Connexions between hair follicle afferent fibres and spinocervical tract neurones in the cat: the synthesis of receptive fields.

1. The morphology and somatotopic organization of the spinal arborizations of identified A beta-hair follicle afferent fibers (HFAs) with receptive fields (RFs) on the digits have been investigated in the cat by the use of intraaxonal injection of the tracer n-(2 aminoethyl) biotinamide. 2. In three cats, the long-ranging projections of six HFAs were examined by selectively injecting afferents with RFs on digit 2, 4, or 5, directly over the digit 3 representation, and examining their collateral morphology in transverse sections of the spinal cord. The rostral and caudal boundaries of the digit 3 representation were determined by mapping the RFs of identified spinocervical tract (SCT) neurons. 3. In two more cats, three HFAs were injected at random rostrocaudal positions and their morphology was examined in parasagittal sections. In one animal (2 HFAs), the somatotopy of the digit representation was again determined by mapping the RFs of SCT neurons. In the remaining cat (1 HFA), the somatotopy of the dorsal horn was mapped from the RFs of unidentified dorsal horn neurons. 4. Hair follicle afferents emitted many more collaterals, over much greater rostrocaudal distances, than indicated by previous horseradish peroxidase studies, and all collaterals gave rise to synaptic boutons. 5. HFAs that have RFs confined to a small part of a digit give rise to bouton-bearing axonal branches throughout the entire rostrocaudal extent of the hindpaw representation.

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Morphology of A beta hair follicle afferent collaterals in dorsal horn of cats with neonatal chronic denervation of digits

Journal of Neurophysiology ◽

10.1152/jn.1993.70.6.2399 ◽

1993 ◽

Vol 70 (6) ◽

pp. 2399-2410

Author(s):

P. Wilson ◽

P. J. Snow

Keyword(s):

Hair Follicle ◽

Dorsal Horn ◽

Distal Part ◽

Receptive Fields ◽

Morphological Plasticity ◽

Collateral Sprouting ◽

Large Numbers ◽

Chronic Denervation ◽

Adult Cat ◽

Neonatal Denervation

1. The effect of neonatal denervation of two adjacent hindpaw digits (digits 3 and 4) in the cat on the morphology of spinal collaterals of identified A beta hair follicle afferents (HFAs) with receptive fields (RFs) on the neighbouring digits has been investigated using intra-axonal injection of horseradish peroxidase. 2. The morphology of collaterals of HFAs innervating intact digits (digit 2 or digit 5) was examined within the neonatally and chronically deprived region of dorsal horn by selectively injecting the afferents directly over this region. 3. Of a total of nine injected axons, seven had RFs on the distal part of digit 2, whereas two had RFs on the distal part of digit 5. With the exception of one of the digit 5 afferents, all injected afferents gave rise to stained collaterals throughout the chronically deprived digit representation. 4. Many collaterals within the chronically deprived region of dorsal horn gave rise to arborizations having relatively large numbers of boutons when compared with previously described somatotopically inappropriate (SIA) collaterals in the normal adult cat. 5. It is suggested that neonatal denervation of digits in the cat may lead to collateral sprouting and bouton formation by SIA collaterals of A beta HFAs innervating adjacent intact digits. This morphological plasticity could explain the previously reported functional reorganization of the RFs of spinocervical tract neurons that occurs in these neonatally deafferented animals.

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Behavior of cutaneous mechanoreceptors recorded in mandibular division of Gasserian ganglion of the rabbit during movements of lower jaw

Journal of Neurophysiology ◽

10.1152/jn.1982.47.2.151 ◽

1982 ◽

Vol 47 (2) ◽

pp. 151-166 ◽

Cited By ~ 29

Author(s):

K. Appenteng ◽

J. P. Lund ◽

J. J. Seguin

Keyword(s):

Hair Follicle ◽

Activity Patterns ◽

Receptive Fields ◽

Firing Frequency ◽

Gasserian Ganglion ◽

Afferent Activity ◽

Cutaneous Mechanoreceptors ◽

Lower Jaw ◽

Movement Parameters ◽

Anterior Posterior

1. The activity of cutaneous mechanoreceptors was recorded extracellularly in the mandibular division of the Gasserian ganglion of hemidecerebrate anesthetized rabbits. Fifty-four hair follicle afferents and 80 skin mechanoreceptor afferents were functionally identified. Their receptive-field characteristics were described and their activity patterns were recorded while the jaw was displaced by hand in the vertical, horizontal, and anterior-posterior directions, and during masticatory movements. 2. All hair follicle afferents were classified as rapidly adapting, whereas skin afferents could be divided into two categories: rapidly adapting and slowly adapting. Rapidly and slowly adapting receptors were found in all regions of the mandibular skin. Only one hair follicle afferent and four skin afferents fired spontaneously with the jaw at rest. 3. Fifty-eight percent (29/50) of the hair follicle afferents were activated by imposed displacement of the jaw and all of these tested also discharged during chewing. They were sensitive to movement in all three axes and their firing frequency was linearly related to the velocity, regardless of direction. 4. Only 10% (8/80) of the skin afferents were activated by imposed displacement of the jaw if their receptive fields were not directly contacted. Firing frequency was not well related to either the amplitude or velocity of movement. During chewing, the discharge frequency was variable but, in general, firing was restricted to the jaw-closing phase. Most skin afferents that were active during jaw movement had receptive fields close to the corner of the mouth. 5. The results are discussed within the context of a possible involvement of cutaneous afferents in kinesthesia and in the control of jaw movements. Hair afferents could make specific contributions to the appreciation of movement because their discharge pattern was clearly related to one of its parameters. The lack of activity of most skin afferents, as well as the absence of a strong correlation between the firing frequency of those that were active and the movement parameters, suggest that they do not make specific contributions to the awareness of movement. 6. Hair and skin afferents may also make different contributions to the control of ongoing movements. It is suggested that skin afferent activity during jaw closure may elicit a reflex reduction in the velocity or duration of this phase. Some evidence from other studies suggests that hair afferent activity may indirectly influence movement via effects on elevator fusimotor neurons.

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Ultrastructure of developing visual cortical synapses in the cat superior colliculus

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100085083 ◽

1991 ◽

Vol 49 ◽

pp. 156-157

Author(s):

Caroline A. Miller ◽

Laura L. Bruce

Keyword(s):

Superior Colliculus ◽

Phosphate Buffer ◽

Receptive Fields ◽

Visual Cortical Area ◽

Cortical Synapses ◽

Visual Cortical ◽

And Function ◽

Phosphate Buffered Saline ◽

The Brain ◽

Cat Superior Colliculus

The first visual cortical axons arrive in the cat superior colliculus by the time of birth. Adultlike receptive fields develop slowly over several weeks following birth. The developing cortical axons go through a sequence of changes before acquiring their adultlike morphology and function. To determine how these axons interact with neurons in the colliculus, cortico-collicular axons were labeled with biocytin (an anterograde neuronal tracer) and studied with electron microscopy.Deeply anesthetized animals received 200-500 nl injections of biocytin (Sigma; 5% in phosphate buffer) in the lateral suprasylvian visual cortical area. After a 24 hr survival time, the animals were deeply anesthetized and perfused with 0.9% phosphate buffered saline followed by fixation with a solution of 1.25% glutaraldehyde and 1.0% paraformaldehyde in 0.1M phosphate buffer. The brain was sectioned transversely on a vibratome at 50 μm. The tissue was processed immediately to visualize the biocytin.

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