Biomedical Engineering Reference
In-Depth Information
when rhesus monkeys were moved to a slightly larger cage
(
Bayne and McCully, 1989
).
In contrast, larger changes in cage size (placing animals
in pens) were reported to reduce whole-body motor
stereotypies (
Draper and Bernstein, 1963; Paulk et al.,
1977
) and SIB (
Fontenot et al., 2006b
). Unfortunately,
however, the change in cage size was confounded with
relocation in all of these studies. For example, in the case of
Fontenot et al. (2006b)
, monkeys were moved individually
from small indoor cages to large outdoor pens. In one study
in which relocation did not occur, abnormal behavior was
not substantially reduced by moving monkeys from indi-
vidual cages to larger pens (
Kaufman et al., 2004
). This
finding suggests that other aspects of environmental quality
(e.g. being outdoors instead of indoors) may be as or more
important than cage size in determining the incidence of
abnormal behavior.
with inanimate objects, although beneficial, is not a one-
size-fits-all means to reducing abnormal behavior.
Different pathologies must be targeted with different
enrichment therapies and no single enrichment technique
will ameliorate all conditions.
Novak and associates (1998)
demonstrated that exposure to puzzle feeders led to short-
term decreases in locomotor stereotypies in rhesus
monkeys but did not have any impact on self-directed
biting. The effect on locomotor stereotypies was present
only during the period of time that monkeys worked to
extract food items. Thus, certain abnormal behaviors may
only be reduced during the period in which the enrichment
device is available and in use whereas other abnormal
behaviors may persist even in the presence of inanimate
enrichment. Furthermore, animals may quickly habituate to
various
forms of enrichment,
thereby limiting their
effectiveness.
Pharmacological Interventions
Pharmacotherapy is generally a treatment of last resort in
research facilities because of the impact of psychoactive
drugs on various neurochemical and physiological systems
and the potential for disrupting and invalidating research
outcomes. Seldom has pharmacotherapy been used to treat
stereotypic behavior. However, in one study, the adminis-
tration of fluoxetine, a selective serotonin reuptake inhib-
itor (SSRI), was associated with significant decreases in
self-directed stereotypies (e.g. saluting, somersaulting,
weaving, and head tossing) in a group of vervet monkeys
(
Hugo et al., 2003
).
In general, pharmacotherapy has more typically been
employed to treat severe cases of abnormal behavior,
e.g. self-wounding monkeys (
Tiefenbacher et al., 2005
).
Various studies (mostly in macaques) have reported
reductions in SIB following treatment with the serotonin
precursor
L
-tryptophan (
Weld et al., 1998; Watson et al.,
2009
), the SSRI fluoxetine (
Fontenot et al., 2006a
), the
alpha-2 adrenergic agonist guanfacine (
Macy et al., 2000
),
and the antiandrogen cyproterone acetate (
Eaton et al.,
1999
). However, none of these treatments have yet been
explored with respect to their long-term efficacy in main-
taining low levels of SIB beyond the period of drug
administration.
Furthermore, a recent study suggests that there may be
different subtypes of SIB that respond differentially to
various pharmacological agents. Treatment with the anxi-
olytic benzodiazepine diazepam resulted in a bimodal
response such that half of the rhesus monkeys improved
with diazepam treatment whereas the remaining subjects
either showed no response or paradoxically got worse
(
Tiefenbacher et al., 2005
). A subsequent study by
Major
et al. (2009)
provided support for the subtype hypothesis.
Rhesus monkeys treated with the anxiogenic compound
Environmental Enrichment
Enriching the environment of captive primates is mandated
by the Animal Welfare Act and is touted as a means to
increase the occurrence of species-typical behaviors and
decrease abnormal behavior. Although there is very strong
evidence to support the view that enrichment increases
species-typical behavior (see Chapter 6), its efficacy as
a therapeutic intervention is less clear, in part, because
there are wide individual differences in response to envi-
ronmental enrichment (
Lutz and Novak, 2005
). In some
monkeys, rubber toys reduce the incidence of self-biting
through a redirection of biting to an object (
Anderson and
Stoppa, 1991
). Foraging/grooming boards have been shown
to decrease hair pulling behavior and locomotor stereoty-
pies in some monkeys (
Bayne et al., 1991, 1993
) and to
reduce hair pulling behavior and regurgitation in chim-
panzees (
Bloomsmith et al., 1988
). Furthermore, Bourgeois
and Brent (2005) reported that a combination of feeding
and physical enrichment led to reductions in partial-body
stereotypy (e.g. head tossing and stereotypic digit move-
ment) and SIB in a colony of baboons.
Despite the positive effects described above, other
studies suggest that environmental enrichment has rela-
tively little effect on abnormal behavior. In one study,
neither physical enhancements to the cage environment
(e.g. perches, toys, and mirrors) nor feeding enrichment
(e.g. foraging boards, frozen juice, and puzzle feeders) had
any impact on the frequency of abnormal behaviors in
rhesus monkeys (
Schapiro and Bloomsmith, 1995
). Similar
failures were noted by
Line and Morgan (1991)
with
monkeys given sticks and balls and by
Runeson and
colleagues (2011)
examining paint rollers as an interven-
tion for hair pulling in pigtailed macaques.
The contrasting studies presented in this section are
intended to demonstrate that environmental enrichment
