Depopulation of the ventromedial hypothalamic nucleus in the diabetic Chinese hamster

The Effect of Diabetes Mellitus on Apoptosis in Hippocampus: Cellular and Molecular Aspects

Background:

Diabetes mellitus is associated with cognitive deficits in humans and animals. These deficits are paralleled by neurophysiological and structural changes in brain. In diabetic animals, impairments of spatial learning, memory, and cognition occur in association with distinct changes in hippocampus, a key brain area for many forms of learning and memory and are particularly sensitive to changes in glucose homeostasis. However, the multifactorial pathogenesis of diabetic encephalopathy is not yet completely understood. Apoptosis plays a crucial role in diabetes-induce neuronal loss in hippocampus.

Methods:

The effects of diabetes on hippocampus and cognitive/behavioral dysfunctions in experimental models of diabetes are reviewed, with a focus on the negative impact on increased neuronal apoptosis and related cellular and molecular mechanisms.

Results:

Of all articles that were assessed, most of the experimental studies clearly showed that diabetes causes neuronal apoptosis in hippocampus through multiple mechanisms, including oxidative stress, inhibition of caspases, disturbance in expression of apoptosis regulator genes, as well as deficits in mitochondrial function. The balance between pro-apoptotic and anti-apoptotic signaling may determine the neuronal apoptotic outcome in vitro and in vivo models of experimental diabetes.

Conclusions:

Dissecting out the mechanisms responsible for diabetes-related changes in the hippocampal cell apoptosis helps improve treatment of impaired cognitive and memory functions in diabetic individuals.

Hypercytolipidemia-induced nuclear lipoapoptosis: cytochemical analysis and integrated review of hypogonadal, diabetes-obesity syndrome-induced female reproductive axis disruption

Expression of the diabetes (db/db) mutation (i.e., leptin receptor defect) in C57BL/KsJ mice results in the functional suppression of the female pituitary-gonadal axis accompanied by premature utero-ovarian lipocytoatrophy. The current studies define the cytostructural, metabolic and endocrine disturbances associated with hypercytolipidemia and coincident nuclear lipoapoptosis following expression of the db/db-mutation. Adult, female C57BL/KsJ control (+/+ and +/? genotypes) and db/db mutant littermates were monitored for systemic alterations in blood glucose, insulin, luteinizing hormone (LH) and 17-B-estradiol (E2) concentrations associated with db/db-enhanced cytolipid depositions and TUNEL-labeled 3'-DNA fragmentation indexed nuclear lipoapoptosis. Obesity, hyperglycemia and hyperinsulinemia, in addition to depressed LH and E2 concentrations, characterized all db/db-mutants relative to control indices. Structural and cytochemical analysis of basophilic gonadotroph cells, ovarian follicular granulosa cells and uterine endometrial epithelial layers indicated that db/db mutants demonstrated prominent hypercytolipidemia relative to control cytoarchitecture profiles. Vasolipidemia and interstitial cytoadiposity were prominent in all db/db tissue compartments. In each affected cell type within the db/db pituitary-reproductive tract axis, hypercytolipidemia was localized with pronounced nuclear lipo-infiltration and 3'-DNA TUNEL-labeled fragmentation. These data indicate that coincident cytostructural, endocrine and metabolic disturbances associated with hypogonadal pituitary-reproductive tract hypercytolipidemia are functional manifestations of the expressed diabetes-obesity syndrome in db/db-mutants. The progressive vaso-, interstitial-, and cyto-lipidemic alterations in cytoarchitecture correlated with the coincident nuclear lipoapoptotic dissolution and pronounced organo-involution, alterations which contributed to the functional disruption of the pituitary-hypogonadal axis in C57BL/KsJ-db/db mice.

Effects of Glucose, Insulin, and Supernatant from Pancreatic β-cells on Brain–Pancreas Relative Protein in Rat Hippocampus

Brain-pancreas relative protein (BPRP) is a novel protein that mainly expresses in brain and pancreas. In our previous study, we found that various stressors significantly decreased the expression of BPRP in pancreas in vivo, accompanied by changes in insulin and glucose levels, and that expression of BPRP in pancreas also decreased significantly in diabetic rats induced by Streptozocin (STZ). All these findings suggest that BPRP may be a glucose or insulin-sensitive protein. However, how the changes in insulin or glucose levels influence the expression of BPRP in hippocampus requires further study. Here, we investigated the effects of insulin or glucose on the expression of BPRP in primary cultured hippocampal neurons. We supplied hippocampal neurons with glucose, insulin, or supernatant from pancreatic beta-cells, which secrete insulin into the supernatant. Our data showed that insulin had beneficial effect on the viability while no significant effect on the expression of BPRP in hippocampal neurons. On the contrary, 40 mM glucose or free glucose culture significantly decreased the expression of BPRP, while had no significant effect on the viability and apoptosis of hippocampal neurons. Further study showed that levels of insulin in the supernatant collected from pancreatic beta-cells medium changed over days, and that supernatant increased the viability of hippocampal neurons, while it had no obvious effect on the expression of BPRP in hippocampal neurons. These results suggest that BPRP may be a glucose-sensitive protein.

The role of impaired insulin/IGF action in primary diabetic encephalopathy

We have previously shown that hippocampal neuronal apoptosis accompanied by impaired cognitive functions occurs in type 1 diabetic BB/Wor rats. To differentiate the contribution by insulin deficiency vs. that by hyperglycemia on neuronal apoptosis, we examined the activities of various apoptotic pathways in hippocampi from type 1 diabetic BB/Wor rats (hyperglycemic and insulinopenic) and type 2 diabetic BBZDR/Wor rats (hyperglycemic and hyperinsulinemic). DNA fragmentation was demonstrated by LM-PCR in type 1 diabetic BB/Wor rats, but was not detectable in duration- and hyperglycemia-matched type 2 BBZDR/Wor rats. Of various apoptotic pathways, Fas activations, 8-OHdG expression, and caspase-12 were demonstrated in type 1 diabetic BB/Wor rats only. In contrast, perturbations of the IGF and NGF systems and PARP activation were demonstrated in type 1 and to a lesser extent in type 2 diabetes. Expressions of Bax and active caspase-3 were significantly increased in type 1, but not in type 2, diabetic rats. These data suggest a lesser apoptogenic stress in type 2 vs. type 1 diabetes. These differences translated into a more profound neuronal loss in the hippocampus of type 1 rats. The results demonstrate that caspase-dependent apoptotic activities dominate in type 1 diabetes, whereas PARP-mediated caspase-independent apoptotic stress is present in both type 1 and type 2 diabetes. The findings suggest that insulin deficiency plays a compounding role to that of hyperglycemia in neuronal apoptosis underpinning primary diabetic encephalopathy.

Structural, metabolic and endocrine analysis of the diabetes (db/db) hypogonadal syndrome: relationship to hypophyseal hypercytolipidemia

Expression of the diabetes (db/db) mutation in C57BL/KsJ mice results in functional suppression of the female pituitary-gonadal axis accompanied by premature utero-ovarian cytolipoatrophy. Cellular gluco- and lipo-metabolic disturbances promoted by the db/db systemic hyperglycemic-hyperinsulinemic state suppress pituitary gonadotropin release in response to gonadotropin-releasing hormone and gonadal steroid stimulation and results in a hypogonadal-infertility syndrome. Adult female C57BL/KsJ control (+/+ and +/? genotypes) and db/db littermates were monitored for associations in systemic and cellular alterations in luteinizing hormone (LH), follicle-stimulating hormone (FSH), gonadal steroid (binding) levels, and pituitary glucometabolic indices associated with db/db-enhanced lipid imbibition and cytostructural disruption. Obesity, hyperglycemia, and hyperinsulinemia characterized all db/db mutants relative to controls. Serum and pituitary progesterone and estradiol concentrations were suppressed in db/db mutants, in association with serum LH and FSH levels, but not with pituitary LH and FSH concentrations, which were comparable between groups. Pituitary insulin receptor binding and glucose utilization rates were suppressed in db/db groups relative to +/? indices. Structural and cytochemical analysis of anterior (AP), intermediate (IL), and neuro-(NP) hypophyseal lobes demonstrated prominent hypercytolipidemia in db/db mutants relative to controls. Prominent cytolipidemia was localized within well-granulated basophilic gonadotrophs and within IL and NP pituicytes. Vasolipidemia and interstitial cytoadiposity were prominent throughout all db/db pituitary lobes. Thus, disturbances associated with pituitary hypercytolipidemia are functional components of the expressed diabetes-associated hypogonadal syndrome in db/db mutants. Progressive alterations in hypophyseal cytoarchitecture are correlated with suppression of pituitary metabolic and endocrine indices, alterations that contribute to functional disruption of the pituitary-hypogonadal axis in C57BL/KsJ-db/db mice.

Insulin, C-peptide, hyperglycemia, and central nervous system complications in diabetes

Diabetes is an increasingly common disorder which causes and contributes to a variety of central nervous system (CNS) complications which are often associated with cognitive deficits. There appear to be two types of diabetic encephalopathy. Primary diabetic encephalopathy is caused by hyperglycemia and impaired insulin action, which evolves in a diabetes duration-related fashion and is associated with apoptotic neuronal loss and cognitive decline. This appears to be particularly associated with insulin-deficient diabetes. Secondary diabetic encephalopathy appears to arise from hypoxic-ischemic insults due to underlying microvascular disease or as a consequence of hypoglycemia. This type of cerebral diabetic complication is more common in the type 2 diabetic population. Here, we will review the clinical and experimental data supporting this conceptual division of diabetic CNS complications and discuss the underlying metabolic, molecular, and functional aberrations.

Hypophyseal lipoapoptosis: diabetes (db/db) mutation-associated cytolipidemia promotes pituitary cellular disruption and dysfunction

Expression of the diabetes (db/db) mutation in C57BL/KsJ mice suppresses the female pituitary-gonadal axis via progressive cytolipidemic disruption of hypophyseal gonadotropin release, culminating in premature involution of the reproductive tract and manifest infertility. The current studies define the systemic, endocrine, cytochemical and structural apoptotic changes that result from pituitary hypercytolipidemia induced by db/db mutation expression in this Type II diabetes-obesity syndrome (DOS) model. Adult female C57BL/KsJ control (+/? genotype) and db/db littermates were monitored for systemic and cellular alterations in LH-, FSH- and gonadal steroid-secretion, and coincident pituitary apoptosis, as indexed by TUNEL labeled 3' nuclear DNA-fragmentation, associated with cytolipid depositions. Obesity, hyperglycemia and hyperinsulinemia characterized all db/db-mutants relative to +/? groups. Serum progesterone (P) and estradiol (E2) concentrations were suppressed in db/db mutants coincident with decreased plasma LH and FSH concentrations relative to +/? values. Cytochemical analysis of anterior (AP) pituitary cell subtypes indicated that db/db mutants demonstrated prominent hypercytolipidemia relative to +/? pituitary cytoarchitecture. Cytolipidemic vacuoles were localized within protein vesiculated db/db hypophyseal basophilic and acidophilic cell populations. Hypophyseal cytoadiposity in db/db AP cells was co-localized with prominent cellular apoptotic TUNEL labeling of nuclear 3'-DNA fragments in cells demonstrating vesicular depopulation and cytolytic vacuolization. These data represent the first demonstration of co-localized hypercytolipidemic and cytoapoptotic disruptive events occurring concurrently in a hypopituitary-hypogonadal syndrome model following expression of the Type II (NIDDM) diabetes-obesity syndrome in db/db-mutants. The coincident and progressive vascular-, interstitial- and cyto-lipidemic alterations in hypophyseal cytoarchitecture correlated with the concurrent apoptotic disruption of pituitary endocrine cytoarchitecture and supressed gonadal steroid synthesis, influences which collectively contribute to the premature involution of the pituitary-gonadal axis in C57BL/KsJ- db/db mice.

Developmental and regional changes in brain norepinephrine levels in diabetic C57BL/KsJ mice: effects of estradiol and progesterone

Developmental and diabetes-associated changes in regional brain norepinephrine (NE) concentrations, and the influence of estradiol (E) and progesterone (P) on NE levels, were correlated with changes in blood glucose levels and body weight (obesity) in developing 4-16-week-old C57BL/KsJ (db/db) mice relative to corresponding age-matched control (+/?) parameters. Regional brain (i.e. amygdala, hypothalamus and medulla) NE levels were determined by high performance liquid chromatography. The (db/db) mice exhibited overt hyperglycemia and obesity relative to controls between 4 and 16 weeks of age. Hypothalamic NE levels in diabetics were chronically elevated as compared to those of age-matched controls by 8 weeks of age, and remained elevated through 16 weeks of age. Regional amygdaloid and medullary NE concentrations were comparable in (+/?) and (db/db) groups by 16 weeks. E-treatments normalized (db/db) hypothalamic NE concentrations to control levels between 8 and 16 weeks of age, but had no effect on amygdaloid or medullary values. In contrast, in 16 week old (db/db) mice, P-treatments elevated hypothalamic and medullary NE levels compared to controls and expected diabetic levels. These data demonstrate that a marked modification in regional brain NE concentrations occurs in association with the overt expression of the diabetes mutation during development in this species. Observed changes in adrenergic influences in specific CNS loci may be therapeutically modulated by ovarian steroid hormones, especially in the hypothalamic locus which is recognized to possess steroid-concentrating neurons. The observed normalization of regional brain NE concentrations by E-therapy may be causally related to the ovarian steroid-modulation of overt hyperglycemia and diabetes-associated neuronal degeneration in (db/db) mice.

Genetic influences on glucose neurotoxicity, aging, and diabetes: a possible role for glucose hysteresis

Glucose may drive some age-correlated impairments and may mediate some effects of dietary restriction on senescence. The hypothesis that cumulative deleterious effects of glucose may impair hypothalamic neurons during aging, leading to hyperinsulinemia and other age-correlated pathologies, is examined in the context of genetic influences. Susceptibility to toxic effects of gold-thio-glucose (GTG) is correlated with longevity across several mouse strains. GTG and chronic hyperglycemia induce specific impairments in the ventromedial hypothalamus similar to impairments which occur during aging. GTG and a high-calorie diet both induce chronic hyperinsulinemia, leading initially to hypoglycemia, followed by the development of insulin resistance and hyperglycemia. Aging in humans and rodents appears to entail a similar pattern of hyperinsulinemia followed by insulin resistance. In humans, genetic susceptibility to high-calorie diet-induced impairments in glucose metabolism is extremely common in many indigenous populations, possibly due to the selection of the 'thrifty genotype'. It is suggested that the 'thrifty genotype' may entail enhanced sensitivity to the neurotoxic effects of glucose, and may represent an example of antagonistic pleiotropy in human evolution. These data are consistent with the hypothesis that genetic susceptibility of hypothalamic neurons to the cumulative toxic effects of glucose (glucose neurohumoral hysteresis) may correlate with genetic influences on longevity.

Age- and diabetes-associated alterations in regional brain norepinephrine concentrations and adrenergic receptor populations in C57BL/KsJ mice

The diabetes-associated changes in regional brain norepinephrine (NE) concentrations and related adrenergic receptor types were correlated with changes in blood glucose levels and body weight (obesity) in 4-16-week-old C57BL/KsJ (db/db) mice relative to corresponding age-matched control (+/?) parameters. Regional brain (i.e. frontal cortex, septal area, amygdala, hypothalamus and medulla) NE levels were determined by high performance liquid chromatography and compared to the associated changes in tissue alpha-1,2 and beta-adrenergic membrane receptor populations. All db/db mice exhibited overt hyperglycemia and obesity relative to controls between 4 and 16 weeks of age. Regional brain NE levels in diabetics were chronically elevated as compared to those of age-matched controls. All of the alpha 1 and alpha 2 adrenergic receptor populations were elevated in the regional brain samples of diabetics relative to controls. In contrast, beta-adrenergic receptor populations were depressed in diabetics as compared with age-matched controls. These data demonstrate that a marked modification in regional brain adrenergic parameters occurs in association with the overt expression of the diabetes mutation in this species. The observed changes in adrenergic influences in specific CNS loci may be causally related to the recognized diabetes-associated alterations in regional brain structure, function and metabolism in C57BL/KsJ (db/db) mice.

Morphometric analysis of obesity (ob/ob)- and diabetes (db/db)-associated hypothalamic neuronal degeneration in C57BL/KsJ mice

The influence of the obese (ob/ob) and diabetes (db/db) genetic mutations on hypothalamic structure was investigated in C57BL/KsJ and C57BL/6J mice strains by morphometric analysis of medial basal nuclei which are recognized to possess glucoregulatory neurons. Brains were collected and prepared for histomorphometric analysis at selected times following the development of expressed obesity and diabetes (Type II, non-insulin dependent) syndromes in order to compare both the strain and genomic influences on neuronal viability in the hypothalamic ventromedial (VMH) and arcuate (ARC) nuclei of mutant and age-matched control mice. The severity of each syndrome was determined by monitoring the concomitant changes in body weight and blood glucose levels in all groups. Both (db/db) and (ob/ob) mutant C57BL/KsJ mice exhibited an increase in the number and distribution of degenerated neurons in the VMH and ARC nuclei relative to corresponding controls. The mutation-associated exacerbation of the normal age-related neuronal loss, as observed in control MBH nuclei, was temporally associated with the overt expression of the hyperglycemic component of the obese and diabetes syndromes in aging C57BL/KsJ mice. No temporal or causal relationships were noted between the enhanced rate of premature neuronal degeneration, and either body weight or blood glucose levels, in either (db/db) or (ob/ob) C57BL/6J mice relative to controls. These data suggest that the hyperglycemic condition which characterizes the (ob/ob) and (db/db) mutant C57BL/KsJ mice is causally associated with the pronounced, premature MBH neuronal degeneration in these mouse strains. Neuronal changes were not pronounced when the genetic mutations were expressed in C57BL/6J mice. The accompanying alterations in brain glucose metabolism, hormone sensitivity, bioamine content and function which are recognized to occur in these mutant C57BL/KsJ mice may be causally associated consequences of the observed changes in MBH structural integrity and neuronal competence, with the severity of the mutation-associated changes being related to genetic background of the murine strain.

Regional brain glucose uptake in genetically diabetic C57BL/KsJ mice: modulation by the opiate antagonist, nalmefene

A novel opiate antagonist, Nalmefene (0.5 or 5.0 mg/kg/day) was tested for its ability to modulate regional brain glucose uptake rates in genetically diabetic C57BL/KsJ mice, which normally exhibit a depressed CNS carbohydrate metabolism relative to age-matched controls. Daily Nalmefene treatment had no effect on circulating blood glucose levels in either normal or diabetic mice over a 7-week test period. However, all brain regions, except the olfactory bulbs, exhibited normalized glucose uptake rates in diabetic mice relative to controls. These data suggest a role for opiate antagonists in the modulation of CNS glucose metabolism during hyperglycemic states.

Morphometric analysis of medial basal hypothalamic neuronal degeneration in diabetes (db/db) mutant C57BL/KsJ mice: relation to age and hyperglycemia

Age- and diabetes-related neuronal degenerative changes were morphometrically evaluated in the arcuate (ARC) and ventromedial (VMH) hypothalamic nuclei of control (+/?) and diabetic (db/db) C57BL/KsJ mice between 4 and 16 weeks of age. By 4 weeks of age, (db/db) mice exhibited marked obesity and hyperglycemia relative to controls. An increase in the population of degenerated ARC neurons was detected at 8 weeks of age in (db/db) mice relative to (+/?) animals. By 16 weeks of age, a significant increase in the number of degenerated VMH neurons in (db/db) mice was found, relative to controls. In addition, the neuronal density (neurons/mm2 area of nucleus) of both the ARC and VMH nuclei was found to be depressed in (db/db) mice, relative to controls, by 16 weeks of age. These data suggest that the normal degenerative loss of ARC and VMH neurons that occurs with age in normal mice is enhanced in the (db/db) mouse. These findings suggest that a functional alteration in hypothalamic nuclei which are recognized to modulate autonomic, pancreatic and pituitary activity may be associated with the onset or expression of the diabetic condition in the C57BL/KsJ (db/db) mouse.

Sensitivity to satiating and taste qualities of glucose in obese Zucker rats

A general "glucoreceptor" defect, demonstrable in pancreatic islet and taste cells, may contribute to the metabolic and taste abnormalities of adult onset diabetes and possibly, if present at the level of the hypothalamus, could produce hyperphagia and the obesity seen in diabetics. To determine if a glucoreceptor defect generally accompanies obesity and glucose intolerance, behavioral responsiveness to glucose was examined in nine obese and nine lean female Zucker rats. Daily food and fluid intake were measured during three two-bottle preference tests, in which rats chose between water and one of several glucose solutions (1%, 3%, and 12%). Taste responsiveness to glucose of obese rats appeared normal; however, increased satiating effects of glucose were found in obese rats, possibly due to an enhanced delivery of glucose to neurons that inhibit feeding, caused by glucose intolerance. Also, obese rats had (a) increased brain weights, and (b) increased volumes of ventromedial and paraventricular hypothalamic nuclei. These findings, perhaps explainable by an increased delivery of nutrients to the developing brain, indicate that the hyperphagia of Zucker rats is due neither to an overt hypothalamic lesion nor to insensitivity to glucose.

Effects of progressive hyperglycemia on ovarian structure and function in the spontaneously diabetic Chinese hamster

The effect of the progressive hyperglycemic condition on ovarian follicular maturation was studied in control, moderate (160-350 mg/dl blood glucose), and overt (greater than or equal to 350 mg/dl blood glucose), spontaneously diabetic Chinese hamsters. Match-paired (age, sex, and weight) control and diabetic animals were sacrificed at specific intervals during the development of the diabetic condition; the ovaries were collected and morphometrically analyzed for changes in ovarian follicular growth relative to blood glucose levels. Follicles were classified according to size, number, and condition. The total number of primary (100-200 micrometers diameter) and secondary (200-350 micrometers diameter) follicles was reduced in both moderate and overt diabetic females as compared with controls. The percentage of viable (i.e., nonatretic) follicles was greatly reduced in the secondary follicle class of overt diabetic animals as compared with controls. No significant differences were observed in the numbers of viable tertiary (i.e., greater than or equal to 350 micrometers diameter) follicles in any of the diabetic animals as compared with controls. The percentage of atretic, secondary follicles was greatly increased in the overt diabetic group as compared with controls. These data indicate that the progressive hyperglycemia associated with diabetes in the Chinese hamster induces a severe depression of normal follicular recruitment resulting in an impaired reproductive performance in this species.

Diabetes-associated changes in estradiol accumulation in the aging C57BL/KsJ mouse brain

The effects of aging and diabetes on the uptake and incorporation of [3H]estradiol (E) in various brain areas was analyzed in C57BL/KsJ mice. Control (C; +/?) and diabetic (D; db/db) mice were pulse treated (30 min) with 10 muCi of [3H]E at 1, 2 and 4 months of age and the brains were subsequently microdissected, digested and the amount of incorporated [3H]E assessed. The pituitary and amygdala exhibited the highest levels of [3H]E incorporation of all brain areas, with the hypothalamus, septal nuclei, midbrain, hippocampus, medulla and parietal cortex exhibiting moderate retention levels at one month of age in C animals. All brain areas in D mice had significantly lower incorporation rates than in matchpaired, C animals. An age-related decrease in [3H]E accumulation was observed in all brain regions in both C and D groups, with a significant depression in [3H]E incorporation occurring between 1 and 4 months of age. These data demonstrate that an age-related decrease in [3H]E uptake occurs in most brain areas in the C57BL/KsJ mouse, and that the diabetic condition exacerbates this phenomenon.

Glucose utilization by the mouse brain: influence of age and diabetes

The effects of diabetes on the age-related changes in glucose utilization by various brain regions were examined in genetically diabetic (db/db) and normal (+/?) C57BL/KsJ mice following a 10 muCi injection of [3H]2-deoxyglucose (2-DOG). Brains were collected from 2 to 16-week-old mice at 30 min postinjection with 2-DOG, and the brain regions isolated by microdissection. Glucose utilization was expressed as mumol/mg/30 min for each brain region from match-paired control +/? and db/db mice. No differences in utilization were seen in brain regions from control and db/db mice at 2 weeks of age. In contrast, the diabetic condition effectively depressed the age-related increase in glucose metabolism associated with maturation in control mice between 4 and 16 weeks of age. Of particular interest was the observation that the pituitary gland of the db/db mice did not demonstrate a maturation-associated increase in glucose utilization typical of +/? mice. By 16 weeks of age, all of the brain regions of db/db mice exhibited a depressed glucose utilization rate as compared with +/? mice. These studies demonstrate that the diabetic condition impairs the normal age-related increase in CNS glucose utilization in the mouse, and suggests that decreased glucose utilization may be causally related to diabetes-associated, CNS and peripheral neuropathy.

Diabetes-associated, ventromedial hypothalamic neuronal degeneration in the Chinese hamster

The hypothalamic neurons of the diabetic Chinese hamster exhibited degradation associated with the hyperglycemic, diabetic condition as compared with matched control animals. In particular, neurons in the arcuate and ventromedial nuclei exhibited characteristic indications of neuronal death associated with diabetes. These studies indicate that hypothalamic depopulation induced by diabetes is characterized by neuronal degradation in the nuclei associated with CNS regulation of pancreatic function.

Diabetes-associated hypothalamic neuronal depopulation in the aging Chinese hamster

Age- and diabetes-associated changes in the neuronal density and area of the ventromedial (VMH) and arcuate (ARC) nuclei of the Chinese hamster hypothalamus were analyzed morphometrically. Neuronal density peaked much sooner in diabetic animals than in matched controls, and subsequently declined at a faster rate than did aging, control animals. Nuclear area measurements were depressed in diabetic animals as compared with controls. These findings indicate that diabetes has severe effects on nuclear maturation and dynamics in the Chinese hamster, which may be causally associated with impaired hypothalamus-pituitary function.

Islet innervation of nondiabetic and diabetic Chinese hamsters. I. Acetylcholinesterase histochemistry and norepinephrine fluorescence

Cholinergic and adrenergic innervation of pancreatic islets from age- and sex-matched nondiabetic (M subline) and diabetic (AC subline) Chinese hamsters was analyzed by acetylcholinesterase (AChE) histochemistry and norepinephrine fluorescence. The AChE activity was significantly diminished in islets of diabetic animals compared with that of nondiabetic controls. The reduction in cholinergic innervation displayed an inverse relationship with respect to nonfasting plasma glucose and ketone levels. On the basis of qualitative analysis, adrenergic activity also appeared to be depressed in islets of diabetic animals. These date suggest that autonomic control of islet function is altered in diabetic Chinese hamsters when plasma glucose and ketone levels arae elevated and may exacerbate metabolic complications in this animal model.

Morphometric evaluation of the hypothalamic-ovarian axis of the ketonuric, diabetic Chinese hamster: relationship to the reproductive cycle

The relationship between diabetes and the morphological alterations which occur in hypothalamic and ovarian tissue was examined in the long-term, ketonuric-diabetic Chinese hamster. Matched diabetic and non-diabetic control hamsters were inspected daily for changes in the reproductive cycle by vaginal lavage. On dioestrus, animals were perfused, the hypothalamus and ovaries collected, prepared for microscopy and morphometrically analyzed. The nuclei in the medial basal hypothalamus of diabetic hamsters exhibited a decreased area (p less than 0.01) and neuronal population (p less than 0.05-0.01) compared with controls. The ovaries of the diabetic animals had a reduced follicular population (p less than or equal to 0.05) and an increased atresia rate (p less than or equal to 0.05) compared with controls. In addition, all diabetic hamsters were acyclic. In diabetic animals, the corpora luteal cells contained a reduced lipid content (p less than or equal to 0.001) which was possibly functionally related to a significant decline in serum progesterone levels (p less than or equal to 0.01). Based on these results it is suggested that the hypothalamic-ovarian axis is both morphologically and functionally impaired in the diabetic hamster.