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A-G Photomicrographs of typical fluorescent injection site (MAT-7 in A) and mesencephalic cells (B-G). B FB-labeled cells in nucleus annularis surrounding the medial longitudinal fasciculus (MLF). C FR-labeled tectospinal cell. D, G FB-labeled cells in the mesencephalic reticular formation. D shows a typical field of cells, and two of the cells are magnified in G. E, F Cells of different sizes in the periaqueductal gray matter. Scale bars 100 µm
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Mesencephalic neurons projecting to the upper cervical spinal cord were examined by mapping the distributions of labeled cells after injecting fluorescent tracers or wheat-germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the C1 segment. Injections into the central or deep regions of the ventral horn produced retrograde labeling i...
Citations
... Likewise, in monkeys, the CnF projects ipsilaterally within segments of the spinal cord. An additional complexity in interpreting the literature is that the size of the PrCnF in cats (Satoda et al., 2002) and possibly monkeys (Castiglioi et al., 1978) is likely underestimated as the boundaries between the PrCnF and CnF in cats are not as distinct (Liang et al., 2011). ...
Over the past decade there has been a renaissance in our understanding of spinal cord circuits; new technologies are beginning to provide key insights into descending circuits which project onto spinal cord central pattern generators. By integrating work from both the locomotor and animal behavioral fields, we can now examine context-specific control of locomotion, with an emphasis on descending modulation arising from various regions of the brainstem. Here we examine approach and avoidance behaviors and the circuits that lead to the production and arrest of locomotion.
... Almost no terminals were present in trochlear IV (g) and abducens (VI) (h) nuclei the nucleus raphe interpositus have a similar distribution, but are fewer in number (Fig. 11a) (Wang et al. 2013). Reticulospinal neurons projecting to cervical spinal cord and medullary reticuloreticular cMRF neurons projecting to the rostral medullary reticular formation occupy just the medial portion of the cMRF (Fig. 11a, blue cross hatch) [primate: (Castiglioni et al. 1978;Perkins et al. 2014;Robinson et al. 1994;Warren et al. 2008); cat: (Perkins et al. 2014;Satoda et al. 2002)]. As we have shown here, the presence of a narrow band of cells labeled from oculomotor injections reveals an unreported subdivision with direct projections to the SOA and III (Fig. 11a, red cross hatch). ...
The central mesencephalic reticular formation is physiologically implicated in oculomotor function and anatomically interwoven with many parts of the oculomotor system's premotor circuitry. This study in Macaca fascicularis monkeys investigates the pattern of central mesencephalic reticular formation projections to the area in and around the extraocular motor nuclei, with special emphasis on the supraoculomotor area. It also examines the location of the cells responsible for this projection. Injections of biotinylated dextran amine were stereotaxically placed within the central mesencephalic reticular formation to anterogradely label axons and terminals. These revealed bilateral terminal fields in the supraoculomotor area. In addition, dense terminations were found in both the preganglionic Edinger-Westphal nuclei. The dense terminations just dorsal to the oculomotor nucleus overlap with the location of the C-group medial rectus motoneurons projecting to multiply innervated muscle fibers suggesting they may be targeted. Minor terminal fields were observed bilaterally within the borders of the oculomotor and abducens nuclei. Injections including the supraoculomotor area and oculomotor nucleus retrogradely labeled a tight band of neurons crossing the central third of the central mesencephalic reticular formation at all rostrocaudal levels, indicating a subregion of the nucleus provides this projection. Thus, these experiments reveal that a subregion of the central mesencephalic reticular formation may directly project to motoneurons in the oculomotor and abducens nuclei, as well as to preganglionic neurons controlling the tone of intraocular muscles. This pattern of projections suggests an as yet undetermined role in regulating the near triad.
... The fact that labeled reticuloreticular neurons are located in the medial MRF following medullary injections suggests that this region of the MRF may be specifically involved in gaze changes that require head movements. This position is supported by previous reports which indicate that MRF cells projecting to the cervical spinal cord also reside in the medial region of the MRF (Holstege and Cowie, 1989;May et al., 2002;Satoda et al., 2002;Warren et al., 2008). However, Cowie and Holstege's (1992) study of MdRF inputs in the cat does not support this regional specialization. ...
Gaze changes involving the eyes and head are orchestrated by brainstem gaze centers found within the superior colliculus (SC), paramedian pontine reticular formation (PPRF), and medullary reticular formation (MdRF). The mesencephalic reticular formation (MRF) also plays a role in gaze. It receives a major input from the ipsilateral SC and contains cells that fire in relation to gaze changes. Moreover, it provides a feedback projection to the SC and feed-forward projections to the PPRF and MdRF. We sought to determine whether these MRF feedback and feed-forward projections originate from the same or different neuronal populations by utilizing paired fluorescent retrograde tracers in cats. Specifically, we tested: 1. whether MRF neurons that control eye movements form a single population by injecting the SC and PPRF with different tracers, and 2. whether MRF neurons that control head movements form a single population by injecting the SC and MdRF with different tracers. In neither case were double labeled neurons observed, indicating that feedback and feed-forward projections originate from separate MRF populations. In both cases, the labeled reticulotectal and reticuloreticular neurons were distributed bilaterally in the MRF. However, neurons projecting to the MdRF were generally constrained to the medial half of the MRF, while those projecting to the PPRF, like MRF reticulotectal neurons, were spread throughout the mediolateral axis. Thus, the medial MRF may be specialized for control of head movements, with control of eye movements being more widespread in this structure.
... In the cat (Nyberg-Hansen, 1966;Kuypers and Maisky, 1975;Holstege and Tan, 1988;Holstege and Cowie, 1989;Isa and Sasaki, 1992a;Satoda et al., 2002) and monkey (Castiglioni et al., 1978;Carlton et al., 1985;Nudo and Masterton, 1988), this nucleus has similar projections to the spinal cord as in the rat. Fibers from this nucleus reach the lumbar cord and mainly terminate in the ipsilateral cord via the dorsal part of the ventral funiculus in cats (Nyberg-Hansen, 1966) and the dorsolateral funiculus in monkeys (Carlton et al., 1985). ...
... The red nucleus has a large number of fibers descending to the contralateral spinal cord in all species studied (anatomy of mouse red nucleus shown in FigI.5 and 6). These fibers originate not only from the magnocellular part (RMC) (In mice: Carretta et al., 2001;Tsukamoto et al., 2003;VanderHorst and Ulfhake, 2006; in rats: Leichnetz et al., 1978;Murray and Gurule, 1979;Watkins et al., 1981;Shiel et al., 1983;Leong et al., 1984a;Schwanzel-Fukuda et al., 1984;Daniel et al., 1987;Shen et al., 1990;Masson et al., 1991;Kudo et al., 1993;Naso et al., 1993;Wang et al., 1996;de Boer-van Huizen and ten Donkelaar, 1999;in cats: Kuypers and Maisky, 1975;Basbaum and Fields, 1979;Holstege and Tan, 1988;Satoda et al., 2002;in monkeys: Castiglioni et al., 1978;Kneisley et al., 1978;Carlton et al., 1985) but also from the parvicellular part of the red nucleus (RPC) (In rats: Leong et al., 1984a;Daniel et al., 1987;In cats: Pong et al., 2002). Most of these neurons, however, are located in the RMC, with a smaller number of neurons in the RPC. ...
... The deep layer of the superior colliculus (SC) issues projections to the contralateral spinal cord (in mice: VanderHorst and Ulfhake, 2006; in rats: Leong et al., 1984a;1984b;in cats: Nyberg-Hansen, 1966;Kuypers and Maisky, 1975;Hayes and Rustioni, 1981;Olivier et al., 1991;Cowie and Holstege, 1992;Satoda et al., 2002) (anatomy of mouse SC shown in FigI.5-7). Some studies also show the presence of spinal projecting neurons in the intermediate gray layer (in rats: Leong et al., 1984a;1984b;Nudo and Masterton, 1989; in cats: Kuypers and Maisky, 1975;Hayes and Rustioni, 1981;Nudo and Masterton, 1989;Olivier et al., 1991;Cowie and Holstege, 1992;Satoda et al., 2002;in monkeys: Nudo and Masterton, 1989;May and Porter, 1992). ...
The cells that project from the brain to the spinal cord have previously been mapped in a wide range of mammalian species, but have not been comprehensively studied in the mouse. We have mapped these cells in the mouse using retrograde tracing after large unilateral Fluoro-Gold (FG) and horseradish peroxidase (HRP) injections in the C1 and C2 spinal cord segments. We have identified over 30 cell groups that project to the spinal cord, and have confirmed that the pattern of major projections from the cortex, diencephalon, midbrain, and hindbrain in the mouse is typically mammalian, and very similar to that found in the rat. However, we report two novel findings: we found labeled neurons in the precuneiform area (an area which has been associated with the midbrain locomotor center in other species), and the epirubrospinal nucleus. We also found labeled cells in the medial division of central nucleus of the amygdala in a small number of cases. Our findings should be of value to researchers engaged in evaluating the impact of spinal cord injury and other spinal cord pathologies on the centers which give rise to descending pathways.
... The distribution of reticulospinal neurons within the caudal MRF (i.e., the cMRF) has also been examined previously in primates (Castiglioni et al., 1978;Nudo and Masterton, 1988;Robinson et al., 1994;Warren et al., 2008). Similarly, the distribution patterns of reticuloand interstitiospinal neurons shown here have been seen in the cat (Huerta and Harting, 1982;Zuk et al., 1983;Holstege, 1988;Spence and Saint-Cyr, 1988;Satoda et al., 2002) and the monkey (Castiglioni et al., 1978). Like previous primate studies (Castiglioni et al., 1978;Kokkoroyannis et al., 1996), we observed a predominantly ipsilateral distribution, but a more bilateral distribution was observed in cat studies (Edwards, 1975). ...
The superior colliculus (SC), which directs orienting movements of both the eyes and head, is reciprocally connected to the mesencephalic reticular formation (MRF), suggesting the latter is involved in gaze control. The MRF has been provisionally subdivided to include a rostral portion, which subserves vertical gaze, and a caudal portion, which subserves horizontal gaze. Both regions contain cells projecting downstream that may provide a conduit for tectal signals targeting the gaze control centers which direct head movements. We determined the distribution of cells targeting the cervical spinal cord and rostral medullary reticular formation (MdRF), and investigated whether these MRF neurons receive input from the SC by the use of dual tracer techniques in Macaca fascicularis monkeys. Either biotinylated dextran amine or Phaseolus vulgaris leucoagglutinin was injected into the SC. Wheat germ agglutinin conjugated horseradish peroxidase was placed into the ipsilateral cervical spinal cord or medial MdRF to retrogradely label MRF neurons. A small number of medially located cells in the rostral and caudal MRF were labeled following spinal cord injections, and greater numbers were labeled in the same region following MdRF injections. In both cases, anterogradely labeled tectoreticular terminals were observed in close association with retrogradely labeled neurons. These close associations between tectoreticular terminals and neurons with descending projections suggest the presence of a trans-MRF pathway that provides a conduit for tectal control over head orienting movements. The medial location of these reticulospinal and reticuloreticular neurons suggests this MRF region may be specialized for head movement control.
... In both species, the vast majority of these neurons were located ipsilaterally. This pattern of label in the cMRF correlates well with that seen previously, and ascribed either to the MRF or cuneiform nucleus (cat: Cowie and Holstege, 1992;Holstege and Cowie, 1989;monkey: Castiglioni et al., 1978;Nudo and Masterton, 1988;Robinson et al., 1994;Satoda et al., 2002). Electrophysiological examination of the monkey cMRF has revealed cells with postsaccadic activity, whose firing appears to correlate with gaze-related head movements. ...
A gaze-related region in the caudal midbrain tegementum, termed the central mesencephalic reticular formation (cMRF), has been designated on electrophysiological grounds in monkeys. In macaques, the cMRF correlates with an area in which reticulotectal neurons overlap with tectoreticular terminals. We examined whether a region with the same anatomical characteristics exists in cats by injecting biotinylated dextran amine into their superior colliculi. These injections showed that a cat cMRF is present. Not only do labeled tectoreticular axons overlap the distribution of labeled reticulotectal neurons, these elements also show numerous close boutonal associations, suggestive of synaptic contact. Thus, the presence of a cMRF that supplies gaze-related feedback to the superior colliculus may be a common vertebrate feature. We then investigated whether cMRF connections indicate a role in the head movement component of gaze changes. Cervical spinal cord injections in both the cat and monkey retrogradely labeled neurons in the ipsilateral, medial cMRF. In addition, they provided evidence for a spinoreticular projection that terminates in this same portion of the cMRF, and in some cases contributes boutons that are closely associated with reticulospinal neurons. Injection of the physiologically defined, macaque cMRF demonstrated that this spinoreticular projection originates in the cervical ventral horn, indicating it may provide the cMRF with an efference copy signal. Thus, the cat and monkey cMRFs have a subregion that is reciprocally connected with the ipsilateral spinal cord. This pattern suggests the medial cMRF may play a role in modulating the activity of antagonist neck muscles during horizontal gaze changes.
... The data obtained show that fibres arising from the upper encephalic areas known to provide control of locomotion reach the lumbo-sacral spinal cord, both in the control and in the affected calves. The LVN and PRF principally activate the motoneurons which control limb extension, whereas the RN and the MRF inhibit the same motoneuronal pool (Carretta et al., 2001; Takakusaki et al., 2001; Satoda et al., 2002). The data obtained in the present study indicate significant differences between MRF and RN. ...
The human spinal cord can be described using a range of nomenclatures with each providing insight into its structure and function. Here we have comprehensively reviewed the key literature detailing the general structure, configuration of tracts, the cytoarchitecture of Rexed's laminae, and the neurochemistry at the spinal segmental level. The purpose of this review is to detail current anatomical understanding of how the spinal cord is structured and to aid researchers in identifying gaps in the literature that need to be studied to improve our knowledge of the spinal cord which in turn will improve the potential of therapeutic intervention for disorders of the spinal cord.
The mesencephalic locomotor region (MLR) serves as an interface between higher-order motor systems and lower motor neurons. The excitatory module of the MLR is composed of the pedunculopontine nucleus (PPN) and the cuneiform nucleus (CnF), and their activation has been proposed to elicit different modalities of movement. However, how the differences in connectivity and physiological properties explain their contributions to motor activity is not well known. Here we report that CnF glutamatergic neurons are more electrophysiologically homogeneous than PPN neurons and have mostly short-range connectivity, whereas PPN glutamatergic neurons are heterogeneous and maintain long-range connections, most notably with the basal ganglia. Optogenetic activation of CnF neurons produces short-lasting muscle activation, driving involuntary motor activity. In contrast, PPN neuron activation produces long-lasting increases in muscle tone that reduce motor activity and disrupt gait. Our results highlight biophysical and functional attributes among MLR neurons that support their differential contribution to motor behavior.
Elements in the medullary ventral respiratory column nuclei and dorsal respiratory group interact with the Kölliker‐Fuse and medial parabrachial nuclei to generate the breathing rhythm and pattern. Triphasic eupnea consists of inspiratory [I], post‐inspiratory [post‐I], and late‐expiratory [E2] phases. Mesencephalic zones exert modulatory influences upon respiratory rhythm generating circuitry, sympathetic oscillators, and parasympathetic nuclei. The earliest evidence supporting this derives from studies performed by Martin and Booker in 1878. These authors demonstrated augmentation of ventilation in response to electrical stimulation of the mesencephalic colliculi in the rabbit. A series of studies performed during the past several decades revealed a critical contribution of the red nucleus in mediating hypoxic ventilatory depression. Stimulation of distributed zones within the midbrain elicited seemingly disparate effects upon respiratory phase timing and transitioning. The works of Schmid and Böhmer demonstrated monosynaptic modulation of medullary inspiratory and expiratory related units in response to stimulation within midbrain zones corresponding with the red nucleus and rubrospinal tract. A plethora of studies have since generated strong evidence demonstrating and underscoring a critical contribution of the mesencephalic colliculi and periaqueductal gray matter in coordinately amplifying the respiratory output and sympathetic tone, blunting the Hering Breuer reflex and barosensitivity, and generating defense reaction behavioral responses to imminent environmental dangers. The lateral and ventrolateral divisions of the periaqueductal gray matter play critical roles in coordinating vocalization with breathing in an integrated circuit with the parabrachial nuclei. Authors have critically highlighted extensive and specific locoregional heterogeneity of effects elicited from periaqueductal gray matter stimulation. Studies have also made significant strides into elucidating the mechanistic basis and monosynaptic and polysynaptic propriobulbar and bulbospinal circuitry mediating periaqueductal gray matter and collicular modulation of breathing and autonomic outflow. The periaqueductal gray matter thus modulates and shapes neural respiratory frequency and amplitude, respiratory phase transitions, and autonomic outflow and appropriately coordinates defense reaction behavioral responses. The data collectively inspire fruitful new avenues of investigation in order to more thoroughly elucidate the mechanistic underpinnings of coordinate effects of the mesencephalic periaqueductal gray matter modulating the cardiovascular and respiratory outputs. We discuss and review the literature evaluating the role of the periaqueductal gray matter in modulating the respiratory and cardiovascular outputs.
