Journals from University of Tartu

The nude mouse is ham without a thymus.In most vertebrates the thymus constitutes a vital part of the immune system. If the thymus is surgically removed from adult mice, no immediate changes can be observed in immune responses, - even if present day refined laboratory techniques can demonstrate alterations in the function of lymfjhocytes of such animals. If the thymus 2's surgically removed from mice within 24 hours of birth, however, there is rapid marked impairment in the animals’ cell—mediated immune responses, and in the formation of humoral antibodies to a number of antigens.
Now, the nude mouse is born without a thymus. This would make one suppose that the made mouse does represent a base line for study of thymic function in the immune system. And furthermore, that the absence of the thymus could be exploited in studies of other biological systems, e.g. malignant tumour tissue, transplanted in the nude mouse.
In the following we summarize some of the evidence in favour of this

Poulsen, Carl O

Rygaard, Jorgen

English

The Nude Mouse

A mixture of fluam'son, 10 mg/ml and fentanyl, 0.2 mg/ml, commercially available as Hypnorm® has been used in rats. Judged by the practical experience over five years it seems that this combination offers an anaesthesia which in certain respects 2'5 superior to that of barbiturates in the rat. It is faster, depresses less autonomic reflexes and there seems to be fewer complications both during and after the anesthesia. The most serious unwanted effect is depression of respiration, but it was only observed at high doses

Hellekant, Göran

Fluanison-Fentanyl Anaesthesia in the Rat
By Ghran Hellehant
A mixture of fluam'son, 10 mg/ml and fentanyl, 0.2 mg/ml, com-
mercially available as Hypnorm® has been used in rats. judged
by the practical experience over five years it seems that this com-
bination offers an anaesthesia which in certain respects 2'5 superior
to that of barbiturates in the rat. It is faster, depresses less auto-
nomic reflexes and there seems to be fewer complications both
during and after the anesthesia. The most serious unwanted effect
is depression of respiration, but it was only observed at high doses.
The term neuroleptanalgesia has
been used to describe an anaesthesia
caused by the combined action of
morphine—like analgesics and neuro—
leptic agents. Neuroleptanalgesia
has been successfully applied in
man since the early sixties. For
the use in animals a combination of
fluanison, a neurolepticum, and fen—
tanyl citrate, an analgeticum (Hyp-
norm®) has been available for some
years. However, it seems that on the
whole its use has been restricted to
the dog, though it can be a useful
anestetic in other species too. In this
study observations will be described
obtained in the rat. The study is
based on practical observations over
more than 5 years. It will show that
Hypnorm offers several advantages
over barbiturates which suggest a
more extensive use of it. The study
is not intended to be a pharmaco-
logical description of its effects,
since the observations have been
collected while the analgeticum was
used as a mean to study other phy—
siological parameters.
Methods
A combination of 10 mg fluanison
and 0.2 mg fentanyl dihydrogen
Fra Forsegsdyrsymposiet i Lund 10.—
11. maj 1976.
citrate per ml solution (Hypnorm®)
has been used in white albino rats
(Sprague Dawley and Wistar) rang-
ing from 200—500 g weight. During
the anaesthesia different kinds of
surgery ranging from simple sutures
0f the skin to intracranial surgery
have been made. The drug has been
used either alone or in combination
with Mebumal sodium, 60 mg per
m1 (Mebumal®), fentanyl citrate
(Leptanal®) and gallamine triethio-
dide (Flaxedil®). The doses of Hyp—
norm used have been fairly stand-
ardized, about 0.25 ml to a 300 g
rat and 0.30—0.35 to a 400 g ani—
mal. Lower doses were used for Ini—
nor surgery. The standard combi—
nation of Mebumal and Hypnorm
has been 0.20—0.25 ml of each to
a 400—450 g rat. Leptanal was only
used after previous administration
of Hypnorm for extended anaesthe—
sia. When this was done Flaxedil
was given in addition. All drugs
except Flaxedil which was given
intravenously were injected intra-
muscularily (i.m.).
Results
Hypnorm injected in the dose de~
scribed above gives in the rat an
anaesthesia Which within 5 min is
15
deep enough to allow even large
surgical operations. All reactions to
pain are abolished, the muscle strain
is very much depressed and the ani—
mal is in a cataleptic stage. After
about 30 min the first signs of re-
turn of consciousness may be obser-
ved. However, despite this surgery
can be continued for about another
15 min. If regarded necessary, about
0.10 ml Hypnorm can be given i‘m.
This should be made as soon as pos-
sible after the first sign of recovery
has been observed. It will keep the
rat sufficiently anaesthtized for an—
other 30—45 min.
With regard to the effects of Hyp«
norm on physiological parameters,
the incidences of respiratory depres—
sion, the major problem with mor-
phine—like types of analgesics, are
low in the rat. Further, the tendency
of defecation commonly seen in the
dog, is rarely seen and of no pro—
blem in the rat. The arterial blood
pressure is well maintained and
circulatory insufficiency seems to
be no problem during Hypnorm
anaesthesia. The temperature con—
trol deteriorates and the body tem-
perature should be controlled. Vesti-
bular reflexes and other reflexes
like swallowing, capability to keep
the respiratory airways open as well
as other unconditional reflexes re-
main though they are depressed.
This is considered as one of the
large advantages of this type of
anaesthesia, and may depend on the
fact that, centrifugal neural activity
from the CNS t0 the periphery re—
mains to a much larger extent than
during barbiturates, which in cer—
tain nerves completely abolishes all
centrifugal activity (Hellekant 1971).
The postoperative recovery offers
16
another main advantage in com—
parison With that of barbiturates,
because the animals are never com-
pletely reflexless. Thus they rarely
die from insuffocation and can be
returned to their cages immediately
after surgery. The only precaution
we have used is to put the rats on
a piece of soft paper tissue in the
cage.
It was initially mentioned that Hyp—
norm sometimes was combined with
Mebumal. This combination is use-
ful for several reasons. Firstly, these
drugs apparently have a synergistic
effect. Therefore lower doses of
each can be used. Secondly the time
for induction and duration of their
effects differ. After i.m. admini—
stration the anaesthesia of Mebumal
has a slower onset but lasts longer
than that of Hypnorm. Thirdly,
their effects on the CNS differ. The
Mebumal acts as a hypnotic agent
and affects cortical levels which
among other things gives relaxation
of muscle tonus and abolishes re-
flexes to which Hypnorm adds its
analgetic effects.
The relationship between the amount
given of these drugs can and shall
be adjusted to the situation. For
more short lasting surgery with
more rapid recovery wanted, more
Hypnorm and less Mebumal are
given and for longer lasting, deeper
anaesthesia more Mebumal and less
Hypnorm are administered in cer-
tain situations: when the experiment
demanded that the centrifugal ac-
tivity from the CNS was left un—
affected as much as possible, the
anaesthesia was maintained with
fentanyl alone (Leptanal) or partly
Leptanal and Hypnorm. In these
cases the rats were given gallarnine
triethiodide (Flaxedil) i.V. or i.p.
and then put on artificial respi—
ration. Flaxedil has a curariform
action and competes with acetyl—
choline for the motor receptor sites
on cross-striated muscles. It has no
analgetic effect but judged by the
general status of these rats and their
blood pressure this combination
seemed adequate.
Discussion
The results described show that
Hypnorm in the rat within 5 min
causes an anaesthesia which is deep
enough to allow even large surgery
but with characteristics which leave
some of the reflexes important for
survival intact. With regard to the
doses of Hypnorm used they were
about twice as large as those re-
commended (Leo), 0.3—0.5 ml/kg
b.w. in the dog. However, for minor
shortlasting operations the dose can
be considerably lowered in the rat
too. But we never considered it Vital
to search for the lowest possible
dose. In spite of this the recovery
was faster and less complicated after
Hypnorm than after Mebumal.
Though this study is not the result
of a specific attempt to study the
pharmacological action of the drug
it seems worthwhile to compare
some of our observations in the rat
with those obtained in other species.
In man neuroleptanalgesia has been
used for more than a decade. Its
effects on man seem not to differ
significantly from those observed
here in rat. Dobhin, Israel & Bytes
(1964) report unconsciousness within
5 min after i.V. injection. Since we
observed similar time periods after
i.m. injection, rate of absorption
from the place of injection seem not
to be the limiting factor in the onset
of anaesthesia in man. The most
severe unwanted effect in man
seemed to be respiratory depression.
This was also the case in the rat.
However, their frequency increased
when the drug was i.V. injected.
After i.m. injection, apnoe was very
rare. In man as in rat the effects on
the blood pressure seemed equally
small. In both species potentiation
of the effect of barbiturate occurred.
We have not recorded the effects
on any metabolic parameter except
the blood sugar level. In man an
elevation has been reported (Doh-
kin, Israel & Byles 1964). During
Hypnorm it seemed not to be sig-
nificantly changed in comparison
with the figures given by others in
the unanaesthetized rat (Altman &
Dittmer 1961). Excitation Which
occurs in the cat was never observed
in the rat and defecation which is
observed in the dog was rare and of
no problem. From the above it seems
that Hypnorm offers a generally
anaesthetic alternative with several
advantages over MebumaI.
In certain situations this type of
anaesthesia seems to be the only
alternative. Such a situation seems
to be when it is essential that the
centrifugal activity from the CNS
remains as much as possible. This
was the case when we studied the
efferent activity to the tongue and
the salivary glands in the chorda
tympani proper nerve (Hellehant
1971). Under barbiturate no efferent
nerve impulses could be recorded in
the nerve. Fig. 1 shows an example
of this effect of barbiturate. The left
record was obtained before Mebu-
mal but under Hypnorm anaesthesia.
17
effichordo tympani actwsty before and 5min after u: pentobarbitat
 
  IN“ 1 , ... 1 '~ is‘‘5
TBOEMM Hg 3?
o L—w—w-mna‘
isec
Fig. I. It shows two recordings obtained from the central part of the cut chorda
tympani proper nerve of a rat. The left recording was obtained under Hypnorm
anaesthesia. It shows a strong spontaneous efferent nerve activity. Immediately
after this record 6 mg Mebumal was injected i.V. The right recording was then
obtained 6 min after the injection. It shows that barbiturate considerably de-
creased the efferent nerve activity.
It shows that during this anaesthesia
a number of efferent impulses in the
nerve could be recorded. Then, 6
min before the right record was
obtained 0.1 ml Mebumal (6 mg)
was injected iv. The right part of
Fig. 1 shows that this diminished
very much the nerve activity. The
effect was not the result of deterior-
ated blood supply to the brain be
cause the systemic blood pressure
was well maintained. It even in-
creased after the Mebumal. This is
shown in the bottom trace. The
efferent activity will continue to
decrease for another 10 min but if
the animal is kept for a sufficient
long time after barbiturate is given
and provided the dose is not too
large, some of the efferent activity
will return.
It should be mentioned that the
fluanison component of the Hyp—
norm also depresses the activity, it
is therefore advisable to continue
the anaesthesia with only fentanyl
citrate. If the aim is to study the
efferent activity then in most cases
muscle relaxantia must be given
18
after which the animal must be
artificially respirated. Judged by
the blood pressure and the general
status of the animals, this procedure
seems to be successful and adequate.
In conclusion this discussion suggests
that the effects of Hypnorm in the
rat are similar and in some cases
more favourable than those observed
during neuroleptanalgesia in other
species. In addition under Hypnorm,
impulse activity can be recorded in
nerves which under Mebumal are
silent.
References
Altman, P. L. & D. S. Dittmer: Blood
and other body fluids. 1961, p. 81.
Dobkin, A. B., ] S. Israel & P. H.
Bytes: Innovan—NZO anaesthesia in
normal men: effect on respiration,
circulatory dynamics7 liver function,
metabolic functions, acid—base ba-
lance, and psychic responses. Cam.
Anaes. Soc. ]. 1964. 1]. 41—71.
Hellekrmt, G..‘ Efferent impulses in the
chorda tympani nerve of the rat.
Acta physio]. stand. 1971. 83. 203—
209.


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The Nude Mouse

Fluanison-Fentanyl Anaesthesia in the Rat

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