Biomedical subjects

T A Lovick

Publications and source records attributed to T A Lovick.

At least 73 records · Page 4Linked to original sources

PubMed1986

Analgesia and the cardiovascular changes evoked by stimulating neurones in the ventrolateral medulla in rats.

In rats anaesthetised with Saffan, selective excitation of neurones in the ventrolateral medulla in the region of nucleus paragigantocellularis lateralis (PGL) by microinjection of the synaptic excitant, D,L-homocysteic acid, produced an increase in the latency of the tail flick response to noxious heat usually accompanied by an increase in blood pressure and heart rate. These findings are discussed in relation to the role of neurones in PGL in generating both tonic descending inhibition in the dorsal horn and sympathetic vasomotor tone as well as their involvement in a descending pathway that mediates the hypoalgesia which is a feature of certain stress-induced hypertensive states.

Analgesia↗

PubMed1985

Vasodilator and vasoconstrictor neurones of the ventrolateral medulla in the cat.

Microinjections of D,L-homocysteic acid into the ventrolateral medulla, in the region of nucleus paragigantocellularis lateralis (PGL) which lies caudal to the facial nucleus and adjacent to the rostral third of the inferior olive, evoke a rise in arterial blood pressure and vasoconstriction in hindlimb muscle. Activation of a group of neurones located in a more rostral strip of tissue ventral to the facial nucleus produces vasodilatation in the hindlimb but no significant change in blood pressure. It appears that the ventrolateral medulla contains several subpopulations of neurones which can alter resistance to blood flow and hence distribution of flow and level of blood pressure by selective control of individual vascular beds.

Animals↗

PubMed1985

Descending projections from the ventrolateral medulla and cardiovascular control.

Antidromic responses were evoked in neurones in nucleus paragigantocellularis lateralis (PGL) by stimulation of the ipsilateral ventrolateral white matter or the contralateral dorsolateral white matter at T13-L1 in the cat. Estimated conduction velocities in the spinally projecting axons ranged from 5.0-61 m/s. Stimulation of cell bodies in PGL, by microinjection of D,L-homocysteic acid, usually produced a rise in blood pressure accompanied by tachycardia or bradycardia and either dilatation or constriction in the hindlimb muscle vasculature. It is suggested from this other and evidence that tonically active neurones in PGL may play a role in setting the resting level of blood pressure but that the output of these and other cells in the nucleus may also be modified to generate different patterns of cardiovascular adjustment.

Animals↗

PubMed1985

Excitatory projections from hypothalamic and midbrain defense regions to nucleus paragigantocellularis lateralis in the rat.

Electrical stimulation of the hypothalamic and midbrain defense regions evoked convergent excitatory responses in neurons in nucleus paragigantocellularis lateralis (PGL) in rats anesthetized with urethane. Stimulation in PGL activated neurons in the periaqueductal gray matter (PAG) and in the hypothalamus antidromically. In the PAG the projecting neurons were localized in the defense region but in the hypothalamus they were more widely distributed lateral and dorsal to it, mainly in the lateral hypothalamic region and the zona incerta. We conclude that there are independent excitatory pathways from the midbrain and hypothalamic defense regions which relay on neurons in PGL. Stimulation in the midbrain defense region may activate the monosynaptic projection to PGL as well as polysynaptic pathways. In contrast, stimulation of the hypothalamic defense region probably excites mainly fibers of passage: the integrated pattern of autonomic changes produced by electrical stimulation may be due to activation of the efferent outflow from widely dispersed cell bodies whose axons run through the defense region.

Afferent Pathways↗

PubMed1985

Ventrolateral medullary lesions block the antinociceptive and cardiovascular responses elicited by stimulating the dorsal periaqueductal grey matter in rats.

In rats anaesthetised with Saffan (Glaxovet), inhibition of the tail flick reflex evoked by electrical stimulation in the dorsal periaqueductal grey matter (PAG) was accompanied by an increase in blood pressure, tachycardia, vasodilatation in hind limb muscle, an increase in respiration, pupillodilatation and widening of the palpebral fissure. Stimulation deeper in the PAG and in the tegmentum ventral to it produced analgesia but without this pattern of autonomic changes. The antinociceptive, cardiovascular and respiratory effects of PAG stimulation were abolished by bilateral lesions in the ventrolateral medulla in the area which lies ventromedial to the facial nucleus (i.e., in nucleus paragigantocellularis lateralis, RPGL). Lesions in nucleus raphe magnus (NRM), or bilateral lesions of nucleus reticularis gigantocellularis (RG) and paragigantocellularis (RPG) or a combination of a lesion in RPGL with one in NRM or the contralateral RG or RPG did not block the effects of stimulating in the dorsal PAG. These findings are discussed in relation to the role of the PAG in mediating behavioural responses to stress.

Animals↗

PubMed1985

Projections from the diencephalon and mesencephalon to nucleus paragigantocellularis lateralis in the cat.

The distribution of labelled cells in the diencephalon and mesencephalon has been mapped following injections of horseradish peroxidase into nucleus paragigantocellularis lateralis in the cat. Most of the labelled cells were found ipsilateral to the injection site. A group of small and medium-sized labelled perikarya (11-40 microns in diameter) was present in the caudal part of the periaqueductal grey matter (A3-P2) and in the adjacent tegmentum. Small, round or fusiform cells (8-25 microns were labelled in the tuberal region of the hypothalamus in the dorsomedial hypothalamus and in the lateral hypothalamic area. It is suggested that the cardiovascular responses which can be elicited by stimulation in these regions of the periaqueductal grey and hypothalamus are mediated via a relay on to spinally projecting neurones in nucleus paragigantocellularis lateralis which synapse on sympathetic preganglionic neurones in the intermediolateral cell column.

Agonistic Behavior↗

PubMed1984

Spinally projecting neurones near the ventral surface of the medulla in the cat.

In anaesthetized cats antidromic responses were recorded in nucleus paragigantocellularis lateralis following stimulation of the ventrolateral funiculus in the ipsilateral thoracolumbar cord. Conduction velocities ranged from 5.4-120 m/s but 50% of the fibres conducted at less than 20 m/s. About half of the neurones were facilitated by stimulation in the hypothalamic or midbrain defence areas. These neurones are superficially located at the site where application of glycine or a lesion blocks the effects of defence area stimulation and reduces blood pressure. They could therefore be involved in the regulation of vasomotor activity.

Animals↗

PubMed1983

The role of 5-HT, GABA and opioid peptides in presynaptic inhibition of tooth pulp input from the medial brainstem.

In decerebrate or chloralose-anaesthetized cats electrical stimulation in the spinal trigeminal nucleus evoked antidromic responses in the mandibular canine tooth pulp. Conditioning stimulation in nucleus raphe magnus (NRM) and in the adjacent contralateral medullary reticular formation, nucleus reticularis gigantocellularis (NRGC) and nucleus reticularis magnocellularis (NRMC), produced a decrease in the threshold for the antidromic responses in a proportion of the tooth pulp inputs. This was interpreted as being due to depolarization of the tooth pulp afferent terminals, reflecting presynaptic inhibition. The primary afferent depolarization (PAD) of tooth pulp afferent terminals by NRM stimulation could be selectively blocked by bicuculline applied intravenously or by iontophoresis in the terminal region. Intravenous naloxone, cinanserin and methysergide had no effect on the PAD evoked from NRM, NRGC or NRMC. Thus NRM appears to exert presynaptic inhibitory control of A delta tooth pulp input to the spinal trigeminal nucleus via GABA-containing neurones.

Afferent Pathways↗

PubMed1983

Enkephalin blocks primary afferent depolarization of A delta tooth pulp afferents evoked by stimulation in nucleus raphe magnus in the decerebrate cat.

Electrical stimulation in nucleus raphe magnus (NRM) in decerebrate cats produced an increase in the excitability of tooth pulp afferent terminals in trigeminal nucleus oralis and caudalis. Iontophoretic application of Met5-enkephalin near the terminal region did not affect resting terminal excitability but reduced the effectiveness of NRM stimulation to increase terminal excitability. This effect of enkephalin was blocked by naloxone. It is concluded that enkephalin may have reduced the primary afferent depolarization (PAD) evoked from NRM by inhibiting GABA-containing neurones which mediate PAD in the spinal trigeminal nucleus.

Afferent Pathways↗

PubMed1983

Substance P-immunoreactive and serotonin-containing neurones in the ventral brainstem of the cat.

Substance P-like immunoreactive cell bodies have been described in the cat brainstem after local injections of colchicine. Substance P-containing neurons were found in the nucleus raphe pallidus, the nucleus raphe obscurus and at the caudal end of the nucleus raphe magnus. Two groups of substance P-positive (+) cells were also found in the ventrolateral medulla. Small substance P+ cells were present in a narrow band immediately ventral to the facial nucleus, and a second group of small and medium sized neurones was found in a strip ventrolateral to the rostral half of the inferior olive. Some of these cells lay in close proximity to the ventral surface of the brain. Double labelling studies indicated that within the raphe nuclei many substance P+ neurones also contained serotonin, while within ventrolateral areas of the medulla, the most rostral cell group stained only for substance P and the more caudal nucleus for both substance P and serotonin.

Animals↗

PubMed1983

Bulbar raphe neurones with projections to the trigeminal nucleus caudalis and the lumbar cord in the rat: a fluorescence double-labelling study.

Retrograde transport of the fluorescent dyes Evans blue and 4,6-diamidino-2-phenyl indole (DAPI) has been used to study projections from the medullary raphe nuclei to the trigeminal nucleus caudalis and to the dorsolateral quadrant of the thoracolumbar cord in the rat. The majority of projecting neurones were found in n. raphe magnus (NRM) and its ventrolateral extensions over the pyramids and inferior olive. Double labelling experiments showed that 94% of raphe-trigeminal neurones sent a collateral branch to the nucleus in the contralateral brainstem. Similarly, 92% of raphe-trigeminal neurones branched to supply the thoracolumbar cord. It is suggested that the widespread nature of the analgesia produced by electrical stimulation in NRM in conscious animals may be due to activation of a population of raphe neurones which inhibit the responses of neurones in the trigeminal nucleus and dorsal horn via an extensive system of collateral projections to these structures.

Animals↗

PubMed1983

Actions of GABA, glycine, methionine-enkephalin and beta-endorphin compared with electrical stimulation of nucleus raphe magnus on responses evoked by tooth pulp stimulation in the medial reticular formation in the cat.

In decerebrate, cerebellectomized cats, a comparison was made between the effects of electrical stimulation in nucleus raphe magnus (NRM) and iontophoretic application of GABA, glycine, met-enkephalin and beta-endorphin on the responses of neurones in the medial brain stem reticular formation to tooth pulp stimulation. NRM stimulation, GABA, glycine and enkephalin produced a short lasting inhibition of tooth pulp evoked responses whilst the time course of the inhibition produced by beta-endorphin was much slower, often lasting up to 1 h following a 3-7 min ejection period. The effects of GABA and glycine could be antagonised by iontophoresis of bicuculline and strychnine respectively whilst intravenous injection of naloxone antagonised the inhibition induced by the opioid peptides. In most neurones tested, inhibition of tooth pulp evoked responses by NRM stimulation was blocked by iontophoretic application of bicuculline but not by strychnine or naloxone (i.v.). We conclude that GABA may act as a transmitter which mediates the inhibitory effects of NRM on the responses of reticular neurones to tooth pulp stimulation. Thus GABA may be involved in stimulation produced analgesia.

Animals↗

PubMed1983

Projections from brain stem nuclei to the spinal trigeminal nucleus in the cat.

Afferent projections to the trigeminal nucleus oralis and caudalis from the brain stem have been investigated by the use of retrograde transport of horseradish peroxidase in the cat. Both n. oralis and n. caudalis receive a projection from nucleus raphe magnus but not from other raphe nuclei in the medulla or pons. N. oralis and n. caudalis receive a bilateral projection from n. paragigantocellularis lateralis. N. oralis receives a projection from n. reticularis gigantocellularis and n. reticularis parvocellularis but not from n. reticularis magnocellularis. N. caudalis receives only sparse projections from n. reticularis gigantocellularis, n. reticularis parvocellularis and n. reticularis magnocellularis but receives an input from a layer of cells over the pyramids in the rostral medulla, here named n. paramagnocellularis ventralis. The study also revealed the presence of ascending and descending interconnections between n. oralis and n. caudalis, as well as contralateral trigeminal interconnections. Projections from the medial vestibular nuclei, n. praepositus hypoglossi and the facial nucleus to the spinal trigeminal nucleus were also noted. Since the spinal trigeminal nucleus has only sensory functions, the results indicate the source of projections, mainly from raphe and reticular nuclei, which are involved in sensory control in the trigeminal system.

Afferent Pathways↗

PubMed1982

The distribution of serotonin, met-enkephalin and beta-lipotropin-like immunoreactivity in neuronal perikarya of the cat brainstem.

The distribution of methionine-enkephalin, serotonin and beta-lipotropin-containing neurones has been mapped immunohistochemically in the brainstem of the cat after local colchicine injections. Serotonin-containing neurons were found in th raphe in nucleus raph magnus (NRM), nucleus raphe pallidus (NRP) and nucleus raphe obscurus (NRO) and in a band extending cross the ventral reticular formation into nucleus paragigantocellularis lateralis (PGL) and nucleus lateralis reticularis (LRM). Enkephalin-positive cell bodies were also found in these raphe nuclei and in most divisions of the caudal reticular formation. Double labelling studies established that enkephalin and serotonin co-exist within some neurons in NRM and NRP. beta-Lipotropin-positive cell bodies were found principally within NRP and within the ventrolateral reticular formation in PGL and LRM.

Animals↗

PubMed1982

An excitatory input to nucleus raphe magnus from the red nucleus in the cat.

In chloralose-anaesthetized cats, with the cerebellum removed, stimulation in the red nucleus excited the majority (60-65%) of neurones in nucleus raphe magnus (NRM), including raphespinal neurones. Evidence was obtained for both monosynaptic and polysynaptic excitation. The projection was confirmed by recording antidromic responses in the red nucleus to stimulation in NRM. It is suggested that the role of NRM in motor control is to inhibit spinal flexion responses to peripheral stimuli so that commands from the red nucleus and other motor control regions may take place without interruption.

Animals↗

PubMed1982

Inhibitory actions of a novel endogenous tripeptide, methyionyl-tyrosyl-lysine, on proprioceptive neurons in the lumbar spinal cord of the cat.

The actions of a tripeptide, methionyl-tyrosyl-lysine (Met-Tyr-Lys), isolated from spinal cord and dorsal root ganglia have been investigated by iontophoretic application to single neurones in the spinal cord of the cat. Met-Tyr-Lys inhibited a group of neurons located mainly in laminae V and VI of the lumbar dorsal horn: excitation was never observed. The inhibition was rapid in onset and was not mimicked by the action of the constituent amino acids. Neurons inhibited by Met-Tyr-Lys received proprioceptive inputs as shown by their excitation or inhibition from stimulation of deep receptors and by their responses to leg or foot movement. Bicuculline and strychnine separately, at doses which antagonized responses to gamma-aminobutyric acid and glycine, respectively, had no or little effect both on responses to Met-Tyr-Lys and on the inhibition evoked in the same neurons by low-intensity (1.5-4T) stimulation of the tibial or common peroneal nerves. Thus receptors for Met-Tyr-Lys are different from those for glycine or gamma-aminobutyrate. In addition it is possible that there is a component of the inhibition evoked by peripheral nerve stimulation which is not mediated by either glycine or gamma-aminobutyrate. Met-Tyr-Lys may have an inhibitory role in relation to proprioception.

Animals↗

PubMed1981

Primary afferent depolarization of tooth pulp afferents by stimulation in nucleus raphe magnus and the adjacent reticular formation in the cat: effects of bicuculline.

In decerebrate cats electrical stimulation in nucleus raphe magnus (NRM) and the adjacent region of the reticular formation (NRGC) produced a decrease in the threshold of antidromic responses evoked in the tooth pulp following stimulation in the trigeminal nucleus oralis. This primary afferent depolarization (PAD) of Adelta afferents was unaffected by naloxone given intravenously. Bicuculline, given intravenously or applied directly to the terminal region by iontophoresis, selectively antagonised the PAD evoked by stimulating in NRM. The results suggest that GABA is involved in mediating presynaptic inhibition of Adelta tooth pulp input following stimulation in NRM.

Afferent Pathways↗

PubMed1981

Evoked potentials in the reticular formation during auditory conditioning of the corneal reflex in the chronic decerebrate rat.

The chronic decerebrate rat preparation was used to study electrical activity in the reticular formation during development of the classically conditioned eyeblink reflex to a tone. With persistent training a conditioned blink reflex was established in 8 out of 11 rats. A control group of four rats received unpaired presentations of the conditioned and unconditioned stimuli and served as a control. Evoked potentials in response to the auditory conditioned stimulus were recorded in medullary and pontine reticular nuclei during conditioning. The amplitude of the main negative wave of the response showed a significant increase during the establishment of a conditioned response but the amplitude of potentials recorded from the medullary reticular formation showed no significant change. There was no change in the amplitude of potentials recorded in either the pontine or medullary reticular nuclei in the control "pseudoconditioning" group or in the three rats which underwent training but did not develop a conditioned response. It is concluded that structures within the pontine reticular formation play an active part in the acquisition phase of the conditioned blink reflex in the chronic decerebrate rat.

Acoustic Stimulation↗