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The effects of septal area lesions on the meal patterns of female rats
BRIEFCOMMUNICATION The Effects of Septal Area Lesions on the Meal Patterns of Female Rats’
546 Licking was monitored by a drinkometer and recorded on an Esterline-Angus event recorder. A capacitor circuit caused the recorder pen to deflect upon drinkometer activation. Event records indicated the distribution of time spent eating over a 24 hour period. The measured amount of eating time accurately reflected food consumption (r = 39). Water was available ad lib in an inverted graduated cylinder. Room lights were automatically turned on at 8:00 a.m. and off at 8:00 p.m. White noise was provided by a Grason-Stadler (Model 4.55~) noise generator at all times. Surgery and Histology The rats were divided into 2 groups; IO sustained bilateral lesions of the septum, while the remaining C sustained sham lesions. Under Equi-Thesin anesthesia, rats were placed in a Kopf stereotaxic instrument. The skull was opened and the midline sinus exposed. With the incisor bar 5 deg above the interaural line, the coordinates for the septal lesions were 2.0 mm anterior to bregma, 0.5 mm lateral to the midline sinus, and 6.5 mm ventral to the skull surface; a I .S mA DC anodal current was passed for 20 sec. using an anal cathode. Sham operated rats were treated identically except that the electrode was not lowered into the brain. Following surgery, all animals received a 0.2 cc dose of bicillin. Following testing, all lesioned rats were anesthetized and perfused with saline and 10% Formalin. Brains were removed, embedded in celloidin, sliced 30 micra thick and stained with cresyl violet. Procedure Upon arrival all animals were adapted to the light/dark cycle and the liquid diet for at least 2 weeks. Then, baseline measures of food and water intake and body weight were obtained for 1 week and at least 4 postoperative weeks, Meal patterns were recorded for sham and septal rats for the entire preoperative and postoperative period. Data Analyses Daily intake was analyzed by meal size, meal frequency and post meal interval for each 24 hr period. Meal patterns were determined separately for day and night, and all analyses were made maintaining this distinction. For each animal the average meal size, meal frequency and post meal interval were computed for both day and night for each 24 hr period. Analyses were performed on: (1) daily body weight, (2) daily food intake, (3) daily water intake, (4) average meal size for day and night, (5) average meal frequency for day and night, and (6) average post meal interval for day and night. Meals were defined as a period of licking greater than IO set which was separated from other periods of licking by at least I min. Since meals were measured in time spent licking, a transformation was made to obtain meal sizes in ml. Each meal (in min) was multiplied by the average amount consumed/minute for that 24 hr period per animal. This produced a measure of meal size in ml. Correlation coefficients were computed to establish the relationship between meal size and the corresponding postmeal interval for each animal. Individual meals and intervals for every other postoperative day were used for
I’I1ELPS sham and septal groups: again analyses for day and night were distinct. All differences are srgnifrcant at p” 0.05. I
:Ileasurev:
Bodjl
Wright.
t“ood
11lruhe and
Water
Postoperative data were collapsed over 7 day periods and the means for each of the postoperative weeks wcrc compared. These means did not significantly differ. indicating there was no change in botiv. weight. food intake or I water intake over the 4 testing week\. There were no differences between the scptal area and sham rats in terms of body weigh! t t = 0.98. 13) or food intake (t = 1.02. 13). It should bt, emphasized that these measures were very stable for both groups. In addition the amount consumed during the day and the night was derived by multiplying the average meal size by the average meal frequency. Again sham and septal rats did not differ: the day/night ratio for shams was 15:7C while it was 35!65 for the septal group. Septal rats were polydipsrc. dt mkmg 3 to -I frmcs as much as shams (t = 4.78. 13).
Meul patterns: Intervul
Meal Size . :Mcal k’rcquet7c:v und Post Meal
The 24 hour daily intake was broken down to examine the distribution of food intake. Data was analyzed by meal SiZC. meal frequency and postmoal interval. For each animal. an average measure of daily meal size, meal frequency and post meal interval was obtained separately for day and night. Daily averages were used in the computation of all statistical tests. All tests were made separately for day and night. Neither the sham nor scptal group showed any changes in meal size. meal frequency or postmeal interval over the 4 postoperative weeks; effects over time will not he further discussed. Sham rats consume equal sized meals during the day as at night, but they eat more meals at night (t = 19.05, 8). In keeping with the greater meal frequency at night, sham rats have shorter postmeal intervals at night than during the day (t = 19.21. 8). In contrast to shams, suptal rats eat smaller meals at night than during the day (t = 7.63, 18). Correspondingly, septal rats eat more frequently at night (t = 10.57. 18); they also have shorter postmeal intervals at night than during the day (t = 10.79. 18). Meal size for septal rats is smaller than for shams during both the day (t = 4.1 I, 13) and the night (t = 12.24, 13). In comparison to sham rats, septal rats show higher meal frequencies during both the day (t = 8.48, 13) and at night (t = 7.0, l3), as well as shorter postmeal intervals during the day (t = 9.74, 13) and night (t = 10.86, 13). There were no significant differences among the magnitude of the correlation coefficients relating meal size to the subsequent postmeal interval. In addition. the COefficients did not differ between the day and the night. (Sham: day-X = 0.45. S.D. = 0.14, night-X = 0.46, S.D. = 0.12; Septal: day-X = 0.31, S.D. = 0.19. night-X = 0.54. S.D. 14.) All coefficients are positive and significantly greater than zero. (p
SEI’J.AL, Lt:Sl()KS
,\F\‘l) 41l::Al.
547
PATI‘EKNS graded
Ijihtological esamination of the brains indicated that the scptal Icsionh wcrc in gcncral quite large. The average lesion dcstroyctl ;lll of the medial and most of the lateral scpturn. .lllcrc W,~S Infrequent minor sparing of the dorsal lateral nucleus. .fhc anterior cxtcnt was to the septo-cortical Jtlnctiou while the posterior cvtent was to the dcsccnding columns 01’ the fornix. l‘hrrc was major damage to the nucleus Irlangularis and ~LICICIIS fimbrialis. Occasionally the Icsion dc\tro!,cd the descc‘nding columns of the fornix with m1n0r d:~mapc to i hc atria mcclullaris. Lxtrancous damage wa\ minimal while in nic)sl L‘:IWS the Icsion destroyed all ~plal
rluilci. I)IS(‘USSlOl\i
‘fhc .~n,~ly\~s ol’ daily intake and mcal patterns following ~ptal ;~rca Ics~onh make\ iI clear why the sepIaI arca has been largely ipnorcd in btudies of dietary regulation: gross mcasurcs ot’ food lnlakc and hdy weight indicate normal rcgulat~on. Howr\er. ;1 tirtailetl analysis of the dis;lribulion ot !‘ootl intake ha\ rcvealcd btrlking cffccts of the lesion. If nlight hc noted that Snowdon and Wampler I I5 1 Asc) t‘ountl grc,sh nicasurcs ~n~ldequ.ile in assessing neural Icsions. A nunlhcr- ot studies ha\c shown rhal following scptal lesions. r.it\ s11oK 3 rccluction in hotly weight 1 I. 2. 0 1: howcvrr. lhc wpt;il i-~1s in the present study niainlainetl normal h0tly’ wcighls. Ihcrc is really no contradiction hcrc. since iiiosl previous work used malcs while this study used onI!, fcni;~lc~ Studies of .scx differences in scptal rats shov. inclccd. rnalcs do rnatntain lower while lcrnalcs IhI. rnalntalrl normal hodg’ wc~ght\ I?. ‘11, The ~nall~s ot dally r‘ood Intake into cornponcnt mcds 2nd po~lnie;~l Intervals hai shown cffccts of the seplal Icsion untlL~~cl~tcd 111 the gross 23 I~our intake mcasurcs. Daily t’ootl I~I.I~C V+;IS\lmilar lor scpt;~l and sham rats: in ,iJdilion SL’~(~II rats ;IIu) ~~n~umcd mosr of their daily intake during cxhibrting normal diurnal cyclicity. HowIhc n~phrliiiic‘. c\cr. 211 c’i;iniin;illon 01’ the distribution of meals and Inrc~r\;il\ 4io\vctl that scplal Icsions product reliable L,hangcs 111 1’ccd1n~ patlcrns. Scp~al r:lt\ consumed much smaller. inoi-c I’rc~cliicnl iiicdls tllan \h;im IKits. II .rppc‘:rr\ III;I~ Ihca prc,viously known characteristic< ot w~~;II IJI\ .Irc unahlc III acc,ount for this disruption in r‘cctl~ng paircrn. ,Icc~ording IO I.cllagnen [XI . oroscnsory ~.tic\ ;irL’ Ilic Iniiior tlclcrrlllll~nt 01’ meal G/r. Since Ihc seplal i-21 ~veirr~pc~ntl~ IO oro\cnsory cuts I I ,2 1. iI would IW ~~\pc~~lcdwhat mc’al si/ds would hc larger than normal. In tac,t. Ilcl\vcvclI nic3l silt dcc,rcascd following septal arc3 Ic\ions. I tic pc~srmcdl 1ntc’rv;il I\ largely drlerminrd hy the i3lof ii L.ontc’nl 01 the prc\ Ious meal. I‘he correlation hc‘tu?c‘n meal \I/C and !IIC suhscqucnt internal i\ thercforc ;I nicdsurc 01 Ills r,if‘\ ,ihillf> IO use caloric I‘fcdback from the prc’vious ii1~~;11 1X 1 Slt7c.c tlic magnitude of these curi~l~t~ons \r.;b lhc s.inic ~1s ionlrol\. th-2 scptal rats nitisf hc responding IO Ihc calorli cc)ntcnt of the meal normall!~. ~2tld1lion;tl hupporl is provitlctl by Holland 1unpubllshztl tlo~.loral tliss~~rlalion) . \Uho f~~lriid scp131 rats showctl ;I
reduction
in
food
intake
following
idrious
con-
centrations of glucose loads. So iI dppcars thal scptal rats &I not have ;I caloric deficit and thclr oLrrrL’sponsivL’iicss to orosensory cues cannot account for Lhr small t’requcnt mc;ll pattern. Other rxplana1ions must hc sou&l. Snowdon and Epstein I I41 have reporled Iwo olhci casts in which rats show the pattern ot small frcqucnr meals characteristic of septal rats. ( I ) Kats in which oroscnsor): cues wc’rc’ eliminated by inrraga\tric fzcding consumed small f’rcqucnt meals. (2) Rats in WI~IL~II the sensory input from t hc esophagus and stoniacli \~‘iis rcducccl hy scvcring the vagtts nerve. also showed Ihe snidl frqucnI incal pattern. III both cast‘s rats maintalncd slablc intake. but Ihcir meal silts were greatly reduced. This cvidcncc suggests that lhc SIIIJII t’rqucnr mc’31 pattern is indicative ot‘ an animal thdl i\ Ic’ss rcsponsivc than normal to orosensory information. \‘L,( I( has been shown that scptal rats ovsrrcspond to oroscnsc~r~ L‘UL‘S I I .2 I In view of thi5 conlradiction, it is possible 1li~l rhc scptal ral’s allered sensitivity I0 oroscnsor!’ int’ornl;itic~n is not rcsponsihlc t’or 1hL>small frcclurnt mc~l p.rttcrn. In support ot this pussihillty IS c+idcncc prcscntd I~) Snowdon I I.3 ] which links the v~gotom~~cd r;ll’\ >n1;11l nlc;~n pal tern\ to :I motor nol d sensory drl’icll. Snowdon 1I.31 suggests that IIIL’LII \I/C IS clstcrnllncd b> the pal3rahility of the diet. Once in rhc s10111~ch. the 111cal cnipfics info the intcsrinc al ;I r.itc Jcpcnding on the osmotic and nutritive propertics 01’ tlic Iood .IS well ;IS the volume of chc mcal. Snowdon 1‘ountl Llial Ilic srornach ~~mplyinp lime was highly correlal~d with Ihc poslincal interval. This implies that another in~il is inili;itetl \vhen the precious meal con~pletely pasts from tlic stomach IO fhc intrsrine. Snowdon deriionslratd th,iI In v;rgoIomizcd rats. liquid dicls unplicd more rapidI!, than normal I’runi the slorna~h lo rhc dtrotlrntlni. ~luiiidns with vdgotoinics also show [his rapid slorna~h cn~pt! ing ;~nd rt’port LICCO~Ipanying cpipaslric discoinfc~rl ;lrlJ Il;lll\c,l I I I J Small frequent meals cllminatd thcsc unic~rllI’c~rl;lhlc \~nsatlonb. Snowdon suggests that fhc v;igo1on11/cd rat\ nl,i! cut \ni;ill mcds to at,oid scns;ifions ~.aus;cd II! 1111, tapid stomach crnptying. Small nicals cnipty fdsl~ti 1112n norni;il \ILC~ incaIs. and consL*qucntl!,. anotlicr n1cdl I\I In111,it~~l sooner. producing the small t‘requenl ni~*;il p,iI IL~III. l‘lius. Snowdon has accotrntcd t’or the VII~I trcquenr msal patlcrr1 01 vagotomi~~d rats 1,): d~n10n~lr~rtin~ ii pd~~ro~ntcsr~nal niolor control deficiency.
3.
Epstein, A. and P. Teitelbaum. Regulation of food intake in the absence of taste, smell and other oropharyngeal sensations. J. romp.
4.
5.
6.
7. 8.
physiol.
Psychol.
55: 753-759,
9.
Behov.
1962.
Gold, R. Hypothalamic obesity: the myth of the ventromedial hypothalamus. Science 182: 488-490. Hamilton, L., Capobianco, S. and E. Worsham. Lowered response to postingestive cues following septal lesions in rats. J. camp. physiol. Psychol. 87: 134- 141, 1974. Hamilton, L. and C. Flarhety. Behavioral patterns associated with drinking in normal and septal rats. J. camp. phyriol. Psychol. 76: 165. 174, 1971. Kondo, C. and S. Lorens. Sex differences in the effects ot septal lesions. Physiol. Behov. 6: 481 --485, 197 I. LeMagnen, J. Advances in studies on the physiological control and regulation of food intake. In: Progress hr physiolo&ol ps_ycholo~!J. Vol. 4. edited by E. Stellar and J. Sprague. New York: Academic Press, 1971.
Lorens, operant
IO. I I.
12.
13. 14. IS.
S. and C‘. Kondo. Differences m consummatory and behaviors of male and female septal rats. Pl?vriol. 6: 487-
491,
1971.
Raisman, G. The connexions o! the septum. HroCr 8Y: 317 347, 1966. Rolxrts, K. The dumping syndrome. In: 1‘11c.Slonr~‘h. edited by G. Thompson, D. Berkowitz and 1;. Polish. New York. Grune and Stratton, 1967. Sclafani. X. Neural pathwa!,s involved In the vcntromedial hypothalamic lesion syndrome in the rat. J. u)vI/.‘. ph~~srol. Pv~chol 77: 70.- 96, 1971. Snowdon, <‘. Gastrointestinal sensor) and moror control ot food intake. .I. c’OW?p. ph.p.siol. Px~~chol. 7 I: 68 76. 1970. Snawdon. C. and A. Epstein. Oral and intragastric feedmg in vagotomized rats. .I. combo. ph~riol. P.~~chol. 71 : 59 67. 1970. Snowdon, C. and R. Wampter. t
546 Licking was monitored by a drinkometer and recorded on an Esterline-Angus event recorder. A capacitor circuit caused the recorder pen to deflect upon drinkometer activation. Event records indicated the distribution of time spent eating over a 24 hour period. The measured amount of eating time accurately reflected food consumption (r = 39). Water was available ad lib in an inverted graduated cylinder. Room lights were automatically turned on at 8:00 a.m. and off at 8:00 p.m. White noise was provided by a Grason-Stadler (Model 4.55~) noise generator at all times. Surgery and Histology The rats were divided into 2 groups; IO sustained bilateral lesions of the septum, while the remaining C sustained sham lesions. Under Equi-Thesin anesthesia, rats were placed in a Kopf stereotaxic instrument. The skull was opened and the midline sinus exposed. With the incisor bar 5 deg above the interaural line, the coordinates for the septal lesions were 2.0 mm anterior to bregma, 0.5 mm lateral to the midline sinus, and 6.5 mm ventral to the skull surface; a I .S mA DC anodal current was passed for 20 sec. using an anal cathode. Sham operated rats were treated identically except that the electrode was not lowered into the brain. Following surgery, all animals received a 0.2 cc dose of bicillin. Following testing, all lesioned rats were anesthetized and perfused with saline and 10% Formalin. Brains were removed, embedded in celloidin, sliced 30 micra thick and stained with cresyl violet. Procedure Upon arrival all animals were adapted to the light/dark cycle and the liquid diet for at least 2 weeks. Then, baseline measures of food and water intake and body weight were obtained for 1 week and at least 4 postoperative weeks, Meal patterns were recorded for sham and septal rats for the entire preoperative and postoperative period. Data Analyses Daily intake was analyzed by meal size, meal frequency and post meal interval for each 24 hr period. Meal patterns were determined separately for day and night, and all analyses were made maintaining this distinction. For each animal the average meal size, meal frequency and post meal interval were computed for both day and night for each 24 hr period. Analyses were performed on: (1) daily body weight, (2) daily food intake, (3) daily water intake, (4) average meal size for day and night, (5) average meal frequency for day and night, and (6) average post meal interval for day and night. Meals were defined as a period of licking greater than IO set which was separated from other periods of licking by at least I min. Since meals were measured in time spent licking, a transformation was made to obtain meal sizes in ml. Each meal (in min) was multiplied by the average amount consumed/minute for that 24 hr period per animal. This produced a measure of meal size in ml. Correlation coefficients were computed to establish the relationship between meal size and the corresponding postmeal interval for each animal. Individual meals and intervals for every other postoperative day were used for
I’I1ELPS sham and septal groups: again analyses for day and night were distinct. All differences are srgnifrcant at p” 0.05. I
:Ileasurev:
Bodjl
Wright.
t“ood
11lruhe and
Water
Postoperative data were collapsed over 7 day periods and the means for each of the postoperative weeks wcrc compared. These means did not significantly differ. indicating there was no change in botiv. weight. food intake or I water intake over the 4 testing week\. There were no differences between the scptal area and sham rats in terms of body weigh! t t = 0.98. 13) or food intake (t = 1.02. 13). It should bt, emphasized that these measures were very stable for both groups. In addition the amount consumed during the day and the night was derived by multiplying the average meal size by the average meal frequency. Again sham and septal rats did not differ: the day/night ratio for shams was 15:7C while it was 35!65 for the septal group. Septal rats were polydipsrc. dt mkmg 3 to -I frmcs as much as shams (t = 4.78. 13).
Meul patterns: Intervul
Meal Size . :Mcal k’rcquet7c:v und Post Meal
The 24 hour daily intake was broken down to examine the distribution of food intake. Data was analyzed by meal SiZC. meal frequency and postmoal interval. For each animal. an average measure of daily meal size, meal frequency and post meal interval was obtained separately for day and night. Daily averages were used in the computation of all statistical tests. All tests were made separately for day and night. Neither the sham nor scptal group showed any changes in meal size. meal frequency or postmeal interval over the 4 postoperative weeks; effects over time will not he further discussed. Sham rats consume equal sized meals during the day as at night, but they eat more meals at night (t = 19.05, 8). In keeping with the greater meal frequency at night, sham rats have shorter postmeal intervals at night than during the day (t = 19.21. 8). In contrast to shams, suptal rats eat smaller meals at night than during the day (t = 7.63, 18). Correspondingly, septal rats eat more frequently at night (t = 10.57. 18); they also have shorter postmeal intervals at night than during the day (t = 10.79. 18). Meal size for septal rats is smaller than for shams during both the day (t = 4.1 I, 13) and the night (t = 12.24, 13). In comparison to sham rats, septal rats show higher meal frequencies during both the day (t = 8.48, 13) and at night (t = 7.0, l3), as well as shorter postmeal intervals during the day (t = 9.74, 13) and night (t = 10.86, 13). There were no significant differences among the magnitude of the correlation coefficients relating meal size to the subsequent postmeal interval. In addition. the COefficients did not differ between the day and the night. (Sham: day-X = 0.45. S.D. = 0.14, night-X = 0.46, S.D. = 0.12; Septal: day-X = 0.31, S.D. = 0.19. night-X = 0.54. S.D. 14.) All coefficients are positive and significantly greater than zero. (p
SEI’J.AL, Lt:Sl()KS
,\F\‘l) 41l::Al.
547
PATI‘EKNS graded
Ijihtological esamination of the brains indicated that the scptal Icsionh wcrc in gcncral quite large. The average lesion dcstroyctl ;lll of the medial and most of the lateral scpturn. .lllcrc W,~S Infrequent minor sparing of the dorsal lateral nucleus. .fhc anterior cxtcnt was to the septo-cortical Jtlnctiou while the posterior cvtent was to the dcsccnding columns 01’ the fornix. l‘hrrc was major damage to the nucleus Irlangularis and ~LICICIIS fimbrialis. Occasionally the Icsion dc\tro!,cd the descc‘nding columns of the fornix with m1n0r d:~mapc to i hc atria mcclullaris. Lxtrancous damage wa\ minimal while in nic)sl L‘:IWS the Icsion destroyed all ~plal
rluilci. I)IS(‘USSlOl\i
‘fhc .~n,~ly\~s ol’ daily intake and mcal patterns following ~ptal ;~rca Ics~onh make\ iI clear why the sepIaI arca has been largely ipnorcd in btudies of dietary regulation: gross mcasurcs ot’ food lnlakc and hdy weight indicate normal rcgulat~on. Howr\er. ;1 tirtailetl analysis of the dis;lribulion ot !‘ootl intake ha\ rcvealcd btrlking cffccts of the lesion. If nlight hc noted that Snowdon and Wampler I I5 1 Asc) t‘ountl grc,sh nicasurcs ~n~ldequ.ile in assessing neural Icsions. A nunlhcr- ot studies ha\c shown rhal following scptal lesions. r.it\ s11oK 3 rccluction in hotly weight 1 I. 2. 0 1: howcvrr. lhc wpt;il i-~1s in the present study niainlainetl normal h0tly’ wcighls. Ihcrc is really no contradiction hcrc. since iiiosl previous work used malcs while this study used onI!, fcni;~lc~ Studies of .scx differences in scptal rats shov. inclccd. rnalcs do rnatntain lower while lcrnalcs IhI. rnalntalrl normal hodg’ wc~ght\ I?. ‘11, The ~nall~s ot dally r‘ood Intake into cornponcnt mcds 2nd po~lnie;~l Intervals hai shown cffccts of the seplal Icsion untlL~~cl~tcd 111 the gross 23 I~our intake mcasurcs. Daily t’ootl I~I.I~C V+;IS\lmilar lor scpt;~l and sham rats: in ,iJdilion SL’~(~II rats ;IIu) ~~n~umcd mosr of their daily intake during cxhibrting normal diurnal cyclicity. HowIhc n~phrliiiic‘. c\cr. 211 c’i;iniin;illon 01’ the distribution of meals and Inrc~r\;il\ 4io\vctl that scplal Icsions product reliable L,hangcs 111 1’ccd1n~ patlcrns. Scp~al r:lt\ consumed much smaller. inoi-c I’rc~cliicnl iiicdls tllan \h;im IKits. II .rppc‘:rr\ III;I~ Ihca prc,viously known characteristic< ot w~~;II IJI\ .Irc unahlc III acc,ount for this disruption in r‘cctl~ng paircrn. ,Icc~ording IO I.cllagnen [XI . oroscnsory ~.tic\ ;irL’ Ilic Iniiior tlclcrrlllll~nt 01’ meal G/r. Since Ihc seplal i-21 ~veirr~pc~ntl~ IO oro\cnsory cuts I I ,2 1. iI would IW ~~\pc~~lcdwhat mc’al si/ds would hc larger than normal. In tac,t. Ilcl\vcvclI nic3l silt dcc,rcascd following septal arc3 Ic\ions. I tic pc~srmcdl 1ntc’rv;il I\ largely drlerminrd hy the i3lof ii L.ontc’nl 01 the prc\ Ious meal. I‘he correlation hc‘tu?c‘n meal \I/C and !IIC suhscqucnt internal i\ thercforc ;I nicdsurc 01 Ills r,if‘\ ,ihillf> IO use caloric I‘fcdback from the prc’vious ii1~~;11 1X 1 Slt7c.c tlic magnitude of these curi~l~t~ons \r.;b lhc s.inic ~1s ionlrol\. th-2 scptal rats nitisf hc responding IO Ihc calorli cc)ntcnt of the meal normall!~. ~2tld1lion;tl hupporl is provitlctl by Holland 1unpubllshztl tlo~.loral tliss~~rlalion) . \Uho f~~lriid scp131 rats showctl ;I
reduction
in
food
intake
following
idrious
con-
centrations of glucose loads. So iI dppcars thal scptal rats &I not have ;I caloric deficit and thclr oLrrrL’sponsivL’iicss to orosensory cues cannot account for Lhr small t’requcnt mc;ll pattern. Other rxplana1ions must hc sou&l. Snowdon and Epstein I I41 have reporled Iwo olhci casts in which rats show the pattern ot small frcqucnr meals characteristic of septal rats. ( I ) Kats in which oroscnsor): cues wc’rc’ eliminated by inrraga\tric fzcding consumed small f’rcqucnt meals. (2) Rats in WI~IL~II the sensory input from t hc esophagus and stoniacli \~‘iis rcducccl hy scvcring the vagtts nerve. also showed Ihe snidl frqucnI incal pattern. III both cast‘s rats maintalncd slablc intake. but Ihcir meal silts were greatly reduced. This cvidcncc suggests that lhc SIIIJII t’rqucnr mc’31 pattern is indicative ot‘ an animal thdl i\ Ic’ss rcsponsivc than normal to orosensory information. \‘L,( I( has been shown that scptal rats ovsrrcspond to oroscnsc~r~ L‘UL‘S I I .2 I In view of thi5 conlradiction, it is possible 1li~l rhc scptal ral’s allered sensitivity I0 oroscnsor!’ int’ornl;itic~n is not rcsponsihlc t’or 1hL>small frcclurnt mc~l p.rttcrn. In support ot this pussihillty IS c+idcncc prcscntd I~) Snowdon I I.3 ] which links the v~gotom~~cd r;ll’\ >n1;11l nlc;~n pal tern\ to :I motor nol d sensory drl’icll. Snowdon 1I.31 suggests that IIIL’LII \I/C IS clstcrnllncd b> the pal3rahility of the diet. Once in rhc s10111~ch. the 111cal cnipfics info the intcsrinc al ;I r.itc Jcpcnding on the osmotic and nutritive propertics 01’ tlic Iood .IS well ;IS the volume of chc mcal. Snowdon 1‘ountl Llial Ilic srornach ~~mplyinp lime was highly correlal~d with Ihc poslincal interval. This implies that another in~il is inili;itetl \vhen the precious meal con~pletely pasts from tlic stomach IO fhc intrsrine. Snowdon deriionslratd th,iI In v;rgoIomizcd rats. liquid dicls unplicd more rapidI!, than normal I’runi the slorna~h lo rhc dtrotlrntlni. ~luiiidns with vdgotoinics also show [his rapid slorna~h cn~pt! ing ;~nd rt’port LICCO~Ipanying cpipaslric discoinfc~rl ;lrlJ Il;lll\c,l I I I J Small frequent meals cllminatd thcsc unic~rllI’c~rl;lhlc \~nsatlonb. Snowdon suggests that fhc v;igo1on11/cd rat\ nl,i! cut \ni;ill mcds to at,oid scns;ifions ~.aus;cd II! 1111, tapid stomach crnptying. Small nicals cnipty fdsl~ti 1112n norni;il \ILC~ incaIs. and consL*qucntl!,. anotlicr n1cdl I\I In111,it~~l sooner. producing the small t‘requenl ni~*;il p,iI IL~III. l‘lius. Snowdon has accotrntcd t’or the VII~I trcquenr msal patlcrr1 01 vagotomi~~d rats 1,): d~n10n~lr~rtin~ ii pd~~ro~ntcsr~nal niolor control deficiency.
3.
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