Ronald F. Mervis

HIV envelope protein-induced neuronal damage and retardation of behavioral development in rat neonates

Cognitive and motor impairment are common symptoms among patients infected with the human immunodeficiency virus (HIV), including children who suffer neurological deficits and are frequently developmentally impaired. The HIV envelope protein, gp120, which has been shown to be toxic to neurons in culture, is shed in abundance by infected cells, and thus may play a significant role in the neuropathology of AIDS. To test this possible mechanism, neonatal rats were injected systemically with purified gp120 and the following consequences were observed: (1) radiolabeled gp120 and toxic fragments thereof were recovered in brain homogenates; (2) dystrophic changes were produced in pyramidal neurons of cerebral cortex; (3) retardation was evident in developmental milestones associated with complex motor behaviors. In parallel studies, co-treatment with peptide T, a gp120-derived peptide having a pentapeptide sequence homologous with vasoactive intestinal peptide, prevented or attenuated the morphological damage and behavioral delays associated with gp120 treatment. These studies suggest that gp120 and gp120-derived toxic fragments may contribute to the neurological and neuropsychiatric impairment related to HIV infection, and that peptide T appears to be effective in preventing gp120-associated neurotoxicity in developing rodents.

Dietary restriction suppresses age-related changes in dendritic spines

The effects of dietary restriction by every-other-day (EOD) feeding on dendritic spines in the aging rat neocortex were evaluated in Golgi preparations. After weaning, male Wistar rats were offered a 24% protein diet either ad lib (AL) or EOD. AL-fed groups were sacrificed at 6 and 24-25 months of age. EOD-fed groups were sacrificed at 6, 24, and 30 months. To assess the effects of EOD feeding late in life, another group was fed AL for 19 months, then EOD for 5 months and sacrificed when 24 months old. Spine density and configuration were quantified along 20 microns terminal tip segments from the basilar tree of layer V pyramidal cells of the parietal cortex. Evaluation of spine densities from the 6 and 24 months AL-fed groups showed that there was a significant loss of spines with normal aging (-38%). In EOD-fed rats, spine density did not differ significantly from AL age-matched controls at either 6 or 24 months of age. However, spine densities in 24-month-old rats diet restricted late in life and EOD-fed 30-month-old rats were the same as 6-month-old AL-fed controls and EOD 6-month-old rats, an observation suggesting protection of dendritic spines from age-related loss. Spines were categorized as either L-type (lollipop-shaped), which are more prevalent in young adults, or N-type (nubbin). With normal aging (comparing 6- and 24-month-old AL-fed groups) there was a significant decrease in L-type spines. However, all dietarily restricted groups showed retention of L-type spines.(ABSTRACT TRUNCATED AT 250 WORDS)

gp120 as an etiologic agent for NeuroAIDS: Neurotoxicity and model systems

The search for an agent that can mediate the symptoms of NeuroAIDS has been directed at gp120, the major envelope protein from HIV. The toxicity associated with gp120 was examined as a model and predictor of the neuropathological and neuropsychiatric manifestations of AIDS. Studies of the neurotoxic effects of purified gp120 on neurons from the rodent CNS cell cultures indicated the following: potent and selective killing of subpopulations of hippocampal neurons; varying potency of gp120s obtained from various HIV isolates; complete and potent protection from gp120 killing action after treatment with peptides related to vasoactive intestinal peptide; and obligatory presence of glia for gp120-related toxicity. Investigations of gp120 treatment of rodents revealed: cortical neurodystrophy with reduced arborizations and swollen processes; delays in developmental behaviors involving motor skills; peptide T prevention or attenuation of the morphological and behavioral deficits/delays produced by administration of gp120; and impairment of learning in the Morris swim maze. In addition, studies of subcutaneously administered, radiolabeled gp120 in neonatal animals demonstrated the presence of toxic fragments of gp120 in the developing brain. With the use of model test systems of non-human derived cell cultures and neonatal rats, we have captured and predicted a number of the morphological and behavioral deficits associated with AIDS. These multi-disciplinary studies of the actions of gp120 and associated fragments in rodents and rodent cells predict that the loss of cognitive and neurological function in patients with AIDS are attributed in part to interference of critical brain functions by the envelope protein, gp120.

Blockade of VIP during Neonatal Development Induces Neuronal Damage and Increases VIP and VIP Receptors in Brain

Vasoactive intestinal peptide (VIP) is a 28-amino-acid peptide that is involved in diverse regulatory functions, including vasodilation, gastric secretion, and glycogenolysis.’ In the central nervous system (CNS), VIP exhibits neurotransmitter and neuromodulator functions, and recent work has highlighted an important role for VIP in the regulation of CNS development. In CNS primary culture experiments, subnanomolar concentrations of VIP were shown to stimulate neuronal survival and astrocyte mitogenesis and to induce the secretion of trophic factors by astrocytes.z-s In the micromolar concentration range, VIP treatment was shown to stimulate neuronal mitosis, neurite extension, and neuronal survival in sympathetic and neuroblastoma cultures.kx In addition, cultured whole embryo studies have demonstrated that a four-hour exposure to VIP resulted in a dramatic increase in growth.

Cytomorphological Alterations in the Aging Animal Brain with Emphasis on Golgi Studies

Neurons in the aging brains of animals such as rodents, dogs, and monkeys share some common morphological alterations at both the light and the electron microscopic levels. Some of the alterations in the aged animal brains are, in fact, comparable to changes seen both in the normal aged, i.e., nondemented, human brain as well as (although to a more limited extent) in the brains of people diagnosed as having dementia of the Alzheimer type. A major reason for studying aging animal brains is to help define a model of the aging central nervous system that can serve to delineate the important features of the “normal” aging process in man. More indirectly, research of this type may also lead to a greater understanding of the pathogenesis of senile brain disease.

Chapter 30: Nerve growth factor affects the cholinergic neurochemistry and behavior of aged rats

Publisher Summary The major central cholinergic systems include (1) the projection neurons of the medial septum and diagonal band of Broca (MS/DB) to the hippocampus; (2) the projection neurons of the nucleus basalis magnocellularis (NBM) to the amygdala and cerebral cortex; (3) the inter-neurons of the striatum. Although the basal forebrain projection neurons have been implicated in learning and memory, and the striatal inter-neurons in motor behaviors, it still is not clear how and to what extent the central cholinergic neurons are involved in specific behaviors. Similarly, relatively little is known about the cellular and molecular mechanisms that regulate animal behaviors mediated by the central cholinergic systems. Although acetylcholine (ACh) was the first neurotransmitter discovered in the central nervous system, it remains unclear how the synthesis, storage, and release of ACh are regulated, or how ACh neurochemistry might be altered by environmental stimuli or synaptic experience, both of which would impact on cholinergically mediated behaviors. The central cholinergic systems are particularly dysfunctional in Alzheimers disease. Thus, our animal research on the regulation of central cholinergic transmission and behavior has focused on the deficits in the systems associated with senescence and the potential amelioration of age-related deficits by the administration of the neurotrophic protein, nerve growth factor (NGF). This chapter describes the current understanding of the regional regulation of ACh synthesis and release in young and old rats, and illustrates several correlations between age-related and NGF-induced alterations in cholinergic neurochemistry, electrophysiology, morphology, and behavior.

Dendritic alterations in cortical pyramidal cells in the sparse fur mouse

Ornithine carbamoyltransferase deficiency, an X-linked trait, leads to toxic hyperammonemia in sparse fur (spf/Y) mice. Quantitative analysis of the basilar dendritic tree of layer V pyramidal cells in frontoparietal cortex stained by the Golgi Kopsch method revealed a significant decrease in both the complexity of the dendritic arbor and in dendritic terminal spine density (60%) in spf/Y mice compared with controls. Such reductions may contribute to behavioral dysfunction observed in spf/Y mice.

Dietary choline affects response to acetylcholine by isolated urinary bladder.

Age-related increases occur in the response of isolated urinary bladders to the parasympathetic neurotransmitter acetylcholine (ACh). Experiments were carried out to determine whether long-term elevation or diminution in the amount of ingested choline can also affect the response of the urinary bladder to ACh. Female C57BL/6J mice were maintained on a choline-deficient chow and on drinking water supplemented with either 0, 1.5, or 4.0 mg/ml choline chloride from 8 to 20 months of age. Isolated bladders from choline deficient animals showed a 46% increase in the maximum response to ACh as compared to those from normal choline animals, while bladders from animals on choline enriched diets showed a 15% decrease in maximum contractile response. Radioligand binding experiments suggested that the functional changes result from alterations in the density of muscarinic receptors in the bladder. The results are consistent with the hypothesis that muscarinic receptors are down-regulated to compensate for increased parasympathetic activity associated with choline-enriched diets and up-regulated to compensate for decreased parasympathetic activity associated with choline-deficient diets.

Neurobehavioral Effects of Chronic Choline-Containing Diets on the Adult and Aging C57BL/6NNIA Mouse Braina

Choline-containing diets were chronically fed to male C57BL/6NNIA mice for either 5 or 11 months: from 8-13 months or 13-24 months, respectively. The choline in the chow was supplied in one of three ways: as free choline (choline chloride) or as bound choline as found in a 95% purified preparation of phosphatidylcholine (PC) and in an oil-free granular lecithin formulation (centrolex). The choline in these diets (either free or bound forms) was enriched at low, medium, or high levels (containing 2.4, 4.8, or 10.8 mg/g of chow, respectively). Two low choline diets contained 0.9 and 1.5 mg/g of choline, respectively, but were regarded as choline-adequate since the minimal nutritional requirement for choline is thought to be 0.6 mg/g of chow. All these diets were isocaloric and isonitrogenous. A standard rodent laboratory chow (Purina) contained 2.3 mg/g of choline. One-trial passive-avoidance testing for retention of learning indicated that mice of the C57BL/6NNIA strain show little normal age-related memory loss between 8-24 months old. As such, dietary enrichments did not significantly improve performance in comparison to the mice on the standard lab chow containing abundant choline. Learning was improved, however, in relation to mice on lower choline control diets, by supplementation with choline, PC, or lecithin. Whereas the younger mice tended to respond better a t higher levels of enrichment, the older (24 months old) mice showed superior retention of learning following low enrichment levels of PC and lecithin. This suggests that there may be an age-related shift in the optimal, potentially prophylactic, dietary “window.” Additional studies are evaluating some parameters reflecting potential membrane changes as a consequence of the various dietary regimens. Analysis of membrane phospholipids in a plasma membrane fraction from mouse forebrain indicated that membrane composition remains remarkably constant; however, diet-modulated enhanced membrane fluidity is suggested by a reduced cholesterol-to-phospholipid ratio in the older mice on low levels of chronic dietary enrichment. Receptor-binding studies from the neocortex (muscarinic, aand 8-adrenergic), hippocampus (musca-

The Effect of Dietary Choline on Brain Phospholipid Content

Considerable interest in dietary choline was generated following the demonstration that it could increase brain acetylcholine (Cohen and Wurtman, 1975). However, the variability of this effect and its small magnitude have led to questions about the mechanism of choline action. In addition to its effects upon acetylcholine synthesis, choline is a phospholipid precursor, and may also act as a weak cholinergic agonist (Krnjevic and Reinhardt, 1979). Despite the controversy regarding the effect of choline on acetylcholine synthesis, choline may be clinically beneficial in treating those conditions which are hypochol inergic.