Behavioral characterization of intracranial self-stimulation from mesolimbic, mesocortical, nigrostriatal, hypothalamic and extra-hypothalamic sites in the non-inbred CD-1 mouse strain

A behavioral analysis of intracranial self-stimulation (ICSS) was provided for mesolimbic/mesocortical, nigrostriatal, hypothalamic and extrahypothalamic sites in the CD-1 mouse. Robust responding and rapid acquisition of mesocortical ICSS appeared dorsally along notably fluorescent sites in rostral and caudal planes. ICSS was diminished demonstrably in medial and ventral positions in posterior planes. Mesolimbic ICSS from the medial and ventral nucleus accumbens (Nas), was accompanied by significant elevations in locomotor activity, corresponding to regions of dopamine (DA) and cholecystokinin co-localization. Stimulation-induced seizures appeared from both the Nas as well as the mesocortex. ICSS from the ventral tegmental field (VTA) was evident along its medial, lateral and dorsal borders with longer pulse durations more likely to elicit responding. Seizure activity was absent from the VTA. Striatal ICSS was conspicuously poor in dorsal and medial locations; regions presumably devoid of tegmental innervation. ICSS emerged from both the ventrocaudal and anteromedial striatum; regions linked to innervation by the dorsolateral and ventromedial VTA. The red nucleus, a previously neglected self-stimulation site supported marked responding for ICSS. Regions supporting rubral ICSS were correlated with thalamic innervation sites; notably the ventrolateral thalamic nucleus and the parafascicular nucleus, regions found to support ICSS. The substantia nigra supported high rates of responding for ICSS when electrode placement was restricted to the dorsomedial portion of the pars compacta. Electrode deviations lateral and dorsal to the substantia nigra pars medialis induced a progressive decline in responding. Hypothalamic sites were found to support significant responding for ICSS, although such performance was frequently associated with seizure induction. Taken together these data (1) provide the first behavioral analysis of ICSS in mice responding from previously unexamined DA sites in the mesolimbic (e.g. VTA, Nas) and nigrostriatal systems (e.g. caudate, red nucleus) (2) suggest an anatomical reconsideration of the assumptions underlying the elicitation of ICSS from the frontal cortex (3) suggest that the neural circuitry underlying thalamic, caudate, rubral and frontal cortical ICSS are interrelated and (4) suggest that the Nas and the frontal cortex, like the hypothalamus, in the mouse appear to be particularly sensitive to stimulation-induced seizures.