Steven E. Hyman

Response and Habituation of the Human Amygdala during Visual Processing of Facial Expression

We measured amygdala activity in human volunteers during rapid visual presentations of fearful, happy, and neutral faces using functional magnetic resonance imaging (fMRI). The first experiment involved a fixed order of conditions both within and across runs, while the second one used a fully counterbalanced order in addition to a low level baseline of simple visual stimuli. In both experiments, the amygdala was preferentially activated in response to fearful versus neutral faces. In the counterbalanced experiment, the amygdala also responded preferentially to happy versus neutral faces, suggesting a possible generalized response to emotionally valenced stimuli. Rapid habituation effects were prominent in both experiments. Thus, the human amygdala responds preferentially to emotionally valenced faces and rapidly habituates to them.

Acute Effects of Cocaine on Human Brain Activity and Emotion

We investigated brain circuitry mediating cocaine-induced euphoria and craving using functional MRI (fMRI). During double-blind cocaine (0.6 mg/kg) and saline infusions in cocaine-dependent subjects, the entire brain was imaged for 5 min before and 13 min after infusion while subjects rated scales for rush, high, low, and craving. Cocaine induced focal signal increases in nucleus accumbens/subcallosal cortex (NAc/SCC), caudate, putamen, basal forebrain, thalamus, insula, hippocampus, parahippocampal gyrus, cingulate, lateral prefrontal and temporal cortices, parietal cortex, striate/extrastriate cortices, ventral tegmentum, and pons and produced signal decreases in amygdala, temporal pole, and medial frontal cortex. Saline produced few positive or negative activations, which were localized to lateral prefrontal cortex and temporo-occipital cortex. Subjects who underwent repeat studies showed good replication of the regional fMRI activation pattern following cocaine and saline infusions, with activations on saline retest that might reflect expectancy. Brain regions that exhibited early and short duration signal maxima showed a higher correlation with rush ratings. These included the ventral tegmentum, pons, basal forebrain, caudate, cingulate, and most regions of lateral prefrontal cortex. In contrast, regions that demonstrated early but sustained signal maxima were more correlated with craving than with rush ratings; such regions included the NAc/SCC, right parahippocampal gyrus, and some regions of lateral prefrontal cortex. Sustained negative signal change was noted in the amygdala, which correlated with craving ratings. Our data demonstrate the ability of fMRI to map dynamic patterns of brain activation following cocaine infusion in cocaine-dependent subjects and provide evidence of dynamically changing brain networks associated with cocaine-induced euphoria and cocaine-induced craving.

Addiction and the brain: The neurobiology of compulsion and its persistence

People take addictive drugs to elevate mood, but with repeated use these drugs produce serious unwanted effects, which can include tolerance to some drug effects, sensitization to others, and an adapted state — dependence — which sets the stage for withdrawal symptoms when drug use stops. The most serious consequence of repetitive drug taking, however, is addiction: a persistent state in which compulsive drug use escapes control, even when serious negative consequences ensue. Addiction is characterized by a long-lasting risk of relapse, which is often initiated by exposure to drug-related cues. Substantial progress has been made in understanding the molecular and cellular mechanisms of tolerance, dependence and withdrawal, but as yet we understand little of the neural substrates of compulsive drug use and its remarkable persistence. Here we review evidence for the possibility that compulsion and its persistence are based on a pathological usurpation of molecular mechanisms that are normally involved in memory.

Animal models of neuropsychiatric disorders

Modeling of human neuropsychiatric disorders in animals is extremely challenging given the subjective nature of many symptoms, the lack of biomarkers and objective diagnostic tests, and the early state of the relevant neurobiology and genetics. Nonetheless, progress in understanding pathophysiology and in treatment development would benefit greatly from improved animal models. Here we review the current state of animal models of mental illness, with a focus on schizophrenia, depression and bipolar disorder. We argue for areas of focus that might increase the likelihood of creating more useful models, at least for some disorders, and for explicit guidelines when animal models are reported.

Grand challenges in global mental health

A consortium of researchers, advocates and clinicians announces here research priorities for improving the lives of people with mental illness around the world, and calls for urgent action and investment.

Computational roles for dopamine in behavioural control

Neuromodulators such as dopamine have a central role in cognitive disorders. In the past decade, biological findings on dopamine function have been infused with concepts taken from computational theories of reinforcement learning. These more abstract approaches have now been applied to describe the biological algorithms at play in our brains when we form value judgements and make choices. The application of such quantitative models has opened up new fields, ripe for attack by young synthesizers and theoreticians.

Neuronal adaptation to amphetamine and dopamine: Molecular mechanisms of prodynorphin gene regulation in rat striatum

Induction of prodynorphin gene expression by psychostimulant drugs may represent a compensatory adaptation to excessive dopamine stimulation and may contribute to the aversive aspects of withdrawal. We therefore investigated the molecular mechanisms by which dopamine psychostimulant drugs induce prodynorphin gene expression in vivo and in rat primary striatal cultures. We demonstrate that three recently described cAMP response elements (CREs), rather than a previously reported noncanonical AP-1 site, are critical for dopamine induction of the prodynorphin gene in striatal neurons. CRE-binding protein (CREB) binds to these CREs in striatal cell extracts and is phosphorylated on Ser-133 after dopamine stimulation in a D1 dopamine receptor-dependent manner. Surprisingly, following chronic administration of amphetamine, levels of phosphorylated CREB are increased above basal in rat striatum in vivo, whereas c-fos mRNA is suppressed below basal levels. D1 receptor-mediated CREB phosphorylation appears to mediate adaptations to psychostimulant drugs in the striatum.

Amphetamine and Dopamine-Induced Immediate Early Gene Expression in Striatal Neurons Depends on Postsynaptic NMDA Receptors and Calcium

Amphetamine and cocaine induce the expression of both immediate early genes (IEGs) and neuropeptide genes in rat striatum. Despite the demonstrated dependence of these effects on D1dopamine receptors, which activate the cyclic AMP pathway, there are several reports that amphetamine and cocaine-induced IEG expression can be inhibited in striatum in vivo by NMDA receptor antagonists. We find that in vivo, the NMDA receptor antagonist MK-801 inhibits amphetamine induction of c-fosacutely and also prevents downregulation of IEG expression with chronic amphetamine administration. Such observations raise the question of whether dopamine/glutamate interactions occur at the level of corticostriatal and mesostriatal circuitry or within striatal neurons. Therefore, we studied dissociated striatal cultures in which midbrain and cortical presynaptic inputs are removed. In these cultures, we find that dopamine- or forskolin-mediated IEG induction requires Ca2+ entry via NMDA receptors but not via L-type Ca2+ channels. Moreover, blockade of NMDA receptors diminishes the ability of dopamine to induce phosphorylation of the cyclic AMP responsive element binding protein CREB. Although these results do not rule out a role for circuit-level dopamine/glutamate interactions, they demonstrate a requirement at the cellular level for interactions between the cyclic AMP and NMDA receptor pathways in dopamine-regulated gene expression in striatal neurons.

Blood-Brain Barrier: Penetration of Morphine, Codeine, Heroin, and Methadone after Carotid Injection

Labeled morphine, codeine, heroin, or methadone was injected as a bolus into the common carotid artery of the rat, and the rat was decapitated 15 seconds later. The brain uptake of the drug was calculated by measurement of the brain content of the drug as a percentage of a labeled, highly diffusible reference substance simultaneously injected. The uptake of morphine was below measurability; the uptake of codeine was 24 percent; heroin, 68 percent; and methadone, 42 percent. Brain uptakes of morphine and codeine were also studied after intravenous injection and correlated well with uptakes after carotid injection; the uptake of codeine being nearly complete by 30 seconds. These studies indicate that brain uptake of certain of these drugs is very rapid and that uptake of heroin injected intravenously is probably limited by the regional flow of blood in the brain. The possible relation of this rapid penetration of the blood-brain barrier by heroin to its strongly addictive properties is discussed.

Proteins bound at adjacent DNA elements act synergistically to regulate human proenkephalin cAMP inducible transcription

Synthesis of the endogenous opioid precursor, proenkephalin, is regulated by neurotransmitters and membrane depolarization. These events act through second messenger dependent signal transduction pathways via a short inducible DNA enhancer to regulate transcription of the proenkephalin gene. Two DNA elements located within this enhancer are essential for the transcriptional response to cAMP and phorbol ester. Inactivation of either element by mutation or by alteration of their stereospecific alignment eliminates inducible enhancer activity. The promoter distal element, ENKCRE‐1, in the absence of a functional adjacent ENKCRE‐2 element, has no inherent capacity to activate transcription. However, in the presence of a functional ENKCRE‐2 element, this element synergistically augments cAMP and phorbol ester inducible transcription. The promoter proximal element, ENKCRE‐2, is essential for both basal and regulated enhancer function. Four different protein factors found in HeLa cell nuclear extracts bind in vitro to the enhancer region. ENKTF‐1, a novel enhancer binding protein, binds to the DNA region encompassing ENKCRE‐1. The transcription factors AP‐1 and AP‐4 bind to overlapping sites spanning ENKCRE‐2, and a fourth transcription factor, AP‐2, binds to a site immediately downstream of ENKCRE‐2. The binding of ENKTF‐1 to mutant ENKCRE‐1 sequences in vitro correlates with the in vivo inducibility of the mutant elements suggesting that ENKTF‐1 acts in combination with factors that recognize the ENKCRE‐2 domain to regulate cAMP inducible transcription. Together, the two DNA elements, ENKCRE‐1 and ENKCRE‐2 and the protein factors with which they interact, play a critical role in the transduction and reception of signals transmitted from cell surface receptors to the proenkephalin nuclear transcription complex.