The present findings, obtained under saline and amphetamine test conditions, provide the first detailed classification of adult rat 50-kHz USVs. Consideration of 50-kHz USV subtypes may advance our understanding of inter-rat communication and affective state.

The localization of sulfated glycoprotein-2 (clusterin; SGP-2) was investigated in the rete testis, efferent ducts, and epididymis of the rat using light (LM) and electron (EM) microscope immunocytochemistry. At the LM level, the epithelial cells of the rete testis and efferent ducts demonstrated an intense immunoperoxidase reaction over their apical and supranuclear regions, and sperm in the lumen of the efferent ducts were unreactive. In the EM, gold particles were found exclusively over the endocytic apparatus of these cells. In the proximal area of the epididymal initial segment, an insignificant immunostaining of epithelial cells and sperm was observed. However, the distal area of the initial segment showed a moderate staining over the epithelial principal cells and sperm, while in the intermediate zone of the epididymis a stronger reaction was observed over these cells. The strongest immunoperoxidase reaction was noted in the caput epididymidis, where it formed a distinct mottled pattern. Thus, while some principal cells were intensely stained, others were moderately or weakly stained; a few were completely unreactive. In the corpus and cauda epididymidis, the staining pattern was similar but not as intense. In the EM, only the secretory apparatus of these cells was found to be immunolabeled with gold particles. Sperm in the lumen of these different regions were also labeled. The epithelial clear cells were unreactive throughout the epididymis. Northern blot analysis substantiated these results and showed the presence of highest levels of SGP-2 mRNA in the caput epididymidis, especially in its proximal area, whereas increasingly lower levels were found in the corpus and cauda epididymidis. In summary, these results suggest that testicular SGP-2 dissociates from the sperm during passage through the rete testis and efferent ducts, where it is endocytosed by the epithelial cells lining these regions. In the epididymis, it is replaced by an epididymal SGP-2 that is secreted by the epithelial principal cells of the epididymis. Furthermore, in the epididymis, the principal cells appear to be in different functional states with respect to the secretion of epididymal SGP-2 within a given region of the duct as well as along the epididymal duct.

Amphetamine (AMPH) increases adult rat 50-kHz ultrasonic vocalizations, preferentially promoting frequency-modulated (FM) calls that have been proposed to reflect positive affect. The main objective of this study was to investigate a possible noradrenergic contribution to AMPH-induced calling. Adult male Long-Evans rats were tested with AMPH (1 mg/kg intraperitoneal) or saline combined with various systemic pretreatments: clonidine (α2 adrenergic agonist), prazosin (α1 antagonist), atipamezole (α2 antagonist), propranolol, betaxolol, and/or ICI 118,551 (β1/β2, β1, and β2 antagonists, respectively), nadolol (β1/β2 antagonist, peripheral only), or NAD-299 (5HT(1A) antagonist). In addition, effects of cirazoline (α1 adrenergic agonist) and cocaine (0.25-1.5 mg/kg intravenous) were studied alone. AMPH-induced calling was suppressed by low-dose clonidine and prazosin. Cirazoline and atipamezole did not significantly affect calling rate. Propranolol, without affecting the call rate, dose dependently promoted 'flat' calls under AMPH while suppressing 'trills,' thus reversing the effects of AMPH on the 'call subtype profile.' This effect of propranolol seemed to be mediated by simultaneous inhibition of CNS β1 and β2 rather than by 5HT(1A) receptors. Finally, cocaine elicited fewer calls than did AMPH, but produced the same shift in the call subtype profile. Taken together, these results reveal differential drug effects on flat vs trill vs other FM 50-kHz calls. These findings highlight the value of detailed call subtype analyses, and show that 50-kHz calls are associated with adrenergic α1- and β-receptor mechanisms. These preclinical findings suggest that noradrenergic contributions to psychostimulant subjective effects may warrant further investigation.

The rate of 50-kHz USVs and the call subtype profile following systemic AMPH administration depends on dopaminergic neurotransmission through D1-like and D2-like receptors. However, inhibiting dopamine and/or noradrenaline reuptake appears insufficient to induce calling.

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