Effect of heroin-conditioned auditory stimuli on cerebral functional activity in rats

Neural responses associated with cue evoked emotional states and heroin in opiate addicts

Ten male opiate addicts, who were current heroin injectors, underwent positron emission tomographic (PET) scanning during exposure to a sequence of six alternating drug related and neutral video cues, on two occasions. After the second scan, each subject received heroin or placebo using a randomised single-blind procedure. This design allowed the investigation of patterns of brain activity during a range of self-reported cue evoked emotional states, both in the presence and absence of heroin. Self-reports of 'urge to use' correlated strongly with increased regional blood flow (rCBF) in the inferior frontal and orbitofrontal cortex target regions of the mesolimbic dopaminergic system, implicated in conditioning and reward. 'Urge to use' was also associated with highly significant increased rCBF in the right pre-cuneus, an area associated with episodic memory retrieval, and in the left insula, implicated in the processing of the emotional components of stimuli. Self-reports of feeling 'high' correlated with rCBF activation in the hippocampus, an area relevant to the acquisition of stimulus-associated reinforcement.

Activation of reward circuitry in human opiate addicts

The neurobiological mechanisms of opiate addictive behaviour in humans are unknown. A proposed model of addiction implicates ascending brainstem neuromodulatory systems, particularly dopamine. Using functional neuroimaging, we assessed the neural response to heroin and heroin-related cues in established opiate addicts. We show that the effect of both heroin and heroin-related visual cues are maximally expressed in the sites of origin of ascending midbrain neuromodulatory systems. These context-specific midbrain activations predict responses to salient visual cues in cortical and subcortical regions implicated in reward-related behaviour. These findings implicate common neurobiological processes underlying drug and drug-cue-related effects.

Alteration of local cerebral glucose utilization following intravenous administration of heroin in Fischer 344 rats

The 2-deoxyglucose method was used to study the effects of acute administration of small intravenous doses of heroin on rates of glucose utilization in rat brain to identify small brain regions that may be involved in the acute behavioral effects of heroin. In contrast to previous studies which have used relatively large doses, the doses of heroin used in this study have been shown to be self-administered [Martin, T.J., Dworkin, S.I. and Smith, J.E., Alkylation of mu-opioid receptors by beta-funaltrexamine in vivo: comparison of the effects on in situ binding and heroin self-administration in rats., J. Pharmacol. Exp. Ther., 272 (1995) 1135-1140.]. Administration of 18 microg/kg of heroin resulted in higher rates of glucose utilization in the medial olfactory tubercle, anterior nucleus accumbens and dorsolateral caudate while having no other effects on limbic structures compared to saline-treated animals. Conversely, the rate of glucose utilization was lower than control in the habenula, dorsal raphe, and central gray following adminstration of 18 microg/kg of heroin. Administration of two higher doses (60 and 100 microg/kg) resulted in lower rates of glucose utilization in the thalamus, habenula, inferior colliculus, dorsal raphe and central gray compared to saline. The higher rates of glucose utilization in the limbic areas were specific for the lowest dose of heroin, whereas the effect of lowering the rate of glucose utilization compared to control in the thalamus and inferior colliculus were an increasing function of dose. In the habenula and dorsal raphe, however, the dose-effect function was inverted. These data indicate that the alterations of glucose utilization in rat brain by heroin are site-specific and the systems involved as well as the nature of the alteration differs for individual doses of heroin.

Effects of heroin and naloxone on cerebral blood flow in the conscious rat

The widespread, heterogeneous distribution of opiate receptors and their endogenous ligands in the nervous system are reflective of the variety of central and systemic effects seen after opiate administration. Most neurons respond to either systemic or local opiate application with a decrease in firing rate, although increased neuronal activity has also been reported in such regions as the caudate, amygdala, ventral tegmentum, and substantia nigra. While regional metabolic studies have consistently reported neuronal suppression, some portion of this might be secondary to systemic hypercapnia. Using a brief blood flow marker, we recently reported a heterogenous increase in activity in more than half of the brain regions examined. To extend that study, we report herein the results of a dose-response and antagonist challenge experiment. Rats received an acute injection of one of the following: heroin (0.1, 0.3 or 1.0 mg/kg), naloxone (1.0 mg/kg), a cocktail of heroin (0.3 mg/kg) plus naloxone or saline. One min after drug administration, 160 muCi/kg [1-14C] octanoate, a marker for cerebral blood flow, was delivered IV. Rats were sacrificed two min later, brains removed and prepared for autoradiography. Of the fifty-eight areas analyzed, heroin caused an increase in blood flow in the caudate, claustrocortex, laterodorsal thalamus and dentate gyrus. Decreases were found for the bed nucleus of the stria terminalis, preoptic area, basolateral nucleus of the amygdala, dorsomedial and paraventricular hypothalamus, entorhinal and cingulate cortices and dorsal raphe. Naloxone resulted in significant increases in the olfactory tubercle and paraventricular nucleus while decreases were seen in the cingulate and basolateral amygdala.