Increase of proenkephalin mRNA and enkephalin content of rat striatum after daily injection of haloperidol for 2 to 3 weeks.

Abstract

Proenkephalin mRNA has been detected in striatum, hypothalamus, cortex, cerebellum, hippocampus, midbrain, and brain stem of rat by RNA ("Northern") blot analysis using a 918-base-pair DNA hybridization probe complementary to proenkephalin mRNA [Comb, M., Enkephalins have been proposed to function as putative neurotransmitters or neuromodulators in brain. Although their distribution and location in various brain structures is known (1, 2), there is no way to determine their rate of utilization. Hence, the changes in enkephalin content of selected brain structures that are elicited by drug treatment cannot be easily interpreted in terms of inhibition or increase of rates of enkephalin utilization. One reason for such difficulty is lack of understanding of the enzymatic processes that regulate the formation of various molecular forms of enkephalins from proenkephalin, the high molecular weight precursor of enkephalin that contains one or more replicas of at least four molecular forms of enkephalin peptides [referred to as proenkephalin A by Kakidani et al. (3)]. The successful cloning and sequence analysis of the mRNA for proenkephalin from bovine adrenal medulla (4,5) and human pheochromocytoma (6) provide a method to determine whether an increase in the content of a given enkephalin in a brain structure is associated with an increase in the amount of the specific mRNA for proenkephalin. We have reasoned that, when an increase in enkephalin content is associated with an increase in proenkephalin mRNA content, one could infer that the increase in enkephalin content might reflect an increase in availability of the peptide.We report the use of the cDNA probe for human pheochromocytoma proenkephalin (6) to determine whether repeated daily injections of haloperidol in doses that cause a selective increase of striatal enkephalin content (7) also cause a selective increase in proenkephalin mRNA content in striatum. In a previous paper, indirect evidence was presented suggesting that repeated daily injection of haloperidol increases enkephalin biosynthesis in striatum (8): we now report that haloperidol increases proenkephalin mRNA in striatum but not in other brain areas in which the enkephalin content fails to in--crease. MATERIALS AND METHODSTreatment of Animals. Sprague-Dawley male rats (Zivic Miller, Allison Park, PA) weighing 200-300 g were maintained at constant temperature (23-250C), six per cage, in a room illuminated with alternating light and dark cycles (14 and 10 hr, respectively). Haloperidol (McNeil Pharmaceutical, Spring House, PA) was dissolved in a few drops of glacial acetic acid, and the solution was adjusted to pH 6 with 10 N NaOH and diluted with saline. Animals were injected intraperitoneally with 1 to 2 mg/kg of body weight daily for 2 to 3 wk and sacrificed 24 hr after the last injection. The animals were decapitated and the brain regions were dissected according to the method of Glowinski and Iverson (9). Tissues were immediately frozen and stored in liquid nitrogen for analysis at a ...

Cellular localization of proenkephalin mRNA in rat brain: gene expression in the caudate-putamen and cerebellar cortex.

“…Radioimmunoassayable [Met]enkephalin, 1.2 nmol/g of wet weight, was measured in the caudate-putamen. These concentrations and those for the octapeptide, [Met]enkephalin-Arg6-Gly7-Leu8, are high in this nucleus relative to other brain regions (14,15). DISCUSSION Cerebellar Cortex.…”

“…Its relative infrequency and morphological appearance make it unlikely that the labeled cells we observed represent Lugaro cells. Based on cellular location, size, and frequency as criteria (11,13) Amr,"'i is relatively low compared to the content of other brain regions (14,15).…”

Endomorphin-1: Induction of Motor Behavior and Lack of Receptor Desensitization

“…A growing body of evidence suggests a role for endogenous opiates in the development of movement disorders. For example, altered opioid transmission in the basal ganglia has been implicated in Parkinson's disease (Sandyk, 1985;Gerfen et al, 1991), Huntington's disease (Sandyk, 1985;Albin et al, 1991), and tardive dyskinesia (Sabol et al, 1983;Tang et al, 1983;Sandyk, 1985). The latter are involuntary abnormal orofacial movements that may follow chronic administration of dopaminergic antagonists (neuroleptics) used to treat schizophrenia (Tarsy and Baldessarini, 1984).…”

Steady-state level and turnover rate of the tripeptide Tyr-Gly-Gly as indexes of striatal enkephalin release in vivo and their reduction during pentobarbital anesthesia.

“…Direct measurement of OPs collected in central nervous system perfusates has been used to evaluate their release (6,7) but the method is not easily applicable without anesthesia and the resulting interference; in addition, it requires complete inhibition of degradation processes, which may interfere with the release mechanisms (8,9). Levels of brain proenkephalin A mRNA were recently shown to be modified by chronic drug treatments (10,11) but their measurement may not provide direct information about transient changes in OP release. Finally, the rates of radiolabeled amino acid incorporation into OPs are not easily measurable, mainly because it is difficult to achieve a reasonable degree of incorporation (4,12,13).…”