Peribrachial Area Research Articles

GABAA receptor agonist at the caudo-lateral peribrachial area suppresses ponto-geniculo-occipital waves and its related states

PurposeIn order to explore the potential role of GABA, acetylcholine and glutamate in the caudo-lateral peribrachial area (C-PBL) over Rapid-Eye-Movement sleep (REM) onset and maintenance as well as on synchronized sleep with ponto-geniculo-occipital (PGO) waves (SP) in cats, a muscimol, carbachol and l-glutamate local application was performed and behavioral states were assessed. MethodsFourteen chronically implanted, adult, male cats underwent a 23hour polysomnographic recording after 3 pharmacological manipulations: carbachol, muscimol and l-glutamate. Each cat received all three drugs randomly with a seven day interval. Results1) Carbachol increases waking, SP and REM sleep while decreases slow wave sleep (SWS). 2) Muscimol decreases SP percentage and number while increases REM sleep onset. 3) Carbachol facilitates PGO activity and increases the latency to both SWS1 and REM sleep but enhances PGO activity while muscimol decreases it. ConclusionsAcetylcholine promotes PGO related states (SP as well as REM sleep), while GABA reduces only SP and specifically PGOs.

Inhibitory effect of state independent ponto-geniculo-occipital waves on seizure occurrence induced by local application of penicillin into the temporal lobe amygdala

Purpose In order to explore the possible inhibitory role of the phasic phenomena of REM sleep ponto-geniculo-occipital (PGO) waves over epilepsy, seizure activity produced by topic administration of Na-penicillin (PCN) has been analyzed during sustained PGO waves irrespective of current state. PGO waves were induced by the injection of carbachol in the peribrachial area. Methods The development of acute experimental epilepsy was compared among nine chronically implanted, adult, male cats, by means of polygraphic 23h recordings. Our protocol consisted of sets of 4 trials: carbachol; PCN; carbachol followed by PCN and finally PCN followed by carbachol. Each cat received one single set and all trials were carried out with a seven days interval, in order to compare the epileptic activity both in the presence of PGOs and without them. Results PGO waves 1) exert an inhibitory influence over number and duration of the Generalized Convulsive Seizures (GCSs) and 2) spike frequency; 3) increase the latency of GCSs; and 4) restores sleep alterations produced by experimental epilepsy. Conclusions PGO waves exhibit an inhibitory influence over seizures induced by PCN. These data support the hypothesis that this phasic phenomenon of REM sleep have a depressant effect on epilepsy, inhibit seizures and normalize sleep architecture changes induced by seizures. We suggest that one possible function of PGO activity is to protect the brain from intense changes in neuronal excitability; namely convulsive activity.

Trigeminal primary afferent projections to the peribrachial area in the guinea pig

Transganglionic transport of horseradish peroxidase (HRP) was used to investigate trigeminal primary afferent endings in the peribrachial area of the guinea pig. After HRP application to several nerve branches of the three divisions of the trigeminal nerve, a projection to the caudal region of the ipsilateral peribrachial region was found for the infratrochlear, ethmoidal, supraorbital, zygomatic, zygomaticofacial, zygomaticotemporal and infraorbital-superior alveolar nerves. Random and scarce endings were also observed for the mental, inferior alveolar, buccal and mylohyoid nerves. No trigeminal primary projection to the peribrachial area was detected when HRP was applied to the sphenopalatine, lingual and auriculotemporal nerves. With the exception of the ethmoidal endings described in the muskrat, a primary afferent projection to the peribrachial region from the other trigeminal nerves has not hitherto been reported in mammals.

Suppression of ponto-geniculo-occipital waves by neurotoxic lesions of pontine caudo-lateral peribrachial cells

Ponto-geniculo-occipital waves precede rapid eye movement sleep and play an important role in triggering and maintaining rapid eye movement sleep. Ponto-geniculo-occipital waves have been implicated in several important functions such as sensorimotor integration, learning, cognition, development of the visual system, visual hallucination, and startle response. Peribrachial area neurons have long been thought to play a key role in the triggering of ponto-geniculo-occipital wave. However, the exact location within the peribrachial area for triggering pontine ponto-geniculo-occipital wave has not been unequivocally demonstrated. In an attempt to address this issue, kainic acid was microinjected (1.0 micrograms) unilaterally into the caudo-lateral peribrachial area of four cats in order to destroy the cell bodies located in that region and thus to study the effects of their destruction upon waking-sleep states and ponto-geniculo-occipital waves. The kainic acid produced a small spherical area of nerve cell loss and/or gliosis centered on the stereotaxic coordinates of P: 4.0, L: 4.5, and H: -2.5. The maximum diameter of that spherical area of cell loss was 0.9 mm. Unilateral lesioning of the caudo-lateral peribrachial area decreased ponto-geniculo-occipital waves during rapid eye movement sleep by 85% ipsi-laterally and 15% contralaterally in the lateral geniculate body without significantly changing the amounts of time spent in wake, slow-wave sleep, and rapid eye movement sleep. These results suggest that the caudo-lateral peribrachial area cells are critical to the genesis of ponto-geniculo-occipital waves, and provide compelling evidence that the different parts of the peribrachial area have quite different roles in the generation of discrete rapid eye movement sleep signs. We propose that caudo-lateral peribrachial cells exert an excitatory influence on rostral peribrachial cells, which then directly activate the ponto-geniculo-occipital waves that are recorded in the lateral geniculate body. Results of this study are not only important to understand the mechanisms generating ponto-geniculo-occipital waves but also could be used as an experimental tool to study the functions of this wave.

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.

Trigeminal projections to the peribrachial region in the muskrat

The anterograde and retrograde transport of wheat germ agglutinin-horseradish peroxidase was used to study the trigeminoperibrachial pathway in the muskrat after injections of tracer into either the medullary dorsal horn or the dorsolateral pons. After injections into the medullary dorsal horn, labeled fibers ascended into the ipsilateral dorsolateral pons via the spinal trigeminal tract, within the neuropil of the trigeminal sensory complex and within the reticular formation adjacent to the spinal trigeminal nucleus. At caudal levels of the ipsilateral peribrachial area, dense terminal-like label distributed in the Kölliker-Fuse nucleus continued into the lateral parabrachial nucleus. At intermediate levels ipsilaterally, the Kölliker-Fuse nucleus again was labeled densely, as were areas analogous to the external lateral and external medial subnuclei of the parabrachial nucleus in the rat. A thin band of label along the ventral spinocerebellar tract outlined an unlabeled area in the central portion of the lateral parabrachial nucleus. Rostrally near the pontomesencephalic junction, the area designated the superior lateral subnucleus in the hamster was labeled, while sparser label was present more dorsally. Contralateral to the injections, caudal and intermediate levels of the peribrachial area contained only scant reaction product. However, the rostral area of the superior lateral subnucleus was labeled densely via fibers ascending in the trigemino thalamic tract. Injections made just rostral to the obex and either centered in or including the dorsal or ventral paratrigeminal nuclei produced similar labeling at caudal and intermediate levels of the peribrachial area. An exception, however, was that the caudal medial parabrachial nucleus was also labeled after the dorsal paratrigeminal injection. Also, only scant label was found in the rostral third of the dorsolateral pons on either side after these injections. Both trigeminothalamic and trigeminolemniscal pathways were labeled contralaterally after these injections. These trigeminal projections to the dorsolateral pons were compared to the projections from the nucleus tractus solitarii and the ventrolateral medulla. Numerous trigeminal neurons were labeled retrogradely after injections of wheat germ agglu tinin-horseradish peroxidase into the dorsolateral pons. In the medullary dorsal horn, they were found almost exclusively in laminae I and V. Labeled neurons in lamina I were especially prominent in rostral ventral levels of the medullary dorsal horn. Labeled cells in lamina I were continuous with others found in the displaced band of substantia gelatinosa at the interface of the subnucleus caudalis and subnucleus interpolaris, as well as with those found in the ventral and dorsal paratrigeminal nuclei. Fewer labeled neurons were found along the ventromedial border of subnucleus interpolaris caudally and in the dorsomedial portion of the subnucleus oralis. These data illustrate a robust trigmeminoperibrachial pathway in the muskrat. Since the parabrachial nucleus receives both somatosensory and visceral sensory information, it may play a role in somatovisceral reflex behaviors.

Neuronal activity in the caudolateral peribrachial pons: relationship to PGO waves and rapid eye movements

1. The present study was performed to examine the hypothesis that the caudolateral peribrachial area (C-PBL) may be directly involved in shifting the brain from the nonpontogeniculooccipital (non-PGO)-related states of waking (W) and slow-wave sleep (S) to the PGO-related states of slow-wave sleep with PGO waves (SP) and rapid eye movement (REM) sleep. 2. To test this hypothesis at the cellular level, we have recorded a sample of 226 spontaneously discharging units of the C-PBL during natural sleep-waking cycles in unanesthetized head-restrained cats and have correlated the action-potential data with the PGO waves. 3. Of these 226 cells, 67.26% (n = 152) were called PGO state-on units because they increased or began firing 15-5 s before the first PGO wave of SP and maintained their high firing rate throughout SP (31.30 +/- 6.0 Hz, mean +/- SD) and REM sleep (39.46 +/- 6.70 Hz); their firing rates in W (0.45 +/- 0.85) and S (0.70 +/- 1.26) were much lower. Among these PGO state-on neurons, 28.94% (n = 44) discharged high-frequency (> 500 Hz) spike bursts on the background of tonically increased firing rates during the PGO-related states. Contrastingly, 14.16% (n = 32) of the cells (called PGO state-off units) fired tonically during W (11.54 +/- 4.15) and S (9.43 +/- 3.87) but stopped or decreased firing 25-15 s before the first PGO wave of SP; their activity remained suppressed throughout SP (0.19 +/- 0.44) and REM sleep (0.03 +/- 0.17). The remaining 18.58% (n = 42) cells fired (9-10 Hz) tonically but were unrelated to the wake-sleeping cycle. 4. During SP and REM sleep, primary PGO waves were found to appear with equal frequency in each lateral geniculate body (LGB). During REM sleep these primary waves were ipsilateral to the direction of phasic rapid eye movements as previously reported by Nelson et al. (1983). 5. During SP and REM sleep PGO state-on burst cells fired high-frequency bursts on a background of tonic activity in association with each ipsilateral primary LGB PGO wave. The first spike of a burst preceded the beginning of the negative component of the ipsilateral LGB PGO waves by 25 +/- 7.5 ms. On the basis of their sustained firing and the latency of their PGO-related bursting, we call these neurons long-lead PGO-on burst-tonic cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Organization of the output of the ventral striatopallidal system in the rat: Ventral pallidal efferents

The efferent projections of the ventral pallidum in the rat were studied using anterograde tracing of Phaseolus vulgaris-leucoagglutinin and retrograde tracing of choleratoxin subunit B. The main aim of this study was to determine the degree of topographical organization in the outputs of the ventral pallidum. In the telencephalon, ventral pallidal fibers reach the prefrontal cortex, the ventral striatum, the lateral septum, the basolateral, lateral, and central amygdaloid nuclei, and the lateral entorhinal area. Diencephalic targets of ventral pallidal fibers are the lateral hypothalamus, the reticular nucleus of the thalamus, the mediodorsal thalamic nucleus, the dorsomedial part of the subthalamic nucleus, the medial part of the parafascicular nucleus and the lateral habenula. In the mesencephalon, ventral pallidal fibers terminate in the ventral tegmental area, the substantia nigra, the retrorubral area, the median raphe nucleus, the nucleus raphe magnus, the peribrachial area, the ventromedial part of the central gray substance and the locus coeruleus. The results of the experiments in which retrograde tracers were injected in different nuclei in the mesencephalon allow the distinction of two main areas in the ventral pallidum. Deposits of retrograde tracers in the substantia nigra, pars reticulata result in labeling of cells in the dorsolateral part of the ventral pallidum, located immediately ventral to the anterior limb of the anterior commissure. Retrograde tracer injections in other targets of the ventral mesencephalon, i.e. the dopaminergic cell groups A10, A9 or A8, or nuclei in the peribrachial area result in labeling of neurons in an extensive ventromedial and ventrolateral zone of the ventral pallidum. The medial part of this ventral pallidal zone projects to the ventral tegmental area, whereas ventral and lateral parts connect with more lateral and caudal mesencephalic targets. The projections from the ventral pallidum to the ventral striatum, the subthalamic nucleus and adjacent lateral hypothalamic area, and the mediodorsal thalamic nucleus are distinctly topographically organized. The ventral pallidostriatal projections preserve a medial-to-lateral, a dorsal-to-ventral and, to a lesser degree, a rostral-to-caudal topography. With respect to the subthalamic region, the dorsolateral part of the ventral pallidum projects to the dorsomedial part of the subthalamic nucleus, whereas the ventromedial and ventrolateral parts of the ventral pallidum are topographically connected with the area of the lateral hypothalamus medially adjacent to the subthalamic nucleus. The ventral pallidal projections to the mediodorsal thalamic nucleus are arranged such that dorsal-to-ventral and medial-to-lateral gradients in the ventral pallidum correspond to medial-to-lateral and rostral-to-caudal gradients in the mediodorsal nucleus, respectively. This topography in the ventral pallidal-mediodorsal thalamic pathways fits in with the parallel arrangement of a number of circuits that involve distinct parts of the prefrontal cortex, the ventral striatum, the ventral pallidum, and the mediodorsal thalamic nucleus. Such a parallel arrangement of the connections of the ventral parts of the basal ganglia with the prefrontal cortex and the mediodorsal thalamus is consistent with the more general concept of parallel, functionally segregated basal ganglia-thalamocortical circuits.

Effect of Specific Muscarinic M2 Receptor Antagonist on Carbachol Induced Long-Term REM Sleep

Six cats were chronically implanted with a standard set of sleep-scoring electrodes and bilateral stainless-steel guide tubes for microinjection of drugs in the peribrachial area (PBL). Pretreatment of drug injection sites in the PBL with the M2 antagonist methoctramine blocks both the immediate triggering of ponto-geniculo-occipital (PGO) waves and the later prolonged enhancement of REM sleep that is induced by carbachol. These results support the hypothesis that the carbachol effects are mediated via the M2 muscarinic receptor that is known to be present in the PBL.

Chapter 47: Acetylcholine as a brain state modulator: triggering and long-term regulation of REM sleep

Publisher Summary One of the major conceptual and empirical challenges confronting behavioral neurobiology is to develop theoretical models and experimental paradigms that will help to understand how single cells and their specific chemical signals come to be organized at the level of population ensembles in order to determine the global behavioral states of waking and sleep. To help meet this challenge, recent discoveries suggesting a role for acetylcholine containing neurons in both the triggering and long-term regulation of REM sleep offer inviting and instructive opportunities. It is the main purpose of this chapter to provide a detailed review of a recent and unexpected discovery: the long-term potentiation of REM sleep following the micro-injection of the cholinergic agonist carbachol into the cholinergic neuronal population of the peribrachial pontine tegmentum. Following a brief summary of the background of the cholinergic hypothesis of REM sleep generation and the current concept of the cellular nature of the REM sleep generator network, this chapter discusses the general neurobiology of the peribrachial area, and focus on its cholinergic neuronal sub-population as a prelude to a detailed account of the long-term REM sleep enhancement that follows the microinjection of carbachol into this zone. It discusses this finding in terms of a new, “cholinergic priming” hypothesis, which attributes the surprisingly long duration of the response to the setting in motion of an endogenous metabolic mechanism.

Neuropeptide Y-containing neuronal pathway from the spinal trigeminal nucleus to the pontine peribrachial region in the rat

The existence of ascending medullary neuropeptide Y (NPY)-containing projection from the spinal trigeminal nucleus to the pontine peribrachial area has been demonstrated by a combination of immunohistochemical methods with surgical transections in the lower brainstem. An NPY immunopositive cluster of varicose fibers was detected in the spinal trigeminal and in the paratrigeminal nuclei. Numerous immunoreactive perikarya could also be visualized here after colchicine treatment. Transections destroying the lateral region of the medulla oblongata resulted in an accumulation of NPY immunoreactivity in several trigeminal neurons ipsilateral to the knife cut, but no such retrograde accumulation was seen in any neuronal perikarya anywhere else in the medulla oblongata.

Neuronal activities in brain-stem cholinergic nuclei related to tonic activation processes in thalamocortical systems

This study was performed to examine the hypothesis that thalamic-projecting neurons of mesopontine cholinergic nuclei display activity patterns that are compatible with their role in inducing and maintaining activation processes in thalamocortical systems during the states of waking (W) and rapid-eye-movement (REM) sleep associated with desynchronization of the electroencephalogram (EEG). A sample of 780 neurons located in the peribrachial (PB) area of the pedunculopontine tegmental nucleus and in the laterodorsal tegmental (LDT) nucleus were recorded extracellularly in unanesthetized, chronically implanted cats. Of those neurons, 82 were antidromically invaded from medial, intralaminar, and lateral thalamic nuclei: 570 were orthodromically driven at short latencies from various thalamic sites: and 45 of the latter elements are also part of the 82 cell group, as they were activated both antidromically and synaptically from the thalamus. There were no statistically significant differences between firing rates in the PB and LDT neuronal samples. Rate analyses in 2 distinct groups of PB/LDT neurons, with fast (greater than 10 Hz) and slow (less than 2 Hz) discharge rates in W, indicated that (1) the fast-discharging cell group had higher firing rates in W and REM sleep compared to EEG-synchronized sleep (S), the differences between all states being significant (p less than 0.0005); (2) the slow-discharging cell group increased firing rates from W to S and further to REM sleep, with significant difference between W and S (p less than 0.01), as well as between W or S and REM sleep (p less than 0.0005). Interspike interval histograms of PB and LDT neurons showed that 75% of them have tonic firing patterns, with virtually no high-frequency spike bursts in any state of the wake-sleep cycle. We found 22 PB cells that discharged rhythmic spike trains with recurring periods of 0.8-1 sec. Autocorrelograms revealed that this oscillatory behavior disappeared when their firing rate increased during REM sleep. Dynamic analyses of sequential firing rates throughout the waking-sleep cycle showed that none of the full-blown states of vigilance is associated with a uniform level of spontaneous firing rate. Signs of decreased discharge frequencies of mesopontine neurons appeared toward the end of quiet W, preceding by about 10-20 sec the most precocious signs of EEG synchronization heralding the sleep onset. During transition from S to W, rates of spontaneous discharges increased 20 sec before the onset of EEG desynchronization.(ABSTRACT TRUNCATED AT 400 WORDS)

Membrane resistance increase induced in thalamic neurons by stimulation of brainstem cholinergic afferents

The synaptic response induced in thalamic relay cells by stimulation of peribrachial cholinergic afferents was studied in cats maintained under urethane anesthesia. Recordings were performed in the ventral lateral nucleus after destruction of the reticular thalamic complex and cortical lesion. Some animals were also pretreated with reserpine (1.2 mg/kg) 24 h before recording sessions. Repetitive stimulation (25–60 Hz for 200–600 ms) of the peribrachial area produced a slow depolarization and tonic firing in thalamic cells. The depolarization was associated with an increase in membrane resistance and its amplitude decreased during membrane hyperpolarization. The reactivity of thalamic relay cells to a corticothalamic volley was also increased during the slow depolarization. Similar results were obtained in reserpinized animals. On the basis of previous data obtained in vitro, it is concluded that the slow depolarization resulted from the activation of muscarinic receptors by brainstem cholinergic afferents.

Neuronal activity of identified posterior hypothalamic neurons projecting to the brainstem peribrachial area of the cat

Following horseradish peroxidase injections in the brainstem peribrachial (PB) area, massive retrograde labeling was found in the posterior hypothalamic region. Single-unit recordings of posterior hypothalamic neurons with antidromically identified projections to the PB area revealed that these neurons have higher firing rates in waking than in slow-wave sleep and dissimilar discharge patterns as compared with intralaminar thalamic neurons. The results are discussed in the context of reciprocal hypothalamo-brainstem circuits.

Basal forebrain cholinergic and noncholinergic projections to the thalamus and brainstem in cats and monkeys

The projections of basal forebrain neurons to the thalamus and the brainstem were investigated in cats and primates by using retrograde transport techniques and choline acetyltransferase (ChAT) immunohistochemistry. In a first series of experiments, the lectin wheat germ-agglutinin conjugated with horseradish peroxidase (WGA-HRP) was injected into all major sensory, motor, intralaminar, and reticular (RE) thalamic nuclei of cats and into the mediodorsal (MD) and pulvinar-lateroposterior thalamic nuclei of macaque monkeys. In cats numerous neurons of the vertical and horizontal limbs of the diagonal band nucleus and the substantia innominata (SI), including its rostromedial portion termed the ventral pallidum (VP), were retrogradely labeled after WGA-HRP injections in the rostral pole of the RE complex, the MD, and anteroventral/anteromedial (AV/AM) thalamic nuclei. Fewer retrogradely labeled cells were observed in the same areas after injections in the ventromedial (VM) thalamic nucleus, and none or very few after other thalamic injections. After RE, MD, and AV/AM injections, 7-20% of all retrogradely labeled cells in the basal forebrain were also ChAT positive, while none of the retrogradely labeled neurons following VM injections displayed ChAT immunoreactivity. The basal forebrain projection to the MD nucleus was shown to arise principally from VP in both cats and macaque monkeys. In a second series of experiments performed in cats, injections of WGA-HRP in the brainstem peribrachial (PB) area comprising the pedunculopontine nucleus led to retrograde labeling of a moderate number of neurons in the lateral part of the VP, SI, and preoptic area (POA), only a few of which displayed ChAT immunoreactivity. In addition, a large number of retrogradely labeled cells were observed in the bed nuclei of the anterior commissure and stria terminalis after PB injections. In a third series of experiments, the use of the retrograde double-labeling method with fluorescent tracers in squirrel monkeys allowed us to identify a significant number of basal forebrain neurons sending axon collaterals to both the RE thalamic nucleus and PB brainstem area, while no double-labeled neurons were disclosed after injections confined to the ventral anterior/ventral lateral (VA/VL) thalamic nuclei and PB area or following injections in the cerebral cortex and PB area. Our findings reveal the existence of cholinergic and noncholinergic basal forebrain projections to the thalamus and the brainstem in both cats and macaque monkeys. We suggest that these projections may play a crucial role in the control of thalamic functions in mammals.

The blockage of ponto-geniculo-occipital waves in the cat lateral geniculate nucleus by nicotinic antagonists

The cholinergic mechanism underlying the genesis of ponto-geniculo-occipital (PGO) waves recorded from the lateral geniculate (LG) nucleus was studied in reserpinized cats under urethane anesthesia. PGO field potentials and their related unit activities occured spontaneously or were triggered by stimulation of the brainstem peribrachial (PB) area. It was found that PGO-related unit activities were strongly depressed by systemic or iontophoretic applications of nicotinic antagonists such as mecamylamine or hexamethonium but remained intact after similar applications of scopolamine. These results suggest that the genesis of thalamic PGO waves involves a nicotinic activation of relay neurons by PB cholinergic afferents.

Electrically induced locomotion in the in vitro brainstem-spinal cord preparation

Electrical stimulation of the brainstem was used to induce locomotion in the in vitro brainstem-spinal cord preparation. Recordings of electromyograms in ‘limb-attached’ preparations revealed an apparently adult-like step cycle. The lowest threshold sites were localized in the posterior midbrain (reticular formation in the peribrachial area and in the ventral reticular formation) and in the medioventral medulla (dorsolateral to the pyramids).

Projections of cholinergic and non-cholinergic neurons of the brainstem core to relay and associational thalamic nuclei in the cat and macaque monkey

The projections of brainstem core neurons to relay and associational thalamic nuclei were studied in the cat and macaque monkey by combining the retrograde transport of wheat germ agglulinin conjugated with horseradish peroxidase with choline acetyltransferase immunohistochemistry.All major sensory (medial geniculate. lateral geniculate, ventrobasal). motor (venlroanterior. ventrolateral. ventromedial), associational (mediodorsal, pulvinar, lateral posterior) and limbic (anteromedial.,interoventral) thalamic nuclei of the cat were found to receive projections from cholinergic neurons located in the peribrachial area of the pedunculopontine nucleus and in the laterodorsal tegmental nucleus as well as from non-cholinergic neurons in the rostral (perirubral) part of the central tegmental mesencephalic field. Specific relay nuclei receive less than 10%) of their brainstem afferents from non-cholinergic neurons located at rostral midbrain levels and receive 85 96% of their brainstem innervation from a region at midbrain pontinc junction where the cholinergic perihrachial area and laterodorsal tegmental nucleus are maximally developed. of the total number of horseradish peroxidase-positive brainstem neurons seen after injections in various specific relay nuclei, the double-labeled (horseradish peroxidase + choline acetyltransferase) neurons represent approximately 70 85%. Three to eight times more numerous horseradish peroxidase-labeled brainstem cells were found after injections in associational (mediodorsal and pulvinar lateral posterior complex) and diffusely cortically projecting (ventromedial) thalamic nuclei of cat than after injections in specific relay nuclei. The striking retrograde cell labeling observed after injections in nuclei with associative functions and widespread cortical projections was due to massive afferentation from non-cholinergic parts of the midbrain and pontine reticular formation, on both ipsi- and contralateral sides.After wheat germ agglutinin horseradish peroxidase injections in the associative pulvinar lateral posterior complex and mediodorsal nucleus of Macaca sylvana.. 45 50% of horseradish peroxidase-positive brainstem peribrachial neurons were also choline acetyltransferase-positive. While cells in the medial part of the cholinergic peribrachial area were found to project especially towards the pulvinar lateral posterior nuclear complex in monkey, the retrograde cell labeling seen after the mediodorsal injection was mostly confined to the lateral part of both dorsal and ventral aspects of the peribrachial area.These findings support the role played by cholinergic and non-cholinergic hrainstem thalamic projections in various tonic and phasic events of behavioral slates of vigilance.

Projections of brainstem core cholinergic and non-cholinergic neurons of cat to intralaminar and reticular thalamic nuclei

We combined the retrograde transport of wheat germ agglutinin conjugated with horseradish peroxidase with choline acetyltransferase immunohistochemistry to study the projections of cholinergic and non-cholinergic neurons of the upper brainstem core to rostral and caudal intralaminar thalamic nuclei, reticular thalamic complex and zona incerta in the cat. After wheat germ agglutinin horseradish peroxidase injections in the rostral pole of the reticular thalamic nucleus, the distribution and amount of retrogradely labeled brainstem neurons were similar to those found after tracer injection in thalamic relay nuclei (see preceding paper42). After wheat germ agglutinin horseradish peroxidase injections in the caudal intralaminar centrum medianum parafascicular complex, rostral intralaminar central lateral paracentral wing, and zona incerta, the numbers of retrogradely labeled brainstem neurons were more than three times higher than those found after injections in thalamic relay nuclei. The larger numbers of horseradish peroxidase-positive brainstem reticular neurons after tracer injections in intralaminar or zona incerta injections results from a more substantial proportion of labeled neurons in the central tegmental field at rostral midbrain (perirubral) levels and in the ventromedial part of the pontine reticular formation, ipsi- and contralaterally to the injection site. Of all retrogradely labeled neurons in the caudal midbrain core at the level of the cholinergic peribrachial area and laterodorsal tegmental nucleus. 45ȁ50% were also choline acetyltransferase-positive alter the injections into central lateral paracentral and reticular nuclei, while only 25% were also choline acetyltransferase-positive after the injection into the centrum medianum parafascicular complex.These findings are discussed in the light of physiological evidence of brainstem cholinergic mechanisms involved in the blockade of synchronized oscillations and in activation processes of thalamocortical systems.

Cholinergic and non-cholinergic projections from the upper brainstem core to the visual thalamus in the cat.

The projections of cholinergic and non-cholinergic neurons of the rostral brainstem reticular formation to the visual thalamic nuclei (dorsal lateral geniculate - LG, lateral posterior - LP, and perigeniculate - PG) were studied in cat by using the retrograde transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA-HRP) combined with choline acetyltransferase (ChAT) immunohistochemistry. After thalamic injections, less than 10% of all retrogradely labeled neurons in the upper brainstem reticular core were located at most rostral (perirubral) levels where there are virtually no cholinergic elements. Approximately 75-80% of all HRP-positive neurons in the reticular formation were found between stereotaxic planes anterior 1 and posterior 2, in the peribrachial (PB) area of the pedunculopontine nucleus and in the laterodorsal tegmental (LDT) nucleus. The brainstem afferents to LG and PG thalamic nuclei essentially derive from PB neurons, with a small contribution from LDT cells, whereas the LP thalamic nucleus receives massive inputs from both PB and LDT brainstem nuclei. Of all HRP-positive elements visualized in the PB nucleus after an LG or a PG injection, 87% and 73%, respectively, were also ChAT-positive. Of all HRP-positive elements in the PB and LDT nuclei after an LP injection, 82% and 92%, respectively, were also ChAT-positive. The numbers of labeled neurons in the contralateral brainstem reticular nuclei reach 30% to 50% of the numbers found in the ipsilateral reticular formation. These findings reveal the existence of a prominent cholinergic projection from the brainstem reticular formation to the visual thalamic nuclei. Such a chemospecific projection is probably involved in phasic and tonic events of activated behavioral states.