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D M Armstrong

Publications and source records attributed to D M Armstrong.

At least 127 records · Page 7Linked to original sources
PubMed1982

Electron microscopic immunocytochemical localization of tyrosine hydroxylase in the area postrema of rat.

The ultrastructural morphology and specialized neuronal, vascular, and ventricular associations of tyrosine hydroxylase-labeled neurons are examined within the area postrema of rat brain. Specific antiserum to the purified enzyme is localized throughout the rostrocaudal and dorsoventral extent of the area postrema by means of the peroxidase-antiperoxidase technique. In all regions, peroxidase immunoreactivity for tyrosine hydroxylase is distributed throughout the cytoplasm of selectively labeled neuronal perikarya and processes. The perikarya contain a large nucleus, infolded nuclear membrane, numerous cytoplasmic organelles, and form axosomatic synapses with unlabeled terminals. The majority of the labeled processes are dendrites, which contain ribosomes, microtubules, mitochondria, and scattered vesicles. These dendrites are postsynaptic to unlabeled axon terminals and show membrane specializations with other labeled dendrites and perikarya. In contrast to dendrites, peroxidase-labeled profiles clearly distinguished as axons or axon terminals are sparse and never show membrane specializations with other neuronal or nonneuronal structures within the area postrema. Numerous large processes which could be either axons or dendrites are associated with blood vessels and the ventricular surface of the area postrema. With respect to blood vessels, processes are located either in direct apposition to the external glial membrane, or less frequently, within the perivascular space. The ventricular processes are either associated with blood vessels in the subpial space or distributed among the cilia and villi at the anterior margins of the area postrema. The neuronal and nonneuronal associations of the tyrosine hydroxylase-labeled processes are consistent with a receptor or chemosensor function for catecholamines in this circumventricular organ.

Animals↗
PubMed1981

Adrenaline neurons in the rostral ventrolateral medulla innervate thoracic spinal cord: a combined immunocytochemical and retrograde transport demonstration.

Adrenaline-containing neurons in the C1 group of the ventrolateral rostral medullary reticular formation which project to the thoracic spinal cord were identified by a combined retrograde transport immunocytochemical technique. No other medullary catecholamine neurons, including the A1 and A2 noradrenaline cells, project to thoracic spinal cord. These data, taken with results of other studies of spinal catecholamine innervation, suggest a segmental segregation of projections to spinal cord by dopaminergic, noradrenergic, and adrenergic neurons.

Animals↗
PubMed1981

Immunocytochemical localization of catecholamine synthesizing enzymes and neuropeptides in area postrema and medial nucleus tractus solitarius of rat brain.

The catecholaminergic and peptidergic neurons in the area postrema and adjacent portion of the medial nucleus tractus solitarii (mNTS) were characterized by the immunocytochemical localization of the catecholamine synthesizing enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) and two neuropeptides, substance P and (Leu5)-enkephalin. The catecholamine synthesizing enzymes TH and DBH, found jointly only in noradrenergic and adrenergic neurons, were localized in cells having a similar morphology and topographical distribution. These cells were located throughout the rostrocaudal and dorsoventral extent of the area postrema, as well as in neurons within the mNTS. The processes showing TH and DBH immunoreactivity appear to form reciprocal connections between the area postrema and mNTS. Phenylethanolamine-N-methyltransferase, the enzymatic marker found only in adrenergic neurons, was detected immunocytochemically in terminals distributed throughout the area postrema and in neuronal perikarya and varicosities within the adjacent mNTS. Like the catecholamine synthesizing enzymes TH and DBH, enkephalin-like immunoreactivity was localized to perikarya, proximal processes and varicose axon terminals within the area postrema and the adjacent mNTS. However, in contrast to the widespread distribution of the enzymes, the enkephalin-like immunoreactivity was localized predominantly along the dorsal and ventrolateral margins of the area postrema. The distribution of substance P immunoreactivity, which was detected only in varicose processes, paralleled the distribution of enkephalin-like immunoreactivity, being predominantly located along the dorsal and ventrolateral margins of the area postrema. Within the mNTS adjacent to the area postrema, substance P immunoreactivity was localized to neuronal perikarya, proximal processes and varicose axon terminals. Based upon the presence of appropriate biosynthetic enzyme markers and neuropeptide localization, these findings suggest that neurons within the area postrema contain noradrenalin and enkephalin and that the afferent axons contain substance P, adrenalin and, probably, noradrenalin.

Animals↗
PubMed1980

Responses in the posterior lobe of the rat cerebellum to electrical stimulation of cutaneous afferents to the snout.

1. Responses in the cortex of the posterior lobe of the cerebellum to electrical stimulation of afferent fibres from the skin of the snout have been analysed in decerebrate and pentobarbitone-anaesthetized rats by means of surface and microelectrode records. Single shocks were applied either to the exposed follicles of the mystachial vibrissae or to the infraorbital branch of the trigeminal nerve. 2. In decerebrate rats responses were mediated only via mossy fibre afferents. Stimulation of one side of the snout yielded responses with mean latency 2.4 ms throughout the uvula (largest ipsilaterally and in lobule IXa). Smaller responses with similar latency were present in both cerebellar hemispheres (largest ipsilaterally). The earliest discharges of Purkinje cells in lobule IXa occurred at latencies between 4.5 and 8.5 ms. 3. All components of the extracellular field potentials generated within the cortex by the mossy fibre input were detectable by surface recording with ball electrodes. 4. The earliest surface potentials had a latency of 0.55 ms (peak latency 0.8 ms); they arose through volume conduction from the brain stem of a potential which signalled arrival of the primary afferent volley. The short delay between this event and the arrival of the mossy fibre volley in the cerebellum suggests that only one synaptic relay occurs in the brain stem. 5. In pentobarbitone-anaesthetized rats surface responses mediated via mossy fibres persisted and were accompanied at slightly higher threshold by responses shown to be mediated via climbing fibres. The latter were present in descending order of amplitude in three sagittally directed zones, one in contralateral Crus 2 (minimum latency 13 ms), one in the vermis contralaterally near the mid line in lobule IXa (latency 16 ms) and a third in ipsilateral Crus 2 (latency 20 ms) 6. In the hemisphere the responses mediated via climbing fibres occurred within the somewhat larger zones activated via mossy fibres but in the vermis the two types of trigemino-cerebellar input influenced quite separate areas of cortex.

Animals↗
PubMed1979

Three types of consciousness.

It is useful to distinguish three senses of the word 'consciousness'. 'Minimal' consciousness is the occurrence of any mental activity, whether or not the subject is aware of this activity. 'Perceptual' consciousness is perceptual activity. Minimal and perceptual consciousness may be present, yet 'introspective' consciousness be lacking. Introspective consciousness is conceived as it was by Locke and Kant: as perception-like awareness of the subject's own current mental states and activities. It includes introspective consciousness of introspective consciousness itself. A useful model for demystifying and naturalizing introspective consciousness is the subject's proprioceptive awareness of bodily states and activities. Introspective consciousness may be further subdivided into 'reflex' introspective consciousness and 'introspection proper'. The distinction is one of degree: the degree of attention involved. We attach a quite special importance to introspective consciousness and are particularly unwilling to identify it with a purely physical process in the brain. It is suggested, however, that this springs from (a) the fact that what is introspected is taken to be a state or activity of a single thing, the self; and (b) the fact that event-memory is generally only possible if the event remembered was the object of introspective consciousness at the time. Without introspective consciousness, therefore, awareness of a self and the past history of that self is lacking.

Adolescent↗
PubMed1979

Responses of neurones in nucleus interpositus of the cerebellum to cutaneous nerve volleys in the awake cat.

1. A method is described which permitted stable extracellular recordings to be made from 115 neurones in nucleus interpositus of the cerebellum in unanaesthetized free-to-move cats. At least 95% of the neurones were cerebellar efferent cells since they were antidromically invaded following electrical stimulation of the brachium conjunctivum in the region of the contralateral red nucleus. 2. In cats in a state of quiet wakefulness the majority of interpositus neurones were tonically active at rates ranging from 12 to 77 impulses/sec (over-all mean 34/sec). The remaining neurones were silent or discharged only a few impulses throughout observation periods of a few minutes. 3. Cutaneous afferent volleys elicited by single shocks to the superficial radial nerves in the forearm at intensities too weak to evoke a flexion reflex or behavioural arousal produced changes in firing frequency in 62% of eighty-one cells tested. Response patterns varied widely but in 86% of the responding cells the earliest change was a short latency (6--20 ms) increase in discharge probability which from post-stimulus time histograms was found usually to average around one impulse per stimulus. In only four cells (8%) the earliest response was a depression of the tonic firing. However, in many cells the initial acceleration was followed by a reduction in firing frequency which lasted between 10 and 85 ms. 4. In 56% of the responding cells a longer latency (25--80 ms) acceleration was present. Such accelerations varied widely in duration (from 55 to 550 ms) but most commonly lasted 100--200 ms. These responses were usually the most prominent feature in the response pattern: in the majority of neurones between two and five impulses were added per stimulus. 5. Considering the whole time course of the responses, the net effect of nerve volleys was to produce an increase in nuclear cell output. 6. These neurones which were influenced by nerve stimulation also discharged in response to taps to the forepaws. 7. The responses to nerve stimulation are compared with those encountered in previous studies using cats anaesthetized with chloralose or barbiturates and with the responses of Purkinje (P) cells and it is suggested that the longer latency excitatory responses result in large part from a reduction in the tonic inhibitory action exerted on the interpositus neurones by Purkinje cells. 8. The possibility is discussed that interpositus responses to cutaneous input from the limbs might contribute (via the rubrospinal system) to the regulation of spinal flexor mechanisms during locomotion and/or contact placing reactions.

Animals↗
PubMed1979

Activity patterns of cerebellar cortical neurones and climbing fibre afferents in the awake cat.

1. Glass-insulated tungsten micro-electrodes were used to record from single neurones in the intermediate zone of the cerebellar cortex of cats in a state of quiet wakefulness. 2. Two hundred and seventy Purkinje (P) cells were recorded extracellularly, 95% of which displayed an irregular tonic discharge at rates between 19 and 95/s (over-all mean 44/s), including complex spikes (c.s.) which occurred at 1.0--2.5/s )over-all mean 1.5/s). The remaining cells discharged c.s. at the usual rate but only one or two simple spikes (s.s.) per minute. C.s. of spike plus wavelet and of multi-spiked type were present in approximately equal numbers of cells. 3. Presumed climbing fibre-e.p.s.p.s were recorded from fifty-six P cells and occurred both singly and in groups of two to six e.p.s.p.s at an intra-group frequency of about 500/s. The cells giving rise to the c.f.s therefore discharge propagated impulses both singly and in short bursts as previously reported for anesthetized animals. A single e.p.s.p. can give rise to more than one spike in the multi-spiked type of c.s., and probably to a complete c.s. event. 4. Following spontaneous c.s. the interval to the next s.s. varied from 8 to 600 ms. There was an inverse correlation between duration of the post-c.s. interval and the rate at which s.s. were discharged in the preceding 100 ms. The duration exceeded the mean s.s. interval provided s.s. rate was less than 40--50/s, and the post-c.s. interval would then constitute a real interruption of s.s. discharge. 5. When the superficial radial (s.r.) nerves were stimulated with single shocks too weak to produce a behavioural response changes in discharge pattern were detected in eighty-eight of 151 P cells tested. The initial responses were almost always excitatory and consisted in seventy-two cells of a c.s., in eleven of a c.s. preceded by a brief increase in s.s. and in two cases of a s.s. discharge alone. The spino-olivo-cerebellar paths responsible for the c.s. showed transmission characteristics similar to those reported for animals anaesthetized with barbiturates. 6. C.s. were readily evoked by tapping or squeezing the forepaws. 7. Excitatory responses to nerve stimulation were usually followed by a depression of the tonic s.s. discharge. Its duration ranged widely in different cells (from 10 to 500 ms) and it would coincide with equally variable periods of facilitation previously seen in neurones of nucleus interpositus. It is therefore likely that such facilitations of the cerebellar nuclear cells result at least in part from reductions in the tonic inhibitory input from the P cells. 8. Thirty-six units were classes as 'probable cortical interneurones'. They discharged more regularly, at rates between 9 and 28/s. Twenty such units (56%) responded to s.r. stimulation with a brief excitation not usually followed by any pronounced depression.

Action Potentials↗
PubMed1979

Discharge patterns of Purkinje cells in cats anaesthetized with alpha-chloralose.

1. Micro-electrodes have been used to record from 119 Purkinje (P) cells in the paramedian lobule of the cerebellum in cats anaesthetized with alpha-chloralose. 2. The spontaneous discharge rate and degree of irregularity of the discharge varied very much from one cell to another; the over-all mean rate (about 25/sec) was a little lower than has been reported either for barbiturate anaesthetized or for decerebrate unanaesthetized preparations. 3. Following electrical stimulation of a peripheral nerve, most P cells responded with both simple spikes and a climbing fibre response. This initial response was usually succeeded by a prolonged period of silence (over-all mean duration 350 msec) before resumption of the tonic simple spike discharge. Similar response-silence sequences could also be evoked by mechanical stimulation such as a tap applied to the pads of the forepaw. 4. Electrical stimulation of the inferior olive evoked climbing fibre responses followed by a prolonged pause in the simple spike discharge of the cell. 5. In six individual preparations, recordings were made both from P cells of the paramedian lobule and from neurones of nucleus interpositus (to which the former project). Comparison of the responses of the two types of neurone to peripheral nerve and inferior olivary stimulation showed that the end of the pauses in P cell firing correlated well with the end of a prolonged period of facilitation of the interpositus neurones. 6. These results support the hypothesis advanced in an earlier report (Armstrong, Cogdell & Harvey, 1975) that the prolonged facilitatory responses of interpositus neurones are essentially disinhibitory responses resulting from reduction in the activity of overlying cells, and that responses of P cells and of interpositus neurones consist, in general, of modulations of activity which are mutually out of phase.

Action Potentials↗
PubMed1978

An investigation of the cerebellar cortico-nuclear projections in the rat using an autoradiographic tracing method. I. Projections from the vermis.

The topography of the projections from the vermis of the cerebellar cortex to the intracerebellar nuclei (excluding the vestibular complex) was newly investigated in the rat using an autoradiographic technique. The projection were strictly ipsilateral and the majority terminated in nucleus fastigus although there were small projections to the medial pole of nucleus interpositus. The only portion of fastigius which was never heavily labelled was the dorsolateral protuberance. Some rostrocaudal localisation was evident with lobules II-V projecting to rostral fastigius (Fm), lobules VI-VIII projecting mainly more caudally (Fcm and Fm) and lobule IX projecting to the caudoventral tip of fastigius. Nevertheless, even the densest portions of the terminal fields often overlapped heavily, suggesting that, in the rat, in contrast to some other species, the rostrocaudal localisation is such that individual lobules do not possess private termination fields of any extent. Such an arrangement should provide ample opportunity for integration by individual nuclear neurones of input from extensive areas of cortex. In the mediolateral plane, localisation was more evident, with the medial vermis projecting to the medial pole of fastigius and the lateral portion to lateral fastigus and less heavily to medial interpositus.

Animals↗