The innervation of the coypu foot pads (digital, metacarpal and metatarsal) is represented by an autonomic and a sensitive components.

The former is constituted by isolated or grouped ganglion cells located along the course of nerve bundles, while the latter is composed by free and encapsulated nerve endings morphologically classified as Pacini, Pacini-like and Golgi-Mazzoni corpuscles.

The above named corpuscles show the typical structure and can be found isolated or grouped to organize simple and complex flower-sprays, opposite-polar corpuscles and poikilomorphous fibres.

The AA. notice the morphological variability of the encapsulated receptors found in this and previous similar investigations but point out also that they are functionally

mechanoreceptors and so compatible with the role of the considered anatomical

district

Acone, Franca

Botti, Maddalena

Dessole, Angelo Antonio

Gazza, Ferdinando

Palmieri, Giovanni

Panu, Rino

Ragionieri, Luisa

UnissResearch

79
Ann. Fac. Medic. Vet. di Parma (Vol. XXVI, 2006) pag. 79 - pag. 90
ON THE AUTONOMIC AND SENSITIVE NERVOUS COM-
PONENTS OF DIGITAL, METACARPAL AND METATARSAL 
PADS OF THE COYPU (MYOCASTOR COYPUS)
 
SULLA COMPONENTE NERVOSA AUTONOMA
E SENSITIVA DEI TORI DIGITALI, METACARPALI
E METATARSALI NELLA NUTRIA (MYOCASTOR COYPUS)
Ferdinando Gazza*, Maddalena Botti*, Luisa Ragionieri*, Angelo Antonio Dessole**,
Rino Panu*, Giovanni Palmieri**, Franca Acone**
PAROLE CHIAVE:
nutria, tori, innervazione autonoma e sensitiva.
KEY WORDS:
coypu, foot pads, autonomic and sensitive innervation.
Riassunto
L’innervazione dei tori digitali, metacarpali e metatarsali della nutria è for-
mata da una componente autonoma e da una sensitiva.
La prima è costituita da cellule gangliari, isolate o raggruppate, situate lun-
go il decorso di fasci nervosi, mentre la seconda è formata da terminazioni libere e 
capsulate classificabili, dal punto di vista morfologico, come corpuscoli di Pacini, 
paciniformi e Golgi-Mazzoni.
I menzionati corpuscoli mostrano struttura tipica e si possono rinvenire iso-
lati, riuniti a costituire infiorescenze semplici e complesse, corpuscoli opposito-po-
lari e fibre pecilomorfe.
Gli AA. rilevano la variabilità morfologica delle forme recettoriali, rinve-
nute in questa ed in analoghe precedenti ricerche, ma puntualizzano che sono tutte, 
funzionalmente, meccanocettori e quindi compatibili con l’impegno richiesto al di-
stretto anatomico in esame.
Summary
The innervation of the coypu foot pads (digital, metacarpal and metatarsal) 
is represented by an autonomic and a sensitive components.
*Dept. of Animal Health, University of Parma, Parma, Italy.
Via del Taglio, 8 - 43100 Parma - Tel. 0521/032647 - Fax 0521/032642
e-mail: ferdinando.gazza@unipr.it
**Dept. of Animal Biology, University of Sassari, Sassari, Italy.
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Ann. Fac. Medic. Vet. di Parma (Vol. XXVI, 2006) pag. 79 - pag. 90
The former is constituted by isolated or grouped ganglion cells located along 
the course of nerve bundles, while the latter is composed by free and encapsulated 
nerve endings morphologically classified as Pacini, Pacini-like and Golgi-Mazzoni 
corpuscles.
The above named corpuscles show the typical structure and can be found 
isolated or grouped to organize simple and complex flower-sprays, opposite-polar 
corpuscles and poikilomorphous fibres.
The AA. notice the morphological variability of the encapsulated receptors 
found in this and previous similar investigations but point out also that they are func-
tionally mechanoreceptors and so compatible with the role of the considered ana-
tomical district.
Introduction
In the support surface of the limbs of different animal species there are par-
ticular formations (footpads, tori) that have the role to absorb the pressure that unload 
on the ground.
Independently by their topography along the digital axis (digital pads) or 
distally to the metacarpo-metatarso-phalangeal joints (metacarpal and metatarsal 
pads), these formations are always covered by skin characterized by thick corneous 
coat that protects a remarkable fibro-elastic component. This last component is often 
characterized by remarkable adipose tissue that has a mechanical and not deposit 
function. In the thickness of the fibro-elastic component the vascular and nervous 
nets are often present.
Probably the nervous net has the role to collect the information about the ground 
characteristics (sandy, stony, uneven, etc) to adjust the limb position and the walk.
The importance of these structures in some animal species, in particular from a me-
chanical point of view, explains why the innervation of the pads are often studied (1-24).
The aim of the present research was to study the autonomic and sensitive 
innervation of the digital, metacarpal and metatarsal pads in the coypu (Myocastor 
coypus, fig. 1) that has never been studied.
Figure 1:
Coypu (Myocastor coypus).
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Ann. Fac. Medic. Vet. di Parma (Vol. XXVI, 2006) pag. 79 - pag. 90
Materials and methods
The study was carried out on samples taken from 3, 18-24 months old, coy-
pus, that were sacrificed with an euthanasic medicine (Tanax®, Hoechst).
From each subject, immediately after the death, the digital, metacarpal and 
metatarsal pads were taken. The samples of same limb and of thoracic and pelvic 
limb were keep distinct (fig. 2). Moreover in the samples made in the metacarpal and 
metatarsal pads, the peripheral area was keep distinct from the central area.
The material taken from one subject was processed with the original gold 
chloride technique according to Ruffini (25). The other samples were processed with 
the aforesaid method modified by Goglia (26).
Figure 2:
Coypu: topography of foodpads in the thoracic limb (TL) and pelvic limb (PL) of the coypu (Myocastor 
coypus).
Results
The observations have documented a conspicuous nervous component rep-
resented by trunks with different diameter, distributed near the blood vessels (fig. 3). 
The finding was more conspicuous in metacarpal and metatarsal pads in respect to 
the digital ones. Always we did not found significant differences between the thoracic 
and pelvic limb.
We also observed an autonomic innervation represented by ganglion cells 
with spherical or ellipsoidal shape (diameter ranging between 7,3 and 23,7 μm). These 
cells were isolated or clustered to constitute little ganglia (9-84 cells) without the cap-
sule. The autonomic cells were located along the nervous trunks. Rarely they were 
found in the epineurium and in the convergence point of 2 or more trunks (fig. 4).
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Ann. Fac. Medic. Vet. di Parma (Vol. XXVI, 2006) pag. 79 - pag. 90
Figure 3:
Coypu: metacarpal pad. The nervous trunk run near the blood vessel. Gold chloride method according to 
Ruffini. 120x.
Figure 4:
Coypu: metatarsal pad. A little ganglion located in the confluence point of more nervous trunks. Gold 
chloride method according to Ruffini. 120x.
Isolated fibres departed from the nervous trunks. These fibres had different 
diameter and terminated in different ways. In fact the most thin fibres drew fine vo-
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Ann. Fac. Medic. Vet. di Parma (Vol. XXVI, 2006) pag. 79 - pag. 90
lutes with different ampleness (fig. 5) and interlacing gave origin to complicated nets. 
Differently, the most thick fibres finished in corpuscles that were morphologically 
referable to Pacini (fig. 6, A-C), Pacini-like (fig. 7), and Golgi-Mazzoni (fig. 8, A, B). 
The Pacini represented the most numerous corpuscles, while the Golgi-Mazzoni the 
most scarce.
Figure 5:
Coypu: metatarsal pad. The picture shows the close relationship between blood vessels and nervous trunks. 
The arrows indicate thin nervous fibres terminate in free nerve endings. Gold chloride method according 
to Ruffini modified by Goglia. 120x.
  
Figure 6 A-C:
Coypu: metacarpal (A), metatarsal (B, C) pads. The pictures show Pacini corpuscles with different mor-
phology and aspect. The lamellar organization of the capsule and the manner of the expansional axon are 
fairly clear. Gold chloride method according to Ruffini. 250x (A), 120x (B,C).
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Ann. Fac. Medic. Vet. di Parma (Vol. XXVI, 2006) pag. 79 - pag. 90
Figure 7: Coypu: metacarpal pad. Isolated Pacini-like corpuscle. Gold chloride method according to Ruf-
fini modified by Goglia. 120x.
 
Figure 8 A, B: Coypu: metatarsal pad. Isolated Golgi-Mazzoni corpuscles. Gold chloride method accor-
ding to Ruffini modified by Goglia. 250x.
Therefore, in the studied area we found not only the autonomic nervous com-
ponent but also a sensitive contingent, represented by free and encapsulated endings. 
The obtained data documented that the nervous component, in particular the sensitive 
ones, was more represented into the metatarsal pads than the metacarpal ones and in 
these last more than digital pads of the same limb. Moreover, the sensitive component 
was generally located in the more superficial layer in respect to the autonomic ones.
The different corpuscles, in particular the Pacinian, were isolated or grouped 
(4-5 corpuscles) into simple (fig. 9, A, B) and complex (fig. 10) flower-sprays or they 
were located one after another along the same nervous fibre to constitute opposite-
polar corpuscles (fig. 11, A, B).
The corpuscles had typical structure, even if the Pacinian with ellipsoidal 
shape could have rectilinear aspect or be curved. The capsule had remarkable thick-
ness and showed a lamellar arrangement. The expansional axon was thick, undivided 
or branched, it showed the same behaviour of capsule and only rarely finished with 
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Ann. Fac. Medic. Vet. di Parma (Vol. XXVI, 2006) pag. 79 - pag. 90
the typical end button. When the axon branched, the branches terminated with a little 
button (fig. 6, C).
We also observed the Pacini-like corpuscles even if they were less numer-
ous. These corpuscles were characterized with a greater length, thinner capsule and 
thinner expansional axon in respect to Pacini.
The Golgi-Mazzoni corpuscles had a thick capsule that showed the lamellar 
arrangement. They had spherical and ellipsoidal shape and the connective of the in-
ner core marked the course of the expansional axon (fig. 8, A, B).
A last finding was represented by poikilomorphous fibres. They dichotomical-
ly divided into 2 branches that ended in morphologically different corpuscles (fig. 12).
        
Figure 9 A, B: Coypu: metacarpal (A) and metatarsal (B) pads. Simple flowers-spray of Pacini corpuscles. 
Gold chloride method according to Ruffini. 40x (A); 120x (B).
Figure 10: Coypu: metacarpal pad. Complex flowers-spray of Pacini corpuscles. Gold chloride method 
according to Ruffini. 40x.
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Ann. Fac. Medic. Vet. di Parma (Vol. XXVI, 2006) pag. 79 - pag. 90
          
Figure 11 A, B: Coypu: metacarpal (A) and metatarsal (B) pads. The pictures show 2 opposite-polar 
Pacini corpuscles. The nervous fibre comes out (arrow, B) from corpuscle and sustains another corpuscle 
that yet disconnected during the isolation. Gold chloride method according to Ruffini modified by Goglia. 
120x (A), 250x (B).
Figure 12: Coypu: metatarsal pad. Poikilomorphous fibre. It divides into 2 branches that innervate 2 cor-
puscles, morphologically different (Pacini corpuscles on the right, Pacini-like on the left). Gold chloride 
method according to Ruffini. 70x
Discussion
The presence of an autonomic and sensitive innervation was documented in 
the digital, metacarpal and metatarsal pads of the coypu, in accordance with that has 
been already reported (8-9, 13, 15, 17-19, 21-24). Both the component and in particu-
lar the autonomic ones, were near the blood vessels and sweat glands as it has been 
already documented in other anatomic districts (24, 27-32).
The sensitive innervation was represented by the presence of receptors (Pa-
cini, Pacini-like and Golgi-Mazzoni). These corpuscles show the typical structure 
and can be found isolated or grouped to organize simple and complex flower-sprays, 
opposite-polar corpuscles and poikilomorphous fibres. They were analogous in the 
thoracic and pelvic limb. Instead we found numerical differences between the recep-
tors of the metatarsal pad (more numerous) and the metacarpal ones. This finding 
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Ann. Fac. Medic. Vet. di Parma (Vol. XXVI, 2006) pag. 79 - pag. 90
could be due to the different involvement of the limbs in the “station” and in the 
“movement” of the animals studied. In fact, both the pads are surely involved in the 
support phase, but the metatarsal pads are also involved into the propulsive push of 
the step. The sensitive nervous component was more conspicuous and located super-
ficially that autonomic ones. In the past, in the pads of human foetuses (13) and in 
the pads of different mammals species (dog, cat, horse, pig, goat, buffalo, mouse, rat, 
guinea-pig, opossum) the encapsulated receptors have been documented (3-4, 7, 9, 
15, 17, 19, 21-23) but non like that we found. In fact the aforesaid authors have been 
documented, as a more frequent finding, the Pacini corpuscles and then Golgi-Maz-
zoni, Pacini-like, Meissner and Ruffini corpuscles.
The Golgi-Mazzoni corpuscles have not been documented by all the afore-
said researchers. In fact these last receptors have been documented in the cat, pig, 
rat, guinea-pig, and goat (9, 17-19) and have not been documented by Goglia (3-4) 
in the dog, cat and buffalo, by Giordano and Rosati (6) in the sheep and by Rosati (7) 
in the horse. In particular, Giordano and Rosati (6) and Rosati (7) have documented, 
respectively in the pads of sheep and horse, the corpuscles with intermediate charac-
teristics between the Pacini and Golgi-Mazzoni, but they have excluded the presence 
of the last ones.
We think that an accurate structural analysis allow to define if a corpuscle is 
a Pacini or Golgi-Mazzoni. Therefore, if it is not possible, the Golgi-Mazzoni corpus-
cles should defined as Pacinian-like.
Finally, we also found the poikilomorphous fibres. They are dicotomically 
branching fibres that terminate with morphologically different corpuscles. Also about 
these findings, there is not unanimity. In fact some authors refuse the presence of 
these fibres in the pads of the sheep (6), horse (7), rat and guinea-pig (18). Differently 
other authors admit the presence of these fibres in the pig (17) and in the goat (19).
In conclusion, we could highlight the casualness of some findings, as the 
presence of Meissner and Ruffini corpuscles, and the presence of corpuscles morpho-
logically different. Moreover, we could affirm that, in the studied pads, the structural 
organization of the corpuscle is not so important as their functional role. Therefore, 
as all the receptors observed are the mechanoreceptors, we think that they perfectly 
correspond to the role that they have in the digital, metacarpal and metatarsal pads in 
the dynamic function of the limb.
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On the autonomic and sensitive nervous components of digital, metacarpal and metatarsal pads of the coypu (<i>Myocastor coypus</i>)

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