Lower packing density of glial fibrillary acidic protein-immunoreactive astrocytes in the prelimbic cortex of alcohol-naive and alcohol-drinking alcohol-preferring rats as compared with alcohol-nonpreferring and Wistar rats.

In chronic alcohol abusers without major neuropathology or neurological deficits, glial cells in the cerebral cortex are significantly affected (Korbo, 1999; Miguel-Hidalgo and Rajkowska, 2003; Miguel-Hidalgo et al., 2002). However, these alterations differ from the gliosis typical of neurodegenerative diseases. In the hippocampus, the dorsolateral prefrontal cortex (PFC), and the orbitofrontal cortex, alcohol dependence is associated with a reduction in the packing density of glial cells, many probably astrocytes (Korbo, 1999; Miguel-Hidalgo and Rajkowska, 2003; Miguel-Hidalgo et al., 2002). More recently, gene microarray studies have shown that mRNA levels of the astrocytic marker glial fibrillary acidic protein (GFAP) are lower in the brains of alcoholics than in matched controls (Hoffman et al., 2003; Lewohl et al., 2000, 2001; Mayfield et al., 2002). Alterations in the number, the morphology, or the functions of astrocytes are important because they perform functions that provide critical support to neuronal activity: promoting the transfer of nutrient to neurons, maintenance of synaptic transmission by uptake and recycling of neurotransmitters, ionic homeostasis of the neuropil, and the support of cerebral glucose metabolism (Coyle and Schwarcz, 2000; Magistretti and Pellerin, 1999; Magistretti et al., 1999). In brain regions like the PFC, known to be involved in the regulation of behaviors directly relevant to drug and alcohol addiction, alteration in the number of astrocytes, in the extent of their processes, or in those astrocytic functions might be an important factor contributing to alcohol abuse and dependence. Lower numbers of astrocytes in the hippocampus and PFC of relatively young alcoholics suggest that alcohol abuse may cause astrocyte depletion or that in individuals at risk for alcoholism there might be a pre-existing deficit in the numbers of glial cells. In chronic alcoholic subjects, alcohol-induced reductions in astrocytes or their markers are consistent with the presence in those subjects of degenerating GFAP-immunoreactive (IR) astrocytes detected with terminal deoxynucleotidyltransferase–mediated dUTP nick end labeling (Ikegami et al., 2003). Depletion of GFAP-IR astrocytes may be associated as well with brain injury. For instance, in the hours immediately after traumatic brain injury in the rat, there is a significant decrease in GFAP-IR astrocytes (Zhao et al., 2003). Alternatively, in regions like the PFC, which heavily influence behaviors of alcohol abuse and dependence (Volkow and Fowler, 2000; Volkow et al., 1992), lower numbers of astrocytes and GFAP levels may precede alcohol abuse and dependence in subjects at risk. In mood disorders (which, like alcoholism, have a significantly heritable component), lower density of glial cells, GFAP-IR astrocytes, and GFAP levels in the PFC of relatively young subjects has been described (Cotter et al., 2002; Miguel-Hidalgo et al., 2000; Ongur et al., 1998; Rajkowska et al., 1999, 2001, 2002; Si et al., 2004). Several lines of alcohol-preferring (P) rats with an inherited risk for the acquisition of alcohol abuse and dependence have been selected at various laboratories (McBride and Li, 1998; Rodd et al., 2004). In the same laboratories, other researchers also selected lines of alcohol-nonpreferring (NP) rats. These animals drink significantly less ethanol than non-selected or P rats and hardly become alcohol dependent. Among those lines of rats, P and NP rats from Indiana University were obtained by repeated selection for alcohol preference in a stock of Wistar rats (Li et al., 1979; McBride et al., 1986). The levels of several neuronal proteins and other neurochemical characteristics differentiate P rats from NP and Wistar rats (McBride and Li, 1998). It is unknown, however, whether the packing density of glial cells and, in particular, of GFAP-IR astrocytes is lower in the PFC of alcohol-naive P rats than in that of NP rats or Wistar rats (which is not the result of a selection related to alcohol preference) and whether prolonged alcohol exposure affects GFAP-IR astrocytes in P rats. The present study aimed to determine whether the packing density of GFAP-IR astrocytes and the area fraction of GFAP-IR structures in the prelimbic cortex (PLC) of the rat PFC are lower in alcohol-naive P rats than in alcohol-naive NP and Wistar rats. We also examined whether the same parameters are altered in P rats after prolonged free-choice consumption of 10% ethanol.