Desensitization and enhancement of neurotensin/neuromedin N mRNA responses in subsets of rat caudate-putamen neurons following multiple administrations of haloperidol

Brain neurotensin, psychostimulants, and stress--emphasis on neuroanatomical substrates

Neurotensin (NT) is a peptide that is widely distributed throughout the brain. NT is involved in locomotion, reward, stress and pain modulation, and in the pathophysiology of drug addiction and depression. In its first part this review brings together relevant literature about the neuroanatomy of NT and its receptors. The second part focuses on functional-anatomical interactions between NT, the mesotelencephalic dopamine system and structures targeted by dopaminergic projections. Finally, recent data about the actions of NT in processes underlying behavioral sensitization to psychostimulant drugs and the involvement of NT in the regulation of the hypothalamo-pituitary-adrenal gland axis are considered.

Neurotensin afferents of the ventral tegmental area in the rat: [1] re-examination of their origins and [2] responses to acute psychostimulant and antipsychotic drug administration

The ventral tegmental area (VTA) is involved in reward-related behaviours and the actions of psychostimulant drugs. It is influenced by afferents expressing a variety of neurotransmitters and neuromodulators; the innervation containing neurotensin is among the densest of these. Intra-VTA neurotensin activates dopaminergic neurons and plays an important role in the development of behavioural sensitization to psychostimulant drugs and possibly in schizophrenia. Using gold-coupled wheatgerm agglutinin as retrograde tracer in combination with nonisotopic in situ hybridization for neurotensin mRNA or neurotensin antibodies after colchicine treatment, the present study was undertaken to demonstrate the neurotensinergic neurons projecting to the VTA and determine whether (and in which subpopulations) neurotensin expression is regulated in VTA-projecting neurons after administrations of the psychostimulant drug methamphetamine or the antipsychotic haloperidol. This study reveals the lateral preoptico-rostral lateral hypothalamic continuum and the medial preoptic area as main sources for the neurotensin afferents of the VTA. Fewer neurotensinergic, VTA-projecting neurons are situated in the dorsal raphe, pedunculopontine and laterodorsal tegmental nuclei, lateral hypothalamic area, ventral endopiriform area, lateral septum, accumbens shell, parabrachial nucleus and different parts of the extended amygdala. The number of neurotensinergic VTA-projecting neurons increased significantly only after methamphetamine administration and exclusively in the accumbens shell. It is concluded that the widespread neurotensinergic VTA-projecting neurons, situated in areas involved in different reward-related behaviours, are well suited to convey distinct reward information to the VTA. The up-regulation of neurotensin expression selectively in VTA-projecting neurons in the accumbens shell following methamphetamine administration may be an important factor in the development of behavioural sensitization.

Neurons of origin of the neurotensinergic plexus enmeshing the ventral tegmental area in rat: retrograde labeling and in situ hybridization combined

The morphological and physiological substrates that underlie the mutual regulatory interactions of neurotensin and dopamine in the rat mesotelencephalic projections and related structures remain to be fully described. A salient candidate for neurotensinergic effects on the mesotelencephalic dopamine projection is the dense plexus of neurotensin immunoreactive axons that enmeshes the ventral tegmental area and substantia nigra, but the locations of the neurons that give rise to this plexus have not been identified and its systemic context remains obscure. To address this, Fluoro-Gold and the cholera toxin beta subunit, retrogradely transported axonal tracers, were injected into the ventral tegmental area of rats and the brains were processed to demonstrate neurons that contained both retrograde tracer immunoreactivity and a probe against neurotensin/neuromedin N messenger RNA. Substantial numbers of double-labeled neurons were observed in the rostral part of the lateral septum, and in a region centered on the shared boundaries of the bed nucleus of stria terminalis, ventromedial ventral pallidum, diagonal band of Broca, lateral preoptic area and rostral lateral hypothalamus. A few double-labeled neurons were also observed in the dorsal raphe nucleus and adjacent periaqueductal gray. Despite the administration of haloperidol and D-amphetamine to elicit and enhance neurotensin/neuromedin N messenger RNA expression in striatum, including the nucleus accumbens and olfactory tubercle, no double-labeled neurons were observed there. These results identify a novel brain substrate for control of midbrain dopamine levels, which affect reward mechanisms and motivation.