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Anuran feeding after hypophysectomy
GE> EK.IL
AND
COMPAR.ATIV,?
ESD:)(‘RINOLOGY
Anuran
17,
Feeding
149-151
after
ROBERT Imtitzcte Lo&a
for
(1971)
Hypophysectomy
S. SCHMIDT
the Study of Mind, Drugs, and Behavior; University Stritch School of Medicine; Mnywood, Illinois (i0153
Received
September
28. 1970
Spontaneous feeding continued in toads (Bzrfo n~mericrtnus) and frogs (Rat&a p. pipierls) for &30 days following removal of the pars distalis. The toads always died within a few days after cessation of feeding. It is concluded that the pars distalis is not as essentiallv involved in normal feeding mechanisms as recently postulated by Dierickx. _
Incidental to a preliminary study of toad learning, WC have recently tested the effect of a number of brain lesions on anuran feeding behavior. The purpose of this paper is to describe some of our results, which di:‘fer somewhat from those recently reported by Dierickx (1969).
2 weeks before use, and were given 2-3 preopcrativc feeding tests to familiarize them with the teat aptlaratus and food location. ,111 toads feed within 16 set on the test, immediately prcceding surgery. The frogs were also starved for at least 2 wccka before use. but were tested only postoperatively. Testing took place in a cement laundry sink (Schmidt and Hudson, 1969) similar to those in which the animals had been ket)t for the previous 3 months. Such frogs feed readily while being ohserved. Aft,er 10 min in the sink. a test was begun by introducing a number of crickets and watching for feeding during the next 5 min. Tht: presence or nbnencc of feeding during this period was recorded. Hypothermic anesthesia was used for all operat#ions. The region of the pituitary was reached through the roof of the mouth, and only the bone immrdiatrly over the area to be ablated was removed. The lesion was produced with a fine suction pipette made from a hypodermic needle. The 16X magnification of a Zeiss operating microscope with a 50-W bulb was used. Since every step of the surgery could be clearly observed, and especially since the pars distalis was always removed as a single, intact unit, no histological examination of the lesions was considered necessary. Nevertheless, the lesions in animals I< and N through Q (Table 1) were exa.minrd h, dissection at, the end of the experiment, and all were found to be as recorded during the surgery. Thrrc types of ablations were performed. One consisted of removal of all of the hypothalamo hyl~ophysial junction from the posterior edge
METHODS Female American toads (B~fo nmer.irrr~i~cs) were purchased in late April from I:. (:. Stcinhilber & Co., Oshkosh, Wisconsin, and used from Mry through July. Male leopard frogs (Ratlu p. pi,iens) were purchased from the same source in early April and used during July. The toads were tested for feeding in an apparatus consisting of a black box, 10 cm X 17 cn1 X 7 cm high, with :L transparent cover and a 4 cm square opening in the floor at the center of onv of the long sides. Mealworms to be used for food were placed in a l)resentntion chamber consisting of a 1 cm deep well in a piccc of plastic. A piece of metal, partly covering the floor of this well. could hc gently agita.ted in order to assure continuous movement of the niealworms. The box was illuminatrd by a 40-W l~ulb directly over the cover and there was a or c-way mirror mounted bctwcen the box :m~l tht, obsrrccr. A toad was left undisturbed in the box for 10 min before tc-sling. A test then consisted of lllacing the worm-l)rrscntation chamber under i hr hole in the box and recording the time until E(~eding. A maximum of 3 min was allowed for a rcq~onsc~. All toads were starred for at least 349
150
ROBERT
S.
of the optic chiasma to the pars distalis and pars intermedia (-PV, Table 1). Thus all of the pars nervosa and median eminence were eliminated. Except for the median eminence, this lesion would seem to correspond to Dierickx’s (1969) “pars ventralis tuberis” lesion. The main point, of course, is that the connections between the hypothalamus and pars distalis were eliminated in each case. The second lesion consisted of removal of t,he pars distalis only (-PD. Table 1). A third lesion re.moved all the structures ablated in the first two lesions, as well as the pars intermedia (-PV and -P. Table 1); i.e. the entire pituitary was ablated. Experiments were begun with Bt~fo and it was soon noted that these lesions were eventually lethal. Therefore, some of the later lesioned toads, and all of the lesioned frogs, were kept in frog Ringer’s solution in the hope of increasing survival. There was no indication that this had the desired effect on the toads, and the effectiveness for the frogs cannot be evaluated since none were kept in tap water. RESULTS
AND
SCHMIDT
mals in which the pars distalis remained in place (A through E, L) eventually stopped feeding. This is consistent with Dierickx’s (1969) observation that after removal of the pars ventralis normal feeding continued for a while and then “the amount of food intake decreased progressively until about 3 weeks after operation. From then on, in all animals, permanent disappearance of spontaneous food intake was observed.” All but two (K, N) of the animals with the pars distalis removed (F through K and M through Q) stopped feeding within the duration of the experiment. Although they did not specifically study feeding behavior, Brown and Frye (1969) also found, in Ram pipiens, that “many of the hypophysectomized frogs appeared to have a decreased appetite.” However, some feeding did continue in both studies. In the case of our hypophysectomizcd animals, feeding continued for 8-30 days after surgery. This is in considerable contrast to Dieri&x’s (1969) finding that “removal of the pars distalis of the hypothalamus produced
CONCLUSIONS
The effects of the lesions upon feeding in Table 1. All of the ani-
are summarized
TABLE POSTOPERATIVE
1
FEEDING
RESPONSES
Days following Species alid lesion Bqfo
-PV
-PI)
Rana
-Pi. -PI) - PV alld - P
I
5
10
ablation 15
20
2;i
30
Animal A B c 1) E F (: H 1 J Ii L M N 0 25
+ + + + + + + +
++s +++ ++x + + + + + + + + ++++++++ ++++++++
+ + + + + + + +++ +++ ++--+
1
5
1) ---1) --I> + + s + + + + +------+++----+++++ -----+------10
- 11 1) - I) D 1) X-1) - I) + +o) -1) -(r.?) + +++ -+----15
20
+ -
+ 25
+(I) --(I) --(I) -(I) SO
Symbols and abbreviations: PV = pars ventralis; PD = pars distalis; P = pituitary; D = dead; -= would not feed; + = fed within 30 set (Bufo), or within 5 min (Rana); X = fed between 30 and 150 set; (1) = discarded while still in good condition; (2) = discarded because of red-leg disease.
ANURAN
FEEDING
AFTER
an immediate [emphasis mine] and permanent disappearance of spontaneous food intake.” The reason for this difference in results is not presently clear, although it will be noted that Dierickx used a different species (Rana temporaria) . Dierickx (1969) concluded “that the pars ventralis t,uberis contains a kind of feeding center, indispensable for the spontaneous food intake,” and that’ this center “acts via the pars distalis.” However, the more prolonged survival of feeding following removal of t,he pars distalis and especially the e&appearance of feeding in toads only shortly before their death, as found in the present study, would lead one to question such a close and direct involvement of the pars distalis in normal feeding behavior. Rather, t,he loss of feeding following these lesions would seem more likely to be a very indirect, nonspecific result of the gross, widespread abnormal physiology associated wit,h the hormonal changes produced. Such a phylogenetically primit’ive system as tie central mechanisms for feeding must have much in common in the various groups of vl:rtebrates. It seems likely that if the pars dist,alis were as essentially and specifi-
151
HYPOPHYSECTOMY
tally involved in feeding as postulated by Dierickx (1969)) clear-cut evidence for such a relationship would have been obtained previously. The early claims of such an involvement in mammals appears to have been based upon lesions that actually involved the hypothalamic feeding centers as well as the hypothesis (e.g., Anand, 1961). ACKNOWLEDGMENT This work was supported by Career Development Award NS-9513 and Research Grant NS06673 from the National Institute of Neurological Diseases and Stroke. REFERENCES B. K. (1961). Nervous regulation of food intake. Phgsiol. Ret>. 41, 677-708. BROWN, I’. S.. AND FRYE, B. E. (1969). Effects of hypophysectomy, prolactin, and growth hormone on growth of postmetamorphic frogs. Gen. Comp. Endocrinol. 13, 139-145. DIERICKS. K. (1969). Hgpothalamo-hypophysial regulation of food intake in Rana temporaria. Gen. Cotmp. ErLdocrinol. 13, 361-366. SCHMIDT, R. S., .%ND HUDSON. W. R. (1969). Maintenance of adult nnurans. Lab. Anim. care 19, 617-620. AN.CVD,
AND
COMPAR.ATIV,?
ESD:)(‘RINOLOGY
Anuran
17,
Feeding
149-151
after
ROBERT Imtitzcte Lo&a
for
(1971)
Hypophysectomy
S. SCHMIDT
the Study of Mind, Drugs, and Behavior; University Stritch School of Medicine; Mnywood, Illinois (i0153
Received
September
28. 1970
Spontaneous feeding continued in toads (Bzrfo n~mericrtnus) and frogs (Rat&a p. pipierls) for &30 days following removal of the pars distalis. The toads always died within a few days after cessation of feeding. It is concluded that the pars distalis is not as essentiallv involved in normal feeding mechanisms as recently postulated by Dierickx. _
Incidental to a preliminary study of toad learning, WC have recently tested the effect of a number of brain lesions on anuran feeding behavior. The purpose of this paper is to describe some of our results, which di:‘fer somewhat from those recently reported by Dierickx (1969).
2 weeks before use, and were given 2-3 preopcrativc feeding tests to familiarize them with the teat aptlaratus and food location. ,111 toads feed within 16 set on the test, immediately prcceding surgery. The frogs were also starved for at least 2 wccka before use. but were tested only postoperatively. Testing took place in a cement laundry sink (Schmidt and Hudson, 1969) similar to those in which the animals had been ket)t for the previous 3 months. Such frogs feed readily while being ohserved. Aft,er 10 min in the sink. a test was begun by introducing a number of crickets and watching for feeding during the next 5 min. Tht: presence or nbnencc of feeding during this period was recorded. Hypothermic anesthesia was used for all operat#ions. The region of the pituitary was reached through the roof of the mouth, and only the bone immrdiatrly over the area to be ablated was removed. The lesion was produced with a fine suction pipette made from a hypodermic needle. The 16X magnification of a Zeiss operating microscope with a 50-W bulb was used. Since every step of the surgery could be clearly observed, and especially since the pars distalis was always removed as a single, intact unit, no histological examination of the lesions was considered necessary. Nevertheless, the lesions in animals I< and N through Q (Table 1) were exa.minrd h, dissection at, the end of the experiment, and all were found to be as recorded during the surgery. Thrrc types of ablations were performed. One consisted of removal of all of the hypothalamo hyl~ophysial junction from the posterior edge
METHODS Female American toads (B~fo nmer.irrr~i~cs) were purchased in late April from I:. (:. Stcinhilber & Co., Oshkosh, Wisconsin, and used from Mry through July. Male leopard frogs (Ratlu p. pi,iens) were purchased from the same source in early April and used during July. The toads were tested for feeding in an apparatus consisting of a black box, 10 cm X 17 cn1 X 7 cm high, with :L transparent cover and a 4 cm square opening in the floor at the center of onv of the long sides. Mealworms to be used for food were placed in a l)resentntion chamber consisting of a 1 cm deep well in a piccc of plastic. A piece of metal, partly covering the floor of this well. could hc gently agita.ted in order to assure continuous movement of the niealworms. The box was illuminatrd by a 40-W l~ulb directly over the cover and there was a or c-way mirror mounted bctwcen the box :m~l tht, obsrrccr. A toad was left undisturbed in the box for 10 min before tc-sling. A test then consisted of lllacing the worm-l)rrscntation chamber under i hr hole in the box and recording the time until E(~eding. A maximum of 3 min was allowed for a rcq~onsc~. All toads were starred for at least 349
150
ROBERT
S.
of the optic chiasma to the pars distalis and pars intermedia (-PV, Table 1). Thus all of the pars nervosa and median eminence were eliminated. Except for the median eminence, this lesion would seem to correspond to Dierickx’s (1969) “pars ventralis tuberis” lesion. The main point, of course, is that the connections between the hypothalamus and pars distalis were eliminated in each case. The second lesion consisted of removal of t,he pars distalis only (-PD. Table 1). A third lesion re.moved all the structures ablated in the first two lesions, as well as the pars intermedia (-PV and -P. Table 1); i.e. the entire pituitary was ablated. Experiments were begun with Bt~fo and it was soon noted that these lesions were eventually lethal. Therefore, some of the later lesioned toads, and all of the lesioned frogs, were kept in frog Ringer’s solution in the hope of increasing survival. There was no indication that this had the desired effect on the toads, and the effectiveness for the frogs cannot be evaluated since none were kept in tap water. RESULTS
AND
SCHMIDT
mals in which the pars distalis remained in place (A through E, L) eventually stopped feeding. This is consistent with Dierickx’s (1969) observation that after removal of the pars ventralis normal feeding continued for a while and then “the amount of food intake decreased progressively until about 3 weeks after operation. From then on, in all animals, permanent disappearance of spontaneous food intake was observed.” All but two (K, N) of the animals with the pars distalis removed (F through K and M through Q) stopped feeding within the duration of the experiment. Although they did not specifically study feeding behavior, Brown and Frye (1969) also found, in Ram pipiens, that “many of the hypophysectomized frogs appeared to have a decreased appetite.” However, some feeding did continue in both studies. In the case of our hypophysectomizcd animals, feeding continued for 8-30 days after surgery. This is in considerable contrast to Dieri&x’s (1969) finding that “removal of the pars distalis of the hypothalamus produced
CONCLUSIONS
The effects of the lesions upon feeding in Table 1. All of the ani-
are summarized
TABLE POSTOPERATIVE
1
FEEDING
RESPONSES
Days following Species alid lesion Bqfo
-PV
-PI)
Rana
-Pi. -PI) - PV alld - P
I
5
10
ablation 15
20
2;i
30
Animal A B c 1) E F (: H 1 J Ii L M N 0 25
+ + + + + + + +
++s +++ ++x + + + + + + + + ++++++++ ++++++++
+ + + + + + + +++ +++ ++--+
1
5
1) ---1) --I> + + s + + + + +------+++----+++++ -----+------10
- 11 1) - I) D 1) X-1) - I) + +o) -1) -(r.?) + +++ -+----15
20
+ -
+ 25
+(I) --(I) --(I) -(I) SO
Symbols and abbreviations: PV = pars ventralis; PD = pars distalis; P = pituitary; D = dead; -= would not feed; + = fed within 30 set (Bufo), or within 5 min (Rana); X = fed between 30 and 150 set; (1) = discarded while still in good condition; (2) = discarded because of red-leg disease.
ANURAN
FEEDING
AFTER
an immediate [emphasis mine] and permanent disappearance of spontaneous food intake.” The reason for this difference in results is not presently clear, although it will be noted that Dierickx used a different species (Rana temporaria) . Dierickx (1969) concluded “that the pars ventralis t,uberis contains a kind of feeding center, indispensable for the spontaneous food intake,” and that’ this center “acts via the pars distalis.” However, the more prolonged survival of feeding following removal of t,he pars distalis and especially the e&appearance of feeding in toads only shortly before their death, as found in the present study, would lead one to question such a close and direct involvement of the pars distalis in normal feeding behavior. Rather, t,he loss of feeding following these lesions would seem more likely to be a very indirect, nonspecific result of the gross, widespread abnormal physiology associated wit,h the hormonal changes produced. Such a phylogenetically primit’ive system as tie central mechanisms for feeding must have much in common in the various groups of vl:rtebrates. It seems likely that if the pars dist,alis were as essentially and specifi-
151
HYPOPHYSECTOMY
tally involved in feeding as postulated by Dierickx (1969)) clear-cut evidence for such a relationship would have been obtained previously. The early claims of such an involvement in mammals appears to have been based upon lesions that actually involved the hypothalamic feeding centers as well as the hypothesis (e.g., Anand, 1961). ACKNOWLEDGMENT This work was supported by Career Development Award NS-9513 and Research Grant NS06673 from the National Institute of Neurological Diseases and Stroke. REFERENCES B. K. (1961). Nervous regulation of food intake. Phgsiol. Ret>. 41, 677-708. BROWN, I’. S.. AND FRYE, B. E. (1969). Effects of hypophysectomy, prolactin, and growth hormone on growth of postmetamorphic frogs. Gen. Comp. Endocrinol. 13, 139-145. DIERICKS. K. (1969). Hgpothalamo-hypophysial regulation of food intake in Rana temporaria. Gen. Cotmp. ErLdocrinol. 13, 361-366. SCHMIDT, R. S., .%ND HUDSON. W. R. (1969). Maintenance of adult nnurans. Lab. Anim. care 19, 617-620. AN.CVD,