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A K McIntyre

Publications and source records attributed to A K McIntyre.

At least 19 recordsLinked to original sources
PubMed1989

Tendon organ afferents in the knee joint nerve of the cat.

This article is concerned with the question of whether some of the slowly adapting responses recorded in the mid-range of joint position from the posterior articular nerve (PAN) of the cat hindlimb and which are therefore candidates for joint position sensors, are in fact coming from muscle receptors of the popliteus muscle. Evidence is provided that in addition to afferents of primary endings of spindles, secondary endings of spindles and tendon organs are represented in PAN as well. Removal of the fleshy part of the popliteus muscle does not reliably remove muscle afferent contamination in PAN.

Afferent Pathways↗
PubMed1989

Responses of electroreceptors in the platypus bill to steady and alternating potentials.

1. This is a report of further observations on the response characteristics of electroreceptors in the bill of the platypus, Ornithorhynchus anatinus, first described by Gregory, Iggo, McIntyre & Proske (1987). 2. The main finding is that, with the bill immersed in water, applying a potential difference between large plate electrodes on either side of the bill, produced detectable responses in a population of electroreceptors to field strengths as low as 4 mV cm-1. Threshold for individual receptors lay between 4 and 25 mV cm-1. 3. An electric dipole placed in the water close to the receptive field could also elicit responses, threshold being lowest when the cathode was near the centre of the field. On several occasions the most sensitive spot was seen, under the microscope, to correspond to the mouth of a mucous sensory gland (Andres & Von Düring, 1984). Response intensity fell when the dipole was moved further away, the drop being less steep in a direction over the top of the bill towards the mid-line. 4. For individual receptors the latency of the first impulse initiated by supramaximal voltage pulses was 1.1-1.8 ms. Latencies tended to be shorter when the site of the receptor lay closer to the recording electrodes. Plotting each latency against conduction path length for eleven receptors gave an approximately linear relation from which was calculated an average axonal conduction velocity of 56 m s-1. The plot yielded an estimate of impulse initiation time of 0.8 ms. It is argued that this is too short to include a synaptic delay. A peripheral synapse is found in all non-mammalian electroreceptors. 5. Electroreceptors responded to both steady and rapidly changing potential gradients. For ramp-shaped gradients of 1-50 V s-1 peak firing rate was approximately proportional to log stimulus velocity. In response to sinusoidal potential changes a 1:1 relation between each afferent impulse and the peak of the stimulating waveform could be obtained over the range 12-300 Hz. Threshold was at its lowest at 50-100 Hz. Tuning curves measured with the bill immersed in water were little different from those obtained by focal stimulation with the bill in air. 6. It is concluded that platypus electroreceptors, supplied by the trigeminal nerve, and which are therefore not part of the acoustico-lateralis system as in non-mammalian electroreceptors, are also unique in not having a peripheral synapse. Furthermore, they are able to respond to both steady and rapidly changing voltage gradients.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1989

Responses of electroreceptors in the snout of the echidna.

1. This is a report of experiments which provide evidence in support of the existence of an electric sense in the echidna, or spiny anteater Tachyglossus aculeatus. It is the first known example of electroreception in a terrestrial animal. 2. In each of four animals anaesthetized with alpha-chloralose, afferent responses were recorded in dissected filaments of the infraorbital branch of the trigeminal nerve which supplies skin of the upper jaw. Recordings were obtained from a total of forty-seven units identified as electroreceptors, by their responses to weak voltage pulses using focal stimulation of the moist skin surface. 3. In the absence of a stimulus, some receptors had an irregular resting discharge; others were silent. The receptive field for each receptor consisted of a discrete spot. Receptive fields were restricted to the tip of the snout. Cathodal stimulation over the receptive spot was excitatory for the duration of an applied voltage pulse. Reversal of stimulus polarity silenced any on-going activity and was followed by a post-anodal rebound excitation. 4. Receptor threshold was best measured not in air but with the snout immersed in tap water. An electric field was applied between a pair of large plate electrodes on either side of the snout. Threshold for thirty receptors lay in the range 1.8-73 mV cm-1. Measurements of response latency and of conduction path length gave estimates of axonal conduction velocities for the afferent fibres of 10-18 m Receptors responded to sinusoidally changing voltage gradients over the range 0.5-200 Hz with a maximum sensitivity at 20 Hz. 5. In one experiment a receptor site was marked with fine pins. Serial sections of the piece of underlying skin revealed a large mucus-secreting gland at the marked spot. Similar glands in skin of the platypus have previously been shown to be the sites of electroreceptors. 6. In a behavioural experiment an echidna was trained to choose between two identical tap water-filled troughs, one of which had a weak electric field across it. The animal learned to detect field strengths down to 1.8 mV cm-1 which corresponded to threshold for the most sensitive receptor measured in a subsequent electro-physiological experiment. It is concluded that the echidna, like the other Australian representative of the monotremes, the platypus, has an electric sense. It remains to be determined what kinds of sources of electric fields the animal encounters in its normal habitat.

Air↗
PubMed1989

Corticofugal action on transmission of group I input from the hindlimb to the pericruciate cortex in the cat.

1. In cats anaesthetized with alpha-chloralose, evidence was sought for a corticofugal action on input from muscle group I afferents projecting to the cerebral cortex via the brain stem relay at nucleus Z. 2. Extracellular recordings were made of responses of thirty-four nucleus Z neurones which could be activated by stimuli at group I strength applied to each of a variety of hindlimb muscle nerves. Afferent input to each nucleus Z neurone was restricted to a single muscle. 3. Nucleus Z neurones typically showed a resting discharge which could be increased or decreased by altering the amount of stretch on the muscle which was the source of the afferent input. Ventral root stimulation gave response patterns which showed these neurones to be driven by input from either tendon organs or muscle spindles, but not both. 4. A brief train of focal, cathodal stimuli applied to a discrete region of pericruciate cortex could consistently inhibit the maintained activity evoked by muscle stretch in nucleus Z neurones, or the response evoked by stimulation of the muscle nerve at group I strength. The inhibition was powerful and lasted 50-400 ms. The effective stimulating site corresponded to area 3a, the main cortical receiving area for hindlimb muscle group I input. 5. Since the ascending spinal axons which project to nucleus Z are collaterals of dorsal spinocerebellar tract fibres, it was possible to stimulate the parent axons at their termination in the anterior lobe of the cerebellum. Cortical stimulation was found to have little or no effect on activity in nucleus Z neurones evoked by cerebellar stimulation over conditioning-test intervals in the range 10-200 ms. 6. It is concluded that over the time intervals for which it has been tested, corticofugal inhibitory action appears to be largely operating at the first spinal segmental relay, in Clarke's column. Thus the inhibitory action arising in area 3a of the cerebral cortex will suppress the action of input from hindlimb group I fibres at the level both of the cerebellum and the cerebral cortex.

Animals↗
PubMed1988

Receptors in the bill of the platypus.

1. Afferent responses were recorded from filaments of the trigeminal nerve in each of two platypuses (Ornithorhynchus anatinus) anaesthetized with alpha-chloralose. All receptive fields were located along the lateral border of the upper bill. Discrete receptive fields could be identified as belonging to two distinct classes of sensory receptor. 2. The most prominent response was an irregular resting discharge which could be increased or decreased by weak electric pulses. These receptors were insensitive to moderately strong mechanical stimulation, and it was concluded that they were electroreceptors. 3. Each electroreceptor had a single spot of maximum sensitivity on the bill surface. When the stimulating electrode over this spot was the cathode it excited the receptor for the duration of the stimulating pulse, using stimulus strengths as low as 20 mV. When it was the anode, it inhibited the discharge. Cathodal excitation was followed by rebound inhibition and anodal inhibition by rebound excitation. 4. Receptors responded to cathodal steps with an initial high-frequency burst of impulses, followed by a lower maintained rate of discharge. Rapidly changing pulses were similarly effective in exciting receptors, adding support to the claim that platypuses are able to detect moving prey by the electrical activity associated with muscle contraction. 5. The centres of the receptive fields of two electroreceptors were marked by the insertion of fine entomological pins. Histological examination established the presence of a large mucus-secreting gland at the marked spot. The epidermal duct of the gland contained an elaborate myelinated innervation, with morphologically distinct axon terminals that we identify as the electroreceptors. 6. As well as electroreceptors, the skin of the bill contained three kinds of mechanoreceptors: slow-adapting receptors, rapidly adapting, vibration-sensitive receptors and receptors with an intermediate adaptation rate. The slowly adapting receptors were characterized by their low threshold to mechanical stimuli, irregular discharge and significant dynamic sensitivity. Vibration receptors showed maintained responses to sinusoidal vibration of the skin up to 600 Hz. 7. These experiments confirm an earlier report that the platypus bill is an electrodetector organ. The presence of electroreceptors of a unique structure and supplied by the trigeminal nerve indicates that electroreception has evolved independently in monotremes. This in turn emphasizes that monotremes are a highly evolved group which split off from the main mammalian stem a long time ago.

Action Potentials↗
PubMed1986

Vibration-evoked responses from lamellated corpuscles in the legs of kangaroos.

A group of lamellated corpuscles are present in the interosseous region of the legs of macropod marsupials. Structurally, they are similar to, but simpler than the Pacinian corpuscles of eutherian mammals, in having fewer lamellae. Responses of mechanoreceptors with axons coursing in the interosseous nerve were recorded from filaments, containing single functional units, dissected from the sciatic nerve of the wallaby Thylogale billardierii. The receptors were all maximally sensitive to stimuli applied in the interosseous region, where the cluster of lamellated corpuscles is located. Most units had low mechanical thresholds and were sensitive to sinusoidal vibration over a wide range of frequencies. Functional properties generally resembled those of eutherian Pacinian corpuscles, but the marsupial receptors were less rapidly adapting. The afferent nerve fibres conducted at 45 to 60 ms-1, while the diameter of axons in the osmium-stained interosseous nerve ranged between 7.5 and 12 micron. It is suggested that one important function of the receptors might be the detection of ground-borne vibration.

Adaptation, Physiological↗
PubMed1985

Pathway to the cerebral cortex for impulses from tendon organs in the cat's hind limb.

In cats anaesthetized with alpha-chloralose, extracellular, recordings were made from neurones lying in nucleus Z. All cells could be excited by electrical stimulation of ipsilateral hind-limb muscle nerves at group I strength. Many cells showed an irregular background discharge. In response to graded contraction of hind-limb muscles, including lateral gastrocnemius, soleus and flexor digitorum longus, cell discharge changed in a manner suggesting that it was driven by input from muscle spindles or from tendon organs. Responses of individual nucleus Z cells were always specific to one kind of receptor and there was no evidence of convergence of afferent impulses from spindles and tendon organs. Nucleus Z neurones excited by muscle group I input could be antidromically driven by stimulation of the contralateral thalamus identifying them as bulbo-thalamic projection neurones. The same cells could be driven trans-synaptically by stimulation of the ipsilateral anterior lobe of the cerebellum. It was possible using a collision test to show that afferent fibres synapsing on nucleus Z cells were collaterals of dorsal spinocerebellar tract cells. It is concluded that nucleus Z is a brain stem relay for afferent information from muscle spindles and tendon organs which is destined for the cerebral cortex.

Action Potentials↗
PubMed1978

Afferent fibres from muscle receptors in the posterior nerve of the cat's knee joint.

The properties of some receptors with afferent fibres in the cat's posterior knee joint nerve have been examined, especially those discharging tonically with the joint in intermediate positions between full flexion and extension. Some of these receptors behave like muscle spindles, and respond to manoeuvres which stretch popliteus muscle. Both in single unit and whole nerve recordings their discharge pauses during a popliteus twitch, and can be strikingly augmented by tetanic stimulation of a number of popliteus fusimotor fibres isolated from ventral root filaments. The action of succinylcholine on these receptors closely resembles its effect on popliteus spindle units with fibres sited normally in the popliteus nerve. Other units with properties suggesting origin from popliteus tendon organs were also observed; their fibres and those of the spindle units conducted at Group I velocity. It is concluded that some afferent fibres from popliteus spindles and possibly tendon organs commonly pursue an aberrant course in the posterior articular nerve of the knee joint.

Afferent Pathways↗
PubMed1976

Long spinal and pyramidal actions on hindlimb motoneurons of the marsupial brush-tailed possum, Trichosurus vulpecula.

The existence of descending propriospinal reflex linkages between forelimbs and hindlimbs has been established in the brush-tailed possum (Trichosurus vulpecula). In animals under chloralose anesthesia and with intact brain stem, forelimb volleys evoked facilitation of flexor and extensor monosynaptic reflexes of both hindlimbs, more pronounced on the ipsilateral side. Powerful inhibition of briefer latency and restricted to ipsilateral flexor digitorum longus (FDL) motoneurons was also brought about by forelimb volleys; at latencies exceeding 20-30 ms, FDL inhibition was usually replaced by facilitation. Distinctness of the two long spinal actions was shown by differences in forelimb receptive fields and in threshold of the executant afferent fibers. The field for reflex inhibition was located distally in the forepaw region, that for facilitation being wider, including deep as well as superficial tissues. Threshold of afferent fibers evoking inhibition was lower than that for facilitation. The descending long spinal actions were compared with those set up by repetitive stimulation of the motor cortex contralateral to the test hindlimb reflexes. In agreement with previous work, strong facilitation of most flexor or extensor motoneurons was produced, including those of quadriceps and ankle flexors, as well as gastrocnemius and hamstring motor nuclei; inhibition consistently appeared only in the FDL motoneuron pool. Weak and inconstant inhibitory action was occasionally observed in other motor pools. Pyramidal tract section abolished the cortical inhibition of FDL, but had little effect on facilitation; both long spinal actions were unchanged. Pyramid-sparing brain stem section greatly reduced both cortical and long spinal facilitatory action, but had little or no effect on FDL inhibition from either source. Interaction experiments demonstrated facilitation of weak inhibitory actions on FDL motoneurons of forelimb and cortical stimulation when elicited together, suggesting a sharing by the two inputs of common interneuronal elements. The observation is consistent with the notion that the long propriospinal system responsible for FDL inhibition from the forepaw might provide the pathway for pyramidal inhibition of the same group of motoneurons.

Animals↗
PubMed1975

Cortical and long spinal actions on lumbosacral motoneurones in the cat.

1. The effects of stimulating forelimb afferents on various ipsilateral motoneurones of the hind limb have been compared with those of volleys set up in the contralateral pericruciate cortex in cats anaesthetized with chloralose. 2. With intact neuraxis, brachial plexus volleys evoke discharge of flexor and extensor motoneurones; short cortical tetani also elicit discharge mainly of flexor motoneurons. After a pyramid-sparing brainstem lesion, little or no firing is evoked by either input. 3. Monosynaptic reflex testing and intracellular recording reveal subthreshold actions on hind-limb motoneurones, inhibition of FDHL and later facilitation of extensors and flexors by forelimb volleys, facilitation of flexors and extensors together with inconstant inhibition of the latter, by cortical stimulation. 4. Interruption of medullary extrapyramidal paths greatly reduces intensity and duration of facilitation from the forelimb, and largely removes cortically evoked extensor facilitation. Inhibition of FDHL from forelimb and cortex is unchanged; cortical volleys continue to facilitate flexors, and have mainly inhibitory action on extensors in these 'pyramidal' preparations. 5. Hyperpolarization of FDHL motoneurones occurs in response to forelimb and cortical volleys, of time course corresponding to depression of test reflexes. Spinal pathways responsible for the two inhibitory actions are independent, and unless each is very strong, their separate actions summate when elicited together. 6. Receptive field for FDHL inhibition from the forelimb is located distally in the forepaw, and its receptors are largely served by cutaneous fibres of low threshold; some Group II fibres in distal muscle nerves also contribute. Receptive field for facilitation embraces the whole limb, and the executant afferent fibres are of higher threshold. 7. Natural stimulation of the forelimb can evoke the long spinal actions, vibration or light pressure on the forepaw eliciting FDHL inhibition, and strong pinching evoking the more general facilitation. Possible functional roles of these actions in the intact animal are discussed.

Animals↗
PubMed1971

Responses of vibration-sensitive receptors in the interosseous region of the duck's hind limb.

1. Responses of receptors with fibres in the interosseous nerve of the duck's leg have been studied by recording unit discharges in filaments dissected from the sciatic nerve.2. Seventy-two of the ninety-four units examined served highly phasic, vibration-sensitive mechanoreceptors in the interosseous region interpreted as being Herbst corpuscles. Receptor types for most of the other units could not be determined, but some were slowly adapting mechanoreceptors.3. Rheobase threshold values for the most sensitive vibration-receptors were similar to those of mammalian Pacinian corpuscles.4. Threshold-frequency relationships for the vibration receptors showed a wider range of low frequency cut-off values, and a greater capacity to signal high frequencies, than is the case with Pacinian corpuscles.5. Fibres of the vibration-receptors had calculated diameters ranging from 5 to 10 mum and account for the bulk of the larger fibres in the interosseous nerve.6. It is suggested that Herbst corpuscles in the legs of birds might act as a warning device by detecting vibratory disturbances of the ground or other supporting surface.

Action Potentials↗
PubMed1971

Memory.

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Animals↗