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Institute of Experimental Endocrinology, Humboldt University Medical School (Charité), 10098 Berlin, Germany
2To whom correspondence should be addressed.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • low protein diet • perinatal malnutrition • insulin • leptin • hypothalamus • rats
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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, Martyn et al. 1998
, Ravelli et al. 1998
). Maternal protein malnutrition during gestation
and lactation
(LP)3
is frequently used as an appropriate animal model for the investigation
of consequences of perinatal malnutrition on the development of
metabolic and cardiovascular alterations during life (Dahri et al. 1991
, Petry et al. 1997
). LP offspring are
persistently underweight, which is associated with hypertension,
impaired glucose tolerance, and reduced insulin secretion in adulthood
(Beck et al. 1983
, Garofano et al. 1999
,
Langley-Evans 1997
, Moura et al. 1996
,
Rasschaert et al. 1995
). Pathophysiologic mechanisms
responsible for this perinatally acquired disposition are unclear.
Body weight, food intake and metabolism are decisively regulated by
hypothalamic nuclei [for reviews, see Bernardis (1985)
and Bray et al. (1990)
]. Among these structures, the
ventromedial hypothalamic nucleus (VMN) and the lateral hypothalamic
area (LHA) are the most intensively investigated hypothalamic
regulatory centers [for reviews, see Bernardis and Bellinger (1993)
and Bray et al. (1990)
]. Stimulation of
the VMN inhibits food intake, body weight gain and pancreatic insulin
secretion, whereas the antagonistic LHA stimulates eating, weight gain
and insulin output (Inoue and Bray 1977
, Kennedy 1957
). The two nuclei are connected to each other, and project
to the dorsomedial hypothalamic nucleus (DMN; Saper et al. 1976
), which likely serves as a kind of "functional
interneuron" (Luiten and Room 1980
).
During recent years, investigations of hypothalamic regulation of
food intake, body weight and metabolism have focused primarily on the
arcuate-paraventricular-nucleus-(ARC-PVN) axis [for review, see
Porte et al. (1998)
]. Within this axis, neuropeptides
play a key role [for review, see Kalra et al. (1999)
].
Among them, neuropeptide Y (NPY), expressed in neurons of the ARC and
released in the PVN, is a potent stimulator of food intake
(Clark et al. 1984
). Injection of NPY into the PVN leads
to the development of hyperphagia and overweight (Stanley et al. 1986
). Galanin (GAL) represents another orexigenic neuropeptide
expressed and released within the ARC-PVN axis (Levin et al. 1987
). It stimulates food intake and preference for fat
ingestion (Leibowitz et al. 1998
, Pedrazzi et al. 1998
). Both orexigenic peptides are counteracted by
neuropeptides that inhibit food intake such as cholecystokinin-8S (CCK)
[for review, see Baldwin et al. (1998)
].
CCK-induced reduction of food intake and CCK-induced satiety
were demonstrated to be mediated by its action, particularly in the PVN
(Faris 1985
, Willis et al. 1984
).
It is important to note that neuroendocrine regulatory systems of the
hypothalamus are vulnerable to hormonal, metabolic and nutritional
disturbances early in life. During critical developmental periods,
altered levels of systemic hormones and neurotransmitters can lead to
long-term persistent disorganization and, consecutively,
dysfunction of central nervous regulators, e.g., in the hypothalamus
[for reviews, see Dörner (1976)
, Goy and McEwen (1980)
and Meaney et al. (1996)
]. In a
series of recent studies in various animal models, we demonstrated that
increased concentrations of insulin during the critical perinatal
period of hypothalamic differentiation might lead to disturbed
organization of hypothalamic regulatory centers of body weight and
metabolism. This is accompanied by the development of overweight and
diabetogenic disturbances later in life (Harder et al. 1998
, Plagemann et al. 1992
, 1998b
, 1999a
, 1999c
, 1999d
and 1999e
).
In the past, neuroscience research on the consequences of maternal low
protein malnutrition was focused primarily on the development of
general brain variables such as brain size and brain weight
[Forbes et al. 1977
, Leprohon and Anderson 1982
, Marin et al. 1995
; for review, see also
Morgane et al. (1993)
]. Some studies focused on
alterations of hippocampal structures and their effect on learning
behavior in LP offspring (Chen et al. 1992
,
Morgane et al. 1993
, Villescas et al. 1981
). However, except for one study, which investigated the
suprachiasmatic nucleus (Cintra et al. 1994
), no data
exist on hypothalamic structures in rats exposed to maternal low
protein malnutrition, in particular on those nuclei known to be
critical for the regulation of body weight and metabolism. Therefore,
we investigated the effect of maternal low protein malnutrition on the
development of mediobasal hypothalamic nuclei in weanling offspring.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The study was performed in the offspring, bred in our institute, of
Wistar rats of an outbred colony strain (Shoe: Wist; Versuchstierzucht
Schönwalde, Schönwalde, Germany). At the age of 3 mo,
virgin female rats were time-mated with normal males. On the day of
conception (d 0 of pregnancy), verified by the presence of sperm in
vaginal smears, pregnant rats were randomly assigned to the control
group (CO) or low protein group (LP). Beginning at d 0 of pregnancy, LP
rats (n = 10) were fed an 8% low protein diet
(C1003; Altromin, Lage, Germany), whereas CO rats (n
= 7) received an isocaloric 17% control protein diet (C1000;
Altromin). Both diets were consumed ad libitum. The compositions are
shown in Table 1
. The groups were fed these diets throughout gestation and lactation.
|
) and were approved by the Local Animal
Care and Use Committee (G 0074/96). Experimental procedures in the offspring.
Body weight was recorded throughout the study. At 3 wk of age, a random sample of 6 of 40 male offspring of CO dams and 6 of 33 male offspring of LP dams was killed after food deprivation at 0800 h by rapid decapitation. Trunk blood was collected for the determination of blood glucose, insulin and leptin, and brains were taken for neuromorphometric investigations.
Metabolic variables.
Glucose was measured by photometric determination using the glucoseoxidase-peroxidase method (Dr. Lange GmbH, Berlin, Germany). Immunoreactive plasma insulin was determined by means of a modified commercial RIA (BioChem ImmunoSystems GmbH, Freiburg, Germany). Rat insulin with a biological potency of 172 pmol/L served as a standard (Novo Nordisk Biolabs, Copenhagen, Denmark). The intra-assay CV ranged between 4.5 and 7.4% in a concentration range between 73 and 761 pmol/L (n = 10). For determination of leptin, a commercial RIA was performed (Linco, St. Charles, MO). Recombinant rat leptin (Linco) served as a standard. The intra-assay CV was 2.0–4.6% in a concentration range between 1.6 and 11.6 µg/L (n = 20).
Staining procedure.
Neuromorphologic variables were obtained as described in detail
elsewhere (Plagemann et al. 1998a
and 1999a
). In brief,
24 h before killing, the rats were treated with a single
intracerebroventricular injection of colchicine (5 µg
dissolved in 5 µL of saline; Fluka, Buchs, Germany).
After decapitation on d 20 of life, brains were quickly removed and
fixed in Bouin solution for 48 h. After embedding in Histoplast
(Shandon, Frankfurt, Germany), 5 µm-thick serial
coronal sections were cut through the hypothalamus at planes 24–32
according to Paxinos and Watson (1986)
.
Alternate sections were Nissl-stained with Cresyl violet (Nissl+) or immunostained for neuropeptide Y (NPY+), galanin (GAL+), cholecystokinin-8S (CCK+), or glial fibrillary acidic protein (GFAP+), using the avidin-biotin-peroxidase complex (ABC) method (Vectastain Kit; Vector Laboratories, Burlingame, CA). To increase antibody penetration, for immunocytochemistry, slides were pretreated with 0.3% Triton X-100 (Ferak, Berlin, Germany), followed by incubation in methanol containing 0.3% hydrogen peroxide for 15 min at room temperature to inhibit endogenous peroxidase activity. After the slides were washed in PBS (pH 7.3) and rinsed with 2% normal horse serum (lot no. F0717; Vector), nonspecific background staining was reduced by treatment with serum-free Dako-Protein Block for 5 min (lot no. 116–3; Dako, Copenhagen, Denmark). Incubation with a rabbit-antibody to rat NPY (1:6000; lot no. 960108–3; Peninsula, Belmont, CA), a rabbit-antibody to rat GAL (1:5000; lot no. 030195–10; Peninsula), a rabbit-antibody to rat CCK-8S (1:750; lot no. 105H4852; Sigma, St. Louis, Missouri), or a rabbit-antibody to cow GFAP [1:800; lot. no. 119 (071); Dako] was performed for 48 h in a humid chamber at 4°C. After being washed, the slides were treated for 2 h with biotinylated anti-rabbit immunoglobulin G (1:500, lot no. F0425; Vector), followed by incubation with ABC for 2 h. Sections were exposed to a 0.05% solution of 3,3 diaminobenzidine tetrahydrochloride (lot no. 08811EZ; Sigma) containing 0.01% hydrogen peroxide for 20 min. Finally, the sections were dehydrated and mounted with Entellan (Merck, Darmstadt, Germany). Specificity of the labeling procedure was verified by the absence of immunocytochemical reaction in sections in which the primary antibody was omitted or was substituted by normal serums. The slides were coded to prevent investigators’ knowledge of the experimental group.
Neuromorphometric investigations.
All morphometric investigations were performed by means of an image
analysis system (KS 400; Kontron, Echingen, Germany) connected to a
light microscope (Axioscope; Zeiss, Oberkochen, Germany). For
evaluation of the volumes of hypothalamic nuclei, to determine their
area at a final magnification of 90X, the boundaries of the PVN and the
VMN were drawn interactively in each of the Nissl-stained serial
sections showing these nuclei. From these measurements, the volume of
each hypothalamic nucleus was calculated by means of the Simpson rule
(Gottlieb et al. 1985
, Uylings et al. 1986
). The brain volume index (BVI), a measure of
whole-brain volume (Jacobson et al. 1980
), was
calculated from measurements at the level of the mediobasal
hypothalamus according to Maecker (1993)
. The relative
volume of each hypothalamic nucleus (PVN and VMN) was calculated by
dividing the volume of the nucleus by the BVI (Maecker 1993
).
Using the successive sections, neurons were counted in topographically
distinct parts of the VMN and the PVN (Paxinos and Watson 1986
, Van Houten and Brawer 1978
), as well as in
the LHA, DMN and ARC at a final magnification of 2000X by one
investigator who had no knowledge of the experimental group. For each
measurement, microscopic fields (MF) were placed in predetermined
locations in hypothalamic nuclei as follows (Fig. 1
).
|
; Fig. 1a
) four MF were placed in the anterior part of the VMN
(VMNpa), with the first MF filling the medio-cranial quadrant of
the nucleus. After measurement, the slice was moved to the lateral
side, and the second MF was placed immediately lateral to the lateral
border of MF1, strictly avoiding overlapping of both MF. The third MF
was then placed immediately below the basis of MF2. MF4 was located by
moving the slice medially, immediately to the medial border of MF3,
thereby situating it below MF1, again avoiding any overlapping with the
neighboring MF. In both the magnocellular (PVNm) and parvocellular part
(PVNp) of the PVN, three MF were placed in triangular form to cover the
whole area of the subnucleus. As a predetermined location, the upper
lateral quadrant of each subnucleus was chosen for MF1. By moving the
slice laterally, MF2 was placed bordering immediately medial to MF1.
After measurement of MF2, by moving the slice toward the basis of the
hypothalamus, the third MF was then placed immediately below MF2 (Fig. 1a
).
At plane 30–31 (Fig. 1b
), four MF were placed bilaterally
in each part of the VMN [dorsomedial part (VMNpd); ventrolateral part
(VMNpv); central part (VMNpc)] in the following way. In the VMNpd and
VMNpv, the upper medial quadrant of the subnucleus was chosen as a
predetermined location for MF1. As described for VMNpa, MF2 and MF3
were located. After measurement of MF3, the slice was moved to the
medial side, and MF4 was located immediately laterally to the lateral
border of MF3, without overlapping the two MF. In the VMNpc, MF1 was
located immediately to the medial border of the subnucleus. After
measurement, the slice was moved medially, and after moving cranially
for half of the length of one MF, MF2 was located laterally to MF1. In
the same way, MF3 and MF4 were located, thereby covering the whole
subnucleus. For measurements in the DMN, at planes 30–31, four MF in
each section and hemisphere, respectively, were investigated as
described above for the VMNpa, but leaving one MF open between MF
measured, thereby covering the whole area of the nucleus (Fig. 1b
).
The ARC was investigated at planes 28–32 (Fig. 1b
),
analyzing three MF on each side of the brain in each section. The MF
were located in triangular form to cover the whole area of the nucleus
as follows. As a predetermined location, the lower lateral quadrant of
the nucleus was chosen for MF1. By moving the slice laterally, MF2 was
placed bordering immediately medially to MF1. After measurement, the
third MF was then placed immediately cranially to MF2.
In the LHA, six MF were placed at all planes, with the first one
located above the top of the optical tract. After measurement, by
moving the slice toward the basis of the hypothalamus, the second MF
was located cranially to MF1, leaving the full space of one MF free. In
the same way, MF3 was located cranially to MF2. From here, MF4 was
located by moving the slice laterally, again leaving the space of one
MF free. MF5 and MF6 were located exactly below MF4, again leaving the
space of one MF free between fields measured (Fig. 1a
,
b
).
For measurements in the periventricular hypothalamic area (PER; Fig. 1a
, b
), three microscopic fields were placed
around the top of the third ventricle in each hemisphere at a final
magnification of 1000X (Plagemann et al. 1999a
) in the
following way. MF1 was located with its lower medial angle immediately
above the top of the third ventricle. After measurement, the slice was
moved cranially, and MF2 was located immediately at the lower border of
MF1. By the same way, MF3 was located below MF2.
All measurements were performed in both hemispheres of the brain in
each section. Only those neurons with a distinct nucleolus were
included (Bereiter and Jeanrenaud 1979
, Erkut et al. 1998
, Erskine and Miller 1995
).
All cell counts were corrected for the size of the structure counted
(nucleolus) by applying a correction factor initially developed by
Carrière and Patterson (1962)
, as cited by
Ebbesson and Tang (1965)
, and Vischer et al. (1989)
. According to this, the corrected value N was calculated
as
 |
where N is the actual cell count, T is the
thickness of the section (5 µm) and d was
calculated as
 |
where Dn is the mean diameter
of the structure counted (nucleolus) and
Ds is the smallest visible fragment of
the structure. Following the method of Vischer et al. (1989)
, the size of the structure to be corrected (nucleolus)
was measured in 10 sections for each hypothalamic structure using an
image analysis system (see above).
In the ARC, the numerical density of neurons positive for NPY was determined as described above. In the PVN, the numerical density of neurons positive for GAL or CCK was measured (see above). For determination of the numerical density of astrocytes (GFAP+), three microscopic fields were placed around the top of the third ventricle in each hemisphere in the PER to cover the whole GFAP-expressing area as described above.
Statistical analysis.
For evaluation of the mean values of each morphometric variable, means
of all investigated sections in each nucleus were calculated for each
rat. These means were used for calculation of the mean values per
group, i.e., the mean values of the CO group compared with the LP
group. Percentages of immunopositive neurons per total number of
neurons, as well as the numerical glia to neuron ratio, were calculated
from the mean values of matched fields of measurement in
Nissl-stained sections and immunostained sections, respectively
(Bragin et al. 1991
, Plagemann et al. 1998a
and 1999a
).
Data are expressed as means ± SEM. ANOVA and Student’s t test, with or without Welch correction, or Mann-Whitney U-test, respectively, were used for determination of significant differences between the groups. Statistical evaluations were performed using the SPSS-for-Windows package (SPSS Software, Munich, Germany).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Maternal protein restriction during pregnancy and lactation resulted in
significantly less body weight gain in the whole population of LP
offspring compared with CO offspring; this was true at birth [CO, 6.4
± 0.1 g (n = 40) vs. LP, 6.0 ± 0.1 g (n = 33); P < 0.05] and
progressed throughout the suckling period until weaning [d 10 of life:
CO, 21 ± 0.4 g (n = 40) vs. LP, 14 ± 0.4 g (n = 33); P < 0.001; d 20
of life: CO, 34 ± 0.7 g (n = 40) vs. LP, 21
± 0.8 g (n = 33); P < 0.001]. Data of the random sample of rats assigned to the metabolic
and neuromorphometric investigations are shown in Figure 2a
.
|
). Leptin levels in the offspring were not
significantly different from those of CO offspring under basal
conditions at weaning (Fig. 2b
). Morphometric variables in the offspring.
On d 20 of life, LP offspring had a significantly lower BVI
(P < 0.001) than CO rat pups. This was accompanied by
a significantly greater relative volume of the VMN (P
< 0.01). The absolute volume of the PVN was lower in LP than in
CO offspring (P < 0.05; Table 2
).
|
. In the PVN, in total , a significantly greater numerical density of
neurons (neurons/mm2) was found in LP offspring
compared with CO rat pups (P < 0.001). Detailed
analysis of distinct parts of this nucleus revealed that this
difference was attributable mainly to more
neurons/mm2 in the magnocellular part of the PVN
(P < 0.01). Significantly more
neurons/mm2 were found in the VMN in total
(P < 0.01), with tendencies for greater density in all
subnuclei examined [VMN-anterior part (P = 0.055),
VMN-dorsomedial part (P = 0.11), VMN-central
part (P = 0.08)] except the ventrolateral part
of the VMN. No significant difference in
neurons/mm2 was observed in the ARC, LHA and DMN
between LP and CO offspring (see Table 3
).
|
, differences of general neuronal densities within distinct hypothalamic
nuclei in LP rats were accompanied by differences in neuronal
subpopulations immunopositive for specific hypothalamic neuropeptides.
LP offspring had a significantly lower mean number and percentage of
neurons positive for NPY in the ARC than CO offspring (P
< 0.05; see Figs. 3
, 4a
, b
). In the PVN, a lower neuronal density and percentage of neurons
immunopositive for GAL were found in LP rat pups compared with CO
offspring (P < 0.001; see Figs. 3
, 4c
, d
). No significant difference between LP and CO offspring
was observed in the density of CCK-positive neurons in the PVN (see
Fig. 3
).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Maternal protein restriction during gestation and lactation results in
growth retardation and underweight in the offspring (Dahri et al. 1991
, Petry et al. 1997
). As described by
other investigators, this is accompanied by decreased glucose levels at
weaning (Gamallo et al. 1989
). The significant decrease
of insulin observed in LP rats can be interpreted as a response to
lower glucose levels, and may also be a result of insufficient
stimulation of the developing pancreatic ß-cells by amino acids
(Kervran and Randon 1980
), which are decreased in plasma
and milk of LP mothers (Malandro et al. 1996
,
Ronayne de Ferrer and Sambucetti 1993
). A permanent
reduction of the number of pancreatic ß-cells, accompanied by a
persistently reduced insulin secretion, has been described in LP
offspring by Dahri et al. (1991)
. Surprisingly,
underweight was not accompanied by significant alterations of leptin
levels, possibly due to a relative increase of fat content in the milk
provided by LP dams (Marin et al. 1995
). On the other
hand, malnutrition might represent a stressful event, leading to
increased levels of glucocorticoids, which are known to stimulate
leptin synthesis and secretion (Wabitsch et al. 1996
).
Underweight and metabolic alterations were associated with a lower BVI
in weanling LP offspring, indicating a diminished brain size as
described by other investigators in this animal model (Forbes et al. 1977
, Leprohon and Anderson 1982
). For the
first time, in our study, mediobasal hypothalamic nuclei decisively
involved in the regulation of body weight and metabolism were
investigated in this animal model. In LP offspring, underweight and
reduced insulin at weaning were accompanied by morphometric signs of an
altered organization of the VMN, showing a greater volume and a higher
numerical density of neurons. Remarkably, at the same stage of early
postnatal life, no increase, but rather a decrease, of the numerical
density of neurons in the VMN was observed in three animal models of
perinatal hyperinsulinism (Dörner et al. 1988
,
Plagemann et al. 1999a
and 1999c
). Therefore,
enlargement of the VMN accompanied by neuronal hyperplasia could be
suggested (with some caution) to result at least in part from low
insulin levels during the critical hypothalamic differentiation period.
This hypothesis seems to be supported by the observations on
periventricular GFAP+ astrocytes in LP offspring. Insulin is known to
stimulate GFAP expression (Toran-Allerand et al. 1991
).
In previous studies, we observed an increased density of GFAP+
astrocytes in the PER of neonatally hyperinsulinemic rats
(Plagemann et al. 1999a
and 1999c
). In our study, in
contrast, a significant reduction in the number of astrocytes, as well
as a reduction in the numerical glia to neuron ratio occurred in
hypoinsulinemic weanling LP rats, possibly due to reduced levels of
insulin during hypothalamic differentiation. Insulin binds to
astrocytes and stimulates GFAP expression in vitro (Albrecht et al. 1982
, Toran-Allerand et al. 1991
); it may
exert organizational effects on astrocytes, particularly during the
early postnatal developmental period, which is characterized by rapid
changes in hypothalamic GFAP expression (Botchkina and Morin 1995
). Furthermore, astrocytes interact with hypothalamic
neurons to modulate neuronal maturation and neuroendocrine activity
(Mc Queen 1994
, Rakic 1981
,
Theodosis and MacVicar 1996
). Therefore, alterations in
the number of astrocytes as well as a disturbed glia to neuron ratio
and glia-neuron interaction might have permanent consequences for
hypothalamic organization and neuroendocrine functions, respectively.
In recent years, special attention has focused on the hypothalamic
ARC-PVN axis and its role in the regulation of food intake and body
weight [for review, see Kalra et al. (1999)
].
Morphometric analysis of these nuclei was performed here, including
investigations of neurons immunopositive for two major neuropeptides
that stimulate food intake, and, in contrast, a neuropeptide that
inhibits food ingestion.
In the ARC of LP offspring, fewer neurons were positive for NPY, which
is a potent stimulator of food intake and body weight (Clark et al. 1984
). In addition, in the PVN, a strong reduction was
observed in the number of neurons immunopositive for GAL, which also
increases food intake (Leibowitz et al. 1998
). On the
other hand, no significant group difference was observed in the
numerical density of neurons expressing the anorectic peptide CCK-8S in
the PVN, underlining that feeding a low protein diet to rat dams does
not lead to a generalized decrease of specific neuropeptidergic neurons
in the mediobasal hypothalamus in the offspring. Whether these
alterations are specific for low protein malnutrition or whether
similar responses could arise from other forms of maternal malnutrition
should be investigated in future studies.
The question arises whether these morphometric alterations may have any
consequences for the long-term outcome of LP offspring. In two
different animal models, i.e., in the offspring of gestational diabetic
rat dams and in neonatally overfed rats raised in small litters, a
persisting increase from weaning to adulthood was observed in the
numerical density of neurons expressing NPY or GAL in the ARC-PVN
system, which was positively correlated with overweight and hyperphagia
in these rats throughout life (Plagemann et al. 1998b
, 1999b
, 1999d
and 1999e
). From these observations, it could be
suggested (with some caution) that hyperplasia of neurons expressing
the orexigenic peptides NPY and GAL could possibly be the result of
increased insulin during the critical period of hormone-dependent
brain differentiation, possibly contributing at least in part to the
development of lasting hyperphagia and overweight in these rats. On the
contrary, rats perinatally hypoinsulinemic due to maternal protein
malnutrition remain underweight and show persisting hypophagia
throughout life (Beck et al. 1983
, Petry et al. 1997
). Remarkably, as shown in this study, these rats display
hypoplasia of neurons expressing NPY and GAL at weaning, i.e., a
decrease of major neuropeptides stimulating food intake and body weight
gain. Therefore, it is suggested here that a perinatally acquired
reduction of the number of neurons expressing these orexigenic peptides
in the ARC-PVN axis could be one factor contributing to hypophagia
and underweight in LP rats throughout life. Nevertheless, the
correlations between morphologic changes and perinatal hypoinsulinism
do not show causality per se, but they appear to be of interest because
they are reciprocal with those observed in animal models of perinatal
hyperinsulinism.
Furthermore, a number of studies reported the appearance of decreased
insulin secretion, increased sympathetic nervous tone and increased
systolic blood pressure in adulthood of LP offspring (Garofano et al. 1999
, Langley-Evans 1997
,
LeonQuinto et al. 1998
, Petry et al. 1997
). In this context, it seems remarkable that the VMN, which
inhibits pancreatic insulin secretion and stimulates sympathetic
activity (Perkins et al. 1981
), displays an increased
neuronal density at the end of the critical hypothalamic
differentiation period in LP rats, as well as the PVN, known to
stimulate blood pressure (Krukoff et al. 1994
). Assuming
that this disturbed organization may persist into adulthood, as was
shown in other experimental models of perinatal malnutrition
(Plagemann et al. 1998b
, 1999b
and 1999e
), we speculate
that these hypothalamic disturbances may contribute to the development
of decreased insulin secretion as well as the hypertension observed in
LP offspring in later life.
In summary, at the end of the critical hypothalamic differentiation period, in the offspring of low protein malnourished rat dams, complex disorganization of main hypothalamic regulators of body weight and metabolism was found. Because mechanisms responsible for persisting hypophagia and underweight, accompanied by metabolic and cardiovascular disturbances, in later life of perinatally malnourished subjects are unclear, a neuroendocrine "malprogramming" of the central nervous regulation of body weight and metabolism may provide a new etiopathogenetic concept in this context. Alterations of the organization and function of hypothalamic regulatory centers, acquired during early development, might possibly play a role in the development of these phenomena. Disturbances of food-dependent and hormone-mediated organization of these nuclei might lead to life-long persistent consequences for the regulation of body weight, metabolism and cardiovascular function. Therefore, future studies should focus on the organization and, particularly, the function of hypothalamic regulatory centers in later life of subjects exposed to early malnutrition during critical periods of development.
|
ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
3 Abbreviations used: ABC, avidin-biotin-peroxidase complex; ARC, arcuate hypothalamic nucleus; BVI, brain volume index; CCK-8S, cholecystokinin-8S; CO, controls; DMN, dorsomedial hypothalamic nucleus; GAL, galanin; GFAP, glial fibrillary acidic protein; LHA, lateral hypothalamic area; LP, low protein; MF, microscopic field; NPY, neuropeptide Y; PER, periventricular hypothalamic area; PVN, paraventricular hypothalamic nucleus; VMN, ventromedial hypothalamic nucleus.
Manuscript received February 10, 2000. Initial review completed March 27, 2000. Revision accepted June 5, 2000.
|
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|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
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