S. Vitiello

Pregnenolone Can Protect the Brain from Cannabis Intoxication

Counteracting Cannabis What is the role of steroid hormones in vulnerability to addiction? Working with rodents, Vallée et al. (p. 94) found that all major drugs of abuse (morphine, cocaine, alcohol, nicotine) increase neurosteroid levels, with the active ingredient in cannabis (THC) inducing a particularly large increase. THC and other drugs increased levels of pregnenolone, long thought to be an inactive precursor of downstream active steroids. Pregnenolone antagonized most of the known behavioral and somatic effects of THC. The universal precursor of steroid hormones acts as a negative allosteric modulator of cannabinoid receptors. Pregnenolone is considered the inactive precursor of all steroid hormones, and its potential functional effects have been largely uninvestigated. The administration of the main active principle of Cannabis sativa (marijuana), ∆9-tetrahydrocannabinol (THC), substantially increases the synthesis of pregnenolone in the brain via activation of the type-1 cannabinoid (CB1) receptor. Pregnenolone then, acting as a signaling-specific inhibitor of the CB1 receptor, reduces several effects of THC. This negative feedback mediated by pregnenolone reveals a previously unknown paracrine/autocrine loop protecting the brain from CB1 receptor overactivation that could open an unforeseen approach for the treatment of cannabis intoxication and addiction.

Brain modulation of the immune system: association between lymphocyte responsiveness and paw preference in mice

An association between handedness and immune disorders has been described in man, left-handers being more susceptible to autoimmune or allergic diseases. However, this correlation was established between handedness and clinical signs of immune disorders without studying immune functions. Using an animal model, we demonstrated for the first time an association between handedness and lymphocyte reactivity. Left-handed mice were shown to exhibit higher mitogen-induced T lymphocyte proliferation than right-handed animals.

Prolonged increase of corticosterone secretion by chronic social stress does not necessarily impair immune functions

The influence of a chronic social stress upon immunity was investigated in Wistar rats, submitted for four weeks to two different behavioral situations, balanced in a factorial design: housing with three females and membership rotation. The combination of these two factor led to adrenal enlargement (43.3%), thymus involution (39.5%) and increased basal corticosterone levels, all indices of activation of the hypothalamic-hypophysis-adrenal axis. However, neither natural killer cell activity, splenocyte reactivity to mitogen nor the rate of spontaneous development of antibodies against Mycoplasma pulmonis, a common pathogen of the respiratory tract, were changed in the endocrine activated animals. Analysis of the data on kinetics of stress at 1, 7 and 28 days after the initial mixing of the animals gave the same results. These data question the immunosuppressant activity usually conferred to corticosteroids, at least when adrenal hyperactivity is induced by chronic environmental stressors.

Natural killer cell activity is associated with brain asymmetry in male mice

The brain is known to modulate the immune system in an asymmetrical way. In mice, there is an association between handedness and immune response and it has also been shown that hemicortical ablation has opposite effects on some immune parameters. An association between autoantibody production and paw preference was previously observed in female mice, but not in males, suggesting that the association between immune reactivity and functional brain asymmetry is a sex-dependent phenomenon. In three independent experiments, natural killer (NK) cell activity, lymphocyte subset distribution, and mitogen-induced lymphoproliferation were assessed in male C3H/OuJIco mice selected for handedness and after unilateral cortical ablation. Handedness was shown to be associated with NK cell activity but not with lymphocyte subset distribution or lymphoproliferation. Left-handers exhibited lower NK cell activity compared to right-handed or ambidextrous animals. In contrast to previous results in female mice, mitogen-induced lymphoproliferation was not associated with handedness in males. Left cortical ablations depressed NK cell activity, while right lesions had no effect. Neither left or right lesions affected lymphocyte subsets. No interaction between paw preference and side of the lesion was found in the modulation of NK cell activity. These and previous data show that the association between paw preference and immune reactivity varies according to the sex of the animal and the immunological parameters studied. This indicates that the brain may modulate different components of the immune system in different ways, through mechanisms apparently involving sex hormones.

Functional brain asymmetry and murine systemic lupus erythematosus

The role of brain lateralization in antibody production was studied in a murine systemic lupus erythematosus model. Male and female New Zealand black mice that spontaneously produce pathogenic auto-antibodies directed against red blood cells and DNA, were divided into right- and left-handers using a paw preference test, and anti-erythrocyte and anti-DNA antibody production was repeatedly determined. In females, antibodies against erythrocytes and double-stranded DNA appeared earlier in left-handers. These results provide the first evidence of an association between a functional brain asymmetry and auto-antibody production and suggest the involvement of the central nervous system in the pathogenesis of autoimmune processes.

Implication of allopregnanolone in the antinociceptive effect of N-palmitoylethanolamide in acute or persistent pain

Summary The role of allopregnanolone in the antinociceptive and antiallodynic effect of palmitoylethanolamide has been addressed in two models of acute and persistent pain in mice. ABSTRACT We investigated the involvement of de novo neurosteroid synthesis in the mechanisms underlying the analgesic and antihyperalgesic effects of N‐palmitoylethanolamine (PEA) in two models of acute and persistent pain, the formalin test and carrageenan‐induced paw edema. The pivotal role of peroxisome proliferator‐activated receptor (PPAR)‐α in the antinocifensive effect of PEA was confirmed by the lack of this effect in PPAR‐α‐null mice. PEA antinociceptive activity was partially reduced when the animals were treated with aminoglutethimide or finasteride, implying that de novo neurosteroid synthesis is involved in the effect of PEA. Accordingly, in the spinal cord, the allopregnanolone (ALLO) levels were increased by PEA treatment both in formalin‐ and carrageenan‐exposed mice, as revealed by gas chromatography–mass spectrometry. In agreement with those data, in both pain models, PEA administration in challenged mice specifically restored the expression of two proteins involved in neurosteroidogenensis, the steroidogenic acute regulatory protein (StAR) and cytochrome P450 side‐chain cleavage (P450scc) in the ipsilateral horns of spinal cord, without affecting their expression in the contralateral side. These results provide new information about the involvement of de novo neurosteroid synthesis in the modulation of pain behavior by PEA.

Functional heterogeneity of the right and left cerebral neocortex in the modulation of the immune system

The cerebral neocortex is now known to modulate the immune system but this modulation is hemispherically asymmetrical. It was previously reported that large ablation, including the anterior prefrontal part of the left cortex decreased whereas symmetrical right lesions enhanced B and T cell-mediated responses. However, the neocortex is an heterogeneous structure from anatomical and physiological points of view and it could be speculated that different aspects of the immune system could be regulated by various cortical areas. In these experiments, restricted neocortical lesions involving the parieto-occipital lobes were performed in C3H/He mice. Animals with right lesions showed depressed mitogen-induced lymphoproliferation and enhanced antibody production to sheep erythrocytes as compared to that of animals with bilateral lesions. Left lesions appeared not to modify these reactions. Furthermore, the percentage of suppressor/cytotoxic T lymphocytes was depressed more in animals with bilateral lesions as compared to any of the other groups. None of the lesions performed appeared to modify the natural killer cell activity. These results confirm that connections between left and right cortex are involved in the modulation of the immune system and suggest that the immunomodulatory functions of the cortex depend upon the specific regions within the right cortex.

Palmitoylethanolamide Stimulation Induces Allopregnanolone Synthesis in C6 Cells and Primary Astrocytes: Involvement of Peroxisome‐Proliferator Activated Receptor‐α

Palmitoylethanolamide (PEA) regulates many pathophysiological processes in the central nervous system, including pain perception, convulsions and neurotoxicity, and increasing evidence points to its neuroprotective action. In the present study, we report that PEA, acting as a ligand of peroxisome‐proliferator activated receptor (PPAR)‐α, might regulate neurosteroidogenesis in astrocytes, which, similar to other glial cells and neurones, have the enzymatic machinery for neurosteroid de novo synthesis. Accordingly, we used the C6 glioma cell line and primary murine astrocytes. In the mitochondrial fraction from cells stimulated with PEA, we demonstrated an increase in steroidogenic acute regulatory protein (StAR) and cytochrome P450 enzyme (P450scc) expression, both comprising proteins considered to be involved in crucial steps of neurosteroid formation. The effects of PEA were completely blunted by GW6471, a selective PPAR‐α antagonist, or by PPAR‐α silencing by RNA interference. Accordingly, allopregnanolone (ALLO) levels were increased in supernatant of PEA‐treated astrocytes, as revealed by gas chromatography‐mass spectrometry, and this effect was inhibited by GW6471. Moreover, PEA showed a protective effect, reducing malondialdehyde formation in cells treated with l‐buthionine‐(S,R)‐sulfoximine, a glutathione depletor and, interestingly, the effect of PEA was partially inhibited by finasteride, a 5α‐reductase inhibitor. A similar profile of activity was demonstrated by ALLO and the lack of an additive effect with PEA suggests that the reduction of oxidative stress by PEA is mediated through ALLO synthesis. The present study provides evidence indicating the involvement of the saturated acylethanolamide PEA in ALLO synthesis through PPAR‐α in astrocytes and explores the antioxidative activity of this molecule, confirming its homeostatic and protective role both under physiological and pathological conditions.

Brain neocortex immunomodulation in rats

The influence of the cerebral neocortex on the immune system was studied in groups of male Wistar rats after lesioning the right or the left fronto-parietal cortex. In left-lesioned rats, mitogenesis of T-lymphocytes induced either by phytohemagglutinin or Urtica Dioca Agglutinin was depressed by about 25-40% as compared to controls. In contrast, T-cell mitogenesis in animals with right lesions, was enhanced by about 20-45% as compared to controls and by about 90% as compared to that observed in left-lesioned animals. Cortical lesions of either side were shown not to modify antibody synthesis and plasma levels of ACTH, or prolactin. These results, quite similar to those that we have previously observed in female mice, suggest that lateralization in brain cortex immunomodulatory functions may exist in both sexes and in several species of mammals.

Different responsiveness of spleen lymphocytes from two lines of psychogenetically selected rats (Roman high and low avoidance)

Roman high- (RHA) and low-avoidance (RLA) rats have been genetically selected on the basis of their active avoidance behavior, and have been shown to differ on numerous behavioral, neurochemical and neuroendocrine parameters, especially in response to stress. We investigated the activity of splenic lymphocytes in vitro. Natural killer cell activity against YAC-1 tumoral cells and the mitotic response to plant lectins concanavalin A and phytohemagglutinin were much lower for lymphocytes isolated from RHA rats, in males as well as in females. The difference between the two strains was even larger when measured in a stressed state, immediately after active avoidance learning. On the other hand, the mitotic response to bacterial lipopolysaccharide, a B-cell-specific mitogen, was not different between the two lines, indicating that the difference in lymphocyte reactivity is limited to the T-lineage. The lower activity of T-cells in the RHA line had no consequence upon the ability of these animals to build up an antibody response against sheep red blood cells. These results indicate that Roman lines are an interesting animal model for the study of the relationships between the brain and the immune system, as well as for the analysis of the genes involved in the control of behavior.