AFFERENT INNERVATION OF THE MAMMARY GLAND IN PIG

Zbigniew Boratyński¹, Agnieszka Pedrycz², Stanisław Flieger¹, Marcin Wieczorski^2
1 Deaprtment of Animal Anatomy and Histology, Agricultural University of Lublin, Poland
² Department of Histology and Embryology, with Lab of Experimental Cytology, Medical University of Lublin, Poland

ABSTRACT

The experiments were performed on 9 sexually mature pigs in the period of their full lactation. In 6 animals, the subsequent complexes of the mammary gland were removed, leaving the skin untouched. Other 3 pigs constituted the control group of the experiment; as to examine the possible impact of the operational procedures on additional changes in the nerve system. The animals were kept alive for the period of 21 days, subsequently put down and sectioned for the following material: thoracic - lumbar - sacral section of the spinal cord with all spinal ganglia. Such preparations were stained according to Klüver-Barrera’s method and modified Nissel’s method. In the course of experiments conducted, one may say that the source of origin of afferent nerve fibres supplying the mammary gland are the nerve cells from the thoracic and lumbar part of the spinal ganglia.

Key words: afferent innervation, spinal ganglions, mammary gland, pig.

INTRODUCTION

The problem of the localisation of the autonomic nerve centres supplying the mammary gland in domestic animals has been quite popular among the research – workers in regard to its close connection with problems of reproduction and production yield of this gland. Most studies conducted in this matter embraced the problem of nerve supplying routes of such nerves as sympathetic and parasympathetic fibres to various organs in the abdominal and pelvic region. This knowledge would enable more precise description of the nerve fibres impact on the gland and their part in nerve - hormone regulation. It has to be stressed that the problem of afferent innervation of the mammary gland has been considered a minor issue and has not been given much attention while conducting many experiments.

In the recent years, some experiments on the nerve centre localisation (also sensory centres) for reproductive organs in sheep [2, 7, 8, 18], cow [4, 5, 9, 11, 16, 17, 21] and pig [3, 12, 13, 15, 19, 20] as well as for the mammary gland in sheep [6] and cow [10] were conducted. However in literature, available there have been no studies devoted to general examination of the visceral - sensory nerve centres for the mammary gland. The following paper is the third part of the experimental cycle devoted to the localisation of the nerve centres for the mammary gland in pig. The first two papers discussed the problem of the sources of origin of parasympathetic and sympathetic fibres supplying this gland in pig.

MATERIAL AND METHODS

The experiments were performed on 9 sexually mature pigs in the period of their full lactation. In 6 animals, the subsequent complexes of the mammary gland were removed, leaving the skin untouched. The complexes were removed unilaterally in number of 2 or 3 (frontal, medial, posterior). Other 3 pigs constituted the control group of the experiment; as to examine the possible impact of the operational procedures on additional changes in the nerve system. In these control animals control operation was performed, being limited to the incision of the skin covering the gland in the line of removing gland parenchyma in the experimental animals. All procedures were accomplished according to classical surgical methods in general anaesthesia proceeded by tranquiliser premedication.

The animals were kept alive for the period of 21 days, subsequently put down and sectioned for the following material: thoracic – lumbar – sacral section of the spinal cord with all spinal ganglia. The material was fixed in formaldehyde, dehydrated in alcohol, embedded in parrafine and sliced into preparations of 15 µm. Such preparations were stained according to Klüver-Barrera's method and modified Nissel's method.

RESULTS

Degenerative changes occurred in nerve cells as a result of the experimental procedure. The localisation of these lesions allows to state that nervous sensory fibres reaching the mammary gland in pig origin mainly from spinal ganglia.

Experimental Animals

In all pigs examined, degenerative lesions in nerve cells in spinal ganglia and spinal cord were observed.

Degenerated cells were spotted in all spinal ganglia in neuromers Th₄ to S₄. The removal of the two frontal mammary gland complexes resulted in intensification of the retrograde changes in the cells of spinal ganglia of Th₄ – Th₉ (3 – 5 % of all ganglionic cells were degenerated) (photo 1); in case of the removal of the three medial complexes, similar degenerative changes were localised in the ganglia of neuromers Th₇ – L₃ (photo 2 and 3), and in the extirpation of the posterior complexes, the greatest number of retrograde cells was visible in the ganglia from Th₁₃ to L₆ (photo 4). In other sacral spinal cord ganglia (S₁ – S₄) only single degenerated cells occurred.

Photo 1. Degenerated nerve cell of the spinal ganglion Th6

Photo 2. Degenerated nerve cell of the spinal ganglion Th12

Photo 3. Degenerated nerve cell of the spinal ganglion L2

Photo 4. Degenerated nerve cell of the spinal ganglion L5

Degenerative changes were also localised in the region of the spinal cord, in the cells creating nucleus intermediomedialis and nucleus motorius lateralis. Single degenerated cells were spotted in these two centres in the Th₄ to L₆ sections.

All these abnormal cells were characterised by the excentrically placed, cell nucleus shifted to the peripherial region, advanced tigroid chromatolysis of cell cytoplasm and enlarged, edematic body cell. Some number of degenerated gleic cells around the ganglion neurons was observed.

Control Animals

The procedure of skin incision in control pigs caused retrograde changes in the nervous cells of spinal ganglia and in single cells of nucleus intermediomedialis and nucleus motorius lateralis in sections Th₄ to L₆ of the spinal cord.

Degenerated cells were observed in all spinal ganglia in the section Th₄ to S₄. In comparison with experimental pigs, the control group presented only single ganglionic cells of a degenerative character. The intensification and the picture of the retrograde changes in the nervous cells localised in the region of the spinal cord was not different than in the case of the experimental pigs.

DISCUSSION

The comparison of the localisation of the retrograde changes occurring in the neurons of the experimental animals with the changes localised in the control group of pigs undergoing only the operational procedure gave rise to quite precise description of the nerve cells being the source of origin of visceral - sensory nerve fibres reaching the mammary gland in pig (Fig.1).

Fig. 1. Schematic representation of the afferent fibres to the mammary gland in pig

In the course of experiments conducted, one may say that the source of origin of afferent nerve fibres supplying the gland are the cells of spinal ganglia from the fourth thoracic segment to 6th lumbar segment. The view presented above is also repeated by other authors [14].

It should be also noticed that in the recent years the research workers studying autonomic nervous system have been especially interested in the issue of conductivity of supplying routes that run from the lowest levels of organ sensation up to sensory centres in cerebral cortex. All kind of disturbances in normal functioning of internal organs give convincing proofs for the existence of visceral stimuli not only reaching the spinal cord but also the sphere of consciousness.

Afferent innervation of the internal organs, as different publications show it, especially in the human medicine [1], seems to be treated as more important one than the efferent innervation; specifically in connection to all disturbances connected with lesion or paralysis of the structures of this part of autonomic nervous system.

The problem of sensory innervation is most often limited to such ideas as: visceral sensation, visceral pain, afferent visceral conductivity and so on.

From the experiments and studies conducted by the authors, it appears clearly that no other animal but a pig presents the largest range of sensory innervation as compared to sheep [6] or cow [5, 10]. In sheep, the mammary gland is innervated by the spinal ganglia from Th₁₁ to S₁, in cow the number of the ganglia connected with this gland is much higher and goes from Th₇ to S₁, while in pig - it is the greatest – Th₄ – L₆. Such a broad range of sensory innervation is probably the consequence of the size of this gland as compared with other animals.

It should also be noticed that other retrograde lesions observed in the spinal cord in experimental and control group and in spinal ganglia in control animals are the consequence of conducting only the operational procedure of incision of the skin and muscles.

REFERENCES

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Zbigniew Boratyński
Deaprtment of Animal Anatomy and Histology,
Agricultural University of Lublin, Poland
Akademicka 12, 20-934 Lublin, Poland
phone: (+48 81) 445-60-33, 445-60-62
email: zbyszek.boratynski@ar.lublin.pl

Agnieszka Pedrycz
Department of Histology and Embryology,
with Lab of Experimental Cytology,
Medical University of Lublin, Poland
Al. Racławickie 1, 20-059 Lublin, Poland


Stanisław Flieger
Deaprtment of Animal Anatomy and Histology,
Agricultural University of Lublin, Poland
Akademicka 12, 20-950 Lublin, Poland
phone: (+48 81) 445-65-84

Marcin Wieczorski
Department of Histology and Embryology,
with Lab of Experimental Cytology,
Medical University of Lublin, Poland
Al. Racławickie 1, 20-059 Lublin, Poland

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