Mechanisms of seizures and coma in hypoglycemia. Evidence for a direct effect of insulin on electrolyte transport in brain

Insulin effects on core neurotransmitter pathways involved in schizophrenia neurobiology: a meta-analysis of preclinical studies. Implications for the treatment

Impairment of insulin action and metabolic dysregulation have traditionally been associated with schizophrenia, although the molecular basis of such association remains still elusive. The present meta-analysis aims to assess the impact of insulin action manipulations (i.e., hyperinsulinemia, hypoinsulinemia, systemic or brain insulin resistance) on glutamatergic, dopaminergic, γ-aminobutyric acid (GABA)ergic, and serotonergic pathways in the central nervous system. More than one hundred outcomes, including transcript or protein levels, kinetic parameters, and other components of the neurotransmitter pathways, were collected from cultured cells, animals, or humans, and meta-analyzed by applying a random-effects model and adopting Hedges'g to compare means. Two hundred fifteen studies met the inclusion criteria, of which 180 entered the quantitative synthesis. Significant impairments in key regulators of synaptic plasticity processes were detected as the result of insulin handlings. Specifically, protein levels of N-methyl-D-aspartate receptor (NMDAR) subunits including type 2A (NR2A) (Hedges' g = -0.95, 95%C.I. = -1.50, -0.39; p = 0.001; I2 = 47.46%) and 2B (NR2B) (Hedges'g = -0.69, 95%C.I. = -1.35, -0.02; p = 0.043; I2 = 62.09%), and Postsynaptic density protein 95 (PSD-95) (Hedges'g = -0.91, 95%C.I. = -1.51, -0.32; p = 0.003; I2 = 77.81%) were found reduced in insulin-resistant animal models. Moreover, insulin-resistant animals showed significantly impaired dopamine transporter activity, whereas the dopamine D2 receptor mRNA expression (Hedges'g = 3.259; 95%C.I. = 0.497, 6.020; p = 0.021; I2 = 90.61%) increased under insulin deficiency conditions. Insulin action modulated glutamate and GABA release, as well as several enzymes involved in GABA and serotonin synthesis. These results suggest that brain neurotransmitter systems are susceptible to insulin signaling abnormalities, resembling the discrete psychotic disorders' neurobiology and possibly contributing to the development of neurobiological hallmarks of treatment-resistant schizophrenia.

Oxidative stress: a common imbalance in diabetes and epilepsy

The brain requires a large amount of energy. Its function can be altered when energy demand exceeds supply or during metabolic disturbances such as diabetes mellitus. Diabetes, a chronic disease with a high incidence worldwide, is characterized by high glucose levels (hyperglycemia); however, hypoglycemic states may also occur due to insulin treatment or poor control of the disease. These alterations in glucose levels affect the brain and could cause epileptic seizures and status epilepticus. In addition, it is known that oxidative stress states emerge as diabetes progresses, contributing to the development of diseases secondary to diabetes, including retinopathy, nephropathy, cardiovascular alterations, and alterations in the central nervous system, such as epileptic seizures. Seizures are a complex of transient signs and symptoms resulting from abnormal, simultaneous, and excessive activity of a population of neurons, and they can be both a cause and a consequence of oxidative stress. This review aims to outline studies linking diabetes mellitus and seizures to oxidative stress, a condition that may be relevant to the development of severe seizures in diabetes mellitus patients.

Peter WL. Hypoglycemia Risk With SGLT2 Inhibitors or Glucagon-Like Peptide 1 Receptor Agonists Versus Sulfonylureas Among Medicare Insured Adults With CKD in the United States

Rationale & Objective

Study Design

Setting & Participants

Exposures

Outcomes

Analytical Approach

Results

Limitations

Conclusions

A higher non-severe hypoglycaemia rate is associated with an increased risk of subsequent severe hypoglycaemia and major adverse cardiovascular events in individuals with type 2 diabetes in the LEADER study

AIMS/HYPOTHESIS

Hypoglycaemia is a common side effect of insulin and some other antihyperglycaemic agents used to treat diabetes. Severe hypoglycaemia has been associated with adverse cardiovascular events in trials of intensive glycaemic control in type 2 diabetes. The relationship between non-severe hypoglycaemic episodes (NSHEs) and severe hypoglycaemia in type 2 diabetes has been documented. However, an association between more frequent NSHEs and cardiovascular events has not been verified. This post hoc analysis of the LEADER (Liraglutide Effect and Action in Diabetes: Evaluation of Cardiovascular Outcome Results) trial aimed to confirm whether there is an association between NSHEs and severe hypoglycaemic episodes in individuals with type 2 diabetes. In addition, the possible association between NSHEs and major adverse cardiac events (MACE), cardiovascular death and all-cause mortality was investigated.

METHODS

LEADER was a double-blind, multicentre, placebo-controlled trial that found that liraglutide significantly reduced the risk of MACE compared with the placebo. In this post hoc analysis, we explored, in all LEADER participants, whether the annual rate of NSHEs (defined as self-measured plasma glucose <3.1 mmol/l [56 mg/dl]) was associated with time to first severe hypoglycaemic episode (defined as an episode requiring the assistance of another person), time to first MACE, time to cardiovascular death and time to all-cause mortality. Participants with <2 NSHEs per year were used as reference for HR estimates. Cox regression with a time-varying covariate was used.

RESULTS

We demonstrate that there is an association between NSHEs (2-11 NSHEs per year and ≥12 NSHEs per year) and severe hypoglycaemic episodes (unadjusted HRs 1.98 [95% CI 1.43, 2.75] and 5.01 [95% CI 2.84, 8.84], respectively), which was consistent when baseline characteristics were accounted for. Additionally, while no association was found between participants with 2-11 NSHEs per year and adverse cardiovascular outcomes, higher rates of NSHEs (≥12 episodes per year) were associated with higher risk of MACE (HR 1.50 [95% CI 1.01, 2.23]), cardiovascular death (HR 2.08 [95% CI 1.17, 3.70]) and overall death (HR 1.80 [95% CI 1.11, 2.92]).

CONCLUSIONS/INTERPRETATION

The analysis of data from the LEADER trial demonstrated that higher rates of NSHEs were associated with both a higher risk of severe hypoglycaemia and adverse cardiovascular outcomes in individuals with type 2 diabetes. Therefore, irrespective of the cause of this association, it is important that individuals with high rates of hypoglycaemia are identified so that the potentially increased risk of cardiovascular events can be managed and steps can be taken to reduce NSHEs.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT01179048).

Proximal Disruption of Brain Energy Supply Raises Systemic Blood Glucose: A Systematic Review

This work joins a series that methodically tests the predictions of the Selfish-Brain theory. The theory postulates a vital ability of the mammalian brain, namely to give priority to its own energy metabolism. The brain behaves “selfishly” in this respect. For the cerebral artery occlusion studied here, the theory predicts an increase in blood glucose concentration, what becomes the hypothesis to be tested. We conducted a systematic review of cerebral-artery-occlusion papers to test whether or not the included studies could confirm this hypothesis. We identified 239 records, screened 231 works by title or abstract, and analyzed 89 by full text. According to strict selection criteria (set out in our PROSPERO preregistration, complying with PRISMA guidelines), 7 papers provided enough information to decide on the hypothesis. Our hypothesis could be fully confirmed for the 3 to 24 h after the onset of a transient 2 h or permanent occlusion. As for the mechanism, the theory predicts that the energy-deprived brain suppresses insulin secretion via the sympathoadrenal system, thereby preventing insulin-mediated glucose uptake into muscle and fat and, as a result, enhancing insulin-independent glucose uptake via the blood-brain barrier. Evidence from our included studies actually demonstrated cerebral insulin suppression. In all, the current work confirms the second major prediction of the Selfish-Brain theory that relates to a proximal bottleneck of the cerebral supply chain, cerebral artery occlusion. Its first major prediction relates to a distal supply bottleneck, caloric restriction, and is fulfilled as shown by our previous work, whereas the prediction of the long held gluco-lipostatic theory, which sees the brain as only passively supplied, is violated (Sprengell et al., 2021). The crucial point was that caloric restriction elicits smaller changes in mass (energy) in the brain than in the body. Taken together, the evidence from the current and previous work clearly shows that the most accurate predictions are possible with a theory that views the brain as an independently self-regulating energy compartment occupying a primary position in energy metabolism.

Oxygen releasing hydrogels for beta cell assisted therapy

Diabetes is a serious chronic disease, which globally affects more than 400 million patients. Beta cell therapy has potential to serve as an effective cure to type 1 diabetes and several studies have already shown promising results in this regard. One of the major obstacles in cell therapy, however, is the hypoxic environment that therapeutic cells are subjected to immediately after the transplantation. In this study, a new approach is presented, based on hydrogels composed of thiolated hyaluronic acid (tHA), 8-arm-Poly(ethylene glycol)-Acrylate (PEGA), and calcium peroxide (CPO) as an oxygen releasing system. Hydrogels containing 0, 7.5, and 30% CPO were prepared, and the presence of CPO was confirmed via FTIR and Alizarin Red within the network. Oxygen release kinetics were monitored over time, and the results revealed that the hydrogels containing 30% CPO could release oxygen for at least 30 h. All three combinations were found to be injectable and suitable for beta cell therapy based on their mechanical and rheological properties. Additionally, to investigate the functionality of the system, insulin secreting INS-1E reporter cell clusters were encapsulated, and their viability was evaluated, which showed that CPO incorporation enhanced cell survival for at least three days.

A Case Report of Nonketotic Hyperglycemic Seizures: A Diagnostic Dilemma

Nonketotic hyperglycemia (NKH) is a rare but serious complication of uncontrolled diabetes mellitus that occurs acutely with a mortality rate of more than 50%. This condition presents with a clinical syndrome consisting of profound hyperglycemia, hyperosmolality, and dehydration. Infrequently, the patients also present with seizure activity. The most common types of seizures observed in this condition are focal seizures, as opposed to the generalized seizures observed in hypoglycemia-induced seizures. Though various hypotheses tried to explain NKH-induced seizure activity, the actual mechanism remains unknown. The treatment modalities include the management of hyperglycemia and circulatory collapse. However, the role of anti-epileptics is controversial. We herein illustrate an atypical case of focal faciobrachial seizures in a young female patient, which occurred as a rare complication of NKH. A 21-year-old female was admitted with multiple jerking and spasmodic movements of the right upper limb and face, with no significant neurological findings. Past medical history was significant for uncontrolled type 2 diabetes mellitus and multiple episodes of focal seizures. On laboratory examination, serum osmolarity was 309 mOsm/L, blood glucose was 364 mg/dL, HbA1c was 12.1%, and ketone bodies were absent. MRI brain showed large subtle T2 FLAIR (T2-weighted fluid-attenuated inversion recovery) cortical hyperintensities in the left frontal, temporal, parietal, and occipital regions with subcortical hypointense areas. The EEG illustrated a background slowing and generalized spikes, polyspikes, and sharp-wave discharges with post-ictal slowing. The patient's seizures were initially refractory to insulin therapy and resolved with the use of dual anti-epileptics. Thus, to conclude, our case represents a diagnostic dilemma with MRI findings pointing towards NKH as the underlying etiology of focal seizures, with the resolution of seizures only occurring with the addition of anti-epileptics to insulin therapy.

Activation of Functional Brain Networks in Children With Psychogenic Non-epileptic Seizures

Objectives

Psychogenic non-epileptic seizures (PNES) have been hypothesized to emerge in the context of neural networks instability. To explore this hypothesis in children, we applied a graph theory approach to examine connectivity in neural networks in the resting-state EEG in 35 children with PNES, 31 children with other functional neurological symptoms (but no PNES), and 75 healthy controls.

Methods

The networks were extracted from Laplacian-transformed time series by a coherence connectivity estimation method.

Results

Children with PNES (vs. controls) showed widespread changes in network metrics: increased global efficiency (gamma and beta bands), increased local efficiency (gamma band), and increased modularity (gamma and alpha bands). Compared to controls, they also had higher levels of autonomic arousal (e.g., lower heart variability); more anxiety, depression, and stress on the Depression Anxiety and Stress Scales; and more adverse childhood experiences on the Early Life Stress Questionnaire. Increases in network metrics correlated with arousal. Children with other functional neurological symptoms (but no PNES) showed scattered and less pronounced changes in network metrics.

Conclusion

The results indicate that children with PNES present with increased activation of neural networks coupled with increased physiological arousal. While this shift in functional organization may confer a short-term adaptive advantage-one that facilitates neural communication and the child's capacity to respond self-protectively in the face of stressful life events-it may also have a significant biological cost. It may predispose the child's neural networks to periods of instability-presenting clinically as PNES-when the neural networks are faced with perturbations in energy flow or with additional demands.

Branched-Chain Amino Acids and Seizures: A Systematic Review of the Literature

BACKGROUND

Up to 40% of patients with epilepsy experience seizures despite treatment with antiepileptic drugs; however, branched-chain amino acid (BCAA) supplementation has shown promise in treating refractory epilepsy.

OBJECTIVES

The purpose of this systematic review was to evaluate all published studies that investigated the effects of BCAAs on seizures, emphasizing therapeutic efficacy and possible underlying mechanisms.

METHODS

On 31 January, 2017, the following databases were searched for relevant studies: MEDLINE (OvidSP), EMBASE (OvidSP), Scopus (Elsevier), the Cochrane Library, and the unindexed material in PubMed (National Library of Medicine/National Institutes of Health). The searches were repeated in all databases on 18 February, 2019. We only included full-length preclinical and clinical studies that were published in the English language that examined the effects of BCAA administration on seizures.

RESULTS

Eleven of 2045 studies met our inclusion criteria: ten studies were conducted in animal models and one study in human subjects. Seven seizure models were investigated: the strychnine (one study), pentylenetetrazole (two studies), flurothyl (one study), picrotoxin (two studies), genetic absence epilepsy in rats (one study), kainic acid (two studies), and methionine sulfoximine (one study) paradigms. Three studies investigated the effect of a BCAA mixture whereas the other studies explored the effects of individual BCAAs on seizures. In most animal models and in humans, BCAAs had potent anti-seizure effects. However, in the methionine sulfoximine model, long-term BCAA supplementation worsened seizure propagation and caused neuron loss, and in the genetic absence epilepsy in rats model, BCAAs exhibited pro-seizure effects.

CONCLUSIONS

The contradictory effects of BCAAs on seizure activity likely reflect differences in the complex mechanisms that underlie seizure disorders. Some of these mechanisms are likely mediated by BCAA's effects on glucose, glutamate, glutamine, and ammonia metabolism, activation of the mechanistic target of rapamycin signaling pathway, and their effects on aromatic amino acid transport and neurotransmitter synthesis. We propose that a better understanding of mechanisms by which BCAAs affect seizures and neuronal viability is needed to advance the field of BCAA supplementation in epilepsy.

Hypoglycemia-induced alterations in hippocampal intrinsic rhythms: Decreased inhibition, increased excitation, seizures and spreading depression

Seizures are the most common clinical presentation of severe hypoglycemia, usually as a side effect of insulin treatment for juvenile onset type 1 diabetes mellitus and advanced type 2 diabetes. We used the mouse thick hippocampal slice preparation to study the pathophysiology of hypoglycemia-induced seizures and the effects of severe glucose depletion on the isolated hippocampal rhythms from the CA3 circuitry.

METHODS AND RESULTS

Dropping the glucose perfusate concentration from the standard 10 mM to 1 mM produced epileptiform activity in 14/16 of the slices. Seizure-like events (SLEs) originated in the CA3 region and then spread into the CA1 region. Following the SLE, a spreading-depression (SD)-like event occurred (12/16 slices) with irreversible synaptic failure in the CA1 region (8/12 slices). CA3 SD-like events followed ~30 s after the SD-like event in the CA1 region. Less commonly, SD-like events originated in the CA3 region (4/12). Additionally, prior to the onset of the SLE in the CA3 area, there was decreased GABA correlated baseline SPW activity (bSPW), while there was increased large-amplitude sharp wave (LASW) activity, thought to originate from synchronous pyramidal cell firing. CA3 pyramidal cells displayed progressive tonic depolarization prior to the seizure which was resistant to synaptic transmission blockade. The initiation of hypoglycemic seizures and SD was prevented by AMPA/kainate or NMDA receptor blockade.

CONCLUSIONS

Severe glucose depletion induces rapid changes initiated in the intrinsic CA3 rhythms of the hippocampus including depressed inhibition and enhanced excitation, which may underlie the mechanisms of seizure generation and delayed spreading depression.

Expression of aquaporin 4 and breakdown of the blood-brain barrier after hypoglycemia-induced brain edema in rats

Background

Hypoglycemia-induced brain edema is a severe clinical event that often results in death. The mechanisms by which hypoglycemia induces brain edema are unclear.

Methods

In a hypoglycemic injury model established in adult rats, brain edema was verified by measuring brain water content and visualizing water accumulation using hematoxylin and eosin staining. Temporal expression of aquaporin 4 (AQP4) and the integrity of the blood-brain barrier (BBB) were evaluated. We assessed the distribution and expression of AQP4 following glucose deprivation in astrocyte cultures.

Results

Brain edema was induced immediately after severe hypoglycemia but continued to progress even after recovery from hypoglycemia. Upregulation of AQP4 expression and moderate breakdown of the BBB were observed 24 h after recovery. In vitro, significant redistribution of AQP4 to the plasma membrane was induced following 6 h glucose deprivation.

Conclusion

Hypoglycemia-induced brain edema is caused by cytotoxic and vasogenic factors. Changes in AQP4 location and expression may play a protective role in edema resolution.

The effects of hypoglycemic and alcoholic coma on the blood-brain barrier permeability

In this investigation, the effects of hypoglycemic coma and alcoholic coma on the blood-brain barrier (BBB) permeability have been compared. Female adult Wistar albino rats weighing 180-230 g were divided into three groups: Control group (n=8), Alcoholic Coma Group (n=18), and Hypoglycemic Coma group (n=12). The animals went into coma approximately 3-4 hours after insulin administration and 3-5 minutes after alcohol administration. Evans blue (4mL/kg) was injected intravenously as BBB tracer. It was observed that the alcoholic coma did not significantly increase the BBB permeability in any of the brain regions when compared to control group. Changes in BBB permeability were significantly increased by the hypoglycemic coma in comparison to the control group values (p<0.01). Our findings suggest that hypoglycemic and alcoholic coma have different effects on the BBB permeability depending on the energy metabolism.

Blinders, phenotype, and fashionable genetic analysis: a critical examination of the current state of epilepsy genetic studies

Although it is accepted that idiopathic generalized epilepsy (IGE) is strongly, if not exclusively, influenced by genetic factors, there is little consensus on what those genetic influences may be, except for one point of agreement: epilepsy is a "channelopathy." This point of agreement has continued despite the failure of studies investigating channel genes to demonstrate the primacy of their influence on IGE expression. The belief is sufficiently entrenched that the more important issues involving phenotype definition, data collection, methods of analysis, and the interpretation of results have become subordinate to it. The goal of this article is to spark discussion of where the study of epilepsy genetics has been and where it is going, suggesting we may never get there if we continue on the current road. We use the long history of psychiatric genetic studies as a mirror and starting point to illustrate that only when we expand our outlook on how to study the genetics of the epilepsies, consider other mechanisms that could lead to epilepsy susceptibility, and, especially, focus on the critical problem of phenotype definition, will the major influences on common epilepsy begin to be understood.

Change in blood-brain barrier permeability during pediatric diabetic ketoacidosis treatment

OBJECTIVE

Cerebral edema is a devastating complication of pediatric diabetic ketoacidosis. We aimed to examine blood-brain barrier permeability during treatment of diabetic ketoacidosis in children.

DESIGN

Prospective observational study.

SETTING

Seattle Children's Hospital, Seattle, WA.

PATIENTS

Children admitted with diabetic ketoacidosis (pH <7.3, HCO3 <15 mEq/L, glucose >300 mg/dL, and ketosis).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Subjects underwent two serial paired contrast-enhanced perfusion (gadolinium) and diffusion magnetic resonance imaging scans. Change in whole brain and regional blood-brain barrier permeability (permeability ratio*100 and % permeability ratio change) between illness and recovery were determined. Time 0 reflects start of insulin treatment. Thirteen children (median age 10.0 +/- 1.1 yrs; seven female) with diabetic ketoacidosis were enrolled. Permeability ratio increased from time 1 (first magnetic resonance image after time 0) to time 2 (second magnetic resonance image after time 0) in the frontal cortex (ten of 13 subjects), occipital cortex (ten of 13 subjects), and basal ganglia (nine of 13). Whole brain permeability ratio increased from time 1 to time 2 (160%) and regional increase in permeability ratio was greatest in the frontal cortex (148%) compared with the occipital cortex (128%) and basal ganglia (112%).

CONCLUSIONS

Overall, whole brain and regional blood-brain barrier permeability increased in most subjects during diabetic ketoacidosis treatment. The frontal region had more blood-brain barrier permeability than other brain regions examined.

Severe unrecognised hypoglycaemia presenting as pseudonormoglycaemia and unexplained coma in two patients with renal failure

We describe the occurrence of pseudonormoglycaemia and the consequences of severe prolonged hypoglycaemia observed in two patients with renal failure requiring renal replacement therapy. There was a persistent discrepancy, in both cases, between glucose levels measured by the hospital laboratory and those measured by the bedside glucometer, resulting in a significantly false high glucose measurement (pseudonormoglycaemia). This inaccurate glucose determination led to a delayed diagnosis of their truly severe and prolonged hypoglycaemia ultimately leading to prolonged coma and death. Icodextrin, a polysaccharide commonly used in continuous ambulatory peritoneal dialysis solutes, and maltose-containing solutions such as immunoglobulins for intravenous administration, can cause a dangerous overestimation of glucose levels determined by capillary blood glucose analysers utilising glucose dehydrogenase. A high level of awareness is required in order to avoid incidents related to misinterpretation of glucose levels.

Hyponatremia with hypoxia: Effects on brain adaptation, perfusion, and histology in rodents

Hypoxia appears to be a prominent component of brain damage among patients with hyponatremic encephalopathy. Effects of hypoxia on brain in the presence of hyponatremia are not known. In order to evaluate the contributions of hypoxia to brain damage, three separate experiments were conducted in three groups of rodents. Experiment I evaluated the effects of hypoxia and acute (< 4 h) hyponatremia (plasma Na < 120 mmol/l) on brain adaptation in rabbits. Experiment II evaluated the effects of hypoxia and chronic (4 days) hyponatremia on cerebral perfusion in rats. Experiment III evaluated the effects of hypoxia and chronic hyponatremia on brain histology in rats. In experiment I, rabbits with acute hyponatremia demonstrated brain adaptation with significant falls in brain Na content (by 14.2%, P < 0.01) and osmolality (by 8.3%, P < 0.01), and a rise in brain water (by 10.6%, P < 0.05). Rabbits with combined hypoxia and hyponatremia failed to demonstrate brain adaptation. In experiment II, rats with chronic hyponatremia plus hypoxia had a decrease in cerebral perfusion index by more than 50% (P < 0.01). In experiment III, 23% of hypoxic rats had brain lesions, which were in the cerebellum, thalamus, reticular formation, and basal ganglia. Hyponatremia without hypoxia resulted in no brain lesions. Hypoxia in normonatremic animals results in cerebral edema and histopathologic lesions similar to those found in rats whose plasma Na was overcorrected. Hypoxia in hyponatremic animals aggravates cerebral edema, impairs brain adaptation, and decreases cerebral perfusion.

Antiseizure activity of insulin: insulin inhibits pentylenetetrazole, penicillin and kainic acid-induced seizures in rats

The present study was undertaken to evaluate the antiseizure activity spectrum of insulin against various behavioral seizure models in rats. Insulin was injected intraperitoneally (i.p.) at a test dose of 1 U/kg. Dextrose (3 g/kg) was administered simultaneously with insulin to counteract its hypoglycemic effect and induce a normoglycemic state. Insulin was found to significantly decrease the incidence, intensity and mortality rate and prolong the latency of generalized tonic-clonic convulsions induced by pentylenetetrazole (60 mg/kg i.p.) and significantly decrease the intensity and mortality rate and prolong the latency of generalized tonic-clonic convulsions induced by penicillin (2000 U/intracerebrocortical). Insulin was not only found to prolong the latency of all the seizure components but was found to reduce the incidence of focal myoclonic twitches and generalized tonic-clonic convulsions induced by kainic acid (12 mg/kg i.p.) as well. Insulin was shown to be ineffective to suppress ouabain (5 micrograms/intracerebroventricular) induced seizures. These findings indicate that insulin possesses a broad spectrum of antiseizure activity in rats. Interaction with brain Na(+)-K(+)-ATPase has been discussed as a possible mechanism of action.

Effects of hypernatraemia in the central nervous system and its therapy in rats and rabbits

1. We studied the effects of acute (1 or 4 h) and chronic (1 week) hypernatraemia (plasma [Na+], 170-190 mM) on brain histology, and brain water and solute contents in rats and rabbits. 2. In rabbits with acute hypernatraemia, there was significant loss of intracellular brain water, with increases in brain [Na+ + K+], amino acid concentration, and undetermined solute (idiogenic osmole). After 1 week of recovery, brain intracellular water content had returned to normal. 3. In hypernatraemic rats there was myelinolysis of brain white matter, with karyorrhexis and necrosis of neurons. 4. Hypernatraemic rabbits were treated with 77 mM NaCl (i.v.) to normalize plasma [Na+] over 4-24 h intervals. Therapy of either acute or chronic hypernatraemia resulted in significant brain oedema because brain osmolality failed to decrease at the same rate as plasma osmolality. 5. It is concluded that: (a) untreated hypernatraemia results in brain lesions demonstrating myelinolysis and cellular necrosis; (b) normalization of hypernatraemia over 4-24 h results in cerebral oedema, due primarily to failure of brain amino acids and idiogenic osmoles to dissipate as plasma [Na+] is decreased to normal.

Insulin in the cerebrospinal fluid

The presence, distribution and specific localization of insulin and its receptors in the central nervous system (CNS) have been described in numerous reports. Insulin in the CNS appears to be similar to pancreatic insulin by biochemical and immunological criteria. While the presence of insulin in the cerebrospinal fluid (CSF)--an essential neurohumoral transport system--has been widely reported, the available information is fragmented and therefore it is difficult to determine the significance of insulin in the CSF and to establish future research directions. This paper presents an integrative view of the studies concerning insulin in the CSF of various species including the human. Evidence suggests that insulin in the CSF and brain may be the result of local synthesis in the CNS, and uptake from the peripheral blood through the blood-brain barrier and circumventricular organs. The passage of insulin from the peripheral blood through the blood-brain barrier may be mediated by a specific transport system coupled to insulin receptors in cerebral microvessels. The transfer of insulin from the peripheral blood through the circumventricular organs is not specific and may depend on simple diffusion. Slow access of insulin to brain interstitial fluid adjacent to the blood-brain barrier and circumventricular organs may be followed by selective transport to other brain sites and into the ventricular-subarachnoideal CSF. It has been hypothesized that the choroid plexuses, which constitute the blood-CSF interface, might be a nonspecific pathway for rapid insulin transport into the CSF. Insulin may also pass from the CSF into the peripheral blood via absorption into the arachnoid villi. This evidence indicates that insulin may be transported in both directions between the CSF-brain and the peripheral blood. Evidence also suggests that the presence of insulin in the CSF is of pivotal importance for its neurophysiological or neuropathophysiological significance.

Blood-brain barrier permeability to sodium. Modification by glucose or insulin?

In order to explore the pathogenetic mechanism underlying the changes in blood-brain barrier sodium transport in experimental diabetes, the effects of hyperglycemia and of hypoinsulinemia were studied in nondiabetic rats. In untreated diabetes, the neocortical blood-brain barrier permeability for sodium decreased by 20% (5.6 +/- 0.7 versus 7.0 +/- 0.8 X 10(5) ml/g/s) as compared to controls. Intravenous infusion of 50% glucose for 2 h was associated with a decrease in the blood-brain barrier permeability to sodium (5.4 +/- 1.2 X 10(5) ml/g/s), whereas rats treated with an inhibitor of insulin-secretion (SMS 201-995, a somatostatin-analogue) had normal sodium permeability (7.3 +/- 2.0 X 10(5) ml/g/s). Acute insulin treatment of diabetic rats normalized the sodium permeability within a few hours as compared to a separate control group (7.7 +/- 1.1 versus 6.9 +/- 1.4 X 10(5) ml/g/s). To elucidate whether the abnormal blood-brain barrier passage is caused by a metabolic effect of glucose or by the concomitant hyperosmolality, rats were made hyperosmolar by intravenous injection of 50% mannitol. Although not statistically significant, blood-brain barrier sodium permeability increased in hyperosmolar rats as compared to the control rats (8.3 +/- 1.0 and 7.0 +/- 1.9 X 10(5) ml/g/s, respectively). It is concluded that either hyperglycemia per se or a glucose metabolite is responsible for the blood-brain barrier abnormality which occurs in diabetes. Further, we suggest that the specific decrease of sodium permeability could be the result of glucose-mediated inhibition of the Na+K+-ATPase localized at the blood-brain barrier.

Electrolyte shifts between brain and plasma in hypoglycemic coma

Hypoglycemia of sufficient severity to cause cessation of EEG activity (coma) is accompanied by energy failure and by loss of ion homeostasis, the latter encompassing a marked rise in extracellular fluid (ECF) K+ concentration and a fall in ECF Ca2+ concentration. Presumably, ECF Na+ concentration decreases as well. In the present study, the extent that the altered ECF-plasma gradients give rise to net ion fluxes between plasma and tissue is explored. Accordingly, whole tissue contents of Ca2+, Mg2+, K+, and Na+ were measured. The experiments were carried out in anaesthetized and artificially ventilated rats given insulin i.p.; cerebral cortical tissue was sampled at the stage of slow-wave EEG activity, after 10, 30, and 60 min of coma (defined as isoelectric EEG), as well as after 1.5, 6, and 24 h of recovery. In the precomatose animals (with a slow-wave EEG pattern), no changes in electrolyte contents were observed. During coma, tissue Na+ content increased progressively and the K+ content fell (each by 20 mumol g-1 during 60 min). During recovery, these alterations were reversed within the first 6 h. The Mg2+ content remained unchanged. In spite of the appreciable plasma to ECF Ca2+ gradient, no significant calcium accumulation was observed. It is concluded significant calcium accumulation was observed. It is concluded that hypoglycemia leads to irreversible neuronal necrosis in the absence of gross accumulation of calcium in the tissue.

Insulin-induced drinking: an analysis of the involvement of renal angiotensin II and insulin-induced changes in plasma volume

Male Long-Evans rats were used to investigate the potential hydrational mechanisms underlying insulin-induced drinking (IID). Plasma volume effects of insulin were assessed using both hematocrit and dye dilution procedures. Evidence is presented indicating that insulin produces a long-lasting and dose-dependent reduction in plasma volume. However, it does not appear that the drinking response is tightly tied to the reduced plasma volume because a 50% blockade of this effect does not reduce water intake. In addition, it does not appear that insulin-induced drinking is related to a release of renal angiotensin because IID is not blocked by nephrectomy. The mechanism underlying IID may be related to the activation of the recently described brain insulin receptor system.

Pathophysiology of type A hypoxic lactic acidosis in dogs

Hypoxic lactic acidosis (HLA) was induced in dogs by ventilating them with a hypoxic gas mixture of 8% O2-92% N2. The animals were studied both in the control state and after development of HLA, where arterial lactate was above 5 mM, pH was below 7.2, bicarbonate was below 12 mM, and arterial PO2 was between 26 and 30 Torr. After hypoxia had been present for 90 min, most of the increase in arterial lactate vs. control was due to increased lactate production from gut and carcass in the presence of a decreased capacity of the liver to extract lactate. The capacity of the liver to extract lactate in the normoxic state was evaluated in another group of six dogs after infusion of L-lactic acid such that arterial pH, lactate, and bicarbonate were similar to hypoxic values. In these experiments it was found that the capacity of the liver to extract lactate was 14.8 +/- 1.7% of the delivered load vs. 4.9 +/- 1.3% observed in hypoxic animals. The decreased liver lactate extraction in HLA was probably secondary to both a decrease in liver oxygen uptake and a decrease in liver intracellular pH and was paralleled by an increase in liver tissue lactate levels. Cardiac output, in contrast to other forms of lactic acidosis, was increased by 40% vs. control and femoral artery flow by 35%, whereas liver blood flow was unchanged and renal blood flow decreased. Hypoxic lactic acidosis thus is the consequence of overproduction of lactate by both gut and carcass, in the presence of impaired utilization of lactate by the liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Nocturnal convulsions and insulin-induced hypoglycaemia in diabetic patients

Convulsions may occur as a consequence of insulin-induced hypoglycaemia. We report three patients with insulin-dependent diabetes, who presented with generalized tonic-clonic seizures associated with nocturnal hypoglycaemia. None of the patients had experienced hypoglycaemia during waking hours and the convulsions were mistakenly diagnosed as idiopathic epilepsy. Recognition of the possible hypoglycaemia aetiology of these convulsions permitted appropriate alteration of the insulin regimens with no recurrence of convulsions. In one case, the seizure was associated with bilateral fractures of the neck of the humerus. Unrecognized hypoglycaemia should be considered as a possible cause of convulsions in insulin-dependent diabetic patients.

Prolactin, growth hormone and thyrotropin-thyroid hormone secretion during stress states in man

Changes in hormone secretion and/or metabolism almost constantly accompany stressful events. The hormonal response to stress is directly related to the intensity of the stimulus, and greatly depends on the individual's perception of potentially stressful situations. Hypoglycaemia, surgery and exercise represent physical, metabolic and psychological stressful events where the activation of the endocrine system plays a great role. These endocrine responses also include the secretion of GH and prolactin, but the response pattern varies with the stimulus. Hypoglycaemia, exercise and surgery are potent stimuli to GH and prolactin release, both in men and women. The available data suggest that prolactin is more responsive than GH to surgical stress, whereas physical exercise and hypoglycaemia preferentially stimulate GH secretion. Prolactin levels during hypoglycaemia rise solely when symptomatic neuroglycopenia is achieved. By contrast, prolactin and GH responses to purely psychological stress are rarely seen, although some forms of reproductive stress may potentiate prolactin release in women. A teleologically satisfactory rationale for the acute GH and prolactin rise in response to these stressful stimuli is not clearly apparent in man. No definite metabolic activity of prolactin on intermediate metabolism has been demonstrated, although prolactin is mildly diabetogenic. The known metabolic actions of GH do not appear to be critical during surgery or acute hypoglycaemia, although GH probably participates in the regulation of metabolic homeostasis during chronic hypoglycaemia and chronic exercise. Changes in secretion and/or metabolism of hypothalamic neurotransmitters can increase the secretion of GH by increasing the secretion of GHRH or by decreasing the secretion of somatostatin. The prolactin rise is brought about by either a decrease in dopamine activity, an increased secretion of a hypothetical PRF, or by both mechanisms. Since multiple neuronal pathways converge on the hypothalamus from many other parts of the brain, the pronounced effects of hypoglycaemia, exercise and surgery on the secretion of GH and prolactin also reflect the action of different and complex neural inputs on the activity of the hypothalamic-pituitary axis. However, the morpho-functional mapping of these excitatory pathways still remains incomplete. TSH secretion is tightly regulated by the negative feed-back mechanism exerted by thyroid hormones. The small changes in TSH level observed during surgery and physical exercise seem to reflect mainly alterations in peripheral T4 metabolism.(ABSTRACT TRUNCATED AT 400 WORDS)

Brainstem auditory and visual evoked potentials in type 1 (insulin-dependent) diabetic patients

Brainstem auditory evoked potentials and pattern shift visual evoked potentials were measured in 34 Type 1 (insulin-dependent) diabetic patients with long-standing disease and in 43 control subjects. Thirty-two percent of diabetic patients had abnormal brainstem auditory evoked potentials and 15% had abnormal visual evoked potentials. These abnormalities were not related to duration of diabetes, diabetic control or individual diabetic complications (retinopathy, nephropathy, peripheral or autonomic neuropathy). The aetiology of the abnormalities must remain a subject for speculation. The findings of this study are consistent with a central diabetic neuropathy involving the brainstem in long-standing diabetic patients.

Cellular basis of direct insulin action in the central nervous system

The in vivo radioautographic method has been applied to elucidate the mechanism of direct peptide hormone "feedback" action in the CNS. Using this method we have identified the circumventricular organs of the brain as general endocrine target tissues for a variety of blood-borne polypeptide hormones, including insulin. In the arcuatemedian eminence region of the hypothalamus blood-borne insulin directly interacts with receptive nerve terminals, suggesting that insulin acts to influence the electrical activity of select hypothalamic nerve circuits at the level of synaptic transmission. Recent results obtained from preliminary surgical and chemical lesion studies of brain indicate that insulin-receptive nerve terminals in the arcuate-median eminence region arise from neurons intrinsic to the medial basal hypothalamus. This has lead us to propose the concept of the hypothalamic tuberoinfundibular insulin-receptive neuron and its axon collaterals as a pathway for the centripetal flow of insulin "signals" in the form of electrical impulses. We envisige that the neuroanatomic pathway, provided by the hypothalamic tuberoinfundibular neuron, functions to link changes in body metabolic activity, as reflected in changing levels of circulating insulin, to the neuronal process of elaborating specific central metabolic-regulatory programs. This pathway could be of key importance in understanding and combating metabolic disease.

The effect of severe hypoglycemia upon cerebrospinal fluid formation, ventricular iodide clearance, and brain electrolytes in rabbits

Severe insulin-induced hypoglycemia in rabbits reduces cerebrospinal fluid (CSF) formation, but not ventricular iodide clearance as measured by ventriculocisternal perfusion. This indicates that CSF production is ultimately glucose-dependent but that ventricular iodide clearance is not. The data suggest that severe hypoglycemia results in intracellular potassium loss within the brain and show that extracellular sodium replaces lost intracellular potassium. Hypoglycemia probably results in cellular adenosine triphosphate (ATP) reduction which affects membrane Na/K ATPase and the ability of the brain cell to maintain a potassium gradient. Potassium levels in the CSF also rise consequent to hypoglycemia. Homeostatic mechanisms that maintain a constant CSF potassium, therefore, are also affected by hypoglycemia.

Insulin binds to brain blood vessels in vivo

The brain has generally been considered an insulin-independent organ, because insulin does not apparently exert a direct effect on brain glucose consumption. Recently, however, insulin receptors have been detected throughout the central nervous system (CNS) of several species. Since important insights into the functional significance of brain insulin receptors might be provided by identification of the cell type(s) possessing these receptors, we have attempted to localise them morphologically using light and electron microscope autoradiography. We report here results indicating that blood vessels throughout the CNS of the rat bind plasma insulin rapidly and with considerable specificity.

Routine use of low-dose intravenous insulin infusion in severe hyperglycaemia

A review if presented of the use of low-dose insulin infusion in the management of 58 episodes of severe diabetic hyperglycaemia. Neutral insulin in a dosage of 2-4 units per hour is infused via a paediatric giving set to achieve a sustained physiological elevation of insulin levels. This method is safe, simple and rapidly effective in lowering the blood glucose level, the mean rate of fall (62 mg/100 ml/hr, or 11% per hour) being unaffected by prior insulin therapy, acidosis or ketonuria. Classification of the hyperglycaemia as ketoacidotic or hyperosmolar is unnecessary before insulin therapy is instituted, as the relative decline in glucose level is the same in the hyperosmolar non-ketotic group as in the others. Proven infection significantly lowers the rate of fall of glucose level. Hypoglycaemia and hypokalaemia are rare during low-dose infusion. Early and adequate replacement with potassium phosphate is recommended, oral potassium supplements being continued for several days. Bicarbonate therapy is rarely indicated in the management of acidosis. No patient had cerebral oedema during treatment, and one elderly patient with extensive pneumonia and empyema died during the infusion. It is suggested that continuation of low-dose insulin infusion, together with 5% dextrose solution, after the plasma glucose level reaches 200 mg/100 ml, may hasten the clearance of ketones, preventing relapse.

Lactic acidosis: an experimental model

A model of spontaneous lactic acidosis was developed in alloxan diabetic rabbits by infusing intravenously beta-hydroxybutyric acid followed by a continuous infusion of NaHCO3. In half of the animals, the arterial lactate/pyruvate ratio rose from 2.5 mM/0.19mM to 20.4 mM/0.28 mM, and arterial pH fell to 7.16. In animals with lactic acidosis, the calculated ratio in blood of NAD/NADH was 1437 +/- 230, versus a normal value of 6754 +/- 1250. Both arterial PO2 and blood pressure were normal. Continued infusion of NaHCO3 led to increased blood lactate levels, with cardiorespiratory arrest in 36% of animals. Lactic acidosis did not develop in normal rabbits who were similarly treated. It is concluded that spontaneous lactic acidosis can be produced in diabetic, but not in normal, rabbits by infusion of beta-hydroxybutric acid followed by infusion of NaHCO3.