Effects of acute and chronic cocaine administration on somatostatin level and binding in the rat brain

A role for the neuropeptide somatostatin in the neurobiology of behaviors associated with substances abuse and affective disorders

In recent years, neuropeptides which display potent regulatory control of stress-related behaviors have been extensively demonstrated to play a critical role in regulating behaviors associated with substance abuse and affective disorders. Somatostatin (SST) is one neuropeptide known to significantly contribute to emotionality and stress behaviors. However, the role of SST in regulating behavior has received relatively little attention relative to other stress-involved peptides, such as neuropeptide Y or corticotrophin releasing factor. This review characterizes our current understanding of the role of SST and SST-expressing cells in general in modulating several behaviors intrinsically linked to substance abuse and affective disorders, specifically: anxiety and fear; stress and depression; feeding and drinking; and circadian rhythms. We further summarize evidence of a direct role for the SST system, and specifically somatostatin receptors 2 and 4, in substance abuse disorders. This article is part of the special issue on 'Neuropeptides'.

Differential potencies of cocaine and its metabolites, cocaethylene and benzoylecgonine, in suppressing the functional expression of somatostatin and neuropeptide Y producing neurons in cultures of fetal cortical cells

Using aggregate cultures derived from 17-day-old fetal rat cortex, we addressed the question: Does cocaine alter the functional expression of neuropeptide Y (NPY) and somatostatin (SRIF) neurons and, if so, are cocaethylene (CE) and benzoylecgonine (BZE) as active as cocaine? NPY/SRIF production in response to brain-derived neurotrophic factor (BDNF) or phorbol-12-myristate-13-acetate (PMA) was used as a functional criterion. A 5-day exposure to cocaine did not affect basal or stimulated (BDNF or PMA) production of NPY but it markedly suppressed BDNF- or PMA-stimulated production of SRIF. Exposure to CE led to a drastic suppression of basal as well as stimulated (BDNF or PMA) production of both NPY and SRIF. These effects of cocaine and CE were concentration dependent (1-100 microM). BZE did not alter any of these functional parameters. Next, we evaluated the fate of cocaine, CE, and BZE in the culture medium. Cocaine was converted to BZE, whereas BZE was not converted to cocaine. CE was converted to cocaine and BZE, with substantial amounts of cocaine and CE remaining in the medium after 72 hr (approximately 20% each). In summary, cocaine, CE, and BZE exhibited differential potencies in suppressing the expression of cultured NPY and SRIF neurons: CE was more potent than cocaine and BZE was inactive. SRIF neurons were more susceptible than NPY neurons to the effects of cocaine. The higher potency of CE may be due to a property of the compound and/or to CE serving as a source for a slow, continuous formation of cocaine by the brain cells themselves.

Somatostatin receptors increase in the olfactory bulb of developing pups after perinatal exposure to cocaine

The effects of chronic prenatal and/or postnatal exposure to cocaine on somatostatin concentration and receptors were studied in the olfactory bulbs of rat pups at birth and at 15 days old. Wistar rats were injected subcutaneously with single daily doses of 40 mg cocaine hydrochloride/kg from days 7 to 19 of gestation, from day 7 of gestation to day 15 postpartum or from parturation to day 15 postpartum. Fetal exposure to cocaine decreased SS concentrations in the olfactory bulb of the newborn pups while prenatal-plus-postnatal exposure increased this parameter. Administration of cocaine only during lactation did not induce any change. Exposure during gestation or during nursing induced an increase in the total number of somatostatin receptors and a decrease in the affinity constant in the olfactory bulb of newborn and 15-day-old pups. These results suggest that the development of somatostatin receptors in the olfactory bulb can be altered by prenatal and/or nursing period exposure to cocaine.

Changes in striatal somatostatin receptors in pups after cocaine administration to pregnant and nursing dams

Primiparous female Wistar rats were injected subcutaneously with single daily doses of 40 mg of cocaine hydrochloride/kg from day 7 to 19 of gestation, from day 7 of gestation to day 15 postpartum or from parturation to day 15 postpartum. At birth, some of the offspring were fostered to control mothers to limit the effect of cocaine to the prenatal period and some were left with their mothers with the aim of studying prenatal plus postnatal exposure to cocaine. Prenatal and/or postnatal cocaine exposure did not affect the content of somatostatin (SS)-like immunoreactivity (SLI) in the striatum of the offspring as compared with the control groups on day 15 in all experimental groups. Prenatal and prenatal-plus-postnatal exposure to cocaine increased the total number of binding sites for 125I-Tyr11-SS in the rat striatum at 15 days of age. Prenatal exposure to cocaine also decreased the apparent affinity of the receptors. Postnatal exposure to cocaine alone had no such post-treatment effect on 125I-Tyr11-SS binding. These results suggest that the development of SS receptors in the rat striatum can be altered by prenatal exposure to cocaine.

Effect of prenatal and postnatal cocaine exposure on somatostatin content and binding in frontoparietal cortex and hippocampus of developing rat pups

The effects of cocaine administration to pregnant and/or nursing rats on somatostatin (SS) concentration and receptors in offspring brains at birth and 15 days of age were studied. SS was measured by radioimmunoassay and SS receptors by radio receptor assay in frontoparietal cortex and hippocampus. In newborn and 15-day-old animals the exposure to cocaine produced an increase in SS concentration in the frontoparietal cortex and a decrease of this parameter in the hippocampus. Administration of cocaine only during lactation did not induce such changes. Exposure during pregnancy or nursing induced in 0- or 15-day-old offspring an increase in the total number of SS receptors and a decrease in the affinity constant only in the cortex.