III. MARCO TEÓRICO 25
2. CONDUCTA ADICTIVA 31
2.3. LOS PROCESOS DE TOLERANCIA, DEPENDENCIA Y ABSTINENCIA 34
Cortisol is an accepted index of distress seen in a variety of animal species.
Cortisol levels may increase to adverse stimuli, but also to what may be considered innocuous or pleasant stimuli.
Cortisol assays are tedious and time consuming.
Opportunities:
Cortisol may serve as a standard by which other indicesmay be compared.
Problems:
There is potential for over-interpretation orinappropriate interpretation of cortisol data.
Plasma cortisol is a commonly used index of distress in both humans and animals, and many investigators identify increased secretion of
corticosteroids as proof for the presence of noxious stimuli. However, cortisol rises are also observed h{situations considered innocuous, e.g., courtship, mating and active food consumption (Broom, 1988). Because cortisol responds to a variety of stimuli, both aversive and advantageous, some (Rushen, 1 986) sug
g
est that plasma cortisol is a poor index by which to assess animal suffering or distress. Difficulties in interpreting themeaning of cortisol responses to various stimuli often arise when the context of the circumstances is insufficiently defined. For example, cortisol levels in cattle accustomed to handling and bleeding differ from cattle which are not (Herd, 1 989), cattle being herded show an affiliated rise in cortisol (Hattingh et al., 1 980), and bulls loose-housed on slatted floors have cortisol levels greater than when they are housed on straw (Schlichting et al., 1 983). It is important to realise that cortisol levels are
situation on a single occasion, and failure to realise this often leads to cortisol being discredited as a valid index of distress. The design of this study with its consistent implementation of the nine treatments allowed confmnation of cortisol as a valid index for pain-induced distress with ovariohysterectomy. Although physiological indices such as neuronal action potentials were not recorded within this study so as to confrrm that the rise in cortisol during surgery in the unconscious bitch was attributable to the noxious stimuli of the surgery itself, this conclusion stands strongly on the collective fmdings from different treatments that exclude other explanations.
The adrenal cortex evolved in animals to assist their coping with various stimuli, and an adrenal cortical response is D.Q1 necessarily evidence of the harmful effect of a stimulus or an indication that the animal is
experiencing a loss of well-being. Before any biological end point can be used to validate distress, it must be established that a distress-induced change in that measurement is correlated with a meaningful change in the animal's well-being. Behavioural change offers additional insight, if not possible substitution, for appraisal of an animal's well-being.
In �s study the response of plasma cortisol to the pain-induced distress from surgery of ovariohysterectomy was quite
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arked, and the effect of butorphanol on this response was significant. However, elevations of plasma cortisol were also noted attributable to other factors which were not considered to compromise the animals' well-being. For the Analgesia alone group elevations of plasma cortisol were attributed to dysphoric side-effects of the butorphanol. Elevation of plasma cortisol in the groups receiving both analgesic and anaesthetic was suggested to result from the animals' inability to express restlessness due' to the sedative effects of the butorphanol. Support for this proposal comes from the.$ork cited by Dantzer ( 1 989), who notes that when confronted with an aversive stimulant, the animal's degree of behavioural control is a major determinant of the behavioural and physiological impact of the stimulation.Behaviour as an Indicator of Distress
A summarising analysis of behaviour as an index of distress might look as follows:
Strengths:
When validated for repeated reliability, behaviours offer a 'real time' index for assessing responses to distress.Weaknesses:
Behaviour as an index of distress is presentlyunderdeveloped for interpretative use.
Great variability exists in behavioural responses among species as well as individuals.
Opportunities:
Animal handlers who become trained to identifybehaviours specific for pain-induced distress as they are presently understood would likely further
develop this index.
Problems:
Behavioural responses to distress from one species canbe unjustifiably attributed to another, or from one individual to another.
The value of behaviour as an index of distress has limitations similar to those for cortisol. It is not known if behaviours in animals respond
linearly to pain-induced distress, and to the degree of noxious stimulus, or with an on-off behavioural response after reaching a given threshold of distress. The latter may confer advantages, e.g. it is counter-productive for animals of prey to change behaviour which would inhibit concealment or flight. In dogs there may be no social advantage within their pack from displaying pain-induced distress. Many behavioural responses in the pet Canis are likely learned responses directed to the pet's owner. A study might best select for learned behavioural responses by selecting pet bitches for all treatments, however in this study there was approximately equal
representation of pet and non-pet bitches.
The ovariohysterectomy model has merit as a base for comparing insult severity to pain-induced distress, because the procedure is usually
uncomplicated, is performed with few variations from veterinarian to veterinarian (although level of surgical skill may differ), and is seldom performed under the influence of multiple interacting drug regimen, e.g., balanced anaesthesia together with balanced analgesia. Exploring the
proposal that behavioural changes are proportional to insult severity would require comparing data from a study such as this to results from other treatments involving procedures presumed to be more painful, e.g� thoracotomies and fractures. The latter could not be performed uniformly because techniques vary widely depending upon individual presentation of the case and many such patients are given a variety of therapeutic drugs, the interaction between which is seldom known. Even within our tightly controlled study it was difficult to specifically identify the influences on behaviour of anaesthesia or differentiate the sedation from the analgesic behavioural effects of butorphanol.
The conduct of this study identifies a very important point regarding clinical trials. Structured investigations of the more painful procedures mentioned above are never likely to be performed because of ethical constraints and prohibitive costs. The only acceptable opportunity to collect such data is through carefully designed prospective clinical trials. Accordingly, it is recommended that clinical research should be a major commitment of academic veterinarians and their institutions of
employment.
Association Between Cortisol and Behaviours
Several studies of laboratory animals have established a relationship between circulating corticosteroid levels and frequency of particular classes of behavioural responses (Leshner, 197.8). In the present study the restricted number of behavioural data points (4) made statistical analysis of associations between change in plasma cortisol concentrations and behavioural frequency impractical. An attempt to do so revealed no significant correlations, but on the basis of changes in cortisol
concentrations that were significant and the change in frequency of
particular behaviours that were significant, six classes of association have been identified (Tables 6. 1 and 6.2): surgical treatments, 1 ) decreasing cortisol concentration I increasing behaviour frequency, 2) decreasing cortisol concentration I decreasing behaviour frequency, 3) high cortisol concentration I high behaviour frequency, 4) unchanging cortisol
concentration I unchanging behaviour frequency; nonsurgical treatments,
5) corresponding cortisol concentration and behaviour frequency, and 6)