News and Publications

In Vivo Neuropharmacology

S.J. Henriksen, S. Steffensen, J. Giacchino, R.-S. Lee, J. Criado, S. Huitron-Resendiz, R. Gallegos, T. Horn,* L. Gombart, O. Prospero-Garcia,** G. Berg, R. Cole, N. Herold, P. Griffin

* Otto-vonoGuericke University Magdeburg, Magdeburg, Germany
** University Nacional Autonoma de Mexico, Mexico City, Mexico

We continue to investigate mammalian neural circuits that underlie complex cognitive functions and motivated behaviors such as learning, sleep, and drug-seeking activity. These same circuits also underlie human cognitive and behavioral abnormalities. The results of studies on the interactions and hierarchies of neural transmitters in these circuits provide new opportunities for understanding and treating these uniquely human diseases. We use experimental animals in which the CNS either is intact or has been compromised by viral infection, genetic manipulations, or molecular engineering. By examining the intact nervous system in whole animals, we can determine the consequences of specific experimental manipulations on brain circuitry thought to be important for normal as well as pathologic behaviors. This year's report focuses on 3 areas of our expanding research portfolio.

BRAIN CIRCUITS UNDERLYING ACTIONS OF DRUGS OF ABUSE

Using neuropharmacologic and neurophysiologic methods, we have further investigated the hypothesis that many drugs of abuse have common actions on neural circuits that reinforce addictive behaviors. These brain areas include both cortical regions and brain-stem neural circuits. Generally, we record data from specific neurons in these areas in both anesthetized and unanesthetized, unrestrained rodents and correlate neuronal discharge with drug administration, spontaneous behaviors, and changes in arousal and sleep.

Recent studies confirmed that conditioning and learning play key roles in drug reinforcement and addiction. Indeed, brain regions such as the hippocampus are involved in learning and may also regulate opiate-seeking behavior. The results of behavioral studies on hippocampal responses, that is, theta rhythm, to environments paired to heroin injections suggest that this rhythm is an important index of the rewarding properties of opioids.

Other results indicated that systemically administered nicotine increases the spontaneous and evoked activity of neurons in the medial prefrontal cortex, an effect opposite to that of heroin. In addition, important age-related differences in nicotine-induced synaptic plasticity occur in this "executive" brain region.

The central nucleus of the amygdala is also a component of a brain reward circuit. Previous studies in rats showed that short-term administration of ethanol induces the expression of the immediate-early gene product c-Fos in this region. In collaborative studies with M. Morales, National Institute on Drug Abuse, Baltimore, we used a combination of in situ hybridization and immunohistochemistry to show that ethanol-responsive neurons within this region are mainly GABAergic (Fig. 1). This observation provides the first anatomic evidence that GABAergic neurons of the central nucleus of the amygdala are responsive to short-term exposure to ethanol and suggests that the GABAergic system of the central nucleus of the amygdala is a key neuronal area for the actions of ethanol on the CNS.

FELINE AIDS: INTERACTIONS WITH DRUGS OF ABUSE

In collaboration with T. Phillips, Department of Neuropharmacology, and J. Elder, Department of Molecular Biology, we continue to investigate the physiopathology of various strains of feline immunodeficiency virus (FIV) as a small-animal model of infection with HIV type 1. We have expanded our investigation to evaluate the effect of morphine on the course of the disease elicited by FIV in cats. Previously, we found that infection with FIV-PPR, a molecular clone of the virus, causes abnormalities in sensory and motor neurologic responses and alterations in sleep. These changes are comparable to the early neurologic deficits observed in patients infected with HIV type 1. Recent findings indicated that morphine enhances FIV replication nearly 10-fold in vitro. However, according to physiologic parameters, short-term treatment of cats with morphine before inoculation with FIV appeared to delay the progression of the disease. We are investigating the potential mechanisms of this finding, which may provide a new window to the role of early immune system function in CNS related-FIV disease.

NOVEL FATTY ACID AMIDES AND SLEEP

In continuing studies with D. Boger and B. Cravatt, Skaggs Institute for Chemical Biology, we are examining the effects of important analogs of oleamide, an endogenous sleep-inducing lipid discovered at TSRI, on several physiologic processes. Protease-resistant analogs of oleamide and synthetic inhibitors of the degradative enzyme of these fatty amides have the same biological effects on temperature and sleep that the native compound does (Fig. 2). These findings provide critical new evidence of the importance of these new fatty amide messengers in regulating important physiologic processes.

PUBLICATIONS

de Lecea, L., Criado, J., Rivera, S., Wen, W., Barry, G., Henriksen, S., Taylor, S., Gall, C., Sutcliffe, J.G. Endogenous protein kinase A inhibitor (PKIa) modulates synaptic activity. J. Neurosci. Res., in press.

de Lecea, L., del Rio, J.A., Criado, J., Alcántara, S., Morales, M., Henriksen, S.J., Soriano, E., Sutcliffe, J.G. Cortistatin is expressed in a distinct subset of cortical interneurons. J. Neurosci. 17:5868, 1997.

Fox, H., Gold, L., Henriksen, S., Bloom, F.E. Simian immunodeficiency virus: A model for neuroAIDS. Neurobiol. Dis. 4:265, 1997.

Giacchino, J., Henriksen, S. Opioid effect on prefrontal cortical neuronal activity and excitatory response. NIDA Res. Monogr. 174:150, 1997.

Gold, L.H., Fox, H.S., Henriksen, S.J., Buchmeier, M., Weed, M., Taffe, M., Huitron-Resendiz, S., Horn, T., Bloom, F.E. Longitudinal analysis of behavioral, neurophysiological, viral and immunological effects of SIV infection in rhesus monkeys. J. Med. Primatol., in press.

Herold, N., Spray, S., Horn, T., Henriksen, S. Measurements of behavior in the naked mole-rat after intraperitoneal implantation of a radio-telemetry system. J. Neurosci. Methods, in press.

Jacobson, S., Henriksen, S., Prospéro-García, O., Phillips, T.R., Elder, J.H., Bloom, F.E., Fox, H.S. Cortical neuronal cytoskeletal changes associated with FIV infection. J. Neurovirol. 3:283, 1997.

Lee, R.-S., Koob, G.F., Henriksen, S. Electrophysiological responses of nucleus accumbens neurons to novelty stimuli and exploratory behavior in the awake, unrestrained rat. Brain Res, in press.

Morales, M., Criado, J.R., Sanna, P.P., Henriksen, S., Bloom, F.E. Acute ethanol induces c-Fos immunoreactivity in GABAergic neurons of the central nucleus of the amygdala. Brain Res. Interact., in press.

Siuzdak, G., Henriksen, S. New directions in the analysis of brain substances related to sleep and wakefulness. In: Molecular Regulation of Arousal States. Lydic, R. (Ed.). CRC Press, Boca Raton, FL, p. 181, 1998.

Steffensen, S.C., Svingos, A.L., Pickel, V.M., Henriksen, S. Electrophysiological, neurochemical and ultrastructural characterization of GABAergic neurons in the ventral tegmental area. J. Neurosci., in press.