Modulation of responses of feline gamma-motoneurones by noradrenaline, tizanidine and clonidine

1. Effects of noradrenaline (NA) and the alpha2 agonists tizanidine and clonidine were tested on extracellularly recorded responses of gamma-motoneurones in deeply anaesthetized cats. Two types of responses were used; firstly, short latency phasic responses evoked by electrical stimulation of group II afferents in a muscle nerve and, secondly, tonic background discharges. 2. Responses evoked by group II muscle afferents were depressed when NA and tizanidine were applied ionophoretically close to a gamma-motoneurone and when clonidine was applied systemically. The number of spike potentials evoked by stimulation of these afferents decreased and their latencies increased. Responses evoked by flexor or extensor afferents in gamma-motoneurones innervating flexors or extensors were similarly depressed. 3. Tonic discharges were inconsistently and/or insignificantly affected by locally applied NA and tizanidine but were depressed by systemically applied clonidine. 4. Control tests indicate specific effects of NA and tizanidine application since similarly ionophoresed H+ ions did not change responses of gamma-motoneurones to stimulation of group II afferents, or only weakly enhanced their background discharges. Furthermore, serotonin ejected from a solution with a similar pH facilitated rather than depressed responses of gamma-motoneurones. 5. The results indicate that some antispastic effects of clonidine and tizanidine may be due to the depression of group II-evoked responses of gamma-motoneurones, resulting in weaker responses of muscle spindles to muscle stretches.

New observations on coupling between group II muscle afferents and feline gamma-motoneurones

1. Extra- or intracellular recordings were made from seventy-six gamma-motoneurones of hindlimb muscles in chloralose anaesthetized cats to re-assess the coupling between secondary muscle spindle afferents (group II muscle afferents) and these neurones. The latencies of a number of responses evoked by group II muscle afferents in gamma-motoneurones were shorter than minimal latencies of responses induced disynaptically in other spinal neurones. These latencies are therefore compatible with monosynaptic coupling between muscle spindle secondaries and gamma-motoneurones. 2. Responses fulfilling criteria for monosynaptically evoked responses were seen in about one third of gamma-motoneurones with input from the group II muscle afferents tested (in 6 of 18 motoneurones recorded intracellularly and in 26 of 74 motoneurones recorded extracellularly). They were usually evoked from only one of the stimulated nerves, stimulation of group II afferents of other nerves being followed by responses at longer latencies. 3. Most gamma-motoneurones were excited by group II afferents from several muscles, both flexors and extensors. However, a comparison of group II input to gamma-motoneurones innervating medial gastrocnemius and four other hindlimb muscles revealed differences in both incidence and sources. 4. This study extends results of previous studies by providing evidence that some synaptic actions of group II afferents, including afferents from the same muscle, are evoked monosynaptically, and may assist in sustaining the activation of gamma-motoneurones by positive feedback.

A leu-enkephalin depresses transmission from muscle and skin non-nociceptors to first-order feline spinal neurones

1. The effects of an opioid (D-Ser-Leu-enkephalin-Thr; DSLET) were tested on synaptic actions of non-nociceptive afferents: group I and II muscle afferents and low-threshold skin afferents. They were tested on population EPSPs (field potentials) evoked in the dorsal horn and the intermediate zone of mid-lumbar segments, and on monosynaptically evoked responses of single interneurones at the same location. DSLET was applied locally (ionophoretically) at locations at which the field potentials were maximal and close to the selected neurones. 2. DSLET potently depressed transmission from group II muscle afferents and from low-threshold skin afferents. Transmission to neurones located in the dorsal horn or in the intermediate zone was depressed to a similar extent. The depression was readily antagonized by naloxone. Transmission from group Ia or Ib muscle afferents to neurones located in the intermediate zone was not affected, or was facilitated by DSLET. 3. The results show that DSLET has similar depressive actions on spinal neurones to monoamines, but its actions are more widespread. Like monoamines it affects transmission from nociceptors and group II muscle afferents, but in addition it gates transmission from low-threshold cutaneous afferents. Furthermore its effects do not appear to be restricted to interneurones at particular locations since it depressed responses of dorsal horn interneurones (gated by serotonin) as well as intermediate zone interneurones (gated by noradrenaline).

Indications for coupling between feline spinocervical tract neurones and midlumbar interneurones

The possibility of collateral segmental actions of spinocervical tract (SCT) neurones upon interneurones with input from cutaneous and group II muscle afferents was investigated in deeply anaesthetized cats. To this end, intracellular and/or extracellular recordings were made from 35 dorsal horn and 15 intermediate zone interneurones in midlumbar segments of the spinal cord and effects of stimulation of the ipsilateral dorso-lateral funiculus (DLF) at C3 and C1 levels, i.e. below and above the lateral cervical nucleus where axons of SCT cells terminate, were compared. The stimuli applied at the C3 segment were within the range of stimuli (50-100 microA) required for antidromic activation of SCT neurones in the same experiment. Those applied at the C segment (200-500 microA) were at least 3 times stronger than C3 stimuli. Under the same experimental conditions, long ascending and descending tract neurones (dorsal spino-cerebellar and rubro-spinal tract neurones) with axons in the DLF were activated at similar thresholds from the C and C3 segments. Intracellular recordings were made from 29 interneurones of which 19 (65%) were dorsal horn and 10 (35%) were intermediate zone interneurones. Excitatory postsynaptic potentials (EPSPs) evoked by single stimuli applied at the C3 segment, but not the C segment, were found in 14 (48%) of those interneurones; their latencies (3.0-5.7 ms) and frequency following with only minimal temporal facilitation were as required for potentials being evoked monosynaptically by the fastest conducting SCT neurones. Extracellular recordings were made from 30 interneurones (24 dorsal horn and 6 intermediate zone interneurones), and in these neurones spike potentials induced from the C3, but not from the C segment, were evoked only by short trains of stimuli. However, their latencies from the first effective stimulus (4.3-5.4 ms) were compatible with mono- or oligosynaptically mediated collateral actions of SCT neurones. They were found in 10 (33%) of the 30 investigated interneurones. Similar effects of C3 stimuli were found in similar proportions of dorsal horn interneurones and intermediate zone interneurones. Indications were also found for synaptic actions evoked by C3 stimuli that could not be attributed to direct collateral actions of SCT neurones. In some intracellularly recorded dorsal horn interneurones, short-latency EPSPs were evoked from the C3 segment by the 2nd or 3rd stimulus in the train, but not by single stimuli. In other dorsal horn and intermediate zone interneurones, inhibitory postsynaptic potentials (IPSPs) were evoked from the C3 segment at minimal latencies (2.7-3.2 ms), which might be too short to allow their mediation via SCT neurones. We conclude that SCT neurones might be used to forward information from muscle group II and cutaneous afferents not only to neurones in the lateral cervical nucleus and via them to thalamus and cerebral cortex but also to interneurones in spinal reflex pathways. Thereby reflex actions evoked from group II and cutaneous afferents might be co-ordinated with responses mediated by supraspinal neurones. We conclude also that dorsal horn and intermediate zone mid-lumbar interneurones might contribute to the previously reported di-and poly-synaptic excitation or inhibition of postsynaptic dorsal column (PSDC), spinothalamic tract (STT) and spinomesencephalic tract (SMT) neurones by collateral actions of SCT cells. Thereby these interneurones might contribute to the co-ordination of responses mediated by various populations of supraspinal neurones.

A confocal and electron microscopic study of contacts between 5-HT fibres and feline dorsal horn interneurons in pathways from muscle afferents

Morphological substrates of actions of serotonin upon dorsal horn interneurons with input from group II muscle afferents were investigated by using two experimental approaches. Twelve interneurons were intracellularly labelled with rhodamine-dextran, and serotoninergic fibres were identified by immunofluorescence. Appositions between the serotoninergic axons and these interneurons were examined with a dual-channel confocal microscope. A further four interneurons were intracellularly labelled with horseradish peroxidase, and serotoninergic axons were identified by immunocytochemistry; these neurons were prepared for combined light and electron microscopy. Confocal microscopy revealed serotoninergic varicosities in apposition to both cell bodies and dendrites. Similar total numbers of appositions were found on the soma, and on dendrites within 100 microm from the soma, on the most completely labelled neurons. The number of appositions on 100-microm segments of dendrites decreased with increasing distances from the soma (from 14.6 within 100 microm, to 3.8 and 2.4 at 100-300 microm, and more than 300 microm distances, respectively). Electron microscopic analysis of two neurons revealed that few of the apparent contacts on cell bodies were synaptic, but, in contrast, many varicosities apposed to proximal dendrites formed synapses. The evidence suggests that serotonin may have more powerful synaptic effects upon the dendrites of this class of dorsal horn interneurons than on their cell bodies.

Modulation of responses of four types of feline ascending tract neurons by serotonin and noradrenaline

Modulation of responses of four types of ascending tract cells by noradrenaline and serotonin was compared in order to investigate how information forwarded by these cells may be gated by monoaminergic tract neurons. Spinocervical tract, postsynaptic dorsal column and dorsal spinocerebellar tract neurons located in Clarke's column and in the dorsal horn were identified by their axonal projections. Noradrenaline and serotonin were applied ionophoretically close to a selected neuron, and their effects were tested on extracellularly recorded responses of this neuron to electrical stimulation of low-threshold skin afferents and group II muscle spindle afferents. The modulatory actions of noradrenaline and serotonin were estimated from changes in the number of responses evoked by 30 successive stimuli, the minimal latencies of these responses, and their firing frequency. All four populations of ascending tract neurons investigated were modulated by serotonin and noradrenaline, but not in the same way. The responses were most often depressed by noradrenaline and facilitated by serotonin, but in some types of neuron they were affected in the same direction. Transmission from low-threshold skin and group II muscle afferents changed in the same direction in some types of neuron but in the opposite direction in other types. The results indicate that transfer of information from skin and group II muscle afferents to supraspinal centres may be gated by descending monoaminergic pathways in a highly differentiated manner, and is adjusted to the requirements of various behavioural situations.

Synaptic connections of dorsal horn group II spinal interneurons: synapses formed with the interneurons and by their axon collaterals

Five dorsal horn interneurons with monosynaptic input from group II primary afferent fibres were physiologically characterized and intracellularly labelled with horseradish peroxidase. The cells were prepared for combined light and electron microscopy, and synaptic arrangements formed by axon collaterals of interneurons and synapses formed with their dendrites and somata were examined with the electron microscope. Immunogold reactions for gamma-aminobutyric acid, glycine and glutamate were performed to determine if these synapses were excitatory or inhibitory. Axon collaterals in lamina VI formed synapses with somata and dendrites of other neurons, and collaterals of one cell also formed axoaxonic synapses. It was concluded that one cell from the sample was inhibitory, whereas the remainder were probably excitatory. Dendrites and cell bodies of interneurons were contacted by several types of synaptic bouton. The first type of bouton displayed immunoreactivity for glutamate, the second type contained both gamma-aminobutyric acid and glycine, the third type contained glycine alone, and the fourth type contained gamma-aminobutyric acid alone. Some large glutamatergic boutons were postsynaptic to other boutons. Presynaptic boutons at these axoaxonic synapses always contained gamma-aminobutyric acid but a minority also contained glycine. The results of this study demonstrate the heterogeneity of dorsal horn group II interneurons and provide evidence that they include inhibitory and probably also excitatory neurons. Boutons originating from several chemically different classes of neuron are responsible for postsynaptic inhibition of these interneurons, and the presence of axoaxonic synapses indicates that their excitatory input is also controlled presynaptically.

How effective is integration of information from muscle afferents in spinal pathways?

Integration of information forwarded by group I and group II muscle afferents to premotor interneurones was estimated from spatial facilitation in oligosynaptic (most likely disynaptic) reflex pathways from these afferents. Indications for mutual facilitation of synaptic actions of group I and group II afferents have been found on both inhibitory and excitatory premotor interneurones but were easier to demonstrate in the inhibitory pathways. However, the facilitation appeared weak under our experimental conditions and depended critically upon the intensity and timing of the stimuli used to activate muscle afferents.

Antispastic effects of L-dopa

Antispastic effects of the noradrenaline and dopamine precursor l-3,4-dihydroxyphelanine (L-dopa) were investigated in 11 subjects in which exaggerated stretch reflexes developed after spinal cord injuries. The effects were evaluated from changes in the electromyographic (EMG) response of the quadriceps muscle during tendon jerks evoked by standardized taps over the patellar tendon, in clonus and in resistance to passive movements of the limb. After administration of L-dopa, EMG responses occurring 30-150 ms after the tendon tap decreased to about 50% of control, and clinical tests revealed a marked decrease in the resistance to muscle stretches and in the degree of clonus. The effects were maximal within about 1 h. The depressive actions of L-dopa are interpreted as being exerted primarily at the spinal level, since they were evoked in paraplegics and tetraplegics. The results support the previous hypothesis that group II muscle afferents contribute to.the exaggerated stretch reflex in spastic patients because L-dopa depresses transmission from group II but not from group I muscle afferents. They also indicate the possibility of using L-dopa in the treatment of spastic patients.

Synaptic relationships between serotonin-immunoreactive axons and dorsal horn spinocerebellar tract cells in the cat spinal cord

Dorsal horn spinocerebellar tract cells were identified according to electrophysiological criteria in adult cats and labelled intracellularly with horseradish peroxidase. Sections containing labelled neurons were processed to reveal serotonin immunoreactivity and examined with light and electron microscopy. Numerous contacts were observed on cell bodies, and on proximal and intermediate parts of dendrites. Electron microscopic examination of contacts revealed that synaptic junctions were usually present at the region of apposition. It is concluded that serotonin has a postsynaptic action on dorsal horn spinocerebellar tract cells and that this action is mediated through conventional synapses.

Depression of transmission from group II muscle afferents by electrical stimulation of the cuneiform nucleus in the cat

The effects of short trains of electrical stimuli applied within the cuneiform nucleus and the subcuneiform region were examined on transmission from group I and group II muscle afferents to first-order spinal neurons. Variations in the effectiveness of transmission from these afferents were assessed from changes in the sizes of the monosynaptic component of extracellular field potentials evoked following stimulation of muscle nerves. Field potentials evoked from group II muscle afferents in the dorsal horn of the midlumbar and sacral segments and in the intermediate zone of the midlumbar segments were reduced when the test stimuli applied to peripheral nerves were preceded by conditioning stimulation of the cuneiform nucleus or the subcuneiform region. The depression occurred at conditioning-testing intervals of 20-400 ms, being maximal at intervals of 32-72 ms for dorsal horn potentials and 40-100 ms for intermediate zone potentials. At the shortest intervals, both group II and group I field potentials in the intermediate zone were depressed. Conditioning stimulation of the cuneiform nucleus depressed group II field potentials nearly as effectively as conditioning stimulation of the coerulear or raphe nuclei. We propose that the nonselective depression of transmission from group I and II afferents at short intervals is due to the activation of reticulospinal pathways by cells or fibers stimulated within the cuneiform area. We also propose that the selective depression of transmission from group II afferents at long intervals is mediated at least partly by monoaminergic pathways, in view of the similarity of the effects of conditioning stimulation of the cuneiform nucleus and of the brainstem monoaminergic nuclei and by directly applied monoamines (Bras et al. 1990). In addition, it might be caused by primary afferent depolarization mediated by non-monoaminergic fibers (Riddell et al. 1992).

Effects of serotonin on dorsal horn dorsal spinocerebellar tract neurons

Effects of ionophoretic application of serotonin and of one of its agonists were tested on responses of dorsal horn dorsal spinocerebellar tract neurons evoked by electrical stimulation of peripheral nerves. Both drugs depressed monosynaptically evoked actions of group II muscle afferents; they decreased the number and/or increased the latency of spike potentials evoked by these afferents. In contrast, synaptic actions of low-threshold cutaneous afferents (mono- or oligosynaptic) were facilitated in the majority of the neurons, as judged by decrease in the latency of spike potentials evoked by stimulation of a cutaneous nerve and/or an increase in the number of these potentials. It is proposed that facilitatory actions assist in maintaining tonic discharges of dorsal spinocerebellar tract neurons in some movements and that the selective control of group II input is used to correlate activity of spinal and supraspinal neurons. Both actions may be subserved by tight contacts between serotoninergic nerve fibres and dorsal spinocerebellar tract neurons, which have been revealed in a parallel study.

Contacts between serotoninergic fibres and dorsal horn spinocerebellar tract neurons in the cat and rat: a confocal microscopic study

Contacts between serotoninergic nerve fibres and dorsal horn dorsal spinocerebellar tract neurons were analysed in order to investigate the morphological basis of actions of serotonin upon dorsal spinocerebellar tract neurons. In a series of experiments dorsal spinocerebellar tract neurons were labelled with intracellularly injected rhodamine-dextran in the cat. The neurons were monosynaptically excited by group II muscle afferents and cutaneous afferents and were identified by antidromic activation following stimuli applied in the cerebellum. In the second series of experiments dorsal spinocerebellar tract neurons were labelled by retrograde transport of Fluorogold injected into the cerebellum in the rat. In both series, serotoninergic fibres were labelled by using a specific anti-serotonin antiserum and were revealed by immunofluorescence. Appositions between the serotoninergic fibres and the cells were inspected with a dual channel confocal microscope. The merged images obtained with the two channels of the microscope were viewed in single optical planes 2 microns apart and in rotated three-dimensional reconstructions. Serotoninergic nerve fibres were found in apposition to cell bodies of all feline dorsal spinocerebellar tract neurons (n = 7) and of 75% of rat dorsal spinocerebellar tract neurons (n = 90). The numbers of putative contacts on cell bodies varied between less than 100 and nearly 300 (mean 160) in the cat and between about five and 30 in the rat. Contacts with dendrites of feline neurons were seen on 96% of 72 dendrites within 300 microns from soma and on 91% of 23 dendrites at distances of 300-500 microns. The number of such contacts varied from less than five to 150 on a single dendrite within these ranges of distances. Their total number within 100 microns from the soma was comparable or exceeded the number of contacts on the soma.

The effect of tropisetron injected into the nucleus accumbens septi on ethanol consumption in rats

Earlier studies have shown that 5-HT3 antagonists possess properties of reducing ethanol (EtOH) preference and intake in EtOH high-preferring rats. In this study we examined the effect of tropisetron (ICS 205-930) microinjection (1 and 10 ng) into the nucleus accumbens septi (NAS) on EtOH drinking in a scheduled access to EtOH paradigm. Control rats received vehicle only. Tropisetron, when injected bilaterally into the NAS, significantly reduced EtOH intake in EtOH high-preferring animals. It is concluded that 5-HT3 antagonists might exert their antipreference activity by influencing the receptors within the NAS and that 5-HT3 receptors might play an important role in reinforcing properties of EtOH.

Alcohol drinking in rats injected ICV with 6-OHDA: effect of 8-OHDPAT and tropisetron (ICS 205930)

6-Hydroxydopamine (6-OHDA) was administered ICV to Wistar male rats. Lesioned animals displayed lower preference for ethanol (ETOH) than sham-operated rats. Among 6-OHDA lesioned rats only 9% became high-preferring whereas 20% of sham-operated animals became high-preferring ones. Both tropisetron (the antagonist of 5-HT3 receptors) and 8-OHDPAT (the 5-HT1A receptor agonist) reduced ETOH drinking in high-preferring rats. However, in 6-OHDA lesioned rats the effect of tropisetron was reduced although 8-OHDA retained its effect on ETOH consumption. These results suggest that brain DA neurons are involved in tropisetron action but are not responsible for antipreference effect of 8-OHDPAT.

Interneurones mediating presynaptic inhibition of group II muscle afferents in the cat spinal cord

1. To investigate whether dorsal horn interneurones with input from group II muscle afferents induce depolarization of sensory fibres, simultaneous recordings were made from single interneurones in the sacral segments and from sacral dorsal root filaments using the spike-triggered averaging technique. 2. The spike potentials of eighteen out of thirty-eight interneurones tested were followed by dorsal root potentials (DRPs). The DRPs occurred at latencies of 2 and 6-8 ms. Interneurones evoking DRPs at latencies of up to 2 ms are considered likely to be last-order interneurones in pathways of presynaptic inhibition, while those inducing DRPs at longer latencies are considered likely to be first-order interneurones. The former were activated by peripheral afferents with somewhat longer latencies than the latter. However, all interneurones were co-activated by group II muscle and cutaneous afferents, indicating that the depolarization of group II muscle afferents, which these afferents induce, may be mediated by the same interneurones. 3. DRPs evoked by electrical stimulation of peripheral nerves were recorded from both sacral and midlumbar dorsal root filaments. The amplitudes of these DRPs were closely related to the potency with which group II afferents of various nerves activate dorsal horn interneurones in the sacral and midlumbar segments and group II afferents contributed to them more effectively than group I afferents. The second stimulus in a train was more effective than the first, while a third stimulus had little additional effect, indicating that the interneurones involved are relatively easily activated. 4. Intraspinal stimuli applied within the dorsal horn, at the sites where the largest field potentials of group II origin were recorded, evoked distinct DRPs. However, the location of the first- and last-order interneurones in pathways of primary afferent depolarization (PAD) could not be differentiated by this approach because the same stimuli induced positive potentials, which masked the onset of DRPs and precluded localization of the sites from which DRPs might be evoked monosynaptically.

Organization of neuronal systems mediating presynaptic inhibition of group II muscle afferents in the cat

1. The organization of neuronal systems mediating presynaptic control of transmission from group II muscle afferent fibres has been investigated by comparing the sources of presynaptic inhibition of fibres terminating in different segments of the spinal cord: fibres of the semitendinosus and lateral gastrocnemius muscle nerves terminating in the sacral segments and of the tibialis anterior and extensor digitorum longus muscle nerves terminating in the midlumbar segments. 2. Two measures of presynaptic inhibition were used: depolarization of the terminals of group II fibres (detected as changes in the excitability of single fibres to electrical stimuli) and a decrease in the effectiveness of their synaptic actions (detected as a decrease in the amplitude of monosynaptic field potentials evoked by group II muscle afferents). 3. Group II muscle afferents strongly depolarized all of the group II afferent fibres, while group I muscle afferents contributed to the depolarization of only a few. The majority of fibres were as effectively depolarized by cutaneous afferents as by the most effective muscle afferents. However, the effectiveness with which afferents of different nerves depolarized group II muscle afferent fibres in the sacral and midlumbar segments differed. The most effective afferents were those of nerves that provide the main input to dorsal horn interneurones in the same region of the spinal cord. The sources of depolarization of flexor and extensor fibres terminating in the same (sacral) segments were very similar. 4. The amplitudes of field potentials evoked by group II afferents were depressed by the same types of afferent as produced depolarization of group II afferent fibres. There was also a strong correlation between the effectiveness with which afferents of a given nerve induced depolarization of single fibres and depression of field potentials in the same segments. Since group II field potentials were depressed to a greater extent (by up to 90%) than group I field potentials (by no more than 20%) concurrently recorded in the intermediate zone of midlumbar segments, it appears that transmission from group II muscle afferents may be more strongly affected by presynaptic inhibition than that from group I muscle afferents. 5. The results suggest that the interneuronal systems responsible for the presynaptic control of transmission from group II muscle afferents have topographically restricted actions and an organization appropriate to a system of negative feedback control.

Alcohol drinking in rats treated with 5,7-dihydroxytryptamine: effect of 8-OH-DPAT and tropisetron (ICS 205-930)

5,7-Dihydroxytryptamine (5,7-DHT) was administered ICV to Wistar male rats. Lesioned rats displayed higher preference for ETOH than sham-lesioned animals. Among 5,7-DHT-pretreated rats 38% became high-preferring, while only 22% of sham-lesioned rats displayed this behavioural pattern (p < 0.05). Both 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; the agonist of serotonin 5-HT1A receptors) and tropisetron (ICS 205-930, the antagonist of 5-HT3 receptors) reduced ETOH consumption in high-preferring, sham-lesioned rats. However, in 5,7-DHT rats the effect of 8-OH-DPAT was completely abolished, while tropisetron retained its antipreference activity. Therefore, it seems that 5-HT1A autoreceptors are critically involved in 8-OH-DPAT action, while 5-HT3 receptor sites responsible for tropisetron action are located beyond the 5-HT system.

New observations on input to spino-cervical tract neurons from muscle afferents

Peripheral input to spino-cervical tract (SCT) neurons located in the L4 and L5 segments of the cat spinal cord was investigated using both extracellular and intracellular recording. The main aim was to find out whether midlumbar SCT neurons are excited monosynaptically not only by cutaneous afferents but also by group II muscle afferents, as in the sacral segments but apparently not in the caudal lumbar segments. Input from group II muscle afferents was found in 73% of investigated neurons; the latencies of excitation by group II afferents were compatible with a monosynaptic coupling between these afferents and 62% of neurons. The majority of the midlumbar SCT neurons were excited by group II afferents of the quadriceps and deep peroneal nerves. The predominant monosynaptic input from cutaneous afferents to the same neurons was from the saphenous nerve.

Effects of monoamines on transmission from group II muscle afferents in sacral segments in the cat

The effects of one 5-HT1A serotonin agonist (8-OH-DPAT) and of two alpha 2 noradrenaline agonists (tizanidine and B-HT 933) were tested on the transmission between group II muscle afferents and spinal neurons in the sacral segments of the spinal cord in the cat. These agonists have previously been found to depress transmission from group II muscle afferents either in the dorsal horn or in the intermediate zone of midlumbar segments, and this study addressed the question of whether their actions in the sacral segments are similarly selective. The drugs were applied ionophoretically and their effects were tested on field potentials evoked from group II muscle afferents. As judged by changes in the amplitude of the early components of these field potentials, the transmission is effectively depressed by the serotonin agonist (to 56 +/- 26% after 2 min of ionophoresis of 8-OH-DPAT) but not by the noradrenaline agonists (to 97 +/- 12% after 6 min of ionophoresis of B-HT 933 and to 95 +/- 17% after 6 min of ionophoresis of tizanidine). These data suggest that transmission from group II muscle spindle afferents in the sacral segments is under control of serotonin releasing neurons, as in the dorsal horn of midlumbar segments, but leave open the question of the similarities or differences in the mechanisms (pre- and/or postsynaptic) of this control.

Studies on the effects of certain 5-HT-3 receptor antagonists on ethanol preference and withdrawal seizures in the rat

We tested how certain antagonists of 5-HT-3 receptors affect ethanol consumption and withdrawal seizures in ethanol-dependent Wistar male rats. Low doses of tropisetron (0.001-0.01 mg/kg ip) and ondansetron (0.00025 mg/kg ip) reduced ethanol consumption and preference. Increased ethanol intake was observed, however, after administration of higher doses of ondansetron (0.125 g/kg ip) and granisetron (0.125-0.25 mg/kg ip). Audiogenic seizures in rats withdrawn from ethanol were attenuated by low doses of tropisetron and ondansetron.

Interneurones in pathways from group II muscle afferents in sacral segments of the feline spinal cord

1. Properties of dorsal horn interneurones that process information from group II muscle afferents in the sacral segments of the spinal cord have been investigated in the cat using both intracellular and extracellular recording. 2. The interneurones were excited by group II muscle afferents and cutaneous afferents but not by group I muscle afferents. They were most effectively excited by group II afferents of the posterior biceps, semitendinosus, triceps surae and quadriceps muscle nerves and by cutaneous afferents running in the cutaneous femoris, pudendal and sural nerves. The earliest synaptic actions were evoked monosynaptically and were very tightly locked to the stimuli. 3. EPSPs evoked monosynaptically by group II muscle afferents and cutaneous afferents of the most effective nerves were often cut short by disynaptic IPSPs. As a consequence of this negative feedback the EPSPs gave rise to single or double spike potentials and only a minority of interneurones responded with repetitive discharges. However, the neurones that did respond repetitively did so at a very high frequency of discharges (0.8-1.2 ms intervals between the first 2-3 spikes). 4. Sacral dorsal horn group II interneurones do not appear to act directly upon motoneurones because: (i) these interneurones are located outside the area within which last order interneurones have previously been found and (ii) the latencies of PSPs evoked in motoneurones by stimulation of the posterior biceps and semitendinosus, cutaneous femoris and pudendal nerves (i.e. the main nerves providing input to sacral interneurones) are compatible with a tri- but not with a disynaptic coupling. Spatial facilitation of EPSPs and IPSPs following synchronous stimulation of group II and cutaneous afferents of these nerves shows, however, that sacral interneurones may induce excitation or inhibition of motoneurones via other interneurones. 5. Comparison of the properties of group II interneurones in the sacral segments with those of previously studied group II interneurones in the midlumbar segments leads to the conclusion that these two populations of neurones are specialized for the processing of information from different muscles and skin areas. In addition, equivalents of only one of the two subpopulations of midlumbar interneurones have been found at the level of the pudendal nucleus: neurones with input from group II but not from group I muscle afferents. Neurones integrating information from group I and II muscle afferents and in direct contact with motoneurones thus seem to be scarce in the sacral segments.(ABSTRACT TRUNCATED AT 400 WORDS)

Ascending tract neurones processing information from group II muscle afferents in sacral segments of the feline spinal cord

1. Ascending tract neurones located in the dorsal horn of sacral segments of the spinal cord have been investigated by extracellular and intracellular recording in the anaesthetized cat. The aim was to determine whether information from group II afferents that terminate within the sacral segments is conveyed to supraspinal structures and which types of neurones are involved. 2. A considerable proportion of ascending tract neurones found in the dorsal horn in the same segments as the pudendal (Onuf's) motor nucleus were excited by group II muscle afferents. The great majority (93%) of these neurones had axons ascending in ipsilateral funiculi. Spinocervical tract neurones constituted the largest proportion (82%) of such neurones, while very few spinocerebellar tract and propriospinal neurones and no postsynaptic dorsal column neurones were found among them. 3. In addition to activation by group II muscle afferents all of the neurones were strongly excited by cutaneous afferents. The most potent excitation was evoked by afferents of the posterior biceps-semitendinosus and gastrocnemius muscle nerves and by afferents of the cutaneous femoris, sural and pudendal nerves. The latencies of intracellularly recorded excitatory potentials were indicative of a high incidence of monosynaptic coupling between the afferents and ascending tract neurones. 4. The highly effective monosynaptic excitation of spinocervical tract neurones in the sacral segments by group II afferents is in contrast to the weak disynaptically mediated actions of group II afferents on such neurones in the L6-L7 segments but comparable to the actions of group II afferents on ascending tract neurones in the midlumbar segments. 5. Both the patterns of peripheral input and the latencies of synaptic actions in ascending tract neurones were similar to those in interneurones at the same locations (accompanying report). Similar information is therefore likely to be processed by both categories of neurones. 6. The role of sacral spinocervical tract neurones as a system for transmitting information from group II muscle afferents to supraspinal centres and the potential contribution of this system to the perception of limb position are discussed.

Morphology of interneurones in pathways from group II muscle afferents in sacral segments of the cat spinal cord

The morphology of 12 sacral interneurones with peripheral input from group II muscle afferents was analyzed after intracellular injection of horseradish peroxidase (HRP). The neurones were located in Rexed's laminae III-V overlying the pudendal (Onuf's) motor nucleus. The interneurones had medium sized elongated somata and dendrites projecting radially. All of the interneurones were funicular neurones and fell into two categories depending on whether their axons ran within the dorsal part of the lateral funiculus (DLF; n = 7) or within the ventral funiculus, or the ventral part of the lateral funiculus (VF or VLF; n = 4). The latter were located more rostrally. Within the DLF similar proportions of stem axons and secondary axonal branches descended and ascended. Within the VF and VLF all of the axons ascended. Collaterals of axons running in the DLF arborized primarily within the dorsal horn and the intermediate zone; none were found to approach the motor nuclei. In contrast, collaterals of axons running in the VF/VLF arborized in both the intermediate zone and the ventral horn and passed close to the motor nuclei. We conclude that sacral interneurones with group II input are morphologically nonhomogenous and that only those located most rostrally might have direct actions upon motoneurones. Both the axonal projections and the input (from group II but not from group I muscle afferents and from skin afferents) of sacral interneurones indicate that they are homologous to dorsal horn group II interneurones in the midlumbar segments. They appear, however, to form part of more local neuronal networks than their midlumbar counterparts.

Effect of glutamate receptor antagonists on N-methyl-D-aspartate- and (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-induced convulsant effects in mice and rats

Selected antagonists of N-methyl-D-aspartate (NMDA) and (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists, acting through different recognition sites were studied in three in vivo experimental procedures: systemic administration of NMDA or AMPA to mice and 7-day-old rats or i.c.v. injection in adult rats. Antagonists were given i.p. before the agonists. Of the substances tested (+)-5-methyl-10,11- dihydro-5H-dibenzocyclohepten-5,10-imine maleate ((+)-MK-801, an uncompetitive NMDA receptor antagonist) and DL-(E)-2-amino-4-methyl-5- phosphono-3-pentanoic acid (CGP-37849, a competitive NMDA receptor antagonist) were the most potent and selective NMDA receptor antagonists, having ED50s below 1 mg/kg in all three tests. 1-Amino-3,5-dimethyladamantane (memantine, an uncompetitive NMDA receptor antagonist) was less potent and, additionally, inhibited AMPA-induced seizures in adult rats. Aminocyclopropane carboxylic acid--a partial agonist at the glycine site coupled to NMDA receptors (GlyB)--was a weak antagonist (ED50 > 150 mg/kg) in mice. Other partial GlyB receptor agonists, aminocyclobutane carboxylic acid, (+,R)-3-amino-1-hydroxy-2-pyrrolidine ((+,R)-HA-966) and d-cycloserine, and antagonists, 5,7-dinitroquinoxaline-2,3-dione (MNQX) and 5,7-dichlorokynurenic acid, were ineffective in mice after systemic administration. The last two agents however were active in adult rats when given i.c.v. Thus affinity, intrinsic activity (GlyB receptor partial agonists) and/or penetration into the brain (GlyB receptor antagonists) seem to be important factors in determining the effectiveness of these agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Primary afferent depolarization of myelinated fibres in the joint and interosseous nerves of the cat

1. Changes in the excitability of the intraspinal terminals of fibres in the posterior knee joint and interosseous nerves were used as a measure of primary afferent depolarization (PAD) which is associated with presynaptic inhibition of transmission from afferent fibres. These were estimated from changes in the intensity of electrical stimuli required to activate the fibres in 50% of trials. In order to avoid the inclusion of group I muscle afferents which contaminate the joint and interosseal nerves, the analysis was restricted to fibres conducting at less than 75 m s-1 and/or displaying patterns of PAD which differed from those of group Ia and Ib muscle afferents in lower lumbar segments of anaesthetized cats. PAD was evoked by electrical stimulation of ipsilateral hindlimb nerves. 2. PAD of fibres in the posterior knee joint nerve was induced from group I (Ia and Ib) and group II muscle afferents and cutaneous afferents but not by stimulation of the joint or the interosseous nerves. The most effective stimuli were those applied to the superficial peroneal, sural, quadriceps and posterior biceps and semitendinosus nerves. 3. PAD of fibres in the interosseous nerve was also induced by stimulation of group I (Ia and Ib) and group II muscle afferents and cutaneous afferents and, in addition, by stimulation of joint and interosseous nerves. The most effective stimuli were those applied to the superficial peroneal, quadriceps, flexor digitorum longus and posterior biceps and semitendinosus nerves. 4. Individual fibres of the joint and the interosseous nerves were depolarized by only some of the conditioning stimuli. Even the most effective stimuli did not produce PAD in all of the fibres tested. Individual fibres of the joint and the interosseous nerves were depolarized by diverse combinations of afferents of different functional types and of different peripheral nerves. The differences in the sources of PAD were not associated with the conduction velocities and hence are unlikely to be related to differences in the receptor origin of the tested fibres. The diversity in the sources of PAD of individual fibres is interpreted as providing a high degree of differentiation in the control of transmission from receptors in joints and interosseal membranes.

A relay for input from group II muscle afferents in sacral segments of the cat spinal cord

1. A neuronal relay for input from group II afferents of hindlimb muscle nerves has been found in the previously little explored sacral segments of the cat spinal cord. 2. Electrical stimulation of group II muscle afferents of a number of nerves evoked negative potentials on the surface (cord dorsum potentials) and population postsynaptic potentials (field potentials) within the sacral segments. The largest potentials were evoked by stimulation of the posterior biceps-semitendinosus and triceps surae nerves which evoke much smaller potentials in other segments. Group II afferents of other nerves, notably those which have their main relay within the middle lumbar segments, were much less effective. 3. The sites at which cord dorsum and field potentials evoked by group II muscle afferents were recorded varied in relation to the external topography of the L7-S2 spinal segments but were consistent in their location relative to the pudendal motor nucleus (Onuf's nucleus). Potentials evoked by group II afferents of the posterior biceps and semitendinosus nerves peaked at a level corresponding to the rostral half of Onuf's nucleus and potentials evoked by afferents of the gastrocnemius nerves peaked just rostral to this nucleus. The largest field potentials (of 0.5-1.0 mV) were recorded within the dorsal horn. Field potentials in the intermediate zone were much smaller (< 0.3 mV) and were seen less frequently. 4. Evidence was obtained that the dorsal horn field potentials are to a great extent evoked monosynaptically by the fast conducting fraction of group II muscle afferents: (i) they were evoked at short latencies (2.4-2.7 ms from the stimulus; 1.3-1.7 ms from group I components of afferent volleys and 0.5-0.7 ms from group II components of these volleys), (ii) the conduction times of impulses in the fastest conducting fraction of group II afferents, between the sacral segments (where these impulses were induced by intraspinal stimuli) and the peripheral nerves, were only about 0.5 ms shorter than the latencies of field potentials recorded at the site of intraspinal stimulation and evoked by stimulation of the same peripheral nerves and, (iii) the field potentials followed repetitive stimuli without temporal facilitation. 5. Negative cord dorsum and field potentials were also evoked by small stretches of the semitendinosus and triceps surae muscles. Although they were smaller than potentials evoked by electrical stimulation of sensory fibres and appeared at longer latencies, their presence is consistent with a contribution of muscle spindle afferents to the actions of group II muscle afferents within the sacral segments.(ABSTRACT TRUNCATED AT 400 WORDS)

Depolarization of group II muscle afferents by stimuli applied in the locus coeruleus and raphe nuclei of the cat

1. Electrical stimuli applied in the locus coeruleus/subcoeruleus (LC/SC) and raphe nuclei produce a profound depression of transmission in reflex pathways from group II muscle afferents. The present experiments were performed to determine whether presynaptic inhibitory mechanisms contribute to these effects. 2. Changes in the excitability of afferent terminals to electrical stimuli have been used as an indication of primary afferent depolarization (PAD) produced by conditioning stimuli applied within the LC/SC and raphe nuclei and, for comparison, in the nucleus ruber. Group II afferents originating from ankle flexor muscles and terminating in the midlumbar segments were used for testing. 3. Clear changes in excitability were observed in fourteen of nineteen group II fibres in which the effects of conditioning stimuli applied in the LC/SC were tested and in twelve of seventeen fibres in which the effects of stimuli applied within the raphe nuclei were tested. By comparison, only one of the twelve fibres tested with conditioning stimuli applied to the nucleus ruber was found to be influenced. These effects matched those of the same conditioning stimuli on field potentials evoked by group II afferents at the location at which the terminals of group II fibres were stimulated. 4. Stimuli applied in the LC/SC and in the raphe nuclei both produced a mean decrease in threshold stimulus current of 19%. These effects are comparable to those produced by the most effective volleys in peripheral afferent which, in the same fibres, produced a mean decrease in threshold stimulus current of 24%. 5. In all cases (twelve) in which the effects of stimuli applied in the LC/SC and raphe nuclei were tested on the same group II fibre, either both or neither were found to be effective. This strengthens previous indications that some populations of neurones might be activated by stimuli applied in each of these regions of the brain. 6. In contrast to group II afferents, group Ia afferents investigated in the same experiments were only exceptionally affected. Of seven fibres tested with stimuli applied in the LC/SC, six with stimuli applied in the raphe nuclei and seven with stimuli applied in the nucleus ruber, only one fibre showed any clear change in threshold and this was a single fibre which was similarly affected by stimuli in all three sites. 7. It is concluded that presynaptic inhibitory mechanisms contribute to the depression of transmission in spinal reflex pathways from group II muscle afferents produced by stimulation in the LC/SC and raphe nuclei.

Gating of transmission to motoneurones by stimuli applied in the locus coeruleus and raphe nuclei of the cat

1. Neuronal systems activated by stimulation in the region of the locus coeruleus/subcoeruleus (LC/SC) and raphe nuclei have previously been shown to depress transmission from group II muscle afferents in regions of the midlumbar spinal segments in which premotor interneurones are located. The aim of the present investigation was to determine the extent to which such depression is paralleled by depression of the reflex actions of group II afferents on motoneurones. 2. The effects of short trains of conditioning electrical stimuli applied within the LC/SC and raphe nuclei were examined on postsynaptic potentials (PSPs) evoked by group I and group II muscle afferents in hindlimb motoneurones. The effects were examined over a wide range of conditioning-test intervals but particular emphasis was placed on the effects produced at long intervals (> 100 ms) since such effects are more likely to be mediated by the descending noradrenergic and serotonergic neurones of the LC/SC and raphe nuclei which are of slow conduction velocity. In addition, conditioning stimuli alone evoked PSPs in motoneurones (with latencies of 7-15 ms and a duration of 50-80 ms) and effects evoked at short conditioning-test intervals might therefore have been secondary to changes in motoneurone membrane properties. 3. At conditioning-test intervals between 100 and 350 ms synaptic actions of group II origin were strongly and consistently depressed. Both EPSPs and IPSPs were affected, two-thirds of those tested being reduced in amplitude by 50% or more. A similar depression was exerted on PSPs evoked from the quadriceps and deep peroneal nerves mediated predominantly by interneurones located in the midlumbar segments and on PSPs evoked from the hamstring and triceps surae nerves mediated by interneurones located in more caudal segments. It is thus concluded that neuronal systems activated by stimuli applied in the LC/SC and raphe nuclei are capable of gating transmission in all those interneuronal pathways which mediate the reflex actions of group II afferents on motoneurones in anaesthetized animals.

Interactions between pathways controlling posture and gait at the level of spinal interneurones in the cat

The properties of three interneuronal populations controlling posture and locomotion are briefly reviewed. These are interneurones mediating reciprocal inhibition of antagonistic muscles and interneurones in pathways from secondary muscle spindle afferents to ipsilateral and contralateral motoneurones, respectively. It will be shown that these interneurones subserve a variety of movements, with functionally specialized subpopulations being selected under different conditions. Mechanisms for gating the activity of these neurones appear to be specific for each of them but to act in concert. Interneurones which are active during locomotion and postural reactions are distributed over many segments of the spinal cord and over several of Rexed's laminae, both in the intermediate zone and in the ventral horn (Berkinblit et al., 1978; Bayev et al., 1979; Schor et al., 1986; Yates et al., 1989). The location of neurones discharging during neck and labyrinthine reflexes is illustrated in Fig. 1A and B but indications that neurones with an even wider distribution contribute to locomotion, scratching and the related postural reactions have been provided by neuronal markers which preferentially label active neurones (WGA-HRP; see Noga et al., 1987) or neurones with active genetic transcription (c-fos; I. Barajon, personal communication; Dai et al., 1991). Such a wide distribution indicates a high degree of non-homogeneity, since neurones of different functional types are usually located in different laminae. It has been demonstrated that some of these neurones may be particularly important for setting up the rhythm of muscle contractions specific for different gaits or scratching, as part of their "pattern generators" (see, e.g., Grillner, 1981). Other neurones may be primarily involved in initiation of these movements or in postural adjustments combined with them. A considerable proportion of neurones mediating these movements are nevertheless likely to be used not in one particular type of movement but in a variety of movements, and contribute to postural reactions and locomotion as well as to various segmental reflexes and centrally initiated movements; they are likely to operate as last order (premotor) interneurones of several spinal pathways to motoneurones. One of the indications that this is the case is the overlap between the areas of location of interneurones active during postural reactions, locomotion, or scratching and the areas of location of premotor interneurones (Fig. 1C,D). The latter were labelled by loading motoneurones with WGA-HRP and by its subsequent retrograde transneuronal transport (see Harrison et al., 1986).(ABSTRACT TRUNCATED AT 400 WORDS)

The involvement of NMDA receptors in acute and chronic effects of ethanol

Recent evidence indicates involvement of excitatory amino acid receptors sensitive to N-methyl-d-aspartate (NMDA) in the action of ethanol (EtOH). Pronounced inhibition of NMDA receptor function is seen in vitro with concentrations of EtOH corresponding to those present during alcohol intoxication in humans. The present study was devoted to investigate the role of NMDA receptors in the action of EtOH in rats. Acute experiments showed antagonism by EtOH of convulsions induced by intracerebroventricular injection of NMDA. A similar effect was seen with a high dose of diazepam. Convulsions induced by an agonist of another excitatory amino acid receptor subtype, kainate, were also inhibited by EtOH. An uncompetitive antagonist of NMDA receptors, 5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine maleate (MK-801), potentiated EtOH-induced loss of righting, but attenuated the hypothermic action of EtOH. Moreover, MK-801 inhibited audiogenic convulsions in EtOH withdrawn rats. At the same time the effect of a proconvulsive dose of NMDA was not enhanced. Tolerance to the myorelaxant action of both EtOH and MK-801 upon repetitive administration was seen. Also some degree of cross-tolerance was observed. Moreover, MK-801 failed to modify EtOH preference in rats. The present results support involvement of NMDA receptors in expression of some acute and subchronic actions of EtOH and in expression of EtOH withdrawal.

Transmission from group II muscle afferents is depressed by stimulation of locus coeruleus/subcoeruleus, Kölliker-Fuse and raphe nuclei in the cat

The effects of brief trains of electrical stimuli applied within the locus coeruleus and subcoeruleus, the Kölliker-Fuse nucleus and the raphe magnus, obscurus and pallidus nuclei were tested on transmission from group I and group II muscle afferent fibres in mid-lumbar spinal segments of chloralose anaesthetized cats. Changes in the effectiveness of transmission from these afferents were assessed from changes in the size of monosynaptic extracellular field potentials evoked by them. The depression of group II field potentials occurred at conditioning-testing intervals of 20-400 ms, and was maximal at intervals of 40-100 ms and 30-60 ms for potentials recorded in the intermediate zone and dorsal horn, respectively. At intervals up to about 30 ms it was combined with the depression of group I components of the intermediate zone field potentials. However, at longer intervals the conditioning stimuli depressed group II components of these potentials as selectively as monoamines applied ionophoretically at the recording site (Bras et al., 1989a, 1990). Thus, only the late depressive actions are considered as being possibly mediated by impulses in descending noradrenergic and/or serotonergic fibres. No major differences were found in the relative degree of depression of transmission from group II afferents by stimulation of the locus coeruleus/subcoeruleus, Kölliker-Fuse or raphe nuclei, either in the dorsal horn or in the intermediate zone. Since field potentials at these locations are preferentially depressed by ionophoretic application of serotonin and noradrenaline (Bras et al., 1990), and since the locus coeruleus/subcoeruleus, Kölliker-Fuse and raphe nuclei are interconnected, the study leads to the conclusion that both noradrenergic and serotonergic descending pathways can be activated by stimuli applied within either of them. Selective depression of field potentials of group II origin was also evoked by stimulation at other sites, e.g. the periaqueductal grey and medullary reticular formation, when conditioning-testing intervals were sufficiently long. Such a depression is considered to be secondary to activation of neurones of the locus coeruleus/subcoeruleus, Kölliker-Fuse or raphe nuclei and attributed to the spread of current or transsynaptic activation of these neurones, or to stimulation of their axon collaterals outside the nuclei rather than to other descending medullo-spinal systems. The non-selective depression of field potentials evoked by group I and group II afferents at shorter conditioning-testing intervals is proposed to be due to actions of reticulo-spinal pathways.

MIF-1 potentiates the action of tricyclic antidepressants in an animal model of depression

In the present paper, the effect of simultaneous treatment of rats with low doses of MIF-1 and tricyclic antidepressants on rat behavior in the forced swim test was studied. It was found that MIF-1 stimulated in a dose-dependent manner "active" behavior of animals in this paradigm. The effect of MIF-1 appeared to be independent of changes in rats' locomotion in the open field test. The combined treatment of rats with MIF-1 (0.01 mg/kg IP) and amitriptyline (5 mg/kg IP) or desipramine (1.25 mg/kg) IP) significantly stimulated active behavior in the forced swim test above the level obtained with each of the drugs given separately. The present data suggest the potential clinical efficacy of a combined therapy of depressive patients with MIF-1 and small doses of tricyclic antidepressants.

Chronic oral treatment with diltiazem or verapamil decreases isolation-induced activity impairment in elevated plus maze

Adult male Wistar rats were either socially isolated or group-housed for 6 weeks and then tested in an elevated plus maze. During isolation the rats received either water or two concentrations of the calcium channel inhibitors, diltiazem or verapamil, in drinking solutions (approximately 5 and 10 mg/kg daily). Isolated rats showed a significantly lower total number of arm entries, a lower percentage of open arm entries and negligible time spent therein than did group-housed animals. Verapamil, in the higher dose, prevented that effect of isolation. Treatment with diltiazem brought about a similar tendency, though the effect did not reach statistical significance. Chronic treatment of group-housed rats with either drug failed to influence their behavior in the plus maze. We conclude that certain calcium channel inhibitors may decrease the behavioral deficit in the elevated plus maze that follows chronic social isolation.

Contralaterally projecting lamina VIII interneurones in middle lumbar segments in the cat

Peripheral input to lamina VIII interneurones was investigated by using extracellular and/or intracellular records from them. The interneurones were located in the L4-L5 spinal segments and projected to contralateral motor nuclei in the L7 segment. They constituted a non-homogeneous population but their input from muscle afferents (mainly group II afferents of quadriceps, flexor digitorum longus and pretibial flexors and group I afferents of triceps surae and hamstring nerves) and from cutaneous and joint afferents resembled the input to ipsilaterally projecting laminae V-VII interneurones of the same segments rather than the input to more caudally located lamina VIII interneurones. Since the ipsilaterally projecting laminae V-VII interneurones with such an input might be involved in locomotion, it is proposed that this is also the case for the contralaterally projecting lamina VIII midlumbar interneurones, especially those excited by stimuli applied in the cuneiform nucleus (mesencephalic locomotor region).

Antidepressant-like action of nicardipine, verapamil and hemicholinium-3 injected into the anterior hypothalamus in the rat forced swim test

Male Wistar rats, chronically implanted with cannulas into the anterior hypothalamus, were acutely injected with the calcium channel inhibitors, diltiazem, nicardipine and verapamil, or the choline uptake blocker hemicholinium-3 and tested in the forced swim test. Hemicholinium-3, nicardipine and verapamil markedly increased the duration of active swimming. This antidepressant-like effect did not appear to reflect merely a hyperactive state as the drug-treated rats did not differ from vehicle-injected controls in their open field motility scores. Diltiazem failed to influence rats' performance in either test. Since nicardipine and verapamil, but not diltiazem, share choline uptake property with hemicholinium-3, it seems that this action plays a role in the antidepressant-like effect of all three drugs in the forced swim test.

[Post-traumatic chylothorax]

A case of post-traumatic chylothorax in a 84 year old man with ILD is presented. The chylothorax was successfully treated after 6 months, which was confirmed at post-mortem, during which a solitary plasmocytoma of the left kidney was also diagnosed.

Light microscopical study of dendrites and perikarya of interneurones mediating la reciprocal inhibition of cat lumbar alpha-motoneurones

Interneurones which mediate disynaptic inhibition from la muscle spindle afferents of the quadriceps nerve to lumbar alpha-motoneurones were stained with intracellular injection of horseradish peroxidase. Seven best stained and most satisfactorily preserved cells were selected for analysis, and the light microscopic morphology of their cell bodies and dendrites were quantitatively investigated in parasagittal sections. The perikarya were located dorsal or dorso-medial to the motoneurones; they had mean diameters of 51 x 27 microns and a mean volume of 35,820 microns 3. The cells had 3 to 7 dendrites, which were arranged asymmetrically around the parent somata. The dendrites extended mainly in the dorso-ventral direction, in which the mean tip to tip distance for each cell was 1742 microns. The dendrites had few spines and they branched almost only in bifurcations. On the average, each process divided 3.5 times and in each cell they gave rise to 14.9 branching points as well as a total combined length of more than 7000 microns. Primary dendrites had a mean length of 193 microns which was generally shorter than the lengths of the branches of higher order. A more detailed analysis of two cells revealed the mean width of primary dendrites to be 5.6 microns while that of the 5th order processes was 1.5 microns. The mean tapering of individual dendritic branches per unit length was 17%, being somewhat more pronounced for the distally located segments, while at branching points the sum of daughter processes approximately equalled the diameter of the parent process.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphology of midlumbar interneurones relaying information from group II muscle afferents in the cat spinal cord

The morphology of midlumbar interneurones with peripheral input from group II muscle afferents was analysed after intracellular injection of horseradish peroxidase (HRP). Twenty-three interneurones were stained intrasomatically and five others intra-axonally. The majority (10 of 13) of interneurones located in lamina VII (intermediate zone and ventral horn interneurones) were found to project ipsilaterally. They had medium-sized somata and dendrites projecting radially over a distance of more than 1 mm. All of these neurones had axons that projected caudally within the ventral part of the lateral funiculus or in the lateral part of the ventral funiculus, although four had in addition an ascending secondary axonal branch. Numerous axon collaterals were given off from these axons, both before and after they left the grey matter. The collaterals arborized within laminae VII, VIII, and IX, where they covered the area of several motor nuclei. Intra-axonal labelling of five neurones with similar input and axon trajectories revealed several axon collaterals given off between the cell body and the terminal projection areas in L7 or S1 segments. Only three of the labelled interneurones located in lamina VII and displaying the same kind of input had axons with different destinations; their axons crossed to the opposite side of the spinal cord and ascended within the contralateral ventral funiculus. These were large neurones with extensive dendritic trees, which had fairly thick axons with initial axon collaterals that branched primarily ipsilaterally (within laminae V-VIII). Interneurones located in lamina V and in the bordering parts of laminae IV and VI (dorsal horn interneurones; n = 10) constituted a very nonhomogenous population. They projected either ipsilaterally or contralaterally and had either ascending or descending axons running in either the lateral or ventral funiculi. Generally, dorsal horn interneurones had cell bodies smaller than those of intermediate zone and ventral horn interneurones, and their dendrites extended less extensively and less uniformly around the soma. Their initial axon collaterals branched primarily in the dorsal horn, or in lamina VII, but not in or close to the motor nuclei. Our results support the conclusions of previous physiological studies that the intermediate zone and ventral horn midlumbar interneurones with group II input and that project to motor nuclei have collateral actions on other interneurones in the L4-L6 segments, and that dorsal horn interneurones do not project to motoneurones, but have as their targets other interneurones or ascending cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Antibody producing cells in the spleens of mice treated with pathogenic mineral dust

Experiments were carried out to assess the effect of intraperitoneal injection of the mineral dusts, titanium dioxide, quartz, or asbestos, on splenic lymphocyte antibody forming cells in immunised mice. Titanium dioxide and quartz caused similar, about one third, reductions in plaque forming cells; asbestos caused substantial reduction to about a quarter of the number found in control spleens. The inhibition of antibody forming cells in the spleen found with chrysotile was dose dependent and both chrysotile and crocidolite asbestos were similar in activity. Systemic immunomodulation after local deposition of mineral dust may be important to the development of disease.

Comparison of effects of monoamines on transmission in spinal pathways from group I and II muscle afferents in the cat

The actions of noradrenaline (NA) and 5-hydroxytryptamine (5-HT; serotonin) were compared with those of L-3,4-dihydroxyphenylalanine methyl ester (Methyl-L-DOPA) on transmission to spinal interneurones in mid-lumbar (L4 and L5) segments of the cat spinal cord. The drugs were applied ionophoretically and their effects were tested on monosynaptic field potentials evoked by nerve impulses in hindlimb group I and group II muscle afferent fibres and on responses of interneurones with synaptic input from these fibres. Of field potentials recorded at various locations, both NA and 5-HT depressed those evoked from group II fibres in the intermediate and ventral horn regions of the spinal cord but not, or only occasionally, in the dorsal horn. Field potentials of group I origin were not depressed. The tested interneurones were located where group II field potentials were affected. NA, 5-HT and Methyl-L-DOPA depressed responses to electrical stimulation of group II fibres but not responses evoked by group I fibres. The depression consisted of an increase in the latency and a decrease in the number of action potentials evoked by the stimuli. All three drugs were also found to decrease the amplitude of intracellularly recorded monosynaptic EPSPs of group II origin but not of monosynaptic EPSPs evoked in the same neurones by group I fibres. Interneuronal firing induced by DL-homocysteic acid was depressed as effectively as responses to electrical stimulation of peripheral nerves. The possibility of presynaptic and/or postsynaptic mechanisms of the selective depression of synaptic actions of group II origin are discussed.

Primary afferent depolarization of central terminals of group II muscle afferents in the cat spinal cord

1. The origin of primary afferent depolarization (PAD) of the central terminals of group II afferent fibres of tibialis anterior and extensor digitorum longus muscles has been investigated in the cat. Changes in the excitability of the terminals to intraspinal stimuli, upon application of conditioning stimuli to muscle nerves (quadriceps, sartorius, gracilis, posterior biceps-semitendinosus, anterior biceps-semimembranosus, gastrocnemius-soleus, deep peroneal), cutaneous nerves (sural, superficial peroneal) and the posterior nerve to the knee joint, were used as a measure of PAD. 2. PAD was most readily evoked by conditioning stimuli which were maximal for group II muscle afferents. However, some PAD was also evoked from group I afferents and evidence is presented that group Ia afferents contributed. Afferents of posterior biceps-semitendinosus and sartorius muscles appeared to be most effective. PAD was also evoked by stimulation of cutaneous and joint nerves, often in the same fibres which were affected by group Ia afferents. 3. It is concluded that there are several common sources of PAD of group II and group Ia afferent terminals on the one hand, and group Ib afferent terminals on the other. 4. The properties of PAD of group II afferents are discussed in relation to the problem of how PAD affects transmission from fibres with long terminal branches of small diameter.

A neuronal system of movement control via muscle spindle secondaries

A recently discovered spinal interneuronal system of movement control is briefly described. It includes a population of midlumbar interneurones with a predominant monosynaptic input from secondary muscle spindle afferents but supplied with information via several other afferent and descending neuronal systems as well. The neurones are in direct contact with both motoneurones and other interneurones. The evidence in favour for their involvement in locomotion is briefly summarized.