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Thelma A. Lovick - One of the best experts on this subject based on the ideXlab platform.

  • Serotonergic transmission in the Periaqueductal Gray Matter in relation to aversive behaviour: morphological evidence for direct modulatory effects on identified output neurons.
    Neuroscience, 2000
    Co-Authors: Thelma A. Lovick, V.v Stezhka, D. M. Parry, Bridget M. Lumb
    Abstract:

    Intracellular recordings were made from 21 cells in the dorsolateral Periaqueductal Gray Matter in coronal midbrain slices. In the majority (n = 20) bath application of 5-hydroxytryptamine (30 or 150 mM) evoked either hyperpolarizing (n = 11) or depolarizing (n = 9) responses. Reconstructions of 11 neurons in the dorsolateral Periaqueductal Gray Matter after filling with biocytin revealed a population of output neurons whose axons followed a dorsolateral trajectory towards the perimeter of the ipsilateral Periaqueductal Gray Matter. In seven cells, the axon could be followed into the adjacent mesencephalic reticular formation. At the light microscopic level, immunostaining for 5-hydroxytryptamine revealed immunoreactive processes throughout the dorsolateral Periaqueductal Gray Matter but no labelled somata or dendrites. Close associations (i.e. no discernible gap) were observed between serotonergic profiles and the somata and dendrites of biocytin-filled cells. At the ultrastructural level, serial sections through 21 appositions on to biocytin-filled dendrites in three slices revealed 19 true appositions (i.e. having closely parallel plasma membranes with no intervening glial cell profiles) with the biocytin-filled dendrite. Only four of the appositions (21%) showed evidence of synaptic specializations which included aggregations of synaptic vesicles, and some thickening of the apposing membrane. The dense reaction product in the biocytin-filled cells precluded identification of the ultrastructure of postsynaptic elements. However, examination of contacts between 5-hydroxytryptamine-immunoreactive profiles and unlabelled elements in material taken from the contralateral side of the Periaqueductal Gray Matter (i.e. no biocytin present) or in material taken from perfusion-fixed whole brain, in which ultrastructural preservation was superior compared with slices, revealed a similar incidence (21% and 23%, respectively) of synaptic specializations. The data indicate that serotonergic transmission on to output neurons in the dorsolateral Periaqueductal Gray Matter is largely mediated by non-junctional contacts, suggesting that the actions of 5-hydroxytryptamine on these cells are mediated predominantly by volume rather than wiring transmission.

  • Involvement of nitric oxide and serotonin in modulation of antinociception and pressor responses evoked by stimulation in the dorsolateral region of the Periaqueductal Gray Matter in the rat
    Neuroscience, 1997
    Co-Authors: M.m Hamalainen, Thelma A. Lovick
    Abstract:

    Abstract In rats anaesthetized with alphaxalone/alphadolone, electrical stimulation in the Periaqueductal Gray Matter in the region lying lateral and dorsolateral to the aqueduct produced a pressor response and an increase in the latency of the tail flick response to noxious heat applied to the tail. The antinociception and the pressor response were significantly attenuated following microinjection of 15 nmol 5-hydroxytryptamine at the site of stimulation in the Periaqueductal Gray Matter. Microinjection of an equal volume of 165 mM saline had no effect. The inhibitory effects of 5-hydroxytryptamine were blocked by prior intracerebroventricular administration of 100  μ g of the nitric oxide synthase inhibitor l -nitroarginine methyl ester. Neither 5-hydroxytryptamine or l -nitroarginine methyl ester had any effect on resting arterial pressure or on the baseline latency of the tail flick reflex. It is suggested that the inhibitory effects of 5-hydroxytryptamine in the dorsolateral Periaqueductal Gray Matter are normally dependent on the functional integrity of local nitric oxide synthase-containing interneurons. Nitric oxide may act in association with 5-hydroxytryptamine to control the excitability of the aversive system in the midbrain.

  • inhibitory and excitatory projections prom the dorsal raphe nucleus to neurons in the dorsolateral Periaqueductal Gray Matter in slices of midbrain maintained in vitro
    Neuroscience, 1994
    Co-Authors: V.v Stezhka, Thelma A. Lovick
    Abstract:

    Abstract Coronal slices of midbrain from adult rats, maintained in an interface chamber at 33–35°C, were used to investigate projections from the dorsal raphe nucleus to the dorsolateral Periaqueductal Gray Matter. Extracellular recordings were made from neurons in the dorsolateral Periaqueductal Gray Matter. The majority of cells were silent but activity could readily be induced by iontophoretic application of d,l -homocysteic acid from the recording pipette. Neuronal perikarya in the dorsal raphe nucleus were activated either by topical application of 15–100 ni droplets of 1 or 10 mM d,l -homocysteic acid or by iontophoresis into the dorsal raphe nucleus of 0.l M d,l -homocysteic acid from a five-barrelled glass micropipette. Both forms of stimulation evoked increases or decreases in firing in neurons in the dorsolateral Periaqueductal Gray Matter. The excitatory responses were evoked only from stimulation sites in the dorsal subnucleus of the dorsal raphe nucleus, whilst inhibitory responses could be evoked by stimulating throughout the nucleus. 5-Hydroxytryptamine was applied by iontophoresis to 55 neurons in the dorsolateral periaqueduetal Gray Matter. Of these, 89% were inhibited whilst the remaining 11% were excited. No unresponsive cells were found. In a second series of experiments anterograde transport of biocytin was used to study projections from the dorsal raphe nucleus to the Periaqueductal Gray Matter in vitro . Following injections of pellets of biocytin into the dorsal subnucleus of the dorsal raphe nucleus, two types of labelled axons could be distinguished which had either smooth or beaded profiles. Both types of axon could be followed into the region of the dorsolateral Periaqueductal Gray Matter, from which recordings were made in the electrophysiological experiments. In contrast, following deposits of biocytin into the ventral half of the Periaqueductal Gray Matter, very few labelled axons were found in the dorsolateral Periaqueductal Gray Matter, although the ventrolateral Periaqueductal Gray Matter was heavily labelled. We conclude that both excitatory and inhibitory projections from the dorsal raphe nucleus to the dorsolateral Periaqueductal Gray Matter are present in the coronal midbrain slice preparation. Excitatory projections originate from the dorsal subnucleus of the dorsal raphe nucleus and may be mediated by a direct pathway. The inhibitory effects evoked from the ventral half of the dorsal raphe nucleus are probably mediated indirectly, perhaps by activation of inhibitory interneurons in the ventrolateral Periaqueductal Gray Matter.

  • Inhibitory and excitatory projections from the dorsal raphe nucleus to neurons in the dorsolateral Periaqueductal Gray Matter in slices of midbrain maintained in vitro.
    Neuroscience, 1994
    Co-Authors: V.v Stezhka, Thelma A. Lovick
    Abstract:

    Coronal slices of midbrain from adult rats, maintained in an interface chamber at 33-35 degrees C, were used to investigate projections from the dorsal raphe nucleus to the dorsolateral Periaqueductal Gray Matter. Extracellular recordings were made from neurons in the dorsolateral Periaqueductal Gray Matter. The majority of cells were silent but activity could readily be induced by iontophoretic application of D, L-homocysteic acid from the recording pipette. Neuronal perikarya in the dorsal raphe nucleus were activated either by topical application of 15-100 nl droplets of 1 or 10 mM D,L-homocysteic acid or by iontophoresis into the dorsal raphe nucleus of 0.1 M D,L-homocysteic acid from a five-barrelled glass micropipette. Both forms of stimulation evoked increases or decreases in firing in neurons in the dorsolateral Periaqueductal Gray Matter. The excitatory responses were evoked only from stimulation sites in the dorsal subnucleus of the dorsal raphe nucleus, whilst inhibitory responses could be evoked by stimulating throughout the nucleus. 5-Hydroxytryptamine was applied by iontophoresis to 55 neurons in the dorsolateral Periaqueductal Gray Matter. Of these, 89% were inhibited whilst the remaining 11% were excited. No unresponsive cells were found. In a second series of experiments anterograde transport of biocytin was used to study projections from the dorsal raphe nucleus to the Periaqueductal Gray Matter in vitro. Following injections of pellets of biocytin into the dorsal subnucleus of the dorsal raphe nucleus, two types of labelled axons could be distinguished which had either smooth or beaded profiles. Both types of axon could be followed into the region of the dorsolateral Periaqueductal Gray Matter, from which recordings were made in the electrophysiological experiments. In contrast, following deposits of biocytin into the ventral half of the Periaqueductal Gray Matter, very few labelled axons were found in the dorsolateral Periaqueductal Gray Matter, although the ventrolateral Periaqueductal Gray Matter was heavily labelled. We conclude that both excitatory and inhibitory projections from the dorsal raphe nucleus to the dorsolateral Periaqueductal Gray Matter are present in the coronal midbrain slice preparation. Excitatory projections originate from the dorsal subnucleus of the dorsal raphe nucleus and may be mediated by a direct pathway. The inhibitory effects evoked from the ventral half of the dorsal raphe nucleus are probably mediated indirectly, perhaps by activation of inhibitory interneurons in the ventrolateral Periaqueductal Gray Matter.

  • Influence of the dorsal and median raphe nuclei on neurons in the Periaqueductal Gray Matter: Role of 5-hydroxytryptamine
    Neuroscience, 1994
    Co-Authors: Thelma A. Lovick
    Abstract:

    Abstract In rats anaesthetized with urethane, selective activation of neuronal perikarya in the dorsal raphe nucleus evoked inhibitory ( n = 17) and excitatory ( n = 10) responses in single neurons recorded in the dorsolateral and lateral sectors of the Periaqueductal Gray Matter and in the adjacent tegmental area. A further 11 cells showed biphasic inhibitory/excitatory responses. Ongoing activity of > 85% of the cells was inhibited by iontophoretic application of 5-hydroxytryptamine (1–70 nA). The duration of the inhibitory response evoked from the dorsal raphe nucleus was increased by 66–725% during iontophoretic application (3–10 nA) of the 5-hydroxytryptamine (serotonin) reuptake blocker paroxetine (five of six cells). In contrast, excitatory responses evoked from the dorsal raphe nucleus were either reduced ( n = 3) or replaced by inhibitory responses ( n = 2) in the presence of paroxetine. Paroxetine also produced a reduction in baseline firing and potentiated the responses of neurons to iontophoretically applied 5-hydroxytryptamine. Stimulation in the median raphe nucleus did not produce any significant changes in the activity of five neurons tested in the Periaqueductal Gray Matter. It is suggested that the inhibitory influence of the dorsal raphe nucleus on cells in the dorsal half of the Periaqueductal Gray Matter is mediated by 5-hydroxytryptamine. This projection may be involved in modulating the level of excitability of neurons in the midbrain aversive system which integrate defence behaviour. In addition, there appears to be a non-serotonergic excitatory projection from the dorsal raphe nucleus to the Periaqueductal Gray Matter. The functional role of this projection remains obscure. The median raphe nucleus does not appear to have a significant influence on the excitability of neurons in the dorsal half of the Periaqueductal Gray Matter.

Yasuo Terayama - One of the best experts on this subject based on the ideXlab platform.

Leda Menescal-de-oliveira - One of the best experts on this subject based on the ideXlab platform.

  • Functional mapping of the Periaqueductal Gray Matter involved in organizing tonic immobility behavior in guinea pigs
    Behavioural brain research, 2010
    Co-Authors: Eveline Bis Vieira, Leda Menescal-de-oliveira, Christie Ramos Andrade Leite-panissi
    Abstract:

    Tonic immobility behavior (TI) is an innate response characterized by profound motor inhibition that is exhibited by prey when physical contact with a predator is prolonged and the situation inescapable. The Periaqueductal Gray Matter (PAG) is intimately associated with the somatic and autonomic components of defensive reactions. This study investigated whether the TI response was able to recruit specific functional columns of the PAG by examining c-fos immunolocalization in guinea pigs. In the TI group, the innate response was invoked in animals through inversion and physical contention for at least 15 min. In the control group, the animals were physically manipulated only. Our results demonstrate that the defensive behavior of TI is capable of promoting the expression of Fos protein in different areas of the PAG, with higher levels of staining in the ventrolateral (vl) and lateral (l) columns. In addition, our results demonstrate increased Fos immunoreactivity (FOS-IR) in the dorsal raphe nucleus, the Edinger-Westphal nucleus, the cuneiform nucleus and the superior colliculus. In contrast, there were no significant alterations in the number of FOS-IR cells in the inferior colliculus or the oculomotor nucleus. Analysis of the results suggests that neuronal activation after the TI response differs by functional column of the PAG.

  • Ventrolateral Periaqueductal Gray Matter and the control of tonic immobility.
    Brain research bulletin, 1999
    Co-Authors: C R Monassi, Christie Ramos Andrade Leite-panissi, Leda Menescal-de-oliveira
    Abstract:

    Tonic immobility is an inborn defensive behavior characterized by a temporary state of profound and reversible motor inhibition elicited by some forms of physical restraint. The Periaqueductal Gray Matter (PAG) contains neural circuits involved in descending pain modulation, as well as in the modulation of TI. We have reported previously that the cholinergic stimulation of the ventrolateral PAG increases the duration of TI in guinea pigs. In the present study, we attempted to characterize further the modulation of TI by pharmacological alteration of the neurochemistry of the ventrolateral PAG circuitry. We observed that both cholinergic (carbachol, 5.4 nmol/0.2 μl) and opioidergic stimulations (morphine, 4.48 nmol/0.2 μl) of the ventrolateral PAG increase the duration of TI and that these effects can be reversed by pre-treatment with naloxone (2.74 nmol/0.2 μl). Our results also showed that microinjection of the GABAergic agonist muscimol (1, 0.5, and 0.26 nmol/0.2 μl) decreased the duration of TI episodes, while microinjection of the GABAergic antagonist bicuculline (1 nmol/μl) increased it. Moreover, we observed that preadministration of muscimol (0.13 nmol/0.2 μl) at a dose that had no effect per se at this site antagonized the potentiating effect of morphine. Our results suggest that this modulation of TI from the ventrolateral PAG circuitry is accomplished by a complex interaction of cholinergic, opioidergic, and GABAergic mechanisms, similar to that proposed for descending antinociceptive circuits.

  • Involvement of the Cholinergic System and Periaqueductal Gray Matter in the Modulation of Tonic Immobility in the Guinea Pig
    Physiology & behavior, 1997
    Co-Authors: C R Monassi, Anette Hoffmann, Leda Menescal-de-oliveira
    Abstract:

    Abstract Monassi, C.R.; A. Hoffmann and L. Menescal-De-Oliveira. Involvement of the cholinergic system and Periaqueductal Gray Matter in the modulation of tonic immobility in the guinea pig. Physiol Behav 62(1) 53–59, 1997.—Unilateral microinjection of carbachol (CCh, 1.0 μ g/0.2 μ l) into the ventrolateral Periaqueductal Gray Matter (vPAG) increased the duration of tonic immobility (TI) episodes induced by postural inversion and by movement restriction maneuvers in adult male guinea pig ( Cavia porcellus ), while stimulation with the same drug at the same concentration into the dorsolateral and dorsomedial Periaqueductal Gray Matter (dl/dmPAG) decreased the duration of TI. Pretreatment with atropine (7.6 μ g/0.4 μ l) showed that the action of CCh is mediated by muscarinic receptors in the ventrolateral PAG but not in the dorsomedial and dorsolateral regions. These data suggest that the PAG and the cholinergic system are involved in the modulation of TI episodes and that different regions of the guinea pig PAG play distinct roles in the organization of this behavior

Arthur D. Loewy - One of the best experts on this subject based on the ideXlab platform.

  • Periaqueductal Gray Matter projections to midline and intralaminar thalamic nuclei of the rat.
    The Journal of comparative neurology, 2000
    Co-Authors: Karl E. Krout, Arthur D. Loewy
    Abstract:

    The Periaqueductal Gray Matter (PAG) projections to the intralaminar and midline thalamic nuclei were examined in rats. Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected in discrete regions of the PAG, and axonal labeling was examined in the thalamus. PHA-L was also placed into the dorsal raphe nuclei or nucleus of Darkschewitsch and interstitial nucleus of Cajal as controls. In a separate group of rats, the retrograde tracer cholera toxin beta-subunit (CTb) was injected into one of the intralaminar thalamic nuclei-lateral parafascicular, medial parafascicular, central lateral (CL), paracentral (PC), or central medial nucleus-or one of the midline thalamic nuclei-paraventricular (PVT), intermediodorsal (IMD), mediodorsal, paratenial, rhomboid (Rh), reuniens (Re), or caudal ventral medial (VMc) nucleus. The distribution of CTb labeled neurons in the PAG was then mapped. All PAG regions (the four columns of the caudal two-thirds of the PAG plus rostral PAG) and the precommissural nucleus projected to the rostral PVT, IMD, and CL. The ventrolateral, lateral, and rostral PAG provided additional inputs to most of the other intralaminar and midline thalamic nuclei. PAG inputs to the VMc originated from the rostral and ventrolateral PAG areas. In addition, the lateral and rostral PAG projected to the zona incerta. No evidence was found for a PAG input to the ventroposterior lateral parvicellular, ventroposterior medial parvicellular, caudal PC, oval paracentral, and reticular thalamic nuclei. PAG --> thalamic circuits may modulate autonomic-, nociceptive-, and behavior-related forebrain circuits associated with defense and emotional responses.

  • Periaqueductal Gray Matter projection to the parabrachial nucleus in rat
    The Journal of comparative neurology, 1998
    Co-Authors: Karl E. Krout, Arthur S.p Jansen, Arthur D. Loewy
    Abstract:

    The efferent projections from the Periaqueductal Gray Matter (PAG) to the parabrachial nucleus (PB) were studied in the rat following microinjections of the anterograde axonal tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) into restricted regions of the PAG. The dorsomedial and dorsolateral PAG columns project almost exclusively to the superior lateral PB subnucleus, whereas the lateral and ventrolateral PAG columns project to five lateral PB sites: dorsal lateral subnucleus, medial and lateral crescent areas (which flank the dorsal lateral PB subnucleus), central lateral subnucleus (rostral portion), and superior lateral subnucleus. The PAG region lying near the cerebral aqueduct projects to five lateral PB sites: external lateral subnucleus (inner subdivision), medial and lateral crescent areas, central lateral subnucleus (rostral portion), and dorsal lateral subnucleus. The internal lateral PB subnucleus, which projects exclusively to the intralaminar thalamic nuclei, and the Kolliker-Fuse nucleus were not innervated by the PAG. The PAG selectively innervates individual PB subnuclei that may be part of the spino-parachio-forebrain pathway. All PAG columns, including the aqueductal region, project to the superior lateral PB subnucleus, a presumed nociceptive relay site that receives inputs from multiple spinal cord regions (laminae I, V, and VIII) and projects to the ventromedial and retrochiasmatic hypothalamic areas-two regions that have been implicated in complex goal-directed behavior (e.g., food intake and reproductive function). Earlier studies demonstrated that the dorsal lateral and external lateral PB subnuclei (inner division) receive overlapping inputs from the superficial dorsal horn (laminae I and II) and the nucleus tractus solitarius, and both PB subnuclei send projections to limbic forebrain areas (e.g., hypothalamus, preoptic region, amygdala). Because the PAG projects to both of these PB subnuclei, this projection system possibly functions as a behavioral state-dependent filter system that modulates ascending nociceptive and/or visceral information as it is relayed through the PB to forebrain sites.

  • Periaqueductal Gray Matter projection to vagal preganglionic neurons and the nucleus tractus solitarius.
    Brain research, 1997
    Co-Authors: E Farkas, Arthur S.p Jansen, Arthur D. Loewy
    Abstract:

    The Periaqueductal Gray Matter (PAG) has been implicated in a variety of different functions, including autonomic regulation. Chemical stimulation of the lateral PAG produces hypertension and tachycardia while activation of the ventrolateral PAG produces the opposite effect. While these effects are the result of alterations in sympathetic activity, little is known about whether the PAG can modulate vagal functions as well. The anterograde axonal tracing method using the plant lectin Phaseolus vulgaris leucoagglutinin (PHA-L) was used to determine whether both of the lateral and ventrolateral PAG columns project to vagal preganglionic neurons and/or to the nucleus tractus solitarius (NTS). Highly restricted PHA-L injections were made in all four PAG columns throughout their rostrocaudal extent in rats. Labeled fibers were visualized by immunohistochemistry and studied in relationship with choline acetyltransferase (ChAT) immunostained parasympathetic preganglionic neurons of the dorsal motor vagal nucleus (DMV) and nucleus ambiguous (NA). The lateral PAG projects to the lateral DMV and to the caudal part of the external NA. The ventrolateral PAG innervates the same regions and also projects to the rostral part of the external NA -- a site that contains cardiac parasympathetic preganglionic neurons. Both the lateral and ventrolateral PAG project to the NTS in a similar fashion innervating the medial, ventrolateral and commissural subnuclei. In summary, the lateral and ventrolateral PAG have similar patterns of innervation of the NTS and DMV, but their projection to the NA is different: the rostral external NA receives innervation only from the ventrolateral PAG and the lateral PAG innervates the caudal part.

Masako Kudo - One of the best experts on this subject based on the ideXlab platform.