Activation of a subset of lumbar spinothalamic neurons after copulatory behavior in male but not female rats - PubMed (original) (raw)

Activation of a subset of lumbar spinothalamic neurons after copulatory behavior in male but not female rats

William A Truitt et al. J Neurosci. 2003.

Abstract

The precise pathways that convey copulation-related information to forebrain regions activated during male and female sexual behavior are poorly understood. Previous work from our laboratory and others has demonstrated the existence of a spinothalamic pathway that is a candidate to relay information to these areas. This pathway originates from a population of spinothalamic neurons in the lumbar spinal cord containing several neuropeptides including galanin, located in laminas 7 and 10 of the lumbar segments 3 and 4. To investigate the involvement of these lumbar spinothalamic neurons in conveying copulation-related information, we tested the hypothesis that these cells are activated after ejaculation in male rats and vaginocervical stimulation in female rats. This was assessed using galanin or cholecystokinin as a marker for this subset of spinothalamic neurons and Fos-immunoreactivity as a marker for neuronal activation. The results demonstrated that activation of these spinothalamic neurons is triggered by stimuli associated with ejaculation. Fos induction was specifically associated with ejaculation, because mounts or intromissions did not trigger expression. Moreover, these spinothalamic neurons were not activated by vaginocervical stimulation in female rats. Spinothalamic neurons have generally been associated with signaling pain and temperature information. The present findings demonstrate that a specific subpopulation of spinothalamic neurons signals information associated with ejaculation.

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Figures

Fig. 1.

Fig. 1.

Schematic drawing of L4 illustrating the area of analysis (800 × 800 μm) for Fos-IR and activated LSt cells.Gray circles indicate the approximate location of LSt cells. This figure was modified from Paxinos and Watson (1998).

Fig. 2.

Fig. 2.

Neural activation of LSt neurons in male but not female spinal cord. A, Galanin neurons are Fos positive in a representative male after two ejaculations. B, Lack of colocalization of Fos and galanin in a male rat after intromissions but no ejaculation. C, Colocalization of galanin and Fos in an 8-OH-DPAT-treated male rat after one ejaculation.D, Lack of colocalization of Fos and galanin in a female rat after ejaculation by her male partner. Scale bar, 20 μm.

Fig. 3.

Fig. 3.

Fos-IR in LSt and non-LSt cells in the L3 and L4 of male rats. A, Percentage of galanin-IR neurons that are Fos-IR in male rats. Mean percentages ± SEM of galanin-IR cells that are Fos-IR per behavioral group (HC, home cage controls; AN, males that were placed with an anestrous female; MN, males that only mounted;IM, males that mounted and displayed intromissions;E1, males that displayed copulatory behavior including 1 ejaculation; E2, males that displayed copulatory behavior including 2 ejaculations). B, Percentage of CCK-IR neurons that are Fos-IR in male rats. Mean percentages ± SEM of CCK-IR cells that are Fos-IR per behavioral group.C, Fos-IR in nongalanin neurons. Mean numbers of Fos-IR in the area surrounding the central canal in L3–L4 per behavioral group in male rats. *p < 0.0001, significantly different from HC and different from all other groups; **p = 0.0003, different from E1;†p = 0.015, greater than home cage controls.

Fig. 4.

Fig. 4.

Percentage of galanin-IR neurons that are Fos-IR after 8-OH-DPAT treatment. Mean percentages ± SEM of galanin-IR neurons expressing Fos in rats injected with 0.8 mg/kg 8-OH-DPAT after copulation to one ejaculation (DP1E;n = 3) or without exposure to a female (DPC; n = 3); *_p_≤ 0.0001.

Fig. 5.

Fig. 5.

Fos-IR in non-LSt neurons in the L3 and L4 in female rats. Mean ± SEM numbers of Fos-IR in the area surrounding the central canal in the L3 and L4 in female control rats (CON; n = 6), females receiving mounts only (MN; n = 4), females receiving 6–15 intromissions including mounts and ejaculations (6–15IM; n = 8), and females receiving 16–25 intromissions (16–25IM;n = 7). *p = 0.04, significantly different from CON (Scheffé test).

Fig. 6.

Fig. 6.

Photomicrographs of coronal sections illustrating decreased galanin-IR fibers in the mSPFp after hemisection at level L1 in male (A, B) and female (C, D) rats.B, D, The mSPFp ipsilateral to the transected side of the spinal cord is devoid of galanin-IR, as indicated by_arrows_. fr, Fasciculus retroflexus;ml, medial lemniscus. Scale bar, 200 μm.

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