Neurosteroids in the cerebellar Purkinje neuron and their actions (review).

Although the brain is a target site of steroid hormones supplied by peripheral steroidogenic glands, it is now established that the brain itself also synthesizes steroids de novo from cholesterol in a variety of vertebrates. Such steroids synthesized in the brain are called neurosteroids. Because certain structures in vertebrate brains have the capacity to produce neurosteroids, the identification of neurosteroidogenic cells in the brain is essential to understand the physiological role of neurosteroids in brain functions. In the brain, glial cells are considered to play a major role in neurosteroid formation and metabolism. Both oligodendrocytes and astrocytes are the primary site for neurosteroidogenesis. However, the concept of neurosteroidogenesis in neurons in the brain has long been unclear. Recently, we demonstrated neurosteroidogenesis in the Purkinje cell, a typical cerebellar neuron, in mammals and other vertebrates. Pregnenolone sulfate, one of neurosteroids synthesized in the cerebellar Purkinje cell, may contribute to some important events in the cerebellum by modulating neurotransmission. Progesterone, produced as other neurosteroid in this neuron only during neonatal life, may be involved in the promotion of neuronal and glial growth and neuronal synaptic contact in the cerebellum. This review summarizes the advances made in our understanding of neurosteroids, produced in the Purkinje neuron, and their actions.     

Neurosteroid biosynthesis in vertebrate brains

In mammals, neurosteroids are now known to be synthesized de novo in the brain as well as other areas of the nervous system through mechanisms at least partly independent of the peripheral steroidogenic glands. However, limited information is available on neurosteroids in non-mammalian vertebrates. We therefore have attempted to demonstrate neurosteroid biosynthesis in the brain of birds and amphibians. These vertebrate brains possessed the steroidogenic enzymes, cytochrome P450 side-chain cleavage enzyme (P450scc) and 3beta-hydroxysteroid dehydrogenase/delta5-delta4-isomerase (3beta-HSD), and produced pregnenolone, pregnenolone sulfate ester and progesterone from cholesterol. Significant seasonal changes in neurosteroids in the brain were observed in seasonally breeding vertebrates. In addition, we attempted to identify the cell type involved in neurosteroidogenesis in mammalian and non-mammalian vertebrates in order to understand the physiological role of neurosteroids. Glial cells are generally accepted to be the primary site for neurosteroid formation, but the concept of neurosteroidogenesis in brain neurons has up to now been uncertain. We recently demonstrated neuronal neurosteroidogenesis in the brain and indicated that the Purkinje cell, a typical cerebellar neuron, actively synthesizes several neurosteroids de novo from cholesterol in both mammals and non-mammals. This paper summarizes the advances made in our understanding of neurosteroid biosynthesis, including neuronal neurosteroidogenesis, in a variety of vertebrate types.     

Organizing actions of neurosteroids in the Purkinje neuron

It is becoming clear that steroids can be synthesized de novo by the brain of vertebrates. Such steroids synthesized de novo in the brain, as well as other areas of the nervous system, are called neurosteroids. To understand neurosteroid actions in the brain, we need data on the specific biosynthesis in particular sites of the brain at particular times. Therefore our studies for this exciting area of neuroscience research have focused on the biosynthesis and action of neurosteroids in the identified neurosteroidogenic cells underlying important brain functions. We have demonstrated that the Purkinje cell, a typical cerebellar neuron, is a major site for neurosteroid formation in the brain. This neuron actively synthesizes progesterone and estradiol de novo from cholesterol only during neonatal life, when cerebellar cortical formation occurs dramatically. This is the first observation of neuronal neurosteroidogenesis in the brain. Subsequently the actions of progesterone and estradiol during cerebellar development have become clear by a series of our studies using an excellent Purkinje cellular model. These neurosteroids promote dendritic growth, spinogenesis and synaptogenesis via each receptor in the Purkinje cell. Here we summarize the advances made in our understanding of organizing actions of neurosteroids in the Purkinje cell, an important brain neuron.     

Neurosteroid modulation of GABAA receptors

Certain metabolites of progesterone and deoxycorticosterone are established as potent and selective positive allosteric modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor. Upon administration these steroids exhibit clear behavioural effects that include anxiolysis, sedation and analgesia, they are anticonvulsant and at high doses induce a state of general anaesthesia, a profile consistent with an action to enhance neuronal inhibition. Physiologically, peripherally synthesised pregnane steroids derived from endocrine glands such as the adrenals and ovaries function as hormones by crossing the blood brain barrier to influence neuronal signalling. However, the demonstration that certain neurons and glial cells within the central nervous system (CNS) can synthesize these steroids either de novo, or from peripherally derived progesterone, has led to the proposal that these steroids (neurosteroids) can additionally function in a paracrine manner, to locally influence GABAergic transmission. Steroid levels are known to change dynamically, for example in stress and during pregnancy. Given that GABA(A) receptors are ubiquitously expressed throughout the central nervous system, such changes in steroid levels would be predicted to cause a global enhancement of inhibitory neurotransmission throughout the brain, a scenario that would seem incompatible with a physiological role as a selective neuromodulator. Here, we will review emerging evidence that the GABA-modulatory actions of the pregnane steroids are highly selective, with their actions being brain region and indeed neuron dependent. Furthermore, the sensitivity of GABA(A) receptors is not static but can dynamically change. The molecular mechanisms underpinning this neuronal specificity will be discussed with particular emphasis being given to the role of GABA(A) receptor isoforms, protein phosphorylation and local steroid metabolism and synthesis.     

Steroid hormones and neurosteroids in normal and pathological aging of the nervous system

Without medical progress, dementing diseases such as Alzheimer's disease will become one of the main causes of disability. Preventing or delaying them has thus become a real challenge for biomedical research. Steroids offer interesting therapeutical opportunities for promoting successful aging because of their pleiotropic effects in the nervous system: they regulate main neurotransmitter systems, promote the viability of neurons, play an important role in myelination and influence cognitive processes, in particular learning and memory. Preclinical research has provided evidence that the normally aging nervous system maintains some capacity for regeneration and that age-dependent changes in the nervous system and cognitive dysfunctions can be reversed to some extent by the administration of steroids. The aging nervous system also remains sensitive to the neuroprotective effects of steroids. In contrast to the large number of studies documenting beneficial effects of steroids on the nervous system in young and aged animals, the results from hormone replacement studies in the elderly are so far not conclusive. There is also little information concerning changes of steroid levels in the aging human brain. As steroids present in nervous tissues originate from the endocrine glands (steroid hormones) and from local synthesis (neurosteroids), changes in blood levels of steroids with age do not necessarily reflect changes in their brain levels. There is indeed strong evidence that neurosteroids are also synthesized in human brain and peripheral nerves. The development of a very sensitive and precise method for the analysis of steroids by gas chromatography/mass spectrometry (GC/MS) offers new possibilities for the study of neurosteroids. The concentrations of a range of neurosteroids have recently been measured in various brain regions of aged Alzheimer's disease patients and aged non-demented controls by GC/MS, providing reference values. In Alzheimer's patients, there was a general trend toward lower levels of neurosteroids in different brain regions, and neurosteroid levels were negatively correlated with two biochemical markers of Alzheimer's disease, the phosphorylated tau protein and the beta-amyloid peptides. The metabolism of dehydroepiandrosterone has also been analyzed for the first time in the aging brain from Alzheimer patients and non-demented controls. The conversion of dehydroepiandrosterone to Delta5-androstene-3beta,17beta-diol and to 7alpha-OH-dehydroepiandrosterone occurred in frontal cortex, hippocampus, amygdala, cerebellum and striatum of both Alzheimer's patients and controls. The formation of these metabolites within distinct brain regions negatively correlated with the density of beta-amyloid deposits.     

Progesterone, progestagens and the central nervous system

Oestrogen, progestagens and androgens are able to modulate several brain functions. Receptors for gonadal steroids have been identified in several brain areas: amygdala, hippocampus, cortex, basal forebrain, cerebellum, locus coeruleus, midbrain rafe nuclei, glial cells, pituitary gland, hypothalamus and central grey matter. The mechanism of action of sex steroids at this level is similar to that observed in the peripheral target organs, including both genomic and non-genomic effects. The increased use of sex steroid hormone derivative therapies has lead to study of the biochemical and metabolic properties of the different progestin molecules available in hormonal therapies. In particular, experimental and clinical studies focused the attention of researchers on interactions between oestrogens and progestins in the neuroendocrine control of the brain functions and its clinical implications. Moreover, steroids are also synthesized de novo in the brain or may be derived from the conversion of blood-borne precursors, suggesting that the brain is also a source of steroids, named neurosteroids. Neurosteroids exert non-classical rapid actions as allosteric agonists of gamma-aminobutyric acid receptor A (GABA(A)) and also modulate classic neurotransmitters in the brain. In addition, progesterone derivatives, e.g. pregnanolone, and 3alpha 5alpha-OH THP (allopregnanolone) are synthesized de novo by astrocytes and oligodendrocites starting from cholesterol. Physiological or pathological modifications of the synthesis and release of neurosteroids play a relevant role in the control of brain function.     

Role of neurosteroids in regulating cell death and proliferation in the late gestation fetal brain

The neurosteroid allopregnanolone (AP) is a GABAergic agonist that suppresses central nervous system (CNS) activity in the adult brain, and by reducing excitotoxicity is considered to be neuroprotective. A role for neurosteroids in the developing brain, particularly in late gestation, is still debated. The aim of this study was to investigate effects on proliferation and cell death in the brain of late gestation fetal sheep after inhibition of AP synthesis using finasteride, a 5α-reductase type 2 (5α-R2) inhibitor. Catheters were implanted in fetal sheep at ∼125 days of gestation. At 3–4 days postsurgery, fetuses received infusions of either finasteride (20 mg/kg/h; n=5), the AP analogue alfaxalone (5 mg/kg/h; n=5), or finasteride and alfaxalone together (n=5). Brains were obtained at 24 h after infusion to determine cell death (apoptotic or necrotic) and cell proliferation in the hippocampus and cerebellum, areas known to be susceptible to excitotoxic damage. Finasteride treatment significantly increased apoptosis (activated caspase-3 expression) in hippocampal CA3 and CA1, and cerebellar molecular and granular layers, an effect abolished by co-infusion of alfaxalone and finasteride. Double-label immunohistochemistry showed that both neurons and astrocytes were caspase-3 positive. Finasteride treatment also increased the number of dead (pyknotic) cells in the hippocampus and cerebellum (Purkinje cells), but not when finasteride+alfaxalone was infused. Cell proliferation (Ki-67-immunoreactivity) increased after finasteride treatment; double-labeling showed the majority of Ki-67-positive cells were astrocytes. Thus, steroids such as AP appear to influence the constitutive rate of apoptosis and proliferation in the hippocampus and cerebellum of the fetal brain, and suggest an important role for neurosteroids in the development of the brain.     

Neurosteroidogenesis: relevance to neurosteroid actions in brain and modulation by psychotropic drugs

Neurosteroids--i.e., steroid produced in brain ex novo or through metabolism of precursors--affect neuronal and brain functions through genomic and nongenomic mechanisms, depending on their molecular structure. Among neurosteroids, 3alpha-hydroxylated, 5alpha-reduced metabolites of progesterone (3alpha-hydroxy,5alpha-pregnan-20one/3alpha,5alpha-THP) and deoxycorticosterone (3alpha,21-dihydroxy,5alpha-pregnan-20one/3alpha,5alpha-THDOC) are positive allosteric modulators of gamma-aminobutyric acid (GABA) action at GABAA receptors. In rodents, a reduction of their endogenous brain concentrations rapidly lowers the potency of GABA in eliciting GABAA receptor-mediated inhibitory postsynaptic currents. This effect is related to anxiety-like behavior, increased aggression, and a reduced sensitivity to the loss of righting reflex induced by GABAA receptor agonist or positive modulators. Conversely, enhancement of 3alpha,5alpha-THP or 3alpha,5alpha-THDOC brain content results in anxiolysis, sedation/hypnosis, anticonvulsant, and anesthetic action. Different classes of psychotropic drugs--i.e., antidepressants, selected atypical antipsychotics, ethanol, gamma-hydroxybutyric acid--increase neurosteroid concentrations in brain, and these increases may be relevant to their pharmacological actions. Drug-induced increases of neurosteroids in rodent brain are often associated with elevation of their plasma content, such that alterations of plasma steroid concentrations are assumed to reflect parallel changes in brain. Nevertheless, brain neurosteroid concentrations are uneven across various regions, and the dose-dependence of their response to a pharmacological challenge shows brain-regional differences as well. These observations are consistent with the present knowledge on the distribution of steroidogenic enzymes in brain--they show not only a brain region, but also a cell-specific expression that may spatially and temporally determine the local concentrations of specific neurosteroids, either produced ex novo or through metabolism of steroid precursors that reach the brain through blood.     

Steroid control of higher brain function and behavior

In higher vertebrates, many behavioral characteristics can be attributed to effects in the central nervous system, in response to gonadal hormones secreted early in development. The lipophilic properties of steroids facilitate their easy passage in free form through the blood-brain barrier. At the cerebral level, the function of many nerve cells is influenced by steroid hormones originating from the periphery (synthesis of gluco-, and mineralocorticosteroids in the adrenal glands and of sex steroids in the gonads and the placenta from cholesterol). However, the relationship between steroids and cerebral function may need reconsidering in light of the recent discovery of a biosynthetic pathway (independently of peripheral sources) of steroidal compounds ensuring the synthesis of neurosteroids from cholesterol in certain brain cells.     

Neuroactive steroids and inhibitory neurotransmission: mechanisms of action and physiological relevance

Dysfunction of GABA(A) receptor-mediated inhibition is implicated in a number of neurological and psychiatric conditions including epilepsy and affective disorders. Some of these conditions have been associated with abnormal levels of certain endogenously occurring neurosteroids, which potently and selectively enhance the function of the brain's major inhibitory receptor, the GABA(A) receptor. Consistent with their ability to enhance neuronal inhibition, such steroids exhibit in animals and humans anxiolytic, anticonvulsant and anesthetic actions. Neurosteroids, exemplified by the potent progesterone metabolite, 5alpha-pregnan-3alpha-ol-20-one can be synthesized de novo in the CNS both in neurones and glia in levels sufficient to modulate GABA(A) receptor function. Neurosteroid levels are not static, but are subject to dynamic fluctuations, for example during stress, or the later stages of pregnancy. These observations suggest that these endogenous modulators may refine the function of the brain's major inhibitory receptor and thus, play an important physiological and pathophysiological role. However, given the ubiquitous expression of GABA(A) receptors throughout the mammalian CNS, changes in neurosteroid levels should be widely experienced, causing a generalized enhancement of neuronal inhibition. Such a non-specific action would seem incompatible with a physiological role. However, neurosteroid action is both brain region and neurone selective. This specificity results from a variety of molecular mechanisms including receptor subunit composition, local steroid metabolism and phosphorylation. This paper will evaluate the relative contribution these mechanisms play in defining the interaction of neurosteroids with synaptic and extra-synaptic GABA(A) receptors.     

Dendritic growth in response to environmental estrogens in the developing Purkinje cell in rats

The cerebellar Purkinje cell is a major site for neurosteroid formation. We have demonstrated recently that the Purkinje cell actively produces sex steroids, such as estradiol and progesterone, de novo from cholesterol only during rat neonatal life, when cerebellar cortical formation occurs. We have further demonstrated that both estradiol and progesterone promote the growth of Purkinje cells through intranuclear receptor-mediated mechanisms during cerebellar development. On the other hand, environmental estrogens, such as octylphenol (OP), bisphenol A (BPA), and nonylphenol (NP) are thought to mimic the action of estrogen in the developing central nervous system. Therefore, in this study, the effect of these environmental estrogens on the growth of Purkinje cells was examined in vivo using newborn rats. OP and BPA promoted a dose-dependent dendritic outgrowth of the Purkinje cell but did not affect its soma and cell number. The stimulatory effect of OP and BPA on Purkinje dendritic growth was induced by an injection of 500 microg/day into the cerebrospinal fluid for 4 days and blocked by the estrogen receptor antagonist tamoxifen. However, there was no significant effect of NP on any Purkinje cell morphology. These results suggest that the environmental estrogens, OP and BPA, promote Purkinje dendritic growth during neonatal life. This effect may be mediated by estrogen receptor in the Purkinje cell.     

Neurotoxic effects of homocysteine on cerebellar Purkinje neurons in vitro

Whilst a plethora of studies that describe the toxicity of homocysteine to CNS neurons have been published, the effects of homocysteine on the Purkinje neurons of the cerebellum that play a vital role in motor function remain wholly unexplored. We have therefore established cultures of embryonic cerebellar Purkinje neurons and exposed them to a range of concentrations of homocysteine and determined its effects on their survival. The experiments revealed that all concentrations of homocysteine studied, from 50 to 500microM, caused a significant decrease in cerebellar Purkinje neuron number. This loss could be counteracted by the pan-caspase inhibitor z-VAD-fmk in the first 24h following homocysteine exposure, revealing that the initial loss was apoptotic. However, z-VAD-fmk could not prevent homocysteine-mediated loss of cerebellar Purkinje neurons in the longer term, after 6 days in vitro. In addition to its effects on Purkinje neuron survival, homocysteine markedly reduced both the overall magnitude and the complexity of the neurite arbor extended by the cerebellar Purkinje neurons, following 6 days incubation with this agent in vitro. Taken together our data reveal that homocysteine is toxic to cerebellar Purkinje neurons in vitro, inhibiting both their survival and the outgrowth of neurites.     

Immunohistochemical localization and biological activity of 3β-hydroxysteroid dehydrogenase and 5α-reductase in the brain of the frog,Rana esculenta,during development

The occurrence of several enzymes responsible for the biosynthesis of neurosteroids in the brain of adult frogs is now firmly established but the expression of these enzymes during ontogenesis has not yet been investigated. In the present report, we describe the immunohistochemical distribution and biological activity of 3β-hydroxysteroid dehydrogenase (3β-HSD) and 5α-reductase (5α-R) in the brain of the European green frog, Rana esculenta, during larval development. The spatio-temporal distribution of 3β-HSD and 5α-R immunoreactivities in the tadpole brain was generally different, although these two enzymes were occasionally detected in the same areas such as the olfactory bulbs and cerebellum. Identification of neurons based on their morphological aspect as well as labeling of astrocytes with an antiserum against glial fibrillary acidic protein (GFAP) revealed that, in the tadpole brain, 3β-HSD- and 5α-R-immunoreactive materials were contained in both neurons and glial cells. Incubation of tadpole brain explants with [³H]-pregnenolone resulted in the formation of several tritiated steroids including progesterone, 17-hydroxyprogesterone, androstenedione, 5α-dihydroprogesterone and 5α-dihydrotestosterone. The present study provides the first immunocytochemical mapping of two key steroidogenic enzymes in the developing frog brain. The data also indicate that neurosteroid biosynthesis occurs in the brain of tadpoles, as previously shown for adult amphibians, birds and mammals. The transient expression of steroidogenic enzymes in several regions of the tadpole brain suggests that, in amphibians, neurosteroids may be implicated in neurotrophic activities during larval development.     

Effect of treadmill exercise on Purkinje cell loss and astrocytic reaction in the cerebellum after traumatic brain injury

The cerebellum is one of the brain areas, which is selectively vulnerable to forebrain traumatic brain injuries (TBI). Physical exercise in animals is known to promote cell survival and functional recovery after brain injuries. However, the detailed pathologic and functional alterations by exercise following an indirect cerebellar injury induced by a TBI are largely unknown. We determined the effects of treadmill exercise on survival of Purkinje neurons and on a population of reactive astrocytes in the gyrus of lobules VIII and IX of the cerebellum after TBI. The rats were divided into four groups: the sham-operation group, the sham-operation with exercise group, the TBI-induction group, and the TBI-induction with exercise group. Cell biological changes of Purkinje neurons following indirect cerebellar injury were analyzed by immunohistochemistry. TBI-induced loss of calbindin-stained Purkinje neurons in the posterior region of the cerebellum and TBI also increased formation of reactive astroyctes in both the granular and molecular layers of the cerebellar posterior region. Treadmill exercise for 10 days after TBI increased the number of calbindin-stained Purkinje neurons and suppressed formation of reactive astroyctes. The present study provides the possibility that treadmill exercise may be an important mediator to enhance survival of Purkinje neurons in TBI-induced indirect cerebellar injury.     

Neurotrophic effects of leptin on cerebellar Purkinje but not granule neurons in vitro

As recent evidence has revealed a pro-survival role for the anti-obesity hormone leptin in the nervous system, we investigated the generality of this finding on cerebellar Purkinje and granule neurons in vitro. We found that whilst leptin promoted cerebellar Purkinje neuron survival, it had no affect on cerebellar granule cells. In addition, we discovered that leptin promoted both the outgrowth of neurites from cerebellar Purkinje neurons and increased the complexity of the neurite arbor. Thus, leptin has different effects on two neighbouring populations of neurons within the cerebellum implying specificity of its actions in the central nervous system.     

Axonal projection patterns visualized with horseradish peroxidase in organized cultures of cerebellum

Neurons of the cerebellum and brain stem region of organotypic cultures were injected intracellularly with horseradish peroxidase. The axonal pattern was analyzed for the three cell types studied—Purkinje neurons, deep cerebellar neurons, and brain stem neurons. There was a consistent pattern for each cell type. The axon of the Purkinje neuron was uniform in diameter throughout, sometimes with one recurrent collateral, and within the deep nuclear region branched to produce a terminal field with many axon bulbs measuring 2–4 μm in diameter. The deep cerebellar neuron gave rise to a single axon which branched into a number of major axons, most of which coursed for long distances along the margin of the cortical region. Where the cortical region was separated off from the deep nuclear area, the axon of the deep cerebellar neuron branched and many axons coursed through the intervening zone to the cortex. The terminals in the cortical region were seen either as expansions along the fibre or as grape-like clusters on small side branches of the axons. The brain stem neuron had multiple axons which branched profusely and produced a system of fine-calibre varicose fibres, many of which coursed far into the outgrowth region.This study characterized the distribution of the axons of each neuron type. The results corroborate the fibre patterns seen in the living, stained and fluorescence studies of these cultures. The axon pattern for each neuron type resembles that of the corresponding neuron in the animal. These results will be correlated with the electrophysiological studies of the connections formed by the same neurons in sister cultures.     

Birdsong and the neural production of steroids

The forebrain circuits involved in singing and audition (the ‘song system’) in songbirds exhibit a remarkable capacity to synthesize and respond to steroid hormones. This review considers how local brain steroid production impacts the development, sexual differentiation, and activity of song system circuitry. The songbird forebrain contains all of the enzymes necessary for the de novo synthesis of steroids – including neuroestrogens – from cholesterol. Steroid production enzymes are found in neuronal cell bodies, but they are also expressed in pre-synaptic terminals in the song system, indicating a novel mode of brain steroid delivery to local circuits. The song system expresses nuclear hormone receptors, consistent with local action of brain-derived steroids. Local steroid production also occurs in brain regions that do not express nuclear hormone receptors, suggesting a non-classical mode of action. Recent evidence indicates that local steroid levels can change rapidly within the forebrain, in a manner similar to traditional neuromodulators. Lastly, we consider growing evidence for modulatory interactions between brain-derived steroids and neurotransmitter/neuropeptide networks within the song system. Songbirds have therefore emerged as a rich and powerful model system to explore the neural and neurochemical regulation of social behavior.     

Altered physiology of Purkinje neurons in cerebellar slices from transgenic mice with chronic central nervous system expression of interleukin-6

The cytokine interleukin-6 is produced at elevated levels within the central nervous system in a number of neurological diseases and has been proposed to contribute to the histopathologic, pathophysiologic, and cognitive deficits associated with such disorders. In order to determine the effects of chronic exposure of interleukin-6 on the physiology of central neurons, we compared the firing properties of cerebellar Purkinje neurons from control mice and transgenic mice that chronically express interleukin-6 within the central nervous system. Extracellular recordings from cerebellar slices revealed that the mean firing rate of spontaneously active Purkinje neurons was significantly reduced in slices from transgenic mice compared to control mice. In addition, a significantly greater proportion of Purkinje neurons from transgenic slices exhibited an oscillatory pattern of spontaneous firing than neurons in control slices. Orthodromic stimulation of climbing fiber afferents evoked similar excitatory synaptic responses (complex spikes) in Purkinje neurons of both transgenic and control mice. However, the inhibitory period following the complex spike (climbing fiber pause) was significantly longer in slices from transgenic mice. Using immunohistochemistry, we also showed that Purkinje neurons express high levels of both the interleukin-6 receptor and its intracellular signaling subunit, gp130, indicating that interleukin-6 could act directly on Purkinje neurons to alter their physiological properties. The interleukin-6 expressing transgenic mice have been shown previously to exhibit a number of histopathological changes in the central nervous system including injury and loss of cerebellar Purkinje neurons. The present data show that these transgenic mice also have altered physiology of cerebellar Purkinje neurons, potentially through a direct activation of interleukin-6 receptors expressed by this neuronal type. Interleukin-6 induced alterations of Purkinje neuron physiology would ultimately affect the flow of information out of the cerebellum, and could thus contribute to the motor deficits observed in the transgenic mice.