM sleep is thought to originate from glutamatergic neurons of the sublaterodorsal nucleus (SLD), which in turn activate glycinergic pre-motor neurons in the spinal cord and/or ventromedial medulla to inhibit motor neurons. Despite work over the past two decades on many neurotransmitter systems that regulate the SLD, gaps remain in our knowledge of the synaptic basis by which SLD REM neurons are regulated and in turn produce REM sleep atonia. Elucidating the anatomical, cellular and synaptic basis of REM sleep atonia control is a critical step for treating many sleep-related disorders including obstructive sleep apnoea (apnea), REM sleep behaviour disorder (RBD) and narcolepsy with cataplexy.

Dissociative states in dreams and brain chaos: implications for creative awareness

This article reviews recent findings indicating some common brain processes during dissociative states and dreaming with the aim to outline a perspective that neural chaotic states during dreaming can be closely related to dissociative states that may manifest in dreams scenery. These data are in agreement with various clinical findings that dissociated states can be projected into the "dream scenery" in REM sleep periods and dreams may represent their specific interactions that may uncover unusual psychological potential of creativity in psychotherapy, art, and scientific discoveries.

Evaluating the Evidence Surrounding Pontine Cholinergic Involvement in REM Sleep Generation

Rapid eye movement (REM) sleep - characterized by vivid dreaming, motor paralysis, and heightened neural activity - is one of the fundamental states of the mammalian central nervous system. Initial theories of REM sleep generation posited that induction of the state required activation of the "pontine REM sleep generator" by cholinergic inputs. Here, we review and evaluate the evidence surrounding cholinergic involvement in REM sleep generation. We submit that: (i) the capacity of pontine cholinergic neurotransmission to generate REM sleep has been firmly established by gain-of-function experiments, (ii) the function of endogenous cholinergic input to REM sleep generating sites cannot be determined by gain-of-function experiments; rather, loss-of-function studies are required, (iii) loss-of-function studies show that endogenous cholinergic input to the PTF is not required for REM sleep generation, and (iv) cholinergic input to the pontine REM sleep generating sites serve an accessory role in REM sleep generation: reinforcing non-REM-to-REM sleep transitions making them quicker and less likely to fail.

International Union of Basic and Clinical Pharmacology. XCII. Urotensin II, urotensin II-related peptide, and their receptor: from structure to function

Urotensin II (UII) is a cyclic neuropeptide that was first isolated from the urophysis of teleost fish on the basis of its ability to contract the hindgut. Subsequently, UII was characterized in tetrapods including humans. Phylogenetic studies and synteny analysis indicate that UII and its paralogous peptide urotensin II-related peptide (URP) belong to the somatostatin/cortistatin superfamily. In mammals, the UII and URP genes are primarily expressed in cholinergic neurons of the brainstem and spinal cord. UII and URP mRNAs are also present in various organs notably in the cardiovascular, renal, and endocrine systems. UII and URP activate a common G protein-coupled receptor, called UT, that exhibits relatively high sequence identity with somatostatin, opioid, and galanin receptors. The UT gene is widely expressed in the central nervous system (CNS) and in peripheral tissues including the retina, heart, vascular bed, lung, kidney, adrenal medulla, and skeletal muscle. Structure-activity relationship studies and NMR conformational analysis have led to the rational design of a number of peptidic and nonpeptidic UT agonists and antagonists. Consistent with the wide distribution of UT, UII has now been shown to exert a large array of biologic activities, in particular in the CNS, the cardiovascular system, and the kidney. Here, we review the current knowledge concerning the pleiotropic actions of UII and discusses the possible use of antagonists for future therapeutic applications.

Endogenous cholinergic input to the pontine REM sleep generator is not required for REM sleep to occur

Initial theories of rapid eye movement (REM) sleep generation posited that induction of the state required activation of the pontine subceruleus (SubC) by cholinergic inputs. Although the capacity of cholinergic neurotransmission to contribute to REM sleep generation has been established, the role of cholinergic inputs in the generation of REM sleep is ultimately undetermined as the critical test of this hypothesis (local blockade of SubC acetylcholine receptors) has not been rigorously performed. We used bilateral microdialysis in freely behaving rats (n = 32), instrumented for electroencephalographic and electromyographic recording, to locally manipulate neurotransmission in the SubC with select drugs. As predicted, combined microperfusion of D-AP5 (glutamate receptor antagonist) and muscimol (GABAA receptor agonist) in the SubC virtually eliminated REM sleep. However, REM sleep was not reduced by scopolamine microperfusion in this same region, at a concentration capable of blocking the effects of cholinergic receptor stimulation. This result suggests that transmission of REM sleep drive to the SubC is acetylcholine-independent. Although SubC cholinergic inputs are not majorly involved in REM sleep generation, they may perform a minor function in the reinforcement of transitions into REM sleep, as evidenced by increases in non-REM-to-REM sleep transition duration and failure rate during cholinergic receptor blockade. Cholinergic receptor antagonism also attenuated the normal increase in hippocampal θ oscillations that characterize REM sleep. Using computational modeling, we show that our in vivo results are consistent with a mutually excitatory interaction between the SubC and cholinergic neurons where, importantly, cholinergic neuron activation is gated by SubC activity.

The substantia nigra conveys target-dependent excitatory and inhibitory outputs from the basal ganglia to the thalamus

The basal ganglia (BG), which influence cortical activity via the thalamus, play a major role in motor activity, learning and memory, sensory processing, and many aspects of behavior. The substantia nigra (SN) consists of GABAergic neurons of the pars reticulata that inhibit thalamic neurons and provide the primary output of the BG, and dopaminergic neurons of the pars compacta that modulate thalamic excitability. Little is known about the functional properties of the SN→thalamus synapses, and anatomical characterization has been controversial. Here we use a combination of anatomical, electrophysiological, genetic, and optogenetic approaches to re-examine these synaptic connections in mice. We find that neurons in the SN inhibit neurons in the ventroposterolateral nucleus of the thalamus via GABAergic synapses, excite neurons in the thalamic nucleus reticularis, and both excite and inhibit neurons within the posterior nucleus group. Glutamatergic SN neurons express the vesicular glutamate receptor transporter vGluT2 and receive inhibitory synapses from striatal neurons, and many also express tyrosine hydroxylase, a marker of dopaminergic neurons. Thus, in addition to providing inhibitory outputs, which is consistent with the canonical circuit, the SN provides glutamatergic outputs that differentially target thalamic nuclei. This suggests that an increase in the activity of glutamatergic neurons in the SN allows the BG to directly excite neurons in specific thalamic nuclei. Elucidating an excitatory connection between the BG and the thalamus provides new insights into how the BG regulate thalamic activity, and has important implications for understanding BG function in health and disease.

Imaging axonal transport in the rat visual pathway

A technique was developed for assaying axonal transport in retinal ganglion cells using 2 µl injections of 1% cholera toxin b-subunit conjugated to AlexaFluor488 (CTB). In vivo retinal and post-mortem brain imaging by confocal scanning laser ophthalmoscopy and post-mortem microscopy were performed. The transport of CTB was sensitive to colchicine, which disrupts axonal microtubules. The bulk rates of transport were determined to be approximately 80-90 mm/day (anterograde) and 160 mm/day (retrograde). Results demonstrate that axonal transport of CTB can be monitored in vivo in the rodent anterior visual pathway, is dependent on intact microtubules, and occurs by active transport mechanisms.

Urotensin II, from fish to human

The cyclic peptide urotensin II (UII) was originally isolated from the urophysis of teleost fish on the basis of its ability to contract intestinal smooth muscle. The UII peptide has subsequently been isolated from frog brain and, later on, the pre-proUII cDNA has been characterized in mammals, including humans. A UII paralog called urotensin II-related peptide (URP) has been identified in the rat brain. The UII and URP genes originate from the same ancestral gene as the somatostatin and cortistatin genes. In the central nervous system (CNS) of tetrapods, UII is expressed primarily in motoneurons of the brainstem and spinal cord. The biological actions of UII and URP are mediated through a G protein-coupled receptor, termed UT, that exhibits high sequence similarity with the somatostatin receptors. The UT gene is widely expressed in the CNS and in peripheral organs. Consistent with the broad distribution of UT, UII and URP exert a large array of behavioral effects and regulate endocrine, cardiovascular, renal, and immune functions.

Narcoleptic orexin receptor knockout mice express enhanced cholinergic properties in laterodorsal tegmental neurons

Pharmacological studies of narcoleptic canines indicate that exaggerated pontine cholinergic transmission promotes cataplexy. As disruption of orexin (hypocretin) signaling is a primary defect in narcolepsy with cataplexy, we investigated whether markers of cholinergic synaptic transmission might be altered in mice constitutively lacking orexin receptors (double receptor knockout; DKO). mRNA for Choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT) and the high-affinity choline transporter (CHT1) but not acetylcholinesterase (AChE) was significantly higher in samples from DKO than wild-type (WT) mice. This was region-specific; levels were elevated in samples from the laterodorsal tegmental nucleus (LDT) and the fifth motor nucleus (Mo5) but not in whole brainstem samples. Consistent with region-specific changes, we were unable to detect significant differences in Western blots for ChAT and CHT1 in isolates from brainstem, thalamus and cortex or in ChAT enzymatic activity in the pons. However, using ChAT immunocytochemistry, we found that while the number of cholinergic neurons in the LDT and Mo5 were not different, the intensity of somatic ChAT immunostaining was significantly greater in the LDT, but not Mo5, from DKO than from WT mice. We also found that ChAT activity was significantly reduced in cortical samples from DKO compared with WT mice. Collectively, these findings suggest that the orexins can regulate neurotransmitter expression and that the constitutive absence of orexin signaling results in an up-regulation of the machinery necessary for cholinergic neurotransmission in a mesopontine population of neurons that have been associated with both normal rapid eye movement sleep and cataplexy.

Exercise-induced improvement in cognitive performance after traumatic brain injury in rats is dependent on BDNF activation

We have previously shown that voluntary exercise upregulates brain derived neurotrophic factor (BDNF) within the hippocampus and is associated with an enhancement of cognitive recovery after a lateral fluid percussion injury (FPI). In order to determine if BDNF is critical to this effect we used an immunoadhesin chimera (TrkB-IgG) that inactivates free BDNF. This BDNF inhibitor was administered to adult male rats two weeks after they had received a mild fluid percussion injury (FPI) or sham surgery. These animals were then housed with or without access to a running wheel (RW) from post-injury-day (PID) 14 to 20. On PID 21, rats were tested for spatial learning in a Morris Water Maze. Results showed that exercise counteracted the cognitive deficits associated with the injury. However this exercise-induced cognitive improvement was attenuated in the FPI-RW rats that were treated with TrkB-IgG. Molecules important for synaptic plasticity and learning were measured in a separate group of rats that were sacrificed immediately after exercise (PID 21). Western blot analyses showed that exercise increased the mature form of BDNF, synapsin I and cyclic-AMP response-element-binding protein (CREB) in the vehicle treated Sham-RW group. However, only the mature form of BDNF and CREB were increased in the vehicle treated FPI-RW group. Blocking BDNF (pre administration of TrkB-IgG) greatly reduced the molecular effects of exercise in that exercise-induced increases of BDNF, synapsin I and CREB were not observed. These studies provide evidence that BDNF has a major role in exercise's cognitive effects in traumatically injured brain.

Identification of cholinergic and non-cholinergic neurons in the pons expressing phosphorylated cyclic adenosine monophosphate response element-binding protein as a function of rapid eye movement sleep

Recent studies have shown that in the pedunculopontine tegmental nucleus (PPT), increased neuronal activity and kainate receptor-mediated activation of intracellular protein kinase A (PKA) are important physiological and molecular steps for the generation of rapid eye movement (REM) sleep. In the present study performed on rats, phosphorylated cyclic AMP response element-binding protein (pCREB) immunostaining was used as a marker for increased intracellular PKA activation and as a reflection of increased neuronal activity. To identify whether activated cells were either cholinergic or noncholinergic, the PPT and laterodorsal tegmental nucleus (LDT) cells were immunostained for choline acetyltransferase (ChAT) in combination with pCREB or c-Fos. The results demonstrated that during high rapid eye movement sleep (HR, approximately 27%), significantly higher numbers of cells expressed pCREB and c-Fos in the PPT, of which 95% of pCREB-expressing cells were ChAT-positive. With HR, the numbers of pCREB-positive cells were also significantly higher in the medial pontine reticular formation (mPRF), pontine reticular nucleus oral (PnO), and dorsal subcoeruleus nucleus (SubCD) but very few in the locus coeruleus (LC) and dorsal raphe nucleus (DRN). Conversely, with low rapid eye movement sleep (LR, approximately 2%), the numbers of pCREB expressing cells were very few in the PPT, mPRF, PnO, and SubCD but significantly higher in the LC and DRN. The results of regression analyses revealed significant positive relationships between the total percentages of REM sleep and numbers of ChAT+/pCREB+ (Rsqr=0.98) cells in the PPT and pCREB+ cells in the mPRF (Rsqr=0.88), PnO (Rsqr=0.87), and SubCD (Rsqr=0.84); whereas significantly negative relationships were associated with the pCREB+ cells in the LC (Rsqr=0.70) and DRN (Rsqr=0.60). These results provide evidence supporting the hypothesis that during REM sleep, the PPT cholinergic neurons are active, whereas the LC and DRN neurons are inactive. More importantly, the regression analysis indicated that pCREB activation in approximately 98% of PPT cholinergic neurons, was caused by REM sleep. Moreover the results indicate that during REM sleep, PPT intracellular PKA activation and a transcriptional cascade involving pCREB occur exclusively in the cholinergic neurons.

Behavioral actions of urotensin-II

Urotensin-II (U-II) and urotensin-II-related peptide (URP) have been identified as the endogenous ligands of the orphan G-protein-coupled receptor GPR14 now renamed UT. The occurrence of U-II and URP in the central nervous system, and the widespread distribution of UT in the brain suggest that U-II and URP may play various behavioral activities. Studies conducted in rodents have shown that central administration of U-II stimulates locomotion, provokes anxiety- and depressive-like states, enhances feeding activity and increases the duration of paradoxical sleep episodes. These observations indicate that, besides the endocrine/paracrine activities of U-II and URP on cardiovascular and kidney functions, these peptides may act as neurotransmitters and/or neuromodulators to regulate various neurobiological activities.

Versatile preparation of fluorescent particles based on polyphosphazenes: from micro- to nanoscale

A series of intrinsically fluorescent hydrophobic and amphiphilic polyphosphazenes with ethyl tryptophan (EtTrp) and poly(N-isopropylacrylamide) (PNIPAAm) or poly(ethylene glycol) (PEG) as hydrophobic and hydrophilic segments, respectively, are synthesized. Depending on polymer composition and preparation procedure, particles with diameters ranging from micro- to nanoscale can be prepared successfully, which might be used as a visible tracer, both in vitro or in vivo, in drug- or gene-delivery systems, as well as in other biomedical studies such as diagnostic medicine and brain research. Most importantly, in combination with the flexible synthesis and versatile modification of polyphosphazene, this method provides a general protocol to engineer a broad range of fluorescent particles with different properties based on diverse polymers.

Neurobiological mechanisms for the regulation of mammalian sleep-wake behavior: reinterpretation of historical evidence and inclusion of contemporary cellular and molecular evidence

At its most basic level, the function of mammalian sleep can be described as a restorative process of the brain and body; recently, however, progressive research has revealed a host of vital functions to which sleep is essential. Although many excellent reviews on sleep behavior have been published, none have incorporated contemporary studies examining the molecular mechanisms that govern the various stages of sleep. Utilizing a holistic approach, this review is focused on the basic mechanisms involved in the transition from wakefulness, initiation of sleep and the subsequent generation of slow-wave sleep and rapid eye movement (REM) sleep. Additionally, using recent molecular studies and experimental evidence that provides a direct link to sleep as a behavior, we have developed a new model, the cellular-molecular-network model, explaining the mechanisms responsible for regulating REM sleep. By analyzing the fundamental neurobiological mechanisms responsible for the generation and maintenance of sleep-wake behavior in mammals, we intend to provide a broader understanding of our present knowledge in the field of sleep research.

The select action of hippocampal calcium calmodulin protein kinase II in mediating exercise-enhanced cognitive function

We found that a single week of exercise enhanced cognitive function on the Morris water maze (MWM), such that exercise animals were significantly better than sedentary controls at learning and recalling the location of the platform. In order to elucidate the role that calcium calmodulin protein kinase II (CAMKII) holds in mediating the exercise-induced enhancement in learning and memory, a specific antagonist of CAMKII, KN-62, was used to block CAMKII in the rat hippocampus during a 1-week voluntary exercise period. Following, a two-trial-per-day MWM was performed for five consecutive days, succeeded by a probe trial 2 days later. Inhibiting CAMKII action during exercise blocked the ability of exercise to enhance memory retention on the MWM; the recall abilities of exercise animals receiving the CAMKII blocker were significantly worse than those of both sedentary and exercise controls. Conversely, CAMKII may not play a significant role in mediating the effects of exercise on learning acquisition as inhibiting CAMKII failed to block the exercise-induced enhancement in learning acquisition. Our results also show that CAMKII activation early during MWM learning may be counterproductive to learning acquisition, as exercising animals given the CAMKII inhibitor performed significantly (P<0.001) better than exercising control animals and sedentary controls only on day 2 of the MWM. Inhibiting CAMKII also blocked the exercise-induced upregulation of molecules critical for learning and memory, brain-derived neurotrophic factor (BDNF) and the transcription activator cAMP response-element-binding protein, which is regulated by and downstream to BDNF action. These findings indicate that hippocampal CAMKII may have a refined role in mediating the effects of exercise on cognition, selectively functioning to regulate memory retention.

Coupling energy metabolism with a mechanism to support brain-derived neurotrophic factor-mediated synaptic plasticity

Synaptic plasticity and behaviors are likely dependent on the capacity of neurons to meet the energy demands imposed by neuronal activity. We used physical activity, a paradigm intrinsically associated with energy consumption/expenditure and cognitive enhancement, to study how energy metabolism interacts with the substrates for neuroplasticity. We found that in an area critical for learning and memory, the hippocampus, exercise modified aspects of energy metabolism by decreasing oxidative stress and increasing the levels of cytochrome c oxidase-II, a specific component of mitochondrial machinery. We infused 1,25-dihydroxyvitamin D3, a modulator of energy metabolism, directly into the hippocampus during 3 days of voluntary wheel running and measured its effects on brain-derived neurotrophic factor-mediated synaptic plasticity. Brain-derived neurotrophic factor is a central player for the effects of exercise on synaptic and cognitive plasticity. We found that 25-dihydroxyvitamin D3 decreased exercise-induced brain-derived neurotrophic factor but had no significant effect on neurotrophin-3 levels, thereby suggesting a level of specificity for brain-derived neurotrophic factor in the hippocampus. 25-Dihydroxyvitamin D3 injection also abolished the effects of exercise on the consummate end-products of brain-derived neurotrophic factor action, i.e. cyclic AMP response element-binding protein and synapsin I, and modulated phosphorylated calmodulin protein kinase II, a signal transduction cascade downstream to brain-derived neurotrophic factor action that is important for learning and memory. We also found that exercise significantly increased the expression of the mitochondrial uncoupling protein 2, an energy-balancing factor concerned with ATP production and free radical management. Our results reveal a fundamental mechanism by which key elements of energy metabolism may modulate the substrates of hippocampal synaptic plasticity.

Urotensin II modulates rapid eye movement sleep through activation of brainstem cholinergic neurons

Urotensin II (UII) is a cyclic neuropeptide with strong vasoconstrictive activity in the peripheral vasculature. UII receptor mRNA is also expressed in the CNS, in particular in cholinergic neurons located in the mesopontine tegmental area, including the pedunculopontine tegmental (PPT) and lateral dorsal tegmental nuclei. This distribution suggests that the UII system is involved in functions regulated by acetylcholine, such as the sleep-wake cycle. Here, we tested the hypothesis that UII influences cholinergic PPT neuron activity and alters rapid eye movement (REM) sleep patterns in rats. Local administration of UII into the PPT nucleus increases REM sleep without inducing changes in the cortical blood flow. Intracerebroventricular injection of UII enhances both REM sleep and wakefulness and reduces slow-wave sleep 2. Intracerebroventricular, but not local, administration of UII increases cortical blood flow. Moreover, whole-cell recordings from rat-brain slices show that UII selectively excites cholinergic PPT neurons via an inward current and membrane depolarization that were accompanied by membrane conductance decreases. This effect does not depend on action potential generation or fast synaptic transmission because it persisted in the presence of TTX and antagonists of ionotropic glutamate, GABA, and glycine receptors. Collectively, these results suggest that UII plays a role in the regulation of REM sleep independently of its cerebrovascular actions by directly activating cholinergic brainstem neurons.

From heart to mind

The discovery of novel biologically active peptides has led to an explosion in our understanding of the molecular mechanisms that underlie the regulation of sleep and wakefulness. Urotensin II (UII), a peptide originally isolated from fish and known for its strong cardiovascular effects in mammals, is another surprising candidate in the regulatory network of sleep. The UII receptor was found to be expressed by cholinergic neurons of laterodorsal and pedunculopontine tegmental nuclei, an area known to be of utmost importance for the on- and offset of rapid eye movement (REM) sleep. Recently, physiological data have provided further evidence that UII is indeed a modulator of REM sleep. The peptide directly excites cholinergic mesopontine neurons and increases the rate of REM sleep episodes. These new results and its emerging behavioral effects establish UII as a neurotransmitter/neuromodulator in mammals and should spark further interest into the neurobiological role of the peptide.

From synapse to gene product: prolonged expression of c-fos induced by a single microinjection of carbachol in the pontomesencephalic tegmentum

It is not known how the brain modifies its regulatory systems in response to the application of a drug, especially over the long term of weeks and months. We have developed a model system approach to this question by manipulating cholinergic cell groups of the laterodorsal and pedunculopontine tegmental (LDT/PPT) nuclei in the pontomesencephalic tegmentum (PMT), which are known to be actively involved in the timing and quantity of rapid eye movement (REM) sleep. In a freely moving feline model, a single microinjection of the cholinergic agonist carbachol conjugated to a latex nanosphere delivery system into the caudolateral PMT elicits a long-term enhancement of one distinguishing phasic event of REM sleep, ponto-geniculo-occipital (PGO) waves, lasting 5 days but without any significant change in REM sleep or other behavioral state. Here, we test the hypothesis that cholinergic activation within the caudolateral PMT alters the postsynaptic excitability of the PGO network, stimulating the prolonged expression of c-fos that underlies this long-term PGO enhancement (LTPE) effect. Using quantitative Fos immunohistochemistry, we found that the number of Fos-immunoreactive (Fos-IR) neurons surrounding the caudolateral PMT injection site decreased sharply by postcarbachol day 03, while the number of Fos-IR neurons in the more rostral LDT/PPT increased >30-fold and remained at a high level following the course of LTPE. These results demonstrate a sustained c-fos expression in response to pharmacological stimulation of the brain and suggest that carbachol's acute effects induce LTPE via cholinergic receptors, with subsequent transsynaptic activation of the LDT/PPT maintaining the LTPE effect.

Hippocampal BDNF mediates the efficacy of exercise on synaptic plasticity and cognition

We found that a short exercise period enhanced cognitive function on the Morris water maze (MWM), such that exercised animals were significantly better than sedentary controls at learning and recalling the location of the platform. The finding that exercise increased brain-derived neurotrophic factor (BDNF), a molecule important for synaptic plasticity and learning and memory, impelled us to examine whether a BDNF-mediated mechanism subserves the capacity of exercise to improve hippocampal-dependent learning. A specific immunoadhesin chimera (TrkB-IgG), that mimics the BDNF receptor, TrkB, to selectively bind BDNF molecules, was used to block BDNF in the hippocampus during a 1-week voluntary exercise period. After this, a 2-trial-per-day MWM was performed for 5 consecutive days, succeeded by a probe trial 2 days later. By inhibiting BDNF action we blocked the benefit of exercise on cognitive function, such that the learning and recall abilities of exercising animals receiving the BDNF blocker were reduced to sedentary control levels. Inhibiting BDNF action also blocked the effect of exercise on downstream systems regulated by BDNF and important for synaptic plasticity, cAMP response-element-binding protein (CREB) and synapsin I. Specific to exercise, we found an association between CREB and BDNF expression and cognitive function, such that animals who were the fastest learners and had the best recall showed the highest expression of BDNF and associated CREB mRNA levels. These findings suggest a functional role for CREB under the control of BDNF in mediating the exercise-induced enhancement in learning and memory. Our results indicate that synapsin I might also contribute to this BDNF-mediated mechanism.

Microinjection of neostigmine into the pontine reticular formation of the mouse: further evaluation of a proposed REM sleep enhancement technique

Microinjections of cholinergic agonists into the pontine reticular formation (PRF) powerfully induce rapid eye movement sleep (REMS) in cats but have comparatively weaker effects in rats. Recently, the cholinomimetic neostigmine has been reported to strongly enhance REMS following microinjection into the PRF of the mouse. That study used behavioral assessments of locomotion in lieu of electrophysiological measures of muscle tone to identify REMS. We sought to confirm that the behavioral state induced in mice by PRF injections of neostigmine meets standard electroencephalogram (EEG) and electromyogram (EMG) criteria for defining REMS. Cortical EEG, nuchal muscle EMG, and PGO waves were recorded from male C57BL/6N mice with chronic indwelling cannulae for the delivery of neostigmine to the PRF. Recordings were made during midday following injections of neostigmine (8.8 mM, 50 nl), 2 h after lights on (LD 12:12). Neostigmine induced a behavioral state characterized by low amplitude, highly desynchronized cortical EEG with little theta, no PGO waves, and a sustained high muscle tone. Behavioral states meeting standard criteria for slow-wave sleep (SWS) and REMS were significantly suppressed compared to baseline recordings, and REMS onset was delayed by 3 h. Consistent with earlier reports, neostigmine did strongly suppress locomotor activity in open field tests and in the home cage. Due to the failure to meet criteria for defining REMS, we conclude that neostigmine microinjection into the PRF of the mouse induces an abnormal waking state rather than REMS.

Exercise induces BDNF and synapsin I to specific hippocampal subfields

To assess the relationship between brain-derived neurotrophic factor (BDNF) and synapsin I in the hippocampus during exercise, we employed a novel microsphere injection method to block the action of BDNF through its tyrosine kinase (Trk) receptor and subsequently measure the mRNA levels of synapsin I, using real-time TaqMan RT-PCR for RNA quantification. After establishing a causal link between BDNF and exercise-induced synapsin I mRNA levels, we studied the exercise-induced distribution of BDNF and synapsin I in the rodent hippocampus. Quantitative immunohistochemical analysis revealed increases of BDNF and synapsin I in CA3 stratum lucidum and dentate gyrus, and synapsin I alone in CA1 stratum radiatum and stratum laconosum moleculare. These results indicate that exercise induces plasticity of select hippocampal transsynaptic circuitry, possibly comprising a spatial restriction on synapsin I regulation by BDNF.

Successful Retrograde Transport of Fluorescent Latex Nanospheres in the Cerebral Cortex of the Macaque Monkey

Retrograde axonal transport of latex nanospheres offers a means of delivering chemical agents to a targeted region of the central nervous system (CNS). In this study we performed microinjections of latex nanospheres into the cerebral cortex of cynomolgus monkeys and observed successful retrograde labeling of neurons in the contralateral region. Our data indicate the successful use of this delivery system, reported in studies using other animals, may also be achievable with primates as well.

Localization of the GABAergic and non-GABAergic neurons projecting to the sublaterodorsal nucleus and potentially gating paradoxical sleep onset

We recently determined in rats that iontophoretic application of bicuculline or gabazine [two GABAa antagonists] and kainic acid (a glutamate agonist) in the sublaterodorsal nucleus (SLD) induces with a very short latency a paradoxical sleep-like state. From these results, we proposed that GABAergic and glutamatergic inputs to the SLD paradoxical sleep (PS)-executive neurons gate the onset of PS [R. Boissard et al. (2002) Eur. J. Neurosci., 16, 1959-1973]. We therefore decided to determine the origin of the GABAergic and non-GABAergic inputs to the SLD combining ejection of a retrograde tracer [cholera-toxin B subunit (CTb)] with glutamate decarboxylase (GAD) immunohistochemistry. The presence of GAD-immunoreactive neurons in the SLD was confirmed. Then, following CTb ejections centred on the SLD, combined with GAD and CTb immunohistochemistry, double-labelled cells were observed in the mesencephalic and pontine reticular nuclei and to a lesser extent the parvicellular reticular nucleus. A large number of GAD-negative retrogradely labelled cells was also seen in these structures as well as in the primary motor area of the frontal cortex, the central nucleus of the amygdala, the ventral and lateral bed nucleus of the stria terminalis, the lateral hypothalamic area, the lateral and ventrolateral periaqueductal grey and the lateral paragigantocellular reticular nucleus. From these results, we propose that the activation of PS-executive neurons from the SLD is due to the removal of a tonic inhibition from GABAergic neurons localized in the SLD, and the mesencephalic and pontine reticular nuclei. Strong non-GABAergic inputs to the SLD could be excitatory and responsible for the tonic glutamatergic input on the PS-on neurons we have previously described. They could also terminate on SLD GABAergic interneurons and be indirectly responsible for the inhibition of the PS-on neurons during waking and slow-wave sleep.

In vivo degradation and biocompatibility of a new class of alternate poly(ester-anhydrides) based on aliphatic and aromatic diacids

The degradation, tissue compatibility, and toxicology of a novel class of alternate poly(ester-anhydrides) were assessed in rats. It was observed that the degradation rate of the polymers in vivo was slower than that in vitro. In addition, erosion and intact zone were observed for all the polymers. IR and SEM analysis of the outer erosion and inner intact zone revealed that the outer zone degraded more rapidly than the inner zone. Such results were similar to that in vitro. All the studied poly(ester-anhydrides) produced mild inflammatory reactions and tissue encapsulation by layers of fibroblastic cells in vivo. Observation of liver and kidney tissue by light microscopy suggested the hydrolytic products of the studied poly(ester-anhydrides) had no harmful effects on the normal tissue/organs. In addition, the polymer and the breakdown products were found to be non-mutagenic by examination of micronucleus in bone marrow.

Rapid eye movement sleep induction by microinjection of the GABA-A antagonist bicuculline into the dorsal subcoeruleus area of the rat

In cats, rapid eye movement sleep (REMS) can be induced rapidly and reliably by injections of the cholinergic agonist carbachol into the anterodorsal pontine tegmentum, also recognized as the perilocus coeruleus alpha, and designated the REMS Induction Zone (RIZ). In rats, the RIZ has been ascribed to a much larger and more ventral region within the entire oral pontine reticular formation. However, carbachol injections throughout this area produce only small, unreliable, and long latency REMS enhancements. The present study investigated whether REMS induction in the rat is possible by microinjection into the dorsal subcoeruleus nucleus (SubCD), a region with similarities to the cat RIZ. In freely moving unanaesthetized rats, microinjection of the GABA-A antagonist bicuculline significantly increased the amount and reduced the latency to REMS during a 2-h recording in the mid-light period. However, at effective doses, bicuculline usually also produced intermittent ipsiversive circling behavior that disrupted REMS maintenance. Attempts at eliminating this side-effect by: (i) coinjection of bicuculline with the NMDA antagonist, APV, (ii) lower bicuculline doses, or (iii) injection of the GABA-B antagonist, phaclofen, were unsuccessful. Other drugs injected into this area did not induce REMS; these included carbachol, the acetylcholinesterase inhibitor neostigmine, the glutamate agonist kainate, and vasopressin. In the rat, the SubCD is a highly sensitive region for both REMS induction and locomotor effects.

Interplay between brain-derived neurotrophic factor and signal transduction modulators in the regulation of the effects of exercise on synaptic-plasticity

This study was designed to identify molecular mechanisms by which exercise affects synaptic-plasticity in the hippocampus, a brain area whose function, learning and memory, depends on this capability. We have focused on the central role that brain-derived neurotrophic factor (BDNF) may play in mediating the effects of exercise on synaptic-plasticity. In fact, this impact of exercise is exemplified by our finding that BDNF regulates the mRNA levels of two end products important for neural function, i.e. cAMP-response-element binding (CREB) protein and synapsin I. CREB and synapsin I have the ability to modify neuronal function by regulating gene-transcription and affecting synaptic transmission, respectively. Furthermore, we show that BDNF is capable of concurrently increasing the mRNA levels of both itself and its tyrosine kinaseB (TrkB) receptor, suggesting that exercise may employ a feedback loop to augment the effects of BDNF on synaptic-plasticity. The use of a novel microbead injection method in our blocking experiments and Taqman reverse transcription polymerase reaction (RT-PCR) for RNA quantification, have enabled us to evaluate the contribution of different pathways to the exercise-induced increases in the mRNA levels of BDNF, TrkB, CREB, and synapsin I. We found that although BDNF mediates exercise-induced hippocampal plasticity, additional molecules, i.e. the N-methyl-D-aspartate receptor, calcium/calmodulin protein kinase II and the mitogen-activated protein kinase cascade, modulate its effects. Since these molecules have a well-described association to BDNF action, our results illustrate a basic mechanism through which exercise may promote synaptic-plasticity in the adult brain.

The neurophysiology of concussion

Cerebral concussion is both the most common and most puzzling type of traumatic brain injury (TBI). It is normally produced by acceleration (or deceleration) of the head and is characterized by a sudden brief impairment of consciousness, paralysis of reflex activity and loss of memory. It has long been acknowledged that one of the most worthwhile techniques for studying the acute pathophysiology of concussion is by the recording of neurophysiological activity such as the electroencephalogram (EEG) and sensory evoked potentials (EPs) from experimental animals. In the first parts of this review, the majority of such studies conducted during the past half century are critically reviewed. When potential methodological flaws and limitations such as anesthetic protocols, infliction of multiple blows and delay in onset of recordings were taken into account, two general principles could be adduced. First, the immediate post-concussive EEG was excitatory or epileptiform in nature. Second, the cortical EP waveform was totally lost during this period. In the second parts of this review, five theories of concussion which have been prominent during the past century are summarized and supportive evidence assessed. These are the vascular, reticular, centripetal, pontine cholinergic and convulsive hypotheses. It is concluded that only the convulsive theory is readily compatible with the neurophysiological data and can provide a totally viable explanation for concussion. The chief tenet of the convulsive theory is that since the symptoms of concussion bear a strong resemblance to those of a generalized epileptic seizure, then it is a reasonable assumption that similar pathobiological processes underlie them both. Further, it is demonstrated that EPs and EEGs recorded acutely following concussive trauma are indeed the same or similar to those obtained following the induction of a state of generalized seizure activity (GSA). According to the present incarnation of the convulsive theory, the energy imparted to the brain by the sudden mechanical loading of the head may generate turbulent rotatory and other movements of the cerebral hemispheres and so increase the chances of a tissue-deforming collision or impact between the cortex and the boney walls of the skull. In this conception, loss of consciousness is not orchestrated by disruption or interference with the function of the brainstem reticular activating system. Rather, it is due to functional deafferentation of the cortex as a consequence of diffuse mechanically-induced depolarization and synchronized discharge of cortical neurons. A convulsive theory can also explain traumatic amnesia, autonomic disturbances and the miscellaneous collection of symptoms of the post-concussion syndrome more adequately than any of its rivals. In addition, the symptoms of minor concussion (a.k.a. being stunned, dinged, or dazed) are often strikingly similar to minor epilepsy such as petit mal. The relevance of the convulsive theory to a number of associated problems is also discussed. These include the relationship between concussion and more serious types of closed head injury, the utility of animal models of severe brain trauma, the etiology of the cognitive deficits which may linger long after a concussive injury, the use of concussive (captive bolt) techniques to stun farm animals prior to slaughter and the question of why some animals (such as the woodpecker) can tolerate massive accelerative forces without being knocked out.

Direct and indirect excitation of laterodorsal tegmental neurons by Hypocretin/Orexin peptides: implications for wakefulness and narcolepsy

Compelling evidence links the recently discovered hypothalamic peptides Hypocretin/Orexin (Hcrt/Orx) to rapid eye movement sleep (REM) control and the sleep disorder narcolepsy, yet how they influence sleep-related systems is not well understood. We investigated the action of Hcrt/Orx on mesopontine cholinergic (MPCh) neurons of the laterodorsal tegmental nucleus (LDT), a target group whose function is altered in canine narcolepsy and appears pivotal for normal REM and wakefulness. Extracellular recordings from mouse brainstem slices revealed that Hcrt/Orx evoked prolonged firing of LDT neurons. Whole-cell recordings revealed that Hcrt/Orx had actions on both presynaptic neurons and at postsynaptic sites. Hcrt/Orx produced an increase in frequency and amplitude of spontaneous EPSCs without equivalent effect on IPSCs, by triggering action potentials and enhancing spike-evoked synaptic transmission in glutamatergic afferents. Postsynaptically, Hcrt/Orx produced an inward current and an increase in membrane current noise, which were accompanied by a conductance increase. These persisted in TTX, ionotropic glutamate receptor antagonists, and low extracellular calcium. Both presynaptic and postsynaptic actions were specific because they were not mimicked by an Hcrt/Orx fragment, and both actions were observed for cholinergic and noncholinergic LDT neurons. Finally, extracellular recordings during postsynaptic potential blockade demonstrated that postsynaptic actions of Hcrt/Orx alone could evoke prolonged firing. In the context of other recent work, our findings suggest that Hcrt/Orx neurons may coordinate the activity of the entire reticular activating system during waking. Moreover, these findings address specific hypotheses regarding the cellular mechanisms underlying REM disregulation in narcolepsy.

Carbachol microinjection into the caudal peribrachial area induces long-term enhancement of PGO wave activity but not REM sleep

This study presents new findings of carbachol-induced long-term ponto-geniculo-occipital (PGO) enhancement lasting five days, but without REM sleep enhancement. A quantitative analysis of the number and types of bilateral PGO wave events during slow wave sleep with PGO activity (SP) and REM was performed in each of four cats over a period of six days following a single unilateral microinjection of carbachol nanospheres into the caudolateral peribrachial area. The results demonstrate increases in the summed total of all PGO wave events to continue for five days postcarbachol reaching a peak sixfold increase on day three in SP and REM. The tendency of PGO waves to occur in clusters of greater than three waves increased sevenfold on day three in SP and fourfold during REM. These findings indicate a dissociation of long-term PGO enhancement from long-term REM enhancement, and suggest that even a sixfold increase in PGO activity alone is not, in itself, sufficient to produce the cholinergic orchestration of REM sleep enhancement.

Brain stem lesion size determined by DEAD red or conjugation of neurotoxin to fluorescent beads

Neurotoxin microinjected into the retrotrapezoid nucleus of anesthetized rats decreases phrenic activity and eliminates the response to CO2. In unanesthetized rats, such treatment has no effect on awake, resting breathing and decreases CO2 sensitivity by 40% (M. Akilesh, M. Kamper, A. Li, and E. E. Nattie. J. Appl. Physiol. 82: 469-479, 1997). One important factor in explaining these disparate results is the actual size of the anatomic lesion. In the present study, we injected ibotenic acid into the retrotrapezoid nucleus of anesthetized rats and evaluated lesion size by using two new approaches: 1) DEAD red, a fluorescent probe that enters impaired cells through leaky membranes and binds to nucleic acids, and 2) conjugation of toxin to fluorescent beads. With the use of DEAD red, the region containing labeled dying cells was 313 +/- 104 nl (n = 4), six times larger than the initial injected volume, and the physiological effects on phrenic amplitude, the CO2 response, and blood pressure began within minutes and were substantial. With conjugated toxin, in theory, neuronal damage would be limited to the region of detectable fluorescence (49 +/- 10 nl; n = 4). Effects on phrenic amplitude, CO2 sensitivity, and blood pressure were absent until approximately 2 h postinjection. Control experiments, with 2 h of in vitro incubation of the neurotoxin-microbead conjugate and injection of the supernatant after centrifugation, showed similar results that suggest release of conjugated neurotoxin. We conclude that DEAD red provides a useful means to monitor neuronal impairment in acute studies in vivo. Conjugation of neurotoxin to microbeads may be less reliable in this regard.

Recovery of cable properties through active and passive modeling of subthreshold membrane responses from laterodorsal tegmental neurons

The laterodorsal tegmental nucleus (LDT) is located in the dorsolateral pontine reticular formation. Cholinergic neurons in the LDT and the adjacent pedunculopontine tegmental nucleus (PPT) are hypothesized to play a critical role in the generation of the electroencephalographic-desynchronized states of wakefulness and rapid eye movement sleep. A quantitative analysis of the cable properties of these cells was undertaken to provide a more detailed understanding of their integrative behavior. The data used in this analysis were the morphologies of intracellularly labeled guinea pig LDT neurons and the voltage responses of these cells to somatic current injection. Initial attempts to model the membrane behavior near resting potential and in the presence of tetrodotoxin (TTX, 1 microM) as purely passive produced fits that did not capture many features of the experimental data. Moreover, the recovered values of membrane conductance or intracellular resistivity were often very far from those reported for other neurons, suggesting that a passive description of cell behavior near rest was not adequate. An active membrane model that included a subthreshold A-type K+ current and/or a hyperpolarization-activated cation current (H-current) then was used to model cell behavior. The voltage traces calculated using this model were better able to reproduce the experimental data, and the cable parameters determined using this methodology were more consistent with those reported for other cells. Additionally, the use of the active model parameter extraction methodology eliminated a problem encountered with the passive model in which parameter sets with widely varying values, sometimes spanning an order of magnitude or more, would produce effectively indistinguishable fits to the data. The use of an active model to directly fit the experimentally measured voltage responses to both long and short current pulses is a novel approach that is of general utility.

Cholinergic and non-cholinergic afferents of the caudolateral parabrachial nucleus: a role in the long-term enhancement of rapid eye movement sleep

A single microinjection of the cholinergic agonist carbachol into the feline caudolateral parabrachial nucleus produces an immediate increase in state-independent ipsilateral ponto-geniculooccipital waves, followed by a long-term rapid eye movement sleep enhancement lasting 7-10 days. Using retrogradely-transported fluorescent carbachol-conjugated nanospheres and choline acetyltransferase immunohistochemistry, afferent projections to this injection site for long-term rapid eye movement sleep enhancement were mapped and quantified. Six regions in the brain stem contained retrogradely-labelled cells: the raphe nuclei, locus coeruleus, laterodorsal tegmental nucleus, pedunculopontine tegmental nucleus, parabrachial nucleus, and the pontine reticular formation. The retrogradely-labelled (rhodamine+) cells in the pontine reticular formation and pedunculopontine tegmental nucleus contributed the predominant input to the parabrachial nucleus injection site (34.3 +/- 5.3% and 28.4 +/- 5.6%, respectively), compared to the laterodorsal tegmental nucleus (5.8 +/- 3.8%), parabrachial nucleus (13.5 +/- 3.1%), raphe nuclei (12.9 +/- 2.7%), and locus coeruleus (5.1 +/- 2.4%). By comparison with findings of afferent input to the induction site for short-latency rapid eye movement sleep in the anterodorsal pontine reticular formation, the parabrachial nucleus injection site is characterized by a similar proportion of afferents, except that the raphe nuclei were found to provide more than a two-fold greater input. Retrogradely-labelled neurons quantified in these nuclear regions consisted of 21.5% double-labelled (rhodamine+/choline acetyltransferase+) cholinergic and 78.5% noncholinergic (rhodamine+/choline acetyltransferase-) cells. The pedunculopontine tegmental nucleus contributed the predominant (51.7 +/- 8.2%) cholinergic input, compared to laterodorsal tegmental nucleus (20.7 +/- 10.2%), parabrachial nucleus (23.1 +/- 7.5%), and pontine reticular formation (4.4 +/- 2.1%). A comparative analysis of the total retrogradely-labelled cells within each nuclear region which were also double-labelled showed the highest proportion in the laterodorsal tegmental nucleus (76.2 +/- 7.5%) compared to pedunculopontine tegmental nucleus (39.4 +/- 3.6%), parabrachial nucleus (37.3 +/- 2.8%), and pontine reticular formation (3.2 +/- 2.1%). These data indicate that while pedunculopontine tegmental nucleus and laterodorsal tegmental nucleus neurons exert a powerful cholinergic influence on the injection site for long-term rapid eye movement enhancement, a major component of the afferent circuitry is non-cholinergic. Since the non-cholinergic input includes contributions from the locus coeruleus and raphe nuclei, it is probable that the caudolateral parabrachial nucleus contains cholinergic and aminergic afferent systems that participate in the long-term enhancement of rapid eye movement sleep.

Sleep patterns after carbachol delivery in the ventral oral pontine tegmentum of the cat

This study examines dose-related effects on sleep produced by low-volume and low-dose carbachol microinjections in the ventral part of the cat nucleus reticularis pontis oralis. Carbachol microinjections (0.04, 0.08, 0.8 or 4 microg; volume 20 nl) in this location triggered paradoxical sleep with a very short dose-unrelated latency. The four carbachol doses effectively generated all the polygraphic and behavioral signs of paradoxical sleep when microinjected at any level within the ventral part of the nucleus reticularis pontis oralis (AP 0.5 to -3.5, L 0.5-3.5, V 3.5-5.0, on the Reinoso-Suárez atlas [Topographischer Hirnatlas der Katze (1961); Merck, Darmstadt]). The dose-related increase of total paradoxical sleep time was due to the increase in both the duration and number of paradoxical sleep episodes. This paradoxical sleep increase was associated with a dose-related decrease in the amount of time spent in both slow wave sleep and drowsiness, but not with any decrease in total wakefulness. The lengthening of the latency to slow wave sleep onset was dose related. These results show that the ventral oral pontine tegmentum is a very sensitive site for the induction and maintenance of paradoxical sleep.

Cellular basis of pontine ponto-geniculo-occipital wave generation and modulation

1. Pontogeniculooccipital (PGO) waves are recorded during rapid eye movement (REM) sleep from the pontine reticular formation. 2. PGO wave-like field potentials can also be recorded in many other parts of the brain in addition to the pontine reticular formation, but their distribution is different in different species. Species differences are due to variation in species-specific postsynaptic target sites of the pontine PGO generator. 3. The triggering neurons of the pontine PGO wave generator are located within the caudolateral peribrachial and the locus subceruleus areas. 4. The transferring neurons of the pontine PGO generator are located within the cholinergic neurons of the laterodorsal tegmentum and the pedunculopontine tegmentum. 5. The triggering and transferring neurons of the pontine PGO wave generator are modulated by aminergic, cholinergic, nitroxergic, GABA-ergic, and glycinergic cells of the brainstem. The PGO system is also modulated by suprachiasmatic, amygdaloid, vestibular, and brainstem auditory cell groups.

Mesopontine organization of cholinergic and catecholaminergic cell groups in the normal and narcoleptic dog

Canine narcolepsy is a unique experimental model of a human sleep disorder characterized by excessive daytime sleepiness and cataplexy. There is a consensus recognition of an imbalance between cholinergic and catecholaminergic systems in narcolepsy although the underlying mechanisms remain poorly understood. Possible substrates could be an abnormal organization, numbers and/or ratio of cholinergic to catecholaminergic cells in the brain of narcoleptic dogs. Therefore, we sought to characterize the corresponding neuronal populations in normal and narcoleptic dogs (Doberman Pinscher) by using choline acetyltransferase (ChAT), nicotinamide adenosine dinucleotide phosphate (NADPH)-diaphorase, tyrosine hydroxylase (TH), and dopamine beta-hydroxylase (DBH). Cholinergic cell groups were found in an area extending from the central to the gigantocellular tegmental field and the periventricular gray corresponding to the pedunculopontine tegmental nucleus (PPT), the laterodorsal tegmental nucleus (LDT), and the parabrachial nucleus. An almost perfect co-localization of ChAT and NADPH-diaphorase was also observed. Catecholaminergic cell groups detected included the ventral tegmental area, the substantia nigra, and the locus coeruleus nucleus (LC). The anatomical distribution of catecholaminergic neurons was unusual in the dog in two important aspects: i) TH- and/or DBH-immunoreactive neurons of the LC were found almost exclusively in the reticular formation and not within the periventricular gray, ii) very few, if any TH-positive neurons were found in the central gray and dorsal raphe. Quantitative analysis did not reveal any significant differences in the organization and the number of cells identified in the LDT, PPT, and LC of normal and narcoleptic dogs. Moreover, the cholinergic to catecholaminergic ratio was found identical in the two groups. In conclusion, the present results do not support the hypothesis that the neurochemical imbalance in narcolepsy could result from abnormal organization, numbers, or ratio of the corresponding neuronal populations.

Quantitative morphology of physiologically identified and intracellularly labeled neurons from the guinea-pig laterodorsal tegmental nucleus in vitro

Mesopontine cholinergic neurons have been implicated in the initiation and maintenance of rapid eye movement sleep via their efferent connections to the thalamus and the medial pontine reticular formation. As a first step toward understanding how these modulatory neurons integrate synaptic input, we have investigated the dendritic architecture of laterodorsal tegmental nucleus neurons. The principal cells of the guinea-pig laterodorsal tegmental nucleus were identified electrophysiologically in a brain slice preparation, then were intracellularly injected with biocytin and reconstructed using a computer-aided tracing system. The somata were large (27 +/- 3 microns; n = 11) and gave rise to an average of 4.8 primary dendrites which, in most cases, emerged from the soma in a pattern that was radially symmetric in the plane of the slice. Primary dendrites had an average of 3.7 endings. A single axon arose from either the soma or a proximal dendrite and exited the nucleus with a medial and/or lateral trajectory. Some axons also gave rise to a local terminal plexus composed of fine fibers bearing numerous punctate swellings that ramified profusely within the neuron's dendritic field. Total dendritic area averaged about 10(5) microns2, and therefore the average contribution of the soma to the total surface area (20%) was significantly larger than the values reported for many other cell types. Dendritic diameters were non-uniform in three respects. Some processes were sparsely spiny. Most processes were varicose, with the degree of varicosity increasing substantially in secondary and tertiary dendritic segments. There was also a large degree of taper in dendritic processes; those processes with a non-negative taper had an average diameter decrease of 40 +/- 25%. Dendritic processes deviated from the criteria necessary for a Rall equivalent cylinder approximation due to non-uniformity in morphotonic path length, failure to conform to the Rall 3/2 branching rule and non-uniformity of dendritic diameter. An analysis was done to assess the impact of dendritic varicosities on the extraction of cable parameters for these cells. Voltage traces were simulated by solving the cable equation for a varicose dendrite and then membrane parameters were recovered using an equivalent cylinder model. Errors in the extracted values of specific membrane conductance and specific membrane capacitance were quite small (< or = 5%), while larger errors were seen for electrotonic length (< or = 21%) and intracellular resistivity (< or = 5%). These data indicate that the principal cells of the laterodorsal tegmental nucleus, while possessing a relatively simple dendritic structure in terms of number and branchiness of dendrites, display a heterogeneity of dendritic process types. Processes range from smooth to markedly varicose, and can be aspiny or sparsely spiny. The possibility that the dendritic varicosities function as sites of either electrical or chemical compartmentalization is discussed. The degree of error resulting from a Rall equivalent cylinder approximation in light of these varicosities indicated that a generalized cable model approach may prove more effective in estimating their cable parameters.

Three-dimensional distribution of [3H]quinuclidinyl benzilate binding to muscarinic cholinergic receptors in the developing human brainstem

Acetylcholine has been implicated in brainstem mechanisms of cardiac and ventilatory control, arousal, rapid eye movement (REM) sleep, and cranial nerve motor activity. Virtually nothing is known about the developmental profiles of cholinergic perikarya, fibers, terminals, and/or receptors in the brainstems of human fetuses and infants. This study provides baseline information about the quantitative distribution of muscarinic cholinergic receptors in fetal and infant brainstems. Brainstem sections were analyzed from 6 fetuses (median age: 21.5 postconceptional weeks), 4 premature infants (median age: 26 postconceptional weeks), and 11 infants (median age: 53 postconceptional weeks). One child and three adult brainstems were examined as indices of maturity for comparison. The postmortem interval in all cases was less than or equal to 24 hours (median: 10 hours). Muscarinic receptors were localized by autoradiographic methods with the radiolabeled antagonist [3H]quinuclidinyl benzilate ([3H]QNB). Computer-based methods permitted quantitation of [3H]QNB binding in specific nuclei and three-dimensional reconstructions of binding patterns. By midgestation, muscarinic cholinergic receptor binding is already present and regionally distributed, with the highest binding levels in the interpeduncular nucleus, inferior colliculus, griseum pontis, nucleus of the solitary tract, motor cranial nerve nuclei, and reticular formation. During the last half of gestation, [3H]QNB binding decreases in most, but not all of the nuclei sampled. The most substantial decline occurs in the reticular formation of the medulla and pons, a change that is not fully explained by progressive myelination and lipid quenching. Binding levels remain essentially constant in the inferior olive and griseum pontis. Around the time of birth or shortly thereafter, the relative distribution of binding becomes similar to that in the adult, with the highest levels in the interpeduncular nucleus and griseum pontis, although binding levels are higher overall in the infant. In the rostral pontine reticular formation, paramedian bands of high muscarinic binding are present which do not correspond to a cytoarchitectonically defined nucleus. By analogy to animal studies, these bands may comprise a major cholinoreceptive region of the human rostral pontine reticular formation involved in REM sleep. In the human interpeduncular nucleus in all age periods examined, muscarinic binding localizes to the lateral portions bilaterally, indicative of a heterogeneous chemoarchitecture. Muscarinic binding is high in the arcuate nucleus, a component of the putative respiratory chemosensitive fields along the ventral surface of the infant medulla. This observation is consistent with the known effects of muscarinic agents on chemosensitivity and ventilatory responses applied to the ventral medullary surface in animal models. The nonuniform distribution of muscarinic binding in the caudorostral plane in individual brainstem nuclei, as illustrated by three-dimensional reconstructions, underscores the need for rigorous sampling at precisely matched levels in quantitative studies. This study provides basic information toward understanding the neurochemical basis of brainstem disorders involving dysfunction of autonomic and ventilatory control, arousal, and REM sleep in preterm and full-term newborns and infants and for developing cholinergic drugs for such disorders in the pediatric population.

An ultrastructural study of cholinergic and non-cholinergic neurons in the laterodorsal and pedunculopontine tegmental nuclei in the rat

Synaptic connectivity and other ultrastructural features of cholinergic and non-cholinergic neurons in the laterodorsal and pedunculopontine tegmental nuclei were investigated with electron microscopy combined with pre-embedding immunohistochemistry for choline acetyltransferase. Quantitative morphometric analyses were conducted on selected immunopositive as well as immunonegative neurons. The ultrastructure of immunoreactive neurons in the laterodorsal and pedunculopontine tegmental nuclei was similar. In both nuclei, immunoreactive neurons were among the larger neurons, and somatic areas of immunopositive neurons in single thin sections were larger than those of immunonegative neurons by an average of 40%. Immunopositive somata varied in shape, appearing polygonal, fusiform or oval. Regardless of immunoreactivity, however, neurons in the pedunculopontine nucleus tended to have more irregular shapes than those in the laterodorsal tegmental nucleus. Immunoreactive neurons in both the nuclei had abundant cytoplasmic organelles and a large, clear nucleus with a few infoldings. Usually, about a quarter of the surface of an immunopositive soma was covered with astrocytic processes, and some immunopositive somata were directly apposed to an astrocyte. Immunoreactive dendrites and, less frequently, axon terminals were seen in close apposition to endothelial cells of blood capillaries or pericytes. Immunoreactive somata and dendrites in the laterodorsal and pedunculopontine tegmental nuclei received many synapses, mainly from unlabelled axon terminals. The mean number (4.7 +/- 1.8) of synapses received by immunolabelled somata in single thin sections was greater, by about 70%, than those received by unlabelled somata. The presynaptic axon terminals synapsing with immunoreactive somata commonly contained small, round and clear vesicles, and 20% of them contained a few dense-cored vesicles as well. Immunoreactive dendrites, in addition, received synapses from unlabelled axon terminals containing flat and clear vesicles, which accounted for 15% of the synapses with immunoreactive dendrites. Many immunopositive axon terminals were present in both the tegmental nuclei. They contained clear round vesicles, and usually synapsed with unlabelled dendrites. A few immunolabelled axons, however, appeared to synapse with immunopositive somata and dendrites. Immunoreactive fibres were also present in both the tegmental nuclei. They were either thinly myelinated or unmyelinated. In conclusion, the ultrastructural morphology of cholinergic neurons in the laterodorsal and pedunculopontine tegmental nuclei is similar, and these neurons represent a distinct population of neurons in both nuclei in that they are larger and receive more synaptic contacts than non-cholinergic neurons. Cholinergic neurons, however, appear to receive synapses from cholinergic axon terminals only rarely, despite the abundance of cholinergic terminals in the tegmental nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuronal activity in the peribrachial area: relationship to behavioral state control

Extensive studies have ascribed a role to the brainstem cholinergic system in the generation of rapid eye movement (REM) sleep and ponto-geniculo-occipital (PGO) waves. Much of this work stems from systemic and central cholinergic drug administration studies. The brainstem cholinergic system is also implicated in cortical activation via basal forebrain, thalamic, and hypothalamic relay neurons. This cholinergic ascending reticular activating hypothesis has also been suggested by in vivo experiments under anesthetics and by in vitro studies using cholinergic agonists in thalamic and hypothalamic slices. During the last ten years, brainstem cholinergic neurons have been discovered to be in the peribrachial area (PBL). With the discovery of PBL cholinergic neurons, many studies were devoted to the examination of PBL neuronal activity and their connectivity. This article reviews PBL neuronal activity in behaving animals and the anatomical features of these neurons in relation to behavioral state control. The role of the PBL in the generation of REM sleep, PGO waves, and the ascending reticular activating system (ARAS) has been evaluated at the cellular and neurochemical level. Based on recent literature, tentative mechanisms of REM sleep generation, PGO waves generation, and the cortical activation process are also outlined.

Non-synaptic diffusion neurotransmission: a novel concept for future migraine research

The concept of non-synaptic diffusion neurotransmission (NDN) is reviewed. Evidence is presented that monoamine neurotransmission is largely by NDN. The role of NDN in pain and sleep is described and its relevance to migraine research is discussed.

Location and anatomical connections of a paradoxical sleep induction site in the cat ventral pontine tegmentum

The brainstem mechanisms for the generation of paradoxical sleep are under considerable debate. Previous experiments in cats have demonstrated that injections of the cholinergic agonist carbachol into the oral pontine tegmentum elicit paradoxical sleep behaviour and its polygraphic correlates. The different results on the pontine structures that mediate this effect do not agree. We report here that limited microinjections of a carbachol solution into the ventral part of the oral pontine reticular nucleus in the cat induce, with a short latency, a dramatic, long-lasting increase in paradoxical sleep. Moreover, neuronal tracing experiments show that this pontine site is connected with brain structures responsible for the different bioelectric events of paradoxical sleep. These two facts suggest that the ventral part of the oral pontine reticular nucleus is a nodal link in the neuronal network underlying paradoxical sleep mechanisms.

State dependency of the effects of microinjection of cholinergic drugs into the nucleus pontis oralis

The microinjection of cholinergic drugs into the pontine reticular formation elicits active sleep-like states that are comprised of the principal physiological patterns of activity that characterize naturally-occurring active sleep, i.e., EEG desynchronization, PGO waves, rapid eye movements and atonia. We have reported that other behavioral states arise even when cholinergic drugs are injected into the exact same reticular location. The present study was conducted to explore the basis for the differences in the drug effect. A combination of acetylcholine and neostigmine was injected by microiontophoresis into the dorsal region of the nucleus pontis oralis in four chronic, unanesthetized cats. The states that were induced by cholinergic drug injection depended on the state of the animal at the time of the injection. When the animal was awake, cholinergic injections resulted in a waking-dissociated state, which was characterized by EEG desynchronization and muscle atonia in a cat that appeared to be awake and was able to track objects in its visual field. If the cat was in quiet sleep at the time of the injection, an active sleep-like state followed that was indistinguishable from naturally-occurring active sleep; on a few occasions following cholinergic injections during quiet sleep there was a quiet sleep-dissociated state, which was characterized by PGO waves and muscle atonia in the cat that by other indices appeared to be in quiet sleep. The results of this study indicate that the state of the animal at the time of drug injection is a critical variable that influences the responses which are induced by cholinergic stimulation of the pontine reticular formation.

Autoradiographic quantification of muscarinic cholinergic synaptic markers in bat, shrew, and rat brain

We employed radioligand binding autoradiography to determine the distributions of pre- and post-synaptic cholinergic radioligand binding sites in the brains of two species of bat, one species of shrew, and the rat. High affinity choline uptake sites were measured with [3H]hemicholinium, and presynaptic cholinergic vesicles were identified with [3H]vesamicol. Muscarinic cholinergic receptors were determined with [3H]scopolamine. The distribution patterns of the three cholinergic markers were similar in all species examined, and identified known major cholinergic pathways on the basis of enrichments in both pre- and postsynaptic markers. In addition, there was excellent agreement, both within and across species, in the regional distributions of the two presynaptic cholinergic markers. Our results indicate that pharmacological identifiers of cholinergic pathways and synapses, including the cholinergic vesicle transport site, and the organizations of central nervous system cholinergic pathways are phylogenetically conserved among eutherian mammals.