Neuronal number increase followed by neuronal hypertrophy may be a compensation mechanism for neuronal loss as a result of unilateral remotion of cranial cervical ganglion in sheep

Author(s)

Emerson Ticona Fioretto

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD)
• Defense date: 2006-04-28

Examining board members

Antonio Augusto Coppi Maciel Ribeiro; Júlio César de Carvalho Balieiro; Eduardo Harry Birgel Júnior; Sheila Canevese Rahal; Angelo João Stopiglia

• Advisor: Antonio Augusto Coppi Maciel Ribeiro

Abstract

The sympathetic nervous system is briefly described in veterinary anatomy text-books and there is little information so far concerning its function in large mammal species. The current concept of the structure and function of the sympathetic ganglia is derived from studies on the cranial cervical ganglia (CCG) carried out in laboratory animals due to very attractive characteristics of CCG in these species such as large size, accessibility and multiplicity of target organs. The CCG unilateral ganglionectomy caused a pathological condition associated with Horner´s syndrome which includes anisocoria, enophtalmos, ptosis and increase in the temperature of ear as a result of peripheral vasodilatation. Using stereology-designed methods, we aimed to study CCG neuroplasticity under experimental functional overloading along distinct periods of time. Neuroplasticity was investigated according to morphoquantitative aspects, mostly size and total number of neurons. We wanted to find out whether or not neuron size, numerical density and nerve cell numbers would vary as a result of CCG ganglionectomy. Gross anatomic differences were considered to the increase in the operated ganglia, means of 8%, 3% and 11% for length, width and thickness, respetively in the group I. For group II it was encountered means increases of 4% for length and width and 5% in thickness. Group III showed means values of 29% increase in length, 4% in width and 7% in thickness. Control and operated sheep CCG revealed significant difference (p=0.0001) in the neuronal density (Nv). The operated ganglia revealed reduction in the neuronal density of 89% for group I, 65% for group II and 47% for group III. This reduction in the operated ganglia reflects its inhomogeneous distribution of neurons. An increase in the global neuronal volume was significantly detected (p= 0.0001), the operated ganglia showed increases in the means of 13% for group I, 24% for group II and 29% for group III, suggesting a functional overload response for the unilateral ganglionectomy. The total number of neurons presented significant differences (p = 0.0514) and two distinct effects in the operated ganglia. In the group I, an increase of 3% was encountered meanwhile reduction in the total number was associated to groups II (8%) and group III (20%). An overlook of the results suggests two consecutive and associated hypotheses: 1) the hypertrophy of neurons would be associated to a compensatory mechanism for contralateral re-innervation although the functional overload would drive these neurons to cellular death, followed by hypertrophy of non-neuronal tissue as reflected in the neuronal density; 2) the neuronal hypertrophy would be associated to a compensatory mechanism to cellular death caused by the functional overload The main quantitative changes in the remaining ganglia are: Significant loss in the total number of neurons from the 8th week of evoloution of the disease; Significant decrease in the numerical density (Nv) from the 8th week and significant increase in both neuron area and neuron volume. (AU)